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HomeMy WebLinkAbout2024-06-04; Beach Preservation Commission; ; Maintenance Dredging Project for the Agua Hedionda LagoonMeeting Date: June 4, 2024 To: Beach Preservation Commission From: Kyle Lancaster, Parks & Recreation Director Staff Contact: Nick Stupin, Parks Planning Manager Subject: Maintenance Dredging Project for the Agua Hedionda Lagoon Recommended Action Receive a report on the upcoming maintenance dredging project for Agua Hedionda Lagoon, to be conducted by Channelside Water Resources (Formerly Poseidon Resources) – the Claude “Bud” Lewis Carlsbad Desalination Plant operator. Discussion Background Since 1954, maintenance dredging projects were conducted at intervals of one to four years to remove a flood-tide shoal that forms in the Agua Hedionda Lagoon outer basin (also referred to as the outer basin), to maintain tidal exchange throughout the lagoon and provide cooling water flowrates required for Cabrillo Power operations. Cabrillo Power discontinued operations requiring the cooling water in December 2018. However, maintenance dredging of the outer basin continues to be necessary to maintain tidal exchange throughout the lagoon, and to provide seawater to support the operation of the Claude “Bud” Lewis Carlsbad Desalination Plant. The most recent maintenance dredging project was conducted February 15 - March 27, 2021, and deposited approximately 304,483 cubic yards [cy]of sand back onto Carlsbad beaches (North Beach 121,667 cy; Middle Beach 100,992 cy; South Beach 81,824 cy). Overview Channelside Water Resources plans to conduct an Agua Hedionda Lagoon maintenance dredging and beach nourishment project in 2024-25 to remove a flood-tide shoal in the outer basin of Agua Hedionda Lagoon in order to maintain tidal exchange between the lagoon and the ocean. Similar operations have been performed over the last six decades ranging from 159,000 to 429,000 cy of sand removed from the lagoon – outer basin. The most recent operation, completed in 2021, accounted for 304,483 cy of sand removed. In keeping with past projects, the dredged sand will be placed on adjacent beaches to replenish sand lost since the last dredging project. The beaches to be replenished are; North Beach (from the lagoon’s inlet jetty to approximately Pine Avenue), Middle Beach (between the lagoon’s inlet and outlet jetties), and South Beach (from the outlet jetty to approximately the Terramar residential development). The dredging project operations will be conducted between October 2024 and April 2025 (permits pending). Sand placement quantities for each receiver beach are determined based on the conditions reflected in a beach profile survey conducted within 45 days of the commencement of the June 4, 2024 Item #2 1 of 143 dredging project. The currently projected quantity of dredged sand (including contingency) to be placed on Carlsbad beaches is approximately 450,000 cy: 150,000 cy on the North Beach, 166,800 cy on the Middle Beach, and 133,200 cy on the South Beach. All dredging work is anticipated to be completed by April 15, 2025. The City of Carlsbad is one of several regulatory agencies, including the San Diego Regional Water Quality Control Board, the California Coastal Commission, the California State Lands Commission, the California Department of Parks & Recreation, and the U.S. Army Corps of Engineers, to review plans and issue permits to Channelside Water Resources for the dredging work. On May 28, 2024, Channelside Water Resources staff distributed a first draft of the Agua Hedionda Lagoon - Outer Basin 2024-25 Maintenance Dredge and Beach Nourishment Cycle Sand Disposition Plan (Exhibit 1) to Carlsbad Parks & Recreation staff for review and comment. The Special Use Permit application to the Carlsbad Community Development staff will follow. Channelside Water Resources will be responsible for funding, monitoring and inspecting the maintenance dredging project. Public Outreach Channelside Water Resources will present an overview of the maintenance dredging project at the Beach Preservation Commission’s regularly scheduled meeting on June 4, 2024. To further inform the public of the project, Carlsbad Parks & Recreation staff and Communications & Engagement staff will coordinate with Channelside Water Resources staff on information to be posted to the city website and distributed via social media. Staff will post and distribute this information - prior to commencement of the dredging project - and will provide updates as needed during the dredging project. Exhibits 1. Agua Hedionda Lagoon - Outer Basin 2024-25 Maintenance Dredge and Beach Nourishment Cycle Sand Disposition Plan June 4, 2024 Item #2 2 of 143 AGUA HEDIONDA LAGOON – OUTER BASIN 2024–2025 MAINTENANCE DREDGE AND BEACH NOURISHMENT CYCLE SAND DEPOSITION PLAN Prepared by: Channelside Water Resources LP (formerly Poseidon Resources LP) 4590 Carlsbad Boulevard Carlsbad, California 92008 Anchor QEA 9700 Research Drive Irvine, California 92618 Prepared for: City of Carlsbad, California in fulfillment of Special Use Permit May 2024 Exhibit 1 June 4, 2024 Item #2 3 of 143 Agua Hedionda Lagoon – Outer Basin 2024–2025 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan i EXECUTIVE SUMMARY This Sand Deposition Plan has been prepared in fulfillment of Conditions 7, 8, and 9 of the City of Carlsbad Special Use Permit (SUP). Channelside Water Resources LP plan to conduct maintenance dredging and beach nourishment in 2024–2025 to remove a flood-tide shoal in the Outer Basin (also referred to as the West Basin) of Agua Hedionda Lagoon and maintain tidal exchange between the lagoon and ocean. Similar operations have been performed over the last seven decades. Approximately 400,000 cubic yards (cy) of sand are proposed to be removed from the Outer Basin. In keeping with past operations, the dredged sand will be placed on adjacent beaches: North Beach, Middle Beach, and South Beach. The proposed dredged sand beach placement volumes and ratios within this Sand Deposition Plan are consistent with previous beach nourishment events and use the 2020 Sand Deposition Plan (Appendix A) analyses. Final beach placement/nourishment volumes and ratios for this 2024–2025 event will be based upon a 2024 pre-construction beach survey (per SUP requirements) and summarized in a supplement to this document released in late 2024. Dredging and beach nourishment operations are proposed to occur between November 2024 and April 15, 2025. In 2020, the permitted sand placement quantities for each receiver beach were determined by regulatory agencies, with the cooperation of local residents and stakeholders, and by Dr. Scott Jenkins’s beach profile optimization modeling based on the then-current beach condition (defined by May 2020 and October 2020 beach profile surveys). The amount of sand placed on each of the receiver beaches was optimized based on computations of equilibrium beach profiles using 2020 conditions and maximizing recreational beach widths in proportion to use (i.e., North Beach is more heavily recreated than Middle Beach or South Beach), while avoiding impact to sensitive hard-bottom habitat. In addition, the 2020 Sand Deposition Plan (Appendix A) was designed to replace sand that had been eroded from the beaches since the 2018 dredge/beach nourishment event. Erosion losses on all three receiver beaches between the 2018 and 2020 dredge/beach nourishment cycles totaled 366,644 cy, with 60% of the erosion losses occurring on North Beach and 40% occurring on Middle Beach and South Beach. Based on the 2020 composite analysis, North Beach was proposed to receive 51% of dredged sand (approximately 150,000 cy) in 2020–2021, placed with beach slopes approximating an elliptic cycloid equilibrium profile in order to maximize retention time. North Beach nourishment was not to exceed 150,000 cy. Middle Beach and South Beach were to receive 49% of the dredged material (approximately 146,600 cy) with an approximate distribution of 55.6% (81,500 cy) and 44.4% (65,100 cy), respectively. Any surplus dredge quantities in excess of 300,000 cy were to be placed on Middle Beach and/or South Beach. In actuality, approximately 304,483 cy was hydraulically dredged and placed on all three receiver beaches (North Beach, Middle Beach, and South Beach) in 2020–2021 (conducted from February 15 to March 27, 2021). North Beach received approximately 121,667 cy (40%), Middle Beach received 100,992 cy (33%), and South Beach received 81,824 cy (27%) of the dredged material. This change in both dredge volume and placement ratios was due to project schedule constraints as well as the City of Carlsbad requirement for a pre-construction beach survey within 45 days of dredging to reassess receiver beach conditions. June 4, 2024 Item #2 4 of 143 Agua Hedionda Lagoon – Outer Basin 2024–2025 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan ii Per the requirements of the City of Carlsbad SUP in 2020–2021, a 2-year post-placement survey was performed at all three receiver beaches to assess beach and sand conditions. The April 2023 profiles at North Beach are either more eroded than, or roughly coincident to, the May 2020 pre-construction condition in the northern and central portions of the subreach. Similarly, the April 2023 profiles at Middle and South Beaches show that the beach was generally more eroded than the pre-construction (May 2020) conditions (Appendix B). The only occurrence of profile accretion was at the two transects located immediately north of the Agua Hedionda north jetties. This outcome suggests that the beach condition has effectively returned to, or eroded beyond, the pre-construction conditions from 2020. In April 2023, the average mean sea level shoreline position at North Beach was 2 feet wider than the May 2020 pre-construction condition. Middle Beach and South Beach retreated beyond the pre-construction condition over the same period (an average loss of 19 and 21 feet, respectively). Like the profile changes, these findings indicate that the shoreline within the study area has retreated to, or eroded beyond, the pre-construction conditions. The proposed 2024–2025 placement quantities, locations, and schedule are summarized in Table ES-1 and depicted in design figures found in Appendix C. Similar to the 2020–2021 beach nourishment cycle, the upcoming 2024–2025 cycle proposes a similar volume distribution between the beaches, acknowledging that North Beach has a similar shoreline position in pre-construction surveys between the cycles, indicating that a maximum volume of approximately 150,000 cy should be maintained to protect offshore habitat. Due to a larger dredge quantity within the Outer Basin to reach design depth and the more eroded conditions of Middle Beach and South Beach, a larger volume is proposed for Middle Beach and South Beach compared to that placed in 2021. Per the SUP, a pre-construction beach survey in fall or winter 2024 will be conducted at all three receiver beaches 45 days prior to the dredge cycle to refine these proposed sand placement volumes. Table ES-1. Beach Placement Quantities and Schedule1 Receiver Site Approximate Placement Quantity (with 2024 bathymetric conditions) Approximate Placement Quantity (with 20% Contingency) Approximate Schedule North Beach2 150,000 cy (37.5%) 150,000 cy (33.3%) January to March 2025 North Inlet Jetty to Maple Avenue 94,500 cy 94,500 cy -- Maple Avenue to Pine Avenue 55,500 cy 55,500 cy -- Middle Beach3 139,000 cy (34.5%) 166,800 cy (37.1%) November to December 2024 South Beach3 111,000 cy (28.0%) 133,200 cy (29.6%) March to April 15, 2025 Total 400,000 cy 450,000 cy -- Notes: 1. Sand placement operations my extend beyond March 2025 if adverse weather conditions or equipment issues are encountered. No sand will be placed on beaches after April 15, 2025, without written approval from appropriate regulatory agencies. Any surplus dredge quantities in excess of 400,000 cy will only be placed on Middle Beach and/or South Beach. June 4, 2024 Item #2 5 of 143 Agua Hedionda Lagoon – Outer Basin 2024–2025 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan iii 2. Sand placement quantity for North Beach is not to exceed 150,000 cubic yards. 3. Sand placement quantities for Middle Beach and South Beach are approximate. Sand placement on the Middle Beach may be completed prior to initiating sand placement on the North Beach if agreed upon by the City of Carlsbad. This is due to closer proximity to outer lagoon, faster mobilization times, and shorter distance to sand placement beach (Middle Beach). 4. For permitting purposes and to account for future sand deposition in the lagoon, a 20% contingency has been added to the design volume quantity for permit applications. --: not applicable June 4, 2024 Item #2 6 of 143 Agua Hedionda Lagoon – Outer Basin 2024–2025 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan iv TABLE OF CONTENTS Title Page No. EXECUTIVE SUMMARY ......................................................................................................... i 1. INTRODUCTION .......................................................................................................... 1 2. PROJECT DESCRIPTION ............................................................................................. 2 2.1 Dredging Operations ....................................................................................... 2 2.2 Beach Placement Operations ........................................................................... 2 2.3 Summary of Project Equipment ....................................................................... 7 2.4 Access and Pedestrian Control ........................................................................ 7 2.5 Contact Information ......................................................................................... 9 3. PROJECT SCHEDULE ................................................................................................ 10 4. SAND PLACEMENT QUANTITY DETERMINATION ........................................... 11 5. REFERENCES ............................................................................................................. 13 APPENDIX A. Agua Hedionda Lagoon – Outer Basin 2020–2021 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan (November 2020) APPENDIX B. Agua Hedionda Outer Lagoon 2020–2021 Dredge Cycle 2-Year Post-Construction Beach Profile Survey (June 2023) APPENDIX C. Agua Hedionda Outer Lagoon 2024–2025 Dredge Cycle Proposed Dredge Design Figures June 4, 2024 Item #2 7 of 143 Agua Hedionda Lagoon – Outer Basin 2024–2025 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 1 1. INTRODUCTION The rubble mound jetties at the Agua Hedionda Lagoon entrance were constructed in 1954 to maintain a stable inlet for the Encina Power Station (EPS) seawater intake (Shaw 1980). Initial dredging to create the cooling water basin was conducted at the same time. Ongoing maintenance dredging performed during the last seven decades has allowed the lagoon entrance to remain open to tidal exchange. Since 1994, maintenance dredging has been conducted at intervals of 1 to 4 years to remove floodtide shoaling that forms in the Outer Basin of Agua Hedionda Lagoon to maintain tidal exchange throughout the lagoon and provide cooling water flow rates required for EPS operations. The EPS discontinued operation in December 2018. However, maintenance dredging of the Outer Basin continues to be necessary to maintain tidal exchange throughout the lagoon and provide seawater to support the operation of the Claude “Bud” Lewis Carlsbad Desalination Plant. Between 1999 and 2015, approximately 3 million cubic yards (cy) of sediment were dredged from the Outer Basin and placed on neighboring beaches (Coastal Frontiers Corporation 2017). Individual dredge cycle quantities have ranged from 155,000 to 422,541 cy. The most recent operation, completed in 2021, accounted for 304,483 cy. Cabrillo Power I LLC (Cabrillo) and Channelside Water Resources LP (Channelside) plan to conduct the next phase of maintenance dredging in 2024–2025. Consistent with past maintenance dredging events, sediment removed from the Outer Basin will be placed on adjacent beaches: North Beach, Middle Beach, and South Beach. The work will be performed in accordance with the stipulations in the following permits: • City of Carlsbad Special Use Permit (SUP) • U.S. Army Corps of Engineers Permit SPL-2001-00328-RRS • California Coastal Commission Coastal Development Permit No. 6-20-0240 • San Diego Regional Water Quality Control Board 401 Water Quality Certification • California Department of Parks and Recreation Right of Entry Permit • California State Lands Commission Lease 932.1 This Sand Deposition Plan has been prepared in fulfillment of Conditions 7, 8, and 9 of the City of Carlsbad’s previously approved SUP. The following sections provide a project description, summarize the project schedule, describe the sand placement quantity calculations, and summarize the findings. June 4, 2024 Item #2 8 of 143 Agua Hedionda Lagoon – Outer Basin 2024–2025 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 2 2. PROJECT DESCRIPTION Dredging will be limited to the Outer Basin of Agua Hedionda Lagoon, which is bordered on the east by the railroad bridge and on the west by Carlsbad Boulevard (Figure 1). In accordance with the former 2020–2021 SUP, up to 500,000 cy were previously permitted to be removed from the Outer Basin, but the present 2024–2025 conditions indicate that the dredge amount will be on the order of 400,000 cy, which is slightly above the average range of dredging over the past 20 years (Table 1). In keeping with past operations, the dredged sand will be placed on adjacent beaches: North Beach, Middle Beach, and South Beach (Figure 1). The amount of sand placed on each of the receiver beaches will be optimized based on computations of equilibrium beach profiles using historical and present conditions balanced against maximizing recreational beach widths in proportion to use (i.e., North Beach is more heavily recreated than Middle or South Beaches), while avoiding impact to sensitive hard-bottom habitat. 2.1 Dredging Operations Dredging of the Agua Hedionda Lagoon Outer Basin will be performed using a diesel-powered hydraulic dredging hull barge. During operations, the dredge hull would be stabilized by wire cables that are secured to existing anchors on the shore of the lagoon. 