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HomeMy WebLinkAboutMS 2018-0006; Breakers View Beach Homes; Drainage Study; 2021-01-07 DRAINAGE STUDY BREAKERS VIEW CONDOMINIUMS CITY OF CARLSBAD APN: 204-232-12 MS2018-0006 GR2020-0027 DWG527-4A Prepared for: Jason Ianni 2337 Catalina Avenue Vista, CA 92084 Prepared by: bha, Inc land planning, civil engineering, surveying 5115 Avenida Encinas, Suite L Carlsbad, CA 92008-4387 (760) 931-8700 January 7, 2021 W.O. 1013-1369-400 Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 2 TABLE OF CONTENTS I. DISCUSSION…………………………………………………………………...3 Vicinity Map…………………………………..…………......3 Purpose and Scope………………………………….……….4 Project Description………………………………………….4 Study Method……………………………………………......5 Hydrology and Hydraulic Calculations ……………………6 Conclusion …………………………………………………..8 Declaration of Responsible Charge………………….……..9 II.EXHIBITS………………………………………………………………………10 Existing Hydrology Map and Proposed Hydrology Map…10 III.HYDRAULIC CALCULATIONS…………………………………………….11 Flow-Through Planter Storage and Outflow Calculations…………………………………………………..12 Flow-Through Planter Detail …………...…………………16 IV.REFERENCES…………………………………………………………………..17 Methodology – San Diego County Hydrology Manual Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 3 I. DISCUSSION VICINITY MAP: ~ VICINITY MAP NTS Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 4 PURPOSE AND SCOPE: The purpose of this report is to publish the results of a hydrology and hydraulic analysis for the proposed condominium project at 3648 Carlsbad Boulevard, City of Carlsbad. The proposed project is a 0.158 acre site. 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, and make recommendations to intercept, contain and convey Q100 to the historic point of discharge. PROJECT DESCRIPTION: The project is located at 3648 Carlsbad Boulevard, near the southwest corner of the intersection of Cherry Avenue and Carlsbad Boulevard, in the City of Carlsbad. The project proposes the development of two condominiums with parking areas. The disturbed area is 0.16 acres; the existing site is 31% impervious pre-redevelopment (2,018 square feet) and 72% impervious post- development (4,938 square feet). The proposed drainage basin matches the existing drainage basin in terms of overall area and basin limits. Storm flows affecting the site are limited to the rainfall that lands directly on this property. The following table summarizes the existing condition runoff information from the site. Please refer to the Existing Condition Hydrology Map for existing drainage area. TABLE 1—Summary of Existing Condition Peak Flows Discharge Location Drainage Area 100‐Year Peak Flow  (acres) (cfs)  Carlsbad Boulevard 0.158 0.59  The proposed drainage pattern will be similar as the existing drainage pattern with some modifications to incorporate the Low Impact Development (LID) Best Management Practices (BMPs) into the project design to mimic the impacts on storm water runoff and quality. The proposed runoff from the project is divided into three separate basin areas. DMA 1). Runoff from the condominium roofs will be captured and conveyed via roof drains to the proposed flow-through planters for storm water treatment. Runoff will be filtered through the media layer and aggregate storage layer before draining via underdrain pipe to a sidewalk underdrains at the southwest and northwest corners of the property. The sidewalk underdrains will direct flow southwesterly into the Carlsbad Boulevard curb and gutter. Flow will then be intercepted by the existing curb inlet in Carlsbad Boulevard, south of the Cherry Avenue. DMA 2). Runoff from the landscape, concrete sidewalk, and permeable pavement areas in the westerly portion of the project will flow towards Carlsbad Boulevard in the curb and gutter. Flow Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 5 will then be intercepted by the existing curb inlet in Carlsbad Boulevard, south of the Cherry Avenue. The permeable pavement areas and landscaping area swill provide pollutant control treatment of the storm water before discharging onto Carlsbad Boulevard. DMA 3). Runoff from the landscape, concrete sidewalk, and permeable pavement areas in the easterly portion of the project will flow towards a existing concrete swale in the alley near the northeast corner of the project. The table below summarizes the expected cumulative 100-year peak flow rate. Please refer to the Proposed Hydrology Map. Per the San Diego County Rainfall Isopluvial maps, the design 100-year rainfall depth for the site area is 2.7 inches. TABLE 2—Summary of Developed Conditions Peak Flows Discharge Location