River Diversions and Shoaling

Sponsored by the Louisiana Coastal Area Science and Technology Office.

This Coastal and Hydraulics Engineering Technical Note describes the current knowledge of the potential impacts of river diversions on channel morphology, especially induced sedimentation in the river channel. Processes considered in this note are those most pertinent to riverine, as opposed to estuarine, aspects of diversions. In particular, this note provides general guidance on the physical process issues, outlines strategies for more effective application of existing tools, and summarizes the needs for developing better tools to address the issues. These issues become critical in the planning and design of diversions when the operation of these structures could adversely impact other authorized uses of the river. For example, the management of water and sediment resources in coastal Louisiana for the mitigation of land and habitat loss must be balanced with the needs for flood control and navigation. In one management scenario, plans are being formulated (U.S. Army Corps of Engineers (USACE) 2004) to divert flow from the Mississippi River to distribute water and sediment as a way of rebuilding marsh areas and sustaining existing wetlands. One concern with this management option is the potential impact these diversions will have on deposition in the navigation channel and the potential for increased maintenance dredging. One of the main obstacles in developing a consensus and an optimum strategy for balancing these needs is the lack of efficient tools and general guidance for evaluating the impacts of diversions on navigation and flood control and, conversely, the impact of navigation and flood control measures on the distribution of the resources to the wetland ecosystem. Impacts are potentially created over a wide range of space and time scales, which the impact assessment approach and tools must consider. For example, the long-term impacts within the river channel are influenced by the long-term response within the distributary area for the diversion.