2.2 Beach Placement Operations The dredged material (slurry) will be pumped to each of the receiver beaches (North Beach, Middle Beach, and South Beach; Figure 1) through a 20-inch-diameter pipeline. A floating section of pipe will convey the slurry from the dredge to the lagoon shoreline, where it will connect with a land-based pipeline that will deliver the material to the receiver beach. Figure 2 shows the approximate dredge pipeline routes for each receiver site. When material is placed at North Beach, the pipeline will traverse under the Carlsbad Boulevard Bridge and then north along the back of the beach as far as Pine Avenue. For the Middle Beach and South Beach receiver sites, an existing underground pipe under Carlsbad Boulevard may be used. In the case of South Beach, the pipelines will be extended along the back of the beach at Carlsbad State Beach to reach the south side of the EPS discharge jetty. Depending on shoal conditions, the pipe to Middle Beach may traverse under the Carlsbad Boulevard Bridge and then south for a portion of the discharge time on Middle Beach. As described previously, the slurry arriving from the dredge discharge pipeline is a mix of sand and water. Temporary dikes and berms will be constructed in the back-beach areas near the discharge points to dewater the slurry and aid in the retention of sand at the receiver beaches. As currently envisioned, two dikes would be constructed: one that is perpendicular to the beach connected to one that is parallel to the beach (forming an “L” shape). The dredged slurry will be discharged behind the dikes. Where sand is not present on the existing beach, an initial quantity of sand will be discharged on the highest portion of the beach and used to construct a dike. Once the sand slurries have been dewatered, the dikes and berms will be spread downslope across the existing beach face to the waterline using conventional earthmoving equipment in order to produce new beach slopes approximating elliptic cycloid equilibrium beach profiles. These methods have been used effectively in the past to maximize the retention of the dredged sands that are placed on the three receiver beaches. The dikes and berms also are used to ensure shoreline ocean turbidity does not exceed the limit as set in the San Diego Regional Water Quality Control Board 401 Water Quality Certifications. June 4, 2024 Item #2 9 of 143 Agua Hedionda Lagoon – Outer Basin 2024–2025 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 3 Table 1. Agua Hedionda Lagoon Maintenance Dredging of the Outer Basin, 1999 to 2021 Year Start Date Finish Date Volume Dredged (cy) Volume Placed (cy) Placement Beach 1999 2/1/1999 5/1/1999 155,000 155,000 North 2000–2001 11/1/2000 4/1/2001 422,541 141,346 North 195,930 Middle 85,265 South 2002–2003 12/2/2002 4/3/2003 354,266 161,525 North 131,377 Middle 61,364 South 2004–2005 1/5/2004 3/5/2005 348,151 100,487 North 170,515 Middle 77,149 South 2006–2007 1/7/2006 4/7/2007 333,373 149,168 North 121,038 Middle 63,167 South 2008–2009 12/8/2008 4/9/2009 299,326 104,141 North 102,000 Middle 93,185 South 2010–2011 12/10/2010 4/11/2011 226,026 62,030 North 93,696 Middle 70,300 South 2014–2015 12/14/2014 4/15/2015 294,661 64,968 North 156,056 Middle 73,637 South 2017–2018 10/17/2017 4/18/2018 205,482 0 North 141,172 Middle 64,310 South 2020–2021 2/15/2021 3/27/2021 304,483 121,667 North 100,992 Middle 81,824 South Total 2,943,309 2,943,309 Average 294,331 -- North Beach Total Placement 1,060,332 Middle Beach Total Placement 1,212,776 South Beach Total Placement 670,201 North Beach Average Placement 106,033 Middle Beach Average Placement 134,753 South Beach Average Placement 74,467 June 4, 2024 Item #2 10 of 143 Agua Hedionda Lagoon – Outer Basin 2024–2025 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 4 Figure 1. Project Location Map June 4, 2024 Item #2 11 of 143 Agua Hedionda Lagoon – Outer Basin 2024–2025 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 5 Figure 2. Dredge Discharge Pipeline Routes June 4, 2024 Item #2 12 of 143 Agua Hedionda Lagoon – Outer Basin 2024–2025 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 6 The discharge point is directed according to this Sand Deposition Plan. Once the material is dewatered, front-end loaders spread the sand on the beach and into the required elliptic cycloid beach profile configuration. As required by Condition 9 of the SUP, the beach berm will be no taller than 6 feet on the eastern aspect and will be groomed and flattened to provide recreational beach space. The elliptic cycloid grading profiles ensure that the dredged sands will be placed in such a manner that the beach profile slopes gradually to the surf zone. In the event that storm events begin to relocate the front aspect of the graded sand slope during the equilibration process, the berm and slope shall be regraded for public safety purposes. Material will not be placed in areas that will block existing drainage. In addition, a minimum 5-foot-wide path of travel will be maintained between sand placement operations and sea walls (both public and private). Target sand placement quantities for North Beach, Middle Beach, and South Beach were developed in the 2020 Sand Deposition Plan based on computations of equilibrium beach profiles using 2020 conditions, maximizing recreational beach widths in proportion use, while avoiding impact to the sensitive hard-bottom habitat (Appendix A). A 2-year post-construction beach transect survey was performed on all three receiver beaches in 2023, which indicates that all three receiver beaches have eroded equivalent to or beyond pre-dredge/beach nourishment conditions from the 2020–2021 dredge event (Appendix B). In 2020, the three receiver beaches were 93,141 cy below their carrying capacity (see Section 4.2 of Appendix A), which is the minimum amount of sand volume needed to maintain an equilibrium beach profile in the presence of historic extreme waves, otherwise known as the beach “critical mass” (Jenkins and Inman 2006). In addition, erosion losses on all three receiver beaches between 2018 and 2020 totaled approximately 366,644 cy (Appendix A). In 2024–2025, approximately 400,000 cy (450,000 cy for permit request purposes) from the Outer Basin is proposed to be dredged to avoid inlet closure and to replenish the sand on the North Beach, Middle Beach, and South Beach beyond the critical mass. To maintain the greatest retention time of sand on the beach, the sand will be configured as an elliptic cycloid. This approach is based on the latest coastal science and was the approach taken in the 2018 and 2021 beach nourishment cycles, and it will be continued in this Sand Deposition Plan for the 2024–2025 beach nourishment cycle. These computations are detailed in Appendix A. Per the SUP, a pre-construction beach survey in fall or winter 2024 will be conducted at all three receiver beaches 45 days prior to the dredge cycle to refine the proposed sand placement volumes. As described above, no more than 150,000 cy of dredge material is proposed for placement at North Beach. The remaining dredge material, approximately 250,000 cy, is proposed for placement at Middle Beach and South Beach, with an approximate distribution of 55.6% and 44.4% of that volume, or 34.5% and 28% of the total 400,000 cubic yards, respectively (Table 2). Any surplus dredge quantities in excess of 400,000 cy will only be placed on Middle Beach and/or South Beach. June 4, 2024 Item #2 13 of 143 Agua Hedionda Lagoon – Outer Basin 2024–2025 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 7 Table 2. Target Placement Quantities1 Receiver Site Approximate Placement Quantity (with 2024 bathymetric conditions) Approximate Placement Quantity (with 20% Contingency) Approximate Schedule North Beach2 150,000 cy (37.5%) 150,000 cy (33.3%) January to March 2025 North Inlet Jetty to Maple Avenue 94,500 cy 94,500 cy -- Maple Avenue to Pine Avenue 55,500 cy 55,500 cy -- Middle Beach3 139,000 cy (34.5%) 166,800 cy (37.1%) November to December 2024 South Beach3 111,000 cy (28.0%) 133,200 cy (29.6%) March to April 15, 2025 Total 400,000 cy 450,000 cy -- Notes: 1. Sand placement operations my extend beyond March 2025 if adverse weather conditions or equipment issues are encountered. No sand will be placed on beaches after April 15, 2025, without written approval from appropriate regulatory agencies. Any surplus dredge quantities in excess of 400,000 cy will only be placed on Middle Beach and/or South Beach. 2. Sand placement quantity for North Beach is not to exceed 150,000 cubic yards. 3. Sand placement quantities for Middle Beach and South Beach are approximate. Sand placement on the Middle Beach may be completed prior to initiating sand placement on the North Beach if agreed upon by the City of Carlsbad. This is due to closer proximity to outer lagoon, faster mobilization times, and shorter distance to sand placement beach (Middle Beach). 4. For permitting purposes and to account for future sand deposition in the lagoon, a 20% contingency has been added to the design volume quantity for permit applications. --: not applicable 2.3 Summary of Project Equipment The designated staging area for equipment and materials is on Fishing Beach located on the west shoreline of the Outer Basin. The following equipment is proposed to be used: • Hydraulic dredge • Slurry discharge pipe o Poly and steel pipe within the lagoon (floating) o Poly pipe along the shoreline • Rubber-tired loaders (one full time, second as needed) • Pickup truck (4x4) for support on the shoreline and public roadways 2.4 Access and Pedestrian Control Cabrillo and Channelside regard safety of the public and personnel foremost over all other tasks. Portable signage will be used at each discharge location to advise pedestrians of current work. An example of this signage is provided in Figure 3, but it will be modified to add Channelside and a revised call number. This signage is relocated as the dredge slurry discharge point moves. June 4, 2024 Item #2 14 of 143 Agua Hedionda Lagoon – Outer Basin 2024–2025 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 8 Figure 3. Example of Public Signage (To Be Revised as Necessary) No forms of public access to the shoreline will be blocked during sand deposition operations. Designated access ways over or around obstructions will be provided. Access for public safety vehicles also will be maintained. When discharging to South Beach, the piping is placed through an opening in the discharge channel fencing to ensure pedestrian safety. At no time will piping be placed on the pedestrian sidewalks along Carlsbad Boulevard. A monitor will be stationed at the north and south ends of the active work area to prevent foot traffic in the immediate discharge location. Appropriate signage and construction fencing will be used to identify the discharge location. The beach access areas will be left in a safe condition at the end of each workday. A flag crew will be used while moving or operating equipment on the beach. The pickup truck used to support the operation will use the shoreline and public roadways to avoid interference with pedestrian flow. As stipulated by Condition 9 of the SUP, a minimum 5-foot-wide path of travel will be maintained between sand placement operations and seawalls (both public and private). Discharge point relocation operations will be conducted during low pedestrian traffic times to the extent possible. In addition, project personnel will be available to answer any questions the public may have about the process. June 4, 2024 Item #2 15 of 143 Agua Hedionda Lagoon – Outer Basin 2024–2025 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 9 2.5 Contact Information The project is being conducted under the supervision of Ms. Isabella Murdy. Her contact information is provided as follows: Isabella Murdy, Executive Assistant Channelside Water Resources LP 4590 Carlsbad Boulevard Carlsbad, California 92008 949-212-1744 imurdy@channelsidedesal.com Should emergency response be necessary for the dredge/beach nourishment activity, you may contact Ms. Murdy, or follow the Hazardous Materials Business Plan Emergency Notification as provided to the Carlsbad Fire Department. June 4, 2024 Item #2 16 of 143 Agua Hedionda Lagoon – Outer Basin 2024–2025 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 10 3. PROJECT SCHEDULE The dredging and sand placement schedule shall be similar to past activities and conform with the requirements stipulated in the California Coastal Commission Coastal Development Permit. The anticipated schedule is shown in Table 3. Permit receipt timing may alter this schedule. Table 3. Schedule for 2024–2025 Dredge/Beach Nourishment Cycle Activity Approximate Dates Dredging November 2024 to April 15, 2025 Sand Placement -- North Beach January to March 2025 Middle Beach November to December 2024 South Beach March to April 15, 20251 Total Period of Activity November 2024 to April 15, 2025 Note: 1. Sand placement operations may extend beyond March 2025 if adverse weather conditions or equipment issues are encountered. No sand will be placed on beaches after April 15, 2025, without written approval from appropriate regulatory agencies. It is anticipated that all work will be conducted during daylight hours and between Monday and Saturday. If the schedule is delayed by storm activity, work may be conducted during daylight hours on Sundays with appropriate authorization. June 4, 2024 Item #2 17 of 143 Agua Hedionda Lagoon – Outer Basin 2024–2025 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 11 4. SAND PLACEMENT QUANTITY DETERMINATION For sand placement quantification, beach profile modeling, beach critical mass capacities, and beach erosion loss calculations, please refer to the 2020–2021 Sand Deposition Plan (Appendix A). A similar approach will be used for determining the volumes and placement locations for the upcoming 2024–2025 dredge/beach nourishment cycle. To determine the proper amount of sand to be placed on the beaches, the receiver beaches will be surveyed in late 2024, and the current sand volume will be calculated from the pre-dredge survey to guide the distribution of dredged sand among the beaches. Per the SUP, the pre-construction beach survey is to be conducted no earlier than 45 days prior to construction. The anticipated schedule for this 2024 survey is fall 2024. This report will be amended and resubmitted to appropriate agencies thereafter. Appendix B contains the Agua Hedionda Outer Lagoon 2020–2021 Dredge Cycle 2-Year Post-Construction Beach Profile Survey, performed in 2023. This survey information from all three receiver beaches supports the proposed beach placement ratios at the receiver beaches based on the similarities between the 2020 and 2023 beach conditions and will be confirmed with the pre-construction beach survey in fall 2024. The minimum carrying capacity of the North Beach, Middle Beach, and South Beach is shown in Table 4. Lesser amounts of beach fill will not be able to sustain an equilibrium profile during the highest-energy wave events. June 4, 2024 Item #2 18 of 143 Agua Hedionda Lagoon – Outer Basin 2024–2025 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 12 Table 4. Carrying Capacity and Target Sand Placement Volumes at Each Receiver Beach Receiver Site Minimum Carrying Capacity (Critical Mass, cy)1 Placement Volume to Re-Establish Critical Mass (2020) Proposed Placement Volume in 2020–2021 Actual Placement Volumes in 2020–2021 Proposed Placement Volume in 2024–2025 2024 Residual Beach Sand Volume Placement Volume to Re-Establish Critical Mass (2024) Permitted Sand Placement Volume North Beach 135,100 53,179 150,000 121,667 150,000 TBD pre-construction survey TBD pre-construction survey TBD pre-construction survey North Jetty to Maple Avenue 79,500 16,470 94,500 76,650 94,500 TBD pre-construction survey TBD pre-construction survey TBD pre-construction survey Maple Avenue to Pine Avenue 55,600 36,709 55,500 45,017 55,500 TBD pre-construction survey TBD pre-construction survey TBD pre-construction survey Middle Beach 134,600 39,962 81,500 100,992 139,000 TBD pre-construction survey TBD pre-construction survey TBD pre-construction survey South Beach 66,300 (6,735) surplus 65,100 81,824 111,000 TBD pre-construction survey TBD pre-construction survey TBD pre-construction survey Middle Beach and South Beach 200,900 33,227 146,600 182,816 250,000 TBD pre-construction survey TBD pre-construction survey TBD pre-construction survey TOTALS 336,000 86,406 296,600 304,483 400,000 -- -- -- Notes: 1. The minimal carrying capacity was developed in the 2020 Sand Deposition Plan (Appendix A) based on the period of record for the most severe wave events between 1998 and 2017 and the median grain size of the proposed dredged material and receiver beaches collected in 2008. No additional volume estimates or modeling was performed to recalculate the critical mass. TBD: to be determined June 4, 2024 Item #2 19 of 143 Agua Hedionda Lagoon – Outer Basin 2024–2025 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 13 5. REFERENCES Coastal Frontiers Corporation, 2017. SANDAG 2016 Regional Beach Monitoring Program – Annual Report. Jenkins, S.A., and D.L. Inman, 2006, “Thermodynamic Solutions for Equilibrium Beach Profiles.” Jour. Geophys. Res., v.3, C02003. doi:10.1029/2005JC002899. Shaw, M.J., 1980. Artificial Sediment Transport and Structures in Coastal Southern California. University of California, San Diego, Scripps Institute of Oceanography, SIO Reference No. 80-41. June 4, 2024 Item #2 20 of 143 APPENDIX A Agua Hedionda Lagoon – Outer Basin 2020–2021 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan (November 2020) June 4, 2024 Item #2 21 of 143 AGUA HEDIONDA LAGOON - OUTER BASIN 2020/21 MAINTENANCE DREDGE AND BEACH NOURISHMENT CYCLE SAND DEPOSITION PLAN Prepared by: Poseidon Resources (Channelside) LP 5780 Fleet Street, Suite 140, Carlsbad, CA 92008 and Prepared for: City of Carlsbad, California in fulfillment of Special Use Permit 06-10X2(A) November 2020 (Revised to incorporate November 5, 2020, California Coastal Commission Approval) June 4, 2024 Item #2 22 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan i EXECUTIVE SUMMARY This sand deposition plan has been prepared in fulfillment of Conditions 7, 8, and 9 of the City of Carlsbad Special Use Permit (SUP) 06-10X2(A). Cabrillo Power I LLC and Poseidon Resources (Channelside) LP plan to conduct maintenance dredging and beach nourishment in 2020/21 to remove a flood-tide shoal in the outer basin (also referred to as the West Basin) of Agua Hedionda Lagoon in order to maintain tidal exchange between the lagoon and ocean. Similar operations have been performed over the last six decades. Approximately 300,000 cubic yards (cy) of sand may be removed from the lagoon – outer basin. In keeping with past operations, the dredged sand will be placed on adjacent beaches: North Beach, Middle Beach, and South Beach. Operations will be conducted between November 2020 and 15 April 2021. The permitted sand placement quantities for each receiver beach were determined by regulatory agencies with the cooperation of local residents and stakeholders and by Dr. Scott Jenkins’ beach profile optimization modeling based on the current beach condition defined by a May 2020 and October 2020 beach profile surveys. The amount of sand placed on each of the receiver beaches was optimized based on computations of equilibrium beach profiles using current conditions and maximizing recreational beach widths in proportion to use (i.e. North Beach is more heavily recreated than Middle or South Beaches), while avoiding impact to sensitive hard bottom habitat. In addition, the proposed sand deposition plan is designed to replace sand that has been eroded from the beaches since the 2018 dredge/beach nourishment event. Erosion losses on all three receiver beaches since the last dredge/beach nourishment cycle in 2018 total 366,644 cy, with 60% of the erosion losses occurring on North Beach and 40% occurring on Middle and South Beach. Based on this composite analysis, North Beach will receive 51% of dredged sand (approximately 150,000 cy), to be placed with beach slopes approximating an elliptic cycloid equilibrium profile in order to maximize retention time. Middle and South Beach will receive 49% of the dredged material (approximately 146,600 cy) with an approximate distribution of 55.6% and 44.4%, respectively. Any surplus dredge quantities in excess of 300,000 cy will only be placed on Middle and/or South beaches. North Beach disposal will not exceed 150,000 cy. The proposed sand placement quantities and approximate schedule are summarized below. June 4, 2024 Item #2 23 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan ii Beach Placement Quantities and Schedule1 Receiver Site Approximate Placement Quantity Approximate Schedule North Beach2 150,000 cy January 2021 - March 2021 North Inlet Jetty to Maple Ave 94,500 cy Maple Ave to Pine Ave 55,500 cy Middle Beach3 81,575.6 cy November 2020 – December 2020 South Beach3 65,060.2 cy March 2021- 15 April 2021 Total 296,635.8 cy 300,000 cy 1Sand placement operations my extend beyond March 2021 if adverse weather conditions or equipment issues are encountered. No sand will be placed on beaches after April 15, 2021 without written approval from appropriate regulatory agencies. Any surplus dredge quantities in excess of 300,000 cy will only be placed on middle and/or south beaches. 