Dam Break Modeling for Tandem Reservoirs — A Case Study Using HEC-RAS and HEC-HMS

The Creekside Development Project is located in Southern Oregon on land owned by the Cow Creek Band of the Umpqua Tribe of Indians. The new development includes the construction of two tandem high-head earth embankment dams for water supply to infrastructure downstream. The two dams are located on an unnamed ephemeral stream in a steep, relatively small watershed. The crest of the lower dam (Dam 1) is about 0.5 miles downstream of the crest of the upper dam (Dam 3). An initial consideration for Dam 1 was that it should provide enough storage capacity and a large enough spillway to be able to safely pass a dam break event from Dam 3. The 1-dimensional unsteady flow hydraulic routing model HEC-RAS and the hydrologic routing model HEC-HMS were used to model this unique dam break application. This paper will discuss the efforts required to construct and successfully run both of these models, the benefits and drawbacks of each of these models for this type of study, and the results of the study.