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HomeMy WebLinkAboutCT 11-02; LA COSTA VISTA; HYDROLOGY STUDY; 2013-06-06Hydrology Study La Costa Vista Project No. CT 11-02 Carlsbad, California (Dwg No. 477-7A) Q § z < rn rn ^ -fl o 2: G) c=> Diste Prepared For: TMS, JEREZ INVESTMENTS, LLC 19196 Sierra Isabelle Irvine, California 92603 Prepared By: Surender Dewan, P.E. DMS Consultants, Inc. 12371 Lewis Street, Suite 203 Garden Grove, California 92840 714.740.8840 June 06, 2013 CONSULTANTS, INC. CIVIL ENGINEERS 1 I P a g e 6 z o LU JEREZ COURT CARLSBAD Site Description The proposed project is located in the City of Carlsbad at the terminus of Jerez Court @ 7500 Jerez Court on a 0.41 acre site. The proposed project is a 7-unit airspace condominium project. Purpose The purpose of this study is to determine the total runoff generated for a storm of six (6) hour duration for one hundred (100) year frequency and design an infiltration system to store the increase in volume of runoff between the pre and post runoff condition. 2 I P a g e Section 1.0 100 Year Hydrology Calculations 1.1 Rainfall I The 100 year 6 hr rainfall depth was taken from the San Diego County Hydrology Manual isopluvial maps. Figure 1 below is an enlarged copy ofthe applicable section ofthe map. 1.1.1 Existing Condition Rainfall Rainfall for the existing condition was taken from the Manual. 1.1.2 Proposed Condition Rainfall The total 100 year storm depth for the proposed condition was calculated by subtracting the Water Quality Depth (see I below) from the 100 year storm from the Manual Figure 1100 Year 6hr Isopluvials 1.2 Soil Type The hydrologic soil type for the area of the proposed tract is listed as "C" in the Manual Appendix A. Runoff Coefficients Runoff coefficients for the pre and post project condition were taken from Table 3-1 ofthe Hydrology Manual. (See attached table 3-1.) 1.3 Time of Concentration (Tc) 1.3.1 Existing Condition Tc The lot currently drains, via overland flow, to the southeast with an average slope of 2%. The initital time of concentration (Ti) was estimated using Table 3-2 of the Hydrology Manual (See attached Table 3-2). The Tt for the rest of the flow distance was estimated using Manning's equation assuming a broad open CARLSBAD Figure 2 Soil Type swaie with a 20:1 side slope to calculate the flow velocity. See the attached hydraulic calculations for the swale travel time. These values were entered into an Excel spreadsheet that calculates the Tc and the corresponding I per the equation on Section 3 page 7 of 26. 1.3.2 Proposed Condition Tc In the proposed condition the lots drain to a concrete swale in the center ofthe tract which conveys the flows via inlet to onsite landscape areas. The initial Ti was estimated using Table 3-2 of the Hydrology Manual. The velocity in the swale was estimated using Manning's equation and the velocity in the pipe was calculated using V = Q/A and assuming the pipe will be flowing full. These values were entered into an Excel spreadsheet that calculates the Tc and the corresponding I per the equation on Section 3 page 7 of 26. 