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Home My WebLink AboutSUP 06-10X2A; AGUA HEDIONDA OUTER LAGOON MAINTENANCE; 2017 NEARSHORE MARINE HABITAT MAPPING; 2018-01-0114‐051‐05 2017 NEARSHORE MARINE HABITAT MAPPING FOR THE AGUA HEDIONDA LAGOON MAINTENANCE DREDGING PROJECT Prepared for: MBC Aquatic Sciences 3000 Red Hill Avenue Costa Mesa, CA 92626 Ph: (714) 850‐4830 and Cabrillo Power I LLC Encina Power Station 4600 Carlsbad Blvd. Carlsbad, CA 92008 Attention: Sheila Henika, P.E. (760) 268‐4018 Prepared by: Merkel & Associates, Inc. 5434 Ruffin Road San Diego, CA 92123 Attention: Keith Merkel (858) 560‐5465 January 2018 2017 Agua Hedionda Lagoon Maintenance Dredging Nearshore Habitat Mapping January 2018 Merkel & Associates #14‐051‐05 i TABLE OF CONTENTS INTRODUCTION......................................................................................................................................1 2017 NEARSHORE HABITAT MAPPING ..................................................................................................6 Interferometric Sidescan Sonar Survey..............................................................................................6 RESULTS..................................................................................................................................................8 Comparison Between November 2016 and November 2017 Surveys.............................................13 Trends Through Time (March 2015 – November 2017)...................................................................15 DISCUSSION..........................................................................................................................................16 REFERENCES.........................................................................................................................................19 LIST OF FIGURES Figure 1. Dredge Footprint and Pre‐dredge Eelgrass Results...............................................................2 Figure 2. Receiver beaches. ..................................................................................................................3 Figure 3. Nearshore Marine Habitat Map Comparison, March and September 2015.........................4 Figure 4. Nearshore Marine Habitat Map Elevation and Habitat Change Comparison, March and September 2015..............................................................................................................................5 Figure 5a. Nearshore Marine Habitat Map, North ‐ November 2017. ...............................................10 Figure 5b. Nearshore Marine Habitat Map, South ‐ November 2017................................................11 Figure 6. Nearshore Marine Habitat Map Comparison, November 2016 and November 2017. ......14 Figure 7. Deviation in Composite Habitat Extent from March 2015 Baseline Levels (acres).............15 LIST OF TABLES Table 1. Summary of 2014/2015 AHL maintenance dredging project. ................................................1 Table 2. Pre‐ and Post‐Construction Habitat types delineated within AHL study area........................6 Table 3. Habitat types delineated within AHL study area in November 2017......................................9 2017 Agua Hedionda Lagoon Maintenance Dredging Nearshore Habitat Mapping January 2018 Merkel & Associates #14‐051‐05 1 INTRODUCTION Agua Hedionda Lagoon (AHL) was originally dredged in 1954 by San Diego Gas and Electric (SDG&E) to provide a cooling water source for the Encina Power Station (EPS). The lagoon is divided into three sections: Inner, Middle, and Outer. The inner lagoon is that portion bordered on the east by the Agua Hedionda Creek and on the west by Interstate 5. The middle lagoon is that portion bordered on the east by Interstate 5 and on the west by the North County Transit District railroad bridge. The outer lagoon is that portion bordered on the east by the railroad bridge and on the west by Carlsbad Boulevard, Highway 101. The inlet jetties to the outer AHL are constructed of rip rap from the Pacific Ocean, and the channel flows under a bridge on Carlsbad Boulevard to the north shore of the outer AHL. In order to maintain design cooling water flow rates, the outer AHL requires