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aa� �! <br /> Areastar <br /> Water Area Water 31 2.7% 99. <br /> Aroa T D 117 10.1 80 <br /> Aro A Be 6 67 <br /> Meatype <br /> 12 <br /> Area0 0.0% 1 <br /> Area9 0.8% 86 <br /> 18 1.8% 39spew 3 03% 81 <br /> Space 0 0 43 0 80 <br /> coded Area 429 7. 30 <br /> » �coded 3 .3% 7Area63 6.0% » <br /> i <br /> Hvdroioaic Model Input <br /> To determine lake rise during a 100-year event, the widely-accepted hydrologic model <br /> HEC4 MS was used to route ftMrshed runoff volumes into the lake. The pertinent model 1 <br /> Input parameters hnvdved In this method watershed size,loss rate/abstracdon,hydrograph <br /> transforndlag,and rainfall depthfdistribution. These four parameters Have been discussed <br /> previously In this memo,with the exceptloaof hydrograph'transfonnAag. This.Is the only j <br /> parameter that does not Influence total nmoff volume,but rather Influences peak flow rate. , <br /> As flaw rate is a non-essential factor in this analysis(due to the hack of lake outlet and the i <br /> lake flood elevation therefore- being determined strictly by total runoff volume) the <br /> hydrograph lag has been assumed to be 30 minutes and no explicit analysis Is warranted. 1 <br /> The 1100-nacre watershed was modeled as two separate areas—one,the take surface Itself ; <br /> of 332 acres with an RCN of 99 (i.e. nearly 100% of rainfall contributes to lake rise — <br /> highest parameter value accepted by modelle and two,the remalnder of the watershed of It <br /> 828 acres with a weighted average RCN of 49.3. <br /> To model the lake's available storm water storage, a stage4torage relationship was <br /> established by.prakxft the lake surface area of 332 acres vertically(i.e.one foot of rise <br /> provides 332 acre-feet of storage, two feet of rise provides 864 acre feet, etc.) This <br /> provides the most conservative flood elevation result as it Is independent of flood storage <br /> available In on-store areas. <br /> The attached Exhibit 6 document Is a HEC-HMS model sduvnatic of thewatershed areas <br /> comm ed. to the lake. An okWjcdc copy of the HMS model (F7s4Leke.hms) Is alsoattac <br /> a <br /> Of m in UlMois,Iowa, Mirmesota,and Wisconsin <br /> 2901 Interrmtlgra)Lane, SuRe 300, madison,WI 537043133 <br /> (006)242-7T79 (800)446-0679 <br /> FAX (608)242-664 WEB ADDRESS: www.msa-ps.com <br /> _ o.�oi.asrr7oot����rras�� <br /> , <br />