http://nova.newcastle.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:9707 Hairsine and Rose developed a mechanistic, one-dimensional, precipitation-driven erosion model that, since its appearance, has been validated by several sets of experimental results. The model allows any sediment particle to be present in one of three zones, viz., the flow zone, the deposited layer, or the original soil. The model has the general form of a two-region model, in which advection is the only transport process. For the special case of a soil composed of a single particle size and for overland flow that occurs at a steady rate and with a uniform depth, it is possible to derive fully explicit analytical solutions to the model. Details of the solutions for a slightly generalized mathematical form of the model are provided. The Goldstein J function, which appears commonly in two-region model solutions, was modified to accommodate some of the solutions presented. The form of the model analyzed indicated that, based only on sediment concentrations in runoff water, it is not possible to distinguish one mechanistic feature of the Hairsine–Rose model, i.e., that raindrop-induced detachment of the undisturbed soil moves directly into the flowing water. From the point of view of the model, it is equally plausible for raindrop impact to move sediment directly into the deposited layer. 2011-12-13T00:50:18.644Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:2241 An approximate analytical solution is obtained for a physically based model of soil erosion on a gentle slope driven by rainfall impact in which there is inflow of clear or nearly clear water to the top of the soil bed. Comparison of the approximate analytical and numerical solutions shows very good agreement, except for the first few minutes of an erosion event. The approximate analytic solution is applied using data from an illustrative experiment to explore its physical features. The importance of adequately defining the soil's settling velocity characteristic through the use of a sufficient number of sediment size classes, especially for prediction at short times, is illustrated. The temporal variation in sediment concentration, except at short times, is shown to be more significant than the spatial variation down the eroding surface. Solution of the equations allows visualization of the rate of convective transport of sediment down the eroding surface, this rate decreasing as sediment size increased due to more frequent return of such particles to the soil surface in deposition. 2010-04-27T06:53:55.564Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:2791 Dynamic changes take place in the nature of sediment eroded from bare soil at low slopes by rainfall impact when there is no inflow of water at the top of the eroding slope. This relates initially to fine soil sediment not settling back onto the soil after the rainfall impact. Coupled partial differential equations describing such dynamic changes have been solved numerically for a bed of soil, bounded at its upper end, and subject to a constant rainfall rate. This solution allows prediction of the change with time and downslope distance in the concentration and settling velocity (or size) characteristics of eroding sediment, allowing critical evaluation of the assumption of space-independent sediment characteristics made in prior approximate analytical solutions of the equations involved. Following the determination of as yet unpredictable soil-related parameters in the equations, the solution was tested by comparison with experimented data on two soils of contrasting structural stability, namely a vertosol [The Australian Soil Classification (1996)] and a aridisol. Investigations included the determination of a minimum number of sediment size classes required to adequately describe the settling velocity characteristics, based on the shape of the underlying basic settling velocity characteristic, which is used to predict the dynamics of sediment deposition. The effect on the solution of observed structural breakdown in soil aggregation due to rainfall impact was investigated, leading to more accurate predictions of the settling velocity characteristics of eroded sediment. Other sources of discrepancy between theory and observation remain to be determined. 2010-04-27T06:04:12.615Z ]]>