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year) event. Figures 17.2 (a-c) illustrate the major management practice features that are <br />proposed to store and treat runoff in the central drainage corridor. This system is <br />designed to proVide volume/peak reduction storage for the runoff, as well as water quality <br />treatment. This approach stats with large detention storage in ponds located on-site in. <br />sub-watersheds 7 and g, followed by similarly sized detention in ponds located in <br />subwatersheds 25 and 26 south of the active development site. This storage is <br />supplemented with additional smaller-scale storage in sub-watersheds 5, 11, 13, 21 and <br />22. Tables 17.1-17.5 describe the water quantity reductions in these p0nds,'and Tables <br />17.6 and 17.7 describe the water quality improvements for TP. ' <br /> <br />The ponding system proVides both permanent pool storage for water quality treatment <br />and temporary flood storage above the permanent pool. The ponds in the central <br />drainage corridor are supplemented-by two areas for additional Storage of pre-treated <br />runoff. These two areas in sub-watersheds 8 and 19 will allow for water levels to raise <br />and take advantage of storage available. This water will be slowly drained by a <br />controlled outlet, but infiltration Will also occur. Figure 17.3 is a schematic cross-sect/on <br />of this approach. Keeping these areas dry except during high flows allows for their use <br />as open space, recreation areas for essentially ail of the year, with the exception of that <br />time when they are needed to absorb flow. They then serve to dampen peaks, reduce <br />volume and enhance recharge. A similar feature is also proposed for sub-watershed 26. <br />This would be the last B1VEP in the chain of BMPs installed throughout the site and south <br />of it before flows reaches the Mississippi River. Table 17.7 showed the dramatic water <br />quality improvement that ri-tis system could provide. Such ma approach is mandated' by <br />the Phase II discharge requirements (next section) and the ivRs'R. RA/Cr/tical Area <br />guidelines (Item 27). <br /> <br />Figure 17.3 Schematic of Flood Storage/Infiltration Portion of Central Corridor. <br /> <br />Grass\parkland <br /> <br /> · ' ' - ~"~":~ Flood Storage <br /> <br /> (lined) <br /> <br />Trail <br /> <br />FfgUr¢ not dra~n to scale <br /> <br />The runoff calculations in this section included determination of the 100-year event ' <br />runoff and a condition supplemented by additional on-site storage. Figures 17.2 (a-c) <br />showed the prelim/nary concept for the central drainage corridor. These figures illustrate <br /> <br />l'l- 1'9 - <br /> <br />21 <br /> <br /> <br />