Drainage Area 100‐Year Peak Flow  (cfs) (acres)  Carlsbad Boulevard 0.158 0.79  STUDY METHOD: The method of analysis was based on the Rational Method according to the San Diego County Hydrology Manual (SDHM). Drainage basin areas were determined from the proposed shown on the tentative parcel map. Initial time of concentration of 5 minutes is used for P6 for 100 year storm, see References. Rainfall Intensity = I = 7.44*(P6)*(Tc)^- 0.645 P6 for 100 year storm = 2.7” In accordance with the County of San Diego standards, runoff coefficients were based on land use and soil type. The runoff coefficient is calculated from the impervious percentage for a given area using the formula from the SDHM. C = 0.9 x (%Impervious) + Cp x (1 - %Impervious) Where: Cp = Pervious Coefficient Runoff Value for the soil type (shown in Table 3-1 as Undisturbed Natural Terrain/Permanent Open Space, 0% Impervious). Soil type is Type B for this project determined from the Web Soil Survey in Appendix soil type map in the References. All landscaping (including raised planters) and permeable paver areas were considered 0% impervious because there is no impermeable liner to reduce the infiltration of water into the soil. Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 6 All roof and concrete areas were considered 100% impervious. For the existing condition, all landscape and concrete areas were tabulated and the total existing site was calculated to be 41% impervious. A runoff coefficient of 0.52 was assigned for the existing hydrology. For the proposed condition, DMA 1, which encompasses the roof area draining to the LID planter (flow-through planters will have a impermeable liner to prevent infiltration), is considered 98% impervious. A runoff coefficient of 0.88 was calculated for DMA 1. DMA 2, which encompasses the landscaping, concrete sidewalk, and pervious pavement areas in the westerly portion of the project that drains towards Carlsbad Boulevard in the curb and gutter is considered 8% impervious. A runoff coefficient of 0.31 was calculated for DMA 2. DMA 3, which encompasses the landscaping, concrete sidewalk, and pervious pavement areas in the easterly portion of the project that drains towards a concrete swale in the alley is considered 38% impervious. A runoff coefficient of 0.50 calculated for DMA 3. See the runoff coefficients and impervious area percentages in the Hydrology and Hydraulic Calculations on the following pages. HYDROLOGY AND HYDRAULIC CALCULATIONS: EXISTING CONDITION HYDROLOGY TOTAL AREA (acres)=0.158 IMPERVIOUS AREA (acres)=  0.066 PERCENT IMPERVIOUS 41.4% Q=CIA P6=2.70 TC=5 MIN C = 0.9 x (%Impervious) + Cp x (1 ‐ %Impervious),  Cp = 0.25 PERCENT IMPERVIOUS 41% CI (in/hr)A (ac)Q (cfs) 0.52 7.11 0.158 0.59 Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 7 DEVELOPED CONDITION HYDROLOGY DMA 1 ‐ ROOF DRAINING DIRECTLY TO LID PLANTERS TOTAL AREA (acres)= 0.102 IMPERVIOUS AREA (acres)=  0.099 PERCENT IMPERVIOUS 97.7% Q=CIA P6=2.70 TC=5 MIN C = 0.9 x (%Impervious) + Cp x (1 ‐ %Impervious),  Cp = 0.25 PERCENT IMPERVIOUS 97.7% CI (in/hr)A (ac)Q (cfs) 0.88 7.11 0.102 0.63 0.32 CFS DRAINS TO EACH LID PLANTER ON EACH SIDE OF THE FRONT PATIO. DMA 2 ‐ AREAS DRAINING TO CARLSBAD BLVD TOTAL AREA (acres)= 0.024 IMPERVIOUS AREA (acres)=  0.002 PERCENT IMPERVIOUS 8.7% Q=CIA P6=2.70 TC=5 MIN C = 0.9 x (%Impervious) + Cp x (1 ‐ %Impervious),  Cp = 0.25 PERCENT IMPERVIOUS 8.7% CI (in/hr)A (ac)Q (cfs) 0.31 7.11 0.024 0.05 DMA 3 ‐ AREAS DRAINING DIRECTLY TOWARD ALLEY TOTAL AREA (acres)= 0.032 IMPERVIOUS AREA (acres)=  0.012 PERCENT IMPERVIOUS 38.0% Q=CIA P6=2.70 TC=5 MIN C = 0.9 x (%Impervious) + Cp x (1 ‐ %Impervious),  Cp = 0.25 PERCENT IMPERVIOUS 38.0% CI (in/hr)A (ac)Q (cfs) 0.50 7.11 0.032 0.11 Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 8 TABLE 3— Summary of Existing and Developed Condition Peak Flows 0.158 0.59 0.79 0.20 SUMMARY OF PEAKS FLOWS  AREA (ac)EXISTING PEAK  FLOW (cfs) DEVELOPED PEAK  FLOW (cfs)DIFFERENCE (cfs) CONCLUSION: As shown in Table 3, the development of the proposed Breakers View Condominium Project will result in a net increase of peak flow discharged from the project site by approximately 0.20 cfs. This increase is considered negligible to the overall drainage discharged into the existing public storm drain downstream where an existing curb inlet located along Carlsbad Boulevard south of Cherry Avenue. Existing City of Carlsbad Improvement Drawing 273-8 (See References) shows an existing 18-inch storm system in Carlsbad Boulevard. Landscape, permeable pavers and impervious dispersion areas will slow runoff discharges, and reduce runoff. These