Anomalous wave statistics induced by abrupt topographical variations*

Laboratory experiments reveal that an abrupt depth change can significantly alter the distribution of randomized surface waves. A normally-distributed, unidirectional wave field becomes strongly skewed upon encountering a step in bottom topography. A short distance downstream of the step, the wave-field conforms closely to a gamma distribution. Importantly, the exponential decay of the gamma distribution is much slower than Gaussian, signifying that extreme events occur more frequently. Under the conditions considered here, the probability of a rogue wave can increase by a factor of 50 or more.