Ripple characteristics in the intertidal zone

Abstract

The first 3D sonar field measurements of ripples in the intertidal area are presented. The measurements were conducted during a 6 week field campaign in Autumn 2014 at the Sand Motor near Den Hague, The Netherlands. Ripple profile, hydrodynamic and suspension data were collected along a cross-shore transect. By means of a 2D Fourier analysis the 3D sonar images of the bedforms were analysed. Key parameters such as ripple height, length and angle were obtained. These parameters correlate to one another as well as to hydrodynamic data. During the measurement period the wave conditions were mostly calm and most waves arrived shore normal. A correlation between relative wave height and ripple length is found. The estimated ripple index, of 17.1, corresponds well to values found in literature. The FFT-routines are a powerful tool for analysing the enormous amount of sonar data, 1100 3D-images, automatically. A rotational diagram method was used to analyse 3D sonar images. A ripple regularity index (RRI) is proposed, as an objective and quantitative way to classify a ripple pattern as ‘regular’ or ‘irregular’.