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HomeMy WebLinkAboutPD 2021-0043; HYDROLOGY STUDY; 2021-08-01HYDROLOGY STUDY FOR 2908-2924 HIGHLAND DRIVE CARLSBAD, CA 92024 PREPARED FOR: CROSS REAL ESTATE INVESTORS P.O. BOX 231077 ENCINITAS, CA 92023 PREPARED BY: PASCO LARET SUITER & ASSOCIATES, INC. 535 N. HIGHWAY 101, SUITE A SOLANA BEACH, CA 92075 (858) 259-8212 DATE: No. 71651 AUGUST 2021 \ Exp. 12/31/21 dv"- 8/26/202 1 BRIAN M. ARDOLINO, RCE 71651 DATE C r' r r r NOV 10 2021 LAND DELL:JJIV1ENT EN1NRING HYDROLOGY STUDY for 2908-2924 HIGHLAND DRIVE TABLE OF CONTENTS SECTION Executive Summary 1.0 Introduction 1.1 Existing Conditions 1.2 Proposed Project 1.3 Conclusions 1.4 References 1.5 Methodology 2.0 Rational Method 2.1 County of San Diego Criteria 2.2 City of Carlsbad Standards 2.3 AES Rational Method Computer Model 2.4 Hydrologic Analysis 3.0 Existing Condition Hydrologic Model Output (100-Year Event) 3.1 Proposed Condition Hydrologic Model Output 3.2 (100-Year Event Undetained) Detention Analysis 3.3 Proposed Condition, Hydrologic Model Output 3.4 (100-Year Event Detained) Hydromodification Management 3.5 Storm Water Pollutant Control 3.6 Appendices Appendix A: Hydrology Support Material Appendix B: Detention Support Material Appendix C: Existing and Proposed Hydrology Maps I I I I AUGUST 2021 PLSA 3661 HYDROLOGY STUDY for 2908-2924 HIGHLAND DRIVE 1.0 EXECUTIVE SUMMARY 1.1 Introduction This Hydrology Study for the proposed project located at 2908-2924 Highland Drive has been prepared to analyze the hydrologic and hydraulic characteristics of the existing and proposed - - project site. This report intends to present both the methodology and the calculations used for determining the runoff from the project site in both the pre-developed (existing) conditions and the post-developed (proposed) conditions produced by the 100-year, 6-hour storm event. 1.2 Existing Conditions The property is located at 2908-2924 Highland Drive. The site is bordered by residential lots to the north and south, an agricultural lot to the east, and Highland drive to the west. Interstate 1-5 is located approximately 1,800 ft to the west. The existing project site contains two single-family residences, an access easement/driveway bisecting the lot, and associated hardscape and landscape. The western three quarters of the site drains via overland flow to the west and is collected and conveyed north via an asphalt berm in Highland Drive. The eastern quarter of the site drains via overland flow into the lot to the east. No offsite flows are expected. Runoff from the project site discharges to public storm conveyance system in Highland Drive which discharges to Buena Vista Creek, then to Buena Vista Lagoon and ultimately the Pacific Ocean at the mouth of the lagoon. Per the United States Department of Agriculture Web Soil Survey, the project site is underlain with Hydrologic Soil Group B. Refer to Appendix A for soil information. Using the Rational Method Procedure outlined in the San Diego County Hydrology Manual dated June 2003 (SDCHM), the 100-year, 6-hour storm event peak flow rate was calculated for the project site in the existing condition. The table below summarizes the existing condition hydrologic analysis. Summary of ExistinR Condition 100-Yr Storm Event Hvdrolo2ic Analysis Drainage Basin Node Area (ac) Q100 (cfs) 1 10.10 1.0 2.10 2 20.10 0.40 0.53 Refer to the existing condition hydrologic calculations included in Section 3.1 of this report for detailed analysis. 1.3 Proposed Project The intent of the proposed project is to develop the existing site into five residential lots. The proposed development consists of demolishing the existing residences, hardscape, and AUGUST 2021 PLSA 3661 HYDROLOGY STUDY for 2908-2924 HIGHLAND DRIVE structures, grading to create pads suitable for the construction of structures including a private access driveway, storm water treatment and hydromodification management (HMP) biofiltration basins, associated underground utilities, and the demolition and realignment of the private access driveway (Lot 6) to the appropriate location within the existing 25' road and utility easement. The proposed project includes the construction of two HMP biofiltration BMPs, two hydraulically-connected underground stormwater storage tanks, area drains, curbs and gutters, and piping. In the proposed condition, storm water runoff from the majority of the site (DMA-1 and DMA-2) will be collected, treated by one of the biofiltration basins, and discharged to Highland Drive. Due to the grades, there's a small portion of the site on the east which cannot be routed to a treatment basin (SM-1) and meets the requirements of a self-mitigating DMA. In order to match existing grade at the PL/ROW for the access easement/driveway, a small portion of the driveway (SR-1) is unable to gravity drain to a treatment BMP. Permeable payers are proposed for SR-1 in order to meet the requirements of a self-retaining area. Overall, the general runoff pattern in the proposed condition is substantially conforming to the existing condition. The BMPs will provide hydromodification management flow control and storm water pollutant control to meet the requirements the MS4 Permit and City of Carlsbad. The BMPs will also mitigate the proposed condition 100-year storm event peak discharge to below the existing condition. The table below summarizes the proposed condition hydrologic analyses. Summary of Pr000sed Condition 100-Yr Storm Event Hydrologic Analysis Proposed Undetained I Proposed Detained Drainage Basin Area (ac) I Q100 (cfs) I I Area (ac) I Q100 (cfs) 1 0.27 0.74 0.27 0.61 2 j 1.03 2.87 1.03 2.19 Refer to the proposed condition hydrologic calculations and detailed detention analysis included in Section 3.2, 3.3, 3.4 and Appendix B. 1.4 Conclusions Based upon the analyses included in this report, the proposed HMP Biofiltration basins are