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HomeMy WebLinkAboutCDP 16-34; HYDROLOGY REPORT; 2017-06-21S ..-. 1 Residence City of Carlsbad, California PREPARED FOR: Brian Lavin 158 Chestnut Avenue Carlsbad, Ca. 92010 PREPARED BY: Coastal Land Solutions 577 Second Street Encinitas, CA 92024 (760) 230-6025 DATE: June 21, 2017 Revised: August 2, 2018 RECEIVED AUG 222018 LAND DEVELOPMENT ENGINEERING HYDROLOGY REPORT for 158 Chestnut Avenue TABLE OF CONTENTS SECTION Executive Summary 1.0 Introduction 1.1 Existing Conditions 1.2 Proposed Project 1.3 Summary of Results and Conditions 1.4 Conclusions 1.5 References 1.6 Methodology 2.0 Introduction 2.1 County of San Diego Criteria 2.2 Runoff coefficient determination 2.3 Hydrology Model Output 3.0 Existing Conditions Hydrologic Model Output 3.1 Proposed Conditions Hydrologic Model Output 3.2 Proposed Storm Drain Hydraulic Calculations 3.3 Attachments Existing Condition Hydrology Map (pocket) Al Proposed Condition Hydrology Map (pocket) A2 Runoff Coefficients for Urban Areas A3 Maximum Overland Flow Length & Initial Time of Concentration A4 Soil Hydrologic Groups A5 Rainfall Isopluvials for 100 year Rainfall Event- 6 hours A6 Rainfall lsopluvials for 100 year Rainfall Event- 24 hours A7 Intensity Duration Design Chart A8 Average Velocity Chart for Overland Flow Time Travel A9 1488 Lavin Residence 8/3/2018 HYDROLOGY REPORT for 158 Chestnut Avenue 1.0 EXECUTIVE SUMMARY 1.1 Introduction This Hydrology Study, for 158 Chestnut Avenue, has been prepared to analyze the hydrologic characteristics of the existing and proposed project site, and determine the existing condition offsite hydrologic characteristics that are conveyed through the proposed project site. This report intends to present 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, as well as the offsite areas, produced by the 100 year 6 hour storm. 1.2 Existing Conditions The proposed project property is located east of Coast Highway 101, West of Highway 5, north of Tamarack Avenue, and is located on the north side of Chestnut Avenue, in the city of Carlsbad, as shown on the vicinity map and aerial shown below. Carlsbad hin , 2 \ Q "ft Tama,,ck Beach Recrl % V41 '\\ \ '\ ?' Sbc 1Jcath d. ' 15SCh.etnotAv.na. '.qeApccmeatcO ThaSta1d <c$ galPu vadaO - ARC C' 00 \\;I, , Ie A, oe C' c' GoogIe .." Vicinity Map 1488 Lavin Residence 8/3/2018 HYDROLOGY REPORT for 158 Chestnu: Avenue Aerial Map The existing site is a 0.10 acre (4,375sf) residential lot with a single family residence. In addition to the existing residential structure, the site currently consists of one driveway, wooden fences, and miscellaneous other hardscape. Existing impervious surface area on the site is 1,900 sf. The percentage of existing impervious surface on the site is 43%. Drainage from the existing site is primarily conveyed in a north to south direction, and sheet flows across the property. This drainage discharges south into the curb and utte at Chestnut Avenue. 