The nontidal flow in the Providence River of Narragansett Bay: A stochastic appraoch to estuarine circulation.

Abstract

Atmospherically driven flow in the Providence River (a partially mixed estuary) has been examined using a 51-day velocity record measured 2 m from the bottom. Velocity fluctuations at time scale between the steady-state gravitational convection and the tidal oscillations were large and almost exlusively wind-induced. The mean and variance of the velocity component lying along the channel axis were 11.7 cm sSUB-SUB1 (landward) and 166.9 cmSUB2 sSUB-SUB2. Of this axial current variance 48% resided at subtidal frequencies as compared to 45% associated with semidiurnal tides (the remaining 7% was mostly due to higher tidal harmonics). Over the most energetic portion of the axial current spectrum (periodicities of 4-5 days), 97% of the variance was coherent with the wind velocity component lying along the direction of maximum fetch, wth the current lagging the wind by about 4 h. Owing to this extremely high coherence, a linear time invariant stochastic model reproduced the axial current from the two orthogonal wind velocity components to within an rms error of 2.3 cm sSUB-SUB1. The wind also had a marked effect upon the density field. It is concluded that the effects of wind can permeate the entire water column of a partially mixed estuary and can be of equal (or greater) importance to the circulation as the tides of gravitational convection. (A)