2 Sand placement quantity for North Beach is not to exceed 150,000 cubic yards. 3 Sand placement quantities for Middle Beach and South Beach are approximate. Sand placement on the Middle Beach shall be completed prior to initiating sand placement on the North Beach. June 4, 2024 Item #2 24 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan iii TABLE OF CONTENTS Title Page No. EXECUTIVE SUMMARY ......................................................................................................... i 1. INTRODUCTION .......................................................................................................... 1 2. PROJECT DESCRIPTION ............................................................................................ 2 2.1 Dredging Operations ....................................................................................... 2 2.2 Beach Placement Operations .......................................................................... 2 2.3 Summary of Project Equipment ....................................................................... 7 2.4 Access and Pedestrian Control ....................................................................... 7 2.5 Contact Information ........................................................................................ 9 3. PROJECT SCHEDULE ................................................................................................. 9 4. SAND PLACEMENT QUANTITY DETERMINATION .......................................... 10 4.1 Beach Profile Survey ..................................................................................... 10 4.2 Sand Quantity Calculation Methods and Results .......................................... 16 5. SUMMARY ................................................................................................................. 22 6. REFERENCES ............................................................................................................. 24 APPENDIX A. Beach Profile Plots ......................................................................................... 25 APPENDIX B. Modeling Detail ............................................................................................. 40 APPENDIX C. Distribution of Dredge Fill on Receiver Beaches Based on Coastal Modeling - Beach Fill Profiles .................................................................................................................. 48 APPENDIX D. Permitted Distribution of Dredge Fill on Receiver Beaches Based on Coastal Modeling - Beach Fill profiles (November 2020) .................................................................... 60 June 4, 2024 Item #2 25 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 1 1. INTRODUCTION The rubble mound jetties at the Agua Hedionda Lagoon entrance were constructed in 1954 to maintain a stable inlet for the Encina Power Station (EPS) seawater intake (Shaw, 1980). Initial dredging to create the cooling water basin was conducted at the same time. Ongoing maintenance dredging performed during the last six decades has allowed the lagoon entrance to remain open to tidal exchange. Since 1994, maintenance dredging has been conducted at intervals of one to four years to remove a flood-tide shoal that forms in the Agua Hedionda Lagoon - Outer Basin to maintain tidal exchange throughout the lagoon and provide cooling water flowrates required for EPS operations. The EPS discontinued operation in December 2018. However, maintenance dredging of the outer basin continues to be necessary to maintain tidal exchange throughout the lagoon and provide seawater to support the operation of the Claude “Bud” Lewis Carlsbad Desalination Plant. Between 1994 and 2015, approximately 3.3 million cubic yards (cy) of sediment were dredged from the outer basin and placed on neighboring beaches (Coastal Frontiers, 2017a). Individual dredge cycle quantities have ranged from 159,000 to 429,000 cy. The most recent operation, completed in 2018, accounted for 205,482 cy. Cabrillo Power I LLC (Cabrillo) and Poseidon Resources (Channelside) LP (Poseidon) plan to conduct the next phase of maintenance dredging in 2020/2021. Consistent with past maintenance dredging events, sediment removed from the lagoon’s outer basin will be placed on adjacent beaches: North, Middle and South Beached. The work will be performed in accordance with the stipulations in the following permits: • City of Carlsbad Special Use Permit (SUP) 06-10X2(A) • US Army Corps of Engineers Permit SPL-2001-00328-RRS • California Coastal Commission Coastal Development Permit No. 6-20-0240 • San Diego Regional Water Quality Control Board 401 Water Quality Certification • California Department of Parks and Recreation Right of Entry Permit • California State Lands Commission Lease 932.1 This sand deposition plan has been prepared in fulfillment of Conditions 7, 8 and 9 of the City of Carlsbad SUP. The following sections provide a project description, summarize the project schedule, describe the sand placement quantity calculations, and summarize the findings. June 4, 2024 Item #2 26 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 2 2. PROJECT DESCRIPTION Dredging will be limited to the Agua Hedionda Lagoon – Outer Basin, which is bordered on the east by the railroad bridge and on the west by Carlsbad Boulevard (Figure 1). In accordance with the SUP, up to 500,000 cy may be removed from the outer basin, but the present conditions indicate the dredge amount will be on the order of 300,000 cy, which is in the average range of dredging over the past 20 years, (see Table-1). In keeping with past operations, the dredged sand will be placed on adjacent beaches: North Beach, Middle Beach, and South Beach (Figure 1). The amount of sand placed on each of the receiver beaches will be optimized based on computations of equilibrium beach profiles using current conditions balanced against maximizing recreational beach widths in proportion to use (i.e. North Beach more heavily recreated than Middle or South Beaches), while avoiding impact to sensitive hard bottom habitat. 2.1 Dredging Operations Dredging of the Agua Hedionda Lagoon - Outer Basin will be performed using a diesel-powered dredging hull barge. During operations, the dredge hull would be stabilized by wire cables that are secured to existing anchors on the shore of the lagoon. 2.2 Beach Placement Operations The dredged material (slurry) will be pumped to each of the receiver beaches (North, Middle and South Beach; Figure 1) through a 20-inch diameter pipeline. A floating section of pipe will convey the slurry from the dredge to the lagoon shoreline, where it will connect with a land-based pipeline that will deliver the material to the receiver beach. Figure 2 shows the approximate dredge pipeline routes for each receiver site. When material is placed at North Beach, the pipeline will traverse under the Carlsbad Boulevard Bridge and then north along the back of the beach as far as Pine Avenue. For the Middle and South Beach receiver sites, an existing underground pipe under Carlsbad Boulevard will be utilized. In the case of South Beach, the pipelines will be extended along the back of the beach at Carlsbad State Beach to reach the south side of the EPS discharge jetty. Depending on shoal conditions, the pipe to Middle Beach may traverse under the Carlsbad Boulevard Bridge and then south for a portion of the discharge time on Middle Beach. As described above, the slurry arriving from the dredge discharge pipeline is a mix of sand and water. Temporary dikes and berms will be constructed in the back-beach areas near the discharge points to de-water the slurry and aid in the retention of sand at the receiver beaches. As currently envisioned, two dikes would be constructed – one that is perpendicular to the beach connected to one that is parallel to the beach (forming an “L”). The dredged slurry will be discharged behind the dikes. Where sand is not present on the existing beach an initial quantity of sand will be discharged on the highest portion of the beach and used to construct a dike. Once the sand slurries have been dewatered, the dykes and berms will be spread downslope across the existing beach face to the waterline using conventional earth moving equipment in order to produce new beach slopes approximating elliptic cycloid equilibrium beach profiles. These methods have been used effectively in the past to maximize the retention of the dredged sands that June 4, 2024 Item #2 27 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 3 Table-1: Agua Hedionda Lagoon Dredging of the Outer (West) Basin, 1998-2018 Year Dredging Disposal Comments Date Volume cubic yard Influx Basin Volume cubic yard Location Start Finish Days Yds3/Day 1998 Dec-97 Feb-98 59,072 92 642 Middle 59,072 M Modification Feb-98 Jul-98 214,509 150 1,430 Inner 120,710 M Modification 93,799 S 1999 Feb-99 May-99 155,000 304 510 Outer 155,000 N Maintenance 2000-01 Nov-00 Apr-01 422,541 701 603 Outer 141,346 N Maintenance 195,930 M 85,265 S 2002-03 Dec-02 Apr-03 354,266 730 485 Outer 161,525 N Maintenance 131,377 M 61,364 S 2004-05 Jan-05 Mar-05 348,151 704 495 Outer 100,487 N Maintenance 170,515 M 77,149 S 2006-07 Jan-07 Apr-07 333,373 763 437 Outer 149,168 N Maintenance 121,038 M 63,167 S 2008-09 Dec-08 Apr-09 299,328 733 408 Outer 104,141 N Maintenance 102,000 M 93,185 S 2010-11 Dec-10 Apr-11 226,026 736 307 Outer 62,030 N Maintenance 93,696 M 70,300 S 2014-15 Dec-14 Apr-15 294,661 736 400 Outer 64,968 N Maintenance 156,056 M 73,637 S 0 N 2017-18 Oct-17 Apr-18 205,482 734 280 Outer 141,172 M Maintenance 64,310 S TOTAL 2,912,407 2,912,407 AVERAGE 291,240 MAINTENANCE TOTAL 2,638,828 June 4, 2024 Item #2 28 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 4 Figure 1. Project Location Map Note: North Beach receiver site used only during maintenance dredge/beach nourishment cycles when sand placement is dictated by existing beach condition. June 4, 2024 Item #2 29 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 5 Figure 2. Dredge Discharge Pipeline Routes Note: North Beach discharge pipeline installed only during maintenance dredge/beach nourishment cycles when sand placement is dictated by existing beach condition. June 4, 2024 Item #2 30 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 6 are placed on the three receiver beaches. The dikes and berms also are used to ensure shoreline ocean turbidity does not exceed the limit as set in the San Diego Regional Water Quality Control Board 401 Water Quality Certifications. The discharge point is directed according to the pre-determined sand deposition plan. Once the material is de-watered, front-end loaders spread the sand on the beach and into the required elliptic cycloid beach profile configuration. As required by Condition 9 of the SUP, the beach berm will be no taller than 6 ft on the eastern aspect and will be groomed and flattened to provide towel space. The elliptic cycloid grading profiles ensure that the dredged sands will be placed in such a manner that the beach profile slopes gradually to the surf zone. In the event that storm events begin to relocate the front aspect of the graded sand slope during the equilibration process, the berm and slope shall be regraded for public safety purposes. Material will not be placed in areas that will block existing drainage. In addition, a minimum 5-ft wide path of travel will be maintained between sand placement operations and sea walls (both public and private). Target sand placement quantities for North, Middle, and South Beach were developed based on computations of equilibrium beach profiles using current conditions and maximizing recreational beach widths in proportion use, while avoiding impact to the sensitive hard bottom habitat. Presently, the three receiver beaches are 93,141 cy below their carrying capacity (see Section 4.2), which is the minimum amount of sand volume needed to maintain an equilibrium beach profile in the presence of historic extreme waves, otherwise known as the beach critical mass, (Jenkins and Inman, 2006). In addition, erosion losses on all three receiver beaches since the last beach nourishment cycle in 2018 total 366,644 cy (see Table 4.) Therefore, approximately 300,000 cy from the lagoon’s outer basin is proposed to be dredged in order to avoid inlet closure and to replenish the sand on the North, Middle, and South Beaches. To maintain the greatest retention time of sand on the beach, the sand will be configured as an elliptic cycloid. This approach is based on the latest coastal science and was the approach taken in 2018 beach nourishment cycle and will be continued in this sand deposition plan for 2020/21 beach nourishment cycle. These computations are detailed in Appendix-B and the resulting elliptic cycloid beach fill grading designs that are plotted in Appendix-C. However, the grading designs in Appendix-C were modified to accommodate other factors of concern, including maximizing recreational beach widths in proportion to use, while avoiding impact to sensitive hard bottom habitat. These modified grading designs are found in Appendix-D and are referred to as permitted. As described above, no more than 150,000 cy of dredge material will be placed at North Beach and the remaining dredge material, of approximately 146,600 cy (146,635.8 cy), will be placed at Middle and South Beach with an approximate distribution of 55.6% and 44.4%, respectively (see Table 2). Any surplus dredge quantities in excess of 300,000 cy will only be placed on Middle and/or South beaches. North Beach disposal will not exceed 150,000 cy. June 4, 2024 Item #2 31 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 7 Table 2. Target Placement Quantities Receiver Site Approximate Placement Quantity North Beach 150,000 cy No. Inlet Jetty to Maple Ave. 94,500 cy Maple Ave. to Pine Ave. 55,500 cy Middle Beach 81,575 cy South Beach 65,060 cy TOTAL 296,635 cy 2.3 Summary of Project Equipment The designated staging area for equipment and materials is on Fishing Beach located on the west shoreline of the outer basin. The following equipment will be utilized. • Hydraulic dredge; • Slurry discharge pipe; o Poly and Steel pipe within the lagoon (floating); o Poly pipe along the shoreline; • Rubber tired loaders – one full time, second as needed; and • Pickup truck (4x4), for support on the shoreline and public roadways. 2.4 Access and Pedestrian Control Cabrillo and Poseidon regard safety of the public and personnel foremost over all other tasks. Portable signage will be used at each discharge location to advise pedestrians of current work. An example of this signage is provided in Figure 3 but will be modified to add Poseidon Resource and a revised the call number. This signage is relocated as the dredge slurry discharge point moves. June 4, 2024 Item #2 32 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 8 Figure 3. Example of Public Signage No forms of public access to the shoreline will be blocked during sand deposition operations. Designated access ways, over or around obstructions, will be provided. Access for public safety vehicles also will be maintained. When discharging to South Beach, the piping is placed through an opening in the discharge channel fencing to ensure pedestrian safety. At no time will piping be placed on the pedestrian sidewalks along Carlsbad Boulevard. A monitor will be stationed at the north and south ends of the active work area to prevent foot traffic in the immediate discharge location. Appropriate signage and construction fencing will be used to identify the discharge location. The beach access areas will be left in a safe condition at the end of each workday. A flag crew will be utilized while moving or operating equipment on the beach. The pickup truck used to support the operation will utilize the shoreline and public roadways to avoid interference with pedestrian flow. As stipulated by Condition 9 of the SUP, a minimum 5-ft wide path of travel will be maintained between sand placement operations and sea walls (both public and private). Discharge point relocation operations will be conducted during low pedestrian traffic times to the extent possible. In addition, project personnel will be available to answer any questions the public may have on the process. June 4, 2024 Item #2 33 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 9 2.5 Contact Information The project is being conducted under the supervision of Ms. Josie McKinley. Her contact information is provided below. Josie McKinley, Director of Project Development Poseidon Water LLC 5780 Fleet Street, Suite 140 Carlsbad, CA 92008 (760) 655-3989 voice (310) 991-3032 (cell) jmckinley@poseidonwater.com Should emergency response be necessary for the dredge/beach nourishment activity, you may contact Ms. McKinley, or follow the Hazardous Materials Business Plan Emergency Notification as provided to the Carlsbad Fire Department. 