Report

Developing a GIS-Based Soil Erosion Potential Model for the Jemez Watershed – Using the Revised Universal Soil Loss Equation (RUSLE) Josh Page CE 547 – GIS in Water Resource Engineering April 23rd 2012 Revised Universal Soil Loss Equation (RUSLE) RUSLE computes average annual erosion from field slopes in tons/acre/year (Renard, 1997) A = R*K*(LS)*C*P A = Computed Average Annual Soil Loss R = Rainfall-Runoff Erosivity factor K = Soil Erodibility Factor L = Slope Length Factor S = Slope Steepness Factor C = Land Cover-Management Factor P = Conservation Practice RUSLE – R Factor The R-Factor is the rainfall and runoff factor spatially distributed by geographic location The greater the intensity and duration of the rain storm, the higher the erosion potential. Isoerodent – Contour lines representing the R-Factor, created by the USDA www.westernexcelsior.com/EEDdocs/Isoerodent_Maps.pdf (ft-ton-in)/(ac-h-yr) RUSLE – K Factor The K-Factor is the average soil loss in tons/acre per unit area for a particular soil in cultivated, continuous fallow with an arbitrarily selected slope length of 72.6 ft. and slope steepness of 9% ( ~ 40 degrees). It is a measure of the susceptibility of soil particles to detachment and transport by rainfall and runoff. Texture is the principal factor affecting K, but structure, organic matter and permeability also contribute. soils.usda.gov/survey/online_surveys/new_mexico/ (Top Soil: 0-10 inches) (Soil Depth: 10-30+ inches) RUSLE – LS Factor The LS-Factor represents a ratio of soil loss under given conditions to that at a site with the "standard" slope steepness of 9% and slope length of 72.6 feet. The LS-Factor was computed from a 10m DEM using an OpenSource C++ Program http://www.iamg.org/ RUSLE – C Factor The C-Factor is used to determine the relative effectiveness of soil and crop management systems in terms of preventing soil loss. It is a ratio comparing the soil loss from land under a specific crop and management system. Important Note: The C factor resulting from this calculation is a generalized C factor value for a specific crop that does not account for crop rotations. (Goldman et al. 1986) RUSLE – P Factor The P-Factor is known as the support practice factor. It reflects the effects of practices that will reduce the amount and rate of the water runoff and thus reduce the amount of erosion. The P factor represents the ratio of soil loss by a support practice to that of straight-row farming up and down the slope. For this study the ratio will be kept at 1, indicating strait-row farming. Support Practice P-Factor Up & Down Slopes 1.0 Cross Slope 0.75 Contour Farming 0.50 Strip Cropping/Cross 0.37 Strip Cropping/Contour 0.25 http://www.omafra.gov.on.ca/english/engineer/facts/00-001.pdf R-Factor K-Factor LS-Factor C-Factor P-Factor For Each 10m x 10m Grid Cell A = R x K x LS x C x P Looking into the Future…. Since all of this data is from 6 years ago, it would be interesting to cross reference my model’s prediction with actual sediment loss in the Jemez Watershed. Although more careful calculations of the P & C Factors would be necessary. Questions