Vertical turbulence exchange in tidal flows

This thesis presents the results of some investigative fieldworkcarried out on the Great Ouse Estuary in May and September 1979 undera joint collaborative study between the Hydraulics Research Station(HRS) and the Tidal Waters Research Group, (TWRG) of the Civil EngineeringDepartment, University of Birmingham.The Growing use of mathematical models to solve engineering problemsin stratified flows has highlighted the need to understand the basicmechanisms behind the exchange of momentum and solutes through turbulentfluctuations.In this study direct readings of turbulent fluctuations have beenobtained in a partially stratified tidal flow. These measurements alongwith data for the turbulent mean velocity and density fields, have beenused. to characterize turbulence, by turbulent parameters, spectral analysis,to evaluate the vertical exchange of momentum and solute, and in particularto examine the mixing length functions of Rossby and Montgomery, and Kentand Pritchard relating to Richardson numbers (Ri) less than 1, when themixing length is most sensitive to change in the vertical density gradient.The turbulent parameters obtained from the data are in reasonableagreement with appropriate results from atmospheric and laboratory data.The mixing length results based upon direct measurements of turbulencehave been used to evaluate the coefficients in the Kent and Pritchard andRossby and Montgomery equations. These coefficients are applicable up toa gradient Richardson number of 0.6 and clearly show the sensitivity ofthe turbulent transport mechanisms in the vertical direction to evensmall values of Ri (^-'0.05). Estimates have been made of some of thecoefficients associated with the second order solution to the turbulenceclosure problem for stratified flows.