Prediction of sand ripple geometry under waves and currents

An experimental investigation of bedforms generated by the combined action of waves and currents is carried out in a wave basin. Tests with different wave conditions are performed on two types of sand beds with 0.15 and 0.5 mm median diameter, respectively. The angles between wave and current directions are 60 degrees and 90 degrees. Data obtained in the present study and by various researchers are analyzed. New empirical formulas are derived for the prediction of ripple length and height under a given combination of waves and currents. pure wave motion is considered as a particular case where current intensity is zero. The proposed formulas are compared with those of Miller and Komar, Nielsen, Mogridge et al., and Tanaka and Shuto for waves alone and those of Tanaka and Shuto and Tanaka and Dang for waves and currents. Improvement of the new predictors is shown for both pure waves and wave-current conditions.