Figure 1
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Figure 1: Both linear and nonlinear interactions in water can lead to the formation of high-intensity waves (so-called freak or rogue waves). Similar nonlinear mechanisms are responsible for the generation of solitons in rivers, such as those traveling upstream on the Severn River during tidal bores, which attract river surfing enthusiasts (see video coverage of the Severn bore at http://www.youtube.com/watch?v=IKA39LQOIck).