SEDIMENT DYNAMICS AND IMPLICATIONS FOR HABITAT REHABILITATION IN THE LOWER MISSOURI RIVER

Sediment erosion, deposition, and redistribution are among the fundamental processes determining habitat availability and quality in riverine ecosystems. Flow regulation and channelization of the Lower Missouri River have greatly reduced the availability of shallow-water habitats thought to be important to both the aquatic and riparian ecosystems. Success of engineering projects intended to increase shallow-water habitat depends on improved understanding of sediment transport dynamics at regional and channel scales. At the regional scale, the quantity of sediment supplied to the lower Missouri River is greatly diminished compared to natural values because of sediment trapping in the mainstem reservoirs. At the same time, river training structures have substantially altered the geometry of the channel and changed its sediment transporting characteristics. Sediment transport data and modeling results indicate that both equilibrium sediment transport and sediment-deficit conditions exist in different parts of the lower river. This regional variation in sediment availability is a substantial constraint on habitat rehabilitation. At the channel scale, local channel geometry and hydraulics affect the distribution of sediment in the water column, and thereby affect sediment dynamics in specific habitats. For example, the nature of the sediment exchanges between the main channel and a chute determines whether a chute fills with sediment, incises to capture the main flow, or is maintained in an equilibrium condition. This partitioning is a function of the geometry of the chute inlet and the position of the chute inlet within the main channel planform. Hydroacoustic maps of sediment flux fields through bends indicate that flow and sediment transport vectors are spatially variable at the scale of the meander bend.