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Flowing to the river

Storm drainage system manages water runoff to mitigate flooding, water pollution

Post Date:09/11/2019 11:00 am

When it rains, it pours. And all that water has to go somewhere.

In Shakopee, surface water ultimately goes one place—the Minnesota River. But managing how it gets there is the responsibility of the city's storm drainage system.

"When you develop land, you're altering the hydrology and the flow of surface water, so we need to design systems that mitigate the rate and flooding concerns," said Water Resources-Environmental Engineer Kirby Templin.

Drainage ditch and storm water pondThe City of Shakopee uses an extensive system of storm sewer, ponds and wetlands to manage surface water and protect against flooding. For example, yards must be graded to help move runoff to catch basins or street drains to avoid pooling. Typically, the water is then transported to a man-made storm water pond for collection.

Ponds help protect against flooding by controlling the rate at which water discharges downstream. This can be especially important during large rain events when localized flooding can cause immediate impacts. 

How storm water is managed can look different based on density and age of development, Templin explained. In rural areas, ditches and road culverts often help water flow to wetlands and streams on its way to the river. In higher density areas, you'll see more catch basins and underground storm pipes since there's less surface area to work with. 

Regardless of whether your street has curb and gutter, there's a designed drainage network that must be maintained to handle the storm water runoff and mitigate issues, Templin said. 

A component of storm water management is volume reduction, which assists both with flood control and water quality. For example, infiltration basins are dry depressions designed to fill up during storm events but dry out within a few days. These pervious basins mitigate the flow of water while also filtering out pollutants from reaching our lakes and rivers.

"In Minnesota, we have a lot of water resources. Keeping them clean and usable for different purposes is everyone's responsibility," Templin said. 

Topography & Soil

Shakopee has several unique challenges due to its topography and soil conditions. The bluffs create large elevation changes within a short distance. The city also has a variety of soil types, ranging from sandy, which allow high infiltration and less runoff in pervious areas, to clay, which does not infiltrate well. Other parts of the city have shallow bedrock, which requires blasting to create ponds or below-ground utilities.

Another unique factor is the quantity of water that flows from adjacent cities and townships. Surface water from Lake O'Dowd and Prior Lake flow through Shakopee via outlet channels, which uses a system of culverts, pipes, wetlands and ditches to transport water to the Minnesota River. There are cost-share agreements with neighboring communities for the construction and maintenance of these systems.

The city is responsible for administering federal and state storm water management requirements, most commonly by reviewing proposed development. The Public Works Department also inspects and maintains the city's storm drainage system for pond cleanouts, erosion or other maintenance issues. Street sweeping minimizes leaves, sand and salt residue from running into the storm system.

To learn more about the city's storm drainage system, visit the city website at www.ShakopeeMN.gov/publicworks.

This story originally appeared in the Fall 2019 Hometown Messenger.

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