The inherent variability of wave-formed ripples

Traditional methods to parameterise wave-formed rippled sediment beds involve the determination of a characteristic ripple height and length from the rippled surface. A substantial number of previous studies have indicated ripple fields formed in shallow water under real sea conditions will have considerable spatial and temporal variation in their parameters. There has been little work undertaken on quantifying the spatial variation of rippled beds in terms of their characteristic ripple height and length. This paper will present a method used to calculate a histogram of the ripple heights and lengths from the rippled surface using the zero up-crossing method. The inherent variability of ripple parameters will be discussed in terms of two sets of laboratory measurements taken at two very different scales. The conclusion of the paper is that traditional methods to predict ripple parameters have a bias towards rippled beds formed under medium mobility conditions. At higher and lower mobility conditions rippled beds will be inherently variable with a distribution of ripple parameters existing on a given bed at any given time