07-19-1976 Planning Packet - Laserfiche WebLink

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•4 w A I ; I • \ « * \ i 1- June Js*) ^ •>o be corrected aand if necessary a spillv/ay be constructed. In our letter of June 1, v;e had recommended that due to the increased runoff from the parking areas of the site, a provision be made for storage of storm water on the building itself v/ith removal of this water occurring normally through evaporation. This recommendation would stand unless storm water from the roof of the-building is diverted to the County Road 19 -• County Road 15 storm sewer v/hich seems to be practical. With the diversion of roof drainage to the storm sewer together v/it:h the drainage from the northeast nortion of the site, the net effect of this w’ould be summarized as follows: Presently approximately 2.6 acres of the site drain to the Kelly Avenue areas. Under the present plan this break in drainage would be retained and the roof drain carrying the storm water to County Road 19 and 15 would effectively reduce the Kelly Avenue drainage area by approximately .37 acres. This ecrease in the overall*Kelly Avenue drainage area would be offset by any increased amount of runoff duo to the hard cover in the parking area. The net increase in runoff to the Kelly Avenue drainage area would be approximately 20 percent (from this site) varying with the duration of the rainfall and the saturation of the soil. Tlje overall increase in runoff to the low lying Kelly Avenue area v;ouid be negligible, hov/ever; when compared to the overall drainage area of approximately along the East side of Kelly Avenue. Wo would estimate the net increase in runoff to be one to two percent. We would caution the City, however, that any in.rease in runoff from any portion of the drainage area will only serve to v/orsen the p<iriodic problems within the draina«}e area. At present the southerly portion of the site will bo covered by a conservation easement and as pro^>osed will be it’s natural state. Since this is presently a low lying area, it would continue to serve as an area in which the pollutants of the parking area runoff would be deposited. It also would serve as a buffering area for the building, since the underbrush and the trees would be retain d and would lessen the visual impact of development on the areas to the south. If you have any questions or comments, please do not hesitate to contact us. . Sincerely, McCOMBS-KNUTSON ASSOCIATES, INC. Richard W. Sathre RWS:slw ' I