A rational approach to seepage flow effects on bottom friction beneath random waves

•A simple analytical tool for estimating seepage effects on bottom friction by random waves.•The results are valid for laminar, smooth turbulent and rough turbulent flow.•Example of results corresponding to typical field conditions.•Relevant for making assessment of seepage effects on bottom friction based on available wave statistics.

The bottom friction beneath random waves is predicted taking into account the effect of seepage flow. This is achieved by using wave friction factors for rough turbulent, smooth turbulent and laminar flow valid for regular waves together with a modified Shields parameter which includes the effect of seepage flow. Examples using data typical to field conditions are included to illustrate the approach. The analytical results can be used to make assessment of seepage effects on the bottom friction based on available wave statistics. Generally, it is recommended that a stochastic approach should be used rather than using the rms values in an otherwise deterministic approach.