Contenu du sommaire : La gestion environnementale des grands bassins fluviaux

Knowledge of environments and of associated mechanisms of change has not advanced at the same rate as the technological ability to effect such transformations, as in many spheres of contemporary life. This has resulted in a number of catastrophic impacts as in the case of Aswan and the Aral Sea. Does this imply, therefore, that such interventions, which are a logical consequence of man's action and have important economic and geopolitical considerations, should be halted ? Problems of environmental management are none the less very real and the need to take them into account represents one of the elements of any integrated management strategy for major river basins.

The notion of a 'major river' is analysed using a series of interrelated criteria, and is applied to a number of actual cases : Nile, Amazon, Yangtse-kiang, Mississippi and Saint Lawrence. For each of these rivers, the author considers the uses of the resource, the pressure that it has to support and the priority actions for environmental management. This latter issue is studied in detail for the Saint Lawrence.

The major basin of the Saint Lawrence - Great Lakes poses delicate problems of management due to its size, the high density of its population (in an American context), the international character of its waters and the creation of the seaway. To help resolve such problems the Secretariat for the Improvement of the Saint Lawrence was created in 1985. This international organisation which, for its Canadian part, is represented primarily by Quebec, deals with concrete issues and aims to reconcile opposing interests rather than to intervene directly. It also plays a double role : first, political, as a result of bringing together in a forum the leaders of the local riverine councils, and second, economic, in the context of the SODES (Société de Développement Economique du Saint Laurent) Saint Lawrence Economie Development

The international Conference of the Mayors of Saint Lawrence and the Great Lakes brings together councillors from communes included in the Saint Lawrence - Great Lakes basin. The aim is to promote common interests and to identify management problems and economic development opportunities which affect this vast region. The province of Quebec is particularly involved in this international structure.

The period of major development projects supported by tacit public approval is over, replaced by a new appreciation of environmental problems. Such recognition expresses itself through different associations combining competence with pluri-disciplinarity and a strong presence on the ground. These associations, which are independent although integrated into certain decision making structures such as the "Comités de bassin" (River Authorities), are seeking to promote a new evaluation policy for development projects. They want to replace an analytical approach which masks key problems by an integrated approach.

The management role pursued by the "Compagnie Nationale du Rhône" since 1939 is limited in space (the river axis), in its objectives, which are essentially economic, and in its responsibilities, which do not include policing the river or pollution risks. The company manages the effects resulting from improvement works carried out in three areas : flood control, the transport of solid material and the redevelopment of wet zones. With respect to its environmental policy, it also takes into account problems of biological and landscape quality.

Based on mixed findings concerning the present condition of the river, the Rhône Action Plan defines quality goals integrated into a three-point programme : recreate a 'living' river, notably through the restoration of cutoffs and abandoned sections ; re-establishing a high ecological quality by reducing pollution of an oxydisable, nutritional or toxic nature ; eliminate the risks of accidental pollution. The implementation of this programme over the period 1992-2000 will cost between 15 and 17 billion francs.

Paris owes its origins and development to its crossroads position on the Seine. Conversely, the river has been completely transformed by the requirements of the city. Not only has it been developed to respond to navigational needs, but also the profile and flow of its tributaries have been modified to allow wood used for heating to be floated downstream. This latter constraint no longer exists, but treatment of waste water has made the works at Achères into a man made tributary having a constant discharge which attains 25 cusecs.

The International Commission for the Protection of the Waters of Lake Geneva was officially recognised by an international agreement in 1960. It defines quality standards for the management of the lake's waters and may coordinate various forms of intervention, notably in emergencies. Its action has led to a reduction in pollution, although the eutrophisation of the waters remains a cause of concern.

The multi-prupose development of the Volga is designed to meet a wide range of objectives and is an exceptional project both in terms of scale and the variety and intensity of its impacts. Using the river to produce hydro-electric power has caused a major change to its seasonal regime and the disappearance of spawning grounds. The churning up of the river's water by the power stations' turbines at peak periods has led to intense erosion of the banks, while newly irrigated areas barely compensate for the large extent of fertile land flooded by the reservoirs. Overall, this represents a major ecological disaster.

The Environmental Atlas of the St. Lawrence aimed at reviewing the state of the river environment. The atlas is intended to sensitize, inform and educate the general public about the basic components of the environment of the St. Lawrence. It aims at informing the public of the uses and degradations of the river and, of the actions of protection and conservation undertaken for its restoration. The paper begins with considerations on the place of the atlas among the other tools of environmental management, especially GIS. The presentation of the atlas aims, structure and contents follows. Data gathering, processing and graphical rendering are also discussed. The atlas will be composed of twenty loose leaf, large size, posterlike plates. Each plate combines maps, graphic arts, graphs, diagrams, photographs and text.

Remote sensing gives the possibility of distinguishing three categories of land cover with Landsat or Spot satellite data. It concerns : damp forest on wet soils ; deciduous gallery forest in valleys and alder, ash or poplar plantations ; shrubby low vegetation associated with ponds and swamps. Such information is particularly interesting in studies which aim to gain knowledge of changes in the watersheds close to major concentrations of small lakes and swamps as well as in the flood plains of major rivers or in the system of hedges in bocage areas, so as to protect or develop these zones. Different examples of the work carried out by the French Ministry of Environment illustrate the interest of studies undertaken by remote sensing on river bank vegetation..

Explanation is given of a coherent method to ensure the integrated management of river ecosystems. The overall aim is to define long term management rules which reconcile the continuing functioning of ecosystems and different uses of the water. The conceptual framework is based on a typological approach relating to factors of ecological dynamics and of the degree of anthropisation of rivers. The method consists of four stages : 1) typological synthesis ; 2) definition and hierarchical ordering of management constraints ; 3) Proposal of scenarios ; 4) choice of options and means. Some general orientations are suggested. The approach implies the creation in each basin of a scientific group capable of understanding the dynamics of the ecosystems.

A complex volume of information needs to be collected to undertake an integrated analysis of the Loire basin. The use of Geographical Information Systems (GIS) for such data offers unquestionable advantages in terms of information management (collection, recording, storage and updating). Above all, such systems provide a valuable means of exploring (consultation and visualisation) and analysing data, making them an ideal tool for a diagnostic approach. This also represents a sound method to consider the question of the integrated management of the entire river basin.

In Canada (the only country considered in this article) the environmental management of the waters of the Saint Lawrence is legally the responsibility of federal, provincial and municipal authorities which act within the framework of existing legislation. Such management does not concern the river's waters as such, but relates to actions which involve their use such as fishing, navigation, taxation and waste disposal. This explains the complexity of the existing legal apparatus which, to be effective, requires collective awareness. The author considers successively the problems of the evaluation of projects likely to have an impact on the river and then the regulatory framework of banned activities. The different areas of competence of the federal, provincial and municipal authorities are outlined.