ABSTRACT
Models are used in the planning process for many different reasons. The scale of the model often but not always determines the level of descriptiveness of the simulation. A model developed for field scale or small watershed scale simulations generally can be expected to possess more descriptiveness than one designed for basin or regional planning. The degree of spatial and physical descriptiveness in a model has a dramatic impact on its applicability in specific planning situations. The use of empirical versus theoretical or calibrated versus deterministic modeling techniques also can have dramatic impacts on modeling costs and results. Lumped models often require calibration. This means that the model's internal parameters are adjusted to produce outputs consistent with observed information. However, these simplifications may undermine the ability of the user to study the impacts of specific placements of tillage or structural practices. A distributed parameter model attempts to describe the spatial configuration of the watershed.
