Channel Networks

Channels are the arteries of terrestrial and submarine landscapes. They are responsible for transporting the water and sediment that either build or erode topography. They also transport important environmental nutrients and act as home to many organisms. Our group is interested in how these networks (both tributary and distributary) form and organize themselves. To study these questions we utilize field work, analysis of digital elevation models (DEMs), laboratory experiments, and computer modeling.


Growth laws for channel networks incised by groundwater flow: with Dan Rothman (M.I.T.) and David Mohrig (U. Texas Austin)

Wherever infiltration exceeds rainfall, runoff must travel at least partially underground. The reemergence of groundwater at the surface can then shape topography by a process called seepage erosion. Along with overland flow, seepage erosion contributes to the initiation and growth of channel networks. Because seepage processes undermine overlying material, they have been suggested as an explanation of enigmatic amphitheater-headed channel networks on Earth and Mars. Nevertheless, the role of seepage in producing such channels remains controversial. Progress requires relating mechanisms of growth to geologic form. By combining field observations from a kilometer-scale channel network in the Florida Panhandle with physical theory, we are working on unraveling the processes responsible for seepage network growth.
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Scaling laws of terrestrial and submarine channel networks: with Dan Rothman (M.I.T.), Doug Jerolmack (U. Penn), and David Mohrig (U. Texas Austin)

Channels are the most common and dynamically significant morphologic feature of sedimentary systems on the continental slope, yet the processes by which these channels evolve and organize themselves are incompletely known. Recent bathymetric surveys have revealed channel networks that are qualitatively similar to their terrestrial cousins. We are studying submarine channel network scaling relationships between contributing basin area and the length of channels and their slopes. These scaling relationships have been used by the terrestrial geomorphology community to analyze drainage basin evolution. We are comparing scaling relationships in submarine basins with terrestrial basins and several numerical models of basin evolution. We are finding that scaling relationships are similar in both terrestrial and submarine environments, supporting theoretical arguments that channel network structure results from the aggretation of random walks.
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Sediment transport and avuslion triggers on the Niobrara River, NE: with Doug Jerolmack (U. Penn) and David Mohrig (U. Texas Austin)

The lower section of the sandy braided Niobrara River, Nebraska, has experienced up to 2.5 m of aggradation over 50 years driven by base-level rise due to reservoir construction on the Missouri River. Over two field seasons I have particiapated in field campaigns aimed at studying the effect of this base-level rise on sediment transport and channel dynamics. An apparent response has been frequent avulsions due to superelevation of the channel, which has led to the creation in some reaches of multiple channels separated by vegetated islands. Results suggest that the river is dynamically adjusted so that the planform geometry has little effect on the routing of flow and sediment through the river.