Wave efficacy is a quantity that indicates the effectiveness of waves to mobilise sediment. It is analogous to kurtosis, the fourth statistical moment, which is a measure of the peakedness of a population.
Wave efficacy is calculated as:
where Hrms is the root mean square wave height over the entire record, Hi is an individual wave height, and i goes over a window of a week or month or quarter.
The figure shows a typical plot of monthly wave efficacy.
In Jul- and Aug-2012, efficacy was high and the potential for transport was high,
but for Sept-2012 to Apr-2013, efficacy was low so the waves were not as effective at mobilising sediment.
However, in Apr-, Jun-, and Aug-2013, efficacy was high, so waves were more effective at mobilising sediment.