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Home My WebLink AboutSDP 16-12; CARLSBAD VETERANS HOUSING; PRELIMINARY DRAINAGE ANALYSES; 2016-11-10Cbang uüL Civil EngineeringoHydrologyRydraulicsSedimentation November 10, 2016 iiCORD COPY Date Rancho Santa Fe, CA 92067-4496 1: 858.692.0760 F: 858.832.1402 wayne@changconsultants.com City of Carlsbad Land Development Engineering 1635 Faraday Avenue Carlsbad, CA 92008 Subject: 3606, 3618, and 3630 Harding Street - Preliminary Drainage Analyses Dear Land Development Engineering: The 3606, 3618, and 3630 Harding Street project proposes 26 veterans' housing units on a 0.543- acre site. The project will contain a three-story building with a ground level parking structure, hardscape, and landscaping. The site is currently developed with three single-family residences, which will be demolished prior to development. A site development plan (SDP) is currently being submitted for entitlements. The City of Carlsbad's Development Permits P-2 form indicates that a Preliminary Hydrology Study is required for projects larger than an acre (see attached). Although the project is less than an acre, this letter provides preliminary hydrologic analyses in support of the SDP application. The County of San Diego's rational method formula (Q=CIA) was used for the analyses. The following describes the rational method input data. The overall drainage area was determined in the SDP SWQMP and covers 0.648 acres (see the attached DMA Exhibit from the SWQMP). The existing and proposed condition impervious areas are included in the SWQMP and are 0.215 and 0.372 acres, respectively, which corresponds to 33 and nearly 60 percent impervious, respectively. The hydrologic soil group is B over the entire site from the attached Web Soil Survey. The C values for B soil and the existing and proposed condition percent impervious values are 0.47 and 0.70, respectively. The 100-year, 6- and 24-hour precipitation values are attached. Since the site is small the minimum time of concentration of 5 minutes was assumed for these preliminary analyses. Based on this, the 100-year intensity is 6.8 inches per hour. Table 1 summarizes the 100-year rational method input data and results. The table indicates that the project will cause a 1 cfs increase in the 100-year flow rate. This increase will be even less if the effects of the seven proposed biofiltration basins is considered. Therefore, the project will have minimal impacts on storm runoff. Condition C I, in/hr A, ac Qioo, cfs Existing 0.47 6.8 0.648 2.1 Proposed 0.70 6.8 0.648 3.1 Table 1. Rational Method Analyses Sincerely, Wayne W. Chang, M.S., P.E. Enclosures OFSS, 4 No. 46548 Exp. 6/30/17J DEVELOPMENT Development Services craty of PERMITS Planning Division 1635 Faraday Avenue Carlsbad P-2 (760) 602-4610 www.carlsbadca.gov Major Coastal Development Permits (including Amendments and Extensions, but excluding Minor COPs and Single Family Residences) Conditional Use Permits (including Minor, Amendments and Extensions) Planned Development Permits (Residential and Non-Residential; including Minor, Amendments and Extensions) Planning Commission Determinations Precise Development Plans South Carlsbad Coastal Review Area and Village Review Area Permits (Major, Minor and Amendments) (A Coastal Development Permit Supplemental Application may also be needed) (SitëDëVëiopmeniPiaij(including Minor, Amendments and Extensions) Special Use Permits (including Amendments, Extensions and Floodplain SUPs) Structure Relocation Permits Tentative Parcel Maps (including Revisions and Extensions) Tentative Tract Maps (including Revisions and Extensions) A proposed project requiring multiple applications must be submitted prior to 3:30 p.m. A proposed project requiring only one application must be submitted prior to 4:00 p.m. All joint application exhibits, i.e. Tentative