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ALTERNATIVE D8 - COMBINE ALTERNATIVES C8 AND S8To achieve flood damage reduction benefits throughout the watershed, this alternativewould combine additional storage at Belleau Lake with conveyance improvements alonglower Farmers Creek. Each <strong>of</strong> these components are described below.Belleau Lake would be lowered 4.2 feet by gravity through a 24-inch diameter outletpipe at the invert <strong>of</strong> Farmers Creek at elevation 622.0. This pipe would be gated to allownormal flows to bypass the lake in Farmers Creek. Steep side slopes, exposed along thewestern edge <strong>of</strong> the lake by lowered water surface elevations, would be graded at 3:1slopes for safety and stability. When stages in Farmers Creek reach elevation 626.0,excess flows would enter the lake over a spillway constructed between the lake andFarmers Creek. The lowered lake would be capable <strong>of</strong> providing up to 52 acre-feet <strong>of</strong>additional flood storage capacity at the 100-year frequency event.Farmers Creek would be widened to 30 feet between the Farmers and Prairie Creeksconfluence and Belleau Lake. The Dempster Avenue bridge and a private bridgeupstream <strong>of</strong> Dempster Avenue would be removed and replaced with twenty foot wideCon Span bridges. The Rand Road crossing <strong>of</strong> Farmers Creek would have an identicalthird barrel added to the existing double 10 foot by 10.5 foot box culvert structure.This combination <strong>of</strong> alternatives would create a project that would provide $17,259 inaverage annual flood damage reduction benefits representing an 12% reduction inaverage annual flood damages in the watershed. Existing flood damages along LowerFarmers Creek would be reduced 37%. Existing flood damages along Upper FarmersCreek would be reduced 11%. This alternative would eliminate flood damages for 6structures currently located in the 100-year frequency floodplain. Project costs <strong>of</strong> thisalternative are estimated at $1,791,065 including $112,500 in estimated land rights costs,as detailed on Table 29. The benefit to cost ratio (B/C ratio) for this alternative is 0.13.106
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