Collaborative Research: RUI: Investigating the role of hillslope processes in modulating topologic change of upland drainage basins.

Watershed boundaries, or drainage divides, control the flux of water and sediment in a landscape and drive evolution and speciation of aquatic organisms. Over geologic time, drainage divides move in response to changes in climate and tectonics. This work explores how the motion of divides differs between gently sloping, soil-mantled landscapes and steep, mountainous, rocky areas. Specifically, the researchers will compare landscapes where soil creeps along hillslopes with those where material is primarily transported through landslides. They will use digital mapping techniques, field measurements of soil and sediment characteristics, and theoretical models of landscape evolution to investigate the ingredients that affect divide motion. Unlike previous research, which focuses on river channels, this work emphasizes processes that occur on hillslopes. Topographic analysis, field measurements of grain size, and erosion rates from cosmogenic nuclides illustrate the role of non-fluvial processes in modulating topographic change of drainage basins. To capture hillslope and colluvial transport regimes in landscapes ranging from soil-mantled to rocky, this work leverages measurements from field sites across a range of regional erosion rates (Ozark Plateau, Oregon Coast Range, San Gabriel Mountains). In addition to testing existing topographic metrics for divide instability, this work seeks quantitative methodological improvements to better incorporate steep landscapes into theoretical frameworks that describe and predict divide instability. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.