Large-Flume Tests on Flow Dislodgment of Rocks Forming Bendway Weirs

Abstract

This paper presents findings from large-flume tests conducted to determine the velocity magnitudes at which water flow dislodges rocks from bendway weirs (BWs), rock structures used primarily to control thalweg alignment in alluvial bends. The tests involved replicating the head of a BW formed from reasonably uniform sizes of quarried rock. Three sizes of rock were tested: 0.10, 0.15, and 0.23 m in representative diameter. The tests indicated three dislodgment thresholds for the rocks. The thresholds were (1) preliminary dislodgment of rock along the toe perimeter (on a fixed base), (2) beginning of rock dislodgment from the crest and face, and (3) major dislodgment of rock from the crest and face (BW failure). These thresholds were related to flow velocity near the end of a BW. Semiempirical relationships are presented for sizing rock used to build BWs. The relationships use a nondimensional parameter expressing the ratio of flow inertia versus rock weight.