sized to accommodate the increase in peak runoff in the proposed condition and are designed to meet the requirements of the MS4 Permit for both pollutant control and hydromodification management. Summary of 100-Yr Storm Event HvdroIoic Analysis Drainage Existing Proposed Undetained Proposed Detained Basin Area (ac) 0100 (cfs) Area (ac) 0100 (cfs) Area (ac) Q100 (cfs) 1 1.0 2.1 0.27 0.74 0.27 0.61 2 0.40 0.53 1.03 2.87 1.03 2.19 AUGUST 2021 PLSA 3661 HYDROLOGY STUDY for 2908-2924 HIGHLAND DRIVE 1.5 References "San Diego County Hydrology Manual", revised June 2003, County of San Diego, Department of Public. Works, Flood Control Section. "California Regional Water Quality Control Board Order No. R9-2013-001, as amended by Order Nos. P9-2015-001 and R9-2015-0100," California Regional Water Quality Control Board, San Diego Region (SDRWQCB). "City of Carlsbad Engineering Standards, Volume 5: Carlsbad BMP Design Manual (Post Construction Treatment BMPs)" revised February 2016 "Low Impact Development Handbook - Stormwater Management Strategies", revised July 2014, County of San Diego, Department of Public Works Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Web Soil Survey. Available online at http://websoilsurvey.nrcs.usda.gov. Accessed June 5, 2021 AUGUST 2021 PLSA 3661 HYDROLOGY STUDY for 2908-2924 HIGHLAND DRIVE 2.0 METHODOLOGY Pursuant to the San Diego County Hydrology Manual dated June 2003, the Rational Method is recommended for analyzing the runoff response from drainage areas up to approximately 1 square mile in size. The proposed project and associated watershed basins are less than 1 square mile, therefore the Rational Method was used to analyze the project's hydrologic characteristics in the existing and proposed conditions. 2.1 Rational Method The Rational Method (RM) formula estimates the peak rate of runoff based on the variables of area, runoff coefficient, and rainfall intensity. The rainfall intensity (I) is equal to: = 7.44 x P5 x D °645 Where: Intensity (in/hr) P6 = 6-hour precipitation (in) D = duration (mm - use Tc) Using the Time of Concentration (Tc) which is the time required for a given element of water that originates at the most remote point of the basin being analyzed to reach the point at which the runoff from the basin is being analyzed, the RM equation determines the storm water runoff rate (Q) for a given basin in terms of flow, typically in cubic feet per second (cfs). The RM equation is as follows: Q=CIA Where: 0= flow (cfs) C = runoff coefficient, ratio of rainfall that produces storm water runoff (runoff vs. infiltration/evaporation/absorption/etc) I = average rainfall intensity for a duration equal to the Tc for the area (in/hr) A = drainage area contributing to the basin (ac) The RM equation assumes that the storm event being analyzed delivers precipitation to the entire basin uniformly, and therefore the peak discharge rate will occur when a raindrop that falls at the most remote portion of the basin arrives at the point of analysis. The RM also assumes that the fraction of rainfall that becomes runoff or the runoff coefficient, C, is not affected by the storm intensity, I, or the precipitation zone number. 2.2 County of San Diego Criteria The County of San Diego has developed its own tables, nomographs, and methodologies for analyzing storm water runoff for areas within the County. The County has also developed precipitation isopluvial contour maps that show even lines of rainfall anticipated from a given storm event (i.e. 100-year, 6-hour storm). The 100-year 6-hour storm event rainfall isopluvial map is included in Appendix A. AUGUST 2021 PLSA 3661 HYDRCLOGY STUDY for 2908-2924 HIGHLAND DRIVE One of the variables of the RM equation is the runoff coefficient, C, which is dependent upon land use and soil type. Table 3-1 Runoff Coefficients for Urban Areas in the County Hydrology Manual categorizes the land use, the associated development density (dwelling units per acre) and the percentage of impervious area. Each of the categories listed has an associated runoff coefficient for each soil type class. A composite runoff coefficient can also be calculated for an area based on soil type and impervious percentage using the following equation from Section 3.1.2 of the County Hydrology Manual: C = 0.90 x (% Impervious) + Cp x (1 - % Impervious) Where: Cp = Pervious Coefficient Runoff Value for the soil type (shown in Table 3-1 as Undisturbed Natural Terrain/Permanent Open Space, 0% Impervious) The calculations contained herein figure a composite runoff coefficient for the onsite project areas based on the percentage of impervious area and the percentage of pervious or landscape area. The County has also illustrated in detail the methodology for determining the time of concentration, in particular the initial time of concentration. The County has adopted the Federal Aviation Agency's (FAA) overland time of flow equation. This equation essentially limits the flow path length for the initial time of concentration to lengths of 100 feet or less, and is dependent on land use and slope. 