Degree
Doctor of Philosophy (PhD)
Department
Department of Civil and Environmental Engineering
Document Type
Dissertation
Abstract
Bed load is an important physical process that greatly impacts the evolution of riverine systems. Even with this recognition of importance, limited measurements have been collected on large sand bed rivers. These larger waterways are vitally important to the nation in terms of navigational and environmental purposes. This research effort documents a developed means of measuring bed-load transport on these large sand bed rivers with quantifiable uncertainty bounds including a field application on the Mississippi River evaluating the bed-load transport rates in conjunction with other measured parameters.
The first step in this research included expansion of the Integrated, Section Surface Difference Over Time, version 2 (ISSDOTv2) basic equation for bed-load transport to a methodology capable of being applied to high fidelity multi-beam data to obtain accurate and repeatable measurements of bed load. This included validation of the method using flume measurements. The results indicated a higher level of accuracy for higher transport rates and indicated errors of approximately 6% for the higher flow/transport conditions. The method was also able to accurately capture the impacts associated with rapid decreases in flow/transport.
The second step in this research included development of an appropriate means of quantifying the uncertainty in the ISSDOTv2 results. This included identification of the primary sources of uncertainty (particle density, bed porosity, acoustically measured bed topography, the timing of measurements, sand wave identification, and regression analysis used for geometric correction of bed-load measurements) along with an appropriate means of propagating the uncertainty throughout the calculations. The greatest contributor to uncertainty was found to be the bathymetric uncertainty, and, at the highest transport rates, total relative uncertainty was found to be approximately 10%. Cumulative relative uncertainties grew rapidly with decreasing flow rates, driven primarily by the higher relative contribution of bathymetric uncertainty on the smaller bedforms that are typically present at lower transport rates.
The last component of this research included a field application of the ISSDOTv2 method on the Mississippi River. The field effort included measurements at five locations (Vicksburg, MS; Greenville, MS; Memphis, TN; Caruthersville, MO; and Hickman, KY) including measurements of the velocities, bed composition, suspended sediment concentrations, and the bed-load transport rates. The results indicate the discharges/velocities are the primary driver of the bed-load transport rates. Comparisons of similar discharges across trips illustrated the bed composition did impact the bed load but at a much lower level than the discharges/velocities. The increases in the discharges (25-30%) across trips for Vicksburg and Greenville resulted in increases in the bed load (55-85%). Memphis, Caruthersville, and Hickman have similar discharges for all three trips, but the bed load is approximately 15% lower for Trip 1 presumably due to the coarser bed conditions.
Date
12-23-2024
Recommended Citation
McAlpin, Tate Overby, "Measuring Bed-Load Transport Rates with Appropriate Uncertainty Bounds in a Flume and on the Mississippi River" (2024). LSU Doctoral Dissertations. 6655.
https://repository.lsu.edu/gradschool_dissertations/6655
Committee Chair
Willson, Clinton