914-918 N Bewley St - REV 1 - Plan

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Illumination Foundation Santa Ana, California Hydrology Report by TAIT & Associates TAIT JOB # SP9104 Page 4 The Existing Hydrology Map is provided in Appendix B and it depicts drainage subareas, elevations, flow lengths and slopes used for the hydrology calculations. The existing condition 25- and 100-year storm events Rational Method analysis results are included in Appendix C. 2 .2.2 Proposed Condition Hydrology Analysis The proposed project will slightly alter the existing drainage patterns. The proposed site will include buildings, parking spaces, and landscaped areas. In the proposed condition the site is relatively flat with slopes varying from 0.0% to 3.2% in paved areas and up to 3.5% in landscaped areas. Site elevations range from 79 to 82 feet above Mean Sea Level. The proposed condition consists of drainage area s A-1 through A-6 which consist of 0.87 acres consisting of 23% pervious area respectively. In general, the overall drainage area A, water sheet flows from the northeast to the previously mentioned existing inlet, which connects to a central 36” x 36” catch basin/sump pump pit. A new pump will be installed by the contractor which is specified to handle 0.5 CFS along with a new larger 4” maximum diameter outlet pipe out to the curb face on N. Bewley St. Roughly, the westerly 3rd of the site similarly to the existing condition diverts flows to a landscape strip along the easterly property line where it is suspected that drainage percolates into the ground as in the existing condition. The existing soils are of type A which typically have a high capacity for percolation. In the proposed condition the overall drainage being diverted to outfall 2 is decreased by the addition of storm drainage inlets which divert flows to Outfall 1. Similarly to the existing condition, in an extreme storm scenario such as the 100-yr event the surrounding property walls would likely cause the site to pond and exit out at the south Easterly property corner at the right-of-way where the interpolated existing condition elevation is (80.69) CFS as shown on the Proposed Hydrology Map. The Proposed Hydrology Maps is provided in Appendix D and it depicts the drainage subareas, elevations, flow lengths and slopes used for the hydrology calculations. The proposed condition 25- and 100-year storm events Rational Method analysis results are included in Appendix E. Section 3 Summary of Results and Conclusions The overall total peak flow for the entire site sees a reduction in peak flows from the existing to proposed condition. The decrease in flows for the 25-year and 100-year storm event by 0.02 cfs & 0.03 cfs respectively. 914-918 N Bewley St5/8/2025