1.3.3 Conclusion Table A gives the pre and post project runoff for the four subareas on the site.The 100 year 6 hr flow rate in the existing condition is 0.46 cfs and the proposed flow rate is 1.27 cfs for an increase from the site of 0.81 cfs. Hydraulic Evaluation Summary - TABLE A Subarea Pre-Project Post-Project C 1 A Q C 1 A a Difference (in/hr) (acres) (cfs) (in/hr) (acres) (cfs) (cfs) A 0.30 3.15 0.070 0.07 0.69 3.87 0.070 0.19 0.12 B 0.30 3.77 0.050 0.06 0.69 3.77 0.050 0.15 0.09 C 0.30 3.27 0.130 0.13 0.69 4.33 0.130 0.39 0.26 D 0.30 3.36 0.210 0.21 0.69 3.81 0.210 0.55 0.34 Total 0.46 1.27 0.81 4 I Page 100 Year Hydrology Calculations for Jerez Townhomes Area A Site Data Value Units Graded Area 3049.2 sf Soil Group C Pre Project Runnoff Coefficient "C" 0.30 Post Project Project Runnoff Coefficient "C" 0.69 Pre Proiect 100 vear 6hr Runoff Pre Project Ti 10.90 min Earth Swale Length 150.00 ft Earth Slope 0.02320 percent Earth Swale Z 20.00 Earth Swale N 0.025 Earth Swale Flow Depth 0.100 ft Earth Swale Velocity 0.34 ft/sec Earth Swale Tt 7.31 min Tc = Ti + Tt 18.21 min 100 year 6 hr Depth 2.75 in 100 year 6 hr intensity 3.15 in/hr 100 Year flow rate 0.07 cfs Post Proiect 100 vear 6hr Runoff Post Project Ti 5.10 min Length 120.00 ft Slope 0.095 percent Swale Z 50.00 Swale N 0.02 Swale Flow Depth 0.086 ft Swale Velocity 0.52 ft/sec Swale Tt 3.88 min Tc 8.98 min 100 year 6 hr Depth 2.75 in Infiltration Depth (See Storm Water Calculations) 0.61 in Effective 100 6hr Depth 2.14 in 100 year 6 hr intensity 3.87 in/hr Graded Area 3049.20 ft'^2 100 Year flow rate 0.19 cfs 100 Year Hydrology Calculations for Jerez Townhomes Area B Site Data Value Units Graded Area 2178 sf Soil Group C Pre Project Runnoff Coefficient "C" 0.30 Post Project Project Runnoff Coefficient "C" 0.69 Pre Proiect 100 vear 6hr Runoff Pre Project Ti 10.90 min Earth Swale Length 150.00 ft Earth Slope 0.02320 percent Earth Swale Z 20.00 Earth Swale N 0.025 Earth Swale Flow Depth 0.059 ft Earth Swale Velocity 0.86 ft/sec Earth Swale Tt 2.89 min Tc = Ti + Tt 13.79 min 100 year 6 hr Depth 2.75 in 100 year 6 hr intensity 3.77 in/hr 100 Year flow rate 0.06 cfs Post Proiect 100 vear 6hr Runoff Post Project Ti 5.10 min Length 78.00 ft Slope 0.015 percent Swale Z 50.00 Swale N 0.02 Swale Flow Depth 0.078 ft Swale Velocity 0.48 ft/sec Swale Tt 2.69 min Tc 7.79 min 100 year 6 hr Depth 2.75 in Infiltration Depth (See Storm Water Calculations) 0.61 in Effective 100 6hr Depth 2.14 in 100 year 6 hr intensity 4.24 in/hr Graded Area 2178.00 ft'^2 100 Year flow rate 0.15 cfs Site Data Value Units Graded Area 5662.8 sf Soil Group C Pre Project Runnoff Coefficient "C" 0.30 Post Project Project Runnoff Coefficient "C" 0.69 Pre Proiect 100 vear 6hr Runoff Pre Project Ti 10.90 min Earth Swale Length 150.00 ft Earth Slope 0.02320 percent Earth Swale Z 20.00 Earth Swale N 0.025 Earth Swale Flow Depth 0.126 ft Earth Swale Velocity 0.40 ft/sec Earth Swale Tt 6.27 min Tc = Ti + Tt 17.17 min 100 year 6 hr Depth 2.75 in 100 year 6 hr intensity 3.27 in/hr 100 Year flow rate 0.13 cfs Post Proiect 100 vear 6hr Runoff Post Project Ti 5.10 min Length 90.00 ft Slope 0.009 percent Swale Z 50.00 Swale