ROBERT B. JACOBSON AND KAREN E. BOBBITT, U.S. Geological Survey, MS 100, 1400 Independence Road, Rolla, Missouri 65401, USA

Streams of the Ozark Plateaus are characterized by abundant unstable channel reaches with extensive unvegetated gravel bars. Gravel bars are used throughout the Ozarks as a source of construction aggregate. The controls on the spatial and temporal distribution of gravel bars in the Current River, Missouri, were studied to evaluate the potential effects of gravel mining on channel instability and the aquatic ecosystem. Historical evidence indicates that alluvial gravel has been released from storage in low-order bottomlands because of riparian disturbances, principally open-range grazing. Waves of gravel have moved downstream into zones of accumulation in third- to sixth-order channels. The spatial distribution of gravel bars along the Current River mainstem was used to indicate controls on gravel accumulation. Results indicate that gravel accumulation areas are related primarily to tributary junctions. The magnitude of gravel input at junctions relates mainly to tributary basin relief and bedrock geology. Downstream of tributary junctions, accumulations of gravel are controlled secondarily by valley physiography and downstream decay of the tributary input. Reaches of accumulation of land-use-derived gravel in Ozarks streams are discrete areas where gravel potentially may be mined from bars with minimal effect on the aquatic ecosystem.