09/26/1995 Minutes - Laserfiche WebLink

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?? • Mr. Basalla, representing Wlutlatch and Company, explained that they have submitted a revised and corrected preliininaiy plan along with other information to the Engineering Department relative to the draiuage calculations for the proposed above ground retention basin which is the relocation of the retention system that was installed in 1991. They believe that this retention will not only serve their developments, but will help improve the storm water requirements of the up stream area. Mr. Deichmanu distributed a copy of a plau showing this property with 15 sublots as it would be developed with no above ground retention. Mr. Basalla clarified a question that•was brought up previously about the prox'vnity of an existing garage to the proposed Maple Ridge extension and explained that the garage would be about 10 feet offthe right of way and its present access is off West 231 Street. He stated that the volume of the retention basin was about 414,000 cubic feet of water and the existing detention facility holds about 143,000 cubic feet aud, even if tlus 143,000 is added to what they are required to retaiu, there would still be a substantial excess. He presented a cross section through the edge of the basin that they have proposed with a five to one side slope with 1-1/2 to 2 percent of the bottom in a concrete chanuel which is a substantial improvement- over what exists now. Mr. Herbster asked what would be requued if tlus were an underground system. City Engiueer Deichmauu advised that when preluniuary draiuage calculations were submitted, they asked for some minor corrections and soine more detail; which have uot beeu submitted. However, conceptually the Engineering Department was in favor of the proposal because they believe it willprovide significantly more retention capabilities thau what would be required by ordinance for au uuderground system and would be an euormous benefit to the residents in the area. They will not have precise numbers until they get down to detailed plans and calculatious. Mr. Basalla stated that they would commit to not less than 50,000 cubic feet of excess capacity and more likely in the area 100,000 cubic feet of excess capacity. He clarified that these calculatious would take both Bridgeport I and II into consideration. They will agree to a fence arouud the area if it is deemed necessary. Mrs. O'Rourke believed that it should be fenced. Mr. Koeth wondered how loug a poud or a lake would remain after a substantial storm before it would empty out. He, too, believed it should be fenced. Mr. Basalla stated the basin would empty out iu a matter of hours since the water does not stay there for an extended period of time. Mr. Deichmann explained that if there were a very heavy stonn with an all day light rain following it, it might take up to 24 hours to empty the basin and he would reconunend that it be fenced in. He stated that he did not tlunk that the commission should accept anytlung less than vinyl clad chain link fence, either green or black, wluch is what the city installs as well as a buffer of trees and shrubs and an appropriate paved access. He reiterated that the Engineering Departinent was in favor of the concept of obtaining siguificantly inore retention at tlus location, rather thau them just meeting code requirements. He went on to explain that the ordinance was changed in 1994 so the code requirements are much stricter than there were previously. Many of the recent flooding problems resulted from developments built under the previous ordinance. These developers are providing in excess of the new code requirements which is siguificantly more than what was required 18 months ago. He explained that the system in the Rice ditch area has lustorically experience severe floodiug problems because it is undersized, but now that they are uicreasing the sewer capacity on Alexander Road with a new 54 inch storm sewer, half the flow will be diverted to the Alexander Road sewer; and coupled with this proposal, there should be a sigivficant improvement dowu streain. Because tlus system will lower the water level, it will de- pressure the storm sewers on Sharou, Woodview, aud Tree Laue which will help alleviate basement flooding. He advised Mrs. O'Rourke that what they are doing on Alexander, would not help the Sharon, Woodview, and Tree area even without the Bridgeport Development and nothing is planued at present. Ms. Caineron Alston asked who would be responsible for maintauung the retention system. N1r. Deichmanu respouded that, because the majority of the home owners in the developments would not abut the system, and because the majority of the people who lived arouud the retention system would not be iu the association, it had beev determined that it would be best if the city maintained it. The Seivice D'u-ector has coinmitted to maintauung it iu on a weekly schedule. Unfortwiately 3