Impacts of Changing Hydrology on Ravine Growth: Experimental Results

Abstract

Ravines grow through head cut propagation in response to overland flow coupled with incision and widening in the channel bottom leading to hillslope failures. Altered hydrology can impact the rate at which ravines grow by changing head-cut propagation, channel incision, and channel widening rates. Using a set of small physical experiments, we tested how changing overland flow rates and flow volumes alter the total volume of erosion and resulting ravine morphology. Ravines were modeled as both detachment-limited and transport-limited systems, using two different substrates with varying cohesion. In both cases, the erosion rate varied linearly with water discharge, such that the volume of sediment eroded was a function not of flow rate, but of total water volume. This implies that efforts to reduce peak flow rates alone without addressing flow volumes entering ravine systems may not reduce erosion. The documented response in these experiments is not typical when compared to larger pre-existing channels where higher flow rates result in greater erosion through non-linear relationships between water discharge and sediment discharge. Ravines do not respond like pre-existing channels because channel slope remains a free parameter and can adjust relatively quickly in response to changing flows.