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recommended empirical methods are summarized in Table 1 below along with the surveyed breach width, reported time of failure and modeled input parameters and peak breach discharge. Table 1 - Havana Street Pond Dam Breach Parameters 7.4 Analysis of Incremental Impacts The incremental impacts of the failure of the spillway were determined by modeling the reservoir assuming that the spillway had not failed for a baseline condition, and then modeling the event with the dam failure. Since the failure mode was easily determined, and the primary purpose of the modeling was to determine impacts of the dam failure on downstream flooding, determining the exact inflow to the reservoir through calibration was deemed unnecessary. The volume impounded by the reservoir was easily determined by the high water marks surveyed during the field investigation and the known stage - storage relationship for the reservoir. The results of the HMS modeling show that the incremental impacts of the dam failure were significant in terms of peak discharge, but relatively low in terms of impacts and damage. The peak discharge calculated with both the HMS and RAS models is approximately 5,600 - 6,400 cfs. This is approximately 3.0 - 3.5 times the discharge that was entering the reservoir (peak inflow was modeled to be approximately 1,600 cfs). However, the duration of this peak flow occurred over a period of approximately 30 minutes was short in comparison to the overall event which lasted for several days. The peak flow discharging from the dam breach was likely significantly attenuated in the wide, flat floodplain and by the railroad embankment downstream of the dam as MLM -WA Bav (ft) 73.3 Zb (_H:1V) 0.5 Tf (hr) 0.36 cfs) 10,223 Froehlich Bav, (ft) 81.4 Zb (_H:1V) 0.7 Tf(hr) 1.20 cfs) 7,553 Surveyed' t) ZB(° Hf 1.5 Reported Tf(hr) 0.75 Modeled HEC -HMS) Bav (ft) 65 Tf (hr) 1.0 Zb (_H:1V) 2.5 hr) 1 5,600 Progression I Sine Wave Qa calculated with SMPDBK Equation Ultimate Geometry Surveyed on September 23, 2013 Q, includes approximately 1,600 cfs of inflow 7.4 Analysis of Incremental Impacts The incremental impacts of the failure of the spillway were determined by modeling the reservoir assuming that the spillway had not failed for a baseline condition, and then modeling the event with the dam failure. Since the failure mode was easily determined, and the primary purpose of the modeling was to determine impacts of the dam failure on downstream flooding, determining the exact inflow to the reservoir through calibration was deemed unnecessary. The volume impounded by the reservoir was easily determined by the high water marks surveyed during the field investigation and the known stage - storage relationship for the reservoir. The results of the HMS modeling show that the incremental impacts of the dam failure were significant in terms of peak discharge, but relatively low in terms of impacts and damage. The peak discharge calculated with both the HMS and RAS models is approximately 5,600 - 6,400 cfs. This is approximately 3.0 - 3.5 times the discharge that was entering the reservoir (peak inflow was modeled to be approximately 1,600 cfs). However, the duration of this peak flow occurred over a period of approximately 30 minutes was short in comparison to the overall event which lasted for several days. The peak flow discharging from the dam breach was likely significantly attenuated in the wide, flat floodplain and by the railroad embankment downstream of the dam as