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<br />Memorandum <br /> <br />To: Mark Statz <br /> <br />Project: Downtown <br />Redevelopment <br /> <br />Oient: Oly of Centerville <br /> <br />Date: 2.23.09 <br /> <br />From: Earth Evans <br /> <br />Re: laMotte Park Potential Pond Locations/RCWD <br />Requirements <br /> <br />File No: 616-08167 <br /> <br />This memo summarizes our assumptions regarding the construction of a proposed <br />pond in either the southwest or southeast corner of laMotte Park as a holding pond <br />for irrigation of the nearby ballfields and to partially satisfy the Rice Creek Watershed <br />District volume control requirements for the Downtown Redevelopment project. <br />Previous analysis has focused on the utilization of 51. Genevieve's Church pond but <br />due to several constraints, the open space in laMotte Park is now being considered. <br /> <br />Based on their current rules, RCWD requires that redevelopment that disturbs greater <br />than 50% of the existing impervious surface or increases impervious surface area by <br />50% or more (Rule C, paragraph 2e) provide volume control for the contributing area <br />equal to the runoff generated by a 2.8-inch event (Rule C, paragraph 5b). <br />Centerville's downtown redevelopment falls under this nule. <br /> <br />Two potential options to provide a portion of the volume control required for the <br />downtown redevelopment is to constnuct a pond in either the southwest or the <br />southeast corner of laMotte Park as shown on the attached figure. The required <br />volume is based on the impervious surfaces listed in Table 1. <br /> <br />Table 1 <br /> <br />Location A B C D I E F <br /> Impervious Area (ac) Volume (ac-It) <br /> Existing Proposed Total Existing' Proposed' Total <br /> (undisturbed) A+6 0.8*A*0.9*1/12 2.8*6*0.9*1/12 D+E <br />Downtown 0.1 13.7 13.8 0.01 2.9 2.9 <br /> <br />I) Per RCWD Rule C paragraph Sc <br />2) Per RCWD Rule C paragraph Sb and 2e <br /> <br />Based on the impervious acreages in table 1 and the formulas shown in columns D <br />and E, a total of 2.9 ac-ft of volume is required. The impervious area for the <br />downtown redevelopment is based on the attached concept plan. Generally Blocks B- <br />G were assumed to develop at 90% impervious and Blocks I -K were assumed to <br />develop at 65% impervious. The assumed tributary area to the pond includes all of <br />the downtown redevelopment south of Main Street as well as Block H. The small <br />piece of existing impervious downtown includes the St Genevieve's Church property <br />on the west side of Block C that is not proposed to be disturbed with this project. <br /> <br />J:\61608167\DeSil7l\ShYfl'lwater <br /> <br />-#- Bonestroo <br /> <br />2335 Highway 36 W <br />St. Paul, MN 55113 <br /> <br />Tel 651--636-4600 <br />Fax 651-636-1311 <br /> <br />www.bonestrOO.com <br />