Evaluation of in-channel gravel storage with morphology-based gravel budgets developed from planimetric data

Gravel budgets developed from changes in river morphology have emerged as an important tool for exploring stream dynamics and sediment transport. In many cases, old aerial photographs are the only data available by which to evaluate past morphologic changes. Existing methods for building morphology-based gravel budgets from air photos are subject to several sources of uncertainty, including difficulty in identifying deposition within the active channel. In-channel deposition sites consist of submerged bars or general increases in bed elevation, both of which are virtually impossible to detect on air photos. However, bed deposition can be inferred when measured gravel storage losses are greater than the quantity of gravel exiting the study area at its downstream boundary. An integrated method combining measurements of gravel storage changes with a gravel routing procedure based on estimated gravel transport path lengths was developed to identify sites of bed aggradation. Inclusion of storage change results in the routing procedure reduces the uncertainty associated with the selection of appropriate transport path lengths. The method was applied to development of gravel budgets for a 50-year period in the lower Duchesne River, Utah. Areas in which the predicted bed aggradation was greatest displayed higher rates of channel activity and greater channel instability during subsequent time periods.