Erosion and sediment transport in the Owens River near Bishop, California
Closure of Pleasant Valley Dam in 1954 has almost eliminated the supply of gravel to the 16-mile (25.7-kilometre) study reach of the Owens River. Because of armoring of the channel, scour has been limited to approximately 1 foot (0.3 metre) in the upper 2.3 miles (3.7 kilometres). This report presents information useful in determining long-term erosion effects below Pleasant Valley Dam, in assessing the feasibility of a proposed bypass channel versus retention of the main channel in its present state, and in determining man's influence on river morphology. Bedload transport is dependent on the hydraulics of a section and the availability of material. Ninety-eight percent by weight of the sampled bedload transported between sites 1 and 6 in the study reach was finer than 8 millimetres, although only 6 to 12 percent of the material in the bed available for transport was finer than 8 millimetres. Bank material, a prime source of new material for transport, is predominantly finer than 16 millimetres. Bank erosion is accelerated by wide ranges in flow release. The bank-erosion rates interpreted from aerial photographs indicate average annual erosion rates of 750 tons (680 tonnes) from 1947 to 1967, 1,970 tons (1,790 tonnes) from 1967 to 1968, and 2,020 tons (1,830 tonnes) from 1968 to 1971. These rates are compatible with the water discharge-sediment discharge relation developed from field data collected during 1972-73. Hydraulic geometry of the six sites indicates a shift in the river system regime since 1954. These changes have progressed downstream from the dam to a point between sites 4 and 5. Farther downstream channel changes will occur until the channel stabilizes.