3. PROJECT SCHEDULE The dredging and sand placement schedule shall be similar to past activities and conform with the requirements stipulated in the California Coastal Commission Coastal Development Permit. The anticipated schedule is shown in Table 3. Table 3. Schedule for 2020/21 Dredge/Beach Nourishment Cycle Activity Approximate Dates Dredging November 2020 to April 15, 2021 Sand Placement North Beach January 2021 - March 2021 Middle Beach November 2020 – December 2020 South Beach March 2021- (15April 2021)1 Total Period of Activity October 2020 to April 15 2021 1 Sand placement operations my extend beyond March 2021 if adverse weather conditions or equipment issues are encountered. No sand will be placed on beaches after April 15, 2021 without written approval from appropriate regulatory agencies. It is anticipated that all work will be conducted during daylight hours and between Monday and Saturday. If the schedule is delayed by storm activity, work may be conducted during daylight hours on Sundays with appropriate authorization. June 4, 2024 Item #2 34 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 10 4. SAND PLACEMENT QUANTITY DETERMINATION 4.1 Beach Profile Surveys A post beach profile survey was conducted on 18 April 2018, immediately following completion of the 2017/2018 maintenance dredge and beach nourishment, as required by City of Carlsbad Special Use Permit (SUP) 06-10X2(A). This survey provided a baseline beach condition assessment. A new pre-beach nourishment profile survey was conducted on 13 May 2020 and 2 October 2020 to document the current condition of the beaches, and to determine erosion rates and erosion patterns following the April 2018 baseline survey. Data were obtained on 15 beach profile transects (Figure 4). Thirteen of the transects had been surveyed in 2018 on behalf of Cabrillo Power, while two were surveyed for the first time in 2020. Six of the Transects (CB-800 to CB 0850) correspond to historical locations included in the SANDAG Shoreline Monitoring Program and the City of Carlsbad Beach Monitoring Program (Coastal Frontiers, 2017a; 2017b). The data acquisition and reduction methods were comparable to those employed on the beach profile surveys conducted under the aforementioned programs. Survey control information was provided by Cabrillo prior to the field activities. The coordinates of the control points were confirmed at the time of the survey using real-time kinematic (RTK) GPS techniques. Survey activities were conducted under ideal conditions, with offshore winds and waves typically less than 3 ft. Data were acquired along each transect from the landward limit of the sandy beach to wading depth, which typically corresponded to 8 to 15 ft below Mean Lower Low Water (MLLW) Datum depending on the prevailing water level. The beach and surf zone were surveyed using a total station and a survey rodman. The total station was used to determine the position and elevation of the beach at each location occupied by the rodman. Each transect was surveyed from the back-beach seaward through the surf zone until the survey rod no longer protruded above the water surface when held erect. The data from the wading survey were processed using software developed by Trimble. The raw total station data were read by the software, and the coordinates and elevation of each data point were calculated. The electronic total station used to conduct the survey is capable of measuring elevation differences to within 0.1 ft and ranges to within 0.5 ft. However, because the swimmer was subjected to waves and currents in the surf zone, the horizontal position perpendicular to each transect (parallel to the shoreline) varied from minimal at short ranges to approximately 15 ft at the offshore end. The beach profile plots developed from the 18 April 2018 post-beach nourishment survey and the 13 May 2020 and 2 October 2020 pre-beach nourishment survey data are provided in Appendix A. The range on each profile plot represents the distance in feet seaward of the transect origin measured along the transect alignment. The elevation is given in feet relative to MLLW (1983-2001 Epoch). The beach profile survey data plotted in Appendix-A were loaded into June 4, 2024 Item #2 35 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 11 Figure 4. Beach Profile Transect Locations June 4, 2024 Item #2 36 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 12 AutoCad Civil 3-d to create 3-d models of the receiver beaches for 2018 post-beach nourishment condition and 2020 pre-beach nourishment conditions. Figure-5a shows the 3-d CAD model of the 2018 post-beach nourishment based on the 18 April 2018 beach profile survey; while Figure 5b plots the 3-d CAD model of the 2020 pre-beach nourishment based on the 13 May 2020 beach profile survey. By performing a spatial subtraction of the 2 October 2020 beach model from the 18 April 2018 model, the most current assessment of the erosion that has occurred since the 2018 beach nourishment is determined. Table-4 presents a detailed break-down of the sand losses that have occurred along each surveyed reach between 18 April 2018 and 2 October 2020. Spatial subtraction of the 2 October 2020 model from the 28 April 2018 model produces an accurate and highly detailed assessment of sand losses, as given in Table-4. Figure-5: Three-dimensional CAD models of the receiver beaches: a) based on the 18 April 2018 post-beach nourishment survey, and b) based on the 13 May 2020 pre-beach nourishment survey. June 4, 2024 Item #2 37 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 13 Table 4: Sand Losses on the Receiver Beaches Between 22 April 2018 and 2 October 2020 Receiver Beach Profile Range Line Distance between Range Lines Local Sand Loss ft3/ft of shoreline Sand Volume Lost between Range Lines, ft3 & yds3 South Beach Cab I-01 -980 750.57 622,034.9 ft3 = 23,038.3 yds3 South Beach Cab I-02 -677.5 513.50 438,785.7 ft3 = 16,251.3 yds3 South Beach Cab I-03 -1031.5 648.92 695,804.5 ft3 = 25,770.5 yds3 Middle Beach Cab I-04 -1,113 667.82 869,167.7 ft3 = 32,191.4 yds3 Middle Beach Cab I-05 -1,490 259.91 386,226.3 ft3 = 14,304.7 yds3 Middle Beach Cab I-06 Cab I-06 to South Inlet Jetty = 639.1 ft. -1,482 947,146.2 ft3 = 35,079.5 yds3 North Inlet Jetty to Cab I-07 = 460.0 ft North Beach Cab I-07 -1,859 1399.51 3,211,373.8 ft3 = 118,939.9 yds3 North Beach Cab I-08 -1,595 350.56 509,188.4 ft3 = 18,858.8 yds3 North Beach Cab I-09 -1,310 541.45 657,861.7 ft3 = 24,365.2 yds3 North Beach Cab I-10 -1120 609.00 697,305 ft3 = 25,826.1 yds3 North Beach Cab I-11 -1,170 728.00 864,500 ft3 = 32,018.5 yds3 North Beach Cab I-012 -1205 Total Sand Loss South Beach 1,756,625.1 ft3 = 65,060.2 yds3 Total Sand Loss Middle Beach 2,202,540.2 ft3 = 81,575.6 yds3 Total Sand Loss Cab I-07 to I-10 (No. of Inlet Jetty to Maple Ave) 4,378,423.9 ft3 = 162,163.9 yds3 Total Sand Loss Cab I-10 to I-12 (Maple Ave to Pine Ave 1,561,805.0 ft3 = 57,844.6 yds3 Total Sand Loss North Beach 5,940,228.9 ft3 = 220,008.5 yds3 Total Sand Loss 9,899,394.2 ft3 = 366,644.3 yds3 June 4, 2024 Item #2 38 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 14 Inspection of Table-4 indicates total erosion losses on all three receiver beaches since the last dredge/beach nourishment cycle in 2018 total 366,644 cy, with 60% of the erosion losses occurring on North Beach and 40% occurring on Middle and South Beach. More sand has been lost to erosion since 2018 on North Beach, (where no sand was placed during the 2018 dredge/beach nourishment cycle), than was lost on Middle and South Beaches combined; i.e. 220,009 cy eroded from North Beach vs only 146,636 cy lost on Middle and South Beach combined (81,576 cy, lost on Middle Beach and 65,060 cy lost on South Beach). This was a significant consideration in posing the 2020/21 sand deposition plan summarized in the Executive Summary. Another point to highlight here is that the definition of the North Beach receiver beach has varied over the years, ever since North Beach disposal has been practiced, beginning in 1998. North Beach disposal originally extended from the north inlet jetty to Maple Ave. Later, City of Carlsbad Special Use Permit (SUP) 06-10X2(A) redefined the North Beach disposal site to be extended to Pine Ave. Therefore, Table- 4 sub-divides the North Beach site between the north inlet jetty at survey range Cab I-07 to Maple Ave. at survey range Cab I-10; and from Cab I-10 to Pine Ave. at Cab I-12. Since the 18 April 2018 post-beach nourishment survey, 162,164 cy of beach sand has been lost between the north inlet jetty and Maple Street, while 57,845 cy has been lost between Maple Street and Pine Ave. In addition to the erosion losses that have occurred on the receiver beaches since the 2018 beach nourishment cycle, it is necessary to assess the remaining quantities of sand on the receiver beaches before beach nourishment quantities can be formulated. The carrying capacity of a beach is limited by the width of the wave-cut platform in the bedrock on which beach sands have accumulated over geologic time scales. To assess the residual sand volume, it is necessary to estimate the profile of the bedrock and basal conglomerate (aka, wave cut platform) on which the residual sand volume rests. Bed rock/basal conglomerate elevation profiles were derived from the composite minimum of SANDAG surveys 1997 -2012, (S97-S12) at transect CB-0800, CB-0810, CB-0820, CB-0830, CB-0840, and CB-0850. The composite minimums occurred during years when portions of the receiver beaches were stripped of sand by severe erosion, leaving only remnant cobble beaches. The composite minimum profiles representing the wave-cut platform are plotted in Appendix-A in Figures A-1, 6, 8, 9, 13, and 16. These profiles were lofted as a 3-d solid in AutoCad Civil 3-d and embedded inside the 3-d CAD models of the receiver beaches in Figures 5a & b. By performing a spatial subtraction of the 2 October 2020 beach model from the bedrock profile model, a reasonably accurate assessment of the residual sand volume remaining on the receiver beaches can be made. Table-5 presents a detailed break-down of the residual sand volume that remains as of 13 May 2020 and 2 October 2020 along each surveyed reach of receiver beach. Inspection of Table-5 indicates total residual sand volume remaining on all three receiver beaches since the last dredge/beach nourishment cycle in 2018 total 249,594 cy. More residual sand volume remains on the combined Middle Beach and South Beach complex (167,673 cy, Middle Beach = 94,638 cy and South Beach = 73,035 cy) than on North Beach, where remaining sand volume is only 81,921.4 cy. (This finding is likely due to beach stabilization by the 3 jetties along Middle and South Beaches). Thus, it is sensible to place more sand on North Beach during the June 4, 2024 Item #2 39 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 15 Table 5: Residual Sand Volume on the Receiver Beaches as of 2 October 2020 Survey Receiver Beach Profile Range Line Distance between Range Lines Residual Sand Volume ft3/ft of shoreline Residual Sand Volume between Range Lines, ft3 & yds3 South Beach Cab I-01 +1610 Cab I-01 to South Discharge Jetty = 1,264 ft. 1,971,945 ft3 = 73,035 cy Middle Beach Cab I-04 +1510 North Discharge Jetty to Cab I-06 = 1,576 ft 1,806,884 ft3 = 66,921 yds3 Middle Beach Cab I-06 +783 Cab I-06 to South Inlet Jetty = 955.7 ft. 748,359 ft3 = 27,717 yds3 North Inlet Jetty to Cab I-07 = 460 ft +510 234,600 ft3 = 8,689 yds3 North Beach Cab I-07 +670 1,750 ft. 1,082,375 ft3 = 40,087 yds3 North Beach Cab I-09 +567 1,878 ft. 894,867 ft3 = 33,143 yds3 North Beach Cab I-012 +386 Residual Sand South Beach 1,971,945 ft3 = 73,035 cy Residual Sand Middle Beach 2,55,226 ft3 = 94,638 yds3 Residual Sand Cab I-07 to I-10 No. of Inlet Jetty to Maple Ave. 1,701,815 ft3 = 63,030 yds3 Residual Sand Cab I-10 to I-12 Maple Ave. to Pine Ave. 510,062 ft3 = 18,891 yds3 Total Residual Sand North Beach 2,211,878 ft3 = 81,921.4 yds3 Total Residual Sand 6,739,049 ft3 = 249,594 yds3 June 4, 2024 Item #2 40 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 16 forthcoming 2020/21 dredge/beach nourishment cycle, then on the Middle/ South Beach complex. 4.2 Sand Quantity Calculation Methods and Results Beaches require a certain minimum sand volume (referred to as the critical mass) to sustain and equilibrium form in the presence of historic extreme waves, which is the theoretical minimum carrying capacity for sand. The carrying capacity of a beach is limited by the width of the wave- cut platform in the bedrock on which beach sands have accumulated over geologic time scales. The carrying capacity is also limited by wave climate, and more sand is required to accumulate on the wave cut platform in the presence of higher wave heights. The bedrock profiles Figures A-1, 6, 8, 9, 13, and 16 of Appendix-A indicate the wave-cut platform along Middle and South Beach is about 400 ft. to 500 ft. in width and only 300 ft. to 400 ft. in width along North Beach. The platforms are narrow because they were carved by wave action into erosion resistant bedrock formations during the present high-stand in sea level, and these narrow wave-cut platforms physically cannot hold large quantities of beach sand; and often become fully stripped during periods of high-energy winter waves. The carrying capacity (or minimal sand volume for each beach) is determined by the critical mass (Jenkins and Inman, 2006 and Jenkins, et al., 2007) based on the elliptic cycloid profile. The critical mass is calculated from maximum wave heights and sand grain sizes according to: ( ) 9.0 1.241023.1    =−HhVcc with:    = 2 o c ecsinh D D kh HKh and: 5/125/15/22   =gH Here ch is the closure depth; is a non-dimensional empirical parameter, D2 is the shorerise median grain size; and Do is a reference grain size ; /2=T is radian frequency; k is the wave number; is the shoaling factor relating breaker height to incident wave height bHH/=; g is acceleration of gravity; and  is a factor relating the depth of wave breaking bh to breaker height, bbhH=. For the critical mass calculations determining minimal placement volume, the following values for free parameters were used: mDK100~and,33.0~,0.2~oe . The minimal carrying capacities (critical mass) for each reach are summarized in Table-6. The minimum sand placement quantities for each receiver beach were determined by comparing the existing beach geomorphology with the critical mass sand volumes determined in Appendix- June 4, 2024 Item #2 41 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 17 B. The results are summarized in Table 6. The volume calculations were performed with surface modeling software using the equations detailed in Appendix-B. It should be noted that the minimal carrying capacity for the reach of North Beach between the north inlet jetty and Maple Ave is 79,500 cy, but when the North Beach disposal site is extended further north to Pine Ave, its minimal carrying capacity increase to 135,100 cy. As indicated in Table 6, the residual sand volume above the wave cut platform at the time of the 2 October 2020 beach profile survey is marginally less than the critical mass calculated in Appendix-B. Only 53,179 cy of dredged sand would be needed on North Beach to re-establish minimal carrying capacity (critical mass), with most of the deficit (36,709 cy) occurring in the Maple Ave. to Pine Ave. reach vs.; vs. only 16,470 cy required to restore critical mass in the Maple Ave to Pine Ave. reach. Presently Middle Beach requires just 39,962 cy of dredged sand to re- establish minimal carrying capacity (critical mass); while South Beach is over-built, with a surplus of 6,735 cy above its critical mass limit of 66,300 cy. Altogether, 93,141 cy of dredged sands are needed to restore all the receiver beaches to critical mass (i.e. the minimal carrying capacity). However, the sustainability of an open inlet to Agua Hedionda Lagoon requires that more than 93,141 cy must be dredged from the flood tide shoal in the West Basin of the lagoon. Approximately 300,000 cy is proposed to be dredged in order to avoid inlet closure; and that sand must be placed somewhere on the North, Middle, and South Beach. Therefore, the beaches will receive an excess of 203,494.8 cy beyond their minimal carrying capacity during the 2020/21 dredging of the lagoon. Even with excess sand beyond that needed to restore critical mass, the sand retention times will be maximized by using beach fill profiles that approximate the elliptic cycloid beach profile, Appendix-B. The elliptic cycloid profile is the beach shape that can be sustained in an equilibrium state during the most severe wave events. Elliptic cycloid beach-fill profiles for 13 of the 15 surveyed transects are developed in Appendix-C using the methodology detailed in Appendix-B. Two of the 15 were newly surveyed transects in May 2020 with no previous profile to estimate sand loss. The sand placement volumes derived from the mathematics in Appendix-B for these elliptic cycloidal beach fill profiles (referred to as distribution of dredge fill on receiver beaches based on coastal modeling) are summarized in Table-7. However, factors other than critical mass and elliptic cycloid mathematics entered into the sand placement quantities to be allocated to the 3 receiver beaches to be used for the 2020/21 dredging of the lagoon. Considerations for maximizing recreational beach widths in proportion to use and avoiding impact to sensitive hard bottom habitat were balanced against distribution of dredge beach fill on receiver beaches based on coastal modeling results in Table-7 and Appendix-C to achieve what is referred to herein as permitted distribution of dredge fill on receiver beaches. Permitted sand placement results in Table-8 and Appendix-D have been derived from discussions/approvals with local residents, stakeholders and regulatory agencies. The increases in mean beach widths derived from these permitted beach fill profiles are listed in Table-9. North Beach is the most heavily recreated of the 3 receiver beaches due to ease of access from the Tamarack parking lot. Access to Middle and South Beach is limited by available parking along the west shoulder of Carlsbad Blvd. Therefore, the largest volume of dredged sand (150,000 cy) is allocated to North Beach using the elliptic cycloid beach fill profiles applied to the permitted sand placement results per Appendix-D which will increase mean beach widths by a modest 33 ft. to 48 ft., resulting in mean beach widths of June 4, 2024 Item #2 42 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 18 Table 6. Carrying Capacity and Target Sand Placement Volumes at Each Receiver Beach Receiver Site Minimum Carrying Capacity (Critical Mass)1 Sand Volume Lost April 2018 to May 2020 Sand Volume Lost April 2018 to Oct. 2020 May 2020 Residual Sand Volume 2 Oct. 2020 Residual Sand Volume Placement Volume to Re-establish Critical Mass 2 Permitted Sand Placement Volume 3 North Beach 135,100 cy 164,780 cy 220,008.5 cy (60% of total) 125,078 cy 81,921.4 cy 53,179 cy 150,000 cy (51% of total) North Jetty to Maple Ave. 79,500 cy 118,248 cy 162,163.9 cy 84,176 cy 63,030.2 cy 16,470cy 94,500.0 cy Maple Ave. to Pine Ave. 55,600 cy 46,532 cy 57,844.6 cy 40,902 cy 18,891.2 cy 36,709 cy 55,500.0 cy Middle Beach 134,600 cy 68,435 81,575.6 cy 113,060 cy 94,638 cy 39,962 cy 81,575.6 cy South Beach 66,300 cy 62,059 cy 65,060.2 cy 76,300 cy 73,035 cy 0 cy 65,060.2 cy Mid + South 200,900 130,494 146,635.8 (40% of total) 189,360 cy 167,673 cy 39,962 cy 146,635.8 cy (49% of total) TOTALS 336,000 cy 295,274 366,644.3 cy 314,438 cy 249,594 cy 93,141 cy 296,635.8 cy Notes: 1 Determined by critical mass per Appendix-B & Jenkins and Inman, (2006) and Jenkins (2017a, 2017b, 2017c). 2 Based on difference between critical mass and October 2020 beach profile survey (Section 4.1). Critical mass determined from 1997-2012 composite minimum. 