Geomorphic Trends and Dynamics, Missouri National Recreational River

Science Center Objects

The two mainstem Missouri River segments of the Missouri National Recreational River (MNRR) represent some of the least altered channel form and most complex physical habitat on the Missouri River. The 39-mile segment is located in an inter-reservoir reach between Fort Randall Dam and Lewis and Clark Lake and the 59-mile segment is located below Gavins Point Dam, the downstream-most water control impoundment in the Missouri River system.

The Issue:

The National Park Service is faced with the challenge of managing river segments for ecological and recreational values where much of the riparian land is held by private landowners and agencies from Nebraska and South Dakota. Predictive tools forecast where the river is likely to migrate over the time frame of planning horizons to help develop long-term river-corridor boundaries and put aside “room for the river”. These predictions are challenging in a system that is adjusting over time to the effects of impoundments and existing bank-stabilization.

 

Addressing the Issue:

Despite considerable alterations to hydrology both the 39-mile and 59-mile reaches of the Missouri National Recreational River (MNRR) retain a high-degree of the channel complexity that was present in the pre-dam Missouri River system. These channel features include a multi-thread, dynamic thalweg, bare sandbars, vegetated islands, large woody debris, eroding banks, backwaters, and wide reaches similar to those that were present in the pre-channelized Missouri River and that do not exist in many other segments of the modern day river system. Downstream from the MNRR the Missouri River has been channelized for navigation from Sioux City, Iowa to St. Louis, Missouri. Channelization through the emplacement of coarse rock for bank revetment and dike structures in the channel on the lower 735 miles of the Missouri River has resulted in a narrower and deeper single-threaded channel with few sandbars or islands. In the downstream portion of the 39-mile segment of the MNRR sedimentation at the confluence of the Niobrara River has created a complex transition zone from free-flowing river to reservoir in the downstream portion of the 39-mile segment. This region that forms the delta of Lewis and Clark Lake is a novel ecosystem that provides unique habitat for waterfowl, waterbirds, and amphibians.  The delta also provides aquatic cover, food resources, and spawning habitat for some fish species as well as recreational areas for fishing and hunting.

Moreover, geomorphic adjustments are not uniform in these river segments because of spatial controls including distance from the dams and natural geologic variation. Understanding the temporal and spatial distributions of channel changes since the closure of Fort Randall and Gavins Point dams will allow for a longer-term view of how the river has adjusted to changes in hydrology and sediment regime and allow for some predictive extrapolation about future trends.

The Missouri National Recreational River is a National Park Service unit

The Missouri National Recreational River (MNRR, above) is a National Park Service unit that includes two Missouri River segments separated by Lewis and Clark Lake. Despite considerable alterations to hydrology these segments retain some aspects of channel complexity that existed in the pre-dam Missouri River.

(Public domain.)

 

Future Steps:

  • CERC scientists will use aerial photography and satellite imagery from a variety of sources to characterize channel dynamics over time. Because these image sources are snapshots in time, they represent specific discharge conditions and therefore need to be analyzed using methods that minimize bias from prevailing discharge conditions.
  • Acquire and synthesize GIS mapping datasets associated with habitats of the MNRR used by floodplain and riverine biota including the Interior Least Tern, Great Plains Piping Plover, Plains Cottonwoods, and pallid sturgeon.
  • Post-2005 imagery and ancillary data will be used to update previous maps documenting changes in the geomorphic high bank and to refine a channel classification that delineated reaches of varying instability and channel complexity within the MNRR. This planform analysis will provide the foundation for a migration zone model.

 

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