Abstract

Bedrock fluvial systems which occur in regions of landscape degradation, are commonly ignored by sedimentologisls. These systems deserve more study because (1) they are locally preserved along unconformities in the ancient record, and (2) they may contain sediments that allow paleohydraulic reconstruction of extreme flood events. Rare, high magnitude floods in narrow, deep bedrock channels produce distinctive hydraulic and sedimentary phenomena. Macroturbulent kolks, boulder transport, and hydraulic jumps occur. Very resistant rocks can induce anastomosing patterns and/or structural control of rapids, pools and riffles. Distinctive depositional macroforms include longitudinal, pendant, and expansion bars. Gravel mesoforms, such as giant current ripples, develop during deep flood flows. Preservation of these bedforms is enhanced by a rapid decrease in discharge coupled with a rapid drop in stage due to very small width/depth ratios.