1.3 Proposed Project The intent of this project is to remove the entire existing single family residence and grade a building pad, build a new single family residences, construct concrete driveway, sidewalks, bic' retention basin, retaining walls, and install a new water meter. The proposed impervious surface area on the site is 3,914 sf. The percentage of proposed impervious surface on the site is 89%. The proposed increase in impervioLs surface is 2,014 sf, a 106% increase. 1488 Lavin Residence 8/3/2018 HYDROLOGY REPORT for 158 Chestnut Avenue The drainage from the proposed development will be facilitated by overland sheet flow and vegetated drainage swales and bio retention basin. The bio retention basin will allow infiltration, volume reduction, detention, and treatment of storm water runoff. Vegetated drainage swales along the side yards will allow storm water to be treated prior to discharge off site. Runoff from the site discharges south into the curb and gutter at Chestnut Avenue. A runoff coefficient for Medium Density Residential will be used to determine the proposed runoff for a future residential building development. 1.4 Summary of Results Hydrologic analysis of the existing (pre-developed) and proposed (post- developed) conditions of the proposed project site is included in this report as section 3.1 and 3.2 respectively. Hydraulic analysis of the proposed conditions are included in this report as section 3.3. The hydrologic analysis is used in this report to approximate a peak flow at an assumed point of discharge in the existing condition, to quantify a pre and post developed condition peak flow. This assumption is made to develop a model that generates conservative peak flows to ensure that the storm drain system will be capable of safely conveying stormwater. The following summarizes the peak discharges at three points of discharge that resulted from performing hydrologic analysis of the project site in both the proposed developed and existing condition: Point of Existing Conditions Developed Conditions Discharge Qioo Tc AREA Qioo Tc AREA (cfs) (mm.) (acres) (cfs) (mm.) (acres) D-25 curb outlet Node 4) 0.29 6.90 0.065 D-27 curb outlet (node 1) 0.14 8.41 0.035 (Chestnut Avenue) 0.31 7.93 0.10 0.40 8.41 0.100 The project site hydrologic models for both the pre- and post-developed conditions encompass a total area of 0.10 acres. Evaluating the two models, the proposed development will increase the amount of runoff from the project site by 0.09 cfs or 30%. This increase is based on having a single family building residences, driveway, and hardscape areas. Flow to the proposed D-27 curb outlet is 0.14 cfs. A double 3" inch pvc pipe sidewalk underdrain, at 1% slope minimum, shall be constructed at that location. 1488 Lavin Residence 8/3/2018 HYDROLOGY REPORT for 158 Chestnut Avenue The double 3" inch pvc pipe can handle 0.13 cfs x 2 = 0.26 cfs (See section 3.3). Flow to the proposed D-25 curb outlet is 0.29 cfs. The sidewalk underdrain shall be constructed at 1% slope minimum (See section 3.3). 