J. Alan Clingenpeel
USDA Forest Service
Ouachita National Forest
PO Box 1270 Hot Springs, AR 71902
Fax : 501-321-5334
IMPACTS is a simulation model that examines silviculture activities on water quality and fisheries at the watershed level. The model uses predicted sediment yields as a surrogate for impacts to water quality. The model calculates the average annual sediment values for the selected watershed. Sediment increases from presently occurring and proposed management alternatives are also calculated. The sediment values from presently occurring activities and proposed management alternatives are expressed as a percent increase over the average annual sediment produced from the watershed. This allows for a comparison of alternatives (expressed as a percent increase). The alternatives can also be compared to a threshold value associated with fisheries.
The model multiplies the number of acres associated with each land practice against a coefficient previously determined for that physiographic zone. The values from the land practices are summed to account for the entire watershed. Acreages are calculated from a 1:24,000 quad map (7 1/2 minute). Land practices are determined from aerial photos (same scale) or from on-site evaluation.