Tidal current amphidromic system in semi-enclosed basins

Abstract

In this paper the behaviour of tidal currents in semi-enclosed basins is examined by treating the Taylor problem and by numerical modeling of the M 2 tide in the North Sea. This study shows that in a large semi-enclosed basin current and nodal (amphidromic) points for a tidal constituent will normally be found. These current amphidromic points (CAPS) can be divided into two groups according to their structure, namely middle CAP and end CAP; the former exists in pairs while the latter exists singularly. The amphidromic systems for current and sea surface elevation are closely connected. Between two elevation amphidromic points (EAPs) there exists one pair of middle CAPS with opposite rotation directions. In real ocean basins, this amphidromic pair is usually separated by a certain distance. The main end CAP appears at the bay head while some end CAPS may occur in small bays of a large basin. Normally, anticlockwise rotation appears at the end CAPS in the northern hemisphere. At CAPs, the current speed is not necessarily zero, but the tidal current ellipse there should reduce to a circle.