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Home My WebLink AboutDEV 2016-0043; VAUGHN RESIDENCE; DRAINAGE SUMMARY; 2017-09-06COFFEY ENGINEERING, INC. September 6, 2017 Engineering Department City of Carlsbad 1635 Faraday Ave Carlsbad, CA 92008 Re: Drainage Summary Vaughn Residence 2605 Crest Drive, Carlsbad, CA 92008 Dear Sir or Madam: #•4 W k\ 1. 4.) SEP O. Oi7 LAND DEVELCPjE:T EN G; The existing site consists of a vacant 0.28 AC lot located at 2605 Crest Drive in Carlsbad, CA. Drainage on the vacant lot can best be described as sheet flow with runoff flowing from the eastern corner of the site in a westerly direction. The grade falls in elevation approximately 9 ft. over a distance of approximately 200 ft. The drainage area tributary to the site consists of the site itself (12,344 ft2), a portion of the fronting road (apprx. 3,000 ft2), and a portion of the neighboring lot to the southeast (apprx. 9,200 ft2). Attached to this letter is an exhibit depicting the extent of the drainage area tributary to the site. Runoff from the area tributary to the subject property exits the site at the western property corner where is continues westerly for approximately 90 ft. where the terrain begins to fall in a southwesterly direction and runoff continues to the next street over (Wilson Street). Current discharge from the tributary area containing the project has been calculated to be 1.34 cfs for a 100-year storm. The proposed construction consists of a new single family residence with a footprint of approximately 21600 ft2, car port, driveway as well as landscaping and minor hardscape. Drainage for the proposed site will be accomplished by surface sheet flow only. No subsurface drainage system is proposed. The proposed development will require minor grading (30 CY - balanced) to create a pad for the proposed home and to fine grade the driveway. No significant changes in overall topography are necessary or proposed from the existing conditions. Rainwater from the house will be collected at the downspouts and routed to a cistern to be used for irrigation purposes. Runoff from the driveway and offsite tributary area will be intercepted by a vegetated swale along the southern edge of the subject property where it will flow westerly then northerly, ultimately discharging to an existing riprap pad at the westernmost corner of the site. Runoff from the remainder of the site (landscaping areas and perimeter of the house) will flow along the - 9666 BUSINESSPARK AVENUE, SUITE 210, SAN DIEGO, CA 92131 PHONE: (858) 831-01 11 FAx: (858) 831-0179 surface to a vegetated swale along the northern edge of the subject property where it will then flow westerly, ultimately discharging to the existing riprap at the westernmost corner of the site. Calculated discharge from the developed condition of the tributary area containing the project has been calculated to be 1.48 cfs for a 100-year storm. The calculated maximum discharge velocity of the proposed vegetated swales to the exiting riprap at the rear of the site is 1.90 fps. The existing riprap (No. 2 Backing per Dwg. No. 485-4A) is an appropriate size for this velocity. If we can be of further assistance in providing any additional information, please feel free to contact us. Thank you. Sincere / 44,7 Daniel Vald , PE Coffey Engineering, Inc rn ly- No. C0760'74 Page 2 of 2 DNI 'ONIèIJNION AdJOD C:E \400 _ \ _ 42 _ '*lot RXI 141 URI .4 rT Aid (eJoE 99o) JS 1!C f1 )! Ik t$k Oki AW iø&'* L 'b Ag :s( W7 low IV V.,.. 4 N1. ji 11 :AS..• .. I ' ____ F' ___ • Table A - Weighted Runoff Coefficients ('C') impervious/ Percent Developed Area Pe 7(SF) s Area Impervious/De DMA (SF) Total (SF) Total (Ac) CValue* veloped Pre 12,200 12,344 24,544 0.56 0.35 49.71% Post 16,470 8,074 24,544 0.56 0.38 67.10% *Impervious Areas C=0.45; Pervious Areas C=0.25; Pervious Payers Cr0.40 Table B - Project Runoff Calculations Natural Watercouce (per Fig 3. Urban Overland (Sheet) Flow (per Fig. 3-3) Pipe/Channel Flow Summary 100-yr P6 = 2.60 minimum) Natural Urban Total time- Element & Change in watercouse watercours Maximum Initial Ttime of Average Pipe travel of- Flow ID Dwelling Watercourse Elevation, H duration, D, e distance, Overland Flow Runoff Concentration Overland Flow Pipe Length, velocity, V time, T concentrati Runoff Coefficient, Rainfall Intensity, I Basin Area, A Q(cfs) = (Basin) Unit/Acre distance, L (ft) Elev. 1 Elev. 2 (ft) (mm) Ti (ft) (!5 LM) Length Watercourse slope, s (%) Coefficient, C (per