small collection techniques foster opportunities to maintain the existing hydrology and provide a much greater range of retention practices. The developed site will also implement source control and site design BMPs in accordance with the “Standard Project” stormwater requirements. Peak flow rates listed above were generated based on criteria set forth in “San Diego County Hydrology Manual” (methodology presented in Chapter 4 of this report). Rational method output is located in Chapter 3. The hydraulic calculations show that the proposed onsite storm drain facilities can sufficiently convey the anticipated Q100 flowrate without any adverse effects. Based on this conclusion, runoff released from the proposed project site will be unlikely to cause any adverse impact to downstream water bodies or existing habitat integrity. Sediment will likely be reduced upon site development. Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 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 Holloway R.C.E. 29271 Date 03-12-21 Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 10 II. EXHIBITS EXISTING HYDROLOGY MAP And PROPOSED HYDROLOGY MAP EXISTING HYDROLOGY MAP BREAKERS VIEW CONDOMINIUMS CITY OF CARLSBAD LEGEND: K:\Civil 3D\1369\DWG\HYDRO&SWMP\1013-1369- EX HYDRO.dwg, 7/10/2019 8:19:19 AM \ \ \ s92 M \ \ 48,8 \ 0 SURFACE NODE SURFACE FLOW. 100 YEAR (CFS) BASIN AREA BASIN UMIT FLOW DIRECTION 8 SEWE MH \ 48,7 0 0 \ \ \ \ \ 1/ 1/ 1/ 1/ 1/ ◊ EXISTING HYDROLOGY MAP BREAKERS VIEW CONDOMINIUMS MH 0 \ / / < /'\ \ / \ \ \ \ \ \ \ / / \ ) / / / / \ \ / \ \ / OBS, PROJECT CHARACTERISTICS APN 204-232-12 SOIL TYPE B 10 5 0 10 20 JO ~111111111111111 PROJECT AREA 0.158 ACRES SCALE: 1" = 10' \ \ \ \ X 18.3 \ / \\ As~h. \ bltA,lnc. land planning, clvll englnee~ng, surveying 5115 AVENIDA ENCINAS SUITE "L" CARLSBAD, CA. 92008-4387 (760) 931-8700 \ \ \ \ \ \ \ \ \ \ LEGEND: PROPOSED HYDROLOGY MAP BREAKERS VIEW CONDOMINIUMS CITY OF CARLSBAD PROJECT CHARACTERISTICS APN SOIL TYPE PROJECT AREA DISTURBED AREA PROPOSED IMPERVIOUS AREA PROPOSED PERVIOUS AREA 50.50 TG 24"X24" BROOKS PCC CATCH BASIN W/ GRATED INLET 2" MULCH 4 "-DIA LID ORIFICE IMPERMEABLE LINER ON VERTICAL WALLS AND BOTTOM, PER SOILS REPORT--..... 4" PVC WITH 3" PVC REDUCER SIDEWALK UNDERDRAIN EXISTING SIDEWALK SIDEWALK UNDERDRAIN CARLSBAD BL VD. 204-232-12 B 0.158 ACRES 0.158 ACRES 4,938 SF (0.113 AC) 1,944 SF (0.045 AC) *ENGINEERED SOIL MIX SHALL PROVIDE A MINIMUM SUSTAINED INFILTRATION RA TE OF 5"/HR. MIX SHALL BE SANDY LOAM TOP SOIL CONSISTING OF 50% SAND, 30% PLANTING SOIL, 20% SHREDDED HARDWOOD MULCH. R/W OEEP ROOTED, DENSE, OROUGHT TOLERANT PLANTING SUITABLE FOR WELL ORA/NED SOIL 1 B" ENGINEERED SOIL MIX* 2" PEA GRAVEL 48.1 FS 10" GRAVEL PERMEABLE PAVERS. 47.53 FL OUT _ __,., 47.55 FL 6" HOPE 47_84~FL---"~ 6" PERFORATED PVC PIPE W/ IN MIN. 3" AGGREGATE BELOW PLACE PIPE WITH 3" PVC IN-~ OUTLET PIPE PIPE 41.57 FL PERFORATIONS OUT AT THE INVERT EXISTING AND PROPOSED ~EXISTING GROUND SEWER LATERALS SHALL BE A MINIMUM OF 5 FT ,,..iL====~:::'.2=%=M=l=N·~==============:]IJ BELOW GRADE AT ·· PROPERTY LINE TYPICAL BASIN OUTLET DETAIL NOT TO SCALE NOTES: 1) ROOF DRAINS TO FLOW-THROUGH PLANTER. 2) LANDSCAPING, CONCRETE SIDEWALK, AND PERMEABLE PAVEMENT AREAS DRAIN TO CARLSBAD BOULEVARD AND REAR ALLEY. 3) ROOF SYSTEM TO INCORPORATE A SYSTEM TO CAPTURE THE FIRST WASH/OFF OF SEDIMENT, DEBRIS DURING A RAINFALL EVENT. SUMMARY OF DEVELOPED CONDITION RESULTS DISCHARGE LOCATION AREA (AC) 100-YEAR DEVELOPED PEAK FLOW (CFS} OMA 1 0.102 0.63 OMA 2 0.024 0.05 DMA 3 0.032 0.11 TOTAL 0.158 0.79 / \ PROPOSED HYDROLOGY MAP ERE ~----RS VIEW CONDOMINIUMS / / 1/ 1/ 1/ 0 SI WALK UNtftk PIPE -3 MH 0 / / < /'\ \ / \ \ \ \ \ \ \ ./ \ ) / I I OMA 1 -ROOF AREAS DRAINING TO LID PLANTER (Q=0.64 CFS, AREA=0.102 AC) R '£CT, BO D Y ---WJJ/1/IJ FLOW-THROUGH PLANTER --------1: ~: v: ~] PERVIOUS PA VERS -----------I:~:~:~:~:~:~:~ :1 CONCRETE SIDEWALK ---------1· , .. ~ ..... j OMA BOUNDARY--------------------------- IS AR AD bliA,lnc. land planning. ell/II englnoorlng, suiveylng 5115 AVENIDA ENCINAS SUITE "L" CARLSBAD, CA. 92008-4387 (760) 931-8700 A EA 10 5 0 10 20 30 -------SCALE: 1" = 10' Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 11 III. HYDRAULIC CALCULATIONS Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 12 FLOW-THROUGH PLANTER BASIN STORAGE AND OUTFLOW CALCULATIONS Table 2.A, Overflow Capacity of 24"x24" Brooks Catch Basin Outlet Basin Elev Coefficient Weir Length (ft)H (ft) Q (cfs) 0.17 3.3 8 0 0.00 0.37 3.3 8 0.20 2.36 0.57 3.3 8 0.40 6.68 0.77 3.3 8 0.60 12.27 0.97 3.3 8 0.80 18.89 1.17 3.3 8 1.00 26.40 Table 2.B, Capacity of (3) 4"-dia Draindown