Abstract: "Tests were conducted on a 1:50-scale model of Isabella Dam Spillway to determine the adequacy of proposed spillway, dam, and channel improvements. The model reproduced an area of the reservoir 800 ft wide by 1,100 ft long, the spillway, and the entire length of the exit channel. Unsatisfactory flow conditions were observed in the vicinity of the spillway crest due to approach conditions to the spillway. Large cross waves, present in the exit channel just downstream of the spillway, resulted in occasional overtopping of the right wall. A grouted rock dike that provided satisfactory flow conditions at the spillway and downstream throughout the exit channel was placed adjacent to the existing spillway approach wall."