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<br />I <br />III <br /> <br />II <br />II <br />II <br />I <br />II <br />II <br />I <br />II <br />II <br />I <br />II <br />II <br />II <br />I <br />II <br />I <br />II <br /> <br />1993 event. <br /> <br />DESCRIPTION OF EXISTING FLOOD PROBLEMS <br /> <br />The flood problems at Pipestone result from rapid spring snowmelt as well as <br />heavy intense rains which primarily occur during the summer months. The city is flood <br />prone due to the relatively flat topography in the areas east and north of the city. <br />Generally. some nuisance flooding will occur each spring. Some areas experience <br />flooding as a result of blocked drainageways and backed up floodwaters along small <br />tributaries. Overbank flows along Main Ditch causing flood damage to structures may <br />not occur until about the 100year event. <br /> <br />EXPECTED FUTIJRE WITHOUT-PROJECT CONDITIONS <br /> <br />Future development within the Pipestone Creek basin is expected to be minimal. <br />For purposes of this study, the expected future without-project conditions in Pipestone are <br />therefore assumed to be the same as the existing conditions. Highway, bridge. or channel <br />modifications in the city are not planned at this time; therefore. flood depths or flood <br />discharges would not be affected. In addition, it is expected that vety little future <br />development will take place within the city of Pipestone which would impact runoff. <br /> <br />HYDROLOGIC ANALYSIS <br /> <br />Hydrologic analyses were performed in order to develop peak discharge- <br />frequency relationships for the Main Ditch and County Ditch A at Pipestone, Minnesota. <br />Discharges were computed using Iowa statewide regression equations (U.S. Geological <br /> <br />15 <br />