Agenda - Public Works Committee - 10/16/2007

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CASE #5 CONSIDER RUM RIVER HILLS DRAINAGE IMPROVEMENTS By: Leonard Linton, Civil Engineer II Background: Rum River Hills Golf Course is located in the northeast section of the City. The project was developed in the mid 1980's. Residents living north of 168th Avenue west ofTH47 contacted staff in October 2005 after heavy rains regarding the water level in the adjacent pond. Drainage from this area runs through ditches and pipes, passing under TH 47 to the ponds on the golf course. The ponds on the golf course are connected by pipes and channels to the Rum River. The golf course also experienced high water levels during this storm. Staff visited the golf course at that time and found that water was moving slowly through their pipes. The topic was discussed at the October 18, 2005 Public Works Meeting. The Committee accepted staff recommendation to perform a drainage study, develop plans for improving the drainage and draft , an agreement with the golf course for cost sharing. The drainage study and plan development would be performed by staff. . Staffhas researched the files to gain background on the development of the golf course. There were several convers~tions between the developer and the City Council regarding drainage for the golf course and the surrounding area. The developer acknowledged that the golf course impacted the natural drainage path from the commercial areawest ofTH47 and from the residential -development to the south. The developer constructed a series of ponds and ditches to accommodate the runoff from off site. The developer dedicated drainage and utility easements to the city. The developer was compensated in the amount equal to the cost of installing the pipes across the golf course. Plans for the pipes were not found. A map of the course and easements is attached. The primary area that floods is the pond 9n the south end of the course east of the maintenance shop. Staffhas visited the site on several occasions to observe the area and to formulate a strategy for correcting the situation. We visited the site in March 2007 shortly after most of the snow had melted. There was approximately 4" of water flowing in the pipe the day we visited the site. There is an outlet pipe which has a submerged end in this south pond and its discharge end is several hundred feet away from the pond. The junction of the pipes was not visible so we dug a shallow (-3" excavation) and found the top of the pipes in the bank adjacent to the pond. It appears the lower edge of the pipe controls the pond elevation. Staff visited the site on October 10, 2007 and shot elevations at the edge of the pond and over the top of the pipe. This work confirmed that the edge of the pond is lower than the top of the pipe. This allows water to flood onto the course before the full capacity of the pipe is realized. The discharge end of this pipe, was observed to be flowing approximately ~ full. The grounds crew indicated the pipe never flows over half full, even when the course is flooded. Staff used the 2003 aerial topography as the basis for the pond. Relative elevations were obtained at the pond, inlets and outlet of the existing pipe. The location of the pipe was sketched on the plan using available landmarks; a full survey was not performed. City staff modeled the pond using hydrology software which confirmed the field observation that the full capacity of the pipe is not used except in extreme storm events when the entire course is flooded. The model was also used to test possible solutions. One solution that would not require 27