Les variations de niveau des réservoirs de la Volga et leurs conséquences sur l'environnement The level variations of the Volga reservoirs and their consequences on the environment

Résumé

Les réservoirs volgiens ont pour but de retenir les eaux de fonte de printemps pour les redistribuer dans le cadre de l'année hydrologique (avril-mars). Cette fonction implique des variations de niveau des lacs de retenue et ceci est à l'origine de conséquences négatives. Le remplissage de printemps peut être une menace hydrologique sérieuse pour l'agriculture. Le déstockage qui suit est mené en saison de navigation (il intéresse donc tous les secteurs impliqués dans l'aménagement) ou en hiver (il n'intéresse plus que l'hydroélectricité). D'après les règles établies, le déstockage devrait être mené selon un rythme précis et devrait être régulier d'une année sur l'autre pour ne pas porter préjudice à la pèche dans les réservoirs et pour ne pas entretenir l'érosion sur les rives. Depuis vingt ans, la pèche attribue toutefois ses mauvais résultats au non-respect des règles. D'autres ministères se plaignent du même fait. Les règles sont-elles respectées? Seule l'étude des niveaux réels des réservoirs permet de répondre à cette question. Elle fait apparattre depuis vingt ans des remplissages de printemps anarchiques, d'importantes et imprévisibles variations de niveau en saison de navigation, des déstoclcages massifs d'hiver. Cette pratique est partiellement responsable du développement en URSS d'un puissant mouvement de contestation écologique.

Mots-clés:

• Aménagement,
• environnement impact,
• Volga,
• URSS

Abstract

Since 1962, the Volga River has become a series of cascades of eight reservoirs. Initially, the main object of the development was hydro-electricity but fishing, irrigation and transport became more and more important. Sine 1962, the function of Volgian reservoirs has been to retain spring water for its redistribution during the navigation season - for all the sectors involved in the management - and during the winter - only for hydro-electricity. This function implies lake level variations, which can generate negative environmental effects.

According to Soviet economic principles, each Ministry manages its own equipment, which means that the Volga development is controlled from Moscow by different Ministries. The Ministry of Energy, controlling dams and turbines, has an enormous power. Hence, there are rules for defending the interests of the other economic sectors. The Ministry of Energy, allegedly, is concerned only about its own plans and does mot comply with the rules, which naturally it denies. These ruses have mot been published but their main lines are well-known as they are largely referred to in scientific publications concerning the Volga management problem. The only way to check is to compare the rules with the available hydrological data on lake levels.

The most significant part of annual Volgian runoff proceeds from the spring melting of snow. This water must be used to fill the Volgian reservoirs and to satisfy the Lower-Volga artificial flood (110 km³). Actual data about Kuybyshev dam water discharge shows that the lower-Volga water requirements are mot satisfied. The true data about Kuybyshev and Rybinsk lakes shows disorganized fillings : the reservoirs are filled up to different levels every year, which contributes to activate bank erosion and prevents the constitution of aquatic vegetation. Bank erosion supplies a lot of sediments which, certain years, obstruct access to storm shelters or, sometimes, to harbours (Dimitrovgrad, for example). The lack of aquatic vegetation reduces the possibilities of fish reproduction.

By raising the level of groundwaters around the reservoirs, this spring filling jeopardizes agriculture, so it is mot allowed to full reservoirs over the maximum water level. Yet, the data shows that the Kuybyshev reservoir, right in the middle of the agricultural zone of the USSR, was filled more than 16 years out of 26.

The drawdown must be carried out with moderation and according to a specific rhythm particularly before winter in order to force the fish to leave the shallows. During the winter it is better to avoid massive drawdowns. The study of winter levels reveals very deep drawdowms. In This case the lake surfaces reduce and the tee collapses down to the lake bottom causing very important prejudice to the aquatic fauna.

According to the numerous scientific publications by Soviet fishing Institutes, the non-observation of the rules accounts for the poor production of fish. (500-600 kg a year per km² on Kuybyshev and Kybinsk lakes) and for the increase of bank erosion. The study of the lake levels shows that the Volgian water is used only in the interest of hydro-electricity and without any care for the other users (agriculture, fishing, navigation) or for the effects on the environment. The Energy lobby is so strong that 25 years of scientific protest bas not changed anything.

Such inconsistent management bas played a great part in the determination of an environmental movement In the USSR. Over the last forty years significant areas of territory have been submerged under the large reservoirs (on the Volga alone more than 300,000 people have been resettled on account of submersion) so the scientific protest met with the approval by a show of hostility to hydro-energy. Since the instauration of the « glasnost », the protest against the « hydro-lobby » has taken a symbolical value, a facet of the opposition to the « old order », and the poor management of Volga development largely contributed to this.

Keywords:

• Development,
• hydro-management,
• environmental effects,
• Volga,
• USSR