Submitted to: Encyclopedia of Hydrological Sciences
Publication Type: Book / Chapter
Publication Acceptance Date: 11/1/2004
Publication Date: 12/1/2005
Citation: Nearing, M.A., Renard, K.G., Nichols, M.H. 2005. Erosion prediction and modeling. In: M.G. Anderson, J.J. McDowell (Editors). Encyclopedia of Hydrological Sciences. Vol. 2. New York. John Wiley and Sons. p. 1221-1228. Interpretive Summary: Soil erosion models play an important role both in meeting practical needs of soil conservation goals and in advancing the scientific understanding of soil erosion processes. They are used to help land managers choose land practices in order to reduce erosion rates on agricultural and other lands. Erosion prediction models are used for assessment and inventory work to track temporal changes in erosion rates over large areas. Erosion models are also used for engineering purposes, such as predicting rates of sediment loading to artificial reservoirs. Increasingly governments are using erosion models and their results as a basis for regulating conservation programs. Essentially, models are used wherever the costs or time involved in making soil erosion measurements are prohibitive. Erosion models play at least two roles with respect to the science of soil erosion. Erosion models are necessarily process integrators. Most often our knowledge of erosion mechanisms from experimental data is limited in scope and scale. Information may sometimes be misleading in terms of the overall effects on large integrated systems where many processes act interdependently. If individual processes which are well described from erosion experiments are correctly integrated via a process-based model, the result may be used to study model predictions and assess the behavior of the integrated system. Erosion models also help us to focus our research efforts. They help us to see where gaps in knowledge exist and where to best focus our efforts in order to increase our overall erosion prediction capabilities.
Technical Abstract: The concept of differentiating between rill and interrill erosional areas outlines a useful, if somewhat arbitrary, division between dominant processes of erosion on a hillslope surface. In the original description of the processes, Meyer et al. (1975) differentiated between areas of the hillslope dominated by shallow sheet flow and raindrop impact and those of small concentrated flow channels, which they termed rills. The concept is useful in terms of mathematical descriptions of erosion, and serves as a basis for many process based erosion simulation models. The concept is also useful in terms of focusing experimental research on the two primary sources of eroded soil. The separation of the two primary sediment sources facilitates the mathematical modeling of non-point source pollutants in surface runoff. However, the concept is somewhat arbitrary because it implies a clear delineation between dominant processes on a given area, where, in fact, overlap occurs. Flow depths on a hillslope would be more correctly described in terms of frequency distributions of depth where processes tend more towards rill or interrill depending on the flow depth (Lewis et al., 1990). Nevertheless, the introduction of the concept of rill vs. interrill sediment source areas is the cornerstone of current erosion research and development of process based erosion prediction technology. It is the subdivision of the erosion process which opened the "black box" which was employed by earlier, statistically based erosion models.