Fig. 3-2) Time, Tt (mm) L (ft) (fps) (mm) on, r (mm) C (in/hr) (acres) C*l*A Pre MDR-4.3 228 186 177 9 1.77 0.00 0.00 5.00 0.35 6.85 0.561 1.34 Post MDR-4.3 ____________ ______ 0 0.00 ________ __________ _________________ ___________ ___________ 0.00 228 1.4 2.81 5.00 0.38 6.85 0.561 1.48 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 B C D I Undisturbed Natural Terrain (Natural) Permanent Open Space I 0* 0.20 I 0.25 I 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 I 30 0.41 I 0.45 I 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 ForcsO. DU/A = dwelling units per acre NRCS = National Resources Conservation Service 3-6 EQUATION L E Tc= (11 i.913\0.385 1Feet LE 5000 Tc = Time of concentration (hours) I = Watercourse Distance (mites) h-400° LE = Change in elevation along effective slope tine (See Figure 3-5) (feet) 3000 Tc I-- Hours Minutes I- 2000 4 L 240 3 I 180 —1000 900 800 2 120 'D0 100 600\ 90 _500\\ Ba —400 \ 70 —NO 1 60 300 50 —200 40 L Miles Feet 30 100 4000 20 18 300 16 -50 0.5--14 -40 2000 12 1800 1600 10 -30 1400 \ 9 1200 8 .20 1000 7 900 800 6 700 5 600 -10 500 4 400 3 300 200 L SOURCE: California Jivisioi of Highways (1941)and Kirpich (1940) FIGURE Nomograph for Determination of Time of Concentration (Tc) or Travel Time (It) for Natural Watersheds 3.4 (1nh111hTcfS2n lhia0 33* 0re _________ Hydrology Manual _________ _________ _____ / .. Riverside County 01 %r Lp k—' Rainfall Isopluvials I _ ______________ . 100 Year Rainfall Event6 Hours 4.0 laopkMal (inches) P6=26 EN 33OO __ 3O -L I I tbt4±Lft -, H - I 'SANDIEOO/ /N \C\l 5 =ON •. /ico '. 245 T ------- DPW --------- _ _ _ M e x I 3230 to - - 3230 3 0 3MHes 6 Oranqej County! L O 3330 I 3315 Cciiinti cfFii, fla0 Hydrology Manual occr Rainfall Isoplu-vials 100 Year Rainfall Event -24 Hours - 8opIaI (Inchos) 3245' t. n I— DPW -GIS SanGIS H— S— T),o (<,vjd! + ( *PCIEU C*aLIflOI &ITFtTLUSTEU1O WE .LUOWARR.H,la r, C*AWNTMWI1VflCFTflfQEApAflflCL,fiflU.O3E UU E 3230 S 3 0 3Mlles C 4 4 33 10 23N Hydrologic Soil Group—San Diego County Area, California (Vaughn Residence - Hydrologic Soil Group) C 4 33° 1023N I 468550 468550 468570 33° 10 21" N 46&190 468E03 4510 42fl 45.5?O 468540 C Map Scale: 1:441 if punted on teidscape (lix 8.5) shea MetersN 0 5 10 20 CD A Aeet 0 20 40 a) 120 Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone uN WGS84 USDA Ndtulal Resources Web Soil Survey Conservation Service National Cooperative Soil Survey 33° 10'21"N C 9/1/2017 Page 1 of 4 13 u C/D • Not rated or not available Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Koads Local Roads Background Aerial Photography Hydrologic Soil Group—San Diego County Area, California (Vaughn Residence - Hydrologic Soil Group) MAP LEGEND MAP INFORMATION Area of Interest (AOl) Area of Interest (AOl) Soils Soil Rating Polygons ND BID CID ri Not rated or not available Soil Rating Lines — A — ND B — B/D -- C D 0 Not rated or not available Soil Rating Points • A • ND • B • B/D The soil surveys that comprise your AOl were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (:31) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: San Diego County Area, California Survey Area Data: Version 10, Sep 12, 2016 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Nov 3, 2014—Nov 22, 2014 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shiffing nf map unit hniunclaries may he evident. USDA Natural Resources Web Soil Survey 9/1/2017 211111111111 Conservation Service National Cooperative Soil Survey Page 2 of 4 Hydrologic Soil Group—San Diego County Area, California Vaughn Residence - Hydrologic Soil Group 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 Prcent of AOl CbC Carlsbad gravelly loamy B 0.2 81.1% sand, 5 to 9 percent slopes MIE Marina loamy coarse B 0.1 18.9% sand, 9 to 30 percent slopes Totals for Area of Interest 0.3 100.0% 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 CID). 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 CID), 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 D are assigned to dual classes. USDA Natural Resources Web Soil Survey - 9/1/2017 Conservation Service National Cooperative Soil Survey Page 3 of 4 Hydrologic Soil Group—San Diego County Area, California Vaughn Residence - Hydrologic Soil Group Rating Options Aggregation Method: Dominant Condition Component Percent Cutoff: None Specified Tie-break Rule: Higher USDA Natural Resources Web Soil Survey 9/1/2017 Conservation Service National Cooperative Soil Survey Page 4 of 4