maintenance dredging. The California Coastal Commission (CCC) Coastal Development Permit (CDP) 6‐17‐0732 allowed dredging up to 500,000 cubic yards (cy) of outer AHL bottom within the dredge limits (Figure 1), and consistent with U.S. Army Corps of Engineers Permit No. 2001‐00328‐RRS and the City of Carlsbad Special Use Permit (SUP 06‐10), dredged material was to be deposited at three Carlsbad beach locations (Figure 2). A summary of the 2014‐2015 cycle is provided in Table 1. Table 1. Summary of 2014/2015 AHL maintenance dredging project. Receiver Site South Beach (cy) Middle Beach (cy) North Beach (cy) Total (cy) December 2014 1,758 1,758 January‐March 2015 73,637 154,298 28,258 256,193 April 2014 36,710 36,710 Total 73,637 156,056 64,968 294,661 cy – cubic yards Permits issued for the project contain various monitoring conditions (Cabrillo Power 2015). The purpose of this report is to satisfy Condition 19 of the U.S. Army Corps of Engineers 404 Permit (SPL‐2001‐00328‐RRS), which required surveys be conducted to identify and delineate coastal habitat types including eelgrass beds, high‐relief reef and low‐relief vegetated reefs (with indicator species including giant and feather boa kelp, large gorgonians, sea palms, and surfgrass), immediately adjacent, upcoast and downcoast of the proposed discharge, with potential to be impacted by the proposed discharge. If monitoring detected project‐related impacts to the above habitat types, the Corps may require remedial measures and/or mitigation for such impacts. Surveys were to be conducted prior to placement of dredge material beyond the middle beach nourishment reach (Cabrillo 2015b), with subsequent surveys being conducted annually in the fall. While the permitting process was completed without adequate time to obtain a fall 2014 pre‐ dredge survey, a non‐obligatory March 2015 survey was completed while material was being placed on Middle Beach, in order to serve as a baseline reference. This survey was completed prior to significant opportunity for sand dispersal and is believed to reflect the condition of reefs at the time and prior to nourishment sand influence. A post‐construction survey was conducted in September 2015. Results of the post‐construction survey and a comparison to the pre‐construction (March 2015) monitoring results were prepared (Merkel 2015) (Figures 3 and 4) (Table 2). Dredge Footprint and Pre-dredge Eelgrass Results 2014 - 2015 Agua Hedionda Lagoon Maintenance Dredging Project Figure 1 14-051-05 µ Merkel & Associates, Inc. 0 100 20050Meters Middle Lagoon Outer Lagoon Study Area Reference Area 2 2 2 Dredge LimitEelgrassOuter Lagoon (entire basin) - 45,529 mOuter Lagoon (within dredge limit) - 1,004 mMiddle Lagoon - 58,462 m Receiver Beaches 2014 - 2015 Agua Hedionda Lagoon Maintenance Dredging Project Figure 2 M&A #14-051-05 NORTH BEACH MIDDLE BEACH SOUTH BEACH Merkel & Associates, Inc. µ 0 500250Meters 0 1,000500Feet -35 -2 5 -30 -20 -1 5 -1 0 -4 0 -5 -4 5 -5-10-40 -4 0 -4 0 -5 -10 -10-40 -10- 4 0 -4 0 -4 0 -1 0 -10 -5 -5µ Merkel & Associates, Inc. 14-051-05 Nearshore Habitat Change Analysis (March 2015 - September 2015)Agua Hedionda Lagoon Maintenance Dredging Program Figure 3 0 2,000 4,000Feet -1 5 -25 - 20 -1 0 -35 -3 0 -40 -5- 4 5-45 -5 -2 5 -5 -1 0 -35 -5-15 -10-40-40-15-5 -5-40 -45 -10-10-5 -5 -45 -3 0 -5 -4 5-10-15-45 -35 -1 5 -25 -30 -40 -20 -3 5 -3 0 -5 -1 0 -10 - 40 -40 -3 5 -20 -4 5 March 2015 September 2015 March 2015 - September 2015Habitat Type Shifts Hard = Bedrock Pavement, Fragmented Bedrock, Sand Scoured Reef, Cobble, Riprap Soft = Shellhash, all Sands CONTOUR INTERVAL - 5ft MLLWCONTOUR INTERVAL - 5ft MLLW SUBSTRATE Bedrock Pavement Cobble Fragmented Bedrock Riprap Sand Scoured Reef Shellhash Intertidal Sand Subtidal Sand Supratidal Sand No Change in Substrate Type = 897.24 ac Hard Bottom to Soft Bottom = 7.22 ac Soft Bottom to Hard Bottom = 22.41 ac NORTHBEACH MIDDLEBEACH SOUTHBEACH NORTHBEACH MIDDLEBEACH SOUTHBEACH NORTHBEACH MIDDLEBEACH SOUTHBEACH µ Merkel & Associates, Inc. 14-051-05 Seafloor Elevation and Habitat Character Change(March 2015 - September 2015)Agua Hedionda Lagoon Maintenance Dredging Program Figure 4 NORTHBEACH MIDDLEBEACH SOUTHBEACH NORTHBEACH MIDDLEBEACH SOUTHBEACHMarch - September 