The objective of the proposed research is to investigate the problem of enhanced sediment mobility due to buildup of excess pore pressure as a result of transient wave loads. This problem is fundamental to the understanding of sediment transport and scour during storm surge and tsunami. Currently, most sediment transport models relate the sediment flux with Shield's parameter, which is the ratio of horizontal force to vertical force in a quasi-steady flow over a flat bed. However, there is an upward (downward) seepage at the trough (crest), which can significantly alter the net vertical force acting on the soil particle. In addition, the local bed slope also affects sediment mobility. Thus, in the proposed work, the fundamental dependence of sediment transport rate on the pore pressure gradient, particle density and grain size, bed slope, and bed shear stress will be systematically examined via numerical and experimental simulations. A numerical model which fully couples the fluid, soil, and sediment transport models will be developed to predict storm surge or tsunami-induced sediment transport and scour. Laboratory studies will be conducted at the small flume in the hydraulics lab at the University of Hawaii to determine the empirical relationship for the sediment erosion rate. The flume has transparent sidewalls and transparent bottom which are suitable for detailed flow visualization and measurement of sediment transport dynamics, and is equipped with a pump that can generate horizontal flow at different flow rates. With the small flume, different flow conditions and topographical configurations can be configured easily and quickly. It should be emphasized that this experiment is not suited, and not necessary, for large wave tanks (such as the ones in OSU); the small flume at UH is perfect for this set of experiment to do systematic, controlled studies.
The proposed research is fundamental to improving the understanding of enhanced sediment transport due to transient wave loads, which is critical to the prediction of storm surge and tsunami-induced sediment transport and scour. The proposed research is also expected to improve future design and retrofit guidelines, urban planning recommendations, and most importantly, disaster mitigation strategies. To broaden the impact, the investigators will incorporate into the research education and outreach activities, including educating the community about the dangers and disaster planning strategies for storm surge and tsunami.
