Bisherige Auswertungen der Erosionsgefährdung stützen sich auf das landesweit verfügbare Digitale Geländemodell (DGM) mit einer Rasterweite von 20 m (DGM20). Das neu erstellte DGM2 bietet durch seine Rasterweite von 2 m erstmalig eine sehr hohe räumliche Auflösung. In Testgebieten wurden die Auswirkungen der neuen Datengrundlage DGM2 (Laserscanbefliegung) auf die Erosionsgefährdungsbewertung analysiert. Verschiedene DGM-Aufbereitungsverfahren sowie DGM-Rasterweiten wurden im Hinblick auf die Erosionsmodelle Erosion-3D und ABAG (Allgemeine Bodenabtragsgleichung) getestet. ABAG und Erosion-3D reagierten zum Teil unterschiedlich empfindlich auf die verschiedenen DGM-Varianten.

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Monitoring nonpoint source pollution in a large area is often impractical. However, estimating nonpoint pollution through use of empirical models such as the Universal Soil Loss Equation (USLE) provides a basis for identifying problem areas, and setting management priorities. The purpose of this study was to determine the feasibility of using Landsat imagery and existing geographic data to estimate the effects of land use changes on water quality in four North Texas watersheds over a twelve year period.

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The major study objectives include determining if a 50-foot streamside management zone (SMZ) as described in the Virginia BMP Manual (VDOF 2002) is generally sufficient to protect stream water quality, riparian soils, and stream bank integrity in headwater streams where forest harvesting has taken place, as well as comparing other SMZ widths with regard to the same environmental protection performance. In 2003, 16 forested watersheds were clear-cut harvested for commercial timber production. Four SMZ treatments were installed across four experimental blocks during harvest. Each of the 16 watersheds was subsequently site-prepared with prescribed burning and planted with loblolly pine (Pinus taeda). Within the watersheds, the established treatments were a 100-foot width with no thinning, a 50-foot width without thinning, a 50-foot width with thinning, and a 25-foot "stringer." Each of the four treatments was conducted within three of four blocks (Incomplete Block Design). After a two-year post-harvest monitoring period, it was determined that the SMZ treatments had no significant effect on water quality, channel geometry, or soil erosion in and around the streams. There was no apparent water quality degradation as a result of harvesting timber, and larger SMZs did not have an impact on any of the parameters studied. It was also apparent that leaving narrower SMZs or thinning within SMZs did not cause any apparent environmental degradation. It was also determined that landowners who leave SMZs on their property have very limited opportunities to manage timber within them for financial gain in the long term. / Ph. D.

Erosion and sediment delivery from upland areas to waterbodies is a major problem impacting water quality in the United States and elsewhere. Measures to reduce these impacts are either targeted at reducing erosion on-site or at reducing delivery of sediment to waterbodies. AMEENA (Areal Modeling of Erosion for Environmental Nonpoint Applications) is a spatially distributed model that estimates erosion and deposition on a watershed scale by predicting erosion and transport over the landscape surface. Erosion is predicted based on the Revised Universal Soil Loss Equation (RUSLE), and sediment transport capacity is estimated as a function of upslope flow volume, local gradient, and land use. Gross erosion is routed to edge-of-stream with a routing algorithm that iteratively compares available sediment with transport capacity on a cell by cell basis from ridge cells to stream cells. The model is implemented completely within a raster GIS to facilitate use of the model as a tool to readily evaluate impact of land use practices on sediment delivery to streams. AMEENA was validated using field data of net erosion and sediment deposition from three field studies. AMEENA predicted the spatial distribution of net erosion and deposition better than WaTEM/SEDEM which is a distributed parameter erosion model based on a similar modeling approach. AMEENA's suitability to simulate the impact of management practices such as filter strips and critical area planting was evaluated on plot (profile) scale and catchment scale simulations. Results of plot scale simulations were intuitive and the model proved more reasonable for these scenarios than did RUSLE2 and WEPP. The catchment scale study highlighted features of AMEENA that are not available in RUSLE2 and WEPP in terms of identifying erosion “hot spots” and the ability to utilize the explicit sediment flow path identification in locating best placement of off-site sediment control measures. Since AMEENA does not account for in-stream erosion processes, it is not suitable for simulating areas dominated by channel or gully erosion. / Ph. D.