2015Erosion/Accretion (ft) -6.9 - -5.0 -4.9 - -4.0 -3.9 - -3.0 -2.9 - -2.0 -1.9 - -1.0 -0.9 - 1.0 1.1 - 2.0 2.1 - 3.0 3.1 - 4.0 4.1 - 5.0 Hard Substrate Bured (March 2015 - September 2015) Hard Substrate Exposed (March 2015 - September 2015) 0 1,000 2,000 3,000 4,000Feet 2017 Agua Hedionda Lagoon Maintenance Dredging Nearshore Habitat Mapping January 2018 Merkel & Associates #14‐051‐05 6 Table 2. Pre‐ and Post‐Construction Habitat types delineated within AHL study area. March 2015 September 2015 Mar. to Sep. 2015 Change Habitat Acres Acres Acres Bedrock Pavement 154.28 163.97 9.69 Cobble 3.70 7.96 4.26 Fragmented Bedrock 135.60 136.79 1.19 Intertidal Sand 81.64 81.30 ‐0.34 Riprap 3.39 3.39 0 Sand Scoured Reef 4.54 4.54 0 Shell Hash 2.59 0.11 ‐2.48 Subtidal Sand 520.99 508.55 ‐12.44 Supratidal Sand 20.83 20.94 0.11 Total 927.55 927.55 0.0 The comparison between the habitat types from March 2015 and September 2015 indicated that a net of approximately 7.2 acres of hard bottom substrate experienced sand burial, while approximately 22.4 acres of soft bottom habitat experienced erosion that led to exposure of hard substrate. This resulted in a net increase of hard over soft substrate of approximately 15.2 acres (Figure 3). However, the majority of the habitat (approximately 897 acres or 97 percent of the survey area) experienced no detected change in substrate type from March to September 2015. Further bathymetric change analyses indicated that the majority of the change occurred in nearshore areas in water less than ‐20 feet MLLW, with maximum erosion of up to approximately 6 feet occurring along the middle beach portion of the project area (Figure 4). Areas experiencing accretion were generally in the intertidal/shallow subtidal area located downcoast of the south beach receiver area, as well as, the shallow subtidal area downcoast of the middle beach receiver site. This present report provides results of the Fall 2017 (November 2017) survey and compares/contrasts findings with Fall 2016 (November 2016) monitoring results. 2017 NEARSHORE HABITAT MAPPING INTERFEROMETRIC SIDESCAN SONAR SURVEY An interferometric sidescan sonar survey was completed offshore, upcoast and downcoast of the 2014‐2015 receiver sites on November 2, 3, and 6, 2017. Additional ground‐truthing data collection was completed on December 5, 2017. The survey was completed over a beach length of approximately 2.6 nautical miles and extended from the edge of the supratidal margin (elevation of +10 feet MLLW or higher) to approximately ‐40 feet MLLW or approximately 5 feet below the recognized littoral cell depth of closure in this area. Data were collected using an interferometric wide‐swath sonar system operating at 468 kHz. The sonar was set to scan out to 31 meters (m) on both the starboard and port channels for a 62‐m wide swath. At these settings, digital pixel resolution is approximately 6.4 centimeters (cm) by 6.4 cm. Parallel survey tracklines were 2017 Agua Hedionda Lagoon Maintenance Dredging Nearshore Habitat Mapping January 2018 Merkel & Associates #14‐051‐05 7 navigated through the project survey area until the entire survey footprint was covered. Adjacent tracklines were spaced to allow overlap such that the area directly beneath the sonar head (nadir gap) was filled with valid data to allow for preparation of a full coverage mosaic during post processing. The sidescan sonar was field calibrated by running patch tests to confirm or adjust sonar head settings. Geographic positioning was provided via a dual antenna RTK GPS/compass receiver with better than 10‐cm accuracy. The collected data were spatially corrected for vessel heave, pitch, and roll via an integrated vessel’s motion sensor. All data were collected in latitude and longitude using the North American Datum of 1983 (NAD 83), converted to the Universal Transverse Mercator system in meters (UTM), and plotted on a geo‐rectified aerial image of the project area. The data from the sonar included multibeam‐like swath bathymetry and sidescan backscatter data. The bathymetric data result from the timing of the return of a sound pulse reflected off the bottom and wave phase differences as it is received at multiple locations on the transducer array. The difference in