Flood Risk Reduction Structure For Morgan Lake Dam

Morgan Lake Dam is located near City of La Grande, Oregon. A dam breach analysis indicates a breach of the dam would result in high life loss and economic damages to the City of La Grande. Oregon Water Resource Department, Dam Safety in conjunction with the City of La Grande plan to build a flood risk reduction structure that will redirect a portion of dam breach hydrograph away from Deal Canyon and into Sheep Canyon to reduce risk associated with the breach.

An U.S. Army Corps of Engineers, Hydrologic Engineering Center’s River Analysis System (HEC-RAS) 2-dimensional model was developed in support of the design of the diversion structure. The sediment introduced into the flow (sediment existing within the reservoir and from erosion of the embankment and streambed within the downstream reach) during the dam breach event could result in non-Newtonian flows to exist near the diversion structure. As a result, both Newtonian and non-Newtonian flow conditions will be considered in the design of the structure.

This paper will provide a brief discussion related to simulating non-Newtonian flows in HEC-RAS, design of the flood risk reduction structure, investigation of the occurrence of non- Newtonian flows, and changes in design for the non-Newtonian flows.