Energy pollution: the relative influence of wind-wave and vessel-wake energy in Tallinn Bay, the Baltic Sea

Abstract

The role of frequent vessel wakes on the wave energy budget of 5cmi-sheltered beaches has been re-evaluated for the almost tideless Tallinn Bay, the Baltic Sea. High-resolution water surface time series containing signals of >650 ship wakes collected over 30 days at a depth of ~2.7 m shows that (i) the daily maximum heights of vessel wakes have increased considerably since the beginning of the decade while (ii) the leading wave periods (W-13 s) and integral properties of vessel wakes such as the total wave energy and its flux have remained largely unchanged. The typical daily largest ship waves (1.2-1.4 m) are equivalent to the annual highest 0.8-1.8% of wind waves and the highest ship waves (l.7 m) to the highest 0.25% of wind waves. Unlike the Baltic Proper, the overall wind wave intensity has varied insignificantly over the last three decades in Tallinn Bay where vessel wakes contribute about 10% in terms of wave energy and 25% in terms of energy flux. Substantial seasonal variation of wave intensity with markedly low wind waves in the biologically most active season suggests that vessel wakes may play a decisive role during some seasons even in areas with overall high wind wave activity.