wave phase and return time to different sensors allows for triangulation of the position of the acoustically reflective surface. The vertical and horizontal accuracy of the bathymetric data are a function of the accuracy of the vessel positioning and the accuracy of adjustments for velocity of sound and pulse angle (pitch, roll, and heave). The horizontal and vertical positioning and compass orientation of the survey vessel is provided by the GPS system. The rest of the survey system was composed of a SWATHplus‐H sonar, Veleport miniSVP sound velocity sensor, and an SMC IMU‐108 motion sensor. The backscatter data were used to determine the distribution of seafloor habitats. The backscatter data are the visual representation of the intensity of the acoustic energy reflected back to the sonar unit from the bottom. Hard objects (e.g., rock, calcareous, siliceous organisms) or soft objects containing air filled voids (e.g., kelp pneumatocysts, eelgrass) reflect sound waves with a greater intensity relative to soft bottom (e.g., mud and sand). The angle of the surveyed object also determines the intensity of the returned sound signal. Rocky outcroppings with greater complexity (e.g., increased relief) and sand waves have greater variation in terms of high signal intensity mixed with low signal return in the areas that lie in the shadows of the reef or sand wave. The backscatter data were interpreted through inspection of the spatially registered acoustic imagery. In conjunction with collection of interferometric sidescan sonar, a video camera with a 270‐degree wide dynamic range (WDR) color camera was deployed vertically below the positional antenna to acquire groundtruthing data to assist in habitat mapping from interferometric sidescan sonar data. Following completion of the field survey, the digital sonar traces (backscatter data) were joined together into a single mosaic and geographically registered using the recorded navigational data. The registered sonar mosaic were then overlaid on an aerial image of the survey area and reviewed for accuracy. A UAV was used to collect approximately 2,200 images along the beach for development of an orthomosaic image. This image was used to map intertidal and supratidal resources that were above the surveyable reach of sidescan sonar survey methods. The UAV was flown at an altitude of 300 feet such that the nearshore margins of flight lines within the middle intertidal zone collected photographic coverage extending onshore to the base of the bluffs or edge of developed lands. 2017 Agua Hedionda Lagoon Maintenance Dredging Nearshore Habitat Mapping January 2018 Merkel & Associates #14‐051‐05 8 Surficial features and marine benthic habitat types were then digitized by a geographic information systems (GIS) specialist who inspected the sonar mosaic and delineated habitats and features using ESRI ArcView GIS software. Habitats were classified according to the U.S. Fish and Wildlife’s “Classification of Wetlands and Deepwater Habitats of the United States” (Cowardin et al. 1979). Collected video imagery was used to inspect habitat breaks and characterize habitats defined by backscatter data. Still photos were “grabbed” from the video to support habitat characterizations for reporting purposes. RESULTS As with the previous surveys, the 2017 survey area encompassed 927.55 acres. Habitat types and coverages are summarized in Table 3 and depicted in Figures 5a and 5b. The dominant habitat type detected both in the intertidal and subtidal zone was sand, comprising approximately 75 acres and 513 acres, respectively. The mapped coarse sediments/shell hash comprised approximately 3.5 acres of the mapped area. This habitat type can be classified as part of the sand habitat, but was mapped separately because the shell hash had a higher reflectance in the backscatter data and is easily distinguished. The second most abundant benthic habitat type mapped was rock bottom habitat (approximately 305 acres). The substrate generally consisted of areas of large bedrock terraces and fragmented bedrock features. Some of the lower‐relief (< 1m high) bedrock substrata within the shallow subtidal zone (<‐5m MLLW) were generally characterized as having a low cover of foliose and sheet