ES10795 - We show that the splitting of channel heads and the evolution of surface topography is strongly influenced by water flow in the subsurface. When ground water emerges at the surface, producing a spring, the flow removes grains from the surface by erosion, progressively digging a deeper channel, which in turn can draw more water, inducing the growth of a river. Seepage erosion is said to shape many examples of valleys, canyons, and river networks and assumed to produce amphitheater-headed valleys. However, the mechanism by which seepage channels grow and form networks is far from clear.By performing model laboratory experiments and analysis of the ground water flow, we find significant differences between the case where the groundwater comes primarily through a boundary from a far away source and the case where it is fed by uniform local rain. Our study supports the notion that a channel network can develop in a homogeneous landscape whereby groundwater flow splits as the channels grow leading the channels to split in turn. Our observations have important implications for the interpretation of field data because numerous perturbations present in nature that could influence channel dynamics. Perturbation of the erosion front due to random avalanching events is shown to not lead to channel splittings unless supported by underlying changes in groundwater flow.
