2009 - Illinois DNR - State of Illinois

An additional 50 acre-feet flood storage would be provided on the Maine Township EastHigh School campus immediately south of the Lutheran General Hospital Pond andDempster Avenue. Existing soccer fields located on the southeast corner of the MaineTownship East High School campus, would be lowered up to 7.5 feet and the sidesgraded at a slope of 3:1 to create a new reservoir. Three soccer fields would fit in thebottom of the reservoir. A ten foot service road around the perimeter of the area wouldprovide maintenance access to the reservoir. A 60-inch diameter culvert would beinstalled to connect the new gravity in and gravity out High School Reservoir to anexisting 60-inch Dempster Avenue storm sewer, tributary to Prairie Creek, on theLutheran General Hospital property, north of Dempster Avenue. The existing DempsterAvenue storm sewer system would be restricted to a 24-inch diameter orifice to forceexcess storm water in the sewer to back flow into the reservoir on the high schoolproperty. In this alternative, the High School Reservoir would reduce peak flowscontributed by the Dempster Avenue storm sewer, and would provide additional storagecapacity for Lutheran General Pond when flood stages in that pond exceed elevation636.0 by accounting for overland flow that would back up through the existing outletpipe at the water tower and back through the junction box into the storage reservoir.Belleau Lake would be lowered 4.2 feet by gravity through a 24-inch diameter outletpipe at the invert of 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 of 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 of providing up to 52 acre-feet ofadditional flood storage capacity at the 100-year frequency event.Combined additional flood storage at various sites in the watershed created by thisalternative, would provide $91,752 in average annual flood damage reduction benefits inthe watershed representing a 63% reduction in average annual flood damages. Existingflood damages along Lower Farmers Creek would be reduced by 76%. Existing flooddamages along Upper Farmers Creek would be reduced by 71%. Existing flooddamages along Prairie Creek would be reduced by 87%. This alternative wouldeliminate flood damages to 47 structures currently impacted by the 100-year frequencyfloodplain.Project costs of this alternative are estimated at $3,207,372, including $920,268 in59