MODELING THE CONTROLS ON CHANNEL CROSS SECTIONS IN SOLUBLE BEDROCK CHANNELS

Channels incising within cave systems often leave long records of erosion in the form of preserved channel morphology and, in some cases, multiple levels of abandoned channels. Preserved channel morphologies reflect cross-section evolution due to forcing by climate, base level change, and sediment supply. Some features, such as wall notches, are thought to result from periods of bed armoring due to increased sediment load and subsequent lateral channel migration. When cave passages form below the water table, paragenesis can occur, where bed armoring results in upward incision of the channel and continuing deposition on the channel floor until the channel reaches the water table. While qualitative interpretation of field data has led to plausible connections between process and form within cave channels, a quantitative understanding of the factors that control channel widths is lacking. In this study, we develop a model of cave stream incision within soluble rocks and use this model to improve understanding on the controls of channel width. Shear stresses are calculated within the cross section and then used to calculate rates of mechanical and chemical erosion across the channel. Dissolution and mechanical erosion rates scale differently with shear stress and produce distinct patterns of erosion within the channel. Because of this, the dissolution process can influence channel width, and purely solutional or mechanically eroding streams will have different controls on their morphology.