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Home My WebLink AboutCT 04-11; Poinsettia Commons; Preliminary Drainage Report; 2004-09-01PRELIMINARY DRAINAGE REPORT POINSETTIA TRANSIT VILLAGE - CONDOMINIUMS CITY OF CARLSBAD SEPTEMBER 2004 Prepared For: Hoffman Planning 5960 Pasteur Court Suite 150 Carlsbad, CA 92008 Prepared By: PROJECTDESIGN CONSULTANTS 701 B Street, Suite 800 San Diego, CA 92101 Job No. 2541.00 Prepared by: Thomas W. Engel Under the supervision of: Gary W. Wesch, PE RCE 27376 Registration Expires 03/31/05 TABLE OF CONTENTS Section Page 1.0 INTRODUCTION 1 2.0 EXISTING AND PROPOSED DRAINAGE PATTERNS AND 3 IMPROVEMENTS 2.1 Existing Conditions Drainage Patterns 3 2.2 Proposed Conditions Drainage Patterns and Improvements 3 3.0 HYDROLOGIC CRITERIA, METHODOLOGY, AND RESULTS 5 3.1 Hydrologic Criteria 5 3.2 Hydrologic Methodology and Results 5 3.3 Water Quality Requirements 6 4.0 HYDRAULIC CRITERIA, METHODOLOGY, AND RESULTS 8 5.0 CONCLUSION 9 FIGURES 1 Vicinity Map 2 TABLES 1 Hydrology Criteria 5 2 Hydrology Summary 5 APPENDICES 1 Lot 2 Hydrology: Rational Method Computer Output 2 Hydrologic Calculations\ Estimate for Avenida Encinas Diversion 3 Hydrologic Soils Group Map From Waters End Report EXHIBITS A Existing Conditions Drainage Map B Developed Conditions Drainage Map 2541DR3.docT:\Water Resources\2541-Poinsettia Slation\254IDR3.doc 1.0 INTRODUCTION This drainage report has been prepared in support of the design of the storm drain improvements for the Poinsettia Transit Village (Project), located in the City of Carlsbad. The project is located adjacent to the Carlsbad Poinsettia NCTD Transit Station encompasses Embarcadero Lane and two vacant areas consisting of natural grasses. The Project proposes to subdivide the lot into 5 lots and vacate a portion of Embarcadero Lane. "Lot 1" will be bounded by Avenida Encinas to the north and east, Embarcadero Lane to the west, and Planning Area 5 to the south. "Lot 2" will be bounded by Avenida Encinas to the north, Embarcadero Lane to the east, the San Diego Northern County Railroad to the west, and Planning Areas 2, 3, and 4 to the south. Lots B and C will be bounded by Avenida Encinas to the north and Lot 1 and Lot 2, respectively. Lot A will encompass a portion of Embarcadero Lane. See Figure 1 for the project vicinity map. The limits of the improvements consist of 5.3 acres. Lot 1 consists of the construction of a 3300 square foot day care center, commercial space, affordable housing, and associated walkways, driveways, utilities, and landscaping. Lot 2 consists of the construction of commercial space, loft units, live/work condominiums, one level of underground parking, and associated walkways, roadways, utilities, landscaping, and surface parking spaces. Lots B and C will primarily be open space with pedestrian walkways. Lot A will include street parking, sidewalks, and travel ways. The total commercial space will encompass an area of 18,000 square feet, including restaraunts. The residential space will cover an area of 147,540 square feet and will consist of 14 affordable housing units and 67 condominiums. Additionally, there will be minor offsite grading on the existing drainage ditch, originating at the southwest end of the Project. The project area currently consists of natural grasses and brush typical of the region. The purpose of this report is to: 1) determine hydrologic and hydraulic impacts, if any, relative to the existing City of Carlsbad storm drain system, and 2) provide