Winter is draining: Melting makes its way to the Big Sioux River

KELOLAND.com Original

SIOUX FALLS, S.D. (KELO) — Melting snow and whatever it carries flows into the city’s storm sewer system and eventually, the Big Sioux River.

Items like leaves, grass clippings, chunks of what appears to be a mix of gravel and dirt and even that pop bottle will land in a storm sewer drain and get carried away.

“The storm drainage system includes the streets and the gutters along the streets,” said Andy Berg, the environmental and storm water manager for the city of Sioux Falls.

The storm drainage system is a network of channels, mains, culverts and other pieces such as drainage ponds. The pieces are both public and private, Berg said.

Storm water drains to three main locations: a drainage channel or pipe, a drainage pond or the river.

The city has 220 miles of stormwater channels, Berg said. It has 500 miles of storm mains and culverts.

Some of the stormwater drains into a pond or Best Management Practice (BMP) before it travels down a pipe or channel to the river.

BMPs are ponds designed to retain storm water, like the melting snow or rainfall, for a certain time.

“They slowly release the water through the storm drainage system,” Berg said.

The city has about 700 site-specific and regional BMPs that each take water from a specific number of acres in an area of the city, Berg said.

Some BMPS are in very visible locations. Like the one at 57th and Western Avenue. Some are not as noticeable, like an underground one at Hy-Vee at the intersection of 49th and Louise Avenue.

The BMPs are fixed with screens which are an X number of feet tall. The screens are made to allow water to slowly drain from the BMP.

One type of BMP “calls for a 40-hour draw time,” Berg said. “There are different lengths of time based on the BMP.”

There are also detention ponds throughout the city.

Berg said a grass boulevard at the convenience store at 69th and Western Avenue “is actually a depressed area where water goes into from the parking lot.”

That detention pond will hold back water from a BMP after a heavy rainfall to help make sure the BMP is not overloaded, Berg said.

Vegetation and natural settling help separate material such as road sand, sidewalk ice melt material and any similar grit from the water. Ultimately, the BMPs help keep grit and other foreign materials from reaching the Big Sioux River.

When the water is released from the BMP it will enter a channel or pipe, then possibly reach a creek in the city and then, the Big Sioux River. The path may vary, depending on where the water comes from as sometimes water may enter a second BMP.

Snow has melted around a storm sewer drain on a street in Sioux Falls. KELOLAND News photo.

BMPs must be approved by the South Dakota Department of Environment and Natural Resources.

Areas of the city developed in the past 15 years will have BMPs, Berg said. The city works with developers so it has a mix of private and public BMPs, pipes and channels.

The city of Sioux Falls developed a master plan for storm water in 2003. The plan called for the development of 28 regional BMPs from 2004 to 2015. The estimated total cost was $63.7 million, with the cost of individual BMPs ranging from $640,000 to $6.5 million, according to the 2003 plan.

BMPs in the plan could include grass buffers, ponds, park-like areas and similar.

While new development would include BMPs, it’s different in older parts of Sioux Falls.

“In the older parts of town, there is a good chance the storm pipe is connected to run into the river,” Berg said. “In the downtown, a majority of the areas do drain straight to the river.”

But, “When there is redevelopment we always try to get in BMPs,” Berg said.

Sometimes the BMP solution is an underground BMP, like the Hy-Vee example, or a mechanical option. A mechanical option separates some grit from the water, he said.

An example of a possible mechanical device is a gravity separator, according to the Iowa Department of Natural Resources.

The BMPs require regular maintenance.

“The (stuff) that washes off the roads accumulates over time. We have too much out (the ponds),” Berg said.

The 2003 stormwater plan stated the important of regular maintenance.

“A regular maintenance program is needed in order for BMPs to continue providing the
water quality benefits intended. Because BMPs trap pollutants over time, those
pollutants, such as sediment, must be removed to restore the BMP to its intended
function and to continue to provide water quality benefits,” the plan said.

The public can help with maintenance of the storm water system.

Stormwater runs into the river at some point, Berg said. Keeping debris, even soapy water, from draining into the stormwater system helps the system and ultimately the river, Berg said.

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