Numerical Modeling of the Spillways for the Dam Raise at Isabella Dam

Abstract

The Sacramento District Corps of Engineers is designing modifications to the Isabella Dam located on the Kern River in the Tulare Lake Basin in the southern portion of the San Joaquin Basin, in Kern County, California. These modifications include raising the elevation of two high head dams (56.4 m or 185 ft and 30.5 m or 100 ft) by 4.88 m (16 ft); modifying a service spillway to better suit the needs of flood capacity, and creating a new labyrinth weir emergency spillway. To aid in the design of both spillways, a series of three-dimensional (3D) computational fluid dynamics (CFD) models of the Isabella Reservoir and outlet works were developed. The design process for the emergency spillway has been streamlined using a composite modeling approach with physical and CFD modeling of the labyrinth weir. The CFD models of the Isabella Dam forebay, the main and auxiliary dams, and service and emergency spillways provide an efficient test bed for design alternatives of the spillways, support for rating curve development, and validation of the information obtained in the physical model. CFD model results were also used to evaluate hydraulic conditions in and down the spillway chute. Velocity, water surface elevation, and stream power were computed so that appropriate measures could be taken to protect the chutes from damaging erosion.