runoff values for the design of the onsite private storm drain system. A combination of existing and proposed private storm drainpipes will collect and convey Project storm flows to the existing storm drain system at the Embarcadero \ Bay Lane intersection and to the existing drainage ditch at the southwest corner of the Project. From a water quality perspective, the storm runoff will be treated to the Maximum Extent Practicable (MEP) prior to entering the storm drain system. See the 2541DR3.docT:\Water Resources\2541 -Poinsettia Station\2541DR3.doc i Stormwater Checklist and Water Quality Technical Report prepared by ProjectDesign Consultants for water quality information. Modified Rational Method hydrology calculations using Advanced Engineering Software and hand-written calculations are provided in this submittal. OCEAN VICINITY MAP NOT TO SCALE Figure 1. Vicinity Map 254IDR3.docT:\Waler Resources\254l-Poinsettia Slalion\254IDR3.doc 2.0 EXISTING AND PROPOSED DRAINAGE PATTERNS AND IMPROVEMENTS The following sections provide descriptions of the existing and proposed drainage patterns and improvements for the Project. 2.1 Existing Drainage Patterns The following section describes the existing drainage improvements. Under existing conditions, excess storm water from Lot 1 sheet flows to the south, where it enters a storm drain inlet. The storm drain inlet connects to the city storm drain system, running south under Embarcadero Lane. Runoff from Avenida Encinas and approximately 140 feet of the north end of Embarcadero Lane flows to the north end of Lot 2. Runoff from Lot 2 sheet flows south to a grass swale (constructed for use as an interim condition) at the southern end of the property, which guides the flow through two sets of dual 12-inch culverts separated by a graded ditch designed in the Waters End Project. The Lot 2 runoff is discharged into an unmaintained earthen drainage swale along the eastern side of the railroad tracks, flowing southward. See Exhibit A for the Existing Conditions Drainage Map. 2.2 Proposed Drainage Improvements The proposed development consists of the construction of a day care center, commercial space, affordable housing, associated walkways, driveways, utilities, loft units, live/work condominiums, underground parking, roadways, utilities, landscaping, and surface parking spaces. Under proposed conditions, the stormwater will be conveyed in the same manner as described in Section 4.5 and Exhibits A, B, and C of the February 2002 Waters End Drainage Report CT 00- 16 DWG No. 396-7 (Waters End Report), with a few exceptions. One discrepancy is the diversion of 0.69 acres on Avenida Encinas being diverted past the project site via a cross-gutter instead of entering the Lot 2 drainage scheme, as directed by pre-submittal meetings with the City of Carlsbad. The runoff will flow in a westerly direction, via a proposed cross gutter, and enter an existing unpaved utility lot adjacent to the railroad after some ponding near the Transit Station driveway. The runoff will enter the same drainage channel as the existing conditions approximately 400' upstream from the current discharge location. 