PRELIMINARY HYDROLOGY STUDY

Transcription

1 PRELIMINARY HYDROLOGY STUDY FOR Tentative Tract Map West Side of Loma Alta Drive City of Oceanside, CA Prepared For: EMERALD HILLS LLC 4272 Dogwood Avenue Seal Beach, CA Contact: Mr. Jimmy Chen Ph: (562) Prepared By: W&W LAND DESIGN & CONSULTANTS 2335 W. Foothill Blvd., Suite 1 Upland, CA (909) winstonliu@ww-technologies.com October 1, 2014 Project job No. 1416

2 HYDROLOGY STUDY Oceanside-10 Lots 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 Oceanside is confined to a review only and does not relieve me, as engineer of work, of my responsibilities for project design. Winston Liu, RCE Date Seal Registered Civil Engineer 1416Hydrology Report

3 HYDROLOGY STUDY Oceanside-10 Lots TABLE OF CONTENTS Section I Section II Section III Appendix A Appendix B Appendix C Introduction Hydrology Methodology Project Description Existing Site Conditions Proposed Site Conditions Findings Vicinity Map Reference (Based on San Diego County Hydrology Manual June 2003): Soil Hydrologic Groups Map Runoff Coefficient for Urban Areas (Table 3-1) Rainfall Isopluvials 10 Year Rainfall Event 6 Hours Rainfall Isopluvials 10 Year Rainfall Event 24 Hours Rainfall Isopluvials 100 Year Rainfall Event 6 Hours Rainfall Isopluvials 100 Year Rainfall Event 24 Hours Hydrology Study: Intensity Duration Design Cart (Figure 3-1) 10 Year storm event Intensity Duration Design Cart (Figure 3-1) 100 Year storm event Existing Conditions Proposed Conditions Back Pocket Existing Hydrology Map Proposed Hydrology Map 1416Hydrology Report

4 HYDROLOGY STUDY Oceanside-10 Lots Section I Introduction The following hydrology study has been prepared for 10 residential lots subdivision project. The site is approximately 4.10 acre site with 8.36 acre drainage tributary area and is located on the west side of Loma Alta, in the City of Oceanside, County of San Diego, California. The general location of the site is illustrated on the Vicinity Map, included in the Appendix A of this report. Section II Methodology For both, the existing and proposed conditions, the peak storm discharge for the drainage sub-areas (see Hydrology Map in the pocket in the rear of this report) were calculated using the San Diego Hydrology Manual June 2003 version. Rational Method Equation was used to calculate the 10-year and 100-year storm event. The storm drain capacities calculations are calculated by using Flowmaster software. Section III Project Description Existing site conditions The existing site is approximately 4.10 acre vacant site with 9.36 acre drainage tributary land area. The site could be divided into six drainage sub areas and drainage towards southerly to the south end of project site, and ponding there in a low elevation at note 302; emergency flows to Walsh Street through an existing 12 drainage pipe crossing adjacent residential property. An existing 6 feet wide storm drain easement for the drainage pipe was shown on City drawing No. R-332. Refer to the Existing Hydrology Map for an illustration of the existing drainage zones. Rational method equation: Q=C x I x A, Soil Type D C Runoff Coefficient for Urban Areas (Table 3-1) C= 0.35 Undisturbed Natural Terrain C= 0.49 Low Density Residential (LDR) The following table illustrates the data and results for the existing 10-year and100-year storm events. 10-Year Storm Event Subarea Runoff Average Intensity Drainage Area Q (Peak Discharge) Coefficient (inch / hour) (acres) CFS H H H H H H Total Hydrology Report

