Mohammed I. El-Sabh

Coastal management and sustainable development: From Stockholm to Rimouski

Abstract Between 1972 (Stockholm) and 1996 (Rimouski), global awareness in relation to coastal management moved from a sectoral to a comprehensive and integrated approach, from the protection of the marine environment and coastal resources to the concept of sustainable development. This paper summarizes the progress made at the international level in relation to coastal management issues, with particular emphasis to the post-UNCED Rio Declaration. A synthesis of the main highlights and outcomes of the Coastal Zone Canada’96 International Conference (CZC’96) held at Rimouski, Canada, is then presented. Two declarations of principle ( The Rimouski Declaration and Call for International Action ) were adopted by the participants at CZC’96. They call for Canada and other international governments to better define national objectives, programs, and mechanisms permitting coastal communities to play a full and active role in the intelligent and practical management of coastal and maritime resources, and to meet their international coastal and ocean obligations thereby contributing to the sustainability of the oceans.

Fronts and Mesoscale Features in the St. Lawrence Estuary

Mesoscale features found in the St. Lawrence estuary range from those encountered in much smaller estuaries to those occuring on continental shelves. The influence of freshwater input, wind forcing and tidal processes on the distribution of temperature, salinity and current fields are discussed. Mechanisms responsible for variability of frontal phenomena, eddy formation and coastal jet dynamics are considered as a function of seasonal changes in the forcing variables. Comparisons of features in the St. Lawrence and in similar regions elsewhere are presented

Storm surges in the Arabian Gulf

The storm surge phenomenon in the Arabian Gulf, including the Strait of Hormuz, is discussed with particular emphasis on the development of mathematical models for prediction purposes. The Gulf is mainly influenced by extra-tropical weather systems, whereas the region south of the Strait of Hormuz is affected by tropical cyclones. The west-to-east directed extra-tropical cyclone tracks and the generally east-to-west directed tropical cyclone tracks converge near the Strait of Hormuz. A meso-scale weather system that deserves special attention in prescribing the meteorological forcing functions is the so-called ‘winter Shamal’. A two-dimensional numerical model is developed to study the storm surges in the Arabian Gulf. The results show that the Gulf is subject to major negative and positive storm surges. Strong winds associated with the Shamal system, coupled with atmospheric pressure gradients, topography and tidal effects, can give rise to water level deviations of several meters. Storm surges observed during the period 17–19 January 1973 show that negative values in the 0.5 to 1.0m range were widespread in the Gulf.

Mitigating the effects of storm surges generated by tropical cyclones: A proposal

One of the regions of the globe that is frequently and very significantly affected by storm surges is Bangladesh. These high amplitude water-level oscillations are generated by the meteorological forcing fields due to tropical cyclones in the Bay of Bengal. The tide also plays a significant role in determining the time history of the total water level. Due to the greenhouse warming associated with the increasing levels of carbon dioxide in the atmosphere, it is expected that the frequency and intensity of tropical cyclones in the Bay of Bengal will increase substantially within the next 50 to 100 years. This new breed of tropical cyclones, referred to as ‘hypercanes’, will generate storm surges on the coast of Bangladesh which could attain amplitudes of up to 15 m, much greater than the present-day amplitudes of up to 6 m. Various mitigation procedures are discussed and compared.

Temporal occurrence of ichthyoplankton in relation to hydrographic and biological variables at a fixed station in the St Lawrence Estuary

Abstract Spring to autumn temporal distributions of ichthyoplankton and other oceanographic variables were measured at three nearshore stations in the lower St Lawrence Estuary in 1977 and 1978. The seasonal occurrence of various species of fish eggs and larvae was similar from one year to the next. Inshore-offshore gradients in abundance of eggs and larvae of different species appeared to be primarily related to the spawning location of each species. The semidiurnal variability was considerably less than the week-to-week variability in all physical and biological variables measured. The weekly variability is predominantly a function of spatiotemporal interactions, due to the geographic displacement of different water masses and their associated plankton in relation to the neap-spring tidal cycle. The timing and duration of spawning for each common species, inferred from ichthyoplankton distributions, suggest a unique combination of spawning and hatching times, ensuring a succession in the occurrence of larvae through time. Results of the temporal and spatial distributions of the different species of ichthyoplankton are discussed in terms of reduced competitive interactions. The relationship between ichthyoplankton distributions and the plankton production cycle in the St Lawrence Estuary is discussed in comparison with other areas.

