Details:

Creators:
Luell, S.K. ; Winston, R. J. ; Hunt, W. F.
Luell, S.K. ; Winston, R. J. ; Hunt, W. F. Less -
Corporate Creators:
North Carolina State University. Department of Biological and Agricultural Engineering
Corporate Contributors:
North Carolina. Dept. of Transportation
Subject/TRT Terms:
[+]
Bioretention Retrofitting Runoff Swales
Resource Type:
Tech Report
Geographical Coverage:
North Carolina
Corporate Publisher:
North Carolina. Dept. of Transportation
Abstract:
Stormwater runoff from roadways is a source of surface water pollution in North Carolina. The North Carolina Department of Transportation (NCDOT) is required to implement stormwater control measures (SCMs) in the linear environment. NCDOT has specific interest in runoff from bridge decks, which is often discharged directly to a stream below. The research presented herein focuses on retrofit stormwater SCMs for bridge deck runoff management. Two bioretention basins and a swale were constructed in the easement of a bridge deck on I-540 at Mango Creek in Knightdale, North Carolina. One bioretention basin was sized to capture (without overtopping) runoff from the 0.7 inch event. The second basin was undersized by one-half (as compared to the large cell) and captured runoff from the 0.4 inch event. Undersized bioretention basins might often be used in retrofit situations when space is limited; therefore, it is important to understand how an undersized bioretention basin performs with respect to hydrology and water quality. Both bioretention basins employed 20 in (51 cm) of fill media, and had an internal water storage layer (IWS) of 2 ft (0.6 m) including the gravel drainage layer. The swale was designed to convey the ten-year storm event without overtopping. Runoff was piped from the northbound and southbound lanes to the bioretention basins and swale, respectively.

Data collection began in October 2009 and continued through April 2010. Weirs and stage recorders were used to monitor inflow to and outflow from each SCM. Flow-proportional, composite water quality samples were obtained at the inlet and outlet of each SCM. Monitored water quality parameters included TKN, NO2,3-N, NH4-N, TN, TP, TSS, Cu, Zn, and Pb. TN was calculated by summing TKN and NO2,3-N. For small storms [those with less than 1 in (25 mm) rainfall depth], flow volume reductions for the large and small bioretention basins were 69% and 47%, respectively. This shows the hydrologic importance of properly sizing bioretention basins when space is available. However, some benefit is also associated with undersized systems, if space is too limited to allow for “full sizing.” There was a 23% volume reduction benefit associated with the swale.

Average concentrations of TN (0.74 mg/L), TP (0.12 mg/L), and TSS (32 mg/L) from the bridge decks were relatively low when compared to other highways and paved surfaces previously monitored in North Carolina. Median effluent concentrations for the large bioretention basin were lower than those for the small bioretention basin for all nutrient forms and sediment.


Format:
PDF
Collection(s):
US Transportation Collection
Main Document Checksum:
[+]
urn:sha256:2390ad616ea713461bdd65bdf6a3855e9209effd4c02cc0af4c81b59e28a2937
Download URL:
https://rosap.ntl.bts.gov/view/dot/22508/dot_22508_DS1.pdf
File Type:

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