forms of red and brown algae, although in some instances these features supported surfgrass. Areas with larger bedrock outcroppings and higher relief (> 1m high) were observed to support understory algae species such as sea palms. Giant kelp has historically been present on reefs below approximately ‐6m MLLW. Cobble fields occur near and within the intertidal beach areas as well as within supratidal locations where large storms have stripped shallow sands off of some of the cobble underlayment. Many factors can affect algal cover and examples include large wave events, water temperature, sedimentation, and predation (Foster and Schiel 1985). During the November 2017 survey, the most common vegetation type on the rocky habitat was ephemeral and foliose algae. Limited canopy kelp was observed on the surface within the shallower areas included in the study area. Surfgrass had a total coverage of 5.19 acres, with the vast majority of the surfgrass being found to the southern end of the study area. 2017 Agua Hedionda Lagoon Maintenance Dredging Nearshore Habitat Mapping January 2018 Merkel & Associates #14‐051‐05 9 Table 3. Habitat types delineated within AHL study area in November 2017. Mar‐15 Sep‐15 Nov‐16 Nov‐17 Nov 2017 minus Sep 2015 Nov 2017 minus Nov 2016 Habitat Acres Acres Acres Acres Acres Acres Marine: Subtidal: Rock Bottom 9.97 13.60 Bedrock Pavement 154.28 163.97 131.33 151.42 ‐2.86 20.09 Fragmented Bedrock 135.6 136.79 159.90 152.52 16.86 ‐7.44 Sand Scoured Reef 4.54 4.54 0.89 ‐4.03 0.51 Marine: Subtidal: Unconsolidated Bottom 20.02 ‐13.47 Subtidal Sand 520.99 508.55 524.68 513.22 20.98 17.29 Shell Hash 2.59 0.11 3.33 3.49 0.90 0.16 Cobble 3.7 7.96 4.01 1.84 ‐1.86 ‐2.17 Marine: Intertidal: Unconsolidated Bottom ‐34.33 ‐4.41 Intertidal Sand 81.64 81.30 79.51 75.49 ‐34.46 ‐32.33 Intertidal Cobble 0.48 0.12 0.12 ‐0.36 Boulders 0.04 0.01 0.01 ‐0.03 Marine: Intertidal: Artificial Substrate 0.18 0.17 Riprap 3.39 3.39 3.40 3.57 0.19 0.17 Supratidal Habitats 4.15 4.11 Supratidal Boulders 0.04 0.84 0.84 0.80 Supratidal Cobble 0.41 0.42 0.41 0.01 Supratidal Sand 20.83 20.94 20.42 23.73 2.90 3.31 Total (Acres) 927.55 927.55 927.55 927.55 0.00 0.00 Nearshore Marine Habitat MapNovember 20172014 - 2015 Agua Hedionda Lagoon Maintenance Dredging Project Figure 5a M&A #14-051-05 -15-2 0 -2 5 -30 -3 5 -1 0 - 4 0 -5 - 1 0 -35-1 0 -1 0 -5-5- 5 -10-1 0 - 5 Merkel & Associates, Inc. µ 0 500250Meters 0 1,000500Feet Habitat Classification Marine: Subtidal: Rock BottomBedrock PavementFragmented BedrockSand Scoured ReefMarine: Subtidal: Unconsolidated BottomSandCobbleShellhashMarine: Intertidal: Unconsolidated BottomSandIntertidal CobbleBouldersMarine: Intertidal: Artificial SubstrateRiprapUpland HabitatsSupratidal SandSupratidal CobbleBoulders/BluffMarine: Subtidal: Vegetation CommunitiesSurfgrassBathymetry (ft MLLW) Nearshore Marine Habitat Map, South November 20172014 - 2015 Agua Hedionda Lagoon Maintenance Dredging Project Figure 5b M&A #14-051-05 -35 -3 0 -25 -20-15-10-5 - 4 0 - 1 0 -35-1 0 -1 0 -5-5-5-5-5 -5 -1 0 Merkel & Associates, Inc. µ 0 500250Meters 0 1,000500Feet Habitat Classification Marine: Subtidal: Rock Bottom Bedrock Pavement Fragmented Bedrock Sand Scoured Reef Marine: Subtidal: Unconsolidated Bottom Sand Cobble Shellhash Marine: Intertidal: Unconsolidated Bottom Sand Intertidal Cobble BouldersMarine: Intertidal: Artificial Substrate Riprap Upland Habitats Supratidal Sand Supratidal Cobble Boulders/Bluff Marine: Subtidal: Vegetation Communities Surfgrass Bathymetry (ft MLLW) 2017 Agua Hedionda Lagoon Maintenance Dredging Nearshore Habitat Mapping December 2017 Merkel & Associates #14‐051‐06 12 Photo 1. Sand bottom habitat. Photo 2. High‐relief reef with turf algae and established surfgrass beds. Photo 3. Surfgrass on high‐relief bedrock reef with red turf algae. Photo 4. Bedrock reef margin transition to sand Photo 5. Partially sanded fragmented bedrock reef with gorgonians and understory algae. Photo 6. High‐relief fragmented bedrock reef with understory algae and giant kelp. 2017 Agua Hedionda Lagoon Maintenance Dredging Nearshore Habitat Mapping January 2018 Merkel & Associates #14‐051‐05 13 COMPARISON BETWEEN NOVEMBER 2016 AND NOVEMBER 2017 SURVEYS To evaluate changes in habitats between