A Study of Tidal Energy Dissipation and Bottom Stress in an Estuary

Abstract

A Method for inferring an area-averaged bottom stress and energy dissipation rate in a tidal estuarine channel is presented. The one-dimensional continuity and momentum relations are developed using simplifying assumptions appropriate for a well-mixed shallow and narrow estuary. The finite-difference form of these relations is derived for a section of the Great Bay Estuary, New Hampshire, an estuary which has been shown to have a relatively large energy dissipation rate. A set of current, bottom-pressure and sea-level measurements from the Estuary is used to estimate time series of all important first- and second-order terms in the momentum equation. Except near slack water, we find that the instantaneous first-order balance must be between the surface-slope-induced pressure gradient and bottom-stress forces. Important second-order contributions to the balance come from the inertial and convective acceleration terms. Time series of bottom stress are inferred by summing the estimated terms. For this study site the 14-day rms bottom stress is 45.1 ± 4,5 dyn cm?2 with a corresponding rms and mean dissipation rate of 3526 ± 420 and 2478 ± 297 ergs cm?2 s?1, respectively. The role of the first-order tidal motion and non-linearities in the mean second-order force balance is discussed.