Bioretention Cell Monitoring, Douglas County, Nebraska

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USGS Nebraska Water Science Center hydrologists, in cooperation with Douglas County, Nebraska, are monitoring the performance of stormwater bioretention cells that use “green” infrastructure techniques in Omaha, Nebraska. Bioretention cells are used to reduce the quantity of stormwater that flows into a combined sewer overflow (CSO) system which reduces discharge of raw sewage into local streams during high precipitation events . Two sites are being monitored: one at the eastern edge of the Douglas County Health Center Campus and one at the Eastern Nebraska Office on Aging.

Stormwater management methodologies are shifting from the traditional detention basin to a more green-infrastructure approach that stresses the importance of capturing, retaining and treating stormwater. The implementation of green infrastructure uses various Best Management Practices (BMPs) to mitigate the detrimental effects on stormwater water quality.

A bioretention cell is a BMP that captures and treats stormwater, by evapotranspiration and infiltration, thereby reducing the quantity of stormwater. Bioretention cells have been used for a number of years in the United States, and factors such as soil type, vegetation, evaporation rate and cell design can affect performance. Site-specific scientific data is needed to evaluate and validate green-infrastructure BMPs.

We are monitoring the water balance and water quality of stormwater in two bioretention cells in Omaha:

These sites are located in the Saddle Creek watershed, which is part of the Papillion Creek Basin. Sanitary and stormwater sewers in the Saddle Creek watershed use a combined pipe system called a combined sewer overflow (CSO). When rainfall is greater than approximately 0.1 inches, the stormwater runoff exceeds the capacity of the combined sewer system causing raw sewage to be discharged into Papillion Creek. 

WATER BALANCE

The water balance is measured using

  • precipitation,
  • surface inflow,
  • outflow through the underflow trench,
  • outflow through the overflow,
  • evapotranspiration, and
  • the change in stored runoff.   

The remaining component of the water balance, infiltration, is being estimated as the residual of the water balance.  

COMMUNITY OUTREACH

Community education also is an important part of this study. The results and the performance of the bioretention cell are valuable for environmental education and to demonstrate the effectiveness of the stormwater-management practices. Our primary mechanism for community outreach is the on-site informational kiosk. Additional details about the study, and other related studies in Omaha are available from our website: Monitoring the Effectiveness of Bioretention Cells