the fall surveys, areas of hard bottom that were converted to soft bottom and reciprocal conversions of soft to hard bottom were examined by GIS spatial analyses. This analysis only allows for examination of habitat type change between fixed points in time and does not document dynamics of sediment shifts. The comparison between the habitat types from November 2016 and November 2017 indicated that a net of approximately 13.60 acres of subtidal rock bottom substrate that was previously covered in sand was exposed between these two periods (Table 3). This is nearly equal to the prior sand burial of 14.07 acres that occurred between September 2014 and November 2016. Between November 2016 and November 2017, unconsolidated bottom decreased by 17.88 acres. Residual differences between these changes are attributed to gains within the supratidal, principally derived from minor high sand beach expansion between 2016 and 2017 sampling periods. There are many different habitat features that make changes in habitat character hard to track on a spatial basis. However, in general, if the analysis is simplified to examine only changes from hard to soft bottom habitats and soft to hard bottom habitats, then the spatial distribution of habitat shifts can be explored. Cobble and boulder are typically considered to be hard bottom habitat, although unconsolidated in nature. When these two habitat classes are considered along with the bedrock, there has been a hard bottom to soft bottom conversion totaling 46.17 acres (Figure 6). There has also been a commensurate soft to hard‐bottom conversion of 58.02 acres. This resulted in a net increase of 11.85 acres of hard bottom between November 2016 and November 2017. Concurrent with the changes in habitats, 822.65 acres (89 percent) of hard and soft bottom did not change between the 2016 and 2017 monitoring period. The principal changes in soft to hard bottom habitat have been loss of sand over shallow sand scoured reef along the shallow shoreline margin, particularly along the north beach placement area. However, a considerable amount of reef exposure has also occurred along the margins of deeper reefs within both the northern and southern ends of the study area. In areas of conversion from hard to soft bottom habitat, the shift generally occurred slightly offshore from the beach and generally within the southern portion of the study area and the far northern portion of the study area. Other areas of conversion include scattered pockets of sand in portions of the reef such as troughs and basins on relatively flat reef areas. µ Merkel & Associates, Inc. M&A #14-051-05 Nearshore Habitat Change Analysis (November 2016 - November 2017)Agua Hedionda Lagoon Maintenance Dredging Program Figure 6 0 2,000 4,000Feet November 2016 November 2017 November 2016 - November 2017Habitat Type Shifts Hard = Bedrock Pavement, Fragmented Bedrock, Boulder, Cobbles, Riprap Soft = Shellhash, all Sands Bedrock PavementFragmented BedrockSand Scoured ReefSandCobbleShellhashSandIntertidal CobbleBouldersRiprapSupratidal SandSupratidal CobbleBoulders/Bluff No Change = 822.64 ac Hard Bottom to Soft Bottom = 46.17 ac Soft Bottom to Hard Bottom = 58.02 ac NORTHBEACH MIDDLEBEACH SOUTHBEACH NORTHBEACH MIDDLEBEACH SOUTHBEACH NORTHBEACH MIDDLEBEACH SOUTHBEACH 2017 Agua Hedionda Lagoon Maintenance Dredging Nearshore Habitat Mapping January 2018 Merkel & Associates #14‐051‐05 15 TRENDS THROUGH TIME (MARCH 2015 – NOVEMBER 2017) From spring 2015 (March) through fall 2017 (November) there have been four sampling events along the nearshore project area. In order to evaluate how the overall environment has changed through time in the study area, the acreage of rock bottom, sand bottom, supratidal habitats, and surfgrass were tracked as a deviation from the conditions in March 2015. This was performed by subtracting the acreage of each habitat aggregation present in March 2015 from that present in each of the subsequent monitoring intervals and plotting the deviation from the March 2015 in acreage (Figure 7). Figure 7. Deviation in Composite Habitat Extent from March 2015 Baseline Levels (acres). Because the data collected thus far has been limited to a short period of time and has not included sampling during