2.3 AES Rational Method Computer Model The Rational Method computer program developed by Advanced Engineering Software (AES). satisfies the County of San Diego design criteria, therefore it is the computer model used for this study. The AES hydrologic model is capable of creating independent node-link models of each interior drainage basin and linking these sub-models together at confluence points to determine peak flow rates. The program utilizes base information input by the user to perform calculations for up to 15 hydrologic processes. The required base information includes drainage basin area, storm water facility locations and sizes, land uses, flow patterns, and topographic elevations. The hydrologic conditions were analyzed in accordance with the 2003 County of San Diego Hydo1ogy Manual criteria as follows: Design Storm 100-year, 6-hour Precipitation Rainfall Intensity Runoff Coefficient* Soil Type 100-year, 6-hour 2.6 inches Based on the 2003 County of San Diego Hydrology Manual criteria Pervious B soil C = 0.25 Impervious cover C = 0.90 B *Weighted runoff coefficients were calculated where appropriate. AUGUST 2021 PLSA 3661 HYDROLOGY STUDY for 2908-2924 HIGHLAND DRIVE 3.0 HYDROLOGIC ANALYSIS The table below summarizes the hydrologic calculations provided in Sections 3.1, 3.2 and 3.4. Summary of 100-Yr Storm Event Hydrologic Analysis Drainage Existing Proposed Undetained Proposed Detained Basin Area (ac) 0100 (cfs) Area (ac) 0100 (cfs) Area (ac) Q100 (cfs) 1 0.3 0.87 0.3 1.54 0.3 0.62 2 0.7 1.71 0.7 3.03 0.7 0.69 1 I I I AUGUST 2021 PLSA 3661 HYDROLOGY STUDY for 2908-2924 HIGHLAND DRIVE 3.1 Existing Condition Hydrologic Model Output (100-Year Event) AUGUST 2021 PLSA 3661 *** RATIONAL METHOD HYDROLOGY COMPUTER PROGRAM PACKAGE Reference: SAN DIEGO COUNTY FLOOD CONTROL DISTRICT 2003,1985,1981 HYDROLOGY MANUAL (c) Copyright 1982-2016 Advanced Engineering Software (aes) Ver. 23.0 Release Date: 07/01/2016 License ID 1452 Analysis prepared by: PASCO LARET SUITER & ASSOCIATES 535 NORTH HIGHWAY 101, STE A SOLANA BEACH, CA 92075 858-259-8212 ************************* DESCRIPTION OF STUDY * * * * * * * * * * * * * * * * * * * * * * * * * * * 3361 DRAKOS * * EXISTING CONDITION * * 100-YR * ************************************************************************* * FILE NAME: 3661E00.DAT TIME/DATE OF STUDY: 09:55 06/22/2021 ------------------------------------------------------------------------ USER SPECIFIED HYDROLOGY AND HYDRAULIC MODEL INFORMATION: ------------------------------------------------------------------------ 2003 SAN DIEGO MANUAL CRITERIA USER SPECIFIED STORM EVENT(YEAR) = 100.00 6-HOUR DURATION PRECIPITATION (INCHES) = 2.600 SPECIFIED MINIMUM PIPE SIZE(INCH) = 3.00 SPECIFIED PERCENT OF GRADIENTS(DECIMAL) TO USE FOR FRICTION SLOPE = 0.90 SAN DIEGO HYDROLOGY MANUAL "C"-VALUES USED FOR RATIONAL METHOD NOTE: USE MODIFIED RATIONAL METHOD PROCEDURES FOR CONFLUENCE ANALYSIS *USERDEFINED 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: Relative Flow-Depth = 0.00 FEET as (Maximum Allowable Street Flow Depth) - (Top-of-Curb) (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 10.00 TO NODE 10.05 IS CODE = 21 ------------------------------------------------------------------------ >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<< *USER SPECIFIED(SUBAREA) USER-SPECIFIED RUNOFF COEFFICIENT = .5000 S.C.S. CURVE NUMBER (AMC II) = 0 INITIAL SUBAREA FLOW-LENGTH(FEET) = 88.00 UPSTREAM ELEVATION(FEET) = 184.80 DOWNSTREAM ELEVATION(FEET) = 181.00 ELEVATION DIFFERENCE(FEET) = 3.80 SUBAREA OVERLAND TIME OF FLOW(MIN.) = 6.222 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 5.949 SUBAREA RUNOFF(CFS) = 0.33 TOTAL AREA(ACRES) = 0.11 TOTAL RUNOFF(CFS) = 0.33 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *** FLOW PROCESS FROM NODE 10.05 TO NODE 10.10 IS CODE = 52 ------------------------------------------------------------------------ >>>>>COMPUTE NATURAL VALLEY CHANNEL FLOW<<<<< >>>>>TRAVELTIME TH?U SUBAREA<<<<< ELEVATION DATA: UPSTREAM(FEET) = 181.00 DOWNSTREAM(FEET) = 163.20 CHANNEL LENGTH THRU SUBAREA(FEET) = 180.00 CHANNEL SLOPE = 0.0989 NOTE: CHANNEL FLOW OF 1. CFS WAS ASSUMED IN VELOCITY ESTIMATION CHANNEL FLOW THRU SUBAREA(CFS) = 0.33 FLOW VELOCITY(FEET/SEC) = 4.72 (PER LACFCD/RCFC&WCD HYDROLOGY MANUAL TRAVEL TIME(MIN.) = 0.64 Tc(MIN.) = 6.86 LONGEST FLOWPATH FROM NODE 10.00 TO NODE 10.10 = 268.00 FEET. ************************************************************* *********** *** FLOW PROCESS FROM NODE 10.05 TO NODE 10.10 IS CODE = 81 ------------------------------------------------------------------------ >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<< 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 5.587 *USER SPECIFIED(SUBAREA) USER-SPECIFIED RUNOFF COEFFICIENT = .3600 S.C.S. CURVE NUMBER (AMC II) = 0 AREA-AVERAGE RUNOFF COEFFICIENT = 0.3754 SUBAREA AREA(ACRES) = 0.89 SUBAREA RUNOFF(CFS) = 1.79 TOTAL AREA(ACRES) = 1.0 TOTAL RUNOFF(CFS) = 2.10 TC(NIN.) = 6.86 *** FLOW PROCESS FROM NODE 20.00 TO NODE 20.05 IS CODE = 21 ------------------------------------------------------------------------ >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<< *USER SPECIFIED(SUBAREA) USER-SPECIFIED RUNOFF COEFFICIENT = .2500 S.C.S. CURVE NUMBER (AMC II) = 0 INITIAL SUBAREA FLOW-LENGTH(FEET) = 87.00 UPSTREAM ELEVATION(FEET) = 184.80 DOWNSTREAM ELEVATION(FEET) = 180.80 ELEVATION DIFFERENCE(FEET) = 4.00 SUBAREA OVERLAND TIME OF FLOW(MIN.) = 8.583 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 4.835 SUBAREA RUNOFF(CFS) = 0.11 TOTAL AREA(ACRES) = 0.09 TOTAL RUNOFF(CFS) = 0.11 ****** k****************************************************************** *** FLOW PROCESS FROM NODE 20.05 TO NODE 20.10 IS CODE = 52 ------------------------------------------------------------------------- >>>>>COMPUTE NATURAL VALLEY CHANNEL FLOW<<<<< >>>>>TRAVELTIME THRU SUBAREA<<<<< ELEVATION DATA: UPSTREAM(FEET) = 180.80 DOWNSTREAM(FEET) = 175.20 CHANNEL LENGTH THRU SUBAREA(FEET) = 106.00 CHANNEL SLOPE = 0.0528 NOTE: CHANNEL FLOW OF 1. CFS WAS ASSUMED IN VELOCITY ESTIMATION CHANNEL FLOW THRU SUBAREA(CFS) = 0.11 FLOW VELOCITY(FEET/SEC) = 3.45 (PER LACFCD/RCFC&WCD HYDROLOGY MANUAL) TRAVEL TIME(MIN.) = 0.51 Tc(MIN.) = 9.10 LONGEST FLOWPATH FROM NODE 20.00 TO NODE 20.10 = 193.00 FEET. ************************************************************************* *** FLOW PROCESS FROM NODE 20.05 TO NODE 20.10 IS CODE = 81 ------------------------------------------------------------------------ >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<< 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 4.657 *USER SPECIFIED(SUBAREA) USER-SPECIFIED RUNOFF COEFFICIENT = .3400 S.C.S. CURVE NUMBER (AMC II) = 0 AREA-AVERAGE RUNOFF