5 HYDROLOGY STUDY Oceanside-10 Lots 100-Year Storm Event Subarea Runoff Coefficient Average Intensity (inch / hour) Drainage Area (acres) Q (Peak Discharge) - CFS H H H H H H Total Proposed site Conditions In the proposed condition, the project site will maintain existing drainage patterns and can be broken down into nine distinct drainage zones (E & A). Sub area E-1, E-2, A- through A- 3 drains to proposed interior private Street A curb and gutter connected into a proposed catch basin with a 24 storm drain pipe; that storm drain pipe drains into a proposal 4 feet wide concrete gutter along project southerly boundary; sub area E-3 through E-5 and A-4 will confluence with all other subareas flow into the 4 feet wife concrete drainage gutter and eventually go into a proposed water quality basin located at south end of the project site. All proposed runoff volume will be detained into the proposed basin and emergency over flow into Walsh Street through an existing 12 drainage pipe crossing adjacent residential property. An existing 6 feet wide storm drain easement for the drainage pipe was shown on City drawing No. R-332. Refer to the Proposed Hydrology Map in Appendix D in this report for an illustration of the proposed drainage zones. The following table illustrates the data and results for the proposed 10-year and100-year storm events. 10-Year Storm Event Subarea Runoff Coefficient Average Intensity (inch / hour) Drainage Area (acres) Q (Peak Discharge) - CFS E E E E E A A A A Total Hydrology Report

6 HYDROLOGY STUDY Oceanside-10 Lots 100-Year Storm Event Subarea Runoff Coefficient Average Intensity (inch / hour) Drainage Area (acres) Q (Peak Discharge) - CFS E E E E E A A A A Findings Total After development, more impervious surface will cover the proposed site than pre development condition. Total runoff was increased 1.07 cfs per 10-year storm event and 0.35 cfs per 100-year storm event only. A proposed water quality basin will be designed and installed to handle both of first ¾ flush in water quality purpose and detain additional runoff in proposed development condition. A detailed design and calculations for all proposed catch basins, concrete drainage gutter, storm drain pipe and water quality basin will be performed during final engineering design phase after entitlement approval. The hydrology and hydraulic analyses prepared in this report are comprehensive and evaluate the drainage impacts associated with the development of this project. The calculations within this report substantiate that the development can be constructed as shown on the proposed plans with no detrimental effect to surrounding properties. 1416Hydrology Report

7 HYDROLOGY STUDY Oceanside-10 Lots APPENDIX A VICINITY MAP 1416Hydrology Report

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9 HYDROLOGY STUDY Oceanside-10 Lots APPENDIX B Reference (Based on San Diego County Hydrology Manual June 2003): Soil Hydrologic Groups Map Runoff Coefficient for Urban Areas (Table 3-1) Rainfall Isopluvials 10 Year Rainfall Event 6 Hours Rainfall Isopluvials 10 Year Rainfall Event 24 Hours Rainfall Isopluvials 100 Year Rainfall Event 6 Hours Rainfall Isopluvials 100 Year Rainfall Event 24 Hours 1416Hydrology Report

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16 HYDROLOGY STUDY Oceanside-10 Lots APPENDIX C Hydrology Study: Intensity Duration Design Cart (Figure 3-1) 10 Year storm event Intensity Duration Design Cart (Figure 3-1) 100 Year storm event Existing Conditions Proposed Conditions 1416Hydrology Report

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19 Oceanside - Rational Method Calculations Q = C * I * A BASED ON SAN DIEGO COUNTY HYDROLGOY MANUAL VERSION JUNE 2003 Proposed Condition 10-Year Storm Event Subarea Runoff Coefficient Average Intensity (inch / hour) Drainage Area (acres) Q (Peak Discharge) - CFS E E E E E A A A A Total 8.36 Total (Q-10) Year Storm Event Subarea Runoff Coefficient Average Intensity (inch / hour) Drainage Area (acres) Q (Peak Discharge) - CFS E E E E E A A A A Total 8.36 Total (Q-100) 10.37

20 Oceanside - Rational Method Calculations Q = C * I * A BASED ON SAN DIEGO COUNTY HYDROLGOY MANUAL VERSION JUNE 2003 Existing Condition 10-Year Storm Event Subarea Runoff Coefficient Average Intensity (inch / hour) Drainage Area (acres) Q (Peak Discharge) - CFS H H H H H H Total 8.36 Total (Q-10) Year Storm Event Subarea Runoff Coefficient Average Intensity (inch / hour) Drainage Area (acres) Q (Peak Discharge) - CFS H H H H H H Total 8.36 Total (Q-100) 10.02

21 HYDROLOGY STUDY Oceanside-10 Lots Back Pocket Existing Hydrology Map Proposed Hydrology Map 1416Hydrology Report

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