Confluence scour in coarse braided streams

Laboratory models of a braided valley flat in coarse material were used in conjunction with field data to study confluence scour at braid anabranches. Correct prediction of the depth of scour is required for the design of buried pipeline crossings. Braid pattern and anabranches constantly shift and avulse so that scour holes have definable lifetimes. Although the scatter is large, the depth of water in the scour hole depends on confluence and relative anabranch discharge; this depth can be as high as six times the ambient depths in the anabranches.