Straight Rock Vane Induced Scour in Central Pennsylvania Lower Order, Gravel Bed Streams

摘要

The purpose of this study was to determine how a straight rock vane affects scour within three lower order gravel bed stream channels in north central Pennsylvania. Scour chains were used to measure the scour and fill associated with flow events of sufficient size as to initiate bedload transport. Networks of 18 to 26 scour chains were installed in a grid that extended across the channel and from above to below the rock vane and were used to determine the amount of aggradation and degradation occurring at these specific sites. Bulk core samples of the bed material were taken in order to determine the size of particles that were moving during these flows. Each of three sites experienced two documented events that initiated bedload movement. The amount of scour occurring at each site was then plotted spatially within the channel to determine the effect of the rock vane. Analysis of scour patterns indicated that flow constriction caused by the vane and the slow velocity areas upstream from the structure and the dissipation of kinetic energy resulting from the drop as the flow passes over the face of the rock vane resulted in greater scour depths through these areas. In addition, discharges greater than bankfull levels occurred at all three sites overthe winter months which altered the channel dimensions in the vicinity of the restoration structures. These results will help to further the understanding of how rock vanes affect bedload transport within gravel bed channels.