Date of Award
Summer 2005
Document Type
Thesis - Restricted
Degree Name
Master of Science (MS)
Department
Civil and Environmental Engineering
First Advisor
Melching, Charles S.
Second Advisor
Crandall, Clifford J.
Third Advisor
Switzenbaum, Michael S.
Abstract
Many communities are attempting to restore urban streams to more natural conditions and to stabilize unstable streams using ecologically friendly methods. However, considerable uncertainty exists in the application of stream restoration design procedures, particularly with respect to stream stability. Uncertainty analysis is a tool to evaluate the impact of uncertain variables on design safety. Uncertainty analysis is applied to one stream restoration design to illustrate its usefulness to improve the design. A review of the hydraulic and geomorphic literature outlines general restoration design concepts and provides context for analyzing stream restoration design. Published uncertainty analyses as applied to stream restoration and hydraulic engineering applications are reviewed. A design procedure used by the Maryland State Highway Administration (MSHA) was selected as an example. This procedure checks the safety of instream structures used to stabilize the stream. It also evaluates the effectiveness of the channel in moving its sediment load through the channel. This procedure consists of two steps. First, the maximum shear stress in the designed channel is computed for the 100-year flow and compared with the critical shear required to move the boulders that compose the instream structures. Second, the average shear stress in the designed channel is computed for the bankfull flow and compared with the critical shear required to move the d85 particle. If the average shear is greater than the critical shear, the channel is considered capable of transporting its sediment load downstream. The uncertainties (in the form of coefficients of variation) in the design procedure are analyzed numerically or assigned based on published uncertainty values. These coefficients of variation are combined to create six simulation scenarios for analysis. It was found that the instream structures had a 34.2, 32.5, and 28.5 percent chance of moving for the 100-, 50-, and 25-year flow, respectively. Failing to consider the uncertainty in design parameters, as is common in most design procedures, could result in a 20 to 40 percent underestimation of the true failure probability. The bankfull flow coefficient of variation was calculated to be 0.253; and the probability that the d85 particle would be transported downstream was 36.7 percent. Uncertainty analysis gives engineers and decision makers a better understanding of the safety of a design.
Recommended Citation
Byrd, Jennifer, "Application of Uncertainty Analysis to Urban Stream Restoration Design" (2005). Master's Theses (1922-2009) Access restricted to Marquette Campus. 4018.
https://epublications.marquette.edu/theses/4018