Sensitivity of tidal characteristics in double inlet systems to momentum dissipation on tidal flats:a perturbation analysis

Abstract

\u3cp\u3eIn a tidal channel with adjacent tidal flats, along–channel momentum is dissipated on the flats during rising tides. This leads to a sink of along–channel momentum. Using a perturbative method, it is shown that the momentum sink slightly reduces the M\u3csub\u3e2\u3c/sub\u3e amplitude of both the sea surface elevation and current velocity and favours flood dominant tides. These changes in tidal characteristics (phase and amplitude of sea surface elevations and currents) are noticeable if widths of tidal flats are at least of the same order as the channel width, and amplitudes and gradients of along–channel velocity are large. The M\u3csub\u3e2\u3c/sub\u3e amplitudes are reduced because stagnant water flows from the flats into the channel, thereby slowing down the current. The M\u3csub\u3e4\u3c/sub\u3e amplitudes and phases change because the momentum sink acts as an advective term during the fall of the tide, such a term generates flood dominant currents. For a prototype embayment that resembles the Marsdiep–Vlie double–inlet system of the Western Wadden Sea, it is found that for both the sea surface elevation and current velocity, including the momentum sink, lead to a decrease of approximately 2% in M\u3csub\u3e2\u3c/sub\u3e amplitudes and an increase of approximately 25% in M\u3csub\u3e4\u3c/sub\u3e amplitudes. As a result, the net import of coarse sediment is increased by approximately 35%, while the transport of fine sediment is hardly influenced by the momentum sink. For the Marsdiep–Vlie system, the M\u3csub\u3e2\u3c/sub\u3e sea surface amplitude obtained from the idealised model is similar to that computed with a realistic three–dimensional numerical model whilst the comparison with regard to M\u3csub\u3e4\u3c/sub\u3e improves if momentum sink is accounted for.\u3c/p\u3