the same seasons prior to and after dredge material placement, it is not presently possible to determine precisely what affect the nearshore nourishment may have on the habitats within the area. However, for the next dredging cycle to be undertaken in winter‐spring 2018, the three fall samplings (2015‐2017) do provide a good overall baseline for examining the extent of change in subsequent seasons. ‐20.00 ‐15.00 ‐10.00 ‐5.00 0.00 5.00 10.00 15.00 Mar 15 Sep 15 ‐ Mar 15 Nov 16 ‐ Mar 15 Nov 17 ‐ Mar 15Change in area from March 2015 (Acres)Rock Bottom Sand Bottom Supratidal Habitats Surfgrass 2017 Agua Hedionda Lagoon Maintenance Dredging Nearshore Habitat Mapping January 2018 Merkel & Associates #14‐051‐05 16 DISCUSSION Previous studies and monitoring programs summarized reef habitat quality based on reef height and differences in relative occurrence of indicator species (SAIC 2007, SANDAG 2011), which were grouped into the following categories according to differences in persistence, sensitivity, or tolerance to sedimentation, as follows: Persistent indicator species considered relatively sensitive to sand scour and sedimentation (giant kelp, gorgonians); Persistent indicator species considered relatively sand tolerant (surfgrass, sea palm); Opportunistic indicator species considered relatively sand tolerant (feather boa kelp); and Substrate without indicator species and/or with only opportunistic turf species. In general, higher quality reefs include the presence and/or relative common occurrence of persistent indicator species (surfgrass, giant kelp, sea palm, gorgonians), while lower quality reefs include dominance by opportunistic turf and foliose algae and/or lack of biological indicator species. Feather boa kelp is considered opportunistic and may be associated with reefs ranging from relatively high to low quality. Life history characteristics of the indicator species are briefly reviewed below to provide a general overview on persistence and response to environmental disturbance and representative photographs are depicted in the photographs below. Feather boa kelp and surfgrass Low relief reef with red turf algae Feather boa kelp and giant kelp Gorgonians Representative photographs of reef indicator species and biota (from SAIC 2007). 2017 Agua Hedionda Lagoon Maintenance Dredging Nearshore Habitat Mapping January 2018 Merkel & Associates #14‐051‐05 17 Surfgrass is a perennial plant that forms beds that expand by vegetative propagation, persisting for many years, and are adapted to seasonal sand movement and partial burial (Littler et al. 1983, Stewart 1989). However, complete burial, or extended deep partial burial can have deleterious effects on surfgrass and burial was suspected of causing widespread loss of surfgrass near Santa Barbara (Reed and Hollbrook 2003). Giant kelp may live up to 8 years (2 to 4 typical) and is generally considered sensitive to sand movement and sedimentation. Although giant kelp adults may withstand thin sand deposits, thicker deposits can adversely affect adult and juvenile plants, while thin deposits may affect kelp recruitment (Foster and Schiel 1985). The understory sea palm is long‐lived (up to 10 years), while feather boa kelp is an opportunistic perennial that grows rapidly, is reproductive within several months of recruitment, and is tolerant to moderate levels of sedimentation (Black 1974, Dayton et al. 1984). For feather boa kelp, it is often not possible to determine if thalli are multiple years old, or from the present year’s recruits. Gorgonians are long‐lived invertebrates that do not become reproductive for 5 to 10 years, filter feed plankton and small particulates from the water column, and generally occur on higher reef elevations suggesting they require greater water motion and have a relatively low tolerance to sedimentation (AMEC 2005). Substrates devoid of vegetation and/or with only low growing ephemeral turf algae often occur in areas with substantial disturbance and/or sand scour (Stewart 1989, Littler et al. 1983). As noted previously, the littoral sand derived inlet flood bar within Agua Hedionda Lagoon has been dredged continuously since 1954 with dredged material being returned to the beaches. In addition, other nearby maintenance