The Lytle and Warm Creeks and Santa Ana River project will provide another important unit under the general comprehensive plan for flood control in San Bernardino County, California. The proposed plan for containing the flood flows will consist of raising levees, excavating streambeds, and constructing grade control structures, energy dissipators, bridges, and several thousand feet of high-velocity concrete channel. The investigation was conducted on a 1:60-scale model that reproduced approximately 10,000 ft of the Santa Ana River, 600 ft of East Twin Creek, and 5300 ft of Warm Creek. The existing and proposed bridges, concrete channels, and natural streambed channels with revetted slopes were also reproduced in the model. Tests were concerned with flow conditions, water-surface elevations, rip-rap stability, and sediment transport at the grade control structures, bridges, confluences, and energy dissipators.