Bed load transport under irregular waves plus current from Monte Carlo simulations of parameterized models with application to ripple migration rates observed in the field

Abstract

The bed load transport rate under random waves plus current has been predicted for a large range of wave–current conditions. A parameterized model valid for regular waves plus current has been used in Monte Carlo simulations, assuming the wave amplitudes to be Rayleigh distributed. The mean value, standard deviation and numerical estimates of the probability density function of the bed load transport rate are presented for a wide range of wave–current conditions. It appears that overall the effect of the current is dominating the bed load transport rate. Moreover, a significant scatter of the bed load transport rate under random waves plus current is found. Such a scatter is also found in field measurements by Amos et al. [J. Coast. Res. 15 (1999) 1]. Predicted ripple migration rates in the bed load regime have been compared with those obtained from field measurements by Amos et al. [J. Coast. Res. 15 (1999) 1], taking the bed load transport rate to be proportional to the ripple migration rate times the ripple height. Overall, the predictions capture the qualitative as well as the quantitative behaviour of the ripple migration rates in a wide range of wave–current conditions; the ripple migration rates, and thereby the bed load, are predicted within the correct order of magnitude for a wide range of wave–current conditions.