Articles | Volume 12, issue 6
Research article
22 Nov 2016
Research article |  | 22 Nov 2016

Predicted ripple dimensions in relation to the precision of in situ measurements in the southern North Sea

Knut Krämer and Christian Winter

Abstract. Ripples are common morphological features in sandy marine environments. Their shapes and dimensions are closely related to local sediment properties and forcing by waves and currents. Numerous predictors for the geometry and hydraulic roughness of ripples exist but, due to their empirical nature, they may fail to properly reflect conditions in the field. Here, measurements of tide and wave generated ripples in a shallow shelf sea are reported. Discrete and continuous methods for the extraction of ripple dimensions from digital elevation models (DEMs) are inter-compared. The range of measured ripple dimensions is quantified and compared to the results of empirical predictors.

The repeatability of a measurement for inactive conditions is taken as the precision of measurements of bedform dimensions. The accuracy of measurement is assessed via comparison to predicted dimensions. Results from field data show that the precision of measurements is limited to 10 % of the absolute ripple dimensions. The application of different methods for the detection of ripple heights may result in form roughness heights differing by a factor of up to 2 between the traditional statistical estimate and a full evaluation of the spatial bathymetry.

Short summary
Ripples are small regular sand waves found on beaches or the floor of rivers and coastal seas. Their shapes and dimensions are controlled by properties of the sand and the strength of waves and currents. The form of ripples can be predicted by mathematical formulas which were often developed from laboratory experiments. In this work, we present methods for measurement of ripple heights and lengths from the North Sea and compare the results to calculated dimensions.