Sand-Dune Geometry of Large Rivers during Floods

The geometry of lower regime bed forms in several large sand-bed rivers is investigated during average and flood conditions. The van Rijn method is revised because it generally underpredicts the dune height of most large rivers around the world. During floods in large sand-bed rivers, upper-regime plane bed is not necessarily obtained when T = 25. Both parameters describing dune height and dune steepness do not decrease as the transport-stage parameter T increases in the range 10 <T< 25. The analysis of bed-form data during large floods on the Meuse River and the Rhine River branches indicates that both the dune height and length generally increase with discharge while dune steepness remains relatively constant. A reasonable approximation of the wavelength is λ≅ 6.5 h , where h is the flow depth. The dune height Δ varies as a function of the depth h and median grain size d50 . Estimates can be obtained by Δ≅ 2.5 h 0.7d0.350 .