Map and Planned Development Permit site plan, should be prepared at the same scale. (Use a scale no smaller than 1" = 40'.) The following materials shall be submitted for each application or for combined applications on a single project. If you have any questions regarding application submittal requirements (i.e., clarification regarding a specific requirement or whether all requirements are necessary for your particular application) please call (760) 602-4610. I. REQUIRED PLANS (All required plans shall be collated into complete sets, stapled together, then folded to 9" x 12" with lower right hand corner of plan visible.) A. SITE PLAN Required copies on 24" x 36" sheet(s): Minor permits: Four (4) copies Major permits: Seven (7) copies Ten (10) copies of the site plan shall be submitted by the applicant upon request of the project planner when the project is scheduled for review by the Planning Commission or City Council. Each site plan shall contain the following information: 1. GENERAL INFORMATION E a. Name and address of owner whose property is proposed to be developed and the name, address, and phone number of the developer. Name, address, and phone number of registered civil engineer, licensed surveyor, landscape architect or land planner who prepared the maps/plans. North arrow and scale. fl d. Vicinity map showing major cross streets. P-2 Page 1 of 9 Revised 02/16 RI. Two copies of preliminary, soils/geologic report for all projects with cut or fill depths exceeding 5 feet. EJ. For all condominium conversions, a signed statement by the owner stating Section 66427.1 of the State Map Act will be complied with. EK. For all condominium conversions, a letter from San Diego Gas and Electric stating that plans to convert the gas and electric system to separate systems have been submitted and are acceptable. EL. For all condominium conversions, one (1) copy of a compliance inspection performed by the Building Department. (Separate fee required.). ___ EM a Pëliiñ Hdiol5 SttVdifiEThhng map andëãlUlâtiänt monstfte capac Iizi dfãiñiñfräffüttfl jw befôë biiiDeending upon the coleity of the may be requi on any EN. Two copies of a completed and signed "Storm Water Standards Questionnaire" (form E-34). This form can be found on the city's website: (Distribute copy to Land Development Engineering). EO. If, when completing the Storm Water Standards Questionnaire, the project is subject to "Standard Project," requirements, submit a completed and signed "Standard Proiect Requirement Checklist" (form E-36) in accordance with the City BMP Design Manual per the City of Carlsbad Engineering Standards, latest version. EP. If, when completing the Storm Water Standards Questionnaire, the project is defined as a "Priority Development Project," submit a preliminary Storm Water Quality Management Plan (SWQMP) prepared in accordance with the City BMP Design Manual per the City of Carlsbad Engineering Standards, latest version. Refer to the city's SWQMP template (form E-35). EQ. Completed "Project Description/Explanation" sheet. ER. Signed "Notice of Time Limits on Discretionary Applications." ES. Noise study consistent with City of Carlsbad Noise Guidelines Manual. ET. Biological resource, cultural resource, and/or other environmental studies that are necessary to make an environmental determination (i.e. EIR, Negative Declaration or Exemption) and to determine compliance with the HMP. EU. Signed "Hazardous Waste and Substance Statement" form. EV. Provide color board(s) (no larger than 9" x 12"), showing building materials and color samples of glass, reveals, aggregate, wood, etc. EW. Photographs of the property from the north, south, east and west. EX Digital copy of Tentative Map along with required number of hard copy maps. EY. Fees: See Fee Schedule for amount. EZ. Early Public Notice Package. Ill. SPECIFIC PROJECT