Hydrology
The construction of the present Hell Hole Dam also changed the course of the Rubicon River. The pre-dam river channel wended its way several miles to its confluence with the Middle Fork of the American River near Ralston Afterbay. Now, In addition to releases from Hell Hole down the pre-dam path, water is diverted through a pipeline to Middle Fork Powerhouse (AKA Stephenson Powerhouse) where it flows into Interbay Reservoir. From here, in addition to releases down the Middle Fork American River, the water is diverted into a tunnel to Ralston Powerhouse and into Ralston Afterbay, where it joins water from the pre-dam path. Oxbow Powerhouse and Oxbow control dam there releases water into the middle fork of the American River just below the spot of the historical confluence.
Water for hydroelectric generation is also shuttled into Hell Hole from French Meadows Reservoir which impounds the Middle Fork of the American River. The water travels through a tunnel to a powerhouse located on the north side of Hell Hole. French Meadows, at 5,200 elevation, is higher than the 4,700-foot (1,400 m) elevation at Hell Hole. The powerhouse at Hell Hole is actually known by the name, French Meadows powerhouse.
The traditional channel of the Rubicon River still maintains water flow from the spillway at Hell Hole Dam and from tributaries of the Rubicon below the dam, such as Gerle Creek (pronounced girly).
The Placer County Water Agency does not take water directly from Hell Hole or the other dam but instead claims rights to the water as it is shipped through the American River System and ends up at Folsom Lake near Sacramento. Folsom dam was originally constructed for the purposes of flood control. The Placer water agency's dams and Ralston are presently known as the Middle Fork Project.
Read more about this topic: Hell Hole Reservoir