3 Permitted sand placement volumes should equal the placement volume required to re-establish elliptic cycloidal beach profiles that will maintain equilibrium in the presence of the historic maximum wave heights per Appendix-C and Column-5 in Table 7. However, maintaining recreational beach widths in proportion to use, while avoiding impact to sensitive hard bottom habitat, is an additional important consideration. Therefore, permitted placement volumes per Column- 8 above have been developed based on discussions/approvals with local residents, stakeholders and regulatory agencies. June 4, 2024 Item #2 43 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 19 Table 7: Required Distribution of Dredge Fill on Receiver Beaches to Achieve Cycloidal Equilibrium Beach Profiles as of 2 October 20201 Receiver Beach Profile Range Line Distance between Range Lines Required Beach Fill1, ft3/ft of shoreline Beach Fill between Range Lines to Achieve Required Cycloidal Equilibrium Profiles1 ft3 & yds3 South Beach Cab I-01 +887 750.57 643,703.4 ft3 = 23,844.2 yds3 South Beach Cab I-02 +828 513.50 515,136.7 ft3 = 19,079 yds3 South Beach Cab I-03 +1,178 648.92 465,231.5 ft3 = 17,230.8 yds3 Middle Beach Cab I-04 +256 667.82 335,836.6 ft3 = 12,438.4 yds3 Middle Beach Cab I-05 +750 259.91 219,315.0 ft3 = 8,122.8 yds3 Middle Beach Cab I-06 Cab I-06 to South Inlet Jetty = 955.7 ft. +938 2203.14 599,227.5 ft3 = 22,193.6 yds3 North Beach Cab I-07 +1,505 1399.51 2,183,410.3 ft3 = 80,867 yds3 North Beach Cab I-08 +1,615 350.56 521,314.3 ft3 = 19,307.9 yds3 North Beach Cab I-09 +1,359 541.45 660,621.6 ft3 = 24,467.5 yds3 North Beach Cab I-10 +1,081 609.00 802,608.4 ft3 = 29,726.2 yds3 North Beach Cab I-11 +1,554 728.00 1,153,493 ft3 = 42,721.9 yds3 North Beach Cab I-12 +1,565 Beach Fill Required for South Beach 1,624,065.4 ft3 = 60,150.6 yds3 Beach Fill Required for Middle Beach 1,154,376.4.1 ft3 = 42,754.7 yds3 Beach Fill Required South of Inlet 2,778,442.5 ft3 = 102,905.3 yds3 Beach Fill Required Cab I-07 to I-10 No. Inlet Jetty to Maple Ave 3,365,357.4 ft3 = 124,642.9yds3 Beach Fill Required Cab I-10 to I-12 Maple Ave to Pine Ave 1,956,104.6 ft3 = 72,448.3 yds3 Beach Fill Required for North Beach 5,321,464.8 ft3 = 197,091.3 yds3 Total Beach Fill Required to Achieve Cycloidal Equilibrium Profiles1 8,099,908.2 ft3 = 299,996.6 yds3 1 Required beach fill is based on difference between the 2 October 2020 beach profiles and the elliptic cycloidal beach profiles that will retain the required amount of lagoon sands that will be dredged in equilibrium. June 4, 2024 Item #2 44 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 20 Table 8: Required Permitted Distribution of Dredge Fill on Receiver Beaches to Achieve Elliptic Cycloidal Equilibrium Beach Profiles While Maintaining Recreational Beach Widths in Proportion to Use1 Receiver Beach Profile Range Line Distance between Range Lines Required Beach Fill ft3/ft of shoreline Beach Fill between Range Lines to Achieve Required Permitted Cycloidal Equilibrium Profiles to be Placed by Dredge Contractor ft3 & yds3 South Beach Cab I-01 +959 750.57 696,341 ft3 = 25,790 yds3 South Beach Cab I-02 +896 513.50 557,179 ft3 = 19,079 yds3 South Beach Cab I-03 +1,274 648.92 503,105 ft3 = 18,633 yds3 Middle Beach Cab I-04 +488 667.82 640,774 ft3 = 23,732 yds3 Middle Beach Cab I-05 +1,431 259.91 418,452 ft3 = 15,498 yds3 Middle Beach Cab I-06 Cab I-06 to South Inlet Jetty = 955.7 ft. +1,790 2203.14 1,143,320 ft3 = 42,345 yds3 North Beach Cab I-07 +1,141 1399.51 1,655,386 ft3 = 61,311 yds3 North Beach Cab I-08 +1,224 350.56 395,242 ft3 = 14,639 yds3 North Beach Cab I-09 +1,030 541.45 660,621.6 ft3 = 18,550 yds3 North Beach Cab I-10 +819 609.00 614,848 ft3 = 22,772 yds3 North Beach Cab I-11 +1,190 728.00 883648 ft3 = 32,728 yds3 North Beach Cab I-12 +1,199 Beach Fill to be Placed on South Beach 1,621,625.4 ft3 = 60,060.2 yds3 Beach Fill to be Placed on Middle Beach 2,202,546 ft3 = 81,575.6 yds3 Beach Fill to be Placed Between Cab I-07 to I-10 (North Inlet Jetty to Maple Ave) 2,551,500 ft3 = 94,500 yds3 Beach Fill to be Placed Between Cab I-10 to I-12 (Maple Ave to Pine Ave) 1,498500 ft3 = 55,500 yds3 Beach Fill to be Placed on North Beach 4,050,000 ft3 = 150,000 yds3 Total Permitted Beach Fill to be Placed on All Receiver Beaches While Maintaining Recreational Beach Widths in Proportion to Use 8,009,167 ft3 = 296,635.8 yds3 1 Recreational beach use requirements determined through discussions/approvals with local residents, stake holders and regulatory agencies. June 4, 2024 Item #2 45 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 21 Table 9: Permitted Mean Beach Widths After 2020/21 Maintenance Dredging Disposal Receiver Beach Profile Range Line Distance between Range Lines Beach widths 2 October 2020, ft. *Beach Widths per Permitted Beach Fill as Elliptic Cycloid Profiles, ft. Increase in Mean Beach Widths, Post- 2020/21 Dredging Disposal, ft. South Beach Cab I-01 180 ft. 281 ft. 101 ft. 750.57 South Beach Cab I-02 190 ft. 265 ft. 75 ft. 513.50 South Beach Cab I-03 170 ft. 265 ft. 95 ft. 648.92 Middle Beach Cab I-04 254 ft. 534 ft. 280 ft. 667.82 Middle Beach Cab I-05 208 ft. 473 ft. 265 ft. 259.91 Middle Beach Cab I-06 Cab I-06 to South Inlet Jetty=955.7ft 200 ft. 420 ft. 220 ft. North Inlet Jetty to Cab I-07 = 460.0 ft 2203.14 North Beach Cab I-07 150 ft. 192 ft. 42 ft. 1399.51 North Beach Cab I-08 145 ft. 178 ft. 33 ft. 350.56 North Beach Cab I-09 130 ft. 178 ft. 48 ft. 541.45 North Beach Cab I-10 150 ft. 191 ft. 41 ft. 609.00 North Beach Cab I-11 150 ft. 195 ft. 45 ft. 728.00 North Beach Cab I-012 135 ft. 169 ft. 34 ft. *Based on water elevations at mean sea level June 4, 2024 Item #2 46 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 22 169 ft. to 195 ft., (see Table-9). Somewhat smaller amounts are allocated to Middle and South Beach, with Middle Beach receiving 81,575.8 cy and South Beach receiving 65,060.2 cy, in proportion to lesser beach use and available on-site parking. Because of the relatively larger existing residual sand volumes on these beaches, the permitted allocations to Middle Beach will increase mean beach widths by as much as 220 ft. to 280 ft., resulting in mean beach widths of 420 ft. to 534 ft.; while mean beach widths at South Beach will increase by as much as 75 ft. to 101 ft., resulting in mean beach widths of 265 ft. to 281 ft. (see Table-9). It should be noted that the heavier allocation of dredged sand to North Beach is consistent with beach nourishment plans approved in 1999, 2002 and 2006, (see Table-1), and due to the ocean’s southern littoral drift, sand will be naturally transported from the North, Middle and South Beaches to beaches located downcoast. 5. SUMMARY Cabrillo and Poseidon plan to conduct maintenance dredging in 2020/21 to remove a flood-tide shoal in the Agua Hedionda Lagoon - Outer Basin in order maintain the tidal exchange between the lagoon and the ocean and provide seawater to support the operation of the Claude “Bud” Lewis Carlsbad Desalination Plant. Similar operations have been performed over the last six decades. Approximately 300,000 cy of sand may be removed from the lagoon – outer basin. In keeping with past operations, the dredged sand will be placed on adjacent beaches: North Beach, Middle Beach, and South Beach. Operations will be conducted between November 2020 and April 2021. Sand placement quantities for each receiver beach was determined based on an assessment of the minimal sand required to re-establish sand carrying capacity, residual sands remaining on the receiver beaches, and maximizing recreational beach widths in proportion to use, while avoiding impact to sensitive hard bottom habitat. The proposed sand placement quantities and approximate schedule are summarized in Table-10 on the following page. June 4, 2024 Item #2 47 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 23 Table 10: Beach Placement Quantities and Schedule1 Receiver Site Approximate Placement Quantity Approximate Schedule North Beach2 150,000 cy January 2021 - March 2021 North Inlet Jetty to Maple Ave 94,500 cy Maple Ave to Pine Ave 55,500 cy Middle Beach3 81,575.6 cy November 2020 – December 2020 South Beach3 65,060.2 cy March 2021- 15April 2021 Total 296,635.8 cy 300,000 cy 1Sand placement operations my extend beyond March 2021 if adverse weather conditions or equipment issues are encountered. No sand will be placed on beaches after April 15, 2021 without written approval from appropriate regulatory agencies. Any surplus dredge quantities in excess of 300,000 cy will only be placed on middle and/or south beaches. 2 Sand placement quantity for North Beach is not to exceed 150,000 cubic yards. 3 Sand placement quantities for Middle Beach and South Beach are approximate. Sand placement on the Middle Beach shall be completed prior to initiating sand placement on the North Beach. June 4, 2024 Item #2 48 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan 24 6. REFERENCES Coastal Frontiers Corporation, 2017a, “SANDAG 2016 Regional Beach Monitoring Program – Annual Report”, Moorpark, CA, 138 pp. + app. Coastal Frontiers Corporation, 2017b, “City of Carlsbad Beach Spring 2017 Beach Profile Survey”, letter report to Ms. Aeryn Donnelly-Terrey dated July 28, 2017, from Coastal Frontiers Corporation, Moorpark, CA. Jenkins, S. A. and D. L. Inman, 2006, “Thermodynamic solutions for equilibrium beach profiles”, Jour. Geophys. Res., v.3, C02003, doi:10.1029/2005JC002899, 2006. 21pp. Jenkins, S. A., Inman, D.L., Michael D. Richardson, M.D., Thomas F. Wever, T.F. and J. Wasyl, 2007, “Scour and burial mechanics of objects in the nearshore”, IEEE Jour.Oc.Eng, vol.32, no. 1, pp 78-90 Jenkins, S. A, (2010), “Hydrodynamic Analysis of Future Dredge Requirements and Inlet Closure Risks for Agua Hedionda Lagoon during Reduced Intake Flow Operations at Encina Power Station”, submitted to NRG Cabrillo Power Operations Inc., 129 pp. Jenkins, S. A., 2017a, “Beach Equilibrium Analysis of North Beach Disposal Options for Dredged Sands from Agua Hedionda Lagoon, Carlsbad, CA,” submitted to Cabrillo Power I LLC, 66 pp. Jenkins, S. A., 2017b, “Beach Equilibrium Analysis of Middle and South Beach Disposal Options for Dredged Sands from Agua Hedionda Lagoon, Carlsbad, CA,” submitted to Cabrillo Power I LLC, 72 pp. Jenkins, S. A., 2017c, “Cabrillo Power I LLC, Encina Power Station, Outer Agua Lagoon Maintenance Dredging Coastal Development Permit.”, letter to Ms. Erin Prahler, California Coastal Commission, San Diego Coast District Office, dated 6 September 2017, Poway, CA. SANDAG, 2017, “Shoreline Management” from http://www.sandag.org/index.asp? subclassid=32&fuseaction=home.subclasshome Shaw, Martha J., 1980, “Artificial Sediment Transport and Structures in Coastal Southern California”, University of California, San Diego, Scripps Institute of Oceanography, SIO Reference No. 80-41, La Jolla, CA, 109pp. \ June 4, 2024 Item #2 49 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix A 25 Appendix-A: Surveys at Beach Disposal Sites Following 2018 Maintenance Dredge/Beach Nourishment Cycle Coordinates of Benchmark: Northing (ft): 1994408.5 Easting (ft): 6228847.4 Figure A-1: Measured beach profiles at survey range Cab I-01 on South Beach, after the most recent Agua Hedionda Lagoon – Outer Basin maintenance dredge/beach nourishment on 22 April 2018, (red line); prior to the 2020/2021 maintenance dredge/beach nourishment on 13 May 2020, (cyan line); and most recent pre-dredging survey on 2 Oct 2020 (dark blue line) Bed rock/basal conglomerate (hard bottom) elevation based on composite minimum of SANDAG surveys 1997 -2012, (S97-S12) at transect CB-0800. June 4, 2024 Item #2 50 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix A 26 Coordinates of Benchmark: Northing (ft): 1995102.9 Easting (ft): 6228562.5 Figure A-2 Measured beach profiles at survey range Cab I-02 on South Beach, after the most recent Agua Hedionda Lagoon – Outer Basin maintenance dredge/beach nourishment on 22 April 2018, (red line); prior to the 2020/2021 maintenance dredge/beach nourishment on 13 May 2020, (cyan line); and most recent pre-dredging survey on 2 Oct 2020 (dark blue line). June 4, 2024 Item #2 51 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix A 27 Coordinates of Benchmark: Northing (ft): 1995576.9 Easting (ft): 6228365 Figure A-3: Measured beach profiles at survey range Cab I-03 on South Beach, after the most recent Agua Hedionda Lagoon – Outer Basin maintenance dredge/beach nourishment on 22 April 2018 (red line); and prior to the 2020/2021 maintenance dredge/beach nourishment on 13 May 2020 (cyan line); and most recent pre-dredging survey on 2 Oct 2020 (dark blue line). June 4, 2024 Item #2 52 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix A 28 Coordinates of Benchmark: Northing (ft): 1995677.7 Easting (ft): 6228319.9 Figure A-4 Measured beach profiles at survey range Cab I-03.2 on South Beach, after the most recent Agua Hedionda Lagoon – Outer Basin maintenance dredge/beach nourishment on 22 April 2018 (red line); and prior to the 2020/2021 maintenance dredge/beach nourishment on 13 May 2020 (cyan line); and most recent pre-dredging survey on 2 Oct 2020 (dark blue line). June 4, 2024 Item #2 53 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix A 29 Coordinates of Benchmark: Northing (ft): 1995925.1 Easting (ft): 6228209.1 Figure A-5: Measured beach profiles at survey range Cab I-03.6 on Middle Beach, after the most recent Agua Hedionda Lagoon – Outer Basin maintenance dredge/beach nourishment on 22 April 2018 (red line); and prior to the 2020/2021 maintenance dredge/beach nourishmenton 13 May 2020 (cyan line); and most recent pre-dredging survey on 2 Oct 2020 (dark blue line). June 4, 2024 Item #2 54 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix A 30 Coordinates of Benchmark: Northing (ft): 1996164.9 Easting (ft): 6228090.5 Figure A-6: Measured beach profiles at survey range Cab I-04 on Middle Beach, after the most recent Agua Hedionda Lagoon – Outer Basin maintenance dredge/beach nourishment on 22 April 2018, (red line); prior to the 2020/2021 maintenance dredge/beach nourishment on 13 May 2020, (cyan line); and most recent pre-dredging survey on 2 Oct 2020 (dark blue line) Bed rock/basal conglomerate (hard bottom) elevation based on composite minimum of SANDAG surveys 1997 -2012, (S97-S12) at transect CB-0810. June 4, 2024 Item #2 55 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix A 31 Coordinates of Benchmark: Northing (ft): 1996778.5 Easting (ft): 6227826.9 Figure A-7: Measured beach profiles at survey range Cab I-05 on Middle Beach, after the most recent Agua Hedionda Lagoon – Outer Basin maintenance dredge/beach nourishment on 22 April 2018 (red line); and prior to the 2020/2021 maintenance dredge/beach nourishment on 13 May 2020 (cyan line); and most recent pre-dredging survey on 2 Oct 2020 (dark blue line). June 4, 2024 Item #2 56 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix A 32 Coordinates of Benchmark: Northing (ft): 1997015.5 Easting (ft): 6227720.2 Figure A-8: Measured beach profiles at survey range Cab I-06 on Middle Beach, after the most recent Agua Hedionda Lagoon – Outer Basin maintenance dredge/beach nourishment on 22 April 2018, (red line); prior to the 2020/2021 maintenance dredge/beach nourishment on 13 May 2020, (cyan line); and most recent pre-dredging survey on 2 Oct 2020 (dark blue line) Bed rock/basal conglomerate (hard bottom) elevation based on composite minimum of SANDAG surveys 1997 -2012, (S97-S12) at transect CB-0820. June 4, 2024 Item #2 57 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix A 33 Coordinates of Benchmark: Northing (ft): 1998772.8 Easting (ft): 6226391.4 Figure A-9 Measured beach profiles at survey range Cab I-07 on North Beach, after the most recent Agua Hedionda Lagoon – Outer Basin maintenance dredge/beach nourishment on 22 April 2018, (red line); prior to the 2020/2021 maintenance dredge/beach nourishment on 13 May 2020, (cyan line); and most recent pre-dredging survey on 2 Oct 2020 (dark blue line) Bed rock/basal conglomerate (hard bottom) elevation based on composite minimum of SANDAG surveys 1997 -2012, (S97-S12) at transect CB-0830. June 4, 2024 Item #2 58 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix A 34 Coordinates of Benchmark: Northing (ft): 1999373.5 Easting (ft): 6226032.4 Figure A-10: Measured beach profiles at survey range Cab I-07.5 on North Beach, after the most recent Agua Hedionda Lagoon - Outer Basin maintenance dredge/beach nourishment on 22 April 2018 (red line); and prior to the 2020/2021 maintenance dredge/beach nourishment on 13 May 2020 (cyan line); and most recent pre-dredging survey on 2 Oct 2020 (dark blue line). June 4, 2024 Item #2 59 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix A 35 Coordinates of Benchmark: Northing (ft): 1999973.2 Easting (ft): 6225671.9 Figure A-11: Measured beach profiles at survey range Cab I-08 on North Beach, after the most recent Agua Hedionda Lagoon – Outer Basin maintenance dredge/beach nourishment on 22 April 2018 (red line); and prior to the 2020/2021 maintenance dredge/beach nourishment on 13 May 2020 (cyan line); and most recent pre-dredging survey on 2 Oct 2020 (dark blue line). June 4, 2024 Item #2 60 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix A 36 Coordinates of Benchmark: Northing (ft): 2000268.7 Easting (ft): 6225483.3 Figure A-12: Measured beach profiles at survey range Cab I-09 on North Beach, after the most recent Agua Hedionda Lagoon – Outer Basin maintenance dredge/beach nourishment on 22 April 2018 (red line); prior to the 2020/2021 maintenance dredge/beach nourishment on 13 May 2020 (cyan line); and most recent pre-dredging survey on 2 Oct 2020 (dark blue line). Bed rock/basal conglomerate (hard bottom) elevation based on composite minimum of SANDAG surveys 1997 -2012, (S97-S12) at transect CB-0840. June 4, 2024 Item #2 61 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix A 37 Coordinates of Benchmark: Northing (ft): 2000741.1 Easting (ft): 6225218.1 Figure A-13: Measured beach profiles at survey range Cab I-10 on North Beach, after the most recent Agua Hedionda Lagoon – Outer Basin maintenance dredge/beach nourishment on 22 April 2018 (red line); prior to the 2020/2021 maintenance dredge/beach nourishment on 13 May 2020 (cyan line); and most recent pre-dredging survey on 2 Oct 2020 (dark blue line). June 4, 2024 Item #2 62 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix A 38 Coordinates of Benchmark: Northing (ft): 2001257.9 Easting (ft): 6224917.9 Figure A-14: Measured beach profiles at survey range Cab I-11 on North Beach, after the most recent Agua Hedionda Lagoon – Outer Basin maintenance dredge/beach nourishment on 22 April 2018 (red line); prior to the 2020/2021 maintenance dredge/beach nourishment on 13 May 2020 (cyan line); and most recent pre-dredging survey on 2 Oct 2020 (dark blue line). June 4, 2024 Item #2 63 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix A 39 Coordinates of Benchmark: Northing (ft): 2001823.9 Easting (ft): 6224695.8 Figure A-15: Measured beach profiles at survey range Cab I-12 on North Beach, after the most recent Agua Hedionda Lagoon – Outer Basin maintenance dredge/beach nourishment on 22 April 2018, (red line); prior to the 2020/2021 maintenance dredge/beach nourishment on 13 May 2020, (cyan line); and most recent pre-dredging survey on 2 Oct 2020 (dark blue line). Bed rock/basal conglomerate (hard bottom) elevation based on composite minimum of SANDAG surveys 1997 -2012, (S97-S12) at transect CB-0850. June 4, 2024 Item #2 64 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix B 40 Appendix-B: Elliptic Cycloid Equilibrium Profiles and Critical Mass The critical mass is the minimum volume of sediment cover required to maintain equilibrium beach profiles and represents the nominal carrying capacity of a particular beach. When a long-term collection of beach profiles are plotted together over a broad range of wave heights, a well-defined envelope of variability