Orifice Plate Assume downstream 3" PVC sidewalk underdrain controls orifice flow1 Using standard submerged Orifice Flow Equation (6-12) Q=COA(2gH)0.5 Orifice Size1 Diameter Dia. (ft) Area (sf) Based on (3) 3" PVC Pipes 0.17 0.00 0.2500 0.14726 0.62 2.91 0.00 0.37 0.20 0.2500 0.14726 0.62 3.11 1.29 0.57 0.40 0.2500 0.14726 0.62 3.31 1.33 0.77 0.60 0.2500 0.14726 0.62 3.51 1.37 0.97 0.80 0.2500 0.14726 0.62 3.71 1.41 1.17 1.00 0.2500 0.14726 0.62 3.91 1.45 NORTH SIDE (UNIT A) FLOW THROUGH PLANTER Using Broad Crested Weir Formula equation (6-10) Q=CLH1.5 where Coefficient C is 3.3. Invert of 4" PVC Orifice (ft) Delta Elevation (ft) Coefficient Head (ft) Qdrain (cfs) Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 13 NORTH SIDE (UNIT A) FLOW THROUGH PLANTER Table 2.C- Main Basin Depth vs. Storage and Discharge Information 51 Elev Depth Volume CF Volume acre-ft Outflow 0.17 0.00 38.25 0.0009 0.00 Total Storage in Soil Media*** 0.37 0.20 48.45 0.0011 1.29 0.57 0.40 58.65 0.0013 1.33 0.77 0.60 68.85 0.0016 1.37 0.97 0.80 79.05 0.0018 1.41 1.17 1.00 89.25 0.0020 1.45 Drawdown calculator: Flow through orifice plate governs drain-down flow 48 Basin Volume @ 3" Depth (ft 3): 0.30 Q of (3) 3" orifices plate at 1" Head Overflow on 24" x 24" Catch Basin Outlet (cfs) 0.04 Drawdown time (hrs) < 24 hrs  ***assuming 25% Void Ratio in Engineered Soil Layer and 40% Void Ratio in Gravel Layer Bottom Basin Area (sf) = Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 14 Table 2.A, Overflow Capacity of 24"x24" Brooks Catch Basin Outlet Basin Elev (ft)Coefficient Weir Length (ft)H (ft) Q (cfs) 0.17 3.3 8 0 0.00 0.37 3.3 8 0.20 2.36 0.57 3.3 8 0.40 6.68 0.77 3.3 8 0.60 12.27 0.97 3.3 8 0.80 18.89 1.17 3.3 8 1.00 26.40 Table 2.B, Capacity of (3) 4"-dia Draindown Orifice Plate Assume downstream 3" PVC sidewalk underdrain controls orifice flow1 Using standard submerged Orifice Flow Equation (6-12) Q=COA(2gH)0.5 Orifice Size1 Diameter Dia. (ft) Area (sf) Based on (3) 3" PVC Pipes 0.17 0.00 0.2500 0.14726 0.62 2.91 0.00 0.37 0.20 0.2500 0.14726 0.62 3.11 1.29 0.57 0.40 0.2500 0.14726 0.62 3.31 1.33 0.77 0.60 0.2500 0.14726 0.62 3.51 1.37 0.97 0.80 0.2500 0.14726 0.62 3.71 1.41 1.17 1.00 0.2500 0.14726 0.62 3.91 1.45 SOUTH SIDE (UNIT B) FLOW THROUGH PLANTER Using Broad Crested Weir Formula equation (6-10) Q=CLH1.5 where Coefficient C is 3.3. Invert of 4" PVC Orifice (ft) Delta Elevation (ft) Coefficient Head (ft) Qdrain (cfs) Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 15 SOUTH SIDE (UNIT B) FLOW THROUGH PLANTER Table 2.C- Main Basin Depth vs. Storage and Discharge Information 60 Elev (ft)Depth (ft) Volume (cf) Volume (acre-ft) Outflow (cfs) 0.17 0.00 45.00 0.0010 0.00 Total Storage in Soil Media*** 0.37 0.20 57.00 0.0013 1.29 0.57 0.40 69.00 0.0016 1.33 0.77 0.60 81.00 0.0019 1.37 0.97 0.80 93.00 0.0021 1.41 1.17 1.00 105.00 0.0024 1.45 Drawdown calculator: Flow through orifice plate governs drain-down flow 57 Basin Volume @ 3" Depth (ft 3): 0.32 Q of (3) 3" orifices plate at 1" Head Overflow on 24" x 24" Catch Basin Outlet (cfs) 0.05 Drawdown time (hrs) < 24 hrs  Bottom Basin Area (sf) = ***assuming 25% Void Ratio in Engineered Soil Layer and 40% Void Ratio in Gravel Layer Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 16 FLOW-THROUGH PLANTER DETAIL Not to Scale 50.50 TG 24"X24• BROOKS PCC CATCH BASIN W/ CRATED INLET 2 • MULCH 4"-DIA UD ORIFICE IMPERMEABLE UNER ON VERTICAL ANO BOTTOM, PER SOILS REPORT 4" PVC WITH J" PVC REDUCER SIDEWALK UNDERDRAIN EXISTING SIDEWALK SIDEWALK UNOERORAIN •ENGINEERED SOIL MIX SHALL PROVIDE A MINIMUM SUSTAINED INF"IL TRA TION RA TE OF 5"/HR. MIX SHALL BE SANDY LOAM TOP SOIL CONSIST/NC OF 50% SAND, 30% PLANTING SOIL, 20% SHREDDED HARDWOOD MULCH. DEEP ROOTED. DENSE. DROUGHT TOLERANT PLANTING SUITABLE FOR WE'LL DRAINED SOIL 51.5 TW 18" ENGINEERED SOIL MIX* 2" PEA CRA VEL PERMEABLE PAVERS. 6" HOPE OUTLET PIPE 6" PERFORATED PVC PIPE W/ MIN. 3 " ACCRECA TE BELOW PLACE PIPE WITH PERFORATTONS EXISTING AND PROPOSED ~EXIST/NC GROUND SEWE"R LATERALS SHALL BE A MINIMUM OF 5 FT -u.::::::::::2:%::::M:JN:,~::::::::::::::::::Jlll BELOW GRADE AT - AT THE INVERT PROPER TY UN£ TYPICAL BASIN OUTLET DETAIL NOT TO SCALE NOTES: 1) ROOF DRAINS TO FLOW-THROUGH PLANTER. 2) LANDSCAPING, CONCRETE SIDEWALK, AND PERMEABLE PA Vfl.AENT AREAS DRAIN TO CARLSBAD BOULEVARD AND REAR ALLEY. 3) ROOF SYSTEM TO INCORPORATE A SYSTEM TO CAPTURE THE FIRST WASH/OFF OF SEDIMENT, DEBRIS DURING A RAINFALL EVENT. Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 17 IV. REFERENCES Breakers View Condominiums bha, Inc. Preliminary Drainage Study land planning, civil engineering, surveying 18 METHODOLOGY – SAN DIEGO COUNTY HYDROLOGY MANUAL Breakers View Condominiums bha, Inc. Preliminary Drainage Study land planning, civil engineering, surveying 19 [. ,TL_ri..:IJ;_c:d. ._rm .. ,iJTJ io7 I I I i ! ~ :7 ~I~·: . -'1 .I. JJ)Jti• ;-'-'' aq~~ •i-. • . I I I I ! ! 1 • • , I l'.:", .. u l·1· 1coilii!it:vll -', 1, ;,;7•: .• :•1 .W. .~+ ----~....... " I I '". ' II I ' '' ,_ l LL __ Ll..J_l 1'lJ t••J L·l.'f-'...._t I I. l -j f i 1.-t-L...[C_1 _I i ' . ~~·-I I I. -R-r'"' 1-; .].-~.:/ ' _! j : ,73h•:1s-I I I ' 1;1 ' I I r, ; ~ I -_J_ .. -· H 'J I j I . I LLL' I I'········,· .. ,lu' .-!-' 1+11 L . , (i·H· r ·) ,-,-......,...:..,~ ... ",.. , 1 , .-"2.5 : --~~-i _1_J_1_J_,_, ,l ' . I,•·•••·-. . T ... I . ,I r' -, r .J. _;_ I ' i t i ;-1-!_ I •-· ':-1~ to ,J '·1· ._I L!J..! ,_•..:.. I Lg.• J. f+-·+;H ,_ -~!, c-,,-h. ,.:, -' I :i27◄s! I .•• ' I ' I ' ' • ' I ' 1 • I ' I 1 _....; . I I· I~ . ...: '·' -~ I I J I I I j ' I I J. 1.' C •..LJ. ~-. I ; I_J -. I. !...,J ... -· I • .I.LI .. :~ '·' , .• ,.: 1'J lft 1:-· LC !· County of San Diego Hydrology Manual • . . Rainfall Isopluvials 100 Year Ralnfall Event -6 Houn [ ········ looplwlol nn<hca) GPS COORDINATES: P6=2.7" P6/P24= 56% DPW ~GIS -=-S11iGIS N ,::;:::-..!.."".:!.~-u. 1 b-. '-.111 l'lii~l'I' I A,~ .. J! 0,-IIM.ffi'wel,_l'CIII•~~~ _.....,_ ........ -______ .. .-ooa._.. E_,_,, __ .. __ ... ------·•-l.L B j·U· · · ·. ,_1 L~ 4 ~=re:~~~~-..=.~ .-1 32•3~-f t I I j r r • I ' 1 f I I I I I I , 1 1 , rl l:1.' ,., -;I...Ugl.·1· ~l-J-!-'1·f.H-§-~·· ][·-'·, , !-1 I, 111 --11 · -IT' · :-lTJt' 1--:-11 t·'. · J-i ' 1-d -1 · • -LJI ·u ~-,Tr ,-;-1; ,l ::-fu,j~· ·'.. 1{ ' -1 -!lllll11)1JI 11. =~.,.=---~ 0 3Mllos ~ Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 20 '-+ 111 · ' ' . I I --I I I I I ' 1 !=! 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""i. . , , 1 . , • , , 11 . , , , ·r~~-~ . .,.[ ,l _, ' l t· ri.J I_ • ! ~ I J I I f ! I j ,. I L ;1 1-,,. ,· t---· ,·h'. f' •j -__ jJa :-H-: t-~ , ::· !±! J.l~U: -. 1•,:~~-n County of San Diego Hydrology Manual Rainfall Jsopluvials JOO Year Rainfall Event• 24 Rours lsopW•I (inches) GPS COORDINATES: P24=4.8" P6/P24= 56% OPW -§:'GJS ~~~::"=: .. S1tiGIS \\'C"IIJ,. '\.J!l l.h.y;i <~•~1.J! J7 •, f"t' I -:i---u---,•r·c-,-l :: •-LI N __. ........ ~-WJJ!aJJff'lt:,Mff'Dl!l,ll'Nt'II~ -LI .. _.._.,,._~TQ,.-....u:11 .. .-TD .,, +~~=.::·::;..-----· , I I -s~32 ---I '.~~dJ-;b ,---YTGJc±Rl::H+EFR~ □JIH---RJ 111 ! I I:., J:: I I: I• : : , :. ---'--l-----":'--'---:'---:-'-:..:.:..::c.,:,..;...-1...'....L..J..-~:-i-.-,.j.32.j.r.Ji,. ___ , ~ =~~~-:---HI" ' Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 21 San Diego c·ounty Hydrology Manual Date: · June 2003 Table 3-1 Section: Page: RUNOFF COEFFICIENTS FOR URBAN AREAS Land Use I Runoff Coefficient "C" Soil Tyee NRCS Elements Cmm Elements %IMPER. A B ndisturbed Natural Terrain (Natural) Permanent Open Space o• 0.20 0.25 Low Density Residential (LOR) Residential, 1.0 DU/A or less 10 0.27 0.32 Low Density Residential (LOR) Residential, 2.0 DU/A or less 20 0.34 0.3$ Low Density Residential (LOR) Residential, 2.9 DU/A or less 25 0.38 0.41 Medium Density Residential (MDR) Residential, 4.3 DU/A or less 30 0.41 0.45 Medium Density Residential (MDR) Residential, 7.3 DU/A or less 40 0.48 0.51 Medium Density Residential (MDR} Residential, 10.9 DU/A or less 45 0.52 0.54 Medium Density Residential (MDR) Residential, 14.5 DU/ A or less 50 0.55 0.58 High Density Residential (HOR) Residential, 24.0 DU/A OT less 65 0.66 0.67 High Density Residential (HOR) Residential, 43.0 DU/A or less 80 0.76 0.77 Commercial/Industrial (N. Com) Ne.ighborhood Commercial 80 0.76 0.77 Commercial/Industrial (G. Com) General Commercial 85 0.80 0.80 Commercial/Industrial (O.P. Com) Office Profossional/Commercial 90 0.83 0 84 Commercialflndusrrial (Limited I.) Limited Industrial 90 0.83 0.84 Commercial/.!ndustrial (General 1,2 General Industrial 95 0.87 0.87 C 0.30 0.36 0.42 0.45 0.48 0.54 0.57 0.60 0.69 0.78 0.78 0.81 0.84 0.84 0.87 3 6 of26 D 0.35 0.41 0.46 0.49 0.52 0.57 0.60 0.63 0.71 0.79 0.79 0.82 0.85 0.85 0.87 "The values associated with 0% impervious may be used for direct calculation of the runoff coefficieat as described in Section 3.1.2 (re1iresenting 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 Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 22 San Diego County Hydrology Manual Date: June 2003 Section: Page: 3 5 of26 Where: C = 0.90 x (% Impervious) + Ci, x (l -% Impervious) Cp = Pervious Coefficient Runoff Value for the soil type (shown in Table 3-1 as Undisturbed atural Terrain/Permanent Open Space, 0% Impervious). Soil type can be determined from the oil type map provided in Appendix A. The values in Table 3-1 are typical for most urban areas. However, if the basin contains rural or agricultural land use parks, golf courses, or other types of nonurban land use that are expected to be pennanent, lbe appropriate value should be selected based upon the soil and cover and approved by the local agency. 