REQUIREMENTS EA. For Density Bonus Projects: A letter signed by the present owner stating what specific incentives are being requested from the City. For any development standards modification or other additional incentive requested, the applicant shall submit a project pro-forma to demonstrate that the standards modification or other requested incentive is necessary to make the project economically feasible. A detailed vicinity map showing the project location and such details as the location of the nearest commercial retail, transit stop, potential employment locations, park or recreation facilities or other social or community service facilities. For condominium conversion requests, a report documenting the following information for each unit proposed to be converted: the monthly income of tenants of each unit throughout the prior year, the monthly rent for each unit throughout the prior year and vacancy information for each unit throughout the prior year. Identify the number and location of lower income dwelling units. P-2 Page 7 of 9 Revised 02/16 LJt J I w 0 cH J 16 1 C'0, - 30' 0 30 Tt1 LEGEND: DRAINAGE BASIN BOUNDARY TRIBUTARY TO PROPOSED BIOFILTRATION BASIN EXISTING IMPERVIOUS AREAS F- PROPOSED DRAINAGE FACILITY 5 I I PROPOSED BIOFILTRATION BASIN PROPOSED IMPERVIOUS SURFACES J (ROOFS, DRIVEWAY, HARDSCAPE) PROPOSED PERVIOUS SURFACES (LAN DSCAPIN C) PROPOSED SELF-MITIGATING AREA PROPOSED DE MINIMIS AREA NOTES: THE HYDROLOGIC SOIL GROUP AT THE SITE IS ENTIRELY B. THE APPROXIMATE DEPTH TO GROUNDWATER IS 11 FEET. THERE ARE NO NATURAL HYDROLOGIC FEATURES OR CRITICAL COURSE SEDIMENT YIELD AREAS AT THE SITE. SEE ATTACHMENT lB FOR TABULATION OF DMAS. BIOFILTRATION BASIN SHOWN HEREON REPRESENTS BASIN FLOOR AREA REQUIRED PER CALCULATIONS. ATTACHMENT 1A - DRAINAGE MANAGEMENT AREAS (DMA) EXHIBIT San Diego County Hydrology Manual Section: 3 Date: June 2003 Page: 6 of 26 Table 3-1 RUNOFF COEFFICIENTS FOR URBAN AREAS Land Use Runoff Coefficient "C" Soil Type NRCS Elements County Elements % IMPER. A () C D Undisturbed Natural Terrain (Natural) Permanent Open Space 0.20 0.25 0.30 0.35 Low Density Residential (LDR) Residential, 1.0 DU/A or less 10 0.27 0.32 0.36 0.41 Low Density Residential (LDR) Residential, 2.0 DU/A or less 20 0.34 0.38 0.42 0.46 Low Density Residential (LDR) Residential, 2.9 DU/A or less 25 0.38 0.41 0.45 0.49 Medium Density Residential (MDR) Residential, 4.3 DU/A or less 30 0.41 0.45 0.48 0.52 Medium Density Residential (MDR) Residential, 7.3 DU/A or less 40 0.48 0.51 0.54 0.57 Medium Density Residential (MDR) Residential, 10.9 DU/A or less 45 0.52 0.54 0.57 0.60 Medium Density Residential (MDR) Residential, 14.5 DU/A or less 50 0.55 0.58 0.60 0.63 High Density Residential (HDR) Residential, 24.0 DU/A or less 65 0.66 0.67 - 0.69 0.71 High Density Residential (HDR) Residential, 43.0 DU/A or less 80 0.76 0.77 0.78 0.79 Commercial/Industrial (N. Corn) Neighborhood Commercial 80 0.76 0.77 0.78 0.79 Commercial/Industrial (G. Corn) General Commercial 85 0.80 0.80 0.81 0.82 Commercial/Industrial (O.P. Corn) Office Professional/Commercial 90 0.83 0.84 0.84 0.85 Commercial/Industrial (Limited I.) Limited Industrial 90 0.83 0.84 0.84 0.85 Commercial/Industrial (General I.) General Industrial 95 0.87 0.87 0.87 0.87 *The values associated with 0% impervious may be used for direct calculation of the runoff coefficient as described in Section 3.1.2 (representing the pervious runoff coefficient, Cp, for the soil type), or for areas that will remain undisturbed in perpetuity. Justification must be given that the area will remain natural forever (e.g., the area is located in Cleveland National Forest). DU/A = dwelling units per acre NRCS = National Resources Conservation Service 3-6 425O 33923N 40 :: 1k * k \ 4 t Hydrologic Soil Group—San Diego County Area, California 33 9'i6 'N o'••' 8 c 8 ' Map scale: 1:1,380 