Contact erosion occurs at the interface of two different soil layers when particles of the finer layer are removed by the flow and transported through the pores of the coarser layer. Whenever this kind of internal erosion occurs in embankment dams, dykes or in their foundations, severe consequences are likely. As contact erosion may be seen as a type of surface erosion, river erosion models have been used by previous authors to model this phenomenon, mainly for contact between sand and gravel layers. Thanks to an specific experimental device, these results are extended to finer soils, broadly-graded, made of clays, silts and sands. The available data for contact erosion is sum-up, and the adequate laws for different situations are underlined. Then, the concept of erosion threshold, useful to evaluate dykes' safety, is discussed and linked with the erosion variability and evolution with time.