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Title: APPLICATION OF THE HEC6T MODEL TO ASSESS POST-FIRE CHANNEL REMEDIATON ALTERNATIVES 1733

Author
item Canfield, Howard
item WILSON, C.
item LANE, L
item THOMAS, W.
item CROWELL, K.
item EARLES, A.

Submitted to: American Society Of Civil Engineers Watershed Management Conference
Publication Type: Proceedings
Publication Acceptance Date: 5/1/2005
Publication Date: 7/19/2005
Citation: Canfield, H.E., Wilson, C.J., Lane, L.J., Thomas, W.A., Crowell, K.J., Earles, A. Application of the hec6t model to assess post-fire channel remediaton alternatives. In: Proceedings American Society Of Civil Engineers Watershed Management Conference, July 19-22, 2005, Williamsburg, VA. 2005 CDROM.

Interpretive Summary: Increased flood peak and erosion have occurred following the Cerro Grande Fire in Los Alamos, New Mexico. Because of concerns about erosion and transport of radionuclides, computer model, HEC6T, was used to describe the observed scour, deposition and sediment movement following the fire. The model was then used to study whether small dams built across the channel would reduce the erosion of the radionuclide bearing sediment in the channels. A computer simulation that simulated fifty-years of channel flow was used to test the effectiveness of these small dams - relative to taking no action. The simulation showed that the most upstream dams trapped the most sediment. By causing sediment to deposit on the upstream side of the dam, the water flowing over the structure is able to scour below the dam because the water is able to pick up some sediment, because it has deposited some upstream of the structure. However, overall the simulations showed that the small dams can be an effective method for reducing scour. However, the design and emplacement of the dams requires analyses and interpretation accounting for hydrology, hydraulics, sediment transport and sediment yield.

Technical Abstract: Increased flood peak discharge and sediment load have been observed following the Cerro Grande Fire in Los Alamos, New Mexico. Because of concerns about the potential migration of radionuclides, a sediment transport model, HEC6T, was used to describe the observed scour, deposition and sediment transport in the wake of the fire. The model was then used to evaluate a grade-stabilization alternative in the portions of the channel, which the model predicted would be the most adversely impacted by post-fire scour. A fifty-year simulation was used to test the effectiveness of grade control - relative to taking no action. The simulation showed that the most upstream grade stabilization structure trapped the most sediment. Scour could occur below the structures. By causing sediment to deposit on the upstream side of the structure, the water flowing over the structure is able to scour because transport capacity is above the concentration in the flow. Overall, the simulations showed that grade stabilization can be an effective method for reducing scour. However, the design and emplacement of the structures requires analyses and interpretation accounting for hydrology, hydraulics, sediment transport and sediment yield.