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Formation and Evolution of Concentrated Flowpaths on a Pinyon-Juniper Woodland
AuthorCostigan, Katie H.
AdvisorWeltz, Mark A.
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There has been a dramatic increase in the last thousand years in Pinyon-Juniper woodlands, which is primarily attributed to global climate change. The focus of this thesis is to describe the hydrologic impact of hand felling Pinyon and Juniper trees perpendicularly to the slope to provide physical barriers to overland flow, reduce velocity of flow, and minimize soil erosion. Experimental design consisted of two cover conditions (naturally occurring bare interspaces and slash piles from felled trees on naturally occurring bare interspaces) at two slope steepnesses (30% and 10%), and three concentrated flow water application rates. Water was applied from a specially designed flow initiator with pressure compensating flow regulators calibrated to rates of 15, 30 and 42 L min-1 for 12 minutes after runoff first occurred to quantify the ability of the treatment to reduce concentrated erosion rates. Each treatment-slope-water application rate combination was replicated three times. The research indicates that hand felling Pinyon and Juniper trees can be highly successful in reducing the size of concentrated flow paths, velocity and sediment load. Results from this research also indicate that soil detachment is a far more complex process that cannot be described in one function. There are processes such as soil armoring, detachment capacity of water, and litter dams that are created that contribute to the complexity of modeling soil detachment rates. This research is being used by the USDA to develop concentrated flow equations for use in the Rangeland Hydrology and Erosion Model (RHEM), which is being developed in support of the USDA‟s Conservation Effects Assessment Project (CEAP).