Rivers : three-dimensional phenomena in straight flumes with mobile bed : report on investigation

Three-dimensional phenomena have been observed during tests carried out in a straight sand flume in the "De Voorst" Laboratory. These three-dimensional phenomena hamper the interpretation of the results of the tests and it is necessary to find a way removing the three- dimensional signal from the records of the tests. A type of FIR filter has been selected to do this but due to overlapping of the spectra of dunes and three-dimensional signals in the tests it is not possible to separate the two signals perfectly. An extensive study on the effect of filtering and on the optimum choice of cut- off wave length has, therefore been made. In addition, the effects of flume width, water depth, aspect ratio (flume width to water depth ratio) and Froude number on the formation and dimensions of the three-dimensional bedforms, the effects of flume width and water depth on the dune dimensions and the effect of the three-dimensional phenomena on the resistance to flow and sediment transport have also been explored. Based on results from this study and some earlier works, an optimum choice of flume width to sediment transport has been proposed for both flow conditions.