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This dissertation examines the dynamics of sediment transport and channel morphology in the lower Mississippi River. The area of research includes the portion of the river where reach-averaged downstream flow velocity responds to the boundary condition imposed by the relatively uniform water-surface elevation of the receiving basin. Observational studies provided data that are used to identify channel-bed sediment composition, and measure bed-material sediment flux and the properties of the fluid-flow field over a variety of water-discharge conditions. The analyses demonstrate that a significant portion of the channel bed of the final 165 kilometers of the Mississippi River consists of exposed and eroding underlying relict sedimentary strata that qualify as surrogate bedrock. The exposed bedrock is confined to the channel thalweg, particularly in river-bend segments, and actively mobile bed-material sediments are positioned on subaqueous bars fixed by river planform. The analyses for sediment flux provides insight to the nature of sediment transport: during low- and moderate-water discharge, bed-material movement occurs primarily as minimal bedform flux, and so bed materials are not transferred between alluvial bars. During high-water discharge, bed-material transport increases one-hundred fold, and sands move as a part of both suspended and bedform transport. Physical models are used to show that skin-friction shear stress increases by a factor of ten for the measured water-discharge range. This change is not possible given conditions of uniform water flow, and therefore non-uniform flow in response to the Mississippi River approaching its outlet has a significant impact on the timing and magnitude of sediment flux through the lower river. In order to estimate the dynamics of bed material movement from the uniform to non-uniform segment of the river (lower 800 km), data for channel morphology are used to construct a model that predicts spatial changes in water-flow velocity and bed-material flux over a range of water-discharge conditions. The model demonstrates that non-uniform flow tends to produce a region of net channel-bed aggradation between 200-700 kilometers above the outlet, and a region of channel-bed degradation for the final 200. The implication for these results for the spatial variability of channel morphology and kinematics is explored. / text

The evolution of landscapes and seascapes in time is the result of the constant interaction between flows and topography. Flows change topography, which in turn change the flow. This feedback causes evolution processes to be highly non-linear and complex. When full analytical derivations of the co-evolution of topography and flow are not possible without oversimplifications, as is the case in river bends, recent large topographical datasets and modern computers allow for correlations between horizontal (planview) and cross-sectional geometry of channels. Numerical analysis in the Mississippi and Trinity rivers indicate that the type of correlation between river radius of curvature and bankfull channel width depends on the migration behavior of the river. In other cases, channel topography may only have a second-order effect on its own evolution, as is the case for fully depositional turbidity currents, and the evolution of aeolian field topography may only be a function of this topography. I show that in these situations, changes in topography may be decoupled from details of the flow field and modeled very easily with a good accuracy. / text

Thesis--University of Minnesota, 1926. / Bibliography ; numb. 1, 106-124.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1961. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 288-296).

Thesis--University of Minnesota, 1926. / Bibliography ; numb. 1, 106-124.

Rehabilitation of sturgeon populations requires an understanding of sturgeon autecology during all life stages, especially during early life when high mortality occurs. To begin to understand sturgeon early-life history I determined river of origin on a multi-basin scale (i.e., potential rivers of origin). I then determined habitat needs and early life demographics on a more localized scale (i.e., specific river). Trace elements differ between river reaches of the central US and may be used to determine origin of age-0 sturgeon. My trace element analyses suggested that age-0 sturgeon captured in the Middle Mississippi River, which extends from the confluence of the Missouri River downstream to the confluence of the Ohio River, drifted from as far upstream as the Gavins Point Dam on the Missouri River (> 1200 km), while other individuals originated locally in the Middle Mississippi River. On a more refined scale of habitats, I used trawling to identify habitat features used. Age-0 Scaphirhynchus sturgeon catch rates were highest around artificial structures (i.e., wing dikes) and island areas while main channel habitat comprised the lowest catch rates. Within these habitats, young sturgeon frequently occupied low velocities (i.e., ~0.1), moderate depths (i.e., 2 to 5 m), and sand substrate. Although determination of river of origin and specific habitats used are imperative for restoration, sturgeon populations are likely regulated by factors within habitats that affect early-life dynamics. Mean sturgeon growth rates ranged from 1.42-1.50 mm/d over the four years but did not differ among years. Individuals hatched over a 25 to 50-d period and peak hatch dates were between 10- 20 May during all years. Hatching coincided with optimum spawning temperatures of 17-20oC and a rise in river stage. Abundance was positively related to river stage, with longer durations of high water related increasing abundance. Mortality of age-0 sturgeon increased with the number of days where water temperature exceeded 28 oC. In the end this study has set benchmarks for understanding factors affecting the early-life ecology of Scaphirhynchus sturgeon.