2541DR3.docT:\Water Resources\2541-Poinsettia StalioD\2541DR3.doc -3 Lot 2, also diverging from the Waters End Report, will have a series of roof and area drains on the western boundary of the Project. These drains will discharge into the existing earth channel currently receiving Lot 2 runoff, as described in Section 2.1. Grading and improvements within the channel may be needed to facilitate sufficient flow between the project site and the outfall, near the railroad tracks. The Waters End Report assumed Lot 2 ties into the existing City of Carlsbad storm drain system at the comer of Embarcadero and Bay Lane, and the downstream storm drain system has been designed as such. Lot 1 runoff will be entering the same inlet as existing conditions, with the addition of a series of area drains. Embarcadero Lane consists of a series of low points with inlets connecting to the existing storm drain system along Embarcadero Lane. Both Embarcadero Lane and Lot 1 drainage schemes are consistent with the assumptions made in the Waters End Report. Proposed pipe sizes will be confirmed at the time of final engineering. An existing headwall and 127 linear feet of 18" RCP near Lot 1 will be removed and replaced in the proposed condition, as well as the lateral storm drains along Embarcadero Lane. See Exhibit B for the proposed drainage patterns. 2541DR3.docT:\Walcr Resources\254I-Poinsettia Station\2541DR3.doc 3.0 HYDROLOGIC CRITERIA, METHODOLOGY, AND RESULTS This section of the report summarizes the drainage criteria that were used in the hydrologic analysis and key elements of the methodology. The AES Rational Method hydrology computer output is located in Appendix 1. 3.1 Hydrologic Criteria Table 1 below summarizes the hydrology criteria for the project. Note that hydrologic criteria presented are congruent with the Waters End Report. This ensures the assumptions, regarding our Project site, made for the downstream improvements in the Waters End Project are adequate. Table 1: Hydrology Criteria Design Storm: Land Use: Runoff Coefficients: Hydrologic Soil Group: Intensity and Time of Concentration: Water Quality BMP Design Flowrate, Qm 100-year, 6-hour storm. Commercial and Multi-Family. Based on criteria presented in the "Standards for Design and Construction of Public Works Improvements in the City of Carlsbad," Drainage - Design Criteria section, dated 4-20-93 and the 1985 County of San Diego Hvdrologv Manual, Soil Group 'A', as per Waters End Report. See Appendix 3 for the County Soil Group Map. Based on criteria presented in the 1985 County of San Diego Hydrology Manual, Based on criteria presented by RWQCB and US EPA. 3.2 Hydrologic Methodology and Results The Modified Rational Method was used to determine the 100-year storm flow for the design of the storm drainpipe. Calculations are provided in Appendix 1. Table 2 presents the results of the hydrologic analysis at Waters End node 1110. 2541 DR3.docT:\WaterResources\2541-PoinsettiaSlation\2541DR3 Joe Table 2. Hydrology Summary Location Waters End Proposed Condition Assumption for Lot 2 Revised Project Proposed Condition for Lot 2 Waters End Proposed Condition Assumption for Total Offsite Flow Entering Storm Drain System at Node 11 10 Revised Total Flow Entering Waters End Storm Drain System as a Result of Project Development Proposed Conditions Drainage Area (acres) 3.9 3.1 21.2 17.3 Proposed Conditions Q100 (cfs) 6.9 6.6 49.7 42.8 The 0.7+/- acres from Avenida Encinas that is being diverted as shown on Exhibit B, eliminates 2.3 cfs from the Lot 2 drainage system assumed in the Waters End Report, discharging at node 1110. However, Table 2 demonstrates that there is only a 0.3 cfs reduction in runoff, compared to the abovementioned 2.3 cfs. This is due to a shift from the "multi-family" land use, expected in the Waters End Report, to a more impervious combination of "multi-family" and "commercial" land use. Multi-family and commercial land-uses correspond to runoff coefficients of 0.45 and 0.7 respectively for hydrologic soil type A. Note that the Hydrologic Criteria in the previous section states that IDF curves, runoff coefficients and soil types were taken from the 1985 Hydrology Manual in order to be consistent with the Waters End Report. 