Astronomical and nonlinear tidal currents in a coupled estuary shelf system

Abstract

We analysed the tidal content of current time series from 53 current meters at 31 mooring locations on the inner continental shelf in the vicinity of Delaware Bay, U.S.A. We distinguish between an astronomically forced short period flow field at diurnal and semi-diurnal frequencies and a nonlinearly generated long period tidal flow field. The latter operates at the difference frequencies of the former. We found short period tidal currents to vary from 90 cm s −1 at the mouth of the estuary to 8 cm s −1 only 30 km to the north. Tidal volume flux through the mouth generates intensified tidal currents on the shelf as far as 50 km away to the southeast. At periods longer than 2 weeks we detected tidal currents with amplitudes from 1 to 3 cm s −1 and phases indicative of a horizontally coherent flow field. We also estimated mean rectified tidal flow fields of about 2–7 cm s −1. These thus contribute substantially to the overall mean currents on the shelf.