3-5 Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 23 tu UJ LL. ~ UJ 0 z ~ 6 w Cl) ~ :::> 0 (.) 0::: UJ i 1001 ,_,5 I #/'" I -' 1 I JJ,i,-# i :yr: / I :/ I :./f 130 (/) w t-:::> z vi-' I ~ 1///:A/ :/! 7 I ~I I ~120~ ~ w ::l? i= 5 _J u.. 10 ~ ~ et:: w 6 ~ 0 EXAMPLE: Given: Watercourse·Distance (D) = 70 Feet Slope (s) =1.3% Runoff Coefficient (C) = 0.41 Overland Flow Time (T) = 9.5 Minutes T = 1.8 (1 1-C) \/iJ 31fs SOURCE: Airport Drainage, Federal Aviation Administration, 1965 FIGURE Rational Formula -Overland Time of Flow Nomograph I 3-3 I Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 24 L:i..E Feet L:i..E 5000 4000 3000 2000 30 20 10 5 Tc Tc L l:l.E EQUATION (1~3)°'385 Time of concentration (hours) ,. Watercourse Distance (miles) Change in elevation along effective slope line (See Agure 3-S)(tcet) Tc t¾ours Minutes L Miles Feet 4000 ' 3000 ' ' 2000 ', 1800 '\. 4 3 2 1600 '\. 1400 '\. 1200 300 200 L Tc 30 7 6 5 4 3 SOURCE: California Division of Highways (1941) and Kirpich (1940) Nomograph for Determination of Time of Concentration (Tc) or Travel Time (Tt) for Natural Watersheds Fl·GURE 3-4 Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 25 <1> a. a ci.i Q) @ i'i5 ..... a '$. l+---1.5'-----------+-I l__,, = .015-....+-I _ 2% ..,,_-n=.0175 ------::..:::_ ___ --..! 2% Conctele Gutter 0.13 Paved RESIDENTIAL STREET ONE SIDE ONLY 20-1------+-"T"--ll--+-+TT-+--l-~f7-----+--~r+--l---f""""l,,- 1s -'-------1---1I'---+-~,---+-#-l---1----1----1---1-~f-.........:s....c v ---+---__,.-,-...__..,...._v ~ I 16 I--I J ~ 101.p I --:::...Z...<t:.o L I ~ ~ I l'Z. 14 ➔--------h,---t--+-,~~r++-1+-+----~'l-.:::+--t--+--rit-+ I ---r---I 7-----... I 12 -I-------A----l---+-#--+----1,-4-~...!--/ I J r--R6'1. I I'----I I ~-,-+---+--,~......___-+-+ 10 9 L... J 8 I ' 7---/ 6 5 I 3 2 1.8 1.6 1.4 1.2 1.0 0.9 0.8 0.7 0.6 0.5 0.4 2 5 6 7 8 9 10 20 30 40 50 Discharge (C.F.S.} EXAMPLE: Given: Q = 10 5 = 2.5% Chart gives: Depth= 0.4, Velocity= 4.4 f.p,s. SOURCE: &in Diego County Department of Special District Services Design Manual F IG U R E Gutter and Roadway Discharge -Velocity Chart ~ Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 26 EQUATION: V = 1.49 R"• s11> n 0.3 0.2 r° 0.2 t 40 0.3 t 0.15 t30 0.4 0.10 0.09 l"' 0.08 20 0.07 0.06 0.6 0.05 ~ 0.04 0.8 "" 0.9 0.03 ~ 1.0 <?6' 10 "" > < 0.02 [I'. /' /] 8 '? di "" a ~ 7 / ~ ,l? .!: <ii Cl) <ii 6 ~ 0. 0. / ii 0.01 D 2 v~ Q) .S! 0.009 <I'. ~ 2 [I'. .!: 0.008 f; g ~-.II ~ w 0.007 .J y ~ ~4 o._ ::::> 0 0.006 3/ .J (/) <>: ct: 0.005 D >-o.oo~&,--I ~ 0.002 0.001 0.0009 0.0008 O.(l(J07 0,0006 0.0005 0.0004 0.0003 6 8 9 10 20 SOURCE: USDOT, FHWA, HDS-3 (1961) ""8 ...J w > GENERAL SOLUTION Manning's Equation Nomograph 3 1.0 0.9 0.8 0.7 0.6 0.5 0.01 0.02 o'l-/ p C ' 003 C: (I) ·u ;f: (I) 0.04 0 0 Cl) Cl) ~ [0.05 I CJ 0.06 ::::> 0 er: 0.07 0.08 0.09 0.10 0.2 0.3 0.4 I' J ~-;REI Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 27 1 I T I l I \.~ I "~ ~ ~ ~ I I ~~ ~~ ~ ~ ~ ~~ ~ I ~ ,~ ~ I - " ( :20 30 40 50 1 Minutes Duralion I I I 1ml I I 111 11 Ill 11111 l 7 I I Il l Ill mn I I 1 11111 Iii EQUATION I = 7.44 Pe o•0.645 I = Intensity (in/hr) P5 = e-Hour Precipitation {in) D = Duration (min) I 1':,.. :,..N :-." :-." 1-. ' r,. ~ I, :,..p,. :,..r,. :,..p,. I II IIIJl-.. I ....... .. ... ', I-. l-1-,, ·-- ~ ',~ ' ~ I• ~~ ~~ ~ ~ ~ ~ ~ ""~ '·~ - - --. - 3 4 Hours I I I ' - I 5 6 ± ~ "lJ ;; .g. 6.0 iif 5.5 "'· 5.0 g 4.s I 4.0 [6 3.5 ~ ,3.0 2.5 2.0 1.5 1.0 Intensity-Duration Design Chart -Template DlracUons for Appllcatlon: (1} From precipitation maps determine 6 hr and 24 hr amounts for the selected frequency. These maps are i'ncluded in the County Hydrology Manual (10, 50, and 100 yr maps Included in the Design and Procedure Manual). (2) Adjust 6 hr preclpfta1ion (if nacessary) so that it Js within the range of 45% to es¾ of the 24 hr precipitalion {not applicaple to Desert). (3) Plot 6 hr precipitation on the right side of the 0art. (4) Draw a fine through the point parallel to the plotted lines. (5) This line is the Intensity-duration CUl'V8 for the location being analyzed. Appllcatlon Form: (a) Selected frequency _.!QQ_ year (b) Pe= _E__ fn., P24 = _i!_ .~ " 56 %(2) 24 (c) Adjusted Pe121 = ___ in . (d) lx "' _5_ min. (e) I = ..1J..!.. in./hr. Note: This chart replaces the Intensity-Duration-Frequency curves used since 1965. 