becomes apparent, (Figure 11a). This envelope of profile variability is referred to as the critical mass envelope, and the volume of sand within critical mass envelope, cV , increases with increasing wave height and period but decreases with increasing beach grain size, as shown in Figure B-1b. The critical mass envelope is always limited by the breadth of the wave cut platform which forms a hard-bottom boundary condition on the critical mass envelope. The best way to calculate the critical mass is to find the volume between the wave cut platform (or its layer of basal conglomerate) and the elliptic cycloid equilibrium profile that corresponds to the native beach grain size in combination with the wave height and period of the extreme event wave in the period of record. The volume integral between the surfaces of the wave cut platform and the extremal event elliptic cycloid then gives the critical mass volume. The extremal elliptic cycloid equilibrium profile is a curve that is traced by a point on the circumference of a rolling ellipse, see Figure 12b. It is calculated from Jenkins and Inman (2006) using the following: 1)2(sin cos1 2 ZI xh e +   − −=  (1) Note this has the same basic formulation of the original Dean (1977 and 1991) solutions in the U.S. Army Corps of Engineers Coastal Engineering Manual Here Z1 is the elevation of the berm crest (see Figure 12a) given by Hunt’s Formula [Hunt, 1959; Guza and Thornton, 1985; Raubenheimer and Guza, 1996]: b1HZ−= (2) In equation (2),  is the runup factor taken herein as 76.0=, and bH is the breaking wave height. The cycloid in (1) is based on the elliptic integral of the second kind that has an analytic approximation, 2/)2(2)2(eIe−=, where e is the eccentricity of the ellipse given by 22/1 abe−=, with, semi-major and semi-minor axes are a, b, (see Figure 12b). The wave parameter,, in equation (1) is given by: 5/2 5/1 5/42/1 2     =   g H g Hb (3) here /period2=is radian frequency,H is incident wave height, g is the acceleration of gravity, and is the wave breaking criteria taken as = 0.8. The rolling angle of the ellipse is: June 4, 2024 Item #2 65 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix B 41 Figure B-1: Features of the critical mass of sand: a) critical mass envelope for waves ranging from 1m to 5m in height; b) volume of critical mass as a function of wave height and sediment grain size; c) variation in the thickness of the critical mass as a function of distance offshore. June 4, 2024 Item #2 66 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix B 42 Figure B-2. Equilibrium beach profile theory: a) nomenclature, b) mathematical basis for an elliptic cycloid, c) Typical range of elliptic cycloids on a 700 m wide wave-cut platform. June 4, 2024 Item #2 67 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix B 43          −=   ch H21arccos (4) where  is the shoaling factor relating breaker height to incident wave height, = H / Hb, which for shoaling Airy waves, becomes 5/125/15/22   =gH . The closure depth, ch in equation (4) is grain size and wave period dependent and is given by:    = 50 0 c ecsinh D D kh HKh (5) where cghk/=is the shallow water form of the wave number, Ke and ~ 2.0 are non- dimensional empirical parameters, set at Ke = 2.0 and ~ 0.33; 50D is the median grain size; and D0 is a reference grain size taken as 0D = 100 m. Equation (5) is transcendental and is solved numerically within the CEM. Calculation of the extremal elliptic cycloid equilibrium profiles at North, Middle and South Beach requires knowledge of the characteristic median grain size, 50D , of the dredged sediments to be placed there. Recent sediment grain size analyses by Merkel, (2008) based on three sampling locations on the flood tide bar in the West Basin of Agua Hedionda Lagoon (Samples L1 – L3) were compared against native sediments on the three receiver beaches (RB1-RB3). These grain size distributions are plotted in Figure B-3. Note Middle and South Beach is represented by samples RB1. Grain sizes at the lagoon sample sites and beach sites were similar with median grain sizes of 0.32 millimeters (320 microns) on the food tide bar in the West Basin of Agua Hedionda, while residual sediments that still remained on Middle and South Beach prior to disposal of material from the 2008/09 dredging averaged 0.374 millimeters (374 microns). To determine the highest waves to reach to effect North, Middle and South Beach disposal sites, the waves measured at ½ hour sampling intervals at CDIP Station 043 were back refracted into deep water from the monitoring location off Camp Pendleton, and then forward refracted into North, Middle and South Beach. An example of this procedure is shown in Figure B-4 for a wave occurring 8 January 2002. This effort produced a continuous wave record throughout the historic period when North, Middle and South Beach disposal of Agua Hedionda dredged sands was practiced, (1998-2015). The highest energy wave (extremal) event occurred in January 2007, when a Gulf of Alaska storm brought 4.8 m high waves approaching Carlsbad at 276 0 with a 15 second periods, (Figure B-5). This extreme event wave was used to calculate the extremal elliptic cycloids and critical mass on North, Middle and South Beach. June 4, 2024 Item #2 68 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix B 44 Figure B-3: Grain size distributions form Agua Hedionda Lagoon (Samples L1 – L3) and from the receiver beaches (RB1-RB3). Note Middle and South Beach is represented by samples RB1, (from Merkel, 2008). June 4, 2024 Item #2 69 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix B 45 Figure B-4: Regional wave shoaling during 8 January 2002 from back-refraction of wave monitoring data at CDIP Station # 043 in 20 m local water depth offshore of Camp Pendleton. June 4, 2024 Item #2 70 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix B 46 Figure B-5: Shoaled significant wave heights, periods and directions at Carlsbad State Beach based on back refraction of wave monitoring data from CDIP Station 043 at Camp Pendleton for the period of record of Middle and South Beach disposal, 1998-2017. June 4, 2024 Item #2 71 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix B 47 To calculate the critical mass of North, Middle and South Beach, we combine the extremal waves with the 50D grain size values from Figure B-3 to solve equations (1) – (5) for the extremal elliptic cycloid profile. These extremal cycloid profiles are plotted in Appendix-C These profiles represent the beach shape that can be sustained in an equilibrium state during the most severe wave events of the period of record, 1998-2017. These profiles form the top of the critical mass envelope, while the most eroded profile (from composite minimum of SANDAG surveys 1997 -2012, (S97-S12) at transect CB-0800 - 850) define the bottom of critical mass envelope. When lofted in the AutoCad Civil 3-d software, the volume tool calculates the total critical mass envelope to hold of 336,000 cubic yards along all of the receiver beaches combined; with 135,100 cubic yards on North Beach, 134,600 cubic yards on Middle Beach and 66,300 cubic yards on South Beach. These volumes represent the minimal carrying capacity of the North, Middle and South Beach disposal sites, respectively. Lesser amounts of beach fill will not be able to sustain an equilibrium profile during the highest energy wave events; and without an equilibrium profile, the beach will not dissipate all the incident wave energy, and the excess wave energy will erode the beach. If North, Middle or South Beach are over-nourished with more than the critical mass of sand, then two processes will intervene: a) the excess sand will spill off the wave cut platform and be re-suspended over the rocky outcrops and hard bottom substrate offshore of the receiver beaches; and/or b) the excess sand will be swept away by the net longshore transport (littoral drift) which flows from north to south throughout the Oceanside Littoral Cell, thereby reducing sand residence time. June 4, 2024 Item #2 72 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix C 48 Appendix - C: Distribution of Dredge Fill on Receiver Beaches Based on Coastal Modeling - Beach Fill Profiles Figure C-1: Required beach fill based on coastal modeling at range line Cab I-01 on South Beach configured as the extremal elliptic cycloid profile that will maintain equilibrium in the presence of historic extreme waves with 4.8 m wave height and 15 second wave period, cf. Figure B-5. June 4, 2024 Item #2 73 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 49 Figure C-2: Required beach fill based on coastal modeling at range line Cab I-02 on South Beach configured as the extremal elliptic cycloid profile that will maintain equilibrium in the presence of historic extreme waves with 4.8 m wave height and 15 second wave period, cf. Figure B-5. June 4, 2024 Item #2 74 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 50 Figure C-3: Required beach fill based on coastal modeling at range line Cab I-03 on South Beach configured as the extremal elliptic cycloid profile that will maintain equilibrium in the presence of historic extreme waves with 4.8 m wave height and 15 second wave period, cf. Figure B-5. June 4, 2024 Item #2 75 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 51 Figure C-4: Required beach fill based on coastal modeling at range line Cab I-04 on Middle Beach configured as the extremal elliptic cycloid profile that will maintain equilibrium in the presence of historic extreme waves with 4.8 m wave height and 15 second wave period, cf. Figure B-5. June 4, 2024 Item #2 76 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 52 Figure C-5: Required beach fill based on coastal modeling at range line Cab I-05 on Middle Beach configured as the extremal elliptic cycloid profile that will maintain equilibrium in the presence of historic extreme waves with 4.8 m wave height and 15 second wave period, cf. Figure B-5. June 4, 2024 Item #2 77 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 53 Figure C-6: Required beach fill based on coastal modeling at range line Cab I-06 on Middle Beach configured as the extremal elliptic cycloid profile that will maintain equilibrium in the presence of historic extreme waves with 4.8 m wave height and 15 second wave period, cf. Figure B-5. June 4, 2024 Item #2 78 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 54 Figure C-7: Required beach fill based on coastal modeling at range line Cab I-07 on North Beach configured as the extremal elliptic cycloid profile that will maintain equilibrium in the presence of historic extreme waves with 4.8 m wave height and 15 second wave period, cf. Figure B-5. June 4, 2024 Item #2 79 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 55 Figure C-8: Required beach fill based on coastal modeling at range line Cab I-08 on North Beach configured as the extremal elliptic cycloid profile that will maintain equilibrium in the presence of historic extreme waves with 4.8 m wave height and 15 second wave period, cf. Figure B-5. June 4, 2024 Item #2 80 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 56 Figure C-9: Required beach fill based on coastal modeling at range line Cab I-09 on North Beach configured as the extremal elliptic cycloid profile that will maintain equilibrium in the presence of historic extreme waves with 4.8 m wave height and 15 second wave period, cf. Figure B-5. June 4, 2024 Item #2 81 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 57 Figure C-10: Required beach fill based on coastal modeling at range line Cab I-10 on North Beach configured as the extremal elliptic cycloid profile that will maintain equilibrium in the presence of historic extreme waves with 4.8 m wave height and 15 second wave period, cf. Figure B-5. June 4, 2024 Item #2 82 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 58 Figure C-11: Required beach fill based on coastal modeling at range line Cab I-11 on North Beach configured as the extremal elliptic cycloid profile that will maintain equilibrium in the presence of historic extreme waves with 4.8 m wave height and 15 second wave period, cf. Figure B-5. June 4, 2024 Item #2 83 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 59 Figure C-12: Required beach fill based on coastal modeling at range line Cab I-12 on North Beach configured as the extremal elliptic cycloid profile that will maintain equilibrium in the presence of historic extreme waves with 4.8 m wave height and 15 second wave period, cf. Figure B-5. June 4, 2024 Item #2 84 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 60 Appendix - D: Permitted Distribution of Dredge Fill on Receiver Beaches Based on Coastal Modeling - Beach Fill Profiles Figure D-1: Permitted beach fill at range line Cab I-01 on South Beach based on fill distribution as elliptic cycloid equilibrium profiles. June 4, 2024 Item #2 85 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 61 Figure D-2: Permitted beach fill at range line Cab I-02 on South Beach based on fill distribution as elliptic cycloid equilibrium profiles. June 4, 2024 Item #2 86 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 62 Figure D-3: Permitted beach fill at range line Cab I-03 on South Beach based on fill distribution as elliptic cycloid equilibrium profiles. June 4, 2024 Item #2 87 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 63 Figure D-4: Permitted beach fill at range line Cab I-04 on Middle Beach based on fill distribution as elliptic cycloid equilibrium profiles. June 4, 2024 Item #2 88 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 64 Figure D-5: Permitted beach fill at range line Cab I-05 on Middle Beach based on fill distribution as elliptic cycloid equilibrium profiles. June 4, 2024 Item #2 89 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 65 Figure D-6: Permitted beach fill at range line Cab I-06 on Middle Beach based on fill distribution as elliptic cycloid equilibrium profiles. June 4, 2024 Item #2 90 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 66 Figure D-7 Permitted beach fill at range line Cab I-07 on North Beach based on fill distribution as elliptic cycloid equilibrium profiles. June 4, 2024 Item #2 91 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 67 Figure D-8: Permitted beach fill at range line Cab I-08 on North Beach based on fill distribution as elliptic cycloid equilibrium profiles. June 4, 2024 Item #2 92 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 68 Figure D-9: Permitted beach fill at range line Cab I-09 on North Beach based on fill distribution as elliptic cycloid equilibrium profiles. June 4, 2024 Item #2 93 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 69 Figure D-10: Permitted beach fill at range line Cab I-10 on North Beach based on fill distribution as elliptic cycloid equilibrium profiles. June 4, 2024 Item #2 94 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 70 Figure D-11: Permitted beach fill at range line Cab I-11 on North Beach based on fill distribution as elliptic cycloid equilibrium profiles. June 4, 2024 Item #2 95 of 143 Agua Hedionda Lagoon - Outer Basin 2020-21 Maintenance Dredge/Beach Nourishment Cycle Sand Deposition Plan Appendix 71 Figure D-12 Permitted beach fill at range line Cab I-12 on North Beach based on fill distribution as elliptic cycloid equilibrium profiles. June 4, 2024 Item #2 96 of 143 APPENDIX B Agua Hedionda Outer Lagoon 2020–2021 Dredge Cycle 2-Year Post-Construction Beach Profile Survey (June 2023) June 4, 2024 Item #2 97 of 143 COASTAL FRONTIERS Coastal Frontiers Corporation 882A Patriot Drive Moorpark, CA 93021-3544 (818) 341-8133 - www.coastalfrontiers.com June 8, 2023 CFC-1177 Josie McKinley Poseidon Water 5780 Fleet Street, Suite 140 Carlsbad, CA 92008 Subject: Agua Hedionda Outer Lagoon 2020-2021 Dredge Cycle Two-Year Post-Construction Beach Profile Survey Ms. McKinley: This letter report presents the methods and results of a beach profile survey conducted to document the condition of the beach approximately two years after beach nourishment activities were completed as part of the Agua Hedionda Outer Lagoon 2020-2021 Dredge Cycle. The survey was conducted on April 25 and 26, 2023 by Coastal Frontiers Corporation. The sections that follow provide an overview of the monitoring program, summarize the beach nourishment activities conducted in the study area, describe the survey activities, present the results, and describe the short and long-term changes that have occurred in the area. Beach profile plots accompany this report in Appendix A. Mean Sea Level (MSL) shoreline positions derived from the profile data are provided in Appendix B. Appendix C contains site-specific photos, which match the locations and perspectives of photos previously captured during beach construction activities. The vertical datum used throughout this report is National Ocean Service (NOS) Mean Lower Low Water (MLLW) for the 1983-2001 Tidal Datum Epoch. Horizontal positions are given in U.S. Survey Feet relative to California State Plane Zone 6, NAD 83 (2011), 2010.00 epoch. BACKGROUND Poseidon Water conducted maintenance dredging in 2021 to remove a flood-tide shoal in the Agua Hedionda Outer Lagoon. The dredged sand was placed on three adjacent beaches: North Beach, Middle Beach, and South Beach (Figure 1). Dredging activities were undertaken by Pacific Dredge and Construction, LLC from February 15 through March 27, 2021. It is estimated that 304,483 cy were dredged from the lagoon, based on progress surveys conducted by Coastal Frontiers throughout the dredging operations (Coastal Frontiers, 2021). North Beach received 121,667 cy (40%), Middle Beach received 100,992 cy (33%), and South Beach received 81,824 cy (27%) of the dredged material. June 4, 2024 Item #2 98 of 143 Ms. Josie McKinley 2020-2021 Agua Hedionda Outer Lagoon Dredge Cycle Page 2 of 12 Two-Year Post-Construction Beach Profile Survey BEACH PROFILE SURVEYS The objective of the current monitoring program is to develop a quantitative understanding of the coastal changes that have occurred near the three receiver sites since beach nourishment activities were conducted in early 2021. Five beach profile surveys were conducted in support of the project (Table 1). Pre-Construction surveys of North, Middle and South Beaches were conducted on May 12 and 13 and October 2, 2020. A Post-Construction survey was conducted on April 13, 2021 immediately following beach nourishment activities. A follow-up survey was conducted approximately one year later, on May 4 and 5, to assess whether the beaches had returned to their pre-deposition conditions. The most recent survey, conducted on April 25 and 26, 2023, captured the condition of the beach approximately two years following completion of the beach construction activities for the same purpose. Table 1. Beach Profile Survey Dates Survey Survey Date Pre-Construction May 12-13 2020 Pre-Construction October 2 2020 Post-Construction April 13 2021 One-Year Post-Construction May 4-5 2022 Two-Year Post-Construction April 25-26 2023 Data Acquisition Beach profile data were obtained on the 15 transects shown in Figure 1. Data were acquired along each transect from the landward limit of the sandy beach to wading depth, which typically corresponded to roughly 10 to 13 ft below Mean Lower Low Water (MLLW) datum depending