A user agency's view of hydrologic, soil erosion and water quality modelling

Abstract

Ž. The Natural Resources Conservation Service NRCS of the US Department of Agriculture provides assistance for land management planning and the use of conservation measures on private farmland in the United States. The NRCS must concern itself with a broad range of issues with regard to models and their application to support the assessments and decision making associated with these activities. These issues include the basic science for the description of physical processes, user issues in the practical application of the model, and software maintenance. In recent years, a significant amount of effort has gone into implementing existing agricultural hydrologyrerosionrwater quality models. There are, however, some important areas of model development that need to be addressed, including: reconciling the strengths and weaknesses of existing models; accounting for spatial variability of precipitation over the catchment; rectifying weaknesses in the stochastic climate generators currently included in some erosion models; improving the representation of runoff generating processes and water flow paths; Ž . and improving our understanding of ephemeral gully thalweg erosion and including algorithms to describe it. New model development also needs to follow modern standards of software engineering to ensure code reusability and maintainability. Although the NRCS is primarily a model user agency, it must be involved in all aspects of model development as well as model application to ensure satisfactory results. q

A third generation erosion model: The combination of probabilistic and deterministic components

“…Therefore, their validation is not satisfactory (Favis-Mortlock, 1998). This can be one of the reasons, why USDA recommended for applications less sophisticated empirical RUSLE (Garen et al, 1999), despite all the efforts spent on the development of process-based models.…”

Curve Number Hydrology in Water Quality Modeling: Uses, Abuses, and Future Directions

“…Scientists might recognize this, but, unfortunately, managers may not (although even scientists can be prone to emphasize the successful part of simulations rather than focus on the difficulties). In addition, many decisions to be made require quantitative, not just relative, information; therefore, like it or not, quantitative results are likely to be used to make major policy and investment decisions, ignoring the uncertainty of the model predictions (Garen et al, 1999). The conclusions one can justifiably make based on highly uncertain model results, then, are limited in scope, and great caution must be taken not to make decisions where greater accuracy than is warranted is attributed (knowingly or unknowingly) to the model results.…”

Documenting catchment suspended sediment sources: problems, approaches and prospects

“…Improved process representation and inclusion are required. Specific areas warranting attention include the effects of scale and uncertainties in accounting for the spatial variability of precipitation, the representativeness of runoff flow paths or the occurrence of ephemeral gully erosion (Garen et al, 1999). Existing models need to include more small-scale processes, especially whilst predicting change over a larger temporal or spatial resolution.…”