COEFFICIENT = 0.3175 SUBAREA AREA(ACRES) = 0.27 SUBAREA RUNOFF(CFS) = 0.43 TOTAL AREA(ACRES) = 0.4 TOTAL RUNOFF(CFS) = 0.53 TC(MIN.) = 9.10 END OF STUDY SUMMARY: TOTAL AREA(ACRES) = 0.4 TC(MIN.) = 9.10 PEAK FLOW RATE (CFS) = 0.53 END OF RATIONAL METHOD ANALYSIS I-IYDRCLOGY STUDY for 2908-2924 HIGHLAND DRIVE 3.2 Proposed Undetained Condition Hydrologic Model Output (100-Year Event) AUGUST 2021 PLSA 3661 ********************* **************************************************** *** RATIONAL METHOD HYDROLOGY COMPUTER PROGRAM PACKAGE Reference: SAN DIEGO COUNTY FLOOD CONTROL DISTRICT 2003,1985,1981 HYDROLOGY MANUAL (c) Copyright 1982-2016 Advanced Engineering Software (aes) Ver. 23.0 Release Date: 07/01/2016 License ID 1452 Analysis prepared by: PASCO LARET SUITER & ASSOCIATES 535 NORTH HIGHWAY 101, STE A SOLANA BEACH, CA 92075 858-259-8212 ************************** DESCRIPTION OF STUDY ************************* * 3361 DRAKOS * * PROPOSED CONDITION * * 100-YR * ************************************************************************* * FILE NAME: 3661P00.DAT TIME/DATE OF STUDY: 10:15 07/20/2021 ------------------------------------------------------------------------ USER SPECIFIED HYDROLOGY AND HYDRAULIC MODEL INFORMATION: ------------------------------------------------------------------------ 2003 SAN DIEGO MANUAL CRITERIA USER SPECIFIED STORM EVENT(YEAR) = 100.00 6-HOUR DURATION PRECIPITATION (INCHES) = 2.600 SPECIFIED MINIMUM PIPE SIZE(INCH) = 3.00 SPECIFIED PERCENT OF GRADIENTS(DECIMAL) TO USE FOR FRICTION SLOPE = 0.90 SAN DIEGO HYDROLOGY MANUAL "C"-VALUES USED FOR RATIONAL METHOD NOTE: USE MODIFIED RATIONAL METHOD PROCEDURES FOR CONFLUENCE ANALYSIS *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: Relative Flow-Depth = 0.00 FEET as (Maximum Allowable Street Flow Depth) - Top-of-Curb) (Depth)*(Velocity) Constraint = 6.0 (FT*FT/S) *SIZE PIPE WITH A FLOW CAPACITY GREATER THAN OR EQUAL TO THE U?STREAM TRIBUTARY PIPE.* ******************** k*************************************************** *** FLOW PROCESS FROM NODE 10.00 TO NODE 10.05 IS CODE = 21 ------------------------------------------------------------------------ >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<< *USER SPECIFIED(SUBAREA) USE?-SPECIFIED RUNOFF COEFFICIENT = .4600 S.C.S. CURVE NUMBER (AMC II) = 0 INITIAL SUBAREA FLOW-LENGTH(FEET) = 117.00 UPSTREAM ELEVATION(FEET) = 168.00 DOWNSTREAM ELEVATION(FEET) = 167.00 ELEVATION DIFFERENCE(FEET) = 1.00 SUBAREA OVERLAND TIME OF.FLOW(MIN.) = 9.453 WARNING: INITIAL SUBAREA FLOW PATH LENGTH IS GREATER THAN THE MAXIMUM OVERLAND FLOW LENGTH = 60.64 (Reference: Table 3-1B of Hydrology Manual) THE MAXIMUM OVERLAND FLOW LENGTH IS USED IN Tc CALCULATION! 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 4.543 SUBAREA RUNOFF(CFS) = 0.17 TOTAL AREA(ACRES) = 0.08 TOTAL RUNOFF(CFS) = 0.17 ************************************************************************* *** FLCW PROCESS FROM NODE 10.05 TO NODE 10.10 IS CODE = 31 ------------------------------------------------------------------------ >>>>>COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<<<<< >>>>>USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW)<<<<< ELEVATION DATA: UPSTREAM(FEET) = 165.50 DOWNSTREAM(FEET) = 164.00 FLOW LENGTH(FEET) = 27.00 MANNINGS N = 0.013 DEPTH OF FLOW IN 3.0 INCH PIPE IS 2.2 INCHES PIPE-FLOW VELOCITY(FEET/SEC.) = 4.45 ESTIMATED PIPE DIAMETER(INCH) = 3.00 NUMBER OF PIPES = PIPE-FLOW(CFS) = 0.17 PIPE TRAVEL TIME(MIN.) = 0.10 Tc(MIN.) = 9.55 LONGEST FLOWPATH FROM NODE 10.00 TO NODE 10.10 = 144.00 FEET. ************************************************************************* *** FLOW PROCESS FROM NODE 10.10 TO NODE 10.10 IS CODE = 81 ------------------------------------------------------------------------ >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<< 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 4.512 *USER SPECIFIED(SUBAREA) USER-SPECIFIED RUNOFF COEFFICIENT = .6600 S.C.S. CURVE NUMBER (AMC II) = 0 AREA-AVERAGE RUNOFF COEFFICIENT = 0.5995 SUBAREA AREA(ACRES) = 0.19 SUBAREA RUNOFF(CFS) = 0.56 TOTAL AREA(ACRES) = 0.3 TOTAL RUNOFF(CFS) = 0.73 TC(MIN.) = 9.55 ************************************************************************* *** FLOW PROCESS FROM NODE 10.10 TO NODE 10.15 IS CODE = 81 ------------------------------------------------------------------------ >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<< 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 4.512 *USER SPECIFIED(SUBAREA) USER-SPECIFIED RUNOFF COEFFICIENT = .2500 S.C.S. CURVE NUMBER (AMC II) = 0 AREA-AVERAGE RUNOFF COEFFICIENT = 0.5859 SUBAREA AREA(ACRES) = 0.01 SUBAREA RUNOFF(CFS) = 0.01 TOTAL AREA(ACRES) = 0.3 TOTAL RUNOFF(CFS) = 0.75 TC(MIN.) = 9.55 ************************************************************************* *** FLOW PROCESS FROM NODE 10.15 TO NODE 20.35 IS CODE = ------------------------------------------------------------------------ >>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<< TOTAL NUMBER OF STREAMS = 2 CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 1 ARE: TIME OF CONCENTRATION(MIN.) = 9.55 RAINFALL INTENSITY(INCH/HR) = 4.51 TOTAL STREAM AREA(ACRES) = 0.28 PEAK FLOW RATE(CFS) AT CONFLUENCE = 0.75 ************************************************************************* *** FLOW PROCESS FROM NODE 20.00 TO NODE 20.10 IS CODE = 21 ------------------------------------------------------------------------ >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<< *USER SPECIFIED(SUBAREA) USER-SPECIFIED RUNOFF COEFFICIENT = .5600 S.C.S. CURVE NUMBER (AMC II) = 0 INITIAL SUBAREA FLOW-LENGTH(FEET) = 171.00 UPSTREAM ELEVATION(FEET) = 181.00 DOWNSTREAM ELEVATION(FEET) = 180.50 ELEVATION DIFFERENCE(FEET) = 0.50 SUBAREA OVERLAND TIME OF FLOW(MIN.) = 8.659 WARNING: INITIAL SUBAREA FLOW PATH LENGTH IS GREATER THAN THE MAXIMUM OVERLAND FLOW LENGTH = 50.00 (Reference: Table 3-1s of Hydrology Manual) THE MAXIMUM OVERLAND FLOW LENGTH IS USED IN Tc CALCULATION! 