Oceanography of a Large-Scale Estuarine System

This paper is an attempt to synthesize current knowledge about tides and tidal modelling efforts in the St. Lawrence Estuary. A sequence of numerical models, increasing in complexity from simple one-dimensional to baroclinic, is discussed. The performance of these models and their limitations are pointed out. In the last section, some recommendations are given for future work to improve our present knowledge of the tidal properties over the estuary. These include complementary in situ observations of offshore tidal elevations and principal tidal currents, in addition to new numerical modelling experiments combining all the positive attributes of the previous models.

On the seasonal response of the Lower St Lawrence Estuary to buoyancy forcing by regulated River Runoff

The seasonal current fluctuations recorded from May to September 1979 in the Lower St Lawrence Estuary (LSLE) were re-examined using complex empirical orthogonal functions analysis. The first mode explained 88% of the seasonal variability, and revealed the presence of an estuary-wide anticyclonic eddy near the mouth, which lasted for 40 days in June and July. Careful inspection of the (regulated) 1979 freshwater runoff and salinity time series indicated that light surface water pulses from the St Lawrence River and the Saguenay fjord arrived in the LSLE during that time. Their duration was about 40 days. The contention is that the anticyclonic eddy results from buoyancy forcing by these light water pulses, isolated in the LSLE by denser waters upwelled upstream and by the buoyancy front at the mouth. A reduced gravity model is used to show that when the width of the LSLE becomes greater than two internal Rossby radii, an initial dynamic height elevation will adjust through geostrophy to an anticyclonic eddy. This seems to occur downstream of Rimouski. The eddy will form within a time scale 0 (f−1), and in the absence of instabilities in the current field, it will conserve potential energy for extended periods of time. During August, the advected river runoff decreased, unstable wave activity developed, and denser Gulf waters entered the LSLE from the north shore producing a cyclonic eddy near the mouth. Concurrent satellite thermal imagery tends to support these findings.

Wind‐driven motions at the mouth of the lower St Lawrence Estuary

Abstract The outflow from the lower St Lawrence Estuary (LSLE) is a major input to the Gulf of St Lawrence. The discharge of the St Lawrence River drives a pair of buoyant coastal jets in the estuary that combine to form the major part of the Gaspe Current, perhaps the dominant feature of the circulation in the Gulf. The dominant forcing agencies of the low‐frequency variability (aside from the seasonal freshwater discharge cycle) of motions in the LSLE and the Gaspe Current have not been definitively identified. Here we examine current data from the mouth of the estuary from two field programs (undertaken in 1962 and 1979) and use spectral and bulk correlation analyses to show that wind‐driven motions apparently exert a strong influence on the variability of the exchange between Gulf and estuarine waters. Meteorologically forced motions are shown to be most prominent in the 10‐ to 15‐d period range (corresponding to the typical interval between the passages of weather systems). The wind‐induced current f...

A two-dimensional numerical modelof the vertical circulation of tides in the St. Lawrence estuary

A two-dimensional numerical model is used to study the vertical circulationof tides in the St. Lawrence estuary. The governing equations, which express the conservation of volume, momentum and salt content are solved by a finite difference initial-value method. This model permits the calculation in real time of the water height, vertical and longitudinal salinity and velocity distributions. The only data required for the application of this model are the topographical data of the estuary, the relevant tidal heights, and measurements of salinity at the estuary mouth and landward boundaries. The model was tested by adjusting the friction and turbulence coefficients. Comparison of the model results with actual measurements shows that the model can provide a realistic reproduction of the vertical instantaneous circulation. In addition, the model permits the simulation of the internal tides which have been observed in the St. Lawrence estuary.

An Autumn Instability Event in the Gasp&aacute: Current

Abstract The Gaspe Current is a buoyant jet driven primarily by the freshwater discharge from the St. Lawrence estuary. Previously, many incidents of unstable wave development in the3 Gaspe Current have been reported under summer, high runoff, conditions. Here we present satellite infrared images and discuss the occurrence and evolution of an autumn episode of current instability; in the fall, runoff is lower. This event is notable in that the pattern observed differs considerably from that of summer events, apparently due to the offshore shift that of the core of the jet in early autumn. A stability analysis suggests that the Gaspe Current instabilities may grow slightly faster in autumn conditions. The possible role of wind forcing in triggering wave growth is discussed.