Agenda - Council - 06/12/2012 - Laserfiche WebLink

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In the fall of 2011, City staff contracted out the investigation of all the significant areas of flooding concern to Hakanson Anderson. The goal was to have an independent third party evaluate the areas, provide options for corrective actions, and associated estimates to implement the work. They completed their analysis and compiled a report that references potential solutions for each area identified (see attached final report). This report was introduced in general terms at the February 2012 Public Works Committee meeting, with the direction being that staff would come back before the committee over the next several months to discuss the merits of each potential improvement in more detail. This case will focus on section three of the report; the Rum River Hills Golf Club. Rum River Hills Golf Club is located east of Trunk Highway 47 at 167th Avenue NW. Several areas were evaluated and summarized in the report. The golf course was platted in the early 1980's, and at that time linear drainage and utility easements were secured on the site to encumber areas where off -site stormwater was routed through the site. Many areas of the site experienced flooding concerns last summer, and they are summarized as follows: Hole #1 (Area 1) There is a large pond located adjacent to Hole #1, which has a 12" plastic pipe that serves as the outlet. This outlet pipe was televised after the flooding was brought to the attention of the City last year, and the video revealed that there were several sags in the line, and many joints have been compromised with root intrusion. This pond was evaluated with the City storm water model, and it was determined that the 12" pipe was the limiting factor and slightly undersized to accommodate the flows. Up -sizing this line to an 18" pipe, and installing a manhole at the outfall would improve the efficiency of the stormwater routing. A small area drain will also be incorporated into the storm sewer design along this pipe run to capture runoff from a low area at the bend point. It should be noted that the City has always worked with the golf course on the outlet to this pond and previously installed a removable weir so they could control the flow leaving the pond with a removable weir. We are proposing to maintain this pond elevation adjustment for the golf course by installing a new manhole structure with a similar feature, as they currently utilize this pond as a course amenity and irrigation supply. The golf course likes to retain as much water as possible in the pond, installing the removable weir will provide the flexibility to retain small storm events and store the water while allowing larger events to pass through the system quickly. Cart path area near the club house (Area 2A, B) There is a pond north of the club house which is connected to the pond on hole #1. There are several cart paths around this smaller pond which experience localized flooding on occasion. By up sizing the existing undersized culvert connections we can allow more water to pass through the system quicker. The elevations on certain areas of the paths are below the maximum elevation of the pond. The paths would need to be raised if the intent is to not have water on the paths during the larger storm events, but doing so would have ramifications on other areas of the site upstream. Saturated soil along Hole #15 (Area 3) Hole #15 is along the Rum River, and there is a rock dam across the main drainage way from the golf course down to the river. This dam creates a ponding area adjacent to the fairway, and the water elevation of this pool is very close to the fairway grades, resulting in saturated soils in the area. The golf course excavated an area adjacent to the fairway last fall in an effort to determine the source of the water and dry the area up. Several draintile lines were uncovered by the excavation and they appeared to be plugged and collapsed in several locations. Staff visited the site May loth and observed the conditions in this area. The golf course has excavated a low area and swale on the edge of the 15th fairway. Golf course representatives said the low area had open water in it that flowed through the swale all winter, but the ponding area behind the dam froze over. This excavated low area has standing water that flows through the swale to the river. The water level behind the dam is approximately 1 foot below the adjacent fairway grades. The recommendations for this area are two -fold; the golf course will undertake work that is outside of the drainage and utility easement (regrading and/or draintile installation), and the City will provide improvements within the drainage and utility easement. The golf course will monitor the low area this summer and are thinking about improving it into another water feature on the course.