Navigating Sand and Waves
On the evolution of sand ripples under combined wave and current conditions
Anneliese Schmidt (TU Delft - Civil Engineering & Geosciences)
Matthieu de Schipper – Mentor (TU Delft - Civil Engineering & Geosciences)
Julia Hopkins – Mentor (TU Delft - Civil Engineering & Geosciences)
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Abstract
Sand ripples are small (10 cm height) bed forms which occur in the nearshore and surf zone under the impact of both waves and currents. They impact the roughness of the bed used in models of this zone, and contribute to sediment transport. Predictions of their geometry are important to properly model roughness, so correlations between the waves and ripples need to be established. In this project, data about the instantaneous bed level and wave conditions at two point locations in the surf zone was used to analyze the relationship between wave conditions and ripples on the bed. Values for significant wave height, peak period, skewness, ripple height and ripple period were found over bins of 15 minutes in length. It was found that there are relationships between ripple height and wave height, wave skewness and ripple height. These correlations are strongest for a zero shift in the signals, meaning the ripple height can adjust to the wave height and/or skewness within 15 minutes. These results can be used with further research, which includes local current measurements, to make more accurate estimates of the ripple height.