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Hydraulic Engineering

HEC 9 tables

Table 6.1. Debris-Control Countermeasures Matrix.
Countermeasure Countermeasure Characteristics
Debris Classification Maintenance Aesthetics4 Env. Impact5 Installation Experience by State Design Guideline6
Floating Debris Flowing Debris Bed Material Estimated Allocation of Resources
Light Medium Large Fine Detritus Coarse Detritus Boulders H = High
M = Moderate
L = Low
Group 1. Structural Countermeasure Group 1.A. Culvert Structures Deflectors   x x       x H A L CA 6.2.1
Racks x x           H A L CT, CA 6.2.2
Risers       x x x   L A L CA 6.2.3
Cribs x         x   M A L CA 6.2.4
Fin     x         M A L SD, TN, CA 6.2.5
Dams and Basins       x x x   H A H Widely Used 6.2.6
Group 1.B. Bridge Structures Deflectors   x x       x H - M U L CA, MS, IN, OR, WI, LA 6.3.1
Fins   x x         M A L CA 6.3.2
Crib Structure   x x           U L MS, CA, KS 6.3.3
R.T.S. - Iowa Vanes         x     M A M IA HEC-23(35)
R.T.S. - Permeable Spurs       x x x   M A M AZ, CA, IA, MS, NE, OK, SD, TX HEC-23(35)
R.T.S. - Impermeable Spurs       x x x   H A H Widely Used HEC-23(35)
In-channel Debris Basins       x x x   H A H Widely Used -
Flood Relief Sections   x x         L A L Widely Used 6.3.6
Debris Sweeper (Bridgeshark)   x x         L A L OK, VA, TN, OR 6.3.7
Booms x x           K U M ID -
D.F. - Freeboard   x x         L D L Widely Used 6.3.8
D.F. - Pier Type, Location, and Spacing   x x         L D L Widely Used 6.3.8
D.F. - Special Superstructure   x x         L D L TX, MS 6.3.8
Group 2. Non-Structural Countermeasure Emergency and Annual Maintenance   x x x       H U M Widely Used -
Debris Management Plan   x x x       H D L   6.4

Notes:

  1. "x" corresponds to a suitable device.
  2. R.T.S. corresponds to River Training Structures.
  3. D.F. corresponds to Design Features.
  4. Classification for Aesthetics is: (1) U for Undesirable, (2) A for Acceptable, and (3) D for Desirable.
  5. Classification for Environmental Impact is: (1) L for Low, (2) M for Medium, and (3) H for High.
  6. Reference made above for the Design Guidance is related to the section indicated in this manual, i.e., information on deflectors for culverts is provided in Section 6.2.1.
Table 6.2. Management Plan for the Large Woody Debris Formations.
Vegetation Type Vegetation Height/ Channel Width Sediment Management Strategy(61)
Agricultural or Open Space n.a. n.a. Substantial debris jams are unlikely to form within the reach since the immediate riparian zone is agricultural land or open water. Therefore, debris removal is unnecessary. Artificial debris input may be desirable for habitat enhancement, stabilization of sand bed channels through backwater sediment retention, or to reduce bank velocities on the outside of meanders.
Forest 1.3W ≤ H n.a. UNDERFLOW jams exist within the reach. Debris clearance is unnecessary since there would be minimal adverse geomorphic impacts associated with the jams (local scour may occur under the debris at high flows) and a significant quantity of heavy floating debris would unlikely be transported downstream. Therefore, bridge and other structures in the reach should not be affected by persistent debris accumulations.
Forest 0.95W < H < 1.3W Coarse Detritus DAM jams exist within the reach. Jams may cause significant local bed scour and bank erosion due to flow constriction. Backwater sediment wedges and bars may form upstream of the jams since the sediment consist of coarse detritus. The jams may also increase the duration of overbank flooding. A limited amount of floating debris may be transported downstream from the reach. Debris clearance may be necessary if the local bed and bank scour results in a significant increase of large woody debris being introduced into the stream.
Forest 0.95W < H < 1.3W Fine Detritus DAM jams exist within the reach. Jams may cause significant local bed scour and bank erosion due to flow constriction. Backwater sediment wedges and bars are unlikely to form upstream of the jams since the sediment consist of fine detritus. The jams may also increase the duration of overbank flooding. A limited amount of floating debris may be transported downstream from the reach. Debris clearance may be necessary if the local bed and bank scour results in a significant increase of large woody debris being introduced into the stream.
Forest 0.60W ≤ H ≤ 0.95W Coarse Detritus DEFLECTOR jams exist within the reach. Jams may cause significant bank erosion of one or both banks that could result in a significant increase of large woody debris being introduced into the stream. Since the sediment consist of coarse detritus, local bed scour induced by the jams will most likely be negligible and backwater sediment wedges may form upstream of the jams. Debris clearance unnecessary except where localized bank erosion results in a significant increase of large woody debris being introduced into the stream.
Forest 0.60W ≤ H ≤ 0.95W Fine Detritus DEFLECTOR jams exist within the reach. Jams may cause significant bank erosion of one or both banks that could result in a significant increase of large woody debris being introduced into the stream. Since the sediment consist of fine detritus, local bed scour induced by the jams might be significant and backwater sediment wedges and bars would most likely not form upstream of the jams. Debris clearance necessary to prevent local bank erosion.
Forest H < 0.60W n.a. FLOW PARALLEL jams exist within the reach. Large woody debris will be transported downstream in high flows from this reach and deposited at bank base in meanders and at run-of-river structures. Adverse geomorphic impacts associated with the jams are minimal. Banks may be stabilized due to debris build-up, and debris may also accelerate formation of mid-channel bars. Debris clearance from channel unnecessary if it is keyed into place at bank toes and bars.
Updated: 02/11/2015
Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000