02/07/2011 Council Packet - Laserfiche WebLink

Home Search

WS — Item 3 WORK SESSION STAFF REPORT Work Session Item 3 Date: February 7, 2011 To: City Council From: James E. Studenski, City Engineer Re: Century Farm North RCWD Pond Issue Background Rice Creek Watershed District (RCWD) has completed a drainage alternative report for the Century Farm North development. The report is in response to the resident concern, in particular a resident along Arabian Circle, regarding the standing water in the infiltration basin (E2 on attached maps) on the north side of the grass -strip runway. They have been unable to maintain desirable vegetation and have concerns regarding safety issues caused by waterfowl attraction due to the standing water. The infiltration basin is currently inundated with water or ice nearly year round with little or no infiltration occurring. The Century Farm North Development received RCWD conditional approval and final plat approval by the City in 2003. In 2006, RCWD became aware of concerns regarding poor performance of stormwater facilities. The initial thoughts were that downstream storm water conveyances were not functioning properly. After significant downstream review, an area was found south of the airpark where the ground and riprap was restricting flow between two ponds. The City corrected this work in 2008. The corrective work lowered the upstream ponds to their normal water elevations and appeared to have addressed the issue. In 2009, the Developer performed re- grading of the ponds on the north side of the airpark to address irregularities in the elevations, making it consistent with the original plans. In 2010, RCWD installed a stormwater structure to lower the ponds on the south side of the airpark. All these projects improved the storm water system. They didn't eliminate the standing water in the infiltration basin on the north side of the airpark. After RCWD improvements the City found a previously unknown storm sewer structure west of the airpark that was acting as an elevation control structure. The City excavated the buried