Evaluation of the Structure of Levee Transitions on Wave Run-Up and Overtopping by Physical Modeling

Coastal regions are continually plagued by high water levels induced by river flooding or hurricane-induced storm surge. As with any protective structure, it is essential to understand potential problematic locations that could result in structural failure and devastating loss. Common coastal protective systems are composed of floodwalls and levees, for each of which practiced methodologies have been used to estimate their performance under design conditions. Methodologies concerning spatial variability are limited, however, and transitions where earthen levees merge with floodwalls are considered areas vulnerable to erosion and possible breaching. Physical modeling of a levee transition is undertaken in a three-dimensional wave basin to evaluate this hypothesis, and the detailed results of this assessment are presented in this paper. From the physical model testing, analysis of the data reveals that overtopping rates tend to be larger immediately near the transition than away from it. The run-up values and floodwall wave heights tend to show potential problematic areas and mimic the variation of overtopping along the levee transition. Under the design conditions tested, extreme overtopping conditions and associated water level values indicate that for the structure to sustain the hydraulic conditions, it must be well armored. It is shown that the variation of the still water level plays the largest role in the magnitude of the measured values, and increasing the peak wave period and wave heights also yields greater overtopping and water levels at the structure. This study highlights the need to understand specific spatial variability along coastal protective systems, and provides a better understanding of the mechanisms affecting overtopping for the specific structure tested.