Pneumatic long-wave generation of tsunami-length waveforms and their runup

• Published in: Coastal engineering (Amsterdam) 2018-08, Vol.138, p.80-97
• Main Authors: McGovern, D.J., Robinson, T., Chandler, I.D., Allsop, W., Rossetto, T.
• Format: Article
• Language: English
• Subjects: Experiments; Long wave; Pneumatic generation; Runup; Tsunami
• ISSN: 0378-3839; 1872-7379
• DOI: 10.1016/j.coastaleng.2018.04.006

An experimental study is conducted using a pneumatic long-wave generator (also known as a Tsunami Generator). Scaled tsunami waveforms are produced with periods in the range of 5–230 s and wave amplitudes between 0.03 and 0.14 m in water depths of 0.7–1.0 m. Using Froude similitude in scaling, at scale 1:50, these laboratory waves are theoretically dynamically equivalent to prototype tsunami waveforms with periods between 1 and 27 min and positive wave amplitude between 1.5 and 7.0 m in water depths of 50 m. The purpose of these tests is to demonstrate that the pneumatic method can generate long waves in relatively short flumes and to investigate their runup. Standard wave parameters, (free-surface, wave celerity and velocity profiles) are used to characterise the waveforms. It is shown that for the purpose of runup and onshore ingression, minimal interference from the re-reflected waves is observed. By generating tsunami waveforms with periods greater than ≈ 80 s (≈9.5 mins prototype scale) the available experimental data set is expanded and used to develop a new runup equation. Contrary to the shorter waves, shoaling of these longer waves is insignificant. For waveforms with periods greater ≈ 100 s the runup is best described by wave steepness not potential energy. When tested against available runup equations the results are mixed; most perform poorly for scaled tsunami length periods. A segmented regression analysis is performed on the data set and an empirical runup relationship is provided based on a new parameter termed the ‘Relative Slope Length’. The tests show the definition of offshore wave amplitude is non-trivial and may greatly affect the predicted relative runup of a given wave. It is noted that this appears to be a general issue for all types of tsunami simulation in the laboratory. Together these observations and proposed runup model provide a framework for future numerical studies of the topic. •Pneumatic simulation of Froude-scaled tsunami-length waves is investigated.•Analysis of wave propagation, reflections and flow velocity demonstrate the method is suitable for studying tsunami runup.•Available runup predictions perform poorly against the current data.•New empirical predictions are found based on a new parameter ‘relative slope length’.•The definition of amplitude at a particular offshore depth is non-trivial and discussed.