Military training activities can have adverse consequences on natural resources. Heavy vehicles compact the soil and damage or destroy both herbaceous and woody vegetation. Exploding munitions can cause soil displacement. Construction of training infrastructure such as emplacements, firing points, targets, fox-holes, and Military Operations on Urban Terrain (MOUT) sites cause extensive localized damage.
Soil erosion may accelerate as the soil surface becomes increasingly disturbed and protective vegetation is lost as a result of the cumulative impacts of military training. Extensive damage from gullying may occur. Such damage is not only expensive to repair, but also diminishes the realism and quality of the military training experience, and jeopardizes the safety of soldiers and equipment.
To meet legal mandates requiring the prevention and control of excessive soil erosion and sediment generation, Department of Defense (DoD) installations need an accurate, easily obtained, and cost-effective method to predict sources and sinks of eroded sediments generated on their properties. Currently available erosion and sediment models are hampered by the fact that they were developed for fairly uniform agricultural landscapes and do not accommodate topographic or land-use complexity. The objective of this project is to demonstrate and validate the Unit Stream Power Erosion and Deposition (USPED) model.
Measuring soil erosion and resultant sediment deposition in order to determine when an installation is out of compliance with regulatory mandates is difficult and subject to considerable error and subjectivity. Hence, estimation of erosion and deposition by computerized models is frequently used. Two of the most commonly used erosion prediction models are the Universal Soil Loss Equation (USLE) and the Revised Universal Soil Loss Equation (RUSLE).
At least part of the popularity of these models can be attributed to the ease with which they are applied. However, a major drawback of these and more complex new-generation process-based models is the 1-dimensional approach used to account for the effects of topography. Landscapes have generally been treated as homogenous planes. Average erosion rates have been assigned to entire hillslopes and watersheds, thus providing no information regarding sources and sinks of eroded materials.
Alternatively, complex landscapes have been computationally divided into semi-homogenous planes, and erosion has been calculated for each plane, thus giving some consideration to slope convexity and concavity. In both approaches, erosion is calculated along straight flow lines without full consideration of the influence of flow convergence and divergence. Neither approach provides adequate spatially-distributed erosion information necessary to effectively optimize erosion and sediment control efforts.
In addition, USLE and RUSLE only predict soil erosion; they do not predict sediment deposition. Furthermore, both models predict erosion ‘universally,’ even where deposition may occur. Thus, at landscape or watershed scales, the spatial distribution of soil erosion, as predicted by these models, may misrepresent actual conditions and may overestimate erosion.
Geographic information systems (GIS) provide the capacity to more fully consider the effects of topographic complexity on soil erosion. Application of erosion models within GIS has become increasingly popular as the technology has evolved. Spatially distributed elevation data stored in a GIS can be analyzed to produce slope length and steepness (LS) values for any given point in a watershed.
More importantly, the effects of flow convergence and divergence can be more fully considered by determination of the upslope area that contributes flow across each point in the watershed. When upslope contributing area is substituted for slope length, the resulting LS-factor is equivalent to the traditional LS-factor on planar surfaces, but has the added benefit of being applicable to complex slope geometries.
Equations for the computation of the LS-factor based on upslope contributing area have been developed. These equations account for topographic complexity by considering both the profile curvature (in the downhill direction) and the tangential curvature (perpendicular to the downhill direction). Net erosion or deposition within a grid cell is calculated as the change in sediment transport capacity in the direction of flow.
The objective of this project is to demonstrate and validate the Unit Stream Power Erosion and Deposition (USPED) model for application in diverse ecoregions and on complex landscapes typical of military training lands. Research is occurring on Eglin Air Force Base in Florida, Fort Hood in Texas, Schofield Barracks in Hawai'i, Fort Campbell in Kentucky, and Yakima Training Center in Washington.
It is anticipated that the USPED model will provide significant capability to DoD land managers to accurately predict soil erosion and sediment deposition both spatially and volumetrically, thereby enabling them to allocate limited land rehabilitation dollars to portions of the landscape with the greatest need of remediation. The model also can be used to identify areas least capable of supporting increased disturbance without becoming noncompliant with non-point source pollution standards.
Warren, S.D., H. Mitasova, M.G. Hohmann, S. Landsberger, F.Y. Iskander, T.S. Ruzycki, and G.M. Senseman. 2005. Validation of a 3-D enhancement of the Universal Soil Loss Equation for prediction of soil erosion and sediment deposition. Catena 64:281–296.