Research and monitoring have identified the Greater Blue Earth River (GBE) as the largest source of sediment to the Minnesota River and Lake Pepin. There is a pressing need to identify the best methods and locations for reducing erosion and to determine the time lag between the implementation of management practices (designed to decrease erosion) and reduction of sediment loads at the mouth of the river.
The GBE naturally has high turbidity due to its location, landforms, and geomorphic history. However, human changes in hydrology and vegetation over the past 150 years also play an important role in the movement of sediment in this area of Minnesota.
Researchers have demonstrated that under current conditions the largest sediment sources are near-channel sources including high bluffs, channel widening, and channel incision; ravines; and agricultural uplands. In addition, results indicate that erosion rates for near-channel sediment sources have increased over pre-settlement rates and flows in this region are changing. Defining the role of near-channel sources in the modern sediment budget helps scientists better understand the sensitivity of the Greater Blue Earth River basin to on-going hydrologic change and the effectiveness of management practices in terms of sediment reduction.
Sediment reduction will require a combination of actions to reduce erosion at its source and more effectively control the physical drivers of erosion. If only sediment sources are addressed, management actions will risk addressing symptoms but not the dominant causes. As high flows in the river are the underlying, systemic driver of near-channel erosion, increased water retention in uplands is needed to reduce sediment loss over the long-term and help mitigate against on-going and future changes in precipitation. One of the goals of this project is to assess the feasibility of Best Management Practices (BMPs) at lowering peak flows and/or reducing the amount of sediment transported to rivers.
Dr. Karen Gran and her research team recently completed an analysis of sediment sources in the Le Sueur watershed (PDF), the largest tributary to the Blue Earth River. That work led to new insights, strengthened previous conclusions and provides a foundation for a similar study in the Greater Blue Earth River watershed. The research objectives for the Blue Earth project are outlined below.
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