1.5 Conclusions As stated in section 1.4, the project site hydrologic models for both the pre- and post-developed conditions encompass a total area of 0.10 acres. Evaluating the two models, the proposed development will increase the amount of runoff from the project site by 0.09 cfs or 30%. The increase in runoff will be mitigated by creating a bio retention basin at the front yard, or west side of the site. The required detention volume is V= 0.09 cfs x (60 s/mm) x 8.41mm (Tc) = 45 cubic feet. The bio retention basin will allow infiltration and volume reduction by adding a gravel drainage layer underneath. Total proposed are of the basin is 17' feet long x 15' feet wide x 6" inch deep, with vegetated detention basin with engineered sandy loam soil media layer and 3/4 inch rock layer. A 12" area drain overflow riser, and 4" perforated pipe placed within the rock layer, shall be constructed to allow the basin to drain to the street. See detail on grading plan. Total proposed detention volume is 127 cubic feet. Drainage from the proposed residence is directed into a bio retention basin and vegetated swale, prior to discharge off site. The bio retention basin and vegetated swales will provide treatment and detention. Based on the calculation in section 3.3, the proposed D-25 and D-27 curb outlet sidewalk underdrains can handle the runoff. It is anticipated that the proposed storm drain system will maintain the historic discharge locations of the existing drainage patterns. The proposed drainage system will safely convey the entire 100-year peak flow generated by onsite runoff. 1.6 References "San Diego County Hydrology Manual" revised June 2003, County of San Diego, Department of Public Works, Flood Control Section. "San Diego County Storm water Urban Mitigation Plan (SUSMP)", revised August 2012, County of San Diego. 1488 Lavin Residence 8/3/2018 HYDROLOGY REPORT for 158 Chestnut Avenue 2.0 METHODOLOGY 2.1 Introduction The hydrologic model used to perform the hydrologic analysis presented in this report utilizes the Rational Method (RM) equation, Q=CIA. The 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 P6 x D 15 Where: = Intensity (in/hi) P6 = 6-hour precipitation (inches) D = duration (minutes - 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) but sometimes as gallons per minute (gpm)). The RM equation is as follows: Q=CIA Where: Q= flow (in cfs) C = runoff coefficient, ratio of rainfall that produces storm water runoff (runoff vs. infiltration/evaporation/absorption/etc) = average rainfall intensity for a duration equal to the Tc for the area, in inches per hour. A = drainage area contributing to the basin in acres. 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, which 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. In addition to the above Rational Method assumptions, the conservative assumption that all runoff coefficients utilized for this report are based on type "D" soils. 1488 Lavin Residence 8/3/2018 HYDROLOGY REPORT for 158 Chestnut Avenue 2.2 County of San Diego Criteria As defined by the County Hydrology Manual dated June 2003, the rational method is the preferred equation for determining the hydrologic characteristics of basins up to approximately one square mile in size. 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). One of the variables of the RM equation is the runoff coefficient, C. The runoff coefficient is dependent on the percent of impervious surface, land use, and soil type, and the County of San Diego has developed a table of Runoff Coefficients for Urban Areas to be applied to basin located within the County of San Diego. The table 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, C, for each soil type class. 