Bridge Stormwater Runoff Analysis and Treatment Options (2014) / Chapter Skim
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Pages 36-49
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From page 36... ...
36 Stormwater Treatment Controls for Bridges This chapter describes the treatment BMPs that the practitioner can consider when treatment of deck runoff is required by the regulatory agency. Installation of treatment BMPs should be reserved for situations where the DOT is required to provide them as part of an MS4 NPDES permit designation, or pursuant to a Section 401 Water Quality Certification, and/or based upon an assessment that considers other special receiving water conditions such as TMDLs, presence of endangered species, the protection of outstanding natural resource waters (ONRW)
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37 a conveyance system cost for their bridge in a separate spreadsheet tool (included as a separate file from the BMP evaluation tool)
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38 withstand vibrations and deflections. Fiberglass and PVC conduits are sometimes specified since they avoid contributing iron or zinc to runoff within the bridge conveyance system and are more flexible than steel and, as such, can better withstand the displacement and associated stresses within a bridge superstructure.
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39 is piped to a suitably sized treatment BMP. The advantage to this approach is that the length of conveyance pipe can be kept to a minimum along portions of the bridge directly over water (which will typically represent the majority of the structure)
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Bridge 1/2 Width (ft) Longitudinal Slope (%)
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41 (Figure 5-2)
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42 Primary dry detention basin features include: • Optional sedimentation forebay • Main basin • Optional low flow channel -- a narrow, shallow gravelfilled trench that runs the length of the basin to drain dry weather flows • Typical dry detention basin design considerations include: – Space allocation: Consider side slope, maximum depth, and forebay requirements to determine space needed – Outlet design: The outlet should preferably be designed to release the bottom 50% of the detention volume (halffull to empty) over 24 to 32 hours, and the top half (full to half-full)
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43 filters provide limited nutrient removal and volume reduction benefits. They typically include a constructed sand bed that receives runoff that spreads over the surface.
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44 The custom bridge deck drain would be cast integrally with the bridge deck for concrete box girder and slab designs. Other design configurations would be required for steel bridges.
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45 expensive than conventional asphalt due to better aggregate quality, but when it is installed to reduce noise and improve wet weather drivability the water quality improvements are essentially free. The good quality of PFC runoff combined with the negligible land and maintenance requirements makes PFC a compelling choice for stormwater treatment in the high-speed highway environment.
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46 of floating pile wetlands. The concept of applying floating wetlands within a transportation project was originally suggested by the WSDOT for the SR 520 bridge replacement and HOV project.
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47 ferred. These characteristics include a relatively small catchment area with high impervious cover.
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48 do not indicate that special characteristics of bridges are consistently the cause of the spills associated with bridge crossings. Further study is needed to better understand if bridge characteristics, in comparison to general roadway characteristics, affect the probability of spill occurrence.
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From page 49... ...
49 Case Study 1: ODOT MAH-80 Project In 2009, the Ohio Department of Transportation (ODOT) completed construction of MAH-80, an extensive $87 million project to widen and reconstruct portions of I-80 and dual 2,500-foot bridges.
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