SEDIHYDROLOGY, SCIENCE, STAKEHOLDERS, AND SUSTAINABILITY

Sustainable management of nonpoint sediment sources is one the most intractable problems in watershed management. Success in improving water quality will require not only reliable prediction of water and sediment flux throughout a watershed, but enormous expense and exceptional social and political collaboration. This talk reports on an effort to reach a consensus strategy to reduce sediment delivery from the Blue Earth River Basin, a 9,000 sq. km tributary to the Minnesota River. Rapid downcutting of the Minnesota River at the end of the Pleistocene triggered rapid incision of tributary streams into the predominantly flat landscape. The region is naturally primed for high turbidity. Widespread artificial drainage and row cropping over the past 150 yrs altered runoff and sediment dynamics, increasing sediment yield by as much as an order of magnitude. A Minnesota Constitutional Amendment will direct substantial funding toward improving water quality. It remains to be shown that these enormous expenditures will produce the desired reductions in turbidity. There is a pressing need to identify the best methods and locations for reducing excess erosion and sediment delivery and to determine the time lag between implementation and reduction of sediment loads at the mouth. We have built a collaborative of local, state, and industry stakeholders with whom we are developing (i) a simulation model that forecasts changes in sediment loading in response to changes in land use, climate, and management actions and (ii) a decision-analysis system in which the costs and benefits of management alternatives can be evaluated consistently and transparently, incorporating the best available scientific information and accounting for uncertainty. For effective decision analysis, hydrologic, geomorphic, and management factors are combined in a reduced complexity sediment source and routing model to estimate the change in loadings in response to different management options. A key feature of the model will be its relative simplicity and speed, such that stakeholders can develop confidence in their interpretation of the results. Excess turbidity and sediment delivery are not unique to the Minnesota River, of course, and our goal is presenting this material is to discuss the application of our approach to Northeast river basins.