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Home My WebLink AboutSDP 15-14; L.W. OFFICE BUILDING; DRAINAGE STUDY & HYDROLOGY REPORT; 2017-07-120N Civil Engineering Design Group ~2: CIVIL & STRUCTUAA-L DRAINAGE STUDY & HYDROLOGY REPORT COMMERCIAL GRADING PROJECT: L.W. OFFICE BUILDING SDP 15-14 GR 2017-0005 2055 CORTE DEL NOGAL, CARLSBAD, CA APN 213-061-08 CDG Project No: 0905315 Prepared for: Mr. ED FUDURICH WELLS LLOYD GIFT TRUST 17083 Old Coach Road, Poway CA 92064 858-229-4001 Prepared by: Civil Engineering Design Group 2420 Grand Avenue, Suite B-I, Vista, CA 92081 760-599-8585 Massood Gaskari, P.E. NO. C47303 - Exp. 12-31-2017 December 1, 2015 Revised July 12, 2017 CEIVED DEC 052017 LAND DEVELOPM , ENGINEERING I 2420 Grand Avenue, Suite B- 1, Vista, CA 92081 Phone 760-599-8566 Fax 760-599-8901 Page 1 , I Civil Engineering Design Group I INTRODUCTION: This report is for a grading plan, which has been prepared by Civil Engineering I Design Group. The subject property is located in the City of Carlsbad, State of California, located at Corte Del Nogal (APN # 213-061-08). The property is partially developed at this time. The grading plan is shown on the City Drawing Number 491- I 2A. The San Diego Hydrology Manual was used to determine the runoff from storm having a 100 year return frequency. The results are shown on the attached calculation sheets. DISCUSSION: The project site consists approximately of 2.95 ± acres. Commercial properties are located immediately adjacent to this property. The site is currently partially developed with a commercial building and associated parking. The project is located on southerly side of Corte Del Nogal, in the City of Carlsbad. More specifically, the property is located at the southeasterly corner of the intersection of Corte Del Nogal with Corte Del Abeto. Areas adjacent to the property are currently developed and there is no runoff contribution from off-site. The current topography shows a differential grade elevation of approximately 35 ± I feet from high points along the northeasterly corner of the property to low point at the southeasterly corner of the property. Currently, the westerly half of the site developed I with a commercial building and associated parking. The building is located along the southeasterly corner of the site and the associated parking located directly to the north and east of the building. Runoff developed through the site currently sheet flows onto I two low points at northwest and at the southeasterly corners. Two basins are formed within the existing (pre-developed) condition. Most of the developed section of the existing site (approximately 1.23 ± acres) flows onto the most northwesterly corner of I the property (POC #1 on existing land use map). The remaining area forms a basin that flows to POC # 2 at southeasterly corner. Approximately 65,000 square feet of existing area consists of pervious surface with the remaining portion (63,000 square I feet) consists of impervious surface and/or rooftop. The entire contribution is collected and discharged without being controlled and/or treated at this time. I The proposed development includes construction a new commercial building with associated parking. The new development will remove portions of the existing pavement and replaces it with new. The new building will be located at the I northeasterly corner of the site with new parking area directly to the south of the new building, at the southeasterly corner. The new development will increase the amount of impervious surface within the property from the current amount of approximately I 63,000 to approximately 86,400 square feet, an increase of approximately 37%. The project proposes underground storage system of "Stormtech" to accommodate the - increased runoff volume that is generated from increase in the impervious area. 2420 Grand Avenue, Suite B-i, Vista, CA 92081 Phone 760-599-8566 Fax 760-599-8901 Page 2 Civil Engineering Design Group 1 Drainage pattern and Point of Compliance (POC) for the property remains the same after the new development is complete. Soil conditions within the property are classified as Group "B", which promote infiltration. The new development will introduce LID design and proposes to treat the runoff through infiltration prior to final discharge. Discharge