4 minute read
Deer Island
Little Sioux, Iowa, United States
Doubling the width of the Missouri River. The Missouri River, the longest river in North America, remains an important navigation channel and water source for communities along it. However, it is also one of the most significantly altered and ecologically impacted rivers in North America. Efforts to control its flow have resulted in a narrow, deep, and fast-flowing river with very little depth or flow diversity. Many areas have seen reductions in width from over 600 meters to closer to 200 meters. To solve these problems, the Kansas City, St. Paul, and Omaha U.S. Army Corps of Engineers (USACE) districts teamed up to create high-quality, shallow-water habitat at Deer Island by excavating over 1.5 million cubic meters of material from the top width of a 3.2-kilometer stretch of the river. They widened the channel by 90 to 200 meters and constructed multiple large, permeable rock structures to split the flow of the river, creating a shallow bench with a diversity of depths and velocities adjacent to the main channel of the river. Now the river’s main channel supports navigation while new shallow-water habitat benefits the federally endangered pallid sturgeon (Scaphirhynchus albus) and other native fish and wildlife.
Article cover: Waterfowl using the sandbars in 2015. (Photo by Dave Crane, USACE Omaha District)
Producing Efficiencies
A team of engineers from the USACE Omaha and St. Paul Districts conducted a significant hydraulic modeling effort using the USACE Adaptive Hydraulics Model, which had never been used on a shallowwater habitat project. The team ran multiple flow and sediment-load scenarios to determine the right balance of widening and structure to maintain a diversity of depths, flow velocities, and physical habitat without negatively affecting the navigation channel. With guidance from this model, the team doubled the width of the reach and created new habitat.
Using Natural Processes
The rock structures and large, woody debris structures placed on the bench created a dynamic and everchanging shallow-water habitat area by precisely splitting the flow of the river. This maintained the depth of the navigation channel while allowing enough flow through the constructed shallow-water habitat to prevent it from filling in with sediment. As the sediment dropped out of the water running through these rock structures, it naturally created a range of depths and velocities.
Broadening Benefits
This project created over 40 hectares of critical channel-border aquatic habitat along the Missouri River, designed specifically not to interfere with any of the other congressionally authorized purposes of the river, such as water supply, flood risk reduction, water quality, hydropower, irrigation, and recreation. Monitoring of fisheries shows that there has been great response to this habitat, and waterfowl are using this new area extensively. Further, in contrast with other areas of the Missouri River with primarily deep water and swift currents, this area also provides easier access for various recreational activities.
Promoting Collaboration
Extensive collaboration between USACE, the Fish and Wildlife Service, the Iowa Department of Natural Resources, and the Nebraska Game and Parks Commission ensured the project design incorporated features that would meet the needs of all, including the endangered pallid sturgeon and other game and nongame aquatic species. As outreach, the project team has shared innovations by providing tours for Missouri River Basin Interagency Roundtable, Congressional representatives and state agency directors from Nebraska and Iowa, Iowa State University Extension Office educators, and a University of Montana student filming a documentary on the Missouri River.
