The tidal power available for electricity generation from in-stream turbines placed in the Minas Passage of the Bay of Fundy is examined. A previously derived theory is adapted to model the effect of turbine drag on the flow through the Minas Passage and the tidal amplitude in the Minas Basin. The theoretical maximum power production over a tidal cycle is determined by the product of the amplitude of the forcing tide in the Bay of Fundy and the undisturbed volumetric flowrate through the Minas Passage. Although the extraction of the maximum power will reduce the flowrate through the Minas Passage and the tides in the Minas Basin by over 30 per cent, a significant portion of the maximum power can be extracted with little change in tidal amplitude as the initial power generation causes only an increase in the phase lag of the basin tides. Two-dimensional, finite-element, numerical simulations of the Bay of Fundy-Gulf of Maine system agree remarkably well with the theory. The simulations suggest that a maximum of 7 GW of power can be extracted by turbines. They also show that any power extraction in the Minas Passage pushes the Bay of Fundy-Gulf of Maine system closer to resonance with the forcing tides, resulting in increased tidal amplitudes throughout the Gulf of Maine. Although extracting the maximum power produces significant changes, 2.5 GW of power can be extracted with a maximum 5 per cent change in the tidal amplitude at any location. Finally, the simulations suggest that a single turbine fence across the Minas Passage can extract the same power as turbines throughout the passage but that partial turbine fences are less efficient.

The ability to estimate the rate of dissipation (ε) of turbulent kinetic energy at middepth in a high-speed tidal channel using broadband acoustic Doppler current profilers (ADCPs) is assessed by making comparisons to direct measurements of ε obtained using shear probes mounted on a streamlined underwater buoy. The investigation was carried out in Grand Passage, Nova Scotia, Canada, where the depth-averaged flow speed reached 2 m s−1 and the Reynolds number was 8 × 107. The speed bin–averaged dissipation rates estimated from the ADCP data agree with the shear probe data to within a factor of 2. Both the ADCP and the shear probe measurements indicate a linear dependence of ε on the cube of the flow speed during flood and much lower dissipation rates during ebb. The ebb–flood asymmetry and the small-scale intermittency in ε are also apparent in the lognormal distributions of the shear probe data. Possible sources of bias and error in the ε estimates are investigated, and the most likely causes of the discrepancy between the ADCP and shear probe estimates are the cross-channel separation of the instruments and the high degree of spatial variability that exists in the channel.

Spectral and structure function methods are implemented to compute the dissipation rate ε from broadband, diverging-beam acoustic Doppler current profiler (ADCP) data collected at four sites in a high-flow tidal channel. This paper shows that middepth estimates of ε obtained from spectral and second-order structure function (SF2) methods are both lognormally distributed with comparable means and variances. Speed bin–averaged ε values agree to within 16%, depending on the site and tidal phase (ebb/flood). The close agreement between the two independent methods provides further support for the argument put forward by McMillan et al.: that is, that the factor-of-2 difference between shear probe and (spectral) ADCP estimates of ε was likely caused by spatial differences in turbulence levels. The agreement between the spectral and both second- and third-order structure function methods also supports the use of for the SF2 universal constant. Notably, however, the SF3 method was less robust for these data. Two additional aspects of the SF2 approach are examined in some detail: 1) the differences from upstream- and downstream-facing beams are shown to arise from the Reynolds stress and 2) the inability of the ADCP to resolve small-scale motions does not affect the estimates of ε but yields apparent Doppler noise levels that—counterintuitively—decrease with increasing flow speed and increasing dissipation rate. A modified SF2 method that accounts for the variance associated with the unresolved scales removes the flow speed dependence and yields noise level estimates that agree with the spectral values.

Abstract. The generation and evolution of solitary waves by intrusive gravity currents in an approximate two-layer fluid with equal upper-and lower-layer depths is examined in a cylindrical geometry by way of theory and numerical simulations. The study is limited to vertically symmetric cases in which the density of the intruding fluid is equal to the average density of the ambient. We show that even though the head height of the intrusion decreases, it propagates at a constant speed well beyond 3 lock radii. This is because the strong stratification at the interface supports the formation of a mode-2 solitary wave that surrounds the intrusion head and carries it outwards at a constant speed. The wave and intrusion propagate faster than a linear long wave; therefore, there is strong supporting evidence that the wave is indeed nonlinear. Rectilinear Korteweg-de Vries theory is extended to allow the wave amplitude to decay as r −p with p = 1 2 and the theory is compared to the observed waves to demonstrate that the width of the wave scales with its amplitude. After propagating beyond 7 lock radii the intrusion runs out of fluid. Thereafter, the wave continues to spread radially at a constant speed, however, the amplitude decreases sufficiently so that linear dispersion dominates and the amplitude decays with distance as r −1 .

Measurements are reported of the pressure fluctuations in the near field of a submerged jet. The mechanisms by which the pressure fluctuations may be generated are discussed and estimates are presented of two of these, namely the transient oscillations of micro-bubbles of air excited by the pressure drop in the nozzle, and the cavitation of micro-bubbles by the turbulent pressure fluctuations in the jet mixing region.