Guidelines for Evaluating and Selecting Modifications to Existing Roadway Drainage Infrastructure to Improve Water Quality in Ultra-Urban Areas (2012) / Chapter Skim
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Pages 83-93
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83 This section presents guidance for planning-level sizing and design of volume-based and flow-based BMPs. A volume-based BMP is one whose performance is limited by size and nature of its storage volume together with the drain time.
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84 Figure 6.1 shows a conceptualization of the modeled ultraurban highway catchment. The general modeling and evaluation approach is as follows: 1.
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85 width is 500 ft and the drainage length is 86 ft. This roughly corresponds to a six-lane highway section with 12 ft lanes, plus two 7 ft shoulders.
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86 a major metropolitan center selected within each zone. The ASOS data have a resolution of 0.01 in.
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87 quality and runoff capture. Continuous hydrologic simulations can specifically be used to evaluate this tradeoff.
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88 a representative PSD based roughly on the NJDEP BMP testing protocol. The effects of alternative PSDs may be estimated by users of the spreadsheet in a post-processing analysis that is included in the accompanying spreadsheet sizing tool.
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89 maintenance frequency and time until clogging depends on the media area and sediment-loading rate. Note, an alternative to using the media conductivity as the hydraulic control is to use a medium with high conductivity and design an outlet control orifice.
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90 • Average TSS concentration: Used to estimate the average annual sediment capture volume for varying detention volumes, drawdown rates, and assumed PSDs. • Particle size distribution: Defines the average mass fraction of clay, silt, and sand particles in runoff.
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91 ment resuspension and washout and improve sediment capture (Landphair et al., 2007; Li et al., 2008a)
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92 Simulation results shown in Figure 6.9 suggest that batch mode operation of small detention vaults can potentially improve sedimentation efficiency in comparison to conventional orifice outlets. Moreover, greater removal efficiency can be achieved with a smaller footprint facility operated in batch mode compared to a larger facility operated in conventional mode.
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From page 93... ...
93 monitoring data from the BMP Database (Table 5.4)
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