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 Runoff Coefficient Determination As stated in section 2.2, the runoff coefficient is dependent on percent impervious surface, land use, and soil type, and the County of San Diego has developed a table of Runoff Coefficients for Urban Areas to be applied to basin located within the County of San Diego. Table 3-1, included in the appendix, categorizes the land use, the associated development density (dwelling units per acre) and the percentage of impervious area. The total number of dwellings proposed is 1, and the total developed lot area is roughly equal to 0.10 acres. The dwelling unit per acre (DU/A) ratio is equal 10 DU/A which corresponds to Medium Density Residential DU/A of 10.9 or less on table 3-1. Assume soil type is D, the runoff coefficient is 0.60. For the both the existing and proposed development on site conditions, a weighted C value is determined by the percentage of impervious and pervious surfaces. The runoff coefficient of 0.90, for impervious surface, and 0.45 for pervious surface are used. 1488 Lavin Residence 8/3/2018 HYDROLOGY REPORT for 158 Chestnut Avenue 3.0 Hydrology Calculations 3.1 Existing Conditions Hydrology Calculations SITE RUNOFF COEFFICIENT (DEVELOPED): C= 0.60 (Table 3-1) SITE RUNOFF COEFFICIENT (WEIGHTED): C = 0.90 (Area impervious) + 0.45 (Area pervious) (Total Lot Area) C= 0.90 (1.900 s.f.) + 0.45 (2.475 s.f 4,375 s.f. C=1.710 s.f.+1 113 s.f. 4,375 s.f. C= 0.65 Flow across initial sub area A, nodes 3 to 2: C= 0.65 A= 0.026 acres L= 25 ft S = (52.40-51.79)/25 = 2.4% Ti =,3.65 mm. (Table 3-2) hoo 5.48 in/hr Qnode2 =CAI = (0.65)(0.026)(5.48) = 0.09 cfs Flow across sub area B nodes 2 to 1: A=0.074 acres L= 77ft S = 51.79-51.63)/77 = 0.02% V = (Pavers) = 0.5 ft/s T(flow) = (77ft I 1 ft/s)/ 60 s/rn = 1.28 mm Tc = T1 + T(Pavers) = 6.65 min.+ 1.28 mm. = 7.93 minutes 1488 Lavin Residence 8/3/2018 HYDROLOGY REPORT for 158 Chestnut Avenue lioo = 4.89 in/hr Qnodel = [CA, + CAb ]1100 = [0.63 (0.026) + 0.63(0.074)] 4.89 Qnode1O.31 cfs 1488 Lavin Residence 8/3/2018 HYDROLOGY REPORT for 158 Chestnut Avenue 3.2 Proposed Conditions Hydrologic Model Output SITE RUNOFF COEFFICIENT (DEVELOPED): C= 060 (Table 3-1) SITE RUNOFF COEFFICIENT (WEIGHTED): C = 0.90 (Area impervious) + 0.45 (Area pervious) (Total Lot Area) 0= 0.90 (3,914 s.f.) + 0.45 (461 s.f.) 4,375 s.f. 0=3,522 s.f. + 207 s.f. 4,375 s.f. 0= 0.85 Flow across initial sub area A, nodes 3 to 2: 0= 0.85 A= 0.026 acres L= 34ft S = (54.53-54.22)/34 = 1% Ti =7.9 mm. (Table 3-2) hoo = 4.90 in/hr Qnode2 =CAI = (0.85)(0.026)(4.90) = 0.11 cfs Flow across sub area C nodes 2 to 1: A=0.009 acres L= 77ft S = (54.22-51.50)/77 = 3.5% V = (ConcreteNegetated swale/pvc pipe) = 2.5 ft/s T(flow) = (77ft / 2.5 ft/s)/ 60 s/m = 0.51 mm Tc = T + T(channel) = 7.9 min.