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Title page for ETD etd-09092010-133107

Type of Document Master's Thesis
Author Roberts, Andrew Scott
Author's Email Address andrew.roberts08@gmail.com
URN etd-09092010-133107
Title Rainsplash induced mound development beneath desert shrubs: Modulations of sediment transport and storage, with implications for hillslope evolution
Degree Master of Science
Department Geology
Advisory Committee
Advisor Name Title
David Furbish Committee Chair
  • desert shrubs
  • sediment transport
  • desert geomorphology
  • rainsplash
Date of Defense 2010-08-27
Availability unrestricted
This study examines the effect that rainsplash-induced sediment mounds beneath desert shrubs have on sediment flux in semi-arid environments. Mounds form beneath shrubs by differential splash of particles beneath shrub canopies (i.e. a grain activity gradient). Measurements of mounds beneath rabbitbrush and broom snakeweed in New Mexico reveal that mounds range in volume from 1,000 to 16,000 cm3. Mound volume increases with increasing shrub size. A sediment transport model is developed to describe how mound development affects sediment flux by solving the Fokker-Planck Equation. Advection of sediment is determined by the local topographic gradient and mass diffusion is controlled by the activity gradient. Sediment stored in mounds is not available for downslope transport, so a local divergence of flux develops, whereby the land surface downslope of a mound experiences decreasing elevation. A decrease in sediment transport rates is observed up to two meters downslope of a mound during 40 years of shrub growth. After shrub mortality, local sediment flux increases due to the increased hillslope gradient of the mound. Within 100 years of simulated mound development, a mound persists for at least 60 years after shrub mortality, causing elevated local sediment flux. On a hillslope scale with a dynamic shrub population, these changes in sediment flux may lead to significant changes in topography over centuries to millennia. The additive effect of shrubs on sediment flux suggests that modeling larger hillslopes may not involve solving the Fokker-Planck Equation, but may be solved algebraically.
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