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PD 2022-0022; CANTOR GARAGE ADDITION; DRAINAGE REPORT CANTOR GARAGE ADDITION; 2022-09-26
DRAINAGE REPORT CANTOR GARAGE ADDITION 4269 HILLSIDE DRIVE CITY OF CARLSBAD PD2022-0022 DWG 538-8A Prepared for: Josh Cantor 4215 Harrison Street Carlsbad, CA 92008 Prepared by: bha, Inc. land planning, civil engineering, surveying 5115 Avenida Encinas, Suite L Carlsbad, CA 92008-4387 (760) 931-8700 September 26, 2022 W.O. 1101-1456-600 Cantor Garage Addition Drainage Report bha, Inc. 2 TABLE OF CONTENTS Chapter 1 – Discussion ....................................................................................................................................... 3 1.1 Vicinity Map .................................................................................................................................. 4 1.2 Purpose and Scope ........................................................................................................................ 5 1.3 Project Description ....................................................................................................................... 5 1.4 Existing Conditions ....................................................................................................................... 6 1.5 Developed Conditions .................................................................................................................. 6 1.6 Summary of Results ...................................................................................................................... 7 1.7 Study Method ................................................................................................................................ 7 1.8 Conclusion ..................................................................................................................................... 9 1.9 Declaration of Responsible Charge .......................................................................................... 10 Chapter 2 – Existing & Developed Hydrology Maps ..................................................................................... 11 Chapter 3 – 100-Year Peak Flow Calculations ............................................................................................... 12 3.1 Existing Hydrology Calculations ................................................................................................ 13 3.2 Developed Hydrology Calculations ........................................................................................... 17 Chapter 4 – References ..................................................................................................................................... 23 4.1 Methodology- Rational Method Peak Flow Determination ................................................... 24 Cantor Garage Addition Drainage Report bha, Inc. 3 Chapter 1 Discussion Cantor Garage Addition Drainage Report bha, Inc. 4 1.1 Vicinity Map NO SCALE VICINITY MAP NOT TO SCALE Cantor Garage Addition Drainage Report bha, Inc. 5 1.2 Purpose and Scope The purpose of this report is to publish the results of hydrology and hydraulic computer analysis for the proposed Cantor Garage Addition project located at 4269 Hillside Drive in the City of Carlsbad. The proposed project is located on a 0.374-acre lot. The scope is to study the existing and proposed hydrology and hydraulics as it influences the surrounding properties during a 100-year frequency storm event (Q100), and make recommendations to intercept, contain and convey Q100 to the historic point of discharge. 1.3 Project Description The Cantor Garage Addition project is proposing to construct a detached garage adjacent to an existing single-family home, a covered breezeway between the proposed garage and existing home, a permeable paver driveway, yard drains, retaining walls and associated hardscape. Existing improvements on the lot include a single-family home, a swimming pool, and concrete block walls along the southerly and easterly boundary of the property. The project site, Assessor’s Parcel Number (APN) 156-160-16, is a 0.374‐acres irregular- shaped developed residential lot located in the City of Carlsbad. The property is bordered by Hillside Drive to the northeast and residential parcels to the north, west, and south. Site location is shown on a Vicinity Map on page 4 of this report. Elevations on the lot range from a high of approximately 99 feet near the southwest property corner to a low of approximately 80 feet near the northeast property corner, near Hillside Drive. Onsite Vegetation range from ice plants to native grasses. Onsite soil classification is Type A (23%) and Type B (77%) as determined from the United States Department of Agriculture (USDA) Web Soil Survey (see references in Chapter 4). The line dividing Type A soils from Type B is shown on the Hydrology Exhibits. To account for the two different soil types, a composite runoff coefficient was calculated for pervious areas. Table 1 summarizes the composite C-values for Type A and B soils. Table 1 – Type A and Type B soils Composite Runoff Value TOTAL AREA (AC) TYPE A SOILS RUNOFF CA TYPE A SOILS AREA (AC) TYPE B SOILS RUNOFF CB TYPE B SOILS AREA (AC) CCOMP 0.772 0.20 0.180 0.25 0.593 0.24 Cantor Garage Addition Drainage Report bha, Inc. 6 1.4 Existing Conditions Storm flows affecting the site are limited to the rainfall that lands directly on the property and undeveloped hillside to the west of the property line. In the existing condition, offsite run-on and run-off from the approximately 25% impervious site sheet flows in a northeasterly direction towards one (1) Point of Compliance (POC-1). POC-1, located near the northeast corner of the property (adjacent to Hillside Drive), discharges into an existing curb and gutter in Hillside Drive. Excessive scouring or erosion is not present. The Existing Hydrology Exhibit shows runoff basins that will drain towards POC-1, located near the northeast corner of the project site (Node 60). Table 2 summarizes the existing runoff information from the site. Refer to the Existing Hydrology Exhibit for drainage patterns, areas, and POC. Table 2 - Summary of Existing Peak Flows DISCHARGE LOCATION DRAINAGE AREA (AC) 100-YEAR PEAK FLOW (CFS) TC (MIN) NODE 30 0.772 1.38 8.25 1.5 Developed Conditions In developed conditions, run-on from the hillside to the west of the property will be intercepted by proposed brow ditches. The brow ditches will convey the offsite flow around the existing home and proposed garage, discharging onto proposed rip-raps located on the north and south side of the existing home. Additionally, yard drainage system is proposed to convey flows from flat areas and discharge the runoff near the proposed permeable paver driveway. One (1) POC has been identified in the developed condition. The Developed Hydrology Exhibit shows storm water runoff being routed to POC-1, located near the northeast corner of the project site. The 0.374-acres site will be approximately 30% impervious post- development. Developed site flow will mimic existing drainage conditions, and will discharge from the site near historical flow rates. Impervious surfaces have been minimized where feasible. Table 3 summarizes the expected cumulative 100-year peak flow rates post-development. Per the San Diego County Rainfall Isopluvial maps, the design 100-year rainfall depth for the site area is 2.69 inches. Refer to the Developed Hydrology Map for drainage patterns, areas, and Points of Compliance. Cantor Garage Addition Drainage Report bha, Inc. 7 Table 3 - Summary of Developed Peak Flow DISCHARGE LOCATION DRAINAGE AREA (AC) 100-YEAR PEAK FLOW (CFS) TC (MIN) NODE 300 0.772 1.45 7.49 1.6 Summary of Results Table 4 compares the cumulative existing and developed peak flow conditions. Table 4 - Summary of Existing vs Developed Peak Flows DRAINAGE AREA (AC) 100-YEAR PEAK FLOW (CFS) EXISTING CONDITION 0.772 1.38 DEVELOPED CONDITION 0.772 1.45 0.00 0.07 1.7 Study Method The method of analysis was based on the Rational Method according to the San Diego County Hydrology Manual (SDCHM). The Hydrology and Hydraulic Analysis were done on Hydro Soft by Advanced Engineering Software 2014. The study considers the runoff for a 100-year storm frequency. Methodology used for the computation of design rainfall events, runoff coefficients, and rainfall intensity values are consistent with criteria set forth in the “2003 County of San Diego Drainage Design Manual.” A more detailed explanation of methodology used for this analysis is listed in Chapter 4 – References of this report. Drainage basin areas were determined from the topography and proposed grades shown on the Preliminary Grading Plan. The Rational Method for this project provided the following variable coefficients: Rainfall Intensity – Initial time of concentration (Tc) values based on Table 3-2 of the SDCHM. Rainfall Isopluvial Maps from the SDCHM were used to determine P6 for 100- year storm, see References. I = 7.44x(P6)x(Tc)- 0.645 Cantor Garage Addition Drainage Report bha, Inc. 8 P6 for 100-year storm =2.69 inches Runoff Coefficient - In accordance with the County of San Diego standards, runoff coefficients were based on land use and soil type. The soil conditions used in this study are consistent with Type-A and Type-B soil qualities. An appropriate runoff coefficient (C) for each type of land use in the subarea was selected from Table 3-1 of SDCHM and multiplied by the percentage of total area (A) included in that class. The sum of the products for all land