Observations of Lateral Shear in the Nearshore Zone of a Great Lake

Abstract

Observations of currents across a nearshore zone from 2 to 6 km offshore indicate that unsteady longshore flow and complete reversals in flow are usually accompanied by large values of lateral shear. These values often approach and may exceed 10?4 sec?1, near the value of the Coriolis parameter at mid-latitude. At times when lateral shear is high, other turbulent properties such as variance at a point are also high. The variations of lateral shear are highly temporal and can be qualitatively related to the cycles of cyclone-anti-cyclone activity in the area. High shear values usually do not coincide with high winds, but are usually related to the inability of the nearshore currents to adjust to a slowly varying wind regime. Simple momentum arguments suggest that the time for adjustment decreases as water depth nearshore decreases.