Tsunamis are waves generated by earthquakes, underwater landslides, volcanic eruptions or major debris slides. Tsunami waves are not particularly big as they travel across the open ocean, but when they reach shallow water nearshore, and at the coastline, they shoal up dramatically. Numerical models can be used to simulate tsunami waves from generation and nearshore transformation. There is a gap in knowledge, however, on the way the tsunami wave propogates in the nearshore region, across the shoreline, and then runs inland.
These flow processes cannot be simplified, and are made more complex by interactions with beaches, sediment, coastal defences and buildings. We can simulate these processes in physical models, but correct generation of the tsunami wave is essential, including the characteristic preceding draw-down wave. Conventional wave generators simply do not have the piston stroke to reproduce the required wavelength, and we therefore designed the tsunami simulator to provide this capability. In many tsunami physical and numerical modelling studies, researchers have fallen back on the simplification of a solitary wave to model a tsunami, but there are major flaws with this simplification.
HR Wallingford's first generation tsunami simulator is unique, and is the only device that has been shown to reproduce realistic time series for tsunami, particularly those that are trough-led. The Mercator time series, from the Indian Ocean tsunami in 2004, has been successfully modelled with the simulator at a scale of 1:50.
The design of our tsunami simulator is based on our pneumatic tide generators, developed to simulate tides in large area hydraulic models. A sealed tank sits at one end of a long flume, with a submerged opening facing shorewards. A vacuum pump extracts air from the tank, drawing water from the test flume. An air control valve releases air back into the tank, generating a wave as the water flows back into the flume. Control of the position of the air valve in the top of the tank gives the desired wave shape. This form of wave generation is ideally suited to simulating tsunami as it allows the controlled movement of large volumes of water in a confined space without expensive high discharge water pumps.
As part of the EPICentre research project, the tsunami simulator was used to simulate earthquake-generated tsunami in the coastal zone and to provide initial estimates of loadings on buildings behind the shoreline. Results from these experiments have allowed researchers to better quantify tsunami run-up and loading regimes on typical buildings, providing essential research input for the future up-grading of structures in areas at risk from tsunami. This work will be expanded as HR Wallingford works with UCL to develop the tsunami simulator in our Fast Flow Facility.