Harry Yeh

Tsunami run-up and draw-down on a plane beach

Tsunami run-up and draw-down motions on a uniformly sloping beach are evaluated based on fully nonlinear shallow-water wave theory. The nonlinear equations of mass conservation and linear momentum are first transformed to a single linear hyperbolic equation. To solve the problem with arbitrary initial conditions, we apply the Fourier–Bessel transform, and inversion of the transform leads to the Green function representation. The solutions in the physical time and space domains are then obtained by numerical integration. With this semi-analytic solution technique, several examples of tsunami run-up and draw-down motions are presented. In particular, detailed shoreline motion, velocity field, and inundation depth on the shore are closely examined. It was found that the maximum flow velocity occurs at the moving shoreline and the maximum momentum flux occurs in the vicinity of the extreme draw-down location. The direction of both the maximum flow velocity and the maximum momentum flux depend on the initial waveform: it is in the inshore direction when the initial waveform is predominantly depression and in the offshore direction when the initial waves have a dominant elevation characteristic.

Defining and quantifying microscale wave breaking with infrared imagery

Breaking without air entrainment of very short wind-forced waves, or microscale wave breaking, is undoubtedly widespread over the oceans and may prove to be a significant mechanism for enhancing the transfer of heat and gas across the air-sea interface. However, quantifying the effects of microscale wave breaking has been difficult because the phenomenon lacks the visible manifestation of whitecapping. In this brief report we present limited but promising laboratory measurements which show that microscale wave breaking associated with evolving wind waves disturbs the thermal boundary layer at the air-water interface, producing signatures that can be detected with infrared imagery. Simultaneous video and infrared observations show that the infrared signature itself may serve as a practical means of defining and characterizing the microscale breaking process. The infrared imagery is used to quantify microscale breaking waves in terms of the frequency of occurrence and the areal coverage, which is substantial under the moderate wind speed conditions investigated. The results imply that ”bursting“ phenomena observed beneath laboratory wind waves are likely produced by microscale breaking waves but that not all microscale breaking waves produce bursts. Oceanic measurements show the ability to quantify microscale wave breaking in the field. Our results demonstrate that infrared techniques can provide the information necessary to quantify the breaking process for inclusion in models of air-sea heat and gas fluxes, as well as unprecedented details on the origin and evolution of microscale wave breaking.

The Flores Island tsunamis

On December 12, 1992, at 5:30 A.M. GMT, an earthquake of magnitude Ms 7.5 struck the eastern region of Flores Island, Indonesia (Figure 1), a volcanic island located just at the transition between the Sunda and Banda Island arc systems. The local newspaper reported that 25-m high tsunamis struck the town of Maumere, causing substantial casualties and property damage. On December 16, television reports broadcast in Japan via satellite reported that 1000 people had been killed in Maumere and twothirds of the population of Babi Island had been swept away by the tsunamis. The current toll of the Flores earthquake is 2080 deaths and 2144 injuries, approximately 50% of which are attributed to the tsunamis. A tsunami survey plan was initiated within 3 days of the earthquake, and a cooperative international survey team was formed with four scientists from Indonesia, nine from Japan, three from the United States, one from the United Kingdom, and one from Korea.

Tsunami scour around a cylinder

A series of scale-model experiments investigated the scouring mechanisms associated with a tsunami impinging on a coastal cylindrical structure. Since scaling effects are significant in sediment transport, a large-scale sediment tank was used. Video images from inside the cylinder elucidated the vortex structures and the time development of scour around the cylinder. The scour development and mechanisms differed according to the sediment substrate – sand or gravel. For gravel, the most rapid scour coincided with the greatest flow velocities. On the other hand, for the sand substrate, the most rapid scour occurred at the end of drawdown – after flow velocities had subsided and shear stresses were presumed to have decreased. This behaviour can be explained in terms of pore pressure gradients. As the water level and velocity subside, the pressure on the sediment bed decreases, creating a vertical pressure gradient within the sand and decreasing the effective stress within the sand. Gravel is too porous to sustain this pressure gradient. During drawdown, the surface pressure decreases approximately linearly from a sustained peak at

Advanced numerical models for simulating tsunami waves and runup

\uDelta P

Sandy signs of a tsunami's onshore depth and speed

to zero over time

Skin layer recovery of free-surface wakes: Relationship to surface renewal and dependence on heat flux and background turbulence

\uDelta T

On turbulence in bores

. The critical fraction

The 11 March 2011 East Japan Earthquake and Tsunami: Tsunami Effects on Coastal Infrastructure and Buildings

\Lambda

Generation and evolution of edge-wave packets

of the buoyant weight of sediment supported by the pore pressure gradient can be estimated as \[ \Lambda = \frac{2}{\sqrt \pi} \frac{\uDelta P}{\gamma_b \sqrt {c_v \uDelta T}}, \] in which