Experimental observations of the retreat of non-cohesive river banks

The topic of bank retreat is of particular relevance in the hydro-morphodynamic models aimed to the study of the planform evolution of rivers. In gravel-bed rivers, banks are often composite with an upper cohesive layer, and a basal layer composed by granular, relatively coarse sediments (gravel and cobbles). This research aims at gaining a better comprehension of some of the basic processes responsible for the retreat of coarse riverbanks; in particular, it focuses on the mass instability mechanisms due to the oscillations of water levels and pore water pressures, and on the particle erosion due to seepage flow. To this aim, a series of first laboratory experimental observations on the behavior of a bank mostly composed by gravel are here reported. The evolution of bank geometry from its initial configuration to the final one at the end of hydrograph is here reported and interpreted using both the measurements about the groundwater flow and mathematical modeling.