Mud and Debris Modeling With Hec-Ras

High sediment concentrations (i.e. more than 5-10% solids) can affect fluid physics. High-concentration geophysical flows begin to diverge from the Newtonian assumptions of the shallow-water flow equations, applied in most flood risk studies. At high concentrations, particle interaction processes can change the depth, velocity, arrival time, damage, and floodplain extent associated with an event.

Debris flows are growing more common as wildfire frequency and intensity increases. Rainfall on high-gradient, recently burned watersheds can erode enough rock and sediment to develop flows with solid concentrations of greater than 50%. Mine tailing dam failures can also generate dangerous and destructive high-concertation flood waves. The risks associated with these structures are also increasing as the global, mine-tailings, dam portfolio ages. Accounting for the particle interactions in these mud and debris flows is critical to appropriately estimate downstream risks.

A multi-laboratory, US Army Corps of Engineers Team developed a non-Newtonian computational library to make single-phase, rheological, physics available for these simulations. This team integrated this library in the Hydrologic Engineering Center’s River Analysis System (HEC-RAS). This presentation will describe the rheological models available in HEC-RAS and how they apply to mud and debris flows. The presentation will also survey the verification and validation tests the team used to evaluate these algorithms and several calibrated, field applications.