3.3 Water Quality Requirements Water Quality requirements are sufficiently met through site design, source control, and treatment BMPs (an existing downstream CDS unit). A CDS unit exists downstream of the project site, which was constructed as part of the Waters End Project. All runoff from the project was assumed to enter the CDS unit and is sized accordingly. Project flows that differ from the 2541DR3.docT:\Water Resources\2541-Poinsettia Station\2541DR3.doc Waters End Report (Lot 2) will be treated with a treatment BMP to the maximum extent practicable, in accordance with the City and Regional Water Quality Control Board. The BMP treating Lot 2 runoff is assumed to be the improved channel at the southwest corner of the project. This BMP will be in the form of a swale or bioretention area, and the channel will be maintained by the owners of Lot 2, via an EMRA with the City. Technical calculations for this facility will be provided at the time of final engineering. See the Water Quality Technical Report for Poinsettia Transit Village provided by ProjectDesign Consultants for further discussion of water quality requirements. 2541DR3.docT:\Water Resources\2541-Poinsettia Stalion\2541DR3.doc 4.0 HYDRAULIC CRITERIA, METHODOLOGY, AND RESULTS The onsite storm drain system and streets were designed to collect and convey the 100-year storm runoff per City Standards. Onsite storm drainpipes within Embarcadero Lane were designed for 100-year storm open channel flow where possible and, as a minimum, contain the 100-year HGL below flowline of the inlet opening and below cleanout top-of-rim elevations. The onsite catch basins and area drains in Lots 1 and 2 will be designed per City standards to intercept the 100-year runoff at the time of final engineering. No HGL calculations for the Embarcadero Lane system were necessary, additional to those provided in the Waters End project, because there was no increase in runoff that was not accounted for (See Waters End, Exhibit C and Appendix 5). Hydraulic calculations for Embarcadero Lane storm drain system will be provided at the time of final engineering if the pipe inverts are altered, but is not anticipated. The earth channel draining Lot 2 was designed for an interim condition. New hydraulic calculations on the revised design of the channel for sufficient conveyance and water quality treatment will be provided during final engineering. Hydraulic calculations will be provided for inlet sizing, area drains, private storm drains, etc. during the time of final engineering. 2541DR3.docT:\Waier Resources\2541-Poinsettia Staiion\2541DR3.doc 5.0 CONCLUSION This drainage report has been prepared in support of the design of the storm drain improvements for the Poinsettia Transit Village. The Project consists of 5.3 acres of condominiums, retail space, and associated utilities and paving. This report concludes that there is no hydrologic/hydraulic impact to the storm drain facilities receiving Project runoff. All runoff entering the storm drain system is accounted for in the Waters End drainage report. The 0.69 acres of