Report evaluating flood protection with New Melones Dam (PDF)

Report, “Channel-Floodplain Disconnection on the Stanislaus River: A Hydrologic and Geomorphic Perspective” – The Stanislaus River, the northernmost major tributary to the San Joaquin River, has undergone profound alterations to its flow regime, channel form, and ecosystems. New Melones Dam (built in 1979) and over 30 smaller dams cumulatively impound 240% of average annual unimpaired runoff, reducing winter floods and spring snow melt runoff, and increasing summer base flows to supply irrigation demand. The frequency and extent of overbank flooding has consequently been reduced. Aerial photographs document reduced channel complexity and extensive encroachment of riparian vegetation into the formerly active channel from 1937 to 1998. Limited historical data and field evidence suggest the channel incised approximately 1-3 ft. since dam construction, so the discharge needed for overbank flows has approximately doubled, further isolating floodplains from the channel, and leading to the loss of important habitats. To reestablish overbank flooding and its attendant ecological benefits, both re-operating New Melones Dam to increase high flows in the river, and setting back or breaching levees to reduce the elevational difference between the floodplain and channel, will probably be needed. University of California, Berkeley