3-1 Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 28 San Diego County Hydrology Manual Date: June 2003 3.2 DEVELOl'lNC !NP T DATA FOR THE RA TlONAL METHOD Section: Page: 3 20 of26 This section describes the development of the necessary data to perfo11n 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 1opograpbic base map, outline the overall drainage area boundary, show~g 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 poinls of interest. These divisions should be based on topography, oil lype, and land usc. 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 uni form. 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 info1mation 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 Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 29 Study Area SC , r_.{ I , : ·1 l... ~ ( / ·, / L-· Study Area LA 0 Define Study Areas (Two-Letter ID) 0 Define Maps (or Subregions on Region Basis) © Define Model Subareas on Map Basis ' ' .. \· ...... M 9 " .. 9 • • 0 Define Major Flowpaths in Study Area @ Define Regions on Study Area Basis Subarea ID== (LA010112) Ni:::_ l Region# ,...., Area (ID)# 1 1 l © Define Model Nodes (Intersection of Subarea Boundaries with Flowpath Lines) GIS/Hydrologic Model Data Base Linkage Setup: Nodes, Subareas, Links LA 01 01 03 0 Number Nodes IF ·~-~R El Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 30 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. Tf the subarea contains more than one type of development classification, use a proportionare average for C. In detenn.i.ning C for the subarea, use future land use taken from the applicable community plan, Multiple pecies Conservation Plan, National Forest land use plan, etc. 9. Calculate the CA value for the subarea. 10. Calculate the 2:(CA) vaJue(s) for the subareas upstream of the point(s) of interest. 11. Detcnnine P6 and P24 for the study using the isopluvial maps provided in Appendix B. Jfnecessary, adjust the value for P6 to be within 45% to 65% of the value for P24. See ection 3.3 for a description of the RM calculation process. 3.3 PERFORMING RAT.TO AL 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: l. Determine T; 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 T; to obtain the Tc. Refer to paragraph 3.1.4.2 (a). 2. Detetmine I for the subarea using Figure 3-l. If T; was less than 5 minutes use the 5 minute time to detennine intensity for calculating the flow. 3. Calculate the peak discharge flow rate for the subarea, where Qp = :E(CA) l. In case that the downstream flow raLe 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 Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 31 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 MODlfTED RATIONAL METHOD (FOR ,JU CTION ANALYSIS) The purpose of th is section is to describe the steps necessary to develop a hydrology repmt 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 app lication 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 J 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 calclLlations for up to an approximately I -square-mile area and then transition the study to the RCS method for additional downstream areas that exceed approximately 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 j unction 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 Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 32 San Diego County Hydrology Manual Dale; 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 conti.nued to the nex.t point of interest. 3.4.2 Procedure for Com bining Independent Drainage Systems at a Junction Calculate the peak Q, Tc, and T for each of the independent drainage systems at the point of the junction. These values will be used for the MRM calculations. Al 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 Te. Based on the approximation that total runoff increases directly in propo,tion to time, a general equation may be written to determine the maximum Q and its corresponding Tc using the peak Q Te, and 1 for each of the independent drainage systems at the point immediately before the junction. The general equation requ ires that contributing Q's be numbered in order of increasing T0• Let Qi, T1, a.nd 11 co1Tespond to the tributary area with the shortest Tc. Likewise, let Q2, T2, and h correspond to the tributary area with the ne,....-t longer T0; Q3, T3, and h correspond to the tributary area with the next longer Tc; and so on. When on ly two independent drainage systems are combined, leave Q3, T3, and I3 out of the equation. Combine the independent drainag systems using the jw1ction equation below: Junction Equation: T1 < T2 < T3 3-24 Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 33 San Diego County Hydrology Manual Date: Junt: 2003 Section: Page: 3 25 of26 Calculate QT1, Qr2, and QTJ. 