Cumulative Watershed Effects: Caspar Creek and Beyond1

2 Research Geologist, USDA Forest Service Pacific Southwest Research Station, Redwood Sciences Laboratory, 1700 Bayview Dr., Arcata, CA 95521 Abstract: Cumulative effects are the combined effects of multiple activities, and watershed effects are those which involve processes of water transport. Almost all impacts are influenced by multiple activities, so almost all impacts must be evaluated as cumulative impacts rather than as individual impacts. Existing definitions suggest that to be significant, an impact must be reasonably expected to have occurred or to occur in the future, and it must be of societally validated concern to someone or influence their activities or options. Past approaches to evaluating and managing cumulative watershed impacts have not yet proved successful for averting these impacts, so interest has grown in how to regulate land-use activities to reverse existing impacts. Approaches being discussed include requirements for “zero net increase” of sediment, linkage of planned activities to mitigation of existing problems, use of more protective best management practices, and adoption of thresholds for either land-use intensity or impact level. Different kinds of cumulative impacts require different kinds of approaches for management. Efforts are underway to determine how best to evaluate the potential for cumulative impacts, and thus to provide a tool for preventing future impacts and for determining which management approaches are appropriate for each issue in an area. Future impact analysis methods probably will be based on strategies for watershed analysis. Analysis would need to consider areas large enough for the most important impacts to be evident; to evaluate time scales long enough for the potential for impact accumulation to be identified; and to be interdisciplinary enough that interactions among diverse impact mechanisms can be understood.