N 0.02 Swale Flow Depth 0.155 ft Swale Velocity 0.62 ft/sec Swale Tt 2.44 min Tc 7.54 min 100 year6 hr Depth 2.75 in infiltration Depth (See Storm Water Calculations) 0.61 in Effective 100 6hr Depth 2.14 in 100 year 6 hr intensity 4.33 in/hr Graded Area 5662.80 ft'^2 100 Year flow rate 0.39 cfs 100 Year Hydrology Calculations for Jerez Townhomes Area D Site Data Value Units Graded Area 9147.6 sf Soil Group C Pre Project Runnoff Coefficient "C" 0.3 Post Project Project Runnoff Coefficient "C" 0.69 Pre Proiect 100 vear 6hr Runoff Pre Project Ti 10.90 min Earth Swale Length 150.00 ft Earth Slope 0.02320 percent Earth Swale Z 20.00 Earth Swale N 0.025 Earth Swale Flow Depth 0.152 ft Earth Swale Velocity 0.45 ft/sec Earth Swale Tt 5.53 min Tc = Ti + Tt 16.43 min 100 year 6 hr Depth 2.75 in 100 year 6 hr intensity 3.36 in/hr 100 Year flow rate 0.21 cfs Post Proiect 100 vear 6hr Runoff Post Project Ti 5.10 min Length 164.00 ft Slope 0.009 percent Swale Z 50.00 Swale N 0.02 Swale Flow Depth 0.155 ft Swale Velocity 0.67 ft/sec Swale Tt 4.07 min Tc 9.17 min 100 year 6 hr Depth 2.75 in Infiltration Depth (See Storm Water Calculations) 0.61 in Effective 100 6hr Depth 2.14 in 100 year 6 hr intensity 3.81 in/hr Graded Area 9147.60 ft'^2 100 Year flow rate 0.55 cfs Hydraulic Evaluation Summary Subarea Preproject Post Project C 1 A Q C 1 A Q Difference (in/hr) (acres) (cfs) (in/hr) (acres) (cfs) (cfs) A 0.30 3.15 0.070 0.07 0.69 3.87 0.070 0.19 0.12 B 0.30 3.77 0.050 0.06 0.69 3.77 0.050 0.15 0.09 C 0.30 3.27 0.130 0.13 0.69 4.33 0.130 0.39 0.26 D 0.30 3.36 0.210 0.21 0.69 3.81 0.210 0.55 0.34 Total 0.46 1.27 0.81 SAN DIEGO HYDROLOGY MANUAL (ATTACHMENTS) Table 3.1 and Table 3.2 San Dk£o Comity Hydrology Miuual Date: June 2003 Section: 3 6 of 26 JAih i-l RUNOFF COEFnCIEXTS FOR ITIB-AN ARE.4S Land Use RnoofiTCoeffioent "C Soil Type NRCS Elements Couaty Elemeiitti SIMPER A B C D Undunubed Natiml Teiraia (Natural) Pennaneot Open Space 0.20 0.25 0.35 Low Density RctidtBtial (LDR) R«i(ientiaL 1.0 DU A or less 10 0.27 0.J6 0.41 Low Density Resifieiitial (LDR) ResidrntiaL 2.0 DU A or less 20 C Undeveloped 0.42 0.46 Low Dentiiy R«»dential (LDR) ReMdential, 2 9 DU'A or less 25 038 041 0.45 0,49 Jrtednua DMsily Kesideotial (MDR) Re«ideiitiaL 4.5 DU.iA ot less 30 0.41 0.45 0.48 0.52 Mednini Density Kestdeutial (MDR) RiKideatiaL 7.3 DU/A ot less 40 0.48 0.51 0.54 0.57 Medttun, Densily Residential (MDR) ResidemiaL 10.9 DU A or less 45 0.32 0.54 0.57 0.60 Medivin Deiuiiy Residcntid (MDR) Resideatial. 14 S DU'A or te^^ 50 055 0 58 0.60 06} Bipk Deo^ Resideeiial (HDR) ResidentiaL 24.0 DU'A or less 65 0.66 0.67 ——> 0.69 0.71 tbpi Deosiiy Rciidcotial (HDR) ResideotiaL 43.0 DU'A or less SO 0.?6 078 0.79 Ccmjniercial'Iiidustnal (N. Com) Neifhbothood Conuatrcial SO C developed 0.7S 0.79 Cotmnmial'Iodtistrial (G. Com) Genera] Commercial 85 080 0.80 0.81 082 C««n»erciali1itdtt$trial (O P COMI) Office PtofiMMOwaWoowwdal 90 0.83 0.84 0.84 085 CoaimerciaL'Iadttitnal (Limited I.) Ltmiied Ifldosirial 90 0.83 0.84 0.S4 0.85 Commtxcial'Iadmtnal (GciKfal I.) General Iiutttsinal 9S 0.87 0.87 0.S7 0.87 •The values associated with 0*.» iiqpervioits