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 3 building pad must be 1 foot above the calculated 100-year water surface elevation for a new development. Per Figure 3-1 from the Orange County Local Drainage Manual (Included in Appendix F) the 100-year Flood Elevation for local streets is equivalent to the highest elevation along the property frontage at the right of way. 2 .2 Hydrology Analysis The following sections describe the existing and proposed drainage patterns for the project site. 2 .2.1 Existing Condition Hydrology Analysis The project site is located within the Anaheim Bay watershed, of the Orange County Flood Control District (OCFCD). The project discharges Santa Ana River-Reach 1 then to the Pacific Ocean. See Appendix F for watershed and downstream tributary maps. The topography of the project site is relatively flat with slopes varying from 0.4% to 4.9%. Site elevations range from 80 to 82 feet above Mean Sea Level. The existing site has buildings, landscape, and parking spaces. The existing condition consists of drainage areas A-1 through A-2, which consist of a total of 0.87 acres with 26% pervious area. See the Drainage Area Breakdown summary table in Section 3 of this report for exact drainage area specifications. In general, the easterly half of the site from the most westerly parking stalls to the right -of-way sheet flows to the central trench drain, drainage structure as shown in the existing conditions hydrology map located in Appendix B. From the trench drain a 4” outlet pipe is connected to a central 36” x 36” concrete catch basin. The catch basin contains a non-operational sump pump discovered by field inspection. From the existing 36” catch basin stormwater is pumped through a 2” curb outlet located along Bewley Street and outlets into the public storm drainage system from there. Stormwater deriving from the westerly half of the site in general tends to flow in many different directions and mainly towards the westerly property line denoted as “Outfall 2”. There appears to be no additional existing drainage improvements on-site other than the central trench drain inlet, the 36” catch basin and a 2” drainage outlet at the curb on Bewley. Additionally, it’s important to note that the north, south and east property lines are all lined with a block screen wall. In extreme storm events the site will pond and enter the central existing catch basin denoted as “Outfall 1”. If the existing pump located at Outfall 1 were to fail stormwater would then exit at the southeasterly property corner at the right-of-way which holds an interpolated existing elevation of (80.69) ft. Field measurements to the bottom of the existing drainage structures are listed on the included Hydrology Maps. 914-918 N Bewley St5/8/2025