ABSTRACT
Dike overtopping starts normally at the lowest crest level or at a local dike discontinuity, e.g. a bridge abutment. Erosion occurs if the shearing stresses induced by the water flow over the downstream dike face exceed the critical shear stress of the dike material or the dike protection system, e.g. grass, gabions, geoweb or soil cement. Any initial small breach represents a weak point where locally high shear stress may develop into a larger breach. The breach development is then mainly depending on the type of soil and the actual soil state (compaction, moisture content). In noncohesive soils, erodibility depends preliminary on the grain size distribution, density and grain shape. The main resistance to erosion by water is offered by the submerged sediment weight. For cohesive soils, erodibility depends on the amount and type of clay fraction, chemical composition of material, organic matter, or temperature. All model tests presented herein were carried out using noncohesive sediments to allow for a simple estimation of the erodibility and the erosion start.
