2022 CSDMS meeting-021
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The Hydrogeomorphic Evolution of Variable Source Areas
David Litwin,
(he/him),Johns Hopkins University Baltimore Maryland, United States. dlitwin3@jhu.edu
In some watersheds saturated areas that shed runoff (variable source areas) and the flowing stream network expand and contract in response to precipitation, while in other watersheds saturated areas are relatively fixed despite changes in precipitation and water storage. These variations in saturated area can be understood as the result of the competition between supply of water from upslope and the ability of the subsurface to transport that water downslope. But this does not explain the genesis of the landscape conditions that determine the outcome of this competition. What geomorphic aspects of these landscapes make their hydrological function different? To what extent are variable source areas the emergent product of long-term critical zone evolution? Here we use a coupled model of landscape evolution and runoff generation from shallow subsurface flow to explore these questions. The model solves the non-linear, transient hydraulic groundwater equations to predict the water table location given prescribed time-varying recharge. Water in excess of the subsurface capacity for transport becomes overland flow, which may detach and transport sediment, modifying the landscape form that in turn affects runoff generation. We nondimensionalize the model and examine the effects of both subsurface and climatic conditions (storm intensity, duration, frequency) on coevolved landscapes under stochastic precipitation. Preliminary results show that we can produce both watersheds with low variability in saturation relative to variability in storage and vice versa by varying subsurface and climatic properties. With the same mean annual precipitation, evolved landscapes have more spatially dynamic saturated areas when the time between storms is large relative to the time to drain hillslope aquifers. Quantifying the coevolution of geomorphic properties and variable source areas will deepen our understanding of runoff generation processes and could improve prediction of trends in saturation and erosion as a result of climate change.
