Endangered pallid sturgeon (Scaphirhynchus albus) (right) and shovelnose sturgeon (Scaphirhynchus platorynchus) (left) from the Lower Missouri River, captured as part of the USGS Comprehensive Sturgeon Research Program. Early spring sampling for reproductive adult pallid sturgeon on Lower Missouri River. High-resolution multibeam bathymetric map to characterize habitat around tagged sturgeon locations. Microscopic image of sturgeon larval stage. Field researchers capture Scaphirhynchus sturgeon for telemetry studies using baited trotlines.

No abstract

Analysis of in-situ-produced Be concentration in sediment delivered by the fluvial system has not changed appreciably over the last 1200 years despite at least two cycles of arroyo cutting and filling. Other samples (n = = = = = 21) were collected along the drainage network. Rio Puerco erosion rates scale directly with a variety of metrics describing vegetation, precipitation, and rock erodibility. Using the headwater basins for calibration, the erosion rates for both the downstream samples and also the data set as a whole, are best modelled by considering a combination of relief and vegetation metrics, both of which co-vary with precipitation and erodibility as inferred from lithology. On average, contemporary sediment yields, determined by monitoring suspended-sediment discharge, exceed cosmogenically determined millennial-scale erosion rates by nearly a factor of two. This discrepancy, between short-term rates of sediment yield and long-term rates of erosion, suggests that more sediment is currently being exported from the basin than is being produced. Because the failure of incised channel walls and the head cutting of arroyo complexes appear to be the main sources of channel sediment today, this incongruence between rates of sediment supply and sediment yield is likely to be transitory, reflecting the current status of the arroyo cycle and perhaps the influence of current or past land-use patterns.

Figure 1. Location of U-Th/He ages and age-elevation transects from Bighorn Mountains. Structure contours indicate elevation (in meters) of Cambrian unconformity. Youngest ages are interpreted to represent time of Laramide deformation and unroofing (geology after Love and Christianson, 1985).

Construction of side-channel chutes has become a popular means to rehabilitate habitat of the Lower Missouri River. We studied various aspects of hydrology, hydraulics, and geomorphology of four side-channel chutes to document a range of existing conditions in the Lower Missouri River. The Cranberry Bend side-channel chute has existed for at least 40 years and is an example of a persistent, minimally engineered chute. The Lisbon Bottom side-channel chute is a young chute, created by extreme floods during 1993 -1996, and allowed to evolve with minimum engineering of inlet and outlet structures. The Hamburg Bend and North Overton Bottoms side-channel chutes were constructed in 1996 and 2000, respectively, as part of the Missouri River Bank Stabilization and Navigation Fish and Wildlife Mitigation Project.These side-channel chutes provide increased areas of sandbars and shallow, slow water -habitats thought to be substantially diminished in the modern Missouri River. Depths and velocities measured in side-channel chutes are also present in the main channel, but the chutes provide more areas of slow, shallow water and they increase the range of discharges over which shallow, slow water is present. The 3.6 km long Lisbon Bottom chute provides as much as 50% of the entire shallow water habitat that exists in the encompassing 15 km reach of the river. At Cranberry Bend and Lisbon Bottom, the side-channel chutes provided 10 -40% of the available sandbar area in the reach, depending on discharge.Each of the side-channel chutes shows evidence of continuing erosion and deposition. The longevity of the Cranberry Bend chute attests to dynamic stability -that is, a chute that maintains form and processes while shifting in position. The Hamburg chute similarly shows evidence of lateral movement and construction of flood plain to compensate for erosion. The Lisbon Bottom chute -the most intensively studied chute -appears to have achieved an equilibrium width and continues to migrate slowly; however, evidence of aggradation indicates that the chute has not reached an ultimate form, and may be continuing to adjust to altered hydrology and sediment availability. The North Overton Bottoms chute is the newest in the study. In its originally constructed form, the North Overton Bottoms pilot chute was extremely stable, even while being subjected to two floods in excess of 2-year recurrence interval and after accumulating large, potentially destabilizing large woody debris jams. Ongoing adaptive re-engineering of the North Overton Bottoms chute has prevented assessment of how the chute might have adjusted its form in the absence of intervention.