Bridge Stormwater Runoff Analysis and Treatment Options (2014) / Chapter Skim
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50 BMP Evaluation Tool The BMP Evaluation Tools are a set of spreadsheets that have been provided as a supplement to this Guide that can be used for planning-level estimates of BMP treatment performance and whole life costs. The tools are Excel© applications, one for each of the various BMPs selected for bridge deck runoff treatment (Section 5.3)
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51 modeling methods can be found in Appendix E: BMP Evaluation Tool Modeling Methodology. 6.1.2.1 Average Annual Runoff Volume Average annual runoff volume to the BMP in the tool is based on the average annual rainfall depth, a computed volumetric runoff coefficient, and the tributary drainage area.
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52 6.1.3.1 Material Quantities Material quantities calculations in the tool were based on the BMP configurations with typical default assumption for design values such as side slopes and length-to-width ratio to estimate excavation volumes, BMP component lengths and volumes, and grading and restoration areas for capital cost calculations. As discussed in Appendix B: Simple and Complex Assessment Methods and Worked Example, many user inputs are customizable to represent desired BMP design configurations for optimized assessment of performance and costs.
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53 within the deck of the bridge. That cost can be estimated separately by using a stand-alone deck drain cost tool created as part of this work effort.
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54 The data and methods used to calculate these concentrations are provided in Appendix E: BMP Evaluation Tool Modeling Methodology. 6.1.6 Tool Supporting Data The tool provides underlying supporting data used to produce the hydrologic and water quality estimates.
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55 Figure 6-5. Marquam Bridge drainage routing for worked example.
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56 The storage volume sizing for the bioretention basins was designed to meet the City of Portland's stormwater regulations of 90% average annual runoff volume capture. To accomplish this, the Goal Seek function under Data → What-If Analysis → Goal Seek was used.
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57 • Total volume reduction = 23% (ET plus infiltration) • Runoff bypassed = 10% (BMP captured= 90%)
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58 6.3 Tool Customization The tool has been designed to be customizable to allow for overwriting of much of the default data so users can use the best available project information for their sites. It is recognized that customization will allow for each DOT to input information based on localized rainfall statistics and water quality data, as well as BMP construction and maintenance specifications, practices, and costs.
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59 benefits of increasing BMP sizing to provide 90% average annual runoff capture instead of 80% can be compared alongside the BMP costs to assess if there is a proportional benefit to increasing the average annual runoff capture. Additionally, BMP sizing can be adjusted to assess the volume and pollutants being captured and treated by the BMP versus the volume and pollutants that bypass or overflow the BMP.
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