Models of dissolution and mechanical erosion in bedrock channels in soluble strata

In the past two decades, a number of phenomenological and physics-based models have been developed for both dissolution and mechanical erosion in caves and surface streams. However, a certain disparity exists in the assumptions of these models. A common assumption in the study of erosion in surface streams is that the dissolution process is slow enough to be negligible, such that mechanical erosion rates dominate. On the contrary, quantitative models of the evolution of caves and karst aquifers have only considered dissolution. Each of these assumptions holds within certain parameter range of the channels and climactic forcings found in nature. However, in cases where both processes are active, as in bedrock channels in highly soluble strata, little is known about the conditions under which each process is dominant. We use the existing models of incision via mechanical erosion and dissolution to explore the potential controls on the relative importance of the two mechanisms, with an emphasis on characterizing the time-variation in rates. The theoretical study is combined with observational work in caves streams, including continuous monitoring of pH and conductivity, studies of cave stream sediments, and observations of micromorphological features characteristic of each process.