Lassoing a Whirlwind: Managing Flow on the Missouri River
When Casey and Jeff asked me to write a blog entry, I was staring at my screen saver which was a picture of a lake sturgeon isolated by the dramatic draw down of the river below Gavins Point dam near Yankton, South Dakota. Along with its more famous cousins, the pallid and shovelnose sturgeons, the lake sturgeon is a prehistoric fish struggling to survive in the altered environment of today’s Missouri River. How this interesting “Jurassic Park” specimen ended up in a pool of water in the Missouri River for folks to gawk at makes for an interesting story.
It’s been an awfully dry summer this year but during the Summer of 2011, the Missouri River basin was saturated from a Spring rain, particularly the upper basin in North Dakota and Montana. Combined with a high snow pack and late season snows in the mountain ranges feeding Great Plains streams, atypical Spring rains produced record amounts of runoff into the six reservoirs managed by the Army Corps of Engineers.
In an effort to protect the infrastructure of the 1950s and 1960s era constructed dams holding back all this excess precipitation and to prevent dam over-topping and possible catastrophic failure, the Corps released water downstream into the lower basin. Normal releases from Gavins Point (the southernmost dam) in mid- Summer are typically about 32,000 cubic feet per second (cfs), but in July 2011, Gavins passed about 160,000 cfs. That amount of water had never been released through the dam and its impact on the dam structures was unknown.
The resulting high water levels innudated the floodplain, displacing residents and damaging crops and property. Levees built to restrict the river to a narrow channel could not hold back the larger volumes of river water, particularly those levees constructed close to the river bank creating ‘pinch points’ for river flow. Repeated failure of several levees, particularly at ‘pinch points’, during multiple high water events has caused the Corps to begin consideration of levee ‘set-backs’ to address an unsustainable levee design which would also open up the floodplain to accommodate more river flow and improve aquatic habitat.
Fast forward to early 2012, and the volume of releases from dams raised concerns about possible damage to structures, and the Corps determined that close inspection at particular locations to verify condition and assess any damage was necessary. This was the case at Gavins Point near Yankton, South Dakota where the Corps actually closed the spillway in order to allow inspectors to assess damage. That is, no river water flowing through the dam, resulting in an extreme photographic contrast from the Summer of 2011.
When the dam was closed in May 2012, the reach of the river extending down almost to Sioux City was transformed, exposing natural and man-made features not seen since the dam was finished in 1955. River organisms were stranded, including many mussels, not commonly found in the lower river.
River scientists know how the lower river’s substrate is dominated by ‘dunes’ of sand which roll and jump along the bottom which was unique to see firsthand. These ‘waves of sand’ create a very dynamic environment for aquatic organisms living in the sediment and coasting above it. It also presents challenges for human engineering to adapt river structures to a moving bottom.
If you are ever in the vicinity of any of the six big Army Corps dams on the Missouri River, call the Corps office at the dam and see if there’s an available tour of the facility. They are each unique in their design and how they are placed in the ‘natural environment.’ My personal favorite is Fort Peck dam near Glasgow, Montana, the uppermost dam operated by the Corps. It was constructed in the 1930s during the Great Depression and its powerhouse has an ‘art deco’ design.
Larry Shepard is an environmental scientist in EPA Region 7’s NEPA program reviewing environmental impact statements and environmental assessments primarily focusing on river-related federal projects. Shepard hails from the shores of Beal Slough in Lincoln, Nebraska, which flows to Salt Creek, then to the Platte River, then to the Missouri River and finally to the Mississippi River.
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