In many parts of the world, a significant form of human impact on the natural environment has been the disruption caused by using hydraulic mining techniques. These techniques, which use pressurized water to loosen and transport enormous amounts of overburden and ore, introduced enormous quantities of sediment and waste water into natural watersheds. The earliest large-scale use of hydraulic mining in the United States took place in the gold fields of northern California between the 1850s and the 1880s. Considerable attention was focused on the processes of human-induced geomorphic change by scientists including G.K. Gilbert in the early decades of this century, but physical geographers, geologists, hydrologists, and other scholars have turned their attention toward other facets of sedimentary processes in more recent decades. This project will build upon earlier studies of the impacts of hydraulic mining in northern California and more recent work on human-related sedimentary activity to examine the ongoing redistribution of sediment in the upper stretches of the Bear and South Yuba rivers. The project will consist of four interrelated parts: (1) past and present locations and volumes of mining sediments will be mapped using aerial photographs, satellite images, and samples taken during field surveys, (2) measurements of sustained sediment mobility will be made, (3) the changes in stream channels and sediment distributions resulting from a record flood in 1986 will be determined, and (4) the extent of mixing between mining and non-mining sediments will be measured. This research will have a number of theoretical and practical benefits. It will provide the first long-term reassessment of a model of sediment transport first developed by Gilbert in the 1910s, using measurement and analytic techniques that can be used by scholars elsewhere. Although focusing on sediments resulting from mining activities, the project will provide more accurate estimates of the rate and volume of movement for all types of sediments within streams. This improved understanding will provide a basis for more effective decision making regarding the cessation and clean-up of accelerated sedimentation in the nation's streams.