+ 0.51 mm. = 8.41 minutes Iwo = 4.71 in/hr 1488 Lavin Residence 8/3/2018 HYDROLOGY REPORT for 158 Chestnut Avenue Qnodel = [CAa + CAC] Ii00 = [0.85 (0.026) + 0.85(0.009)] 4.71 Qnodel = 0.14 cfs Qnodel = [CAa + CA0 + CAb] 1100 = [0.85 (0.026) + 0.85(0.009) + 0.85(0.065)] 4.71 Qnodel total = 0.40 cfs Flow across sub area B nodes 5 to 4: A=0.065 acres L= 74ft S = (55.60-54.00)/74 = 2 % Tc = 6.9 minutes Iioo = 5.35 in/hr Qnode4 =CAI = (0.85)(0.065)(5.35) = 0.29 cfs Qnode4 = 0.29 cfs Flow across sub area B nodes 4 to 1: Channel Flow V = (pvc pipe/paved gutter) = 4 ft/s T(flow) = (74ft / 4.0 ft/s)/ 60 s/rn = 0.30 mm Tc = T + T(channel) = 6.9 min.+ 0.30 mm. = 7.2 minutes 1100 = 5.20 in/hr Qnode4 =CAI = (0.85)(0.065)(5.20) = 0.28 cfs Qnodel =0.28 cfs 1488 Lavin Residence 8/3/2018 HYDROLOGY REPORT for 158 Chestnut Avenue 3.3 Proposed Storm Drain Hydraulic Calculations 3" PVC PIPE, 5=1% (D-27 CURB OUTLET) Worksheet for Circular Channel Project Description Project File c:\from rooioIthhaestad\academicfmw4 inch p.fm2 Worksheet 3 PVC DRAIN PIPE Row Element Circular Channel Method Manning's Formula Solve For Discharge Input Data Mannings Coafficienl 0.009 Channel Slope 1.0000% Depth 3.0 in Diameter 3.00 in Results Discharge 013 cts Flow Area 0.05 ft2 Wetted Perimeter 0.79 ft Top Width 0.00 It Critical Depth 0.21 ft Percent Full 100.00 Critical Slope 0.009342 ftf It Velocity 2.60 ft's Velocity Head 0,11 ft Specific Energy FULL ft Froide Number FULL Maximum Discharge 0,14 cis Full Flow Capacity 0.13 cis Full Flow Slope 0.010000 WIt 1488 Lavin Residence 8/3/2018 HYDROLOGY REPORT for 158 Chestnut Avenue D-25 CURB OUTLET (SIDEWALK UNDERDRAIN) Worksheet for Rectangular Channel Project Description Project File cMrorn root.oldhsIadacademi6\fmw'4 inch p.frn2 Worksheet D25 Rectangular channel Flow Element Rectangular Channel Method Mannings Formula Solve For Channel Depth Input Data Mannings Coefficient 0.013 Channel Slope 1.00000/0 Bottom Width 3.00 ft Discharge 0.29 cfs Results Depth 0.7 in Flow Area 0,17 ft2 Wetted Perimeter 3.12 It Top Width 3.00 ft Critical Depth 0.07 ft Critical Slope 0.1006448 Wft Velocity 1.67 ftis Velocity Head 0.04 ft Specific Energy 0,10 ft Froude Number 1.22 Flow is supercritical. 1488 Lavin Residence 8/3/2018 HYDROLOGY REPORT for 158 Chestnut Avenue 0-25 CURB OUTLET (SIDEWALK! NDERDRAIN) Worksheet for Rectangular Channel Project Description Project Filee cMrom rootoldthaestathacademicfmw14 inch pim2 Worksheet D-25 Rectangt.Iar channel Flow Element Rectangular Channel Method Mannings Formula Solve For Discharge Input Data Mannings Coefficient 0.013 Channel Slope 1.0000% Depth 3.0 in UottomWdth 3.00 ft Results Discharge 307 cIa Flow Area 0.75 112 Wetted Perimeter 3.50 It Top Width 3,00 ft Critical Depth 0.32 It Critical Slope 0.004660 ftift Velocity 4.09 ftFs Velocity Read 0.26 ft Specific Energy 0.51 ft Frotide Number 1.44 Row is supercrlticaL 1488 Lavin Residence 8/3/2018 LEGEND ITEM SYMBOL urCARa.oay NOW SUB AA NAME FLOW PATH 9JB-BAMN NCIJAXIARY 9J8-BASN AREA RECAX1Y BOJPWARY PROPORED coNTouRs aw OCISTING CONTOURS -- - + GRAPAIC SCALE i•-iO 0 10 20 30 EXISTING CONDITION HYDROLOGY MAP 0 COAMMLLAPWsmunomm !77 XIT c)BCFAI Fli O ==CA mm FAX t CLS# 1448 LEGEND ITEM SYMBOL HYDROLOGY NODE () SUB AREA NAME () FLOW PATH SUB-BASIN BOUNDARY SUB-BASIN AREA BUILDING FOOTPRINT PROPOSED CONCRETE HARDSCAPE PROPERTY BOUNDARY PROPOSED CONTOURS EXISTiNG CONTOURS - - -S---- - D-27 CURB OUTLET WITH DOUBLE 3' PIPE D=25 CURB OUTLET BROOKS BOX DRAIN INLET 0 1+ GRAPHIC SCALE 1=10 0 10 20 30 r . PROPOSED CONDITION HYDROLOGY MAP It FS-55.60 1. LLJ • AREA B - 0.065 Ad IE-5 L50 EX FL -51.50 eft FS-553 __ /Qu-o29 - p - -\ . =-S,• yS.