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I I I I I I I I I I I I I I I I I I I I'JOlTE BEYOND ENGINEERING City of Brush Storm Drainage Master Plan Service (NRCS) Curve Number method for a 2-hour duration storm. Rainfall depths and distributions for the 10-year and 25-year storms were obtained from the previous Carter Burgess study (Ref. 1). NRCS Hydrologic Soil Group C was used for the entire study area based on soils information in the previous study. This methodology is consistent with that used in the previous Carter Burgess study. In the previous Carter Burgess study, the methodology for determining the retention pond volumes was not specified, although the volumes appear to be less than the runoff volume from a 2-hour duration, 10-year or 25-year storm. Since there is no discharge from a retention pond, volumes would typically be based on providing storage for a 100- year, 24-hour duration storm or larger to safeguard against potential overflows from a series of smaller storms. To provide an alternative with additional protection for drainage basins where retention ponds were considered, runoff depths and volumes were also determined for the 100-year, 24-hour duration storm based on the NRCS Curve Number method. Results Peak discharges were determined with HEC-1 for 19 drainage basins varying in size from approximately 20 to 260 acres. The drainage basins are shown on the Drainage Plan in the pocket at the end of this report. It should be noted that stormwater discharges are computed for each basin individually as closed basins and discharges are not combined. Additional analysis should be done during final design to determine the possibility of runoff from one basin overflowing that basin and contributing to an adj acent basin. Resulting stormwater discharges for the 1 O-year and 25-year storms are shown on Table 1 along with hydrologic parameters for the drainage basins. Nolte Associates,Inc. 3