runoff on Avenida Encinas being diverted by a cross gutter at the intersection with Embarcadero Lane, running westward, will be sufficiently intercepted into City facilities per pre- submittal discussions between PDC and the City. Lot 2 will drain similar to existing conditions, differing from the Waters End Report, due to discussions between PDC and the US Fish and Wildlife Service on 17 September 2005. Hydrologic runoff values for the Project are provided in the Waters End Report, and Appendices 1 and 2 contain hydrologic calculations for those areas that differed from the Waters End project. Concerning hydraulics, all downstream facilities (Waters End pipes and graded ditch) have been shown to sufficiently convey Project flows per the Waters End Report. 2541DR3.docT:\Water Resources\2541-Poinsettia Station\2541DR3.doc APPENDIX 1 Lot 2 Hydrology: Rational Method Computer Output REP\1800\1801DR.DOC APPENDIX 2 Hydrologic Calculations\ Estimate for Avenida Encinas Diversion REP\1800\1801DR.DOC APPENDIX 3 Hydrologic Soils Group Map From Waters End Report REP\1800\1801DR.DOC APPENDIX 1 Lot 2 Hydrology: Rational Method Computer Output REP\1800\1801DR.DOC RATIONAL METHOD HYDROLOGY COMPUTER PROGRAM PACKAGE Reference: SAN DIEGO COUNTY FLOOD CONTROL DISTRICT 2003,1985,1981 HYDROLOGY MANUAL (c) Copyright 1982-2003 Advanced Engineering Software (aes) Ver. 1.5A Release Date: 01/01/2003 License ID 1509 Analysis prepared by: ProjectDesign Consultants San Diego, CA., 92101 Suite 800 619-235-6471 ************************** DESCRIPTION OF STUDY ************************** * POINSETTIA TRANSIT VILLAGE * * PROJECT #2541 DRAINAGE REPORT FOR PROPOSED CONDITIONS * * 1OO YR - 6 HR STORM EVENT * FILE NAME: PPA6-100.DAT TIME/DATE OF STUDY: 16:53 07/20/2004 r********************************* USER SPECIFIED HYDROLOGY AND HYDRAULIC MODEL INFORMATION: 1985 SAN DIEGO MANUAL CRITERIA USER SPECIFIED STORM EVENT(YEAR) = 100.00 6-HOUR DURATION PRECIPITATION (INCHES) = 2.500 SPECIFIED MINIMUM PIPE SIZE(INCH) = 8.00 SPECIFIED PERCENT OF GRADIENTS(DECIMAL) TO USE FOR FRICTION SLOPE =0.90 SAN DIEGO HYDROLOGY MANUAL "C"-VALUES USED FOR RATIONAL METHOD NOTE: ONLY PEAK CONFLUENCE VALUES CONSIDERED *USER-DEFINED STREET-SECTIONS FOR COUPLED PIPEFLOW AND STREETFLOW MODEL* HALF- CROWN TO STREET-CROSSFALL: CURB GUTTER-GEOMETRIES: MANNING WIDTH CROSSFALL IN- / OUT-/PARK- HEIGHT WIDTH LIP HIKE FACTOR NO. (FT) (FT) SIDE / SIDE/ WAY (FT) (FT) (FT) (FT) (n) 1 30.0 20.0 0.018/0.018/0.020 0.67 2.00 0.0313 0.167 0.0150 GLOBAL STREET FLOW-DEPTH CONSTRAINTS: 1. Relative Flow-Depth = 0.00 FEET as (Maximum Allowable Street Flow Depth) - (Top-of-Curb) 2. (Depth)*(Velocity) Constraint = 6.0 (FT*FT/S) *SIZE PIPE WITH A FLOW CAPACITY GREATER THAN OR EQUAL TO THE UPSTREAM TRIBUTARY PIPE.* FLOW PROCESS FROM NODE 100.00 TO NODE 105.00 IS CODE = 21 >»»RATIONAL METHOD INITIAL SUBAREA ANALYSIS<«« COMMERCIAL DEVELOPMENT RUNOFF COEFFICIENT = .7000 SOIL CLASSIFICATION IS "A" S.C.S. CURVE NUMBER (AMC II) = 89 INITIAL SUBAREA FLOW-LENGTH(FEET) = 120.00 UPSTREAM ELEVATION(FEET) = 56.30 DOWNSTREAM ELEVATION(FEET) = 55.70 ELEVATION DIFFERENCE(FEET) = 0.60 URBAN SUBAREA OVERLAND TIME OF FLOW(MIN.) = 9.937 *CAUTION: SUBAREA SLOPE EXCEEDS COUNTY NOMOGRAPH DEFINITION. EXTRAPOLATION OF NOMOGRAPH USED. 