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 4.807 SU3AREA RUNOFF(CFS) = 0.55 TOTAL AREA(ACRES) = 0.20 TOTAL RUNOFF(CFS) = 0.55 ************************************************************************* *** FLOW PROCESS FROM NODE 20.10 TO NODE 20.15 IS CODE = 31 ------------------------------------------------------------------------ >>>>>COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<<<<< >>>>>USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW:) <<<<< ELEVATION DATA: UPSTREAM(FEET) = 178.00 DOWNSTREAM(FEET) = 166.20 FLOW LENGTH(FEET) = 67.00 MANNING!S N = 0.013 DEPTH OF FLOW IN 6.0 INCH PIPE IS 2.0 INCHES PPE-FLOW VELOCITY(FEET/SEC.) = 9.40 ESTIMATED PIPE DIAMETER(INCH) = 6.00 NUMBER OF PIPES = PIPE-FLOW(CFS) = 0.55 PIPE TRAVEL TIME(MIN.) = 0.12 Tc(MIN.) = 8.78 LONGEST FLOWPATH FROM NODE 20.00 TO NODE 20.15 = 238.00 FEET. ************************************************************************* *** FLOW PROCESS FROM NODE 20.15 TO NODE 20.15 IS CODE = 81 ------------------------------------------------------------------------ >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<< 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 4.765 *USER SPECIFIED(SUBAREA) USER-SPECIFIED RUNOFF COEFFICIENT = .6100 S.C.S. CURVE NUMBER (AMC II) = 0 AREA-AVERAGE RUNOFF COEFFICIENT = 0.5998 SUBAREA AREA(ACRES) = 0.79 SUBAREA RUNOFF(CFS) = 2.29 TOTAL AREA(ACRES) = 1.0 TOTAL RUNOFF(CFS) = 2.83 TC(MIN.) = 8.78 ************************************************************************* *** FLCW PROCESS FROM NODE 20.20 TO NODE 20.25 IS CODE = 31 ------------------------------------------------------------------------ >>>>>COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<<<<< >>>>>USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW)<<<<< ELEVATION DATA: UPSTREAM(FEET) = 166.20 DOWNSTREAM(FEET) = 165.50 FLOW LENGTH(FEET) = 27.00 MANNING'S N = 0.013 DEPTH OF FLOW IN 12.0 INCH PIPE IS 6.1 INCHES PIPE-FLOW VELOCITY(FEET/SEC.) = 7.01 ESTIMATED PIPE DIAMETER(INCH) = 12.00 NUMBER OF PIPES = 1 PI?E- FLOW (CFS) = 2.83 PIPE TRAVEL TIME(MIN.) = 0.06 Tc(MIN.) = 8.84 LONGEST FLOWPATH FROM NODE 20.00 TO NODE 20.25 = 265.00 FEET. ************************************************************************* *** FLOW PROCESS FROM NODE 20.25 TO NODE 20.30 IS CODE = 81 ------------------------------------------------------------------------- >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<< 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 4.743 *USER SPECIFIED(SUBAREA) USER-SPECIFIED RUNOFF COEFFICIENT = .2500 S.O.S. CURVE NUMBER (AMC II) = 0 AREA-AVERAGE RUNOFF COEFFICIENT = 0.5872 SUBAREA AREA(ACRES) = 0.04 SUBAREA RUNOFF(CFS) = 0.04 TOTAL AREA(ACRES) 1.0 TOTAL RUNOFF(CFS) = 2.87 TC(MIN.) = 8.84 ****** k****************************************************************** *** FLOW PROCESS FROM NODE 20.30 TO NODE 20.35 IS CODE = 31 ------------------------------------------------------------------------ >>>>>COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<<<<< >>>>>USING COMPUTER-ESTIMATED PIPESIZE (NON-PRESSURE FLOW)<<<<< ELEVATION DATA: UPSTREAM(FEET) = 162.30 DOWNSTREAM(FEET) = 162.00 FLOW LENGTH(FEET) = 5.00 MANNING'S N = 0.013 DEPTH OF FLOW IN 9.0 INCH PIPE IS 5.8 INCHES PIPE-FLOW VELOCITY(FEET/SEC.) = 9.54 ESTIMATED PIPE DIAMETER(INCH) = 9.00 NUMBER OF PIPES = 1 PIPE-FLOW(CFS) = 2.87 PIPE TRAVEL TIME(MIN.) = - 0.01 Tc(MIN.) = 8.85 LONGEST FLOWPATH FROM NODE 20.00 TO NODE 20.35 = 270.00 FEET. ************************************************************************* *** FLOW PROCESS FROM NODE 10.15 TO NODE 20.35 IS CODE = 1 ------------------------------------------------------------------------ >>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<< >>>>>AND COMPUTE VARIOUS CONFLUENCED STREAM VALUES<<<<< TOTAL NUMBER OF STREAMS = 2 CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 2 ARE: TIME OF CONCENTRATION(MIN.) = 8.85 RAINFALL INTENSITY(INCH/HR) = 4.74 TOTAL STREAM AREA(ACRES) = 1.03 PEAK FLOW RATE(CFS) AT CONFLUENCE = 2.87 ** CONFLUENCE DATA ** STREAM RUNOFF Tc INTENSITY AREA NUMBER (CFS) (MIN.) (INCH/HOUR) (ACRE) 1 0.75 9.55 4.512 0.28 2 2.87 8.85 4.740 1.03 RAINFALL INTENSITY AND TIME OF CONCENTRATION RATIO CONFLUENCE FORMULA USED FOR 2 STREAMS. ** PEAK FLOW RATE TABLE ** STREAM RUNOFF To INTENSITY NUMBER (CFS) (MIN.) (INCH/HOUR) 1 3.56 8.85 4.740 2 3.47 9.55 4.512 COMPUTED CONFLUENCE ESTIMATES ARE AS FOLLOWS: PEAK FLOW RATE(CFS) = 3.56 Tc(MIN.) = TOTAL AREA(ACRES) = 1.3 LONGEST FLOWPATH FROM NODE 20.00 TO NODE FEET. 20.35 = 270.00 ************************************************************************* *** FLOW PROCESS FROM NODE 20.35 TO NODE 20.35 IS CODE = 81 ------------------------------------------------------------------------ >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<< 1CO YEAR RAINFALL INTENSITY(INCH/HOUR) = 4.740 *USER SPECIFIED(SUBAREA) USER-SPECIFIED RUNOFF COEFFICIENT = .8200 S.C.S. CURVE NUMBER (AMC II) = 0 AREA-AVERAGE RUNOFF COEFFICIENT = 0.5902 SUBAREA AREA(ACRES) = 0.02 SUBAREA RUNOFF(CFS) = 0.07 TOTAL AREA(ACRES) = 1.3 TOTAL RUNOFF(CFS) = 3.72 TC(MIN.) = 8.85 END OF STUDY SUMMARY: TOTAL AREA(ACRES) = 1.3 TC(MIN.) = 8.85 PEAK FLOW RATE (CFS) = 3.72 END OF RATIONAL METHOD ANALYSIS HYDROLOGY STUDY for 2908-2924 HIGHLAND DRIVE 3.3 Detention Analysis (100-Year Event) The HMP Biofiltration basins (BMPs) provide pollutant control, hydromodification management flow control and mitigation of the 100-year storm event peak flow rate. The 100-year storm event detention analysis was performed using HydroCAD Stormwater Modeling software. The inflow runoff hydrographs to the BMPs were modeled using RatHydro which is a Rational Method Design Storm Hydrograph software that creates a hydrograph using the results of the Rational Method calculations. HydroCAD has the ability to route the 100-year 6-hour storm