Yongsheng Wu

Environmental Impacts Caused by Tidal Power Extraction in the Upper Bay of Fundy

ABSTRACT Environmental impacts, including tidal regimes and sediment transport in the Minas Basin, caused by tidal power extraction in the Minas Passage have been investigated using a three-dimensional hydrodynamic model in which tidal power extraction is represented using an arbitrary method that adds a friction term to the standard momentum equations. Using the model results, changes in tidal processes and sediment transport in the Minas Basin are examined by comparing model results with and without power extraction. With the presence of power extraction, the tidal level decreases by 0.5–1.5% and the tidal phase increases by 1.2–1.8°. Tidal currents decrease by 15–35% at the western head of the Minas Basin and increase by a comparable magnitude at the Southern Bight. The presence of power extraction could move the location of the tidal residual gyre in the western head of the Minas Basin south by about 2 km. Model results also show that less sediment would move into the central area of the Minas Basin but more sediment would be deposited into the Southern Bight at a rate of 8–12 mm y−1. The effect of the deposition rate might be negligible in the northern part of the Bight where the water is deep but could be important in the intertidal areas.

Modelling Extreme Storm-Induced Currents over the Grand Banks

Extreme storm-induced currents over the Grand Banks are investigated using a three-dimensional (3-D) ocean circulation model forced by 22 storms selected from the past 50 years with return intervals ranging from 1 to 34 years. Wind data for the storms are historical atmospheric data. The modelled currents are compared with current meter measurements made during a storm in March 1983. The results indicate good agreement between the model and measurements. In the surface layer of the Grand Banks, the model extreme current speeds are approximately 80 cm s−1 over a large portion of the Grand Banks, and some areas have extreme current speeds higher than 120 cm s−1. The highest extreme current speeds occur at St. Pierre Bank, where the speed reaches 140 cm s−1. In the bottom layer, the region with high extreme current speeds is mainly in the periphery of the Grand Banks, with magnitudes over 40 cm s−1. The results also show that the response of the water to storm forcing in the Grand Banks area varies from place to place because the mechanisms of current generation are different at different locations.

A modeling study of the impact of major storms on waves, surface and near‐bed currents on the Grand Banks of Newfoundland

Waves and current processes, both surface and near-bed were simulated for major storms on the Grand Banks of Newfoundland using integrated wave, 3-D tidal and ocean current models. Most storms track southwest to northeast and pass to the north or northwest of the Grand Banks. Significant wave heights can reach up to ∼14 m and are predominantly to the northeast at the peak of storms. Extreme surface currents reach approximately 1 m s−1 and are largely to the southeast. The strongest bottom currents, up to 0.8 m s−1, occur on St. Pierre Bank and are dominantly to the south and southeast. While wave height and wind-driven current generally increase with wind speed, factors such as storm paths, the relative location of the storm center at the storm peak, and storm translation speed also affect waves and currents. Surface and near-bed wind-driven currents both rotate clockwise and decrease in strength as the storm traverses the Grand Banks. While the spatial variability of the storm impact on surface currents is relatively small, bottom currents show significant spatial variation of magnitude and direction as well as timing of peak current conditions. These spatial variations are controlled by the changes of bathymetry and mixed layer depth over the model domain. The storm-generated currents can be 7 to 10 times stronger than the background mean currents. These strong currents interact with wave oscillatory flows to produce shear velocities up to 15 cm s−1 and cause wide occurrences of strong sediment transport over nearly the entire Grand Banks.

A comparative study of satellite-based operational analyses and ship-based in-situ observations of sea surface temperatures over the eastern Canadian shelf

The satellite-based operational sea surface temperature (SST) was compared to the ship-based in-situ SSTs established by the Atlantic Zone Monitoring Program (AZMP) over the eastern Canadian shelf (ECS) for a 3-year anal-ysis period (2005–2007). Two sets of operational SST analyses were considered in this study, with one set produced by the Canadian Meteorological Centre (CMC) and the other produced by the National Centers for Environmental Predic-tion (NCEP). The comparative study indicated that there was no appreciable systematic difference between the CMC and NCEP SST analyses over the ECS. The root mean squared difference (RMSD) between the AZMP ship-based in-situ SSTs and the satellite-based STT analyses over the ECS was about 1.0°C, without any obvious seasonal or geo-graphic trend. The RMSDs were relatively larger over the outer flank of the Grand Banks than the other regions of the ECS, mainly due to dynamically complicated circulation and hydrographic conditions over this shelf break area associated with the Labrador Current.

Effects of rainfall on oil droplet size and the dispersion of spilled oil with application to Douglas Channel, British Columbia, Canada

Raindrops falling on the sea surface produce turbulence. The present study examined the influence of rain-induced turbulence on oil droplet size and dispersion of oil spills in Douglas Channel in British Columbia, Canada using hourly atmospheric data in 2011-2013. We examined three types of oils: a light oil (Cold Lake Diluent - CLD), and two heavy oils (Cold Lake Blend - CLB and Access Western Blend - AWB). We found that the turbulent energy dissipation rate produced by rainfalls is comparable to what is produced by wind-induced wave breaking in our study area. With the use of chemical dispersants, our results indicate that a heavy rainfall (rain rate>20mmh-1) can produce the maximum droplet size of 300μm for light oil and 1000μm for heavy oils, and it can disperse the light oil with fraction of 22-45% and the heavy oils of 8-13%, respectively. Heavy rainfalls could be a factor for the fate of oil spills in Douglas Channel, especially for a spill of light oil and the use of chemical dispersants.

A modeling study of the impact of major storms on seabed shear stress and sediment transport on the Grand Banks of Newfoundland

Waves, current, and sediment transport processes in major storms on the Grand Banks of Newfoundland were simulated using integrated wave, three-dimensional tide and circulation, and combined-flow sediment transport models. While the tidal and nontidal currents are generally low and cause little sediment transport, storm-induced waves and currents enhance bed shear velocity by more than 5 times and cause significant sediment transport over the entire Grand Banks. The impact of storms on shear stress and transport strongly depends on water depths and the greatest impact occurs over the bathymetric highs on southeastern Grand Bank where the maximum shear velocity reaches 15 cm s−1 and the maximum transport rates are >5 kg m−1 s−1. The direction of sediment transport rotates clockwise progressively through nearly 360° during the passage of a storm. Although peak transport typically occurs on central and southeastern Grand Bank with a southeastward direction, the magnitude, direction, and timing of peak transport show strong spatial and temporal variability. The variability of the peak transport largely depends on the timing and relative intensity of the waves and the total bottom currents which in turn depends on the addition of the storm-induced and tidal currents. The calculation of the maximum transport potential suggests that sediments as coarse as small pebbles are mobile in water depths <80 m under 1:1 year storms and that medium sand is transported in water depths as deep as 200 m during major storms. Results of the sediment transport models corroborate the observed sediment erosion and accretion patterns.