The Online Lower Minnesota River Watershed District News, June 2005
June 2005 home page


Prior Lake outlet to be redone, new weir built

In 2000 the District joined a technical advisory group to study the Prior Lake Spring Lake (PLSL) Watershed District’s needs for an improved Prior Lake channel outlet. Funded by the PLSL and the city of Shakopee, this study was one of several that developed a hydrological model for the district.

According to Shannon Lotthammer, district administrator, the Prior Lake channel outlet box was built in 1983 to release high waters to the Minnesota River, but has degraded over time.

The 2000 study revealed the need for outlet box replacement and channel enhancement.

The channel itself consists of two parts, one manmade and one natural:

  • a half-mile-long, 36-inch-diameter concrete outlet pipe that connects Prior Lake to Jeffers Ponds

  • the natural drainage system that begins in Jeffers Ponds

As a PLSL report puts its, the new box — a “fix-crested weir set at an elevation of 902.5 feet … will eliminate the need to manually open and close the outlet to discharge water from the lake.” It will also be more efficient and look better, consisting of concrete imprinted and stained to look like rock.

As this same report makes clear, PLSL management goals include

  1. Reduction of flooding on the lake and channel

  2. Enhancement of recreation, wildlife, and esthetic opportunities

  3. Control of lakeshore and channel erosion

Administrator Lotthammer anticipates completion of the new outlet box by 2006 or 2007, while channel restoration and enhancement will occur over several years starting in 2006. “The new control structure will help us control erosion and other damage to the lake shore. We found through the study that we didn’t need to expand the channel — capacity was sufficient in most places — but we will reslope the banks of the outlet in some spots to make it more gradual; this will add some capacity to the channel but, more important, increase the channel’s long-term stability and prevent erosion.”

In addition to reconfiguring the slope, the PLSL district will stabilize the banks and enhance habitat by

  1. Placing boulders in strategic places to keep the water flow in the center of the channel and prevent erosion around the bends, and

  2. Planting native vegetation, like willows, dogwoods, and native grasses, on the sides of the slopes so root systems can stabilize soils and hold banks.

The work on the channel and the outlet box will be funded by the PLSL district, the cities of Shakopee and Prior Lake, and the Shakopee Mdewakanton Sioux Community, some of whose stormwater gets into the Prior Lake channel.

The PLSL district will start the channel work this winter, says Lotthammer, in order to “minimize disturbance to the residents of the area, both established back yards and, in fact, newly developing neighborhoods, as in Prior Lake south of County Road 42 and perhaps in Shakopee where two developments have been proposed.” Thereafter, work will proceed as land is developed in order to minimize disturbance to the new residents.

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