if printed on A landscape (11" x 8.5") sheet N 0 20 40 80 120 A Feet ,\\0 50 100 200 300 Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone uN WGSB4 usa& Natural Resources Web Soil Survey Conservation Service National Cooperative Soil Survey 4 330 9'23" N '8 8 330 9'16'N 5/4/2016 Page 1 of 4 Hydrologic Soil Group—San Diego County Area, California MAP LEGEND MAP INFORMATION Area of Interest (AOl) c The soil surveys that comprise your AOl were mapped at 1:24,000. El Area of Interest (AOl) • cio Warning: Soil Map may not be valid at this scale. Soils D Soil Rating Polygons Enlargement of maps beyond the scale of mapping can cause A D Not rated or not available misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting AID Water Features soils that could have been shown at a more detailed scale. -...- Streams and Can3l -. Transportation Please rely on the bar scale on each map sheet for map B/D -- Rails measurements. EJ C Interstate Highways Source of Map: Natural Resources Conservation Service C/D Web Soil Survey URL: http:I/websoilsurvey.nrcs.usda.gov EJ us kOIJ?P.S Coordinate System: Web Mcrcotor (EPSG:3857) 0 Major Roads Maps from the Web Soil Survey are based on the Web Mercator Not rated or not available Local Roads projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Soil Rating Lines Background Albers equal-area conic projection, should be used if more accurate ~ A Aerial Photography calculations of distance or area are required. _- AID This product is generated from the USDA-NRCS certified data as of _- B the version date(s) listed below. B/D Soil Survey Area: San Diego County Area, California Survey Area Data: Version 9, Sep 17, 2015 -- C Soil map units are labeled (as space allows) for map scales 1:50,000 C/D or larger. D Date(s) aerial images were photographed: Nov 3,2014—Nov 22, , Not rated or not available 2014 Soil Rating Points The orthophoto or other base map on which the soil lines were • A compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting • AID of map unit boundaries may be evident. - • B/D USIM Natural Resources Web Soil Survey 5/4/2016 Conservation Service National Cooperative Soil Survey Page 2 of 4 Hydrologic Soil Group—San Diego County Area, California Hydrologic Soil Group Hydrologic Soil Group— Summary by Map Unit - San Diego County Area, California (CA638) Map unit symbol Map unit name Rating Acres in AOl Percent of AOl Manna loamy coarse sand, 2 to 9 percent slopes 7.6 100.0% Totals for Area of Interest 7.6 100.0% Description Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms. The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (AID, BID, and 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, B/D, or do), 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 0 are assigned to dual classes. Rating Options Aggregation Method: Dominant Condition Component Percent Cutoff None Specified USDA Natural Resources Web Soil Survey 5/4/2016 Conservation Service National Cooperative Soil Survey Page 3 of 4 IIIj!!III ..-..:iuuiIi' Ih1flk liii !UIIhIhL County of San Diego orange . .. . . . Hydrology Manual County Riverside County ± Rainfall Isopluvials __________ 51 100 Year RaInfall Event -6 Hours , 5 - ----- —s---' -- -- -- isopIuI(inthes) CAJIL!8AU .-. -- o wrs Lf / 33•Ø• I -'i-.' c_ a.M4AsEAc 5 D cOt41Y C) I 2 - - WTEE L -'--iTh ITM- --- - , - N I N 46 P6 = 2.6' - GROVE L - DPW IS I1 kxI REACH tMeXt HH - b -.-----'--'- 33O S 3 0 3Mlies County of San Diego Orang - - Hydrology Manual 33- County Riverside County ",L- 9t cc ... -, •.. . . \... / Rainfall Isophials 4 - ........ .. 100 Year Rainfall Event- 24 Hours . .,.-, .. .. .. .\' - SITE : I 70 - o I 33 O SQ j B oe. 0 ..:j:_'/'. JP ,t•• r .! \\\.( L I -.. -. ... ,- '--- ... . - - 45' P24 = 4.5" / _ ........... '•..:L-- % 32 - I j p çr GIS 1-4 TiiIII4Itjfftr f W. ERIAL ACM - - __ - M e X I C w E 33 30 3Wes