uses is the weighted runoff coefficient (∑[CA]). Table 5 and 6 summarizes the composite C-values calculated in the existing and proposed conditions, respectively. Table 5 – Existing Condition Composite Runoff Coefficient Value UP NODE DOWN NODE TOTAL AREA (AC) C1 PERVIOUS AREA A1 (AC)C2 IMPERVIOUS AREA A2 (AC) CCOMP 10 20 0.189 0.24 0.185 0.90 0.004 0.26 20 60 0.340 0.24 0.263 0.90 0.077 0.39 30 40 0.090 0.24 0.090 0.90 0.000 0.24 40 50 0.153 0.24 0.104 0.90 0.049 0.45 Notes:C-values taken from Table 3-1 of San Diego County Hydrology Manual, consistent with on-site existing soil types from the USDA Web Soil Survey. See References. Table 6 – Developed Condition Composite Runoff Coefficient Value UP NODE DOWN NODE TOTAL AREA (AC) C1 PERVIOUS AREA A1 (AC) C2 IMPERVIOUS AREA A2 (AC) CCOMP 10 10 0.026 0.24 0.007 0.90 0.019 0.73 20 20 0.009 0.24 0.002 0.90 0.007 0.72 30 30 0.006 0.24 0.002 0.90 0.004 0.72 40 120 0.271 0.24 0.206 0.90 0.066 0.40 50 60 0.189 0.24 0.185 0.90 0.004 0.26 60 70 0.028 0.24 0.028 0.90 0.000 0.24 80 90 0.090 0.24 0.090 0.90 0.000 0.24 100 110 0.153 0.24 0.104 0.90 0.049 0.45 Notes:C-values taken from Table 3-1 of San Diego County Hydrology Manual, consistent with on-site existing soil types from the USDA Web Soil Survey. See References. Cantor Garage Addition Drainage Report bha, Inc. 9 1.8 Conclusion The Cantor Garage Addition will result in a 0.07 CFS increase of runoff originating from the project site. The City of Carlsbad storm drain systems are designed to account to fractional increases in runoff during the 100-year storm event. Based on this conclusion, runoff released from the proposed project site will unlikely cause any adverse impact to downstream water bodies or existing habitat integrity. Sediment will likely be reduced upon site development. Cantor Garage Addition Drainage Report bha, Inc.10 1.9 Declaration of Responsible Charge I hereby declare that I am the Engineer of Work for this project, that I have exercised responsible charge over the design of the project as defined in section 6703 of the business and professions code, and that the design is consistent with current standards. I understand that the check of project drawings and specifications by the City of Carlsbad is confined to a review only and does not relieve me, as Engineer of Work, of my responsibilities for project design. Ronald L. Holloway R.C.E. 29271 Expires 3/31/23 Date 9-28-22 Cantor Garage Addition Drainage Report bha, Inc. 11 Chapter 2 Existing & Developed Hydrology Maps 57//#4;1(&'8'.12'&%10&+6+105 POC ID DRAINAGE AREA (ACRES) UNDETAINED 100-YEAR PEAK FLOW (CFS) POC-1 0.77 1.38 LEGEND SURFACE NODE SURFACE RUNOFF (CFS) 30 1.38 BASIN AREA (ACRES)0.340 RUNOFF COEFFICIENT C=0.39 POINT OF COMPLIANCE (POC)POC BASIN BOUNDARY SUB-BASIN BOUNDARY PROPERTY LINE FLOWLINE LIMITS OF SOIL TYPE EXISTING IMPERVIOUS AREA FLOW DIRECTION ELEVATION 80.20 RIGHT-OF-WAY EXISTING CONDITION HYDROLOGY EXHIBIT SHEET 1 OF 1 CITY OF CARLSBAD I - \ \ ~ - "' '-.... '-.... I 01 I -------------- \ ----------I t 0 ------------- LOT 4 BLOCK £ MAP 2152 K: Civil JD 1456 _CANTOR DWG HYDRO 1456 -EXISTING HYDROLOGY.dwg Sep 26, 2022 -10: 02am 7 \ \ \ \ \ r --....._ --....._ l ---..___ I ----------.: ------\ ------------I ------ '--- PROPERTY LINE / EL•79.64 --------(§)----------------I c-o.45 I -----;. P.M. 21808 ~ PARCEL J ___J. ----....._ "---- ---------. -,.."-".....,~-~ COVERED PORC~ -J;_.,~~==sr--1 .... ,_ .. er, -I ~~ I I EXISTING POOL (PERMIT CBR2021-0901) ---------_....,---------.....__ ------- L N13'0J'06'Y'-J_5A.EW--I--~I " PROPERTY----------' __,---L/liTE -----------I El.=99.80 I I / ~ I / \ / \ I / \ / / '\_, :· / '-r ' ' ' 15, 30' 15 7.5 0 45' SCALE: 1" = 15' ------------ XISTING CMU / WALL ON _,,.--.-,-- PROPERTY /JNE / PROPERTY LINE _,,., --------------- LOCKIT 6 ------------8tO KE MAP 2152 -------------------- _,,., / \ \ I \ \ ---------..___ / ---..___ -/ -----~ ----------..___ I \ ----- I I \ / / / / / ----- / / / / / I --------....._ --------- ------------------------ ----- / / / / / I \ I ~ "' ---....._ --------....._ - \ / _,,-, l --, ~ -~ --...... ---..___ ---..___ /---....._ / I I / / BRUCE L. 1» RICE I NO. 60676 CJV\\, OF C~ bl-lA,lnc. land planning, civil engineeling, suNeying 5115 AVENIDA ENCINAS SUITE "L" CARLSBAD, CA. 92008-4387 (760) 931-8700 8 C) ----- ----- CANTOR GARAGE ADDITION DEVELOPED CONDITION HYDROLOGY EXHIBIT SHEET 1 OF 1 CITY OF CARLSBAD LEGEND SURFACE NODE SURFACE RUNOFF (CFS) 120 1.42 BASIN AREA (ACRES)0.271 RUNOFF COEFFICIENT C=0.40 POINT OF COMPLIANCE (POC)POC BASIN BOUNDARY SUB-BASIN BOUNDARY PROPERTY LINE FLOWLINE LIMITS OF SOIL TYPE EXISTING IMPERVIOUS AREA FLOW DIRECTION ELEVATION 80.20 RIGHT-OF-WAY 57//#4;1(&'8'.12'&%10&+6+105 POC ID DRAINAGE AREA (ACRES) UNDETAINED 100-YEAR PEAK FLOW (CFS) POC-1 0.77 1.45 PROPOSED CONCRETE PROPOSED DECOMPOSED GRANITE PERMEABLE PAVERS RIP-RAP ENERGY DISSIPATER I - \ \ "' ---------- '-.... '-.... I 01 I -------------- \ I LOT 4 BLOCK E MAP 2752 PROPERTY- LINE t 0 --------~ ----- ---·-,r ------- 1 7 K: Civil JD 1456 _CANTOR DWG HYDRO 1456 -DEVELOPED HYDROLOGY.dwg Sep 26, 2022 -9. 4Jam \ \ \ \ 0.271 C=0.40 \ I \ r l PROPERTY LINE ... --...::: --------------I ---------.: ------------------------------------------ ----------,,----...., ••• --...::: ,. 9' ----------110 -----------••• ----~ ti}v r--------------~~ ----,, I 0.45 ------------------------------••• --...::: • 54, .......____ -------....____ . -. I / EL•79.64 ---...... ---...... ...._____--...::: • ·.--...::: ~ -----, -------------...... ---...... ---...... -------------~ ....-.----.:::::: ( -------"' --------------------~ ------------------------"' PARCEL J P.M. 21808 C-0.45 -------t '-.... I ---.___ .______ ~ "----~ ~ t ~ "-.,; "l EXISTING POOL (PERMIT BR2021-0907) . (Ji t ~"' "' 'iw?ca_ 1 --___..... P.M. 21808 ___..... XISTING CMU / ------- EL=99.80 ___..... I I I ' ' ' ' 15, 30' 15 7.5 0 45' SCALE: 1" = 15' WALL ON _,,..-__,.- PROPERTY /JNE / PROPERTY LINE ___..... -------LO~___......,---- --Bt01.,K E MAP 2152 ------- \ \ \ I \ \ ___..... - -------/ ...._____ -/ -----~ ...------- ------- I \ ----- I I \ / / / / / ----- / / / / / I ----------...... ------------------ ---------------------------- ------ / / / / / I \ I ~ "' -----------------...... - \ / .,----1--, ----------------------------- / I I / / BRUCE L. 1» RICE I NO. 60676 CJV\\, OF C~ bl-lA,lnc. land planning, civil engineeling, suNeying 5115 AVENI0A ENCINAS SUITE "L" CARLSBAD, CA. 92008-4387 (760) 931-8700 8 C) ----- ----- CANTOR GARAGE ADDITION Cantor Garage Addition Drainage Report bha, Inc. 12 Chapter 3 100-Year Peak Flow Calculations Cantor Garage Addition Drainage Report bha, Inc. 13 3.1 Existing Hydrology Calculations 100-YEAR STORM ************************************************************************************* RATIONAL METHOD HYDROLOGY COMPUTER PROGRAM PACKAGE Reference: SAN DIEGO COUNTY FLOOD CONTROL DISTRICT 2003,1985,1981 HYDROLOGY MANUAL (c) Copyright 1982-2014 Advanced Engineering Software (aes) Ver. 21.0 Release Date: 06/01/2014 License ID 1459 Analysis prepared by: BHA Inc 5115 Avenida Encinas, Suite L Carlsbad, CA 92008 ************************** DESCRIPTION OF STUDY ************************** * EXISTING CONDITION 100-YEAR STORM HYDROLOGY * * CANTOR GARAGE ADDITION * * JN 1124-1456-600 * ************************************************************************** FILE NAME: K:\HYDRO\1456C\1456E100.DAT TIME/DATE OF STUDY: 10:49 07/08/2022 ---------------------------------------------------------------------------- USER SPECIFIED HYDROLOGY AND HYDRAULIC MODEL INFORMATION: ---------------------------------------------------------------------------- 2003 SAN DIEGO MANUAL CRITERIA USER SPECIFIED STORM EVENT(YEAR) = 100.00 6-HOUR DURATION PRECIPITATION (INCHES) = 2.690 SPECIFIED MINIMUM PIPE SIZE(INCH) = 3.00 SPECIFIED PERCENT OF GRADIENTS(DECIMAL) TO USE FOR FRICTION SLOPE = 0.95 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: 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 10.00 TO NODE 20.00 IS CODE = 21 ---------------------------------------------------------------------------- >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<< ============================================================================ *USER SPECIFIED(SUBAREA): USER-SPECIFIED RUNOFF COEFFICIENT = .2600 S.C.S. CURVE NUMBER (AMC II) = 0 Cantor Garage Addition Drainage Report bha, Inc. 14 INITIAL SUBAREA FLOW-LENGTH(FEET) = 100.00 UPSTREAM ELEVATION(FEET) = 121.50 DOWNSTREAM ELEVATION(FEET) = 99.80 ELEVATION DIFFERENCE(FEET) = 21.70 SUBAREA OVERLAND TIME OF FLOW(MIN.) = 7.019 WARNING: THE MAXIMUM OVERLAND FLOW SLOPE, 10.%, IS USED IN Tc CALCULATION! 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 5.695 SUBAREA RUNOFF(CFS) = 0.28 TOTAL AREA(ACRES) = 0.19 TOTAL RUNOFF(CFS) = 0.28 **************************************************************************** FLOW PROCESS FROM NODE 20.00 TO NODE 60.00 IS CODE = 51 ---------------------------------------------------------------------------- >>>>>COMPUTE TRAPEZOIDAL CHANNEL FLOW<<<<< >>>>>TRAVELTIME THRU SUBAREA (EXISTING ELEMENT)<<<<< ============================================================================ ELEVATION DATA: UPSTREAM(FEET) = 99.80 DOWNSTREAM(FEET) = 80.20 CHANNEL LENGTH THRU SUBAREA(FEET) = 190.00 CHANNEL SLOPE = 0.1032 CHANNEL BASE(FEET) = 3.00 "Z" FACTOR = 5.000 MANNING'S FACTOR = 0.030 MAXIMUM DEPTH(FEET) = 1.00 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 5.132 *USER SPECIFIED(SUBAREA): USER-SPECIFIED RUNOFF COEFFICIENT = .3900 S.C.S. CURVE NUMBER (AMC II) = 0 TRAVEL TIME COMPUTED USING ESTIMATED FLOW(CFS) = 0.62 TRAVEL TIME THRU SUBAREA BASED ON VELOCITY(FEET/SEC.) = 2.57 AVERAGE FLOW DEPTH(FEET) = 0.07 TRAVEL TIME(MIN.) = 1.23 Tc(MIN.) = 8.25 SUBAREA AREA(ACRES) = 0.34 SUBAREA RUNOFF(CFS) = 0.68 AREA-AVERAGE RUNOFF COEFFICIENT = 0.344 TOTAL AREA(ACRES) = 0.5 PEAK FLOW RATE(CFS) = 0.93 END OF SUBAREA CHANNEL FLOW HYDRAULICS: DEPTH(FEET) = 0.09 FLOW VELOCITY(FEET/SEC.) = 3.05 LONGEST FLOWPATH FROM NODE 10.00 TO NODE 60.00 = 290.