Mean and Turbulence Characteristics in a Tidal River

Simultaneous measurements of longitudinal and vertical components of instantaneous velocities and salinities have been performed continuously during two spring tides in the Ota River estuary. Stability influence of stratification changes widely during tidal cycles. The flux Richardson number, Rf , is large during ebb tides and small during flood tides. Turbulence parameters (namely turbulence intensity, u′,w′, turbulence scale) are sensitive to both Rf and mean velocity but they are not directly affected by the flow depth. The maximum values of the momentum transport correlation coefficient, -/u′w′, and its ratio to the turbulence kinetic energy, k, -/k, are 0•4-0•6 and 0•2-0•3, respectively. Although the integral vertical length-scale, Lw, decreases with increasing Rf , the systematic variation of the longitudinal length-scale, Lu, with Rf is not observed. The Reynolds shear stresses are larger for near well-mixed conditions in the deceleration than in the acceleration phase, as shown in previous work. However, the time lag of the maximum Reynolds stress to the maximum mean velocity is not observed. Since the Reynolds shear stress and mean velocity gradients are larger in the deceleration phase, the turbulence production rate in this phase is approximately two times larger than in the acceleration phase. Results of the quadrant analysis for the Reynolds stress in the acceleration, deceleration phase and stratified condition are discussed. The Reynolds stress is very intermittent under the stratified condition; in the second ebb (Rf≈ 0•3), it is found that approximately 160% of the total stress is contributed in only 10% of the time.