An Oceanographic Study of James Bay before the Completion of the La Grande Hydroelectric Complex

From observations made at a number of oceanographic stations established in the northern part of James Bay, data for freshwater budget ice conditions, salinity, temperature distribution and water circulation are presented and discussed. With the completion of the hydroelectric complex, the mean annual rate of discharge of the La Grande River will increase by 88 per cent, through addition of the diverted head waters of other rivers, but will become approximately constant throughout the year instead of being subject to spring peaks and winter lows. Changes to be expected in oceanographic conditions in James Bay are discussed, and recommendations made for the planning of future studies

Estuarine mean flow estimation revisited: Application to the St. Lawrence estuary

Mean value estimate errors for estuarine (and oceanic) parameters which exhibit serial correlation and nonstationarity over a finite record length are discussed. It is shown that when trends are nonlinear over the record length, the mean value estimate error does not decrease with time. Instead, it goes through a minimum and then increases again. An optimal averaging time over which the mean estimate error is minimum is presented. The mean circulation in the lower St. Lawrence estuary is described over a record length of 78.5 days in 1979. Standard, bias, and rms errors in mean value estimates are discussed, and an averaging time yielding a minimum error is suggested for the lower St. Lawrence estuary. New measured features of the mean circulation are: a coastal current flowing downstream near the north shore which deflects to the right at the mouth, and a 2 cm/s inflow in the bottom layer at mid-channel location

Low frequency variability in the lower St. Lawrence Estuary

The lower St. Lawrence Estuary is a good example of wide estuaries with a second lateral boundary within several internal Rossby radii. We compare direct measurements from the 1979 lower St. Lawrence estuary mesoscale current meter array with satellite thermal images observed during the same period. The current field appears to show two quasi-steady states: one configuration is characterized by strong outflow along the north shore of the estuary with a transverse front at the mouth. The other current pattern is more typical of estuaries, with inflow along the north shore and outflow along the south shore. Transitions between these configurations are likely to be due to instability of the current field

A Numerical Forecast of Shoreline Evolution after Harbour Construction in Nouakchott, Mauritania

The construction of a deepwater harbour jetty near Nouakchott, the capital city of Mauritania, significantly modified the southward longshore sand transport, causing severe shoreline recession. The UNIBEST numerical model was used to study the actual impact of this infrastructure and assess the future shoreline evolution. The results, validated by field measurements, indicate that the shoreline evolution rate has undergone a 10-fold increase after harbour construction, with significant accretion to the north and severe erosion to the south of the harbour. Such findings are well documented by past and present observations. Model predictions also suggest that erosion south of the harbour may lead in the near future to inundation of parts of Nouakchott lying below sea level. Finally, this type of numerical hindcast–forecast approach, used for a simple sediment transport case, is useful for the prediction of future shoreline morphodynamic evolution, and may be a valuable surrogate for more expensive physical hydraulic modeling