Rapid City Reduces Pollution in Stormwater Runoff

Diverting stormwater runoff to wetland channels is credited with improving water quality of Rapid Creek
Rapid City Reduces Pollution in Stormwater Runoff
Hydrologic technicians from the U.S. Geological Survey measure stream flow for a stormwater monitoring study in Rapid City, South Dakota. (photo credit: USGS)

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Wetland channels constructed in downtown Rapid City, South Dakota, effectively reduced many pollutants in stormwater runoff, according to a recent U.S. Geological Survey report.

Measurements collected by the USGS during 2013-14 showed that concentrations of total suspended solids, metals, nutrients and bacteria decreased in runoff to Rapid Creek when stormwater was routed through wetland channels in downtown Rapid City. However, chloride concentrations increased, likely due to the movement of salts deposited during prior runoff events. 

“Water quality is important because the portion of Rapid Creek that flows through Rapid City is a valuable spawning area for trout, is used for recreation and is a seasonal municipal water supply for the city,” says Galen Hoogestraat, a USGS hydrologist and the author of the report. “Controlling sediment from construction sites and urban land use is critical for maintaining healthy water quality in the creek.”

The USGS monitored water quality of stormwater runoff in the three Rapid City drainage basins.

Stage plate at Arrowhead drainage basin upstream from Arrowhead Country Club in Rapid City, South Dakota. Runoff from this drainage discharges into Rapid Creek. 

“The largest reductions of total suspended solids and lead measured between wetland inlets and outlets were greater than 40 percent,” Hoogestraat says. “This significant percentage highlights the overall success of using wetland channels to improve water quality in Rapid City.”

Bacteria concentrations decreased by about 21 percent at the 1st Street wetland channel and 36 percent at the 2nd Street channel, but did not decrease at the 3rd Street channel. Total nitrogen, phosphorus, copper and zinc concentrations were reduced by at least 20 percent at all three wetland channels.

A total of 357 water-quality samples were collected during 2008-12 at monitoring sites within the Arrowhead and Meade-Hawthorne drainage basins. Results indicated substantial sediment and bacteria transport from these basins into Rapid Creek.

Water-quality effects differed between open vegetated channels in the Arrowhead drainage basin and concrete channels and conduits in the Meade-Hawthorne drainage basin.

Stormwater runoff from urban lands harms surface water resources by increasing stream velocities, destroying natural habitat and increasing pollution in receiving waters. As runoff flows over the land or impervious surfaces such as roads and parking lots, it picks up debris, chemicals, sediment and other pollutants that could adversely affect water quality if discharge is not treated.

Photos: USGS


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