Masters Theses

Date of Award

12-2008

Degree Type

Thesis

Degree Name

Master of Science

Major

Civil Engineering

Major Professor

John S. Schwartz

Committee Members

Eric C. Drumm, Daniel C. Yoder

Abstract

Among river engineers there is growing recognition that the success of a stream restoration project is dependent on the accurate prediction of sediment transport along a reach. To aid the design process, several numerical one- and multi-dimensional models have been developed to quantify in-stream sediment transport and hydraulic characteristics, and multiple sampling techniques have been proposed to establish the upstream sediment supply. However, the governing physical boundaries and variables (i.e., Manning’s ‘n’ variable, energy slope, and upstream sediment supply) required to initiate a sediment transport simulation are time consuming and difficult to measure in the field, and the estimation of these variables based on best professional judgment can lead to inaccurate predictions of sediment transport, resulting in the design of unstable projects. Thus, there exists a demand to understand the model sensitivity to key input parameters (i.e., Manning’s n value and sediment rating curves), and their effects on sediment transport simulations, especially when input parameters must be estimated and results can not be verified easily.

The goal of this study was to evaluate the performance of CCHE2D, a twodimensional sediment transport model, in a Cumberland Plateau mountainous stream reach with complex morphology and coarse substrate. The model was utilized to simulate sediment transport through a single hydrograph. Bed elevation change along a reach (100-m scale), was evaluated by comparing the deviation between simulated and measured elevations at multiple monitoring points before and after the simulated flood event. The study objective included testing the sensitivity of overall bed change at a reach, local, and point scales to two key model inputs parameters, the Manning’s n value and sediment supply.

Despite the relative stability observed along the site, simulated results show the model overestimated aggradation at a reach, local, and point scales. Statistical analysis of simulated results showed that bed elevation change was most sensitive to the bedload rating curve and Manning’s n value input parameters. Importantly, the site-specific bedload rating curve and measured roughness coefficient have the potential to reduce the error between simulated and measured results if accurate simulations of sediment transport can be achieved by a computational model.

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