The Noutidal Flow in the Providence River of Narragansett Bay: A Stochastic Approach to Estuarine Circulation

Robert H. Weisberg Graduate School of Oceanography, University of Rhode Island, Kingston 02881

Search for other papers by Robert H. Weisberg in
Current site
Google Scholar
PubMed
Close
Full access

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 scales between the steady-state gravitational convection and the tidal oscillations were large and almost exclusively wind-induced. The mean and variance of the velocity component lying along the channel axis were 11.7 cm s−1 (landward) and 166.9 cm2 s−2. 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 harmonies). 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, with 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 s−1. 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 arid can be of equal (or greater) importance to the circulation as the tides or gravitational convection.

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 scales between the steady-state gravitational convection and the tidal oscillations were large and almost exclusively wind-induced. The mean and variance of the velocity component lying along the channel axis were 11.7 cm s−1 (landward) and 166.9 cm2 s−2. 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 harmonies). 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, with 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 s−1. 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 arid can be of equal (or greater) importance to the circulation as the tides or gravitational convection.

Save