on the prevailing water level at the time of the survey. The beach and surf zone were surveyed using a total station and a survey rodperson. The total station was used to determine the position and elevation of the beach at each location occupied by the rodperson. Each transect was surveyed from the back beach seaward through the surf zone until the survey rod no longer protruded above the water surface when held vertically. Data Reduction Data from each survey were collected and processed using software developed by Spectra Precision. The raw total station data were input to the software, and the coordinates and elevation of each data point were calculated. The data were subsequently inserted into a computer-aided design (CAD) file for analysis and preparation of the data products. June 4, 2024 Item #2 99 of 143 Ms. Josie McKinley 2020-2021 Agua Hedionda Outer Lagoon Dredge Cycle Page 3 of 12 Two-Year Post-Construction Beach Profile Survey The electronic total station used to conduct the survey is capable of measuring elevation differences to within 0.1 ft and ranges to within 0.5 ft. However, because the swimmer was subjected to waves and currents in the surf zone, the horizontal position perpendicular to each transect (parallel to the shoreline) varied from minimal at short ranges to approximately 15 ft at the offshore end. Figure 1. Beach Profile Transect Locations June 4, 2024 Item #2 100 of 143 Ms. Josie McKinley 2020-2021 Agua Hedionda Outer Lagoon Dredge Cycle Page 4 of 12 Two-Year Post-Construction Beach Profile Survey RESULTS The Two-Year Post-Construction survey data are included in a digital archive (*.zip) attached to the electronic submittal of this report. The archive contains ASCII files comprising: (1) range and elevation for each profile; and (2) northing, easting, and elevation triplets (n,e,z) for the entire survey. Elevations are provided in feet relative to National Ocean Service (NOS) Mean Lower Low Water (MLLW) for the 1983-2001 Tidal Datum Epoch. Horizontal positions are given in U.S. Survey Feet relative to California State Plane Zone 6, NAD83(2011)2010.00 epoch. Beach profile plots illustrating the data obtained as part of each survey are provided in Appendix A. The range on each profile plot represents the distance in feet seaward of the transect origin measured along the transect alignment. Mean Sea Level (MSL) shoreline positions are provided in Attachment B. The shoreline position was computed as the horizontal distance, in feet, between the transect origin (typically a permanent marker located near the back beach) and the point at which the beach profile intersected the plane of the MSL datum. In the study area, MSL lies 2.73 ft above MLLW. Notwithstanding the use of MLLW as the elevation reference for the profile data, MSL was adopted as the shoreline reference since it is considered to provide a more accurate indicator of changes in beach configuration. MSL shoreline position changes are tabulated below in Table 2, while illustrations of these changes are contained within Appendix B. Site photos are provided in Appendix C to qualitatively document the beach condition approximately two years following beach nourishment activities. The location and perspective of each photo matches those images previously provided in weekly progress reports during beach construction. Those weekly progress reports are contained within the final survey report provided following the 2020-21 Dredge Cycle construction activities (Coastal Frontiers, 2021). OBSERVATIONS Profile Changes (Appendix A) While the Fall 2020 (October 2, 2020) Pre-Construction survey was performed within the closest temporal proximity to the beach nourishment activities, the preceding Spring 2020 (May 12-13, 2020) Pre-Construction survey was selected as the basis for comparison to remain seasonally consistent with the subsequent spring surveys. North Beach Sediment gains resulting from the project are evident at six of the seven North Beach monitoring transects (Cab I-07 through Cab I-11) through comparison of the Pre-Construction (May 2020) and Post-Construction (April 2021) profiles. The northernmost transect (Cab I-12) was the only location where above-water June 4, 2024 Item #2 101 of 143 Ms. Josie McKinley 2020-2021 Agua Hedionda Outer Lagoon Dredge Cycle Page 5 of 12 Two-Year Post-Construction Beach Profile Survey (subaerial) losses occurred. These losses were limited to the upper beach profile above approximately +8 ft, MLLW. A trend of profile erosion is evident during the two-year period following beach nourishment activities (April 2021 to April 2023). The sole exception occurred at the southern end of the sub-reach (Transect Cab I-07), where above-water gains prevailed during this period. Sediment losses generally occurred from the seaward edge of the berm to roughly -5 ft, MLLW. The April 2023 profile is more eroded than, or roughly coincident to, the May 2020 Pre-Construction condition in the northern and central portions of the sub-reach (Transects Cab I-12 through Cab I- 08). In contrast, the April 2023 profile shows sediment gains relative to the pre-construction condition at the southern end of the sub-reach (Transects Cab I-07.5 and Cab I-07). This outcome is likely attributable to accumulation of sediment on the updrift side of the Agua Hedionda intake channel jetties. Middle Beach At Middle Beach (Transects Cab I-03.6 through Cab I-06), sediment gains resulting from the beach nourishment are evident through comparison of the May 2020 Pre-Construction and April 2021 Post-Construction profiles. Over the two-year period following beach nourishment activities (April 2021 to April 2023), erosion occurred at all four sites within the Middle Beach sub-reach. The April 2023 above-water beach condition was more eroded than that documented during the May 2020 Pre-Construction survey at all transects. South Beach Within the South Beach sub-reach (Cab I-03.2 through Cab I-01), sediment gains resulting from the project are evident through comparison of the May 2020 Pre- Construction and April 2021 Post-Construction profiles at all four sites. A trend of profile erosion subsequently prevailed at all four sites during the two-year period following beach nourishment activities (April 2021 to April 2023). At the time of the April 2023 survey, the profiles at all four sites within the South Beach sub-reach (Cab I-03.2 through Cab I-01) show that the beach was generally more eroded than the Pre-Construction (May 2020) condition. MSL Shoreline Position Changes (Table 2, Appendix B) 1. Pre- to Post-Construction Period Shoreline Changes (May 2020 to April 2021): During the roughly one-year period encompassing beach nourishment activities (May 2020 Pre-Construction to April 2021 Post-Construction), shoreline gains predominated at the three receiver beaches (Figure B2). The MSL shoreline position increased at 14 of the 15 sites (Transect Cab I-06 being the sole exception). June 4, 2024 Item #2 102 of 143 Ms. Josie McKinley 2020-2021 Agua Hedionda Outer Lagoon Dredge Cycle Page 6 of 12 Two-Year Post-Construction Beach Profile Survey At North Beach, the MSL shoreline increased 39 ft, on average. The shoreline position at Middle and South Beaches advanced an average of 26 and 37 ft, respectively. 2. Two-Year Post-Construction Period Shoreline Changes (April 2021 to April 2023): In April 2023, two years after nourishment activities were completed, MSL shoreline losses prevailed at all but one site in comparison to the April 2021 Post-Construction condition. The exception occurred at Tamarack Beach (Cab I-07 / CB-0830), which was essentially unchanged (Table 2, Figure B3). Shoreline retreat at North Beach ranged from 16 to 67 ft. These changes produced an average shoreline loss of 37 ft over the two-year period. Losses at Middle Beach ranged from 19 to 65 ft, while losses at South Beach ranged from 53 to 64 ft. On average, the shoreline at Middle Beach retreated 45 ft, while South Beach eroded 58 ft. 3. Pre- to Two-Year Post-Construction Shoreline Changes (May 2020 to April 2023): The April 2023 shoreline position at North Beach was 2 ft wider, on average, compared to the May 2020 Pre-Construction condition. At Middle Beach, the average shoreline position decreased 19 ft over the same three-year period. Similarly, the shoreline at South Beach retreated 21 ft (Table 2, Appendices B4). June 4, 2024 Item #2 103 of 143 Ms. Josie McKinley 2020-2021 Agua Hedionda Outer Lagoon Dredge Cycle Page 7 of 12 Two-Year Post-Construction Beach Profile Survey Table 2. Mean Sea Level Shoreline Position Changes Sub-Reach Transect MSL Shoreline Position Change (ft) Pre- to Post-Construction Two Years Post-Construction Pre-Construction to Two Years Post-Construction May 2020 April 2021 May 2020 to to to April 2021 April 2023 April 2023 ~1 Year ~2 Years ~3 Years North Beach Cab I-12 (CB-0850) 21 -31 -10 Cab I-11 47 -50 -3 Cab I-10 57 -67 -10 Cab I-09 (CB-0840) 58 -56 2 Cab I-08 47 -43 4 Cab I-07.5 27 -16 11 Cab I-07 (CB-0830) 17 1 18 AVERAGE 39 -37 +2 Middle Beach Cab I-06 (CB-0820) -1 -19 -20 Cab I-05 14 -33 -19 Cab I-04 41 -63 -22 Cab I-03.6 49 -65 -16 AVERAGE 26 -45 -19 South Beach Cab I-03.2 32 -64 -32 Cab I-03 30 -53 -23 Cab I-02 45 -54 -9 Cab I-01 40 -61 -21 AVERAGE 37 -58 -21 Notes: (1) Red indicates shoreline loss. Green indicates shoreline gain. Black indicates essentially no change (change of 10 ft, or less). June 4, 2024 Item #2 104 of 143 Ms. Josie McKinley 2020-2021 Agua Hedionda Outer Lagoon Dredge Cycle Page 8 of 12 Two-Year Post-Construction Beach Profile Survey Long-Term Changes Among the fifteen monitoring transects surveyed as part of the current monitoring program, four of the sites have been surveyed semiannually since 1988 on behalf of the City of Carlsbad and the San Diego Association of Governments (SANDAG, 2022). Three of the sites are located within the North Beach sub-reach (Cab I-12/CB-0850, Cab I-09/CB-0840, and Cab I-07/CB-0830), while one site exists at Middle Beach (Cab I-06/CB-0820). No coincident data are available within the South Beach sub-reach as part of either the SANDAG or City of Carlsbad programs. These publicly available beach profile data were acquired in a similar manner as the current monitoring program. In consequence, the results are directly comparable, and are used as the basis for evaluating long-term changes relative to the 2020-2021 Dredge Cycle beach nourishment. The Spring 2012 survey (conducted May 7 - 11, 2012) was selected as the basis of comparison to (1) remain seasonally consistent with the 2020-21 Dredge Cycle Spring beach surveys, and (2) to serve as the baseline pre-condition prior to the influence of SANDAG’s Regional Beach Sand Project II (RBSP II) beach nourishment, conducted in November and December 2012 at North Carlsbad. During the eleven-year period between the Spring 2012 and Spring 2023 surveys, over one million cubic yards of beach quality sediment were delivered to Carlsbad-area beaches (Table 3). Nourishment within the study area consisted of the RBSP II in 2012. Sediment bypassing at Agua Hedionda Lagoon was conducted in 2015, 2018, and 2021. Table 3. Carlsbad Nourishment and Bypassing Quantities (cy), 2012 to Present Receiver Site 2021 Bypassing (1) 2018 Bypassing (2) 2015 Bypassing (3) 2012 RBSP II (4) TOTAL Feb. 15, 2021 to Mar. 27, 2021 Feb. 16, 2018 to Apr. 13, 2018 Dec. 31, 2014 to Apr. 15, 2015 Nov. 24, 2012 to Dec. 7, 2012 North Beach 121,667 0 64,968 219,000 405,635 Middle Beach 100,992 141,172 156,056 0 398,220 South Beach 81,824 64,310 73,637 0 219,771 TOTAL 304,483 205,482 294,661 219,000 1,023,626 Notes: (1) Coastal Frontiers, 2021 (3) Henika, 2015 (2) Coastal Frontiers, 2018 (4) Coastal Frontiers, 2013 June 4, 2024 Item #2 105 of 143 Ms. Josie McKinley 2020-2021 Agua Hedionda Outer Lagoon Dredge Cycle Page 9 of 12 Two-Year Post-Construction Beach Profile Survey Figure 2 presents a time series of the weighted average MSL shoreline change at the time of each Spring survey relative to the Spring 2012 condition for the North Beach sub-reach. The uneven spacing between transects was accounted for by weighting each value according to the alongshore distance associated with the corresponding transect. The initial shoreline advance in response to the RBSP II beach nourishment was sustained through 2017, despite strong El Niño conditions during the 2015-16 winter. It is noteworthy that the sediment contributions from lagoon bypassing in 2015 likely contributed to the longevity of the gains. From 2017 through 2020, persistent erosion prevailed, with the average shoreline position retreating to below pre-RBSP II levels. North Beach did not receive nourishment material as part of the 2018 Agua Hedionda Lagoon bypassing. In 2021, shoreline advance prevailed as a result of the most recent bypassing activities. However, by the time of the April 2023 survey, the shoreline retreated below the baseline pre-RBSP II level and essentially matched the 2020 Pre-Construction condition. Figure 2. Time Series of Weighted Average MSL Shoreline Change Relative to Spring 2012 Condition in the North Beach Sub-Reach A time series of shoreline position changes relative to Spring 2012 for the sole historical transect at Middle Beach (Transect Cab I-06/CB-0820) is provided in Figure 3. Middle Beach did not receive direct nourishment as part of the RBSP II. As such, modest shoreline loss prevailed during the first two years of the period. Substantial shoreline advance occurred in 2015 in response to the Agua Hedionda Lagoon bypassing activities. However, by Spring 2016 these gains were erased by the energetic wave activity that occurred during the strong 2015-16 El Niño. The shoreline advanced again in 2018 as an apparent result of the next phase of lagoon bypassing. While the shoreline retreated in 2019, the losses were not as severe as those noted during the 2015-16 El Niño season. Shoreline changes were modest from 2019 through 2021 despite the current bypassing efforts. The apparent lack of shoreline gains attributable to the 2021 bypassing may be due Pre-Construction Post-Construction One Year Post-Construction Two Years Post-Construction 121,667 cy 64,968 cy (3)219,000 cy (2) -100 -80 -60 -40 -20 0 20 40 60 80 100 20 1 2 20 1 3 20 1 4 20 1 5 20 1 6 20 1 7 20 1 8 20 1 9 20 2 0 20 2 1 20 2 2 20 2 3 20 2 4 We i g h t e d A v g . M S L S h o r e l i n e C h a n g e ( f t ) Year Cab I-12 (CB-0850)(1) Cab I-09 (CB-0840)(1) Cab I-07 (CB-0830)(2) (1) Data Source (2012-2019) -City of Carlsbad (2) Data Source (2012-2019) -SANDAG (3) Henika, 2015 RBSP II Bypassing Bypassing June 4, 2024 Item #2 106 of 143 Ms. Josie McKinley 2020-2021 Agua Hedionda Outer Lagoon Dredge Cycle Page 10 of 12 Two-Year Post-Construction Beach Profile Survey to the limited spatial coverage, with only one historical transect located within the sub-reach. Modest losses occurred in 2022, followed by relative stability in 2023. However, the shoreline position remained above the baseline pre-RBSP II level at the time of the 2023 survey. Figure 3. Time Series of MSL Shoreline Change Relative to Spring 2012 Condition in the Middle Beach Sub-Reach As noted previously, similar long-term data have not been collected within the South Beach sub-reach. Pre-Construction Post-Construction One Year Post-Construction Two Years Post-Construction 100,992 cy141,172 cy(3)156,056 cy(2) -100 -80 -60 -40 -20 0 20 40 60 80 100 20 1 2 20 1 3 20 1 4 20 1 5 20 1 6 20 1 7 20 1 8 20 1 9 20 2 0 20 2 1 20 2 2 20 2 3 20 2 4 MS L S h o r e l i n e C h a n g e ( f t ) Year Cab I-06 (CB-0820)(1) (1) Data Source (2012-2019) -City of Carlsbad (2) Henika, 2015 (3) NRG, 2018 Bypassing Bypassing Bypassing June 4, 2024 Item #2 107 of 143 Ms. Josie McKinley 2020-2021 Agua Hedionda Outer Lagoon Dredge Cycle Page 11 of 12 Two-Year Post-Construction Beach Profile Survey Key Findings The latest profiles (April 2023) at North Beach are either more eroded than, or roughly coincident to, the May 2020 Pre-Construction condition in the northern and central portions of the sub-reach. Similarly, the April 2023 profiles at Middle and South Beaches show that the beach was generally more eroded than the Pre-Construction (May 2020) condition. The only occurrence of profile accretion was at the two transects located immediately north of the Agua Hedionda north jetties. This outcome suggests that the beach condition has effectively returned to, or eroded beyond, the Pre- Construction condition. In April 2023, the average MSL shoreline position at North Beach was 2 ft wider than the May 2020 Pre-Construction condition. Middle and South Beaches retreated beyond the Pre-Construction condition over the same period (an average loss of 19 and 21 ft, respectively). Like the profile changes, these findings indicate that the shoreline within the study area has retreated to, or eroded beyond, the Pre-Construction condition. We have sincerely appreciated the opportunity to assist Poseidon Water. Please feel free to reach out to me personally if we can clarify any questions that may arise. Sincerely, Coastal Frontiers Corporation Lee Dodds Coastal Scientist II Enclosures: Appendix A – Beach Profile Plots Appendix B – MSL Shoreline Positions Appendix C – Site Photos Digital Data Deliverables June 4, 2024 Item #2 108 of 143 Ms. Josie McKinley 2020-2021 Agua Hedionda Outer Lagoon Dredge Cycle Page 12 of 12 Two-Year Post-Construction Beach Profile Survey REFERENCES Coastal Frontiers, 2022, “SANDAG 2021 Regional Beach Monitoring Program Annual Report”, Moorpark, CA, 114 pp. + Appendices. Coastal Frontiers, 2021, “Agua Hedionda Outer Lagoon 2020-2021 Dredge Cycle Beach Profile and Outer Lagoon Surveys”, Moorpark, CA, 9 pp. + Appendices. Coastal Frontiers, 2018, “Encina Power Station Outer Lagoon 2018 Dredge Cycle Pre- and Post-Condition Beach Profile and Outer Lagoon Surveys”, Moorpark, CA, 8 pp. + Appendices. Coastal Frontiers, 2013, “SANDAG 2013 Regional Beach Monitoring Program Annual Report”, Moorpark, CA, 136 pp. + Appendices. Henika, S., 2015, personal communication, Outer Agua Hedionda Dredge 2014/2015 Spoils Summary, NRG Encina Power Station, Carlsbad, CA. June 4, 2024 Item #2 109 of 143 Appendix A Beach Profile Plots June 4, 2024 Item #2 110 of 143 -50 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 Cross-Shore Distance (Feet Seaward of Transect Origin) -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 El e v a t i o n ( F e e t , M L L W ) Transect Cab I-12, Nearshore MSL 08 May 2012 13 May 2020 02 Oct 2020 13 Apr 2021 04 May 2022 26 Apr 2023 June 4, 2024 Item #2 111 of 143 -50 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 Cross-Shore Distance (Feet Seaward of Transect Origin) -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 El e v a t i o n ( F e e t , M L L W ) Transect Cab I-11, Nearshore MSL 13 May 2020 02 Oct 2020 13 Apr 2021 04 May 2022 26 Apr 2023 June 4, 2024 Item #2 112 of 143 -50 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 Cross-Shore Distance (Feet Seaward of Transect Origin) -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 El e v a t i o n ( F e e t , M L L W ) Transect Cab I-10, Nearshore MSL 13 May 2020 02 Oct 2020 13 Apr 2021 04 May 2022 26 Apr 2023 June 4, 2024 Item #2 113 of 143 -50 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 Cross-Shore Distance (Feet Seaward of Transect Origin) -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 