5 Braewood Hills | KPFF Consulting Engineers STORMWATER ANALYSIS Analysis The water quality facilities have been sized using the Eugene Stormwater Facility Calculator. The calculator determines runoff using the Santa Barbara Urban Hydrograph (SBUH) Method and NRCS 24-Hour Type 1A Hyetograph as outlined in Appendix M of the City of Eugene’s Stormwater Management Manual. The facility capacity is based on the requirements and facility details found in the Eugene Stormwater Management Manual (see Appendix 3 for the Stormwater Facility Calculator results). Detention has been calculated using Storm and Sanitary Analysis (SSA). SSA modeled runoff from the developed lots, time of concentration, pipe capacity and detention volumes. For analysis purposes, each basin of the property required the following information as input data for the computer model: • Impervious Area (Ai), in acres • Curve Number (CNi), impervious • Travel Time (Tc) • Total Precipitation Precipitation data for the respective storms are City of Eugene design storms are shown in Table 1 below. TABLE 1: 24-Hour Precipitation for Eugene, OR (NOAA Atlas 2, Volume X) Storm Event Inches WQ 1.56 2-Year 3.12 5-Year 3.6 10-Year 4.46 25-Year 5.18 50-Year 6.0 100-Year 6.48 See Appendix 3 for Water Quality Calculations and Appendix 4 for Detention Calculations. Engineering Conclusions Based on the requirements of the Stormwater Management Manual, no errors were found in the stormwater system design. The facilities and conveyance components have enough capacity to handle the required storm events and should be approved as designed. 2100216-kg