Creating Sustainable Conditions for Foreland Forestry Within Complex System of Trained Water Streams

by Milivoje Brajković, Zoran Gavrilović and Milutin Stefanović ^[1]

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

The Danube-Tisza-Danube Hydrosystem is one of the great river engineering projects executed in Europe. The whole hydrosystem is constructed in the Province of Vojvodina and it provides for flood control and drainage of the area surrounded by the Danube river, cut by the rivers Tisza and Tamiš on their way to join the Danube, and permanently endangered by floods and groundwater before the system construction. The hydrosystem is also navigable. Beside all partial backwaters at navigation locks and gates of the hydrosystem, the "Ðerdap" hydro power plant construction has caused a special deterioration of the conditions for the normal existence of forest vegetation, which under natural conditions, had existed along the river banks in the zone of flood waters influence. As to the Danube flow, its regime has