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 60.00 TO NODE 60.00 IS CODE = 1 ---------------------------------------------------------------------------- >>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<< ============================================================================ TOTAL NUMBER OF STREAMS = 2 CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 1 ARE: TIME OF CONCENTRATION(MIN.) = 8.25 RAINFALL INTENSITY(INCH/HR) = 5.13 TOTAL STREAM AREA(ACRES) = 0.53 PEAK FLOW RATE(CFS) AT CONFLUENCE = 0.93 **************************************************************************** FLOW PROCESS FROM NODE 30.00 TO NODE 40.00 IS CODE = 21 ---------------------------------------------------------------------------- >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<< ============================================================================ *USER SPECIFIED(SUBAREA): USER-SPECIFIED RUNOFF COEFFICIENT = .2400 S.C.S. CURVE NUMBER (AMC II) = 0 INITIAL SUBAREA FLOW-LENGTH(FEET) = 100.00 UPSTREAM ELEVATION(FEET) = 125.52 DOWNSTREAM ELEVATION(FEET) = 99.40 ELEVATION DIFFERENCE(FEET) = 26.12 Cantor Garage Addition Drainage Report bha, Inc. 15 SUBAREA OVERLAND TIME OF FLOW(MIN.) = 7.186 WARNING: THE MAXIMUM OVERLAND FLOW SLOPE, 10.%, IS USED IN Tc CALCULATION! 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 5.609 SUBAREA RUNOFF(CFS) = 0.12 TOTAL AREA(ACRES) = 0.09 TOTAL RUNOFF(CFS) = 0.12 **************************************************************************** FLOW PROCESS FROM NODE 40.00 TO NODE 50.00 IS CODE = 51 ---------------------------------------------------------------------------- >>>>>COMPUTE TRAPEZOIDAL CHANNEL FLOW<<<<< >>>>>TRAVELTIME THRU SUBAREA (EXISTING ELEMENT)<<<<< ============================================================================ ELEVATION DATA: UPSTREAM(FEET) = 99.40 DOWNSTREAM(FEET) = 79.64 CHANNEL LENGTH THRU SUBAREA(FEET) = 161.00 CHANNEL SLOPE = 0.1227 CHANNEL BASE(FEET) = 3.00 "Z" FACTOR = 5.000 MANNING'S FACTOR = 0.030 MAXIMUM DEPTH(FEET) = 1.00 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 5.055 *USER SPECIFIED(SUBAREA): USER-SPECIFIED RUNOFF COEFFICIENT = .4500 S.C.S. CURVE NUMBER (AMC II) = 0 TRAVEL TIME COMPUTED USING ESTIMATED FLOW(CFS) = 0.29 TRAVEL TIME THRU SUBAREA BASED ON VELOCITY(FEET/SEC.) = 2.13 AVERAGE FLOW DEPTH(FEET) = 0.04 TRAVEL TIME(MIN.) = 1.26 Tc(MIN.) = 8.44 SUBAREA AREA(ACRES) = 0.15 SUBAREA RUNOFF(CFS) = 0.35 AREA-AVERAGE RUNOFF COEFFICIENT = 0.372 TOTAL AREA(ACRES) = 0.2 PEAK FLOW RATE(CFS) = 0.46 END OF SUBAREA CHANNEL FLOW HYDRAULICS: DEPTH(FEET) = 0.06 FLOW VELOCITY(FEET/SEC.) = 2.48 LONGEST FLOWPATH FROM NODE 30.00 TO NODE 50.00 = 261.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 50.00 TO NODE 60.00 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.) = 8.44 RAINFALL INTENSITY(INCH/HR) = 5.05 TOTAL STREAM AREA(ACRES) = 0.24 PEAK FLOW RATE(CFS) AT CONFLUENCE = 0.46 ** CONFLUENCE DATA ** STREAM RUNOFF Tc INTENSITY AREA NUMBER (CFS) (MIN.) (INCH/HOUR) (ACRE) 1 0.93 8.25 5.132 0.53 2 0.46 8.44 5.055 0.24 RAINFALL INTENSITY AND TIME OF CONCENTRATION RATIO CONFLUENCE FORMULA USED FOR 2 STREAMS. ** PEAK FLOW RATE TABLE ** STREAM RUNOFF Tc INTENSITY NUMBER (CFS) (MIN.) (INCH/HOUR) 1 1.38 8.25 5.132 2 1.38 8.44 5.055 Cantor Garage Addition Drainage Report bha, Inc. 16 COMPUTED CONFLUENCE ESTIMATES ARE AS FOLLOWS: PEAK FLOW RATE(CFS) = 1.38 Tc(MIN.) = 8.25 TOTAL AREA(ACRES) = 0.8 LONGEST FLOWPATH FROM NODE 10.00 TO NODE 60.00 = 290.00 FEET. +--------------------------------------------------------------------------+ | POC-1 | | | | | +--------------------------------------------------------------------------+ ============================================================================ END OF STUDY SUMMARY: TOTAL AREA(ACRES) = 0.8 TC(MIN.) = 8.25 PEAK FLOW RATE(CFS) = 1.38 ============================================================================ ============================================================================ END OF RATIONAL METHOD ANALYSIS Cantor Garage Addition Drainage Report bha, Inc. 17 3.2 Developed Hydrology Calculations 100-YEAR STORM ************************************************************************************** RATIONAL METHOD HYDROLOGY COMPUTER PROGRAM PACKAGE Reference: SAN DIEGO COUNTY FLOOD CONTROL DISTRICT 2003,1985,1981 HYDROLOGY MANUAL (c) Copyright 1982-2014 Advanced Engineering Software (aes) Ver. 21.0 Release Date: 06/01/2014 License ID 1459 Analysis prepared by: BHA Inc 5115 Avenida Encinas, Suite L Carlsbad, CA 92008 ************************** DESCRIPTION OF STUDY ************************** * DEVELOPED CONDITION 100-YEAR STORM HYDROLOGY * * CANTOR GARAGE ADDITION * * JN 1124-1456-600 * ************************************************************************** FILE NAME: K:\HYDRO\1456C\1456P100.DAT TIME/DATE OF STUDY: 10:38 07/08/2022 ---------------------------------------------------------------------------- USER SPECIFIED HYDROLOGY AND HYDRAULIC MODEL INFORMATION: ---------------------------------------------------------------------------- 2003 SAN DIEGO MANUAL CRITERIA USER SPECIFIED STORM EVENT(YEAR) = 100.00 6-HOUR DURATION PRECIPITATION (INCHES) = 2.690 SPECIFIED MINIMUM PIPE SIZE(INCH) = 3.00 SPECIFIED PERCENT OF GRADIENTS(DECIMAL) TO USE FOR FRICTION SLOPE = 0.95 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: 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 10.00 TO NODE 10.00 IS CODE = 22 ---------------------------------------------------------------------------- >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<< ============================================================================ *USER SPECIFIED(SUBAREA): USER-SPECIFIED RUNOFF COEFFICIENT = .7300 S.C.S. CURVE NUMBER (AMC II) = 0 Cantor Garage Addition Drainage Report bha, Inc. 18 USER SPECIFIED Tc(MIN.) = 5.000 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 7.087 SUBAREA RUNOFF(CFS) = 0.13 TOTAL AREA(ACRES) = 0.03 TOTAL RUNOFF(CFS) = 0.13 **************************************************************************** FLOW PROCESS FROM NODE 10.00 TO NODE 20.00 IS CODE = 41 ---------------------------------------------------------------------------- >>>>>COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<<<<< >>>>>USING USER-SPECIFIED PIPESIZE (EXISTING ELEMENT)<<<<< ============================================================================ ELEVATION DATA: UPSTREAM(FEET) = 89.07 DOWNSTREAM(FEET) = 88.97 FLOW LENGTH(FEET) = 13.00 MANNING'S N = 0.013 DEPTH OF FLOW IN 4.0 INCH PIPE IS 2.8 INCHES PIPE-FLOW VELOCITY(FEET/SEC.) = 2.06 GIVEN PIPE DIAMETER(INCH) = 4.00 NUMBER OF PIPES = 1 PIPE-FLOW(CFS) = 0.13 PIPE TRAVEL TIME(MIN.) = 0.11 Tc(MIN.) = 5.11 LONGEST FLOWPATH FROM NODE 10.00 TO NODE 20.00 = 13.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 20.00 TO NODE 20.00 IS CODE = 81 ---------------------------------------------------------------------------- >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<< ============================================================================ 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 6.993 *USER SPECIFIED(SUBAREA): USER-SPECIFIED RUNOFF COEFFICIENT = .7200 S.C.S. CURVE NUMBER (AMC II) = 0 AREA-AVERAGE RUNOFF COEFFICIENT = 0.7274 SUBAREA AREA(ACRES) = 0.01 SUBAREA RUNOFF(CFS) = 0.05 TOTAL AREA(ACRES) = 0.0 TOTAL RUNOFF(CFS) = 0.18 TC(MIN.) = 5.11 **************************************************************************** FLOW PROCESS FROM NODE 20.00 TO NODE 30.00 IS CODE = 41 ---------------------------------------------------------------------------- >>>>>COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<<<<< >>>>>USING USER-SPECIFIED PIPESIZE (EXISTING ELEMENT)<<<<< ============================================================================ ELEVATION DATA: UPSTREAM(FEET) = 88.97 DOWNSTREAM(FEET) = 88.81 FLOW LENGTH(FEET) = 17.00 MANNING'S N = 0.013 DEPTH OF FLOW IN 4.0 INCH PIPE IS 3.2 INCHES PIPE-FLOW VELOCITY(FEET/SEC.) = 2.40 GIVEN PIPE DIAMETER(INCH) = 4.00 NUMBER OF PIPES = 1 PIPE-FLOW(CFS) = 0.18 PIPE TRAVEL TIME(MIN.) = 0.12 Tc(MIN.) = 5.22 LONGEST FLOWPATH FROM NODE 10.00 TO NODE 30.00 = 30.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 30.00 TO NODE 30.00 IS CODE = 81 ---------------------------------------------------------------------------- >>>>>ADDITION OF SUBAREA TO MAINLINE PEAK FLOW<<<<< ============================================================================ 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 6.891 *USER SPECIFIED(SUBAREA): USER-SPECIFIED RUNOFF COEFFICIENT = .7200 S.C.S. CURVE NUMBER (AMC II) = 0 AREA-AVERAGE RUNOFF COEFFICIENT = 0.7263 SUBAREA AREA(ACRES) = 0.01 SUBAREA RUNOFF(CFS) = 0.03 Cantor Garage Addition Drainage Report bha, Inc. 19 TOTAL AREA(ACRES) = 0.0 TOTAL RUNOFF(CFS) = 0.21 TC(MIN.) = 5.22 **************************************************************************** FLOW PROCESS FROM NODE 30.00 TO NODE 40.00 IS CODE = 41 ---------------------------------------------------------------------------- >>>>>COMPUTE PIPE-FLOW TRAVEL TIME THRU SUBAREA<<<<< >>>>>USING USER-SPECIFIED PIPESIZE (EXISTING ELEMENT)<<<<< ============================================================================ ELEVATION DATA: UPSTREAM(FEET) = 88.81 DOWNSTREAM(FEET) = 86.75 FLOW LENGTH(FEET) = 58.00 MANNING'S N = 0.013 DEPTH OF FLOW IN 4.0 INCH PIPE IS 2.2 INCHES PIPE-FLOW VELOCITY(FEET/SEC.) = 4.21 GIVEN PIPE DIAMETER(INCH) = 4.00 NUMBER OF PIPES = 1 PIPE-FLOW(CFS) = 0.21 PIPE TRAVEL TIME(MIN.) = 0.23 Tc(MIN.) = 5.45 LONGEST FLOWPATH FROM NODE 10.00 TO NODE 40.00 = 88.