event inflow hydrograph through the BMPs considering dynamic tailwater effects. Based on the BMP cross sectional geometry, stage storage and outlet structure data, HydroCAD calculates the detained peak flow rate and detained time to peak. Each BMP consists of a basin with 18 inches of engineered soil and 12 inches of gravel. Runoff will be biofiltered through the engineered soil and gravel layers, then collected in a series of small PVC drainpipes and directed to a catch basin located in the BMP where runoff will be mitigated via a small orifice to comply with HMP requirements. In larger storm events, runoff not filtered through the engineered soil and gravel layers will be conveyed via an overflow outlet structure. Runoff conveyed via the outlet structure will bypass the small orifice and be conveyed directly to the proposed storm drain discharge pipe. Refer to the plans for cross- sections of each BMP. For the proposed detained hydrologic analysis, the effects of the detention provided by the 2 BMPs were incorporated into the AES analysis. This was done by inserting the results from the HydroCAD analysis, detained peak flow rate and detained time to peak, into the proposed undetained condition AES model to create the proposed detained condition model. Refer to Section 3.4 for the detained AES output. Based on the results of the HydroCAD analysis; mitigation for the 100-year storm event peak flow rate is provided, detaining the proposed peak flow rates to below the existing condition. Refer to Appendix B for the HydroCAD detention detailed output. AUGUST 2021 PLSA 3661 HYDROLOGY STUDY for 2908-2924 HIGHLAND DRIVE 3.4 Proposed Detained Condition Hydrologic Model Output (100-Year Event) AUGUST 2021 PLSA 3661 I I I n L I I I I Inflow to BMP-1 BMP-1 Alt I I I I Inflow to Tank Tank Alt 5 I I I L I I 4 ubuat > Reachj I 3661 Prepared by Pasco Laret Suiter & Associates Pirited 7/21/2021 HydroCAD® 13.10-6a s/n 10097 © 2020 HydroCAD Software Solutions LLC Page 2 Summary for Link IL: Inflow to BMP-1 Inflow = 0.74 cfs @ 4.17 hrs, Volume= 0.031 af Primary = 0.74 cfs © 4.17 hrs, Volume= 0.031 af, Atten= 0%, Lag= 0.0 rrin Routed to Pond 8P: BMP-1 Alt 5 Primary outflow = Inflow, Time Span= 0.00-96.00 hrs, dt= 0.01 hrs DISCHARGE Imported from BMP-1 RatHydro.csv Link IL: Inflow to BMP-1 Hydrograph Inflow Primay 5 10 15 20 25 30 35 40 45 5C 55 GO 65 70 75 80 85 90 95 Time (hours) I I I I I I I I I I I I U I I I I 1 I 3661 Prepared by Pasco Laret Suiter & Associates Printed 7/21/2021 HydroCAD 10.10-6a s/n 10097 © 2020 HydroCAD Software Solutions LLC Page 4 Summary for Pond 8P: BMP-1 Alt 5 Inflow = 0.74 cfs @ 4.17 hrs, Volume= 0.031af Outflow = 0.61 cfs @ 4.20 hrs, Volume= 0.031 af, Atten= 17%, Lag= 2.3 mm - Primary = 0.61 cfs @ 4.20 hrs, Volume= 0.031 af Routing by Dyn-Stor-Ind method, Time Span= 0.00-96.00 hrs, dt= 0.01 hrs Peak Elev= 101.06'@ 4.20 hrs Surf.Area= 500 sf Storage= 881 cf Plug-Flow detention time= 489.6 min calculated for 0.031 af (100% of inflow Center-of-Mass det. time= 489.6 mm (722.7 - 233.1 ) Volume Invert Avail .Storage Storage Description #1 97.50' 950 cf Custom Stage Data (Conic) Listed below (Recalc) Elevation Surf.Area Voids lnc.Store Cum.Store Wet.Area (feet) (sg-ft) (%) (cubic-feet) (cubic-feet) (sg-ft) 97.50 500 0.0 0 0 500 98.50 500 40.0 200 200 579 100.00 500 20.0 150 350 698 101.20 500 100.0 600 950 793 Device Routing Invert Outlet Devices #1 Primary 97.50' 8.0" Round Culvert L= 10.0' RCP, groove end projecting, Ke= 0.200 Inlet! Outlet Invert= 97.50'/97.40' S=0.0100 '/' Cc= 0.900 n=0.013, Flow Area= 0.35sf #2 Device I 97.50' 0.5" Vert. Orifice C= 0.600 Limited to weir flow at low heads #3 Device 1 101.00' 36.0" x 36.0" Horiz. Grate C= 0.600 in 36.0" x 36.0" Grate (100% open area) Limited to weir flow at low heads Primary OutFlow Max=0.61 cfs © 4.20 hrs HW=101.06' (Free Discharge) t...1=Culvert (Passes 0.61 cfs of 3.68 cfs potential flow) T--2=Orifice (Orifice Controls 0.01 cfs © 9.06 fps) 3Grate (Weir Controls 0.59 cfs @ 0.81 fps) I - s 1SIsF1(- iMfrI}1I II , diIi. lU 41 •••• _____ I '' •155ii — 1' 4 \i • I • I ø'-"- • II, I I I I I I I I I I I I I I I I Fi—I 0 Primary 0 5 0 15 20 25 30 35 4 45 50 55 60 65 70 75 80 85 90 95 Time (hours) 3661 Prepared by Pasco Laret Suiter & Asso:iates Pr nted 7/2112021 HydroCAD® 10.10-6a s/n 10097 © 2020 HydrcCAD Software Solutions LLC Page 3 Summary for Link 7L: Inflow to Tank Inflow = 2.87 cfs@ 4.20 hr's, Volume= 0.122af Primary = 2.87 cfs @ 4.20 hrs, Volume= 0.122 af, Atten= 0%, Lag= 0.0 mm Routed to Pond 13P : Tank Alt 5 Primary outflow = Inflow, Time Span= 0.00-96.00 hrs, dt= 0.01 hrs DISCHARGE Imported from BMP-2 RatHyiro.csv Link 7L: Inflow to Tank hydrograph I I I I I I I I I I I I 3661 Prepared by Pasco Laret Suiter & Associates Printed 7/21/2021 HydroCAD® 10.10-6a sIn 10097 © 2020 HydroCAD Software Solutions LLC Page 6 Summary for Pond 13P: Tank Alt 5 Inflow = 2.87 cfs @ 4.20 hrs, Volume= 0.122 af Outflow = 2.19 cfs @ 4.24 hrs, Volume= 0.121 af, Atten= 24%, Lag= 2.6 mm Primary = 2.19 cfs @ 4.24 hrs, Volume= 0.121 af Routed to Pond 19P: BMP-2 Alt 5 Routing by Dyn-Stor-Ind method, Time Span= 0.00-96.00 hrs, dt= 0.01 hrs Peak Elev= 104.50'@ 4.24 hrs Surf .Area= 900 sf Storage= 3,421 cf Plug-Flow detention time= 1,257,6 min calculated for 0.121 af (99% of inflow Center-of-Mass det. time= 1,256.3 mm (1,475.7-219.4) Volume Invert Avail. Storage Storage Description #1 100.70' 3,600 cf Custom Stage Data (Conic) Listed below (Recalc) Elevation Surf.Area Voids lnc.Store Cum.Store Wet.Area (feet) (sg-ft) (%) (cubic-feet) (cubic-feet) (sg-ft) 100.70 900 0.0 0 0 900 101.70 900 100.0 900 900 1,006 102.70 900 100.0 900 1,800 1,113 103.70 900 100.0 900 2,700 1,219 104.20 900 100.0 450 3,150 1,272 104.70 900 100.0 450 3,600 1,325 Device Routing Invert Outlet Devices #1 Primary 100.70' 8.0" Round Culvert L= 27.0' RCP, groove end projecting, Ke= 0.200 Inlet/ Outlet Invert= 100.70'! 