El e v a t i o n ( F e e t , M L L W ) Transect Cab I-09, Nearshore MSL 08 May 2012 13 May 2020 02 Oct 2020 13 Apr 2021 04 May 2022 26 Apr 2023 June 4, 2024 Item #2 114 of 143 -50 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 Cross-Shore Distance (Feet Seaward of Transect Origin) -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 El e v a t i o n ( F e e t , M L L W ) Transect Cab I-08, Nearshore MSL 13 May 2020 02 Oct 2020 13 Apr 2021 04 May 2022 26 Apr 2023 June 4, 2024 Item #2 115 of 143 -50 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 Cross-Shore Distance (Feet Seaward of Transect Origin) -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 El e v a t i o n ( F e e t , M L L W ) Transect Cab I-07.5, Nearshore MSL 13 May 2020 02 Oct 2020 13 Apr 2021 04 May 2022 26 Apr 2023 June 4, 2024 Item #2 116 of 143 -50 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 Cross-Shore Distance (Feet Seaward of Transect Origin) -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 El e v a t i o n ( F e e t , M L L W ) Transect Cab I-07, Nearshore MSL 08 May 2012 13 May 2020 02 Oct 2020 13 Apr 2021 04 May 2022 26 Apr 2023 June 4, 2024 Item #2 117 of 143 -50 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 Cross-Shore Distance (Feet Seaward of Transect Origin) -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 El e v a t i o n ( F e e t , M L L W ) Transect Cab I-06, Nearshore MSL 08 May 2012 12 May 2020 02 Oct 2020 13 Apr 2021 04 May 2022 26 Apr 2023 June 4, 2024 Item #2 118 of 143 -50 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 Cross-Shore Distance (Feet Seaward of Transect Origin) -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 El e v a t i o n ( F e e t , M L L W ) Transect Cab I-05, Nearshore MSL 12 May 2020 02 Oct 2020 13 Apr 2021 04 May 2022 26 Apr 2023 June 4, 2024 Item #2 119 of 143 -50 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 Cross-Shore Distance (Feet Seaward of Transect Origin) -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 El e v a t i o n ( F e e t , M L L W ) Transect Cab I-04, Nearshore MSL 12 May 2020 02 Oct 2020 13 Apr 2021 04 May 2022 26 Apr 2023 June 4, 2024 Item #2 120 of 143 -50 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 Cross-Shore Distance (Feet Seaward of Transect Origin) -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 El e v a t i o n ( F e e t , M L L W ) Transect Cab I-03.6, Nearshore MSL 12 May 2020 02 Oct 2020 13 Apr 2021 04 May 2022 26 Apr 2023 June 4, 2024 Item #2 121 of 143 -50 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 Cross-Shore Distance (Feet Seaward of Transect Origin) -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 El e v a t i o n ( F e e t , M L L W ) Transect Cab I-03.2, Nearshore MSL 13 May 2020 02 Oct 2020 13 Apr 2021 04 May 2022 26 Apr 2023 June 4, 2024 Item #2 122 of 143 -50 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 Cross-Shore Distance (Feet Seaward of Transect Origin) -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 El e v a t i o n ( F e e t , M L L W ) Transect Cab I-03, Nearshore MSL 13 May 2020 02 Oct 2020 13 Apr 2021 04 May 2022 26 Apr 2023 June 4, 2024 Item #2 123 of 143 -50 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 Cross-Shore Distance (Feet Seaward of Transect Origin) -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 El e v a t i o n ( F e e t , M L L W ) Transect Cab I-02, Nearshore MSL 13 May 2020 02 Oct 2020 13 Apr 2021 04 May 2022 26 Apr 2023 June 4, 2024 Item #2 124 of 143 -50 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200 Cross-Shore Distance (Feet Seaward of Transect Origin) -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 El e v a t i o n ( F e e t , M L L W ) Transect Cab I-01, Nearshore MSL 13 May 2020 02 Oct 2020 13 Apr 2021 04 May 2022 26 Apr 2023 June 4, 2024 Item #2 125 of 143 Appendix B Mean Sea Level Shoreline Positions June 4, 2024 Item #2 126 of 143 Table B1 - MSL Shoreline Positions Sub-Reach Transect MSL Shoreline Position (ft) Two-Year Post-Construction One-Year Post-Construction Post-Construction Pre-Construction Pre-Construction (April 25-26, 2023) (May 4-5, 2022) (Apr 13, 2021) (Oct 2, 2020) (May 12-13, 2020) Spring 2023 Spring 2022 Spring 2021 Fall 2020 Spring 2020 North Beach Cab I-12 (CB-0850) 232 247 263 262 242 Cab I-11 145 168 195 148 148 Cab I-10 150 187 217 155 160 Cab I-09 (CB-0840) 152 163 208 144 150 Cab I-08 165 175 208 141 161 Cab I-07.5 192 205 208 176 181 Cab I-07 (CB-0830) 201 207 200 144 183 Middle Beach Cab I-06 (CB-0820) 171 171 190 200 191 Cab I-05 184 192 217 208 203 Cab I-04 230 262 293 252 252 Cab I-03.6 268 300 333 274 284 South Beach Cab I-03.2 115 128 179 173 147 Cab I-03 104 113 157 165 127 Cab I-02 132 144 186 181 141 Cab I-01 223 257 284 270 244 June 4, 2024 Item #2 127 of 143 Figure B2 - MSL Shoreline Position Change Pre-Construction to Post-Construction June 4, 2024 Item #2 128 of 143 Figure B3 - MSL Shoreline Position Change Post-Construction to Two Years Post-Construction June 4, 2024 Item #2 129 of 143 Figure B4 - MSL Shoreline Position Change Pre-Construction to Two Years Post-Construction June 4, 2024 Item #2 130 of 143 Appendix C Site Photos June 4, 2024 Item #2 131 of 143 Photos N. Carlsbad 1 (looking south from north end of seawall) – April 25, 2023 N. Carlsbad 2 (looking north from vicinity of Tower 36) – April 25, 2023 June 4, 2024 Item #2 132 of 143 Photos (continued) N. Carlsbad 3 (looking south from vicinity of Tower 36) – April 25, 2023 N. Carlsbad 4 (looking north from vicinity of Tower 36 stairway) – April 25, 2023 June 4, 2024 Item #2 133 of 143 Photos (continued) N. Carlsbad 5 (looking south from vicinity of Tower 36 stairway) – April 25, 2023 N. Carlsbad 6 (looking north from Agua Hedionda Inlet North Jetty) – April 25, 2023 June 4, 2024 Item #2 134 of 143 Photos (continued) Middle Beach 1 (looking south from Agua Hedionda Inlet South Jetty) – April 25, 2023 Middle Beach 2 (looking north from Agua Hedionda Outlet North Jetty) – April 25, 2023 June 4, 2024 Item #2 135 of 143 Photos (continued) S. Carlsbad 1 (looking south from Agua Hedionda Outlet South Jetty) – April 25, 2023 S. Carlsbad 2 (looking south from prior location of groin) – April 25, 2023 June 4, 2024 Item #2 136 of 143 APPENDIX C Agua Hedionda Outer Lagoon 2024–2025 Dredge Cycle Proposed Dredge Design Figures June 4, 2024 Item #2 137 of 143 © 2024 Microsoft Corporation © 2024 TomTom DRAFT Publish Date: 2024/04/04 9:42 AM | User: jbigsbyFilepath: K:\Projects\0648-Poseidon\Agua Hedionda Lagoon Maintenance Dredging\0648-RP-001 (Vicinity Map).dwg Figure 1 SOURCE: ©2024 Microsoft Corporation ©2024 Maxar©CNES (2024) Distribution Airbus DSHORIZONTAL DATUM: California State Plane, Zone VI,NAD83, U.S. Survey Feet Figure 1Vicinity Map Preliminary Dredge DesignAgua Hedionda Lagoon Maintenance Dredging 0 Feet 2000 CALIFORNIA San Francisco Los Angeles San DiegoNot to Scale CARLSBAD June 4, 2024 Item #2 138 of 143 MiddleLagoon Pa c i f i c C o a s t H i g h w a y C a r l s b a d B l v d Pacific Ocean InnerLagoon OuterLagoon B B' A A ' C C' Zone 1C Zone 1B Zone 1A Zone 2 Zone 3 Zone 4 DRAFT SOURCE: Aerial ©2024 Microsoft Corporation ©2024 Maxar©CNES (2024) Distribution Airbus DSHORIZONTAL DATUM: California State Plane, Zone VI,NAD83, U.S. Survey FeetVERTICAL DATUM: MLLW LEGEND: Existing Contours (1' & 5' Intervals) Proposed Contours (1' & 5' Intervals) Proposed Dredge Extents Zone Boundary Previously Permitted Dredge Limits Dredge Obstacle Publish Date: 2024/04/04 9:43 AM | User: jbigsbyFilepath: K:\Projects\0648-Poseidon\Agua Hedionda Lagoon Maintenance Dredging\0648-RP-002 (Site Plan & Sections).dwg Figure 2 Figure 2Site Plan Preliminary Dredge DesignAgua Hedionda Lagoon Maintenance Dredging 0 Feet 400 NOTES: 1. Existing bathymetry based on survey conductedJanuary 12, 2024 by Coastal Frontiers Corp. 2. Preliminary dredge volumes assume a dredge depthelevation of -22 ft MLLW, with two feet of overdredge(OD) and 2 horizontal to 1 vertical (2H:1V) side slopesto existing grade. DESIGN VOLUME (EXISTING BATHY vs DESIGN): ·Zone 1A = 19,000 cy (2.3 Acres) ·Zone 1B = 63,000 cy (2.5 Acres) ·Zone 1C = 78,000 cy (3.2 Acres) ·Zone 2 = 81,000 cy (5.2 Acres) ·Zone 3 = 33,000 cy (2.9 Acres) ·Zone 4 = 53,000 cy (2.5 Acres) Design Subtotal = 327,000 cy (202.7 Acres) OD VOLUME (OD vs DESIGN): ·Zone 1A = 7,000 cy ·Zone 1B = 8,000 cy ·Zone 1C = 10,000 cy ·Zone 2 = 17,000 cy ·Zone 3 = 9,000 cy ·Zone 4 = 8,000 cy OD Subtotal = 59,000 cy TOTAL DREDGE VOLUME (DESIGN + OD) = 386,000 CY June 4, 2024 Item #2 139 of 143 MiddleLagoon Pa c i f i c C o a s t H i g h w a y C a r l s b a d B l v d Pacific Ocean Difference in Elevation BetweenBase Surface and Comparison Surface(Positive Values Indicate the ComparisonSurface is a Higher Elevation) Vertical Difference in Feet -23.0 to -22.0 -22.0 to -21.0 -21.0 to -20.0 -20.0 to -19.0 -19.0 to -18.0 -18.0 to -17.0 -17.0 to -16.0 -16.0 to -15.0 -15.0 to -14.0 -14.0 to -13.0 -13.0 to -12.0 -12.0 to -11.0 -11.0 to -10.0 -10.0 to -9.0 -9.0 to -8.0 -8.0 to -7.0 -7.0 to -6.0 -6.0 to -5.0 -5.0 to -4.0 -4.0 to -3.0 -3.0 to -2.0 -2.0 to -1.0 -1.0 to 0.0 0.0 to 1.0 1.0 to 2.0 2.0 to 3.0 3.0 to 4.0 4.0 to 5.0 Color InnerLagoon OuterLagoon B B' A A ' C C' Zone 1C Zone 1B Zone 1A Zone 2 Zone 3 Zone 4 DRAFT SOURCE: Aerial ©2024 Microsoft Corporation ©2024 Maxar©CNES (2024) Distribution Airbus DSHORIZONTAL DATUM: California State Plane, Zone VI,NAD83, U.S. Survey FeetVERTICAL DATUM: MLLW Publish Date: 2024/04/04 9:43 AM | User: jbigsbyFilepath: K:\Projects\0648-Poseidon\Agua Hedionda Lagoon Maintenance Dredging\0648-RP-002 (Site Plan & Sections).dwg Figure 3 Figure 3Isopach Preliminary Dredge DesignAgua Hedionda Lagoon Maintenance Dredging 0 Feet 400 NOTES: 1. Existing bathymetry based on survey conductedJanuary 12, 2024 by Coastal Frontiers Corp. 2. Preliminary dredge volumes assume a dredge depthelevation of -22 ft MLLW, with two feet of overdredge(OD) and 2 horizontal to 1 vertical (2H:1V) side slopesto existing grade. LEGEND: Existing Contours (1' & 5' Intervals) Proposed Dredge Extents Zone Boundary Previously Permitted Dredge Limits Dredge Obstacle DESIGN VOLUME (EXISTING BATHY vs DESIGN): ·Zone 1A = 19,000 cy (2.3 Acres) ·Zone 1B = 63,000 cy (2.5 Acres) ·Zone 1C = 78,000 cy (3.2 Acres) ·Zone 2 = 81,000 cy (5.2 Acres) ·Zone 3 = 33,000 cy (2.9 Acres) ·Zone 4 = 53,000 cy (2.5 Acres) Design Subtotal = 327,000 cy (202.7 Acres) OD VOLUME (OD vs DESIGN): ·Zone 1A = 7,000 cy ·Zone 1B = 8,000 cy ·Zone 1C = 10,000 cy ·Zone 2 = 17,000 cy ·Zone 3 = 9,000 cy ·Zone 4 = 8,000 cy OD Subtotal = 59,000 cy TOTAL DREDGE VOLUME (DESIGN + OD) = 386,000 CY June 4, 2024 Item #2 140 of 143 El e v a t i o n i n F e e t ( M L L W ) Horizontal Distance in FeetNo Vertical Exaggeration -60 -40 -20 0 20 -60 -40 -20 0 20 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520 540 560 580 600 620 640 660 680 700 A A' El e v a t i o n i n F e e t ( M L L W ) Horizontal Distance in FeetNo Vertical Exaggeration -60 -40 -20 0 20 -60 -40 -20 0 20 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520 540 560 580 600 620 640 660 680 700 B B' Existing Bathymetry Preliminary Dredge Elevation -22.0' MLLW 2' Maximum Overdredge Allowance, -24.0' MLLW Existing Bathymetry Preliminary Dredge Elevation -22.0' MLLW 2' Maximum Overdredge Allowance, -24.0' MLLW DRAFT Publish Date: 2024/04/04 9:43 AM | User: jbigsbyFilepath: K:\Projects\0648-Poseidon\Agua Hedionda Lagoon Maintenance Dredging\0648-RP-002 (Site Plan & Sections).dwg Figure 4 Figure 4Cross Sections 0 Feet 50 Preliminary Dredge DesignAgua Hedionda Lagoon Maintenance Dredging June 4, 2024 Item #2 141 of 143 El e v a t i o n i n F e e t ( M L L W ) Horizontal Distance in FeetNo Vertical Exaggeration -60 -40 -20 0 20 -60 -40 -20 0 20 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520 540 560 580 600 620 640 660 680 700 C C' El e v a t i o n i n F e e t ( M L L W ) Horizontal Distance in FeetNo Vertical Exaggeration -60 -40 -20 0 20 -60 -40 -20 0 20 700 720 740 760 780 800 820 840 860 880 900 920 940 960 980 1000 1020 1040 1060 1080 1100 1120 1140 1160 1180 1200 1220 1240 1260 1280 1300 1320 1340 1360 1380 1400 C C' El e v a t i o n i n F e e t ( M L L W ) Horizontal Distance in FeetNo Vertical Exaggeration -60 -40 -20 0 20 -60 -40 -20 0 20 1400 1420 1440 1460 1480 1500 1520 1540 1560 1580 1600 1620 1640 1660 1680 1700 1720 1740 1760 1780 1800 1820 1840 1860 1880 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100 C C' Existing Bathymetry Preliminary Dredge Elevation -22.0' MLLW 2' Maximum Overdredge Allowance, -24.0' MLLW Existing Bathymetry Preliminary Dredge Elevation -22.0' MLLW 2' Maximum Overdredge Allowance, -24.0' MLLW Existing Bathymetry Preliminary Dredge Elevation -22.0' MLLW 2' Maximum Overdredge Allowance, -24.0' MLLW DRAFT Publish Date: 2024/04/04 9:43 AM | User: jbigsbyFilepath: K:\Projects\0648-Poseidon\Agua Hedionda Lagoon Maintenance Dredging\0648-RP-002 (Site Plan & Sections).dwg Figure 5 Figure 5Cross Sections 0 Feet 50 Preliminary Dredge DesignAgua Hedionda Lagoon Maintenance Dredging June 4, 2024 Item #2 142 of 143 MiddleLagoon Pacific C o a s t H i g h w a y Carlsbad Blvd Pacific Ocean InnerLagoon OuterLagoon South Beach Placement AreaNorth Beach Placement Area -10 -5 05101520 Middle Beach Placement Area -10 -10 -5 0510 DRAFT SOURCE: Aerial ©2024 Microsoft Corporation ©2024 Maxar©CNES (2024) Distribution Airbus DSHORIZONTAL DATUM: California State Plane, Zone VI,NAD83, U.S. Survey FeetVERTICAL DATUM: MLLW LEGEND: Proposed Dredge Extents Previously Permitted Dredge Limits Beach Placement Areas Publish Date: 2024/04/04 9:43 AM | User: jbigsbyFilepath: K:\Projects\0648-Poseidon\Agua Hedionda Lagoon Maintenance Dredging\0648-RP-003 (Beach Sampling).dwg Figure 6 Figure 6Beach Sampling Plan Preliminary Dredge DesignAgua Hedionda Lagoon Maintenance Dredging NOTES: 1. Existing beach topography based on survey conductedApril 26, 2023 by Coastal Frontiers Corp.0 Feet 800 5 Existing Contours (1' & 5' Intervals) June 4, 2024 Item #2 143 of 143 Agua Hedionda Lagoon Outer Basin Maintenance Dredging and Beach Nourishment Nick Stupin, Parks Planning Manager Dominic Massaro, Anchor QEA Parks & Recreation Department June 4, 2024 RECOMMENDED ACTION ITEM NO. 2: AHL Maintenance Dredging Receive a report on the upcoming maintenance dredging project for Agua Hedionda Lagoon, to be conducted by Channelside Water Resources (Formerly Poseidon Resources) – the Claude “Bud” Lewis Carlsbad Desalination Plant operator. 2 TODAY’S PRESENTATION •Introductions •Background •Permitting •Dredge volume and sand placement •Schedule •Outreach 3 ITEM NO. 2: AHL Maintenance Dredging BACKGROUND ITEM NO. 2: AHL Maintenance Dredging •Operators of the site have changed over the years. Initially, Encina Power Station seawater cooling intake was dredged (created) in 1954 •Re-occurring maintenance dredging conducted since 1959 •Channelside is the current operator •Serves the Claude “Bud” Lewis Carlsbad Desalination Plant, which provides approximately 10% of San Diego county’s water supplies—nearly 50 million gallons of drinking water each day 4 PROJECT OVERVIEW To remove a flood-tide shoal in the Agua Hedionda Lagoon - Outer Basin in order to maintain the tidal exchange between the Lagoon and the ocean 5 ITEM NO. 2: AHL Maintenance Dredging OPEN INLET IS CRITICAL TO HEALTHY LAGOON •Maintenance Dredge to remove a flood- tide shoal in the Agua Hedionda Lagoon – Outer Basin inlet is needed to maintain: –The lagoon environment –Intake water flow for Claude “Bud” Lewis Carlsbad Desalination Plant •Since 2018, Cabrillo no longer intakes water from the lagoon 6 ITEM NO. 2: AHL Maintenance Dredging 7 ITEM NO. 2: AHL Maintenance Dredging WHY IS IT IMPORTANT TO PRESERVE & PROTECT THE AGUA HEDIONDA LAGOON? 8 BACKGROUND & PROJECT OVERVIEW •Dredge and Beach Nourishment •Similar operations have been performed over the last six decades. Dredge and Beach Nourishment quantities have ranged from 159,000 to 429,000 cy. The most recent operation, completed in 2021, accounted for 304,483 cy. •All Dredging and Beach Nourishment activities occurs between September 15th thru April 15th, outside the nesting and high beach usage season. 9 ITEM NO. 2: AHL Maintenance Dredging 10 ITEM NO. 2: AHL Maintenance Dredging PROPOSED DREDGE AREA 11 SAND DEPOSITION PLAN – MAY 2024 •Beach profile surveys – Fall 2024 •Sand placement –Re-establish sand equilibrium profiles –Replace sand erosion since 2021 – 304,483 cy –Maximize recreation width proportionate to use –Avoid impact to sensitive hard bottom habitat 12 ITEM NO. 2: AHL Maintenance Dredging PERMITS ITEM NO. 2: AHL Maintenance Dredging •The work will be performed in accordance with the stipulations in the following permits: City of Carlsbad Special Use Permit (SUP) US Army Corps of Engineers Permit California Coastal Commission Coastal Dev. Permit San Diego Regional Water Quality Control Board 401 Water Quality Certification California Department of Parks and Recreation Right of Entry Permit California State Lands Commission Lease13 14 ITEM NO. 2: AHL Maintenance Dredging DREDGE VOLUME, SAND PLACEMENT AND SCHEDULE Receiver Site Approximate Placement Quantity (with 2024 bathymetric conditions) Approximate Placement Quantity (with 20% Contingency)Approximate Schedule North Beach1 150,000 cy (37.5%)150,000 cy (33.3%)January to March 2025 North Inlet Jetty to Maple Avenue 94,500 cy 94,500 cy -- Maple Avenue to Pine Avenue 55,500 cy 55,500 cy -- Middle Beach1 139,000 cy (34.5%)166,800 cy (37.1%)November to December 2024 South Beach1 111,000 cy (28.0%)133,200 cy (29.6%)March to April 15, 2025 Total 400,000 cy 450,000 cy -- 1Sand placement operations my extend beyond March 2021 if adverse weather conditions or equipment issues are encountered. No sand will be placed on beaches after April 15, 2021. 15 PERMIT COMPLIANCE - SURVEY, PLANS AND MONITORING ITEM NO. 2: AHL Maintenance Dredging •Pre/post-dredge bathymetric surveys & beach profiles •Pre-dredge Sand Deposition Plan •Pre-dredge sampling and analysis •Pre-dredge Caulerpa taxifolia •Pre/post-dredge eelgrass •Pre/post-dredge nearshore habitat mapping •Grunion Monitoring Plan 16 •Green Sea Turtle Monitoring Plan •Water Quality Monitoring Plan •Pre- Project Monitoring Plan •Dredging/Disposal Operations Plan •Best Management Practices •Pre/post-notifications & reporting •Public safety postings •Timing: Sept. 15 to April 15 cycle for Least Tern nesting season, recreational benefit, etc. PUBLIC OUTREACH AND MEETINGS ITEM NO. 2: AHL Maintenance Dredging •March 21, 2024 – Initial meeting with City of Carlsbad Parks & Recreation Department •April 24, 2024 – Southern California – Dredged Material Management Team •June 4, 2024 - Beach Preservation Committee Meeting •June 26, 2024 – Southern California – Dredged Material Management Team 17 CONTACT INFORMATION ITEM NO. 2: AHL Maintenance Dredging •Evariste (Butch) Poissot, III at EPoissot@channelsidedesal.com •Adam Gale at Agale@AnchorQEA.com •Dominic Massaro at Dmassaro@AnchorQEA.com 18 PROJECT COMPARATIVE SCHEDULES ITEM NO. 2: AHL Maintenance Dredging •Agua Hedionda Lagoon Dredging: Fall 2024 – Spring 2025 •Batiquitos Lagoon Dredging: Winter 2025 – Spring 2025 •Oceanside Harbor Dredging: Spring 2025 •Regional Beach Sand Project III: TBD •Buena Vista Lagoon Enhancement Project: TBD 19 QUESTIONS AND COMMENTS Thank you ITEM NO. 2: AHL Maintenance Dredging