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., QT1 = Qn > Qn), use the shorter of the Tc's associated with that Q. This equation may be expanded for a junction of more than three iJ1dependent 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., Q1), the Q from the subarea with the shorter Tc is reduced by the ratio of the l's (12/T1); 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). ote #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 !3 = 0. When T, and T2 are the same, I I and Ii are also the same, and Ti/f2 and Ii/I 1 = I. Ti/f 2 and Ii/I I are cancelled from the equations. At this point, Q·n = Qn = Q, + Q2• ote #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 = :E(CA)I. Note #3:. An optional method of determining the Tc is to use the equation Tc -[(1: (CA)7.44 P6)/Q] us This equation is from Q = :E(CA)I = 1:(CA)(7.44 PJTc·w ) 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 Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 34 ;n• ~O"H I I I I I 32'f/!19"H I • ~ • ~ • '\I • ~ ~ Hydrologic Soil Group-San Diego County Area, California 46lS15 = """"' 46lSl6 4175C "'7fBJ 417"15 "5/0ll. "67829 411""' 43700 '6lffiO """SG!II"' L303f~bad"1A~(11"x8.S-)si-N ----====-------=======>_, 16 24 A o--•,"'o===-:lll-----40""'====60FW. Mop P"'lodi<n: -~-ecm.,,=-: WGS8<I Edgetlc5: U1M 21:,r,o 11N WGS8<I Natural Resources Conservation Service Web Soil Survey National Cooperative Soll Survey _, 115/fJi/ 41""4 "'7671 """" '67871 _,, 417678 $ t, Iii ~ ;. Ii, 1ii ~ I 33"9'CfN I I I m I ~ !ll """"'" 6/18/2019 Page 1 of 4 Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 35 ~ Hydrolc)&ic Soll Group-San Diego County Area, California MAP LEGEND MAP INFORMATION Area or Interest (AOI► l_J Area of lntwast (AOO Soll, Soll Roting Polygons D A D AID D D BID oc D CID 0D D Not rated or not eva.i!a.bte Soll Roting Li'los A AID .-BID C CID D Not rated or not ava.i!abl• Soll Rating Points C A C AID • ■ BID Natural Resources Conservation Service C c C CID 0 □ Not rated or n at avallabla WMuFearures Slttiams Md Canal'!i Ttansportallon +++ --Ralls: Interstate Highways USR01.1IH Major Roecls Local Roads Backgrot.nd • Aeria I Pllolograph)> Web Soil Survey Nationa I Cooperative Soil Survey The scil surveys that con-prise your AOI we,e mapped al 1;24,000, 'Naming: Seil Map may not be valid at this scale. Enlargemenl or maps beyond the scale of mapping can cause mlsunderslancing 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 delalled scale. Please rely on the bar sca!e on each map sheet for map measuremenls. Soorce o:f Map: Natural Resoorces Conservation Service Web Soil Survey URL: Coordinate System: Web MercetOf (EPSG:3857) Maps from lhe Web Soil Survey are based on lhe web Mercalor projection, which preserves cirection and shape but distorts dis:tance and area. A prcjecfioo tha1 preserves area, such as the Albers equal-area conic projection, should be use<I if more accurate calculalioos ol dlslance or area are required. This producl is generaled from the USOA-NRCS certified dala as of the version dale(s) listed below. Soil Survey Area: San DregoCountyArea, California Survey Area Data: Version 13, Sep 12, 2018 Soil map unlls ere labeled (as space allows) for map scales 1 :50,000 or larger. Date(s) aerial images we,e phdographed: Nov 3, 2014-Nov 22. 2014 The cr1hophoto or other base map on which lhe soil lines were OOfnpiled and drgitlzed probably dil'rers from the background image')• displayed oo these maps. As a resul, some minOf shifting al map unit boundaries maybe evident 611612019 Page2of4 Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 36 Hydrologic Soil Group-San Diego County Area, California Hydrologic Soi l Group Map unit symbol Map unit name Rating Acres In AOI Percent of AOI MIC Marina loamy coarse B 0.2 sand, 2 to 9 percent slopes Totals for Area of Interest 0.2 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 (f:,.JD, BID, 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 (AID, BID, 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. Rating Options Aggregation Method: Dominant Condition Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 100.0% 100.0% 6/18/2019 Page 3 of 4 Breakers View Condominiums bha, Inc. Drainage Study land planning, civil engineering, surveying 37 Hydrologic Soil Group-San Diego County Area, California Component Percent Cutoff: None Specified Tie-break Rule: Higher Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 6/18/2019 Page 4 of 4