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 4.229 SUBAREA RUNOFF(CFS) = 2.52 TOTAL AREA(ACRES) = 0.85 TOTAL RUNOFF(CFS) = 2.52 **************************************************************************** FLOW PROCESS FROM NODE 105.00 TO NODE 110.00 IS CODE = 31 >»»COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<«« >»»USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW)<«« ELEVATION DATA: UPSTREAM(FEET) = 54.10 DOWNSTREAM(FEET) = 52.10 FLOW LENGTH(FEET) = 420.00 MANNING'S N = 0.010 DEPTH OF FLOW IN 12.0 INCH PIPE IS 8.3 INCHES PIPE-FLOW VELOCITY(FEET/SEC.) = 4.32 ESTIMATED PIPE DIAMETER(INCH) = 12.00 NUMBER OF PIPES = 1 PIPE-FLOW(CFS) = 2.52 PIPE TRAVEL TIME(MIN-) = 1.62 Tc(MIN.) = 11.56 LONGEST FLOWPATH FROM NODE 100.00 TO NODE 110.00 = 540.00 FEET. FLOW PROCESS FROM NODE 110.00 TO NODE 110.00 IS CODE = 81 >»»ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<«« 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 3.836 COMMERCIAL DEVELOPMENT RUNOFF COEFFICIENT = .7000 SOIL CLASSIFICATION IS "A" S.C.S. CURVE NUMBER (AMC II) = 89 SUBAREA AREA(ACRES) = 0.55 SUBAREA RUNOFF(CFS) = 1.48 TOTAL AREA(ACRES) = 1.40 TOTAL RUNOFF(CFS) = 3.99 TC(MIN.) = 11.56 FLOW PROCESS FROM NODE 115.00 TO NODE 120.00 IS CODE = 31 »»>COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<«« >»»USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW)<«« ELEVATION DATA: UPSTREAM(FEET) = 52.10 DOWNSTREAM(FEET) = 50.90 FLOW LENGTH(FEET) = 250.00 MANNING'S N = 0.010 DEPTH OF FLOW IN 15.0 INCH PIPE IS 9.5 INCHES PIPE-FLOW VELOCITY(FEET/SEC.) = 4.90 ESTIMATED PIPE DIAMETER(INCH) = 15.00 NUMBER OF PIPES = 1 PIPE-FLOW(CFS) = 3.99 PIPE TRAVEL TIME(MIN-) = 0.85 Tc(MIN.) = 12.41 LONGEST FLOWPATH FROM NODE 100.00 TO NODE 120.00 = 790.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 115.00 TO NODE 115.00 IS CODE = 81 >»»ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<«« 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 3.665 MULTI-UNITS DEVELOPMENT RUNOFF COEFFICIENT = .4500 SOIL CLASSIFICATION IS "A" S.C.S. CURVE NUMBER (AMC II) = 75 SUBAREA AREA(ACRES) = 0.79 SUBAREA RUNOFF(CFS) = 1.30 TOTAL AREA(ACRES) = 2.19 TOTAL RUNOFF(CFS) = 5.30 TC(MIN.) = 12.41 FLOW PROCESS FROM NODE 115.00 TO NODE 120.00 IS CODE = 31 >»»COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<«« >»»USING COMPUTER-ESTIMATED PIPESIZE (NOW-PRESSURE FLOW)<«« ELEVATION DATA: UPSTREAM(FEET) = 50.90 DOWNSTREAM(FEET) = 49.60 FLOW LENGTH(FEET) = 240.00 MANNING'S N = 0.010 DEPTH OF FLOW IN 15.0 INCH PIPE IS 11.2 INCHES PIPE-FLOW VELOCITY(FEET/SEC.) = 5.41 ESTIMATED PIPE DIAMETER(INCH) = 15.00 NUMBER OF PIPES = 1 PIPE-FLOW(CFS) = 5.30 PIPE TRAVEL TIME(MIN-) = 0.74 Tc(MIN.) = 13.15 LONGEST FLOWPATH FROM NODE 100.00 TO NODE 120.00 = 1030.00 FEET. FLOW PROCESS FROM NODE 120.00 TO NODE 120.00 IS CODE = 81 »»>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW««< 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 3.530 MULTI-UNITS DEVELOPMENT RUNOFF COEFFICIENT = .4500 SOIL CLASSIFICATION IS "A" S.C.S. CURVE NUMBER (AMC II) = 75 SUBAREA AREA(ACRES) = 0.83 SUBAREA RUNOFF(CFS) = 1.32 TOTAL AREA(ACRES) = 3.02 TOTAL RUNOFF(CFS) = 6.61 TC(MIN.) = 13.15 END OF STUDY SUMMARY: TOTAL AREA (ACRES) PEAK FLOW RATE (CFS) 3.02 TC(MIN.) = 6.61 13.15 END OF RATIONAL METHOD ANALYSIS APPENDIX 2 Hydrologic Calculations\ Estimate for Avenida Encinas Diversion REP\1800\1801DR.DOC PROJECTDESIGN CONSULTANTS PLANNING ENGINEERING SURVEYING 701 B Street, Suite 720, San Diego, CA 92101 (619)235-6471 • Fax (619) 234-0349 PROJECT SUBJECT PAGE OF- JOB NO. _ 5 _ 2J DRAWN BY TX DATE (V AK n 0 Y CHECKED BY A/o4e 0. • fi'c.\i(A <?. • 7 ,^,.v. APPENDIX 3 Hydrologic Soils Group Map From Waters End Report REP\1800\1801DR.DOC ^ PROJECT LOCATION o