from the new development will sheet flow through landscaped areas and infiltration basins to two low points within the property; one located at the southerly side of the property where a bio-retention basin is proposed for treatment purposes. Grass lined swales and filtration basins within the planters provide for first flush treatment. The bio-retention basin at the final discharge is sized to contain the developed flows and will act as a treatment center and trap targeted pollutants. Final discharge from the basin will be through an overflow pipe at POC #2, and will be no more than the historical rate for the deve1oed area. The existing improvements along the westerly half of the property will also be improved upon in terms of hydrology and stormwater treatment. A portion of the existing building and the existing parking area will drain towards the westerly side where a grass lined swale is designed to accommodate for the first flush treatment. The grass swale will discharge into a bio retention facility at the northeasterly corner of the property for infiltration. An overflow pipe is designed for discharge at the curbside on Corte Del Nogal, POC #1. Flow based BMPs shall be installed per the City of Carlsbad requirements and in accordance with San Diego WQCB "California Storm Water Best Management Practices" handbook. CONCLUSION: The proposed grading plan and drainage facilities have been designed in accordance with standard engineering practices and per the requirements of the County of San Diego Hydrology Manual. The proposed grading plan and drainage facilities will accommodate the run-off generated on-site for the storm having a 100-year return frequency. It will be the responsibility of the owner to train employees and / or contract with a qualified company to maintain the approved BMPS installed on this Project. 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, and that the design is consistent with current standards. 2420 Grand Avenue, Suite B-i, Vista, CA 92081 Phone 760-599-8566 Fax 760-599-8901 Page 3 ,- M Civil Engineering Design Group 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. 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I -1 . - .. ... . . 2420 Grand Avenue, Suite B-i, Vista, CA 92081 Phone 760-599-8566 Fox 760-599-8901 Pe Ic' z-p 7;,e (i-tJA U I I I I I I Civil Engineering Design Group 2420 Grand Ave, suite B- 1, Vista, CA 92081 Phone (760) 599-8566 Fax (760) 599-8901 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 Undisturbed Natural Terrain (Natural) Permanent Open Space 0* 0.20 (EO 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 0.85 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 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 (Ti Element* DU/ Acre .5% 1% 2% 3% 5% 10% LM Tj LM T1 LM Tj LM T1 LM Tj LM T 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 1 11.3 70 1 10.5 1 85 9.2 100 8.8 1 100 7.4 100 5.8 LDR 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 10.9 50 8.7 1 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 6.5 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 O.P./Com 50 4.2 60 3.7 70 3.1 80 2.9 2.6 100 22 Limited 1. 50 4.2 60 3.7 70 3.1 80 2.9 90 2.6 100 2.2 General I. 1 50 3.7 1 60 3.2 1 70 1 2.7 80 2.6 90 2.3[100 1.9 *See Table 3-1 for more detailed description 3-12 2.50% slope-4 2.0- -i 100 15- 30 - - - - .75 - -.5 0 cP ç P I— _—: w I.- w IL 0 C,-. z I 20 w U I w z p 2? 0 -J Cl, U- 0 o - - - - - - •jg 0 Ir w Ix w> 0 0 EXAMPLE: Given: Watercourse Distance (D) = 70 Feet Slope(s)=1.3% 1.8(1.1-C)V5 Runoff Coefficient (C) = 0.41 T= Overland Flow Time (T) = 9.5 Minutes SOURCE: Airport Drainage, Federal Aviation Administration, 1965 FIGURE Rational Formula - Overland Time of Flow Nomograph 3m3 EQUATION: V 1.49 R2' s1'2 n 0.3 .0.2 50 .0.01 0.15 1-'\ 30 L 0.4 0.10 .0.09 0.08 0.5 0.07 20 0.06 0.05 0.04 08 p0.02 1.0 \fQ \ 10 _ 0.03 ol CL D -,-...--- ......-- 0.04 CL I 0.009 < 2 .?K \,\L\ 5 un 0.008 0 '. w 0.05 0.005 of 4 I' \ , 0.08 :1: \0.09 1 0.001 9 0.0009 0.0008 10 1.0 0.2 0.0007 0.9 .0.0006 0.8 0.0005 10.7 0.0004 .0.3 0.6 0.0003 20 0.5 0.4 GENERAL SOLUTION SOURCE: USD01 FHWA, HDS-3 (1961) FIGURE Manning's Equation Nomograph 37 L FT r j TT4 ru 1-h ..H_L.4..I...,.,.4 - FH 4----4--4-F -1-44-4--F -.*--F . 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