One-dimensional and two-dimensional modeling approaches were compared for their abilities in predicting overland runoff and sediment transport. Both the I-D and 2-D models were developed to test the hypothesis that the 2-0 modeling approach could improve the model predictions over the 1-0 approach, based on the same mathematical representations of physical processes for runoff and sediment transport. Runoff processes were described based on the St. Venant equations and the sediment transport was based on the continuity relationship. The finite element method was employed to solve the governing equations. The nonlinear, time-dependent system of equations obtained by the finite element formulation was solved by the substitution method and the implicit method. The models were verified by comparing the analytical solutions presented by Singh and Regl (1983) and the solution by the Izzard method (Chow, 1959). The comparison showed that both the 1-0 and 2-D models provided reasonable estimations of runoff and sediment loadings. Evaluation of the models was based on four different hypothetical case studies and two experimental studies. The hypothetical case studies investigated the effects of the discretization level, cross slopes, and the size of the field area on the model predictions. The two experimental studies provided a comparison of model predictions with observed data. The results of the hypothetical case studies indicated that the maximum differences in the model predictions at the outlet were about 30% between the two modeling approaches. When the discretization level was sufficient to reasonably describe the shape of the surface, the 1-0 model prediction were almost the same as the 2-D model predictions. Even though cross slopes existed in the field, the differences in the model predictions at the outlet were not significant between the 1-0 and 2-0 models. The differences in the model predictions of runoff and sediment loading were not affected by the changes in the size of the field. Since the 2-D model resulted in 10 to 20% differences in model predictions when different boundary conditions were used and the 1-D model predictions were also affected by the choice of element length, the differences in model predictions at the outlet, shown in model application results, which were less than 30% in most cases, could not be considered significant. The model applications to the experimental studies also showed that no substantial differences existed in the model predictions between the I-D and 2-D models. Even though the spatial distributions of the flow depth and sediment concentration were significantly different, runoff volumes and sediment yields at the outlet showed less than 10% differences. Compared with the I-D model, the 2-D model required much more computational time and effort to simulate the same problems. In addition, convergence problems due to negative flow depths limited the 2-D model applications. The 2-D simulations required more than twice the computational time needed for the I-D simulations. As long as the model predictions at the outlet are concerned, the much greater computational costs and efforts could not justify the use of the 2-D approach. Based on the simulation results from the selected hypothetical case and experimental studies, the 2-D model provided better representations of spatial distribution of flow depths and sediment concentrations than the I-D model. However, no substantial differences in predictions of total runoff volume and sediment yield at the outlet area were found between the I-D and 2-D models. / Ph. D.

The multiangle submerged jet test device (JTD) provides a simple in situ method of measuring streambank critical shear stress (Ï c) and soil erodibility (kd). Previous research showed streambank kd and Ï c can vary by up to four orders of magnitude at a single site; therefore, it is essential to determine if the large range is due to natural variability in soil properties or errors due to the test method. The study objectives were to evaluate the repeatability of the JTD and determine how it compares to traditional flume studies. To evaluate the repeatability, a total of 21 jet tests were conducted on two remolded soils, a clay loam and clay, compacted at uniform moisture content to a bulk density of 1.53 g/cm^3 and 1.46 g/cm^3, respectively. To determine the similarity between JTD and a traditional measurement method, JTD Ï c and kd measurements were compared with measurements determined from flume tests. The JTD kd and Ï c ranged from 1.68-2.81 cm³/N-s and 0.28-0.79 Pa, respectively, for the clay loam and 1.36-2.69 cm³/N-s and 0.30-2.72 Pa, respectively, for the clay. The modest variation of kd and Ï c for the remolded soils suggests the JTD is repeatable, indicating the wide range of parameters measured in the field was a result of natural soil variability. The JTD median kd and Ï c, except clay loam kd (clay loam kd = 2.31 cm^3/N-s, Ï c = 0.45 Pa; clay kd = 2.18 cm^3/N-s, Ï c = 1.10 Pa) were significantly different than the flume values (clay loam kd = 2.43 cm³/N-s, Ï c = 0.23 Pa; clay kd = 4.59 cm³/N-s, Ï c = 0.16 Pa); however, considering the range of potential errors in both test methods, the findings indicate the multiangle submerged jet test provides reasonable measurement of erosion parameters in a field setting. / Master of Science

A grid type portable rainfall simulator, developed at Virginia Tech from support by the Office of Surface Mining, Department of Interior under Grant NO. G5114009, was used to apply 2.3 inch per hour “storms” to three replicated plots to determine surface mine soil erodibility factors for two distinctly different soils in southern West Virginia. Other variables included in the study were detailed soil descriptions for each site, initial and final soil moistures, plot rainfall distributions and the particle size distributions of the eroded materials. The soil erodibility indexes for the silt silt-loam and sandy respectively. loam soils averaged 0.408 and 0.735. Erodibility indexes for the silt silt-loam decreased, while indexes for the sandy loam soil remained constant for repeated rainfall applications. Using statistical analysis, rainfall distributions were shown to be uniform across plots for most rainfall applications. From a particle size distribution analysis of the eroded soil material, the percentage of silt and clay decreased, while the percentage of sand increased at each site with repeated rainfall applications. A rock mulching effect was present at the end of each testing sequence. / Master of Science