100.00' S=0.0259 '/' Cc= 0.900 n=0.013, Flow Area= 0.35sf #2 Device 1 100.70' 0.6" Vert. Orifice C= 0.600 Limited to weir flow at low heads #3 Primary 104.20' Custom Weir, Cv 2.62 (C= 3.28) Head (feet) 0.00 0.50 0.50 Width (feet) 4.00 4.00 0.00 Primary OutFlow Max=2.18 cfs @ 4.24 hrs HW=104.50' 1W98.14' (Dynamic Tailwater) (Passes 0.02 cfs of 3.37 cfs potential flow) lt 1Culvert ....2Orifice (Orifice Controls 0.02 cfs @ 9.36 fps) 3=Custom Weir (Weir Controls 2.16 cfs @ 1.80 fps) 3661 Prepared by Pasco Laret Suiter & Asscciates Printed 7/21/2021 HydroCAC® 10.10-6a s/n 10097 © 2020 HydroCAD Software Solutions LLC Page 7 Pond 13P: Tank Alt 5 Hydrograph I I I I I I I I I I I iflhlillulllE PIIHhhIhI1NllhII rlhlflhhlHhhhhhhhi 4v4 0 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 Time {hours) Inflow D Primary I I I I I I I 3661 Prepared by Pasco Laret Suiter & Associates Printed 7/21/2021 HydroCAD® 10.10-6a sIn 10097 © 2020 HydroCAD Software Solutions LLC Page 8 Summary for Pond 19P: BMP-2 Alt 5 Inflow = 2.19 cfs @ 4.24 hrs, Volume= 0.121 af Outflow = 0.02 cfs © 6.24 hrs, Volume= 0.119 af, Atten= 99%, Lag= 120.0 mm Primary = 0.02 cfs @ 6.24 hrs, Volume= 0.119 af Routing by Dyn-Stor-Ind method, Time Span= 0.00-96.00 hrs, dt= 0.01 hrs Peak Elev= 100.55'@ 6.24 hrs Surf.Area= 1,600sf Storage= 1,994 cf Plug-Flow detention time= 1,021.5 min calculated for 0.119 af (98% of inflow Center-of-Mass det. time= 945.2 mm (2,420.8 - 1,475.7) Volume Invert Avail. Storage Storage Description #1 97.50' 3,040 cf Custom Stage Data (Conic) Listed below (Recalc) Elevation Surf.Area Voids lnc.Store Cum.Store Wet.Area (feet) (sg-ft) (%) (cubic-feet) (cubic-feet) (sg-ft) 97.50 1,600 0.0 0 0 1,600 98.50 1,600 40.0 640 640 1,742 100.00 1,600 20.0 480 1,120 1,954 101.20 1,600 100.0 1,920 3,040 2,125 Device Routing Invert Outlet Devices #1 Primary 97.50' 8.0" Round Culvert L= 5.0' RCP, groove end projecting, Ke= 0.200 Inlet/ Outlet Invert= 97.50'! 97.20' S=0.0600 '/' Cc= 0.900 n=0.013, Flow Area= 0.35sf #2 Device 1 97.50' 0.7" Vert. Orifice C= 0.600 Limited to weir flow at low heads #3 Device 1 100.83' 36.0' x 36.0" Horiz. Grate. C= 0.600 in 36.0" x 36.0" Grate (100% open area) Limited to weir flow at low heads Primary OutFlow Max=0.02 cfs © 6.24 hrs HW=100.55' (Free Discharge) t....1CuIvert (Passes 0.02 cfs of 3.46 cfs potential flow) T--2=Orifice (Orifice Controls 0.02 cfs @ 8.36 fps) 3=Grate (Controls 000 cfs) I I 3661 Prepared by Pasco Laret Suiter & Associates Primed 7/21/2021 HydroCAD® 0.10-6a s/n 10097 ©2020 HydroCAD Software Solutions LLC Page 9 I Pond 19P: BMP-2 Alt 5 Hydrograph I •Inflow IZ19cfs 10 Primary lq~ - PV4O 2 tórag' e=1,Ø94 61 LL I ---- I II I I I I I I Time (hours) I I I L I I I I I HYDROLOGY STUDY for 2908-2924 HIGHLAND DRIVE 3.5 Hydromodification Management To satisfy the requirements of the MS4 Permit, a hydromodification management strategy has been developed for the project based on the Final Hydromodification Management Plan dated March 2011, (Final HMP). A continuous simulation model, the Environmental Protection Agency (EPA) Storm Water Management Model (SWMM) version 5.1, was selected to size mitigation measures. The SWMM model is capable of modeling hydromodification management facilities to mitigate the effects of increased runoff from the post-development conditions and use changes that may cause negative impacts (i.e. erosion) to downstream channels. For HMP calculations refer to the report titled "Priority Development Project Storm Water Quality Management Plan for 141 Quail Drive" dated September 2020, prepared by Pasco Laret Suiter & Associates. 3.6 Storm Water Pollutant Control To meet the requirements of the M54 Permit, the HMP Biofiltration basins are designed to treat onsite storm water pollutants contained in the volume of runoff from a 24-hour, 85th percentile storm event by slowly infiltrating runoff through an engineered soil layer and gravel layer. For detailed pollutant control calculations refer to the report titled "Priority Development Project Storm Water Quality Management Plan for 141 Quail Drive" dated September 2020, prepared by Pasco Laret Suiter & Associates. AUGUST 2021 PLSA 3661 HYDROLOGY STUDY for 2908-2924 HIGHLAND DRIVE APPENDIX A Hydrology Support Material AUGUST 2021 PLSA 3661 - - - - - - - - - - - - - - - - - - - I lydrologic Soil Group—San Diego County Area, California 4370 468380 4683g3 464W 4410 468420 459433 468440 459400 468483 459470 468483 46848) 468000 468510 468520 468533 468540 33°10'3'N , 33°103N Ak 71 Ilk "low yjr _y\ , 333100 N Map vjati ss@ile : 33 10'0'N 468370 468200 4680 4684(X) 468410 468420 468468 468440 468490 468480 468470 46848) 46849) 468500 468510 468520 468533 468540 5 8 Map Scale: 1:818ifprintonA landscape (1i"x8.5')sbeet. N 0 10 2) 40 06 Feet 0 35 70 140 210 Map ptttion: Web Mercator Corner worcilnates: WGS84 Edge tics: LffM Zone uN WGS84 USDA Natural Resources Web Soil Survey 6/8/2021 Conservation Service National Cooperative Soil Survey Page 1 of 4 MAP LEGEND Area of Interest (AOl) Area of Interest (AOl) Soils Soil Rating Polygons ND BID C CID F__1D Not rated or not available Soil Rating Lines — A — ND B BID C CID ,. D a Not rated or not available Soil Rating Points • A • ND • B Rin DC • • D D Not rated or not available Water Features Streams and Canals Transportation +44 Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography - - - - - - - - - - - - - - - - - - - Hydrologic Soil Group—San Diego County Area, California MAP INFORMATION The soil surveys that comprise your AOl were mapped at 1.24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed ocale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: San Diego County Area, California Survey Area Data: Version 15, May 27, 2020 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Jan 24, 2020—Feb 12, 2020 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. USDA Natural Resources Web Soil Survey 6/8/2021 Conservation Service National Cooperative Soil Survey Page 2 of 4 Hydrologic Soil Group—San Diego County Area, California Hydrologic Soil Group Map unit symbol Map unit name Rating Acres in AOl Percent of AOl MlC Marina loamy coarse sand, 2 to 9 percent slopes B 0.7 60.4% MIE Marina loamy coarse sand, 9 to 30 percent slopes B 0.5 39.6% Totals for Area of Interest 1.2 100.0% Description Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms. The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (AID, BID, and CID). The groups are defined as follows: Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission. Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture. These soils have a moderate rate of water transmission. Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission. Group D. Soils having a very slow infiltration rate (high runoff potential) .when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission. If a soil is assigned to a dual hydrologic group (AID, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes. USDA Natural Resources Web Soil Survey 6/8/2021 Conservalion Service National Cooperative Soil Survey Page 3 of 4 Hydrologic Soil Group—San Diego County Area, California Rating Options Aggregation Method: Dominant Condition Component Percent Cutoff. None Specified Tie-break Rule: Higher USDA Natural Resources Web Soil Survey 6/8/2021 Conservation Service National Cooperative Soil Survey Page 4 of 4 - - - - - - - - - - - - - - - - - - - San Diego County Hydrology Manual Section: 3 Date: June 2003 Page: 6of26 Table 3-1 RUNOFF COEFFICIENTS FOR URBAN AREAS Land Use Runoff Coefficient "C" Soil Type NRCS Elements County Elements % IMPER. A B C D Undisturbed Natural Terrain (Natural) Permanent Open Space 0* 0.20 0.25 0.30 0.35 Low Density Residential (LDR) Residential, 1.0 DU/A or less 10 0.27 0.32 0.36 0.41 Low Density Residential (LDR) Residential, 2.0 DU/A or less 20 0.34 0.38 0.42 0.46 Low Density Residential (LDR) Residential, 2.9 DU/A or less 25 0.38 0.41 0.45 0.49 Medium Density Residential (MDR) Residential, 4.3 DU/A or less 30 0.41 0.45 0.48 0.52 Medium Density Residential (MDR) Residential, 7.3 DU/A or less 40 0.48 0.51 0.54 0.57 Medium Density Residential (MDR) Residential, 10.9 DU/A or less 45 0.52 0.54 0.57 0.60 Medium Density Residential (MDR) Residential, 14.5 DU/A or less 50 0.55 0.58 0.60 0.63 High Density Residential (HDR) Residential, 24.0 DU/A or less 65 0.66 0.67 0.69 0.71 High Density Residential (HDR) Residential, 43.0 DU/A or less 80 0.76 0.77 0.78 0.79 Commercial/Industrial (N. Corn) Neighborhood Commercial 80 0.76 0.77 0.78 0.79 Commercial/Industrial (G. Com) General Commercial 85 0.80 0.80 0.81 0.82 Commercial/Industrial (O.P. Corn) Office Professional/Commercial 90 0.83 0.84 0.84 0.85 Commercial/Industrial (Limited I.) Limited Industrial 90 0.83 0.84 0.84 0.85 Commercial/Industrial (General I.) General Industrial 95 0.87 0.87 0.87 0.87 *The values associated with 0% impervious may be used for direct calculation of the runoff coefficient as described in Section 3.1.2 (representing the pervious runoff coefficient, Cp, for the soil type), or for areas that will remain undisturbed in perpetuity. Justification must be given that the area will remain natural forever (e.g., the area is located in Cleveland National Forest). DU/A = dwelling units per acre NRCS = National Resources Conservation Service 3-6 r- t IT'J I County of Sari Diego Orange _ . - Hydrology Manual 3330 ---.—... __- 3330 r iJ i f'l tt IL . Rainfalllsopluvials yT T 100 Year Rainfall Event 6 Hours 3315 3315 / S - 25 0CESIDE SITE IsopluvIal (inches) Deth=2.6in r .ESC D1D . . . - BAD + . . - .+ . - - -fi- ---.._.-- . ...... -, . ...,.,.. ----- ------------- -- . ENCINITAS .... - - :..i .. .. - . --! / 3300 - —' I_. /] 300 ,. - Ar---.--, ..-+---- Q DEL - ................:°-- / . . ( -..............MA • + - CD \ --- , NTE 7 I I +1.................. r -I - --+ . -+,- ._ - . ._. - -. ....+ u. . :-. .•• - .... :.-........ __________ .... -. -. . ______ ______________________ , _______________________ 4 - 245 DPW GIS SanGIS '). Ha Deg (a cred. — - IMPERIAL EAC e x I W E If flA r.em.ym,. M.meth++S am -3230 - - -— 3230' y S _________________________ . - • - - +. + - - + . - + . *+ + 3 0 3 Miles HYDROLOGY STUDY for 2908-2924 HIGHLAND DRIVE APPENDIX C Existing and Proposed Hydrology Maps AUGUST 2021 PLSA 3661 DMA lB 38,629 SF I f M.89 A = 0.36 =185' - DMA 2 AREA = 15,886 SF (0.3A IMP V. = 1,504 SF (0. o:W) C = 0.31 L=200' L=106' / /1 EX/ST/NC HYDRO MAP 2908-2924 HIGHLAND DRIVE - - -.- . - - . N 552456 E 324.83'Y II DMA 1A 4,803 SF II It 01 j/ \FL '163.2 •IU /1 11 \ \çL=94' -DMA 2A 3,056 SF (0.07 AC) C = 0.25 L = 94' \ FL \ / FL 182.1 L=60 DMA It AREA = 43,432 IF (1 0 A IMPV = 8203 SF1 (0 1 ) / I \' I N 552422 E 324.83' - DMA 2B 12,830 SF (0.29 AC) C = 0.33 L=106' N NODE 20. FL 175.2 LEGEND HYROLOGIC INFORMATION PROJECT BOUNDARY FLOW PATH DMA BOUNDARY SUB-DMA BOUNDARY IMPERVIOUS AREA HYDROLOGIC SOIL GROUP = B PER VIOUS C = 0.25 IMPERVIOUS C = 0.90 PCCSYA=NIA GROUNDWATER = N/A NATURAL HYDROLOGIC FEATURES = N/A Air / l V 644 c-=o41 "I t7 NOEE 1005 NODI& DMA2A I I1 I AREA 4.845 S1 (0 03 A V N L !MPV .= 4,159 SF 095 A.( L=171' I PROPOSED HYDRO MAP 2908-2924 HIGHLAND DRIVE -DMA 1A AREA = 3,571 SF (0.082 Ac) IMPV. = 1,163 SF (0.027 Ac) C = 0.46 = 117' .. N 557456'E 324.83"c AREA = 8, /MP V. = DMA 1 SF (0.200 'AC), SF (0.118 AC C6 L 66 S R-1 ('SELF-RET.IN!NG) = 912 SF (0.00 AC) = 0 SF (O.o Ac) NODE 20.35 FL 162.0 L=5' rIM V 23 010 F O 28 Acfç/ 11 I i - I H J 11h I I N 552422 E SM-i (SEL F-MI 11GA 17NG) 1,380 SF (0.032 Ac) C = 0.25 LEGEND PROJECT BOUNDARY DMA 1 & 2 BOUNDARY SUB-DMA BOUNDARY HYROLOGIC INFORMATION HYDROLOGIC SOIL GROUP = B PERVIOUS C = 0.25 IMPERVIOUS C = 0.90 PCCSYA=NIA GROUNDWATER = N/A NATURAL HYDROLOGIC FEATURES = N/A FLOW PATH IMPERVIOUS AREA IPAsco LARET SUITER 1=30' I &AS8OCIATES I. .IR.IMm VLSA 3bb1