Sustainable Foreland Forests Managing in the Danube River Bed Forelands

by Zoran Gavrilović, Milutin Stefanović and Duško Isaković, ^[1]

abstract of the article published in Danubius 1-2/1998

Large areas between the river and the protection embankments along the flow of the Danube and its tributaries the Sava, Tisza, Tamiš and Velika Morava, are called "foreland" and are usually covered with wood, mostly poplar and willow trees.

After the construction of the HPP Ðerdap I a great lake has been formed in the Danube and its tributaries, which prolonged the foreland flooding into the vegetation season. In the period 1979 to 1990 extensive research of the backwater influence in the vegetation and nonvegetation season, were carried out bringing new knowledge and conclusions. The analyses have shown that changed flooding regime had caused a serious deterioration of natural conditions in the foreland, which resulted in the forest degradation of both autochtone and cultivated forests.

All large rivers are characterized by long lasting floods directly related to climatic cycles of rains and snow melting. which makes them regular occurrences. As all natural phenomena, floods also have various intensities, so that there are extreme catastrophic floods on one side and extreme droughts on the other.

The areas close to big rivers with relatively stable year flooding cycle have always been inhibited by autochtonous plants and animal habitats. Depending on species adaptability, these areas are inhibited by forest habitats of oak, ash, poplar and willow.

In order to satisfy their needs, people have transformed the flooding areas into agricultural land, and since ancient times executed large training works on big rivers to control floods, and in arid areas to irrigate and to improve navigable routes, up to present times. The controlled areas nowadays much widened, to the detriment of vast forest areas. The present state in the Danube foreland is stabilized at the end of 19th and beginning of 20th century.

Namely, the navigable routes were improved, large flooding areas reclaimed for agricultural production and all suitable space for urban expansions towards flooding areas, defined. The consequence of this development is a considerable narrowing of the flooding area covered by forests after the construction of embankments, for which the German word "foreland" is used. A real value and role of these forests within the flood control system is known only to the experts who deal with flood control and growing of these forests.

The aim of forestry is to produce as much as possible of wood mass, however, when we consider the foreland woods, they have other very important tasks within the flood control system to which the forestry-economic plans have to be subdued.

From the water resources development point of view, narrow forest areas within forelands play a double role: the protection of the upstream embankment slope from wave strokes caused by wind, and water flow velocity decrease in the vicinity of the embankment. Such forest areas should be managed only in the way which enables a permanent survival of the zones without periods of barren embankments.

At the other hand, vast areas in forelands should receive the excess water in the times of floods and decrease the discharge at downstream parts of flows. This solution is usually applied upstream of big cities. The woods are managed in the way which is best from the forestry point of view, except in the immediate vicinity of embankments, where a method of management for the narrow zones is applied.

All above said represents the world practice, however, in Yugoslavia, some changes occurred after the construction of the HPP Ðerdap I on the Danube in the Ðerdap gorge situated between Yugoslavia and Romania.

A construction of a dam on every river, especially on a big river like the Danube, disturbs the natural regime of waters and flooding. During the very designing time possible disturbances of water regime and possible environmental damages upstream and downstream of the dam, have been calculated, and the system for the consequences prevention and alleviation designed.

Considering the foreland woods which for thousands of years grow in the area, and which for centuries represent a part of the flood control system, it was clear that a great area will be devastated due to the water level rise for a few meters. On the basis of the designed water regime disturbance, the forest areas having no more survival chances were defined, as well as the areas on which a species conversion should be made (e.g. plant willow in the poplar area).

The protecting embankments have been placed to the new protection elevation, and the places on the it with no more conditions for the protection vegetation growth, paved by concrete. The Ðerdap Lake was closed in 1972 and after that the water level has been elevated several times in accordance with the degree of the protection system completion. In 1978 the peak level was established and it has been maintained up to now. A systematic multidisciplinary research on the HPP Ðerdap I backwater impact on the foreland, also started at that time. The backwater impact on foreland woods was one of the research fields. Since the scope of the research is very wide, this paper will present a synthesized review of the achieved results in the period 1978-1990.

[1] Institute for the Development of Water Resources "Jaroslav Černi"
Address: Jaroslava Černog 80, 11223 Belgrade (Beli Potok), SCG
e-mail: zgavrilo@EUnet.yu

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