By combining FEMA's HAZUS-MH (Hazards U.S. Multi-Hazard) flood-loss estimation software and the HEC-RAS hydraulic modeling package, this study was able to quantify potential beneficial and adverse impacts of flood-control and navigational structures along the Middle Mississippi River (MMR; between Mississippi-Missouri River confluence and Thebes, IL). The goal of this investigation was to assess changes in water-surface elevations and associated flood losses to: 1) quantify the potential exposure of flooding under different flood-control configurations along the Middle Mississippi River (MMR), and 2) assess the relative contributions of various engineered structures and flood-loss strategies to potential flood losses. Assessment of the impact of engineering structures was accomplished by modeling five scenarios for the 100- and 500- year floods: 1) current MMR levee configuration (levee protecting for ≤50-year flood); 2) removal of all flood-control structures on the MMR; 3) increasing the height of levees and floodwalls in metropolitan St. Louis to protect urban areas to the 500-year flood level while simultaneously removing all agricultural levees downstream; 4A) a less engineered MMR channel and floodplain with fewer flood control and navigation structures, simulating conditions from 65 years ago (1942-1947) with 1940's levees; and 4B) a less engineered MMR channel and floodplain with fewer flood control and navigation structures, simulating conditions from 65 years ago (1942-1947) with current levee configuration. Comparison of scenarios 2 and 3 relative to scenario 1 allows for quantitative assessment of the flood-control structures on stages and flood losses. Results from scenario 2 revealed that removing all levees along the MMR reduces the average stages from 2.2 m (100-year) to 2.5 m (500-year, but also increased economic and social impacts relative to scenario 1. Scenario 3 revealed that removing agricultural levees downstream of St. Louis on the MMR decreased stages by 1.4 m (100- and 500-year); however, flood losses for the 100-year flood were increased. Flood losses for the 500-year flood were decreased relative to scenario 1. These results suggest that agricultural levees along the MMR protect against medium size floods (50- or 100-year flood) but cause more damage than they prevent during large floods such as the 500-year flood. Comparison of scenarios 4A and 4B relative to scenario 1 allows for a quantitative assessment of river engineering structures and modern buildings constructed over the last 65 years. In scenarios 4A and 4B, a less engineered river decreased stages by 1.2 m (for the 100-year flood) relative to scenario 1. In scenario 4A, the 1940's levees expose modern buildings in the floodplain to flooding, causing economic building losses to increase; however, in scenario 4B, current levee configuration protects modern buildings in the floodplain from flooding causing, economic building losses to decrease. If the current flood-control structures were not built, it is likely that the land in the floodplain for scenarios 4A and 4B would not be developed and the land used would be more flood-tolerant. Sensitivity analyses were run to assess the impact of using the default HAZUS-MH national-level data; this was done by comparing results produced by using aggregate analysis (coarse data) versus results using UDF analysis (detailed data). The aggregate analysis estimated 51% fewer buildings damaged than the UDF analysis. Conversely, the aggregate analysis increased the economic building losses by 51% relative to the UDF analysis. Although collecting local data for a study is not always feasible, the large differences documented here need to be considered when discussing HAZUS-MH results. Overall, this project shows implications for historic and future flood-control and navigational structure projects on the MMR and other rivers. It also emphasizes the importance of studying the impact future engineering structures will have on water-surface elevations and flood losses before implementing them.

The construction of levees along the Mississippi River [MR], beginning in the mid-to-late nineteenth century, have isolated the river along many segments from its floodplain. Sediment from the river is currently deposited in the hydrologically connected floodplain [HCF], the area between the channel margin at low water and the levees. Researchers have studied the amount and rates of sediment deposition along the Upper and Lower Mississippi River segments from the headwaters to Pool 22 and from the Ohio River to the delta; however, no such assessments have been undertaken along the Middle Mississippi River [MMR]. This study attempts to fill the knowledge gap by assessing sedimentation along three islands within the Middle Mississippi River National Wildlife Refuge. On these islands two approaches were undertaken to assess sedimentation along the MMR’s HCF: dendrogeomorphology and the DEM of Difference [DoD] approach. The dendrogeomorphic approach uses tree-ring analyses to document and interpret geomorphic processes and the rates at which they are occurring. The DoD approach subtracts an older DEM from a newer DEM in order to see the change in elevation/depth over time. The geomorphology of the islands and then the entire MMR HCF (from the confluence of the Missouri River to Thebes, IL) were mapped. Using the sedimentation rates for the geomorphic landforms from the three study islands, the sedimentation rates and volumes for the aforementioned portion of the MMR’s HCF were estimated. The estimated volume of sediment was then compared to the MMR’s suspended sediment flux to determine how much of the suspended sediment was going into storage within the MMR’s HCF. The dendrogeomorphic and DoD methods for the study islands yielded average sedimentation rates of 13.3-16.9 mm year-1 and 21.5-80.1 mm year-1, respectively. The rates for the individual landforms on the islands using the dendrogeomorphic results ranged from 5.2 mm year-1 for the splay to 21.8 mm year-1 for the natural levee and splay, with a weighted average of 16.6 mm year-1 for the MMR HCF. Using these rates and the likely range of densities for the floodplain sediments, it is estimated that 4.9-6.6 million metric tons of sediment is accumulating within the MMR annually. This is approximately 5.4-7.4% of the average annual suspended sediment load of the Mississippi River at St. Louis. This means that the MMR is a major sediment sink. If these relatively rapid rates of deposition continue, they have the potential to substantially reduce the HCF’s ability to convey and store flood water which will result in increased flood levels and, consequently, flood risk within the MMR’s levee protected floodplain in the coming decades.