Time evolution of scour at comparatively long abutments

The effects of the approach flow velocity and obstacle-length on the time evolution of scour depth at comparatively long abutments are discussed in the framework of the equations suggested by Ettema (1980) and by Franzetti et al. (1982). This discussion stands for clear-water flow conditions and vertical wall abutments in rectangular mobile-bed open-channels. The evaluation of the coefficients involved in the equations leads to conclude that those of Franzetti et al. (1982) seem to be universal, while those of Ettema (1980) clearly depend on the approach flow intensity and on the dimensionless obstacle length. Time to equilibrium also depends on the same parameters