• EX Fl. -51.50 rs Ac—o.009Ci — ooutjo t-1114 cfa - Tc-O0 IE=l.85 1 COASTAL LAND SOLUTIONS, INC. ll 577 SECDO STREET CA SM ) ETCDIITAS PH C7I 23O- FAX (7w) -EO CLS# 1'I4B A2 ........................................... San Diego County Hydrology Manual Section: 3 Date: June 2003 Page: 6of26 Table 3-1 RUNOFF COEFFICIENTS FOR URBAN AREAS Land Use I Runoff Coefficient "C" Soil Type NRCS Elements County Elements -- % J.MPER. A B C D Undisturbed Natural Terrain (Natural) Low Density Residential (LDR) Low Density Residential (LDR) LOW Density Residential (LDR) Medium Density Residential (MDR) Medium Density Residential (MDR) dium Densit -Residential (MDR),) Medium Density Residential (MDR) High Density Residential (HDR) High Density Residential (HDR) Commercial/industrial (N. Corn) Commercial/Industrial (G. Corn) Commercial/Industrial (O.P. Corn) Commercial/Industrial (Limited I.) Commercial/industrial (General 1.) Permanent Open Space Residential, 1.0 DU/A or less Residential, 2.0 DU/A or less Residential, 2.9 DU/A or less Residential, 4.3 DU/A or less Residential, 7.3 DU/A or less di)9DU/A -or less' Residential, 14.5 DU/A or less Residential, 24.0 DU/A or less Residential, 43.0 DU/A or less Neighborhood Commercial General Commercial Office Professional/Commercial Limited Industrial General Industrial 0.25 0.30 0.35 0.32 0.36 0.41 0.38 0.42 0,46 0.41 0.45 0.49 0.45 0.48 0.52 0.51 0.54 0.57 Q) 0.58 0.60 0.63 0.67 0.69 0.71 0.77 0.78 0.79 0.77 0.78 0.79 0.80 0.81 0.82 0.84 0.84 0.85 0.84 0,84 0.85 0.87 0.87 0.87 0* 0.20 10 0.27 20 0.34 25 0.38 30 0.41 40 0,48 50 0.55 65 0.66 80 0.76 80 0.76 85 0.80 90 0.83 90 0.83 95 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 '43 San Diego County Hydrology Manual Section: 3 Date: June 2003 Page: 12of26 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 T1 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. Table 3-2 MAXIMUM OVERLAND FLOW LENGTH (LM) & INITIAL TIME OF CONCENTRATION (T' Element* DU/ Acre .5% 1% 2% 3% 5% 10% LM Tj LM Ti LM T1 LM TiLM Tj LM T1 Natural 50 13.2 70 12.5 85 10.9 100 10.3 100 8.7 100 6.9 LDR 1 50 12.2 70 11.5 85 10.0 100 9.5 100 8.0 100 6.4 LIJR 2 50 11.3 70 10.5 85 9.2 100 8.8 100 7.4 100 5.8 LIER 2.9 50 10.7 70 10.0 85 8.8 95 8.1 100 7.0 100 5.6 .MDR 4.3 50 10.2 70 9.6 80 8.1 95 7.8 100 6.7 100 5.3 MDR 7.3 50 9.2 65 8.4 80 7.4 95 7.0 100 6.0 100 4.8 (MDR (ö) (j) MDR 14.5 50 8.2 65 7.4 80 6.5 90 6.0 100 5.4 100 4.3 HDR 24 50 6.7 65 6.1 75 5.1 90 4.9 95 4,3 100 3.5 HDR 43 50 5.3 65 4.7 75 4.0 85 3.8 95 3.4 100 2.7 N. Corn 50 5.3 60 4.5 75 4.0 85 3.8 95 3.4 100 2.7 G. Corn 50 4.7 60 4.1 75 3.6 85 3.4 90 2.9 100 2.4 G.P./Corn 50 4.21 60 3.7 70 3.1 80 2.9 90 2.6 100 2.2 Limited 1. 50 4.2 60 3.7 70 3.1 80 2.9 90 2.6 100 2.2 General I. 50 3.7 60 3.2 70 2.7 80 2.6 90 2.3 100 1.9 *See Table 3-1 for more detailed description ,411 3-12 b Orange County ........................................... County of San Diego Hydrology Manual Soil Hydrologic Groups Soil Groups [1111] Group A Group B Group C Group Undetermined Data Unavailable Ip 7 E S 3 0 3MHes ........................................... County of San Diego 33-3 orange Counti I 3330 Hydrology Manual - Riverside County Rainfall Isopluvials 33 15- - - - .