The Senator Wash facility, although not considered a diversion structure, can divert water from the river immediately above Imperial Dam for storage in Senator Wash Reservoir. This is done only when flow arriving exceeds the requirements of the diverters at Imperial Dam.

The need for additional storage near Imperial Dam resulted in the construction of Senator Wash Dam on Senator Wash, a short distance upstream of Imperial Dam. Senator Wash is an off stream facility that has capabilities for pumping to storage when a surplus of water is available and generation of power. Generation occurs when releases are made back to the river above Imperial Dam to meet unforeseen demands in excess of available river water. This facility was designed for use only in case of emergencies and is supplied normally by regulation of releases at Parker Dam. It has greatly improved the availability of water in these emergency situations as well as providing space for storage of unpredictable flood inflow.

The pumping and release capacities at the plant at 80% of maximum head are approximately 1,200 cfs (34 m3/s), as compared to flows in the river that range from 2,000 cfs to 10,000 cfs (57 m3/s to 283 m3/s). The active capacity of the reservoir is approximately 12,000 AF (14,800,000 m3). The reservoir active storage is normally maintained at approximately 7,000 AF (8,600,000 m3/s) so that approximately 5,000 AF (6,200,000 m3/s) of space is available to receive excess water. Since the Senator Wash facility and the procedure for estimating and monitoring transient flow changes have been in operation, over-deliveries and wastes to the Gulf of California have been negligible.