Stormwater pollution treatment BMP discharge structures.

Details

• Creators:
  Simmons, Miles F. ; Admiraal, David M.
• Corporate Creators:
  University of Nebraska--Lincoln. Dept. of Civil Engineering
• Corporate Contributors:
  United States. Dept. of Transportation. Research and Special Programs Administration
• Subject/TRT Terms:
  • Runoff
  • Pollutants
  • Sewage treatment
  • Best practices
  • Filtration
  • Structural design
  • Detention basins
  • Water quality management
• Publication/ Report Number:
  M304
• Resource Type:
  Tech Report
• Geographical Coverage:
  Nebraska
• Corporate Publisher:
  Nebraska. Dept. of Roads
• Abstract:
  Structural best management practices (BMPs) are used to capture and treat stormwater runoff. Most structural BMPs provide treatment by filtering ; runoff through a filter media or collecting it in a detention basin and slowly discharging it over an extended period of time to allow suspended solids and ; associated contaminants to settle out. The purpose of this study is to design an effective outlet structure that provides adequate filtration or slows ; discharge to 40 hours. ; A model detention basin was constructed in the Civil Engineering Hydraulics Laboratory at the University of Nebraska-Lincoln (UNL) and ; two full scale outlet structures were tested in it. The first outlet device was an orifice controlled perforated riser. Discharge from the device was ; measured at many head levels and the results correlated well with discharge given by the orifice equation. The orifice controlled perforated riser ; adequately provided a 40 hour drain time and can be sized for various detention basin sizes using the orifice equation. At low heads, however, it was ; observed that perforations in the riser pipe could also control flow rates, depending on the size, elevation, and number of the lowest perforations. ; The second outlet structure tested was a filtered perforated riser. An 18” diameter barrel was placed around the perforated riser and filled ; with coarse (D50=0.11 in) sand. Fifteen tests were run where sediment laden water was cycled through the filtered riser. The device provided good ; filtration but showed significant clogging. The filter media, in series with the orifice, impacted flow rates and was modeled using an unconfined aquifer ; equation. The unconfined aquifer equation was used to estimate changes in hydraulic conductivity as the filter began to clog with sediment. However, ; clogging of the filter screen was also observed and was modeled as a minor loss. Estimation of the minor loss coefficient provided a better fit to the data ; than the hydraulic conductivity. Therefore, it was concluded that the clogging of the filter screen was the primary driver of increases in head loss. ; Additional tests with coarse filter screen confirmed this conclusion. Independent of the method used to model head losses in the filtered riser, the ; filtered riser showed a dramatic initial increase in head loss after the first suspended sediment test, followed by much smaller increases in head loss ; associated with subsequent tests. When designing the filtered riser these changes in head loss should be considered and the filtered riser should be sized ; based on flow rates after initial clogging. Optionally, very coarse filter material and filter screens can be used to reduce the chances of clogging. If ; coarse filter screens and coarse filter material are used, the filter will only be effective for removing coarse debris, but this function can still help to ; prevent the orifice from becoming blocked.
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• Format:
  PDF
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/27414/dot_27414_DS1.pdf
• File Type:
  [PDF - 3.13 MB]
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha256:66316fe3efbf2830a22f11f37ca4a2a4aa3fcdcd44834969b9066a8eaadb2436