Erosion prediction

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There are dozens of erosion prediction models. Most have been developed for agricultural areas and are design to compare predicted annual rates of soil loss from broad areas under various cropland and rangeland management techniques. Some are purely statistical models, others mechanistic. Two of the more widely used methods in North America are the Revised Universal Soil Loss Equation (RUSLE)and Water Erosion Prediction Project erosion model (WEPP). Much of the research on erosion rates is directed towards supporting or fitting these competing models. In particular much of the mineland erosion literature is solely focussed on fitting or improving RUSLE parameters. Aside from a few new deterministic gully erosion models, these models do not consider gully erosion – mostly due to difficulties in modelling, and partly because gullies are often repaired in agricultural, forestry, or mining environments.

Because there is a wide discrepancy between predicted and observed erosion rates, models are better as research tools than as public policy and regulatory instruments or for prescriptive design measures for constructed landforms. But some models may provide useful guidance for the design engineer if adequately calibrated and verified for local conditions and if the design accounts for the uncertainty.

Most erosion modelling is applied to existing sites of known topography and material properties to guide land management activities. Designers of constructed landforms, however, have considerable control over the topography, cover soil placement, initial revegetation, and to a lesser extent the substrate properties – flexibility that is generally uneconomical for farmers and ranchers and most users of erosion models. On the other hand, miners have little input into post closure land use practices and management.

Methods to estimate erosion rates include: - purely statistical models - subjectively determined erosion rates using expert judgement combined with a database of erosion rates of natural and reclaimed sites (natural and industrial analogs) - surveying of existing erosional or depositional features of known age (or as determined by dating of deposits) to determine average erosion rates. Analysis of historical aerial photographs is often employed. - site-specific empirical models that relate slope, watershed size, and rainfall - empirical and semi-empirical or deterministic models based on laboratory and field flume measurements of erosion under simulated rainfall or flow conditions - physically based gully erosion models - landform and landscape scale models, often GIS based, that apply erosion mechanics or statistical relationships to predict changes in topography and erosion rates - sediment-budget models based on watershed monitoring