dredging projects occur annually (e.g., Oceanside Harbor) that contribute sediments to this portion of the littoral cell, and less frequent programs such as Sand Compatibility and Opportunistic Use Program (SCOUP) and Regional Beach Sand Project (RBSP) may also contribute sediment. The project area has been previously surveyed, mapped, and monitored as part of San Diego Association of Governments (SANDAG) Regional Beach Sand Project (RBSP) I and II (SANDAG 2005, 2011), and the Coastal Inventory Program (2003). In addition, the project area is included in a long‐term beach monitoring program (i.e., coastal profile monitoring program since 1996) and it is anticipated that those beach profile data would also be used for this monitoring program, although results are generally not available until the following year. Approximately 295,000 cy of sediment was placed on the beach in winter/spring 2015. This sand remained on the beach through the September 2015 survey. The November 2016 survey revealed movement of the sand to offshore environments. By November 2017 it was not clear where the sand from dredging was distributed. The sand migration away from the shore has also exposed rocky reefs supporting surfgrass to the south of nourishment beaches in areas that were mostly buried in sand in March 2015, prior to beach nourishment in the area and in September 2015 following nourishment. The exposure of the shallow reef to the south of the South Beach placement area between 2015 and 2016 resulted in a dramatic increase in detectible surfgrass. The surfgrass in the study area increased from 4.24 acres in September 2015 to 8.19 acres in November 2016. In November 2017, surfgrass had declined to 5.19 acres with most of the loss of eelgrass occurring at the southern end of the study area. The multiple surveys within the Agua Hedionda Lagoon nearshore habitat study area indicate that a dynamic nearshore environment exists. This is evidenced by the increase in hard substrate 2017 Agua Hedionda Lagoon Maintenance Dredging Nearshore Habitat Mapping January 2018 Merkel & Associates #14‐051‐05 18 coverage observed between the March 2015 and September 2015 surveys even following a period when sand was being placed on the beaches. This exposed approximately 22.4 acres of hard bottom habitat, generally in the shallow subtidal area (<20 ft water depth). In addition, approximately 7.2 acres of hard bottom habitat experienced sedimentation primarily downcoast of the south beach receiver site during the same period. Between September 2015 and November 2016, additional shallow reef habitat was exposed at the expense of burial in low relief bedrock pavement further offshore. This change, while resulting in a net reduction of hard bottom habitat, resulted in an increase in reef structure since the pavements that were buried were generally low, highly scoured surfaces, while the sand removed in the shallows exposed greater extents of surfgrass as well as ridges and overhangs in terraced reefs in fragmented bedrock formations. Between November 2016 and November 2017 additional reef structure was exposed while other areas were buried in a process that resulted in a net 11.85 acre increase in hard bottom habitat. The late winter storms of 2016‐2017 included some particularly large wave events and sand movement at depth was likely a factor influencing the gains in extent of hard bottom habitat. Sand present on the deeper reef terraces at the north end of the study area in November 2016 was purged by November 2017 as was sand on the upper shore margins at the north end of the study area. For future surveys, occurrence frequency maps will be prepared for hard bottom in order to assist in identifying areas of greater or lesser persistence. Surveys are to continue annually during the term (5 years) of the Corps of Engineers permit SPL‐2001‐00328‐RRS. 2017 Agua Hedionda Lagoon Maintenance Dredging Nearshore Habitat Mapping January 2018 Merkel & Associates #14‐051‐05 19 REFERENCES Allee, R. J. Dethier, M., Brown, D., Deegan, L., Ford, R. G., Hourigan, T. F., Maragos, J., Schoch, C., Sealey, K., Twilley, R., Weinstein, M. P., Yoklavich, M. Roff, John C. Taylor, Mark E.. 2000. 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