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HANSEN PARK 8 <br /> <br />5.2 PROPOSED HYDRAULICS AND COMPARISONS <br />The effect of the proposed dam replacement and pond excavation on flows and water surface elevations <br />from Hansen Park and downstream to Long Lake was evaluated by modifying the existing conditions <br />SWMM model. <br /> <br />A summary of the modeling results detailing proposed conditions and comparisons to existing conditions <br />are summarized in the report sections below. <br />5.2.1 HANSEN POND AND DAM HYDRAULIC STRUCTURE DATA <br />Table 2 describes the existing and proposed condition pond, dam, and outlet. <br />Table 2: Hydraulic Data Summary <br /> Existing Condition Proposed Condition <br />Downstream Stream Bed Elevation 866.7 866.7 <br />Pond Bottom Elevation 872.0 869 <br />NWL (outlet Elevation) 875.3 873.0 <br />Model Starting Water Surface 875.4 873.0 <br />Outlet Pipe Size NA 30-inch <br />Outlet Pipe Elevation NA 869.5 <br />Outlet Structure Stoplog Elevation (normal operations) NA 873.0 <br />Primary Weir Elevation 875.3 877.3 <br />Primary Weir Length 21 feet 21 feet <br />Primary Weir Shape Rectangular Trapezoidal <br />Secondary Weir Elevation 878.3 881.0 <br />Overland Overflow Elevation 877.54 NA <br />Reservoir Area at NWL (Acres) 8.8 8.6 <br />Reservoir Area at Primary Weir Elevation (Acres) 8.8 17.3 <br />Dead Storage Provided (acre-feet) 10.5 26.7 <br />Storage Provided at Primary Weir Elevation (acre-feet) 10.5 77.4 <br />Live Storage Provided during 100-yr, 24-hour rainfall <br />(acre-feet) 107.2 134.6 <br />Depth at NWL 3.3 4 <br />Watershed Area (Square Miles) 7.3 7.3 <br />*All elevations reference NAVD88 <br />5.2.2 HANSEN PARK POND – ABOVE DAM <br />Table 3 shows the peak water surface elevations at Hansen Park resulting from the 2-, 10-, and 100- <br />year, 24-hour rainfall events, along with critical structure elevations. <br />Table 3: Hydraulic Data and Critical Structure Elevations at Hansen Park <br />Stage (NAVD88) <br />Rainfall Event Existing Condition Proposed Condition Difference <br />2-year, 24-hour 877.29 878.28 0.99 <br />10-year, 24-hour 878.21 878.73 0.52 <br />100-year, 24-hour 881.01 880.92 -0.09 <br />Discharge (cfs) <br />Rainfall Event Existing Condition Proposed Condition Difference <br />2-year, 24-hour 301 294 -7