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 40.00 TO NODE 120.00 IS CODE = 51 ---------------------------------------------------------------------------- >>>>>COMPUTE TRAPEZOIDAL CHANNEL FLOW<<<<< >>>>>TRAVELTIME THRU SUBAREA (EXISTING ELEMENT)<<<<< ============================================================================ ELEVATION DATA: UPSTREAM(FEET) = 86.75 DOWNSTREAM(FEET) = 80.20 CHANNEL LENGTH THRU SUBAREA(FEET) = 79.00 CHANNEL SLOPE = 0.0829 CHANNEL BASE(FEET) = 3.00 "Z" FACTOR = 5.000 MANNING'S FACTOR = 0.030 MAXIMUM DEPTH(FEET) = 1.00 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 6.282 *USER SPECIFIED(SUBAREA): USER-SPECIFIED RUNOFF COEFFICIENT = .4000 S.C.S. CURVE NUMBER (AMC II) = 0 TRAVEL TIME COMPUTED USING ESTIMATED FLOW(CFS) = 0.55 TRAVEL TIME THRU SUBAREA BASED ON VELOCITY(FEET/SEC.) = 2.29 AVERAGE FLOW DEPTH(FEET) = 0.07 TRAVEL TIME(MIN.) = 0.58 Tc(MIN.) = 6.03 SUBAREA AREA(ACRES) = 0.27 SUBAREA RUNOFF(CFS) = 0.68 AREA-AVERAGE RUNOFF COEFFICIENT = 0.443 TOTAL AREA(ACRES) = 0.3 PEAK FLOW RATE(CFS) = 0.87 END OF SUBAREA CHANNEL FLOW HYDRAULICS: DEPTH(FEET) = 0.09 FLOW VELOCITY(FEET/SEC.) = 2.65 LONGEST FLOWPATH FROM NODE 10.00 TO NODE 120.00 = 167.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 120.00 TO NODE 120.00 IS CODE = 1 ---------------------------------------------------------------------------- >>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<< ============================================================================ TOTAL NUMBER OF STREAMS = 3 CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 1 ARE: TIME OF CONCENTRATION(MIN.) = 6.03 RAINFALL INTENSITY(INCH/HR) = 6.28 TOTAL STREAM AREA(ACRES) = 0.31 PEAK FLOW RATE(CFS) AT CONFLUENCE = 0.87 **************************************************************************** FLOW PROCESS FROM NODE 50.00 TO NODE 60.00 IS CODE = 21 ---------------------------------------------------------------------------- >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<< Cantor Garage Addition Drainage Report bha, Inc. 20 ============================================================================ *USER SPECIFIED(SUBAREA): USER-SPECIFIED RUNOFF COEFFICIENT = .2600 S.C.S. CURVE NUMBER (AMC II) = 0 INITIAL SUBAREA FLOW-LENGTH(FEET) = 100.00 UPSTREAM ELEVATION(FEET) = 121.50 DOWNSTREAM ELEVATION(FEET) = 99.80 ELEVATION DIFFERENCE(FEET) = 21.70 SUBAREA OVERLAND TIME OF FLOW(MIN.) = 7.019 WARNING: THE MAXIMUM OVERLAND FLOW SLOPE, 10.%, IS USED IN Tc CALCULATION! 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 5.695 SUBAREA RUNOFF(CFS) = 0.28 TOTAL AREA(ACRES) = 0.19 TOTAL RUNOFF(CFS) = 0.28 **************************************************************************** FLOW PROCESS FROM NODE 60.00 TO NODE 70.00 IS CODE = 51 ---------------------------------------------------------------------------- >>>>>COMPUTE TRAPEZOIDAL CHANNEL FLOW<<<<< >>>>>TRAVELTIME THRU SUBAREA (EXISTING ELEMENT)<<<<< ============================================================================ ELEVATION DATA: UPSTREAM(FEET) = 99.80 DOWNSTREAM(FEET) = 88.50 CHANNEL LENGTH THRU SUBAREA(FEET) = 143.00 CHANNEL SLOPE = 0.0790 CHANNEL BASE(FEET) = 0.00 "Z" FACTOR = 2.000 MANNING'S FACTOR = 0.015 MAXIMUM DEPTH(FEET) = 1.00 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 5.459 *USER SPECIFIED(SUBAREA): USER-SPECIFIED RUNOFF COEFFICIENT = .2400 S.C.S. CURVE NUMBER (AMC II) = 0 TRAVEL TIME COMPUTED USING ESTIMATED FLOW(CFS) = 0.30 TRAVEL TIME THRU SUBAREA BASED ON VELOCITY(FEET/SEC.) = 5.00 AVERAGE FLOW DEPTH(FEET) = 0.17 TRAVEL TIME(MIN.) = 0.48 Tc(MIN.) = 7.49 SUBAREA AREA(ACRES) = 0.03 SUBAREA RUNOFF(CFS) = 0.04 AREA-AVERAGE RUNOFF COEFFICIENT = 0.257 TOTAL AREA(ACRES) = 0.2 PEAK FLOW RATE(CFS) = 0.30 END OF SUBAREA CHANNEL FLOW HYDRAULICS: DEPTH(FEET) = 0.17 FLOW VELOCITY(FEET/SEC.) = 5.12 LONGEST FLOWPATH FROM NODE 50.00 TO NODE 70.00 = 243.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 70.00 TO NODE 120.00 IS CODE = 1 ---------------------------------------------------------------------------- >>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<< ============================================================================ TOTAL NUMBER OF STREAMS = 3 CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 2 ARE: TIME OF CONCENTRATION(MIN.) = 7.49 RAINFALL INTENSITY(INCH/HR) = 5.46 TOTAL STREAM AREA(ACRES) = 0.22 PEAK FLOW RATE(CFS) AT CONFLUENCE = 0.30 **************************************************************************** FLOW PROCESS FROM NODE 80.00 TO NODE 90.00 IS CODE = 21 ---------------------------------------------------------------------------- >>>>>RATIONAL METHOD INITIAL SUBAREA ANALYSIS<<<<< ============================================================================ *USER SPECIFIED(SUBAREA): USER-SPECIFIED RUNOFF COEFFICIENT = .2400 S.C.S. CURVE NUMBER (AMC II) = 0 Cantor Garage Addition Drainage Report bha, Inc. 21 INITIAL SUBAREA FLOW-LENGTH(FEET) = 100.00 UPSTREAM ELEVATION(FEET) = 125.52 DOWNSTREAM ELEVATION(FEET) = 99.40 ELEVATION DIFFERENCE(FEET) = 26.12 SUBAREA OVERLAND TIME OF FLOW(MIN.) = 7.186 WARNING: THE MAXIMUM OVERLAND FLOW SLOPE, 10.%, IS USED IN Tc CALCULATION! 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 5.609 SUBAREA RUNOFF(CFS) = 0.12 TOTAL AREA(ACRES) = 0.09 TOTAL RUNOFF(CFS) = 0.12 **************************************************************************** FLOW PROCESS FROM NODE 90.00 TO NODE 100.00 IS CODE = 51 ---------------------------------------------------------------------------- >>>>>COMPUTE TRAPEZOIDAL CHANNEL FLOW<<<<< >>>>>TRAVELTIME THRU SUBAREA (EXISTING ELEMENT)<<<<< ============================================================================ ELEVATION DATA: UPSTREAM(FEET) = 99.40 DOWNSTREAM(FEET) = 88.50 CHANNEL LENGTH THRU SUBAREA(FEET) = 66.00 CHANNEL SLOPE = 0.1652 CHANNEL BASE(FEET) = 0.00 "Z" FACTOR = 2.000 MANNING'S FACTOR = 0.015 MAXIMUM DEPTH(FEET) = 1.00 CHANNEL FLOW THRU SUBAREA(CFS) = 0.12 FLOW VELOCITY(FEET/SEC.) = 5.04 FLOW DEPTH(FEET) = 0.11 TRAVEL TIME(MIN.) = 0.22 Tc(MIN.) = 7.40 LONGEST FLOWPATH FROM NODE 80.00 TO NODE 100.00 = 166.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 100.00 TO NODE 110.00 IS CODE = 51 ---------------------------------------------------------------------------- >>>>>COMPUTE TRAPEZOIDAL CHANNEL FLOW<<<<< >>>>>TRAVELTIME THRU SUBAREA (EXISTING ELEMENT)<<<<< ============================================================================ ELEVATION DATA: UPSTREAM(FEET) = 88.50 DOWNSTREAM(FEET) = 79.64 CHANNEL LENGTH THRU SUBAREA(FEET) = 137.00 CHANNEL SLOPE = 0.0647 CHANNEL BASE(FEET) = 3.00 "Z" FACTOR = 5.000 MANNING'S FACTOR = 0.030 MAXIMUM DEPTH(FEET) = 1.00 100 YEAR RAINFALL INTENSITY(INCH/HOUR) = 4.960 *USER SPECIFIED(SUBAREA): USER-SPECIFIED RUNOFF COEFFICIENT = .4500 S.C.S. CURVE NUMBER (AMC II) = 0 TRAVEL TIME COMPUTED USING ESTIMATED FLOW(CFS) = 0.29 TRAVEL TIME THRU SUBAREA BASED ON VELOCITY(FEET/SEC.) = 1.77 AVERAGE FLOW DEPTH(FEET) = 0.05 TRAVEL TIME(MIN.) = 1.29 Tc(MIN.) = 8.70 SUBAREA AREA(ACRES) = 0.15 SUBAREA RUNOFF(CFS) = 0.34 AREA-AVERAGE RUNOFF COEFFICIENT = 0.372 TOTAL AREA(ACRES) = 0.2 PEAK FLOW RATE(CFS) = 0.45 END OF SUBAREA CHANNEL FLOW HYDRAULICS: DEPTH(FEET) = 0.07 FLOW VELOCITY(FEET/SEC.) = 2.05 LONGEST FLOWPATH FROM NODE 80.00 TO NODE 110.00 = 303.00 FEET. **************************************************************************** FLOW PROCESS FROM NODE 110.00 TO NODE 120.00 IS CODE = 1 ---------------------------------------------------------------------------- >>>>>DESIGNATE INDEPENDENT STREAM FOR CONFLUENCE<<<<< >>>>>AND COMPUTE VARIOUS CONFLUENCED STREAM VALUES<<<<< ============================================================================ TOTAL NUMBER OF STREAMS = 3 CONFLUENCE VALUES USED FOR INDEPENDENT STREAM 3 ARE: TIME OF CONCENTRATION(MIN.) = 8.70 Cantor Garage Addition Drainage Report bha, Inc. 22 RAINFALL INTENSITY(INCH/HR) = 4.96 TOTAL STREAM AREA(ACRES) = 0.24 PEAK FLOW RATE(CFS) AT CONFLUENCE = 0.45 ** CONFLUENCE DATA ** STREAM RUNOFF Tc INTENSITY AREA NUMBER (CFS) (MIN.) (INCH/HOUR) (ACRE) 1 0.87 6.03 6.282 0.31 2 0.30 7.49 5.459 0.22 3 0.45 8.70 4.960 0.24 RAINFALL INTENSITY AND TIME OF CONCENTRATION RATIO CONFLUENCE FORMULA USED FOR 3 STREAMS. ** PEAK FLOW RATE TABLE ** STREAM RUNOFF Tc INTENSITY NUMBER (CFS) (MIN.) (INCH/HOUR) 1 1.42 6.03 6.282 2 1.45 7.49 5.459 3 1.41 8.70 4.960 COMPUTED CONFLUENCE ESTIMATES ARE AS FOLLOWS: PEAK FLOW RATE(CFS) = 1.45 Tc(MIN.) = 7.49 TOTAL AREA(ACRES) = 0.8 LONGEST FLOWPATH FROM NODE 80.00 TO NODE 120.00 = 303.00 FEET. +--------------------------------------------------------------------------+ | POC-1 | | | | | +--------------------------------------------------------------------------+ ============================================================================ END OF STUDY SUMMARY: TOTAL AREA(ACRES) = 0.8 TC(MIN.) = 7.49 PEAK FLOW RATE(CFS) = 1.45 ============================================================================ ============================================================================ END OF RATIONAL METHOD ANALYSIS Cantor Garage Addition Drainage Report bha, Inc. 23 Chapter 4 References Cantor Garage Addition Drainage Report bha, Inc. 24 4.1 Methodology – Rational Method Peak Flow Determination Cantor Garage Addition Drainage Report bha, Inc. 25 33°30' ~ 33•30 Riverside County 33°15'~- Long. 117" 32'45' County of San Diego Hydrology Manual e Rainfall fsopluvials 100 Year Rainfall E\'cnt -6 Hours lsopluvial(inches) I P6=2.69" I DPW •GIS ~~=--*N ::':,';0::::~a~="'••.