Soil and Landforms

Discussion forum
Chair: Prof. Patrick Lynett, University of Southern California <plynettATusc.edu>

Purpose of this working group
In regions where it is known from geologic evidence that tsunamis have occurred, yet none have been witnessed in modern history, the ability of engineers and scientists to plan for and mitigate the possible tsunami hazard is severely degraded. However, field surveys of tsunamis in the past decades have shown that as a tsunami inundates and floods the land, it leaves behind a calling card in the form of widespread sediment deposits. If the skill to look back into geologic history to estimate tsunami intensity and extreme event recurrence from deposits existed, the implications for efficient hazard planning are tremendous.

There are a number of research gaps that must be addressed before this skill is attained, as detailed by the NSF-Sponsored Tsunami Deposits Workshop in June, 2005 at the University of Washington. First, it must be determined what hydrodynamic information can be extracted from modern deposits created by observed and well constrained tsunamis. Next, it must be understood how a deposit might transform after being buried for centuries or millennia. With these two pieces of information, the widespread study of paleo-deposits would provide an abundance of invaluable information on paleo-tsunamis. The significance of this work will reveal itself when it is possible for tsunami researchers to take a record of deposits, and state with some confidence the intensity of previous, unobserved tsunamis.

Benchmarking Hydrodynamic Numerical Models

Discussion forum
Chair: Prof. Harry Yeh, Oregon State University <harryATengr.orst.edu>

Purpose of this working group
A series of three workshops addressed how to advance numerical models for long-water-wave problems (in 1990 at the Wrigley Marine Science Center of the University of Southern California on Catalina Island; in 1995 at Friday Harbor, San Juan Island, WA; and in 2004, again at the Wrigley Marine Science Center). The primary objective of the workshops was to discuss how numerical models could be validated through the use of benchmark problems. The benchmark problem exercises used for the workshops proved extremely useful in identifying absolute and comparative modeling capabilities. Significant improvements have been made, due to advances in both numerical algorithms and computational capabilities, especially for those models based on depth-averaged hydrodynamics theories by solving shallow-water-wave equations, KdV equation, KP equation, Boussinesq equations, and “extended” Boussinesq equations. At the same time, model improvements have given rise to new and important problems. In particular, although there is no question that actual long-wave inundation motions are turbulent – nor that runup flow patterns, impacts, scouring effects, and sediment transport are all affected by turbulence – the quantification of its effects remains an open question. This working group specifically focuses on that problem.

Benchmark problems will be identified so that predictive models can be evaluated, compared qualitatively and quantitatively, and discussed. The basic strategy will be to provide participants with initial and geometric data for the problems, so that predictions at specific locations can be prepared in a specified format. Corresponding laboratory measurements will be presented in the same format during a virtual workshop, allowing the comparison of predictions with measurements in a blind-test format. Targeted numerical models are those based on Reynolds Averaged Navier-Stokes (RANS) equations, k-Ɛ type turbulence equations, large-eddy simulations, Marker-and-Cell (MAC) method, and Smooth-Particle-Hydrodynamics (SPH) method.