may be med for direct calculstioo of tbe runoff coefiTicieut as described m Sec (too 312 (lepresecting tbe pervious runoff coefficKOt. Cp, for the soil type), or for areas that will re mam undistwbed in perpetuity. Justification must be given that lhe area will remajn nannal f6re\-ei (e.g.. the area is localed in ClcvelMidKstioaal Forest). DU A - dwelling umts per acre NRCS - NatioBal Resources Conscr\-alioa ServKC 3-6 Table 3-2 Undeveloped Ti MAXIMUM OVERLAND FLOW^NGTH (LM) & INITIAL TIME OF CONCEI Element* DU/ Acre .5% 1% 2% / 3% 5% 10% Element* DU/ Acre LM Ti LM T. LM LM Tx LM T, LM Tl 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 LDR 2 50 11.3 70 10.5 85 9.2 100 8.8 100 7.4 100 5.8 LDR 2.9 50 10.7 70 10.0 85 8.8 95 Q 1 1 r\r\ 6 LDR 2.9 50 10.7 70 10.0 85 8.8 95 6.J 3evetoped Ti 6 MDR 4.3 50 10.2 70 9.6 80 8.1 95 3evetoped Ti MDR 4.3 50 10.2 70 9.6 80 8.1 95 /7.8 lUU b.l 100 5.3 MDR 7.3 50 9.2 65 8.4 80 7.4 9/ 7.0 100 6.0 100 4.8 MDR 10.9 50 8.7 65 7.9 80 6.9 /90 6.4 100 5.7 100 4.5 MDR 14.5 50 8.2 65 7.4 80 6./ 90 6.0 100 5.4 100 4.3 HDR 24 50 6.7 65 6.1 75 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.COJH 50 5.3 60 4.5 75 4.0 85 3.8 95 3.4 100 2.7 G. COTQ 50 4.7 60 4.1 75 3.6 85 3.4 90 2.9 100 2.4 O.P7Com 50 4.2 60 3.7 70 3.1 80 2.9 90 2.6 100 2.2 Limited L 50 4.2 60 3.7 70 3.1 80 2.9 90 2.6 100 2.2 General L 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 INTENSITY-DURATION DESIGN CHART Figure 3-1 Olr*ctior* tar Application: (11 From precipitation maos determine 6 tif and 24 iv amounts fof !h)E selected frequency, Ttiasa maps are included in tlie County Hydrology Manual (10.50, and 10S yr maps indudetl in ttie Design and PrcJoedure Manual), (21 Adjust 6 tir preopitation (<f neceasar^l so that rl is wilhin tlie range of 45% to 65% of \he 24 hf preci pitalion (not applcaple to Desert). (31 Plot 6 tir precspitalion Dn the right side of lhe cti.irt, 141 Draw a iine ifirtxjgh the point par^jilei to ttie piolted lines. (61 Ttiis line is ttie Intensity-duration cur.'e for ihe ocatioii toeing snat^/ed Application Form: |81 Setected frequency >^ar ibtPr= in , P. 24 • [Oi = mm. (B) I = in./Iir. 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' 2401 orj axi 0 4:i OS,". a /8 D8/ O'H •5 CW ) m 1 :'X}' 0 19 038 Si?-i>66 0 75 om Odd ICS IK*' MO ' 0 1-0^-5 0 Z3 !>5e 06? 0 OSM 092 1 30 ] Intonslty.Oui'atloii Doslgn Chart - Tamplata FIGURE 3-1 32?30'' County of San Diego Hydrology Manual Rainfall Isopluvials ion Wear Rainfall Event - 6 Hours Isopluvial (incties) GIS GIS •BOVlOFDVvnUOLJJ WARRANHOf / a EJTHEREXPRESS nd-K-p- 'ED •^CLIJOIHG'BOTHOT'LIMHEO TO.'THE IMPLIED wARHAKTies Cop^riohl i>»"G1S. W Ritfii* ResorvcJ, E wi'ih™ptrmis*^iMi cl SAMDAtl. 3 0 3 Miles CALCULATIONS FOR 6" STORM DRAIN PIPE (Drains to Bioretention area with vault) Input Parameters Diameter, Flow, Manning's coeff., Area, Hydraulic radius. D= Q= N= A= R= Z= Wetted perimeter, WP= Friction slope. 0.5 0.55 0.013 0.19635 0.125 1.486 1.5708 ©Full capacity Sf = HGL @ outlet Length of Pipe HGL @ inlet 0.009541625 40.05 53 40.56 Top of Grate elevation @ Inlet = 40.80 HGL @ inlet < Top of Grate elevation =>0K