VII Effects Of Transportation Structures On Fluvial Systems

VII. Effects Of Transportation Structures On Fluvial Systems A. Riverine Systems 1. 2. 3. 4. Analytical Tools to Evaluate Impacts Single Channel Braided Meandering B. Non-Riverine Systems 1. Alluvial Fans/Distributary Flow 2. Sheet Flow 3. At-Grade Crossings C. Recommended Best Management Practices 1

VII. Effects Of Transportation Structures On Fluvial Systems A. Riverine Systems 1. Analytical Tools to Evaluation Roadway Impacts: l Sediment Transport Function Qs = W n 1. 77 V 4. 32 G 0. 45 Y-0. 3 D 50 -0. 61 l Lane’s Relation: Q S QS D 50 l Manning’s Equation V (A) = 1. 49 n-1 R 0. 67 S 0. 5 (W * d) 2

VII. Effects Of Transportation Structures On Fluvial Systems A. Riverine Systems 2. Single Channel Streams n Lateral Impacts Narrow the Floodplain or Channel l Widen the Channel l Prevent Channel Movement l n Analysis Increase V & D or decrease upstream l Decrease V & D l Decrease Qs l Vertical Impacts l Base Level Adjustments (+/-) l Change Slope (+/-) 3

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VII. Effects Of Transportation Structures On Fluvial Systems A. Riverine Systems Analysis 3. Braided Channels n Lateral Impacts Narrow/Widen Channel l Cut Off Braids l Concentrate Flow l Obstruction l n Same as single channel l Increase Q, V & D l Increase Qs l Upstream impacts l Vertical Impacts l Base Level Adjustments (+/-) l Same as single channel 6

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VII. Effects Of Transportation Structures On Fluvial Systems A. Riverine Systems Analysis 4. Meandering Streams n Lateral Impacts l Prevents Natural Channel Migration Roadway approach l Channel training l 10

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VII. Effects Of Transportation Structures On Fluvial Systems B. Non-Riverine Systems 1. Alluvial Fan Impacts n Limit Channel Movement n Upstream Channel Location n Crossing Alignment n Vertical Impacts l Long-Term Aggradation Analysis Shift fan location l Discharge changes l Cross above apex or below avulsions l Maintenance l Induce degradation l 12

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VII. Effects Of Transportation Structures On Fluvial Systems B. Non-Riverine Systems Analysis 2. Sheet Flow Areas: Culverts n Concentrate Flow n n n Perpendicular Alignment Identify Flow Paths n Vertical Impacts n l Invert Elevation n n Induce degradation Downstream and upstream damages Roadways become drainage paths Too low - headcut 14

VII. Effects Of Transportation Structures On Fluvial Systems B. Non-Riverine Systems 3. At-Grade Crossings n Paved n Wide and Flat n Widen or Narrow Channel Analysis Lower n, Increase V l Decrease S l Downstream drop l l Same as single channel 15

VII. Effects Of Transportation Structures On Fluvial Systems C. Recommended Best Management Practices 1. Don’t obstruct or narrow main channel 2. Mimic bankfull width and depth 3. Relief culverts 4. Match natural grade 5. Energy dissipation 6. Inspection, maintenance and documentation 16