International Dredging Review

International Dredging Review

By Jon S. Hendrickson St. Paul District Corps of Engineers

Sediment management on the Upper Mississippi River involves providing a safe and reliable inland navigation channel improving habitat quality and diversity and maintaining the aesthetic integrity of the river for recreational users and riparian land owners. These challenges must be met while balancing the multiple competing uses of the river.

In the St. Paul District sediment management for the navigation channel includes sediment traps reduced depth dredging improved hydrographic surveying techniques expanding beneficial use of dredge material and construction of training structures. Habitat restoration includes island construction backwater dredging hard and soft bank stabilization methods and water level management. Monitoring and research on these projects has increased our knowledge of river mechanics sediment transport and biology. Improved design tools such as geographic information systems and multi-dimensional numerical models have allowed engineers to accurately quantify river responses and to present those results to a broad array of people.

The accompanying photograph illustrates the complexity of sediment management on the Upper Mississippi River. Sediment dredged from the navigation channel is placed at Crats Island which is the designated placement site for this reach of river per the St. Paul District’s Channel Maintenance Management Plan. Sediment moving down Indian Slough is building the Indian Slough Delta into Big Lake. Although the delta habitat is highly desirable the habitat in Big Lake is gradually disappearing as the delta expands. Sediment management actions must take into account both the desired condition of the navigation channel and the habitat goals for this river reach.

River engineering in the 21st century will be based on the foundation of experience knowledge and tools already available. Studies such as the restructured UMR-navigation study will add significantly to this foundation. Planning efforts underway to define habitat needs and the desired condition of the river will help set the goals and constraints for these efforts. New challenges such as water level and watershed management must be addressed. Water level management is being considered to establish annual cycles of wetting and drying necessary for the propagation of marsh plants. Watershed management involves land-use improvements and restoring river channels that may have been altered by levees or channelization The broad goals associated with these activities include maintaining or enhancing the value of the Upper Mississippi River as quality habitat for fish and wildlife as an important inland navigation route and as a destination for recreational interests.