Numerical computation of seepage erosion below dams (piping)

In delta areas the land is protected from floods and high tides by dikes. In general these are constructed of impervious clays and built on a sandy aquifer as subsoil. Such structures are vulnerable to an erosion effect called piping. The actual word 'piping' refers to the development of shallow channels in the sand below the dike, which begins at the downstream side of the structure. Here often a ditch is situated with a burst bottom due to excess water pressures. The subsequent erosion process develops backwards to the high head side. The natural nonhomogeneity in the soil causes the shallow channels to be irregularly shaped. Below a critical value of the hydraulic head over the structure the erosion process eases down until water only is transported through the channels. It is common to observe sand boils behind the dike, which produce water alone. However, if a critical head difference is reached, the erosion process continues and the structure may in the end collapse.