-- _--..—::: 25 l0O Year Rainfall Event -6Hours OCANSIOE * 25 .--- '0 -. I IsopuviaI (inches) I - cARL58AD .-..- - NcIMrs - 33 00 0 _? _'" 0Y SOLAP4ABEACH ,ow V - 3 — Q DEL MAR - -.. - ---S / I -. -., Q :- •----, - (T 1l1r3. ON V j - .- 32'45- SO ............ DPW C A IMPERIAL BEACH -) -. - / - - .- - -- - - M e X I C - WO N ca,tes E s 3 0 3Mltes ........................................... 33 3O Orange -. County 1 .. .•--.?. - - -..___ ____ .____ _______ County of San Diego Hydrology Manual Riverside County " - Rainfall Is V.- - V*V0._VV__ 33 100 Year Rainfall Event 24 Hours .--- _______ V /. : . ./. . ... .:.:• .. •. ....6. a tsop4uvial (Inches) 4.0 —• ' ' 50 C) - . - . ... 'S 3300 3300 - CD 0 DEL.'J . -~ /: .bp.•........ OD . .. .... .. — i..i ': .. . . . 0 • . :'-. •. . \ 3 - 32*46 - ;. . ... .. ........ ..•• ... _______________________________ ..-. • ' ..-. 0. -,.......... . 'GIS SanGIS N A - POVOEOWflflt flYOfflftE.4MEfl IMPERIAL B .. I .. .. .... . . .. A e x i C E 32'3V -.. - ........ .• ______________ - 32'30 -a-n-WA----- 3 0 3Miles - M/ Minutes Hours Duration Directions for Application: From precipitation maps determine 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). 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). Plot 6 hr precipitation on the right side of the chart. Draw a line through the point parallel to the plotted tines. This line is the intensityduration curve for the location being analyzed. Application Form: 1 (a) Selected frequency year (b)P6 2.5in.P24 =4.O= 62 %2 . (c) Adjusted P6t2t in. 55 so (d) t 3 •,,,,,,,,,,,,,,,,,,mtn. 4.5 (e) I in/hr. 4.0 35 Note: This chart replaces the Intensity-Duration-Frequency 3.0 curves used since 1965. 9 ç PS I 18 2 25 3 35 4 I I 45 5 I 65 6 S 2,63 3.96 5.27 6.59 7,90 9,22 1004 1186 13,17 1449 1581 7 21 3 6424 530 636 742 848 94 1000 1186 1272 10 1.58 253 3.37 4.21 5.05 5.90 8.76 7.58 8.42 927 10.11 15 1.30 1,95 2.59 3.24 3.89 4.54 519 5.84 6.49 7.13 778 20 9.08 1.32 3,15 2.55 3.23 3.77 4.31 425 5.39 5.92 546 25 023 ',40 1.87 2.23 2.80327 3.73 4.20 4.67 5.13 0.60 30 0.83 1.24 1.86 2.07 2.49290 3.32 3,73 4.15 4.56 4.88 40 8.09 1.03 i.:39 1.72 2.07 2.41 276 3.10 3.45 3,79 50 060 0.90 1.19 1.40 9.79 2.03 2.39 2.69 2.96 3.28 3.56 60 8.53 0.30 1.06 1.33 1.59 1.86 2.12 2.39 255 2.92 ' 3.18 90 0.41 0.61 0.62 1.02 1.23 1,43 1.63 1.84 2.04 2.25 ' 2.45 120 0.34 0.51 0.65085 1.02 11,19 1.36 1.53, 1.70 167 2.04 150 0.29 0.44 0.59 0,73 0.88 1 03 116 1.32 1.47 1.62 1.75 180 8.26 0.39 0,5' 0,65 0.78 0,91 1.04 1.18 1.31 J,1W 1.57 240 0.22 0330.430240.65 0.76 0.87 0.98 108 '1.19 i30 300 0.19 0.28038 0.47 0.58 0.65 0.75 0.80 0.84 1.03 1.13 360 0.17 025 013 042 0t'O 0'8 0' 07. 084 092 100 2.0 1.5 1,0 F I G U R E Intensity-Duration Design Chart - Template II 30 1 0.5 0.1 0.2 0.3 0.5 1 2 3 5 10 20 velocity (ft/sec) Reprinted from SCS TR-55-1975. TR-55--1986 citains a simi- lar graph for shallow-concentrated flow over paved and unpaved surfaces, but it does not contain this particular graph. Figure 20.4 SCS Average Velocity Chart for Overland Flow Travel Time