•~,.;.,,~~-' ~-A ......... •--. w I: ~~...!;:;;."'.t~ ........ .., ....... ~ ... --.... .. _.,.,.... __ ,.,.~,....... • s 3 O 3 Miles l""liiiii"" Cantor Garage Addition Drainage Report bha, Inc. 26 33"15' Project Locati Lat. 33 Long. 117" 33•ro 32•45•~~ 32°30' County of San Diego Hydrology Manual Rainfall fsopluvials 100 Year Rainfall [\'ent _ 24 Hours lsopluvial(inches) 3 0 3 Miles I""'.."""' Cantor Garage Addition Drainage Report bha, Inc. 27 NOAA Atlas 14, Volume 6, Version 2 Location name: Carlsbad, California, USA• Latitude: 33.1501°, Longitude: -117.327° Elevation: 90.95 nu •source: ESRIMaps ••source:USGS POINT PRECIPITATION FREQUENCY ESTIMATES Sanja Perica, Sarah Dietz, Sarah Heim, Lillian Hiner, Kazungu Maitaria, Deborah Martin, Sallclra Pavlovic, lshani Roy, Carl Trypaluk, Dale Unruh, Fengtin Yan, Michael Yekta, Tan Zhao, Geoffrey Bonnin, Daniel Brewer, Li-Chuan Chen, Tye Paaybok, John Yarchoan NOAA, National 1/oJeather Sef\lice, Silver Spring, Marylallcl ~ I ff_grallll@! I Ml!~ PF tabular PF graphical Cantor Garage Addition Drainage Report bha, Inc. 28 30 C 25 .c C. i 20 C 0 -~ 15 ·a "j 10 30 C 25 .c C. ~ 20 C 0 -~ 15 ·a. -~ 10 PDS-based depth-duration-frequency (DDF) curves Latitude: 33.1501°, Longitude: -117.3270° C E fil Duration 25 50 100 200 Average recurrence interval (years) 500 1000 NOAA Atlas 14, Volume 6, Version 2 Created (GMT): Wed Jul 6 21:50:08 2022 Maps & aerials Small scale terrain Average recurrence mteival (years) -1 2 -5 -10 -25 -50 -100 -200 -500 -1000 Duration -5--mln -2-aay -10-mln -3-day 1&<nln -4--day -JG-min -7-day -60-min -10-day -2-hr -20-aay -3-hr -30-day -6-nr -45-Clay -12-hr -60-day -24---tlr Cantor Garage Addition Drainage Report bha, Inc. 29 -~----~a1!n~ra: scaJev~::;~me SA,vBE. Los A~geles Riverside""'..., ~1\1,1,(lbt,vo . • vlltvr,. LongBeach • 1:ahe1m CathedralCit)'••'Ns SantaAna PalmDes t •1ndio Oxnard 0 Murri@ta• I S,1/ton Oce1111si4-Se.? San Diego ffi: • Me:IU + .. " Tijuana _ 100km 1-------...'J:m; Large scale aerial Cantor Garage Addition Drainage Report bha, Inc. 30 lll!l.ls..12 .. nrn ~Par1ment of Commerce National Oceanic and Atmospheric Administration National Weather Service National \fliater Center 1325 East West Highway Silver Spring, MD 20910 Questions?: HDSC auestions@noaa qQY Disclaimer Cantor Garage Addition Drainage Report bha, Inc. 31 San Diego County Hydrology Manual Date: June 2003 SECTION3 Section: Page: RATIONAL METHOD AND MODIFIED RATIONAL METHOD 3.1 THE RATIONAL METHOD 3 1 of26 The Rational Method (RM) is a mathematical formula used to determine the maximum runoff rate from a given rainfall. It has particular application in urban storm drainage, where it is used to estimate peak runoff rates from small urban and rural watersheds for the design of storm drains and small drainage structures. The RM is recommended for analyzing the runoff response from drainage areas up to approximately 1 square mile in size. It should not be used in instances where there is a junction of independent drainage systems or for drainage areas greater than approximately I square mile in size. In these instances, the Modified Rational Method (MRM) should be used for junctions of independent drainage systems in watersheds up to approximately 1 square mile in size (see Section 3.4); or the NRCS Hydrologic Method should be used for watersheds greater than approximately I square mile in size (see Section 4). The RM can be applied using any design stonn frequency (e.g., 100-year, SO-year, IO-year, etc.). The local agency determines the design storm frequency that must be used based on the type of project and specific local requirements. A discussion of design storm frequency is provided in Section 2.3 of this manual. A procedure has been developed that converts the 6-hour and 24-hour precipitation isopluvial map data to an Intensity-Duration curve that can be used for the rainfall intensity in the RM fonnula as shown in Figure 3-1. The RM is applicable to a 6-hour storm duration because the procedure uses Intensity-Duration Design Charts that are based on a 6-hour storm duration. 3.1.1 Rational Method Formula The RM formula estimates the peak rate of runoff at any location in a watershed as a function of the drainage area (A), runoff coefficient (C), and rainfall intensity (I) for a duration equal to the time of concentration (Tc), which is the time required for water to 3-1 Cantor Garage Addition Drainage Report bha, Inc. 32 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 0.6 0.5 0.4 0.3 0.2 0.1 ' r-.. ' r-.. r--. ' r-. r-..r-.. 'r-.. r-.. r-..r-.. ", 'r-.. r-.. r-..r-.. 5 .... i-.. .... ~ r-.. ... ' .... 'i-.. i-.. ' r-..r-.. r,..~ ' ',, r-..r-.. 'i-.. r,.. ... r,..~ i-.. '"r-.. r-.., "", ~, 7 8 9 10 15 I I I ~ ~ ~ ~I t ~ 1~ I I n r~ H ~I I ll 1~ I t I I I '{ 20 30 40 50 1 Minutes Duration I 11111111111 1 I I 11 111111 1111 11111111111 1 I I 11 111111 1111 11111111111 1 I 1111 1111 I = I = Pe= D = EQUATION 7.44 Ps D-o.64s Intensity (in/hr) 6-Hour Precipitation (in) Duration (min) i-.., ', ,, '1' ,r-- ' ' ' ,' I , ' ' 1', ' ... ' ', ' ' .... , ', ~ ~~ ~ ~ ~~ ~ ~ ~ ~~ 3 Hours I ' I I I ' I I I ~ I 3.0 2.5 2.0 1.5 1.0 Intensity-Duration Design Chart • Template Directions for Application: (1) From precipitation maps detennine 6 hr and 24 hr amounts for the selected frequency, These maps are included in the County Hydrology Manual (10, 50, and 100 yr maps included in the Design and Procedure Manual). (2) Adjust 6 hr precipitation (if necessary) so that it is within the range of 45% to 65% of the 24 hr precipitation (not applicaple to Desert). (3) Plot 6 hr precipitation on the right side of the chart. (4) Draw a line through the point parallel to the plotted lines. (5) This line is the intensity-duration curve for the location being analyzed. Application Form: (a) Selected frequency 100 year p (b) Ps = 2.69 in., P24 = 4.40 .~ = _§_1_ %(2) 24 (c) Adjusted p6(2) = ___ in. (d) tx = __ min. (e) I = __ in./hr. Note: This chart replaces the Intensity-Duration-Frequency curves used since 1965. 20 1.00 1.s2 2.1s 2.69 3.23 3.n 4.31 4.85 5.39 s.93 6.46 2s -9.~ 1,,40 i..le1 2.!J.1 2~01 a.~ 33 •. =7332 ~3._2703: ••·.•,'s s4._~~ ~.-.6098 30 0.83 1.24 1.66 2.07 2.4912.90 <IV :--K:-i:: !:: ~:~~ ~:~~~~:~ ~:~ ~:~~-~::; ~:~t-{~ --60 0.53 0.80 1.06 1.33 1.59 1.86 2.12 2.39 2.65 2.92 3.18 90 0.41 0.61 0.82 1.02 1.2311.43 1.63 1.84 2.04 2.25 2.45 120 0.34 0.51 0.68 0.85 1.02 1.19 1.36 ~~·72.-1.87 2.04 1so o.29 0..44 o.59 o.73 o.est 1.03 1.1a 1.32 1.~_!:~~ 180 0.28 0.39 0.52 0.65 0.78J0.91 1.04 1.18 1.31 1.~~ 240 o.~ ~?·33 o.43 o.54 o.6sf0.76 o.a1 o.98 1.oa 1.19 1.30 ~ ~:~r~:~: ~:~ ~~i l~::1~:: ~:~ ~:~ ~::}~:: ~:~ FIGURE ~ Cantor Garage Addition Drainage Report bha, Inc. 33 Hydrologic Soil Group-San Diego County Area, California (CANTOR GARAGE ADDITION: 4269 HILLSIDE DRIVE, CARLSBAD, CA 92008) 33<' g l"N 33" 8'9:J'N Map Scale: 1: 518 t printe:1 011 A lardscape ( 11" X 8S') sheet N --~==----~=====Me!eis 10 2'.l 3:J A ---~===~-------=======-0 • ~ ® ~ Map projE<lion: \\eb Men:alllr COO'erroordirates: WGS84 Edge tics: l/TM Zone 11N WGS84 USDA Natural Resources aiii Conservation Service Web Soil Survey National Cooperative Soil Survey 7/6/2022 Page 1 of4 33" 9'1"N 33" 8'59'N Cantor Garage Addition Drainage Report bha, Inc. 34 Hydrologic Soil Group-San Diego County Area, California (CANTOR GARAGE ADDITION: 4269 HILLSIDE DRIVE, CARLSBAD, CA 92008) MAP LEGEND Area of Interest {AOI) D Area of Interest (AOI) Soils Soil Rating Polygons D A D ND D B D BID D C D CID D D D Not rated or not available Soil Rating Lines A -ND -B -BID C CID -D .. " Not rated or not available Soil Rating Points C A EJ ND ■ B ■ BID USDA Natural Resources aiii Conservation Service C C C CID C D □ Not rated or not available Water Features Streams and Canals Transportation t-++ Rails Interstate Highways US Routes Major Roads Local Roads Background • Aerial Photography Web Soil Survey National Cooperative Soil Survey MAP INFORMATION The soil surveys that comprise your AOI 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 scale. 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 16, Sep 13, 2021 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 digrtized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. 7/6/2022 Page 2 of4 Cantor Garage Addition Drainage Report bha, Inc. 35 Hydrologic Soil Group-San Diego County Area, California CANTOR GARAGE ADDITION: 4269 HILLSIDE DRIVE, CARLSBAD, CA 92008 Hydrologic Soil Group Map unit symbol Map unit name Rating Acres in AOI Percent of AOI CsC Corralitos loamy sand, 5 A 0.2 to 9 percent slopes LvF3 Loamy alluvial land-B 0.6 Huerhuero complex, 9 to 50 percent slopes, severely eroded Totals for Area of Interest 0.8 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 (A/D, B/D, and C/D). 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 (A/D, 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 Dare assigned to dual classes. Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 23.4% 76.6% 100.0% 7/6/2022 Page 3 of4 Cantor Garage Addition Drainage Report bha, Inc. 36 Hydrologic Soil Group-San Diego County Area, California Rating Options Aggregation Method: Dominant Condition Component Percent Cutoff: None Specified Tie-break Rule: Higher Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey CANTOR GARAGE ADDITION: 4269 HILLSIDE DRIVE, CARLSBAD, CA 92008 7/6/2022 Page 4 of4 Cantor Garage Addition Drainage Report bha, Inc. 37 San Diego County Hydrology Manual Date: June 2003 Table 3-1 Section: 3 Page: 6 of26 RUNOFF C0EFFIClENTS FOR URBAN AREAS Land Use Runoff Coetlicient "C" Soil T e N RCS Elements Coun Elements % IMPER. A B C D Undisnlfbed Nan,ral Terrain (Natural) Permanent Open Space o• !0 20! !025! 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 (HOR) Residential, 43.0 DU/A or less 80 0.76 0.77 0.78 0.79 Commercial/lndustrial (N. Com) Neighborhood Commercial 80 0.76 0.77 0.78 0.79 Commercial/lnduslrial (G. Com) General Commercial 85 0.80 0.80 0.81 0.82 Commercial/Industrial (O.P. Com) Office Protessional/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 *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 undisnlfbed 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 THE DRAINAGE AREA IS COMPOSED OF TYPE A (7,827 SF) AND B (25,821 SF) SOILS. A COMPOSITE RUNOFF COEFFICIENT FOR PERVIOUS AREAS IS CALCULATED TO ACCOUNT FOR THE DIFFERENT SOILS. (0.18 X 0.20 + 0.59 X 0.25) C=------ (A, + A2) (0.77) 1□24! Cantor Garage Addition Drainage Report bha, Inc. 38 San Diego County Hydrology Manual Date: June 2003 3.1.3 Rainfall Intensity Section: Page: 3 7 of26 The rainfall intensity (I) is the rainfall in inches per hour (in/hr) for a duration equal to the Tc for a selected storm frequency. Once a particular storm frequency has been selected for design and a Tc calculated for the drainage area, the rainfall intensity can be determined from the Intensity-Duration Design Chart (Figure 3-1). The 6-hour storm rainfall amount (P6) and the 24-hour storm rainfall amount (P24) for the selected storm frequency are also needed for calculation of I. P6 and P24 can be read from the isopluvial maps provided in Appendix B. An Intensity-Duration Design Chart applicable to all areas within San Diego County is provided as Figure 3-1. Figure 3-2 provides an example of use of the Intensity-Duration Design Chart. Intensity can also be calculated using the following equation: Where: I = 7.44 p6 ffo64s adjusted 6-hour storm rainfall amount (see discussion below) duration in minutes (use Tc) Note: This equation applies only to the 6-hour storm rainfall amount (i.e., P6 cannot be changed to P24 to calculate a 24-hour intensity using this equation). The Intensity-Duration Design Chart and the equation are for the 6-hour storm rainfall amount. In general, P6 for the selected frequency should be between 45% and 65% of P24 for the selected frequency. If P6 is not within 45% to 65% of P 24, P6 should be increased or decreased as necessary to meet this criteria. The isopluvial lines are based on precipitation gauge data. At the time that the isopluvial lines were created, the majority of precipitation gauges in San Diego County were read daily, and these readings yielded 24-hour precipitation data. Some 6-hour data were available from the few recording gauges distributed throughout the County at that time; however, some 6-hour data were extrapolated. Therefore, the 24-hour precipitation data for San Diego County are considered to be more reliable. 3-7 Cantor Garage Addition Drainage Report bha, Inc. 39 I ¾~:~~Eiiii33333iEEEffEufiffi ~o.el- Jo.11-++++++-1-+-+++++++++++++++++ o.,H-+++-++-+-++-++.++++>+++++- •. ,,-, +++++-+-+'~-4-=4"-'=~ 5 6 78910 Duration Intensity-Duration Design Chart -Example Direct.Ions for Application: (1) From precipitation maps determine 6 hr and 24 hr amounts for the selected frequency. These maps are in duded in the County Hydrology Mcinual (10, 50, .ind 100 yr maps included in the Design and Procedure Manual). (2) Adjust 6 hr precipitation (if necessary) so that it is within the range of 45% to 65% of the 24 hr precipitation (not applicaple to Desert) (3) Plot 6 hr precipitation on the right side of the chart. (4) Draw a line through lhe point parallel to the plotted lines (5) This line is the intensity-duration a.Jrve for the location beil'\Q analyzed. Ap~JcatJon Form: (a) Selecte<l frequency~ year (b) Ps = _3_ in., p24 = ~ ,~ = ~ %121 (c) Adjusted p6<2l = _3 _ io (d) Ix = ~ min. (e)l=____!L_in.!hr. Note: This chart replaces the Intensity-Duration-Frequency curves used since 1965 . ~ ~ Cantor Garage Addition Drainage Report bha, Inc. 40 San Diego County Hydrology Manual Date: June 2003 3.1.4 Time of Concentration Section: Page: 3 9 of26 The Time of Concentration (Tc) is the time required for runoff to flow from the most remote part of the drainage area to the point of interest. The Tc is composed of two components: initial time of concentration (Ti) and travel time (T1). Methods of computation for Ti and T1 are discussed below. The Ti is the time required for runoff to travel across the surface of the most remote subarea in the study, or "initial subarea." Guidelines for designating the initial subarea are provided within the discussion of computation of Ti. The T1 is the time required for the runoff to flow in a watercourse (e.g., swale, channel, gutter, pipe) or series of watercourses from the initial subarea to the point of interest. For the RM, the Tc at any point within the drainage area is given by: Methods of calculation differ for natural watersheds (nonurbanized) and for urban drainage systems. When analyzing storm drain systems, the designer must consider the possibility that an existing natural watershed may become urbanized during the useful life of the storm drain system. Future land uses must be used for Tc and runoff calculations, and can be determined from the local Community General Plan. 3.1.4.1 Initial Time of Concentration The initial time of concentration is typically based on sheet flow at the upstream end of a drainage basin. The Overland Time of Flow (Figure 3-3) is approximated by an equation developed by the Federal Aviation Agency (FAA) for analyzing flow on runaways (FAA, 1970). The usual runway configuration consists of a crown, like most freeways, with sloping pavement that directs flow to either side of the runway. This type of flow is uniform in the direction perpendicular to the velocity and is very shallow. Since these depths are ¼ of an inch (more or less) in magnitude, the relative roughness is high. Some higher relative roughness values for overland flow are presented in Table 3.5 of the HEC-1 Flood Hydro graph Package User's Manual (USACE, 1990). 3-9 Cantor Garage Addition Drainage Report bha, Inc. 41 w u g 15 w <f) Cl'. :, D ~ w i EXAMPLE: Given· Watercourse Distance (D) = 70 Feet Slope(s)=1.3% Runoff Coefficient (C} = 0.41 Overland Flow Time (T) = 9.5 Minutes SOURCE: Airport Drainage, Federal Aviation Administra~on, 1965 T = 1.8 (1.1-C) VD 'Vs FIGURE Rational Formula• Overland Time of Flow Nomograph I 3-3 I Cantor Garage Addition Drainage Report bha, Inc. 42 San Diego County Hydrology Manual Date: June 2003 Section: Page: 3 11 of26 The sheet flow that is predicted by the FAA equation is limited to conditions that are similar to runway topography. Some considerations that limit the extent to which the FAA equation applies are identified below: • Urban Areas -This "runway type" runoff includes: 1) Flat roofs, sloping at 1 % ± 2) Parking lots at the extreme upstream drainage basin boundary (at the "ridge" of a catchment area). Even a parking lot is limited in the amounts of sheet flow. Parked or moving vehicles would "break-up" the sheet flow, concentrating runoff into streams that are not characteristic of sheet flow. 3) Driveways are constructed at the upstream end of catchment areas in some developments. However, if flow from a roof is directed to a driveway through a downspout or other conveyance mechanism, flow would be concentrated. 4) Flat slopes are prone to meandering flow that tends to be disrupted by minor irregularities and obstructions. Maximum Overland Flow lengths are shorter for the flatter slopes (see Table 3-2). • Rural or Natural Areas -The FAA equation is applicable to these conditions since (.5% to 10%) slopes that are uniform in width of flow have slow velocities consistent with the equation. Irregularities in terrain limit the length of application. 1) Most hills and ridge lines have a relatively flat area near the drainage divide. However, with flat slopes of .5% ±, minor irregularities would cause flow to concentrate into streams. 2) Parks, lawns and other vegetated areas would have slow velocities that are consistent with the FAA Equation. The concepts related to the initial time of concentration were evaluated in a report entitled Initial Time of Concentration, Analysis of Parameters (Hill, 2002) that was reviewed by the Hydrology Manual Committee. The Report is available at San Diego County Department of Public Works, Flood Control Section and on the San Diego County Department of Public Works web page. 3-11 Cantor Garage Addition Drainage Report bha, Inc. 43 San Diego County Hydrology Manual Date: June 2003 Section: Page: 3 12 of26 Note that the Initial Time of Concentration should be reflective of the general land-use at the upstream end of a drainage basin. A single lot with an area of two or less acres does not have a significant effect where the drainage basin area is 20 to 600 acres. Table 3-2 provides limits of the length (Maximum Length (LM)) of sheet flow to be used in hydrology studies. Initial Ti values based on average C values for the Land Use Element are also included. These values can be used in planning and design applications as described below. Exceptions may be approved by the "Regulating Agency" when submitted with a detailed study. Element* Natural LDR LDR LDR MDR MDR MDR MDR HDR HDR N.Com G.Com O.P./Com Limited I. General I. Table 3-2 MAXIMUM OVERLAND FLOW LENGTH (LM) & INITIAL TIME OF CONCENTRATION (Ta DU/ .5% 1% 2% 3% 5% Acre LM Ti LM Ti LM Ti LM Ti LM Ti 50 13.2 70 12.5 85 10.9 100 10.3 100 8.7 1 50 12.2 70 11.5 85 10.0 100 9.5 100 8.0 2 50 11.3 70 10.5 85 9.2 100 8.8 100 7.4 2.9 50 10.7 70 10.0 85 8.8 95 8.1 100 7.0 4.3 50 10.2 70 9.6 80 8.1 95 7.8 100 6.7 7.3 so 9.2 65 8.4 80 7.4 9S 7.0 100 6.0 10.9 so 8.7 65 7.9 80 6.9 90 6.4 100 S.7 14.5 so 8.2 65 7.4 80 6.5 90 6.0 100 S.4 24 so 6.7 65 6.1 75 S.1 90 4.9 9S 4.3 43 50 5.3 65 4.7 75 4.0 85 3.8 9S 3.4 50 5.3 60 4.5 75 4.0 85 3.8 95 3.4 50 4.7 60 4.1 75 3.6 8S 3.4 90 2.9 50 4.2 60 3.7 70 3.1 80 2.9 90 2.6 50 4.2 60 3.7 70 3.1 80 2.9 90 2.6 50 3.7 60 3.2 70 2.7 80 2.6 90 2.3 *See Table 3-1 for more detailed description 3-12 10% LM Ti 100 6.9 100 6.4 100 5.8 100 5.6 100 5.3 100 4.8 100 4.S 100 4.3 100 3.5 100 2.7 100 2.7 100 2.4 100 2.2 100 2.2 100 1.9 Cantor Garage Addition Drainage Report bha, Inc. 44 San Diego County Hydrology Manual Date: June 2003 3.1.4.lA Planning Considerations Section: Page: 3 13 of26 The purpose of most hydrology studies is to develop flood flow values for areas that are not at the upstream end of the basin. Another example is the Master Plan, which is usually completed before the actual detailed design of lots, streets, etc. are accomplished. In these situations it is necessary that the initial time of concentration be determined without detailed information about flow patterns. To provide guidance for the initial time of concentration design parameters, Table 3-2 includes the Land Use Elements and other variables related to the Time of Concentration. The table development included a review of the typical "layout" of the different Land Use Elements and related flow patterns and consideration of the extent of the sheet flow regimen, the effect of ponding, the significance to the drainage basin, downstream effects, etc. 3.1.4.lB Computation Criteria (a) Developed Drainage Areas With Overland Flow -Ti may be obtained directly from the chart, "Rational Formula -Overland Time of Flow Nomograph," shown in Figure 3-3 or from Table 3-2. This chart is based on the Federal Aviation Agency (FAA) equation (FAA, 1970). For the short rain durations (<15 minutes) involved, intensities are high but the depth of flooding is limited and much of the runoff is stored temporarily in the overland flow and in shallow ponded areas. In developed areas, overland flow is limited to lengths given in Table 3-2. Beyond these distances, flow tends to become concentrated into streets, gutters, swales, ditches, etc. 3-13 Cantor Garage Addition Drainage Report bha, Inc. 45 San Diego County Hydrology Manual Date: June 2003 Section: Page: 3 14 of26 (b) Natural Or Rural Watersheds -These areas usually have an initial subarea at the upstream end with sheet flow. The sheet flow length is limited to 50 to 100 feet as specified in Table 3-2. The Overland Time of Flow Nomograph, Figure 3-3, can be used to obtain Ti. The initial time of concentration can excessively affect the magnitude of flow further downstream in the drainage basin. For instance, variations in the initial time of concentration for an initial subarea of one acre can change the flow further downstream where the area is 400 acres by 100%. Therefore, the initial time of concentration is limited (see Table 3-2). The Rational Method procedure included in the original Hydrology Manual (1971) and Design and Procedure Manual (1968) included a 10 minute value to be added to the initial time of concentration developed through the Kirpich Formula (see Figure 3-4) for a natural watershed. That procedure is superceded by the procedure above to use Table 3-2 or Figure 3-3 to determine Ti for the appropriate sheet flow length of the initial subarea. The values for natural watersheds given in Table 3-2 vary from 13 to 7 minutes, depending on slope. If the total length of the initial subarea is greater than the maximum length allowable based on Table 3-2, add the travel time based on the Kirpich formula for the remaining length of the initial subarea. 3.1.4.2 Travel Time The T1 is the time required for the runoff to flow in a watercourse (e.g., swale, channel, gutter, pipe) or series of watercourses from the initial subarea to the point of interest. The Ti is computed by dividing the length of the flow path by the computed flow velocity. Since the velocity normally changes as a result of each change in flow rate or slope, such as at an inlet or grade break, the total T1 must be computed as the sum of the Ti's for each section of the flow path. Use Figure 3-6 to estimate time of travel for street gutter flow. Velocity in a channel can be estimated by using the nomograph shown in Figure 3-7 (Manning's Equation Nomograph). 3-14 Cantor Garage Addition Drainage Report bha, Inc. 46 San Diego County Hydrology Manual Date: June 2003 Section: Page: 3 15 of26 (a) Natural Watersheds -This includes rural, ranch, and agricultural areas with natural channels. Obtain T1 directly from the Kirpich nomograph in Figure 3-4 or from the equation. This nomograph requires values for length and change in elevation along the effective slope line for the subarea. See Figure 3-5 for a representation of the effective slope line. This nomograph is based on the Kirpich formula, which was developed with data from agricultural watersheds ranging from 1.25 to 112 acres in area, 350 to 4,000 feet in length, and 2.7 to 8.8% slope (Kirpich, 1940). A maximum length of 4,000 feet should be used for the subarea length. Typically, as the flow length increases, the depth of flow will increase, and therefore it is considered a concentration of flow at points beyond lengths listed in Figure 3-2. However, because the Kirpich formula has been shown to be applicable for watersheds up to 4,000 feet in length (Kirpich, 1940), a subarea may be designated with a length up to 4,000 feet provided the topography and slope of the natural channel are generally uniform. Justification needs to be included with this calculation showing that the watershed will remain natural forever. Examples include areas located in the Multiple Species Conservation Plan (MSCP), areas designated as open space or rural in a community's General Plan, and Cleveland National Forest. (b) Urban Watersheds -Flow through a closed conduit where no additional flow can enter the system during the travel, length, velocity and T1 are determined using the peak flow in the conduit. In cases where the conduit is not closed and additional flow from a contributing subarea is added to the total flow during travel (e.g., street flow in a gutter), calculation of velocity and T1 is performed using an assumed average flow based on the total area (including upstream subareas) contributing to the point of interest. The Manning equation is usually used to determine velocity. Discharges for small watersheds typically range from 2 to 3 cfs per acre, depending on land use, drainage area, and slope and rainfall intensity. Note: The MRM should be used to calculate the peak discharge when there is a junction from independent subareas into the drainage system. 3-15 Cantor Garage Addition Drainage Report bha, Inc. 47 ..6. E Feet 5000 4000 Tc Tc L .L'>.E EQUATION (1~tt385 Time of concentration (hours) Watercourse Distance (miles) Change in elevation along effective slope line (See Figure 3-5)(feet) 3000 2000 1000 0 0 0 ~, 500' 400 300 200 100 30 20 10 5 ' ' '~ ,<9,,, ,{'✓-, ' ' ' ' ' ' SOURCE: California Division of Highways (1941) and Kirpich (1940) ' ' L MIies Feet '1 3000 ' 2000 1800 1600 1400 1200 1000 900 800 700 600 500 400 300 200 L ' Nomograph for Determination of Tc Hours Minutes 4 3 2 30 ' ' ' ' ' 7 6 5 4 3 Tc Time of Concentration (Tc) or Travel Time (Tt) for Natural V«Jtersheds FIGURE ~ Cantor Garage Addition Drainage Report bha, Inc. 48 ------- Design Point >-----------------L-----------------1 Watershed Divide Effective Slope Line ;+-----------------L ________________ ____., Area "A" = Area "B" SOURCE: California Division of Highways (1941) and Kirpich (1940) FIGURE Computation of Effective Slope for Natural Watersheds ~ Cantor Garage Addition Drainage Report bha, Inc. 49 Ql a. 0 cii ., ~ ui 0 ~ 0 1-+--n = .015-~--2% _ -n=.0175 ------::..:.::.. ___ --! 2% Concrete Gutter Paved RESIDENTIAL STREET ONE SIDE ONLY 20 -;,-------t--,--i---1-~1"'--lrt-~l-1"-~IT------'i"--~rt----t--'i"-TI'" 18 -+-------'-----+---+---+->,_----1,---1--+-,..."-.---.. v --+----,.7----.... v ~ f -J.-----+.J.•---~==l=-d------,ltl~-J.-t--lJlq...__~....:::::::..., ~10, I ....::..Z..< ,:,, I 16 ~ ~-~ ,__ 14 -+--------1#'------1--+~,-1-P.....i::-......._-+-......_+,~t----____;::,"""::,,-......_,__,-+--+-,#t--+ 12 ➔------#1---+--'"""'--ll-+'--il-P,-.,t-/ I i --~8 '-.D . .s f "'---..... I L. J , ~ J I ............__ 10 3 2 1.8 1.6 1.4 1.2 1.0 0.9 0.8 0.7 0.6 0.5 0.4 6 7 8 9 10 20 30 40 50 Discharge (C.F.S.) EXAMPLE: Given: Q = 10 S = 2.5% Chart gives: Depth = 0.4, Velocity = 4.4 f.p.s. SOURCE; San Diego County Department of Special District Services Design Manual FIGURE Gutter and Roadway Discharge -Velocity Chart ~ Cantor Garage Addition Drainage Report bha, Inc. 50 EQUATION: V = 1.49 R"• s "2 n 0.3 0.2 0.15 0,10 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0.009 0.008 0.007 0.006 (.) ::::; ::::i ~ 0.005 Cl >-000\)~ I -?a: 0.002 0.001 0.0009 0.0008 0.0007 0.0006 0.0005 0.0004 0.0003 0.2 0.3 0.4 E 0.5 10 20 SOURCE; USDOT, FHWA, HDS-3 (1961) GENERAL SOLUTION Manning's Equation Nomograph 30 20 :;; 6 C. 1.0 0,9 0.8 0.7 0.6 0.5 0.01 0.02 C ' 0.03 C Q) ·o Ii= Q) 0.04 0 (.) (J) (J) ~ r0.05 I (.') 0.06 ::::i 0 Cl'. 0.07 0.08 0.09 0.10 0.2 0.3 0.4 FIGURE ~ Cantor Garage Addition Drainage Report bha, Inc. 51 San Diego County Hydrology Manual Date: June 2003 3.2 DEVELOPING INPUT DATA FOR THE RATIONAL METHOD Section: Page: 3 20 of26 This section describes the development of the necessary data to perform RM calculations. Section 3.3 describes the RM calculation process. Input data for calculating peak flows and Tc's with the RM should be developed as follows: 1. On a topographic base map, outline the overall drainage area boundary, showing adjacent drains, existing and proposed drains, and overland flow paths. 2. Verify the accuracy of the drainage map in the field. 3. Divide the drainage area into subareas by locating significant points of interest. These divisions should be based on topography, soil type, and land use. Ensure that an appropriate first subarea is delineated. For natural areas, the first subarea flow path length should be less than or equal to 4,000 feet plus the overland flow length (Table 3-2). For developed areas, the initial subarea flow path length should be consistent with Table 3-2. The topography and slope within the initial subarea should be generally uniform. 4. Working from upstream to downstream, assign a number representing each subarea in the drainage system to each point of interest. Figure 3-8 provides guidelines for node numbers for geographic information system (GIS)-based studies. 5. Measure each subarea in the drainage area to determine its size in acres (A). 6. Determine the length and effective slope of the flow path in each subarea. 7. Identify the soil type for each subarea. 3-20 Cantor Garage Addition Drainage Report bha, Inc. 52 Study Area SC .. , ... , I . : '7 0 l.i / ', ,, L,- Study Area LA G) Define Study Areas !Two-letter ID) © Define Mapa (or Subregions on Region Basis, © Define Model Subarauon Map Basis @ Define Major Aowpatha in Study Area © Define Regiona on Study Area Buis ••••• ,. Map I • •• Region I • studyA~a(ID)I~ 111 \,, © Define Model Nodea (Intersection of Subaru Boundaries with Aowpath Linea) GIS/Hydrologic Model Data Bue Linkage Setup: Nodu, Subareu, Llnka LA 01 01 03 0 Number Nodu ; FIGURE ~ Cantor Garage Addition Drainage Report bha, Inc. 53 San Diego County Hydrology Manual Date: June 2003 Section: Page: 3 22 of26 8. Determine the runoff coefficient (C) for each subarea based on Table 3-1. If the subarea contains more than one type of development classification, use a proportionate average for C. In determining C for the subarea, use future land use taken from the applicable community plan, Multiple Species Conservation Plan, National Forest land use plan, etc. 9. Calculate the CA value for the subarea. 10. Calculate the L(CA) value(s) for the subareas upstream of the point(s) of interest. 11. Determine P6 and P24 for the study using the isopluvial maps provided in Appendix B. If necessary, adjust the value for P6 to be within 45% to 65% of the value for P24. See Section 3.3 for a description of the RM calculation process. 3.3 PERFORMING RATIONAL METHOD CALCULATIONS This section describes the RM calculation process. Using the input data, calculation of peak flows and Tc's should be performed as follows: 1. Determine Ti for the first subarea. Use Table 3-2 or Figure 3-3 as discussed in Section 3 .1.4. If the watershed is natural, the travel time to the downstream end of the first subarea can be added to Ti to obtain the Tc Refer to paragraph 3.1.4.2 (a). 2. Determine I for the subarea using Figure 3-1 . If T; was less than 5 minutes, use the 5 minute time to determine intensity for calculating the flow. 3. Calculate the peak discharge flow rate for the subarea, where Qp = L(CA) I. In case that the downstream flow rate is less than the upstream flow rate, due to the long travel time that is not offset by the additional subarea runoff, use the upstream peak flow for design purposes until downstream flows increase again. 3-22 Cantor Garage Addition Drainage Report bha, Inc. 54 San Diego County Hydrology Manual Date: June 2003 4. Estimate the T1 to the next point of interest. 5. Add the T1 to the previous Tc to obtain a new Tc. Section: Page: 6. Continue with step 2, above, until the final point of interest is reached. 3 23 of26 Note: The MRM should be used to calculate the peak discharge when there is a junction from independent subareas into the drainage system. 3.4 MODIFIED RATIONAL METHOD (FOR JUNCTION ANALYSIS) The purpose of this section is to describe the steps necessary to develop a hydrology report for a small watershed using the MRM. It is necessary to use the MRM if the watershed contains junctions of independent drainage systems. The process is based on the design manuals of the City/County of San Diego. The general process description for using this method, including an example of the application of this method, is described below. The engineer should only use the MRM for drainage areas up to approximately I square mile in size. If the watershed will significantly exceed I square mile then the NRCS method described in Section 4 should be used. The engineer may choose to use either the RM or the MRM for calculations for up to an approximately I-square-mile area and then transition the study to the NRCS method for additional downstream areas that exceed approximately 1 square mile. The transition process is described in Section 4. 3.4.1 Modified Rational Method General Process Description The general process for the MRM differs from the RM only when a junction of independent drainage systems is reached. The peak Q, Tc, and I for each of the independent drainage systems at the point of the junction are calculated by the RM. The independent drainage systems are then combined using the MRM procedure described below. The peak Q, Tc, and I for each of the independent drainage systems at the point of the junction must be calculated prior to using the MRM procedure to combine the independent drainage systems, as these 3-23 Cantor Garage Addition Drainage Report bha, Inc. 55 San Diego County Hydrology Manual Date: June 2003 Section: Page: 3 24 of26 values will be used for the MRM calculations. After the independent drainage systems have been combined, RM calculations are continued to the next point of interest. 3.4.2 Procedure for Combining Independent Drainage Systems at a Junction Calculate the peak Q, Tc, and I for each of the independent drainage systems at the point of the junction. These values will be used for the MRM calculations. At the junction of two or more independent drainage systems, the respective peak flows are combined to obtain the maximum flow out of the junction at Tc• Based on the approximation that total runoff increases directly in proportion to time, a general equation may be written to determine the maximum Q and its corresponding Tc using the peak Q, Tc, and I for each of the independent drainage systems at the point immediately before the junction. The general equation requires that contributing Q's be numbered in order of increasing Tc. Let Q1, T,, and 11 correspond to the tributary area with the shortest Tc. Likewise, let Q2, T2, and lz correspond to the tributary area with the next longer Tc; Q3, T3, and l3 correspond to the tributary area with the next longer Tc; and so on. When only two independent drainage systems are combined, leave Q3, T3, and 13 out of the equation. Combine the independent drainage systems using the junction equation below: Junction Equation: T, < T 2 < T 3 3-24 Cantor Garage Addition Drainage Report bha, Inc. 56 San Diego County Hydrology Manual Date: June 2003 Section: Page: 3 25 of26 Calculate Qn, Qn, and Qn Select the largest Q and use the Tc associated with that Q for further calculations (see the three Notes for options). If the largest calculated Q's are equal (e.g., Qn = Qn > QT3), use the shorter of the Tc's associated with that Q. This equation may be expanded for a junction of more than three independent drainage systems using the same concept. The concept is that when Q from a selected subarea (e.g., Q2) is combined with Q from another subarea with a shorter Tc (e.g., Qi), the Q from the subarea with the shorter Tc is reduced by the ratio of the I's (h/11); and when Q from a selected subarea (e.g., Q2) is combined with Q from another subarea with a longer Tc (e.g., Q3), the Q from the subarea with the longer Tc is reduced by the ratio of the Tc's (T2/T3). Note #1: At a junction of two independent drainage systems that have the same Tc, the tributary flows may be added to obtain the Qp, This can be verified by using the junction equation above. Let Q3, T3, and 13 = 0. When T1 and T2 are the same, I1 and hare also the same, and T1/T2 and lz/11 = 1. T1/T2 and h/11 are cancelled from the equations. At this point, QT1 = Qn = Qi + Qz. Note #2: In the upstream part of a watershed, a conservative computation is acceptable. When the times of concentration (Tc's) are relatively close in magnitude (within 10%), use the shorter Tc for the intensity and the equation Q = L(CA)I. Note #3: . An optional method of determining the Tc is to use the equation Tc = [(I (CA)7.44 P6)/Q] 155 This equation is from Q = I(CA)I = I(CA)(7.44 P~c645 ) and solving for Tc, The advantage in this option is that the Tc is consistent with the peak flow Q, and avoids inappropriate fluctuation in downstream flows in some cases. 3-25