The National Academies Press

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From page 130... ... B-1 Simple and Complex Assessment Methods and Worked Example Overview of Appendix This appendix provides two methods, the simple assessment and complex assessment to estimate the impact of a bridge crossing on receiving water quality and illustrates the dilution calculations. This appendix also provides a worked example problem that uses the entire recommended procedure in the Guide (except the simple and complex examples, previously provided) Read the entire page →
From page 131... ... B-2 depict the in-stream kinetics to which some constituents, such as nitrogen compounds and coliforms, are subjected. If K, ca, Qa, E, cs, and V are taken constant, and Qs is the averaged storm flow over the time from 0 to t, the solution to (1) Read the entire page →
From page 132... ... B-3 becomes that of the watershed, 104 km2. In summary, the orders of magnitude of the terms in Equation (5) Read the entire page →
From page 133... ... B-4 to comply with local NPDES requirements regarding stormwater treatment of runoff to the MEP. In this case, installing structural BMPs on bridges is probably the correct decision for urban watersheds, although feasibility will be affected by cost and limited area to work with: The DOT may find that equivalent or better pollutant removal to the receiving water can be achieved for a lower cost by treating runoff from the adjacent roadway where construction cost and maintenance cost are much more favorable. Read the entire page →
From page 134... ... B-5 where the Load Increase is the percentage of the load downstream of the bridge contributed by the bridge itself, Bridge Load is the load conveyed by the bridge runoff, and Upstream Load is the load in the receiving water upstream of the bridge. Bridge Load Rainfall Runoff Coefficient Area of the Bridge Deck Concentration = × × × Where the Rainfall is the average annual rainfall for the specific location, the runoff coefficient is typically about 0.9, and the Concentration is the average concentration of the constituent of concern (see Table B-2) Read the entire page →
From page 135... ... B-6 Similarly, the dissolved P upstream load can be calculated as: DP Upstream Load Annual discharge of the receiving water Average Stream Concentration = × DP Upstream Load 237 ft /s 86,400 s/d 365 d/yr 0.015 mg/L 28.3 L/ft 3 3 = × × × × DP Upstream Load 3,172,726,584 mg/yr = 3,173 kg/yr= The nitrate load increase is given by: Nitrate Load Increase 0.274 kg/yr/ 0.274 kg/yr 122,679 kg/yr 100( ) = + × Nitrate Load Increase 0.0002%= Finally, the dissolved phosphorus load increase is given by: ( ) Read the entire page →
From page 136... ... B-7 (or some other quantitative criterion for a specific waterquality parameter) Read the entire page →
From page 137... ... Figure B-4. Output of annual mean discharges. Read the entire page →
From page 138... ... B-9 The simplest, and most conservative, calculation is the relative dilution given by Equation (5) , in which E = 0 and K = 0. Read the entire page →
From page 139... ... B-10 If we assume that the only runoff from the storm originates from the bridge, i.e., we neglect Qp and Qd in (5) , then (4) Read the entire page →
From page 140... ... B-11 If we assume that the only runoff from the storm originates from the bridge, i.e., we neglect Qp and Qd in (5) , then (4) Read the entire page →
From page 141... ... B-12 of protecting water quality and are briefly considered here for this example. • Collection and conveyance. Read the entire page →
From page 142... ... B-13 is used for the bridge deck and roadway and zero percent is used for the embankment. Tools for five BMP treatment options are provided with this guide and are considered here. Read the entire page →
From page 143... ... B-14 Figure B-8. Bioretention design parameter screen shot. Read the entire page →
From page 144... ... B-15 Figure B-9. Dry detention design parameter screen shot. Read the entire page →
From page 145... ... B-16 The Deck Drain Tool is used for this purpose. The parameters governing the design storm event and bridge configuration are entered into the Tool. Read the entire page →
From page 146... ... B-17 Since this is less than the gutter capacity of 1.84 cfs calculated by the Tool and shown in Figure B-12, the design flow can be carried on the bridge deck within the 10 ft shoulder without any need of a collection and pipe conveyance system. If the shoulder width is reduced in the future as a result of changing the lane configuration, this must be reevaluated. Read the entire page →

From page 130...

... B-1 Simple and Complex Assessment Methods and Worked Example Overview of Appendix This appendix provides two methods, the simple assessment and complex assessment to estimate the impact of a bridge crossing on receiving water quality and illustrates the dilution calculations. This appendix also provides a worked example problem that uses the entire recommended procedure in the Guide (except the simple and complex examples, previously provided)