2009 - Illinois DNR - State of Illinois

ALTERNATIVE S5 - HIGH SCHOOL RESERVOIRThis alternative provides an additional 50 acre-feet flood storage provided on the MaineTownship East High School campus immediately south of the Lutheran General HospitalPond and Dempster Avenue. Existing soccer fields located on the southeast corner ofthe Maine Township East High School campus, would be lowered up to 7.5 feet and thesides graded at a slope of 3:1 to create a new reservoir. These athletic fields currentlyprovide some detention for local storm water runoff. Three soccer fields would still fitin the bottom of the reservoir. A ten foot service road around the perimeter of the areawould provide 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 new 60-inch diameter culvert andflow to the reservoir on the high school property. This Alternative is intended to greatlyreduce peak flows contributed by the Dempster Avenue storm sewer and would control15% of the Prairie Creek watershed.Added flood storage on the high school property for the Dempster Avenue storm Sewersystem tributary to Prairie Creek created by this alternative, would provide $71,666 inaverage annual flood damage reduction benefits in the watershed representing a 50%reduction in average annual flood damages. Sixty-seven percent of those flood damagereduction benefits would occur along Lower Prairie Creek between the Lutheran GeneralHospital Pond and Farmers Creek. This alternative would benefit all 48 floodpronestructures along Lower Prairie Creek by reducing average annual flood damages 80%overall in that reach. All 43 floodprone structures along Farmers Creek would alsobenefit from this Prairie Creek storage alternative as average annual flood damages drop43% along Lower Farmers Creek and 43% along Upper Farmers Creek. This alternativewould eliminate flood damages for 37 structures currently located in the 100-yearfrequency floodplain.Project costs of this alternative are estimated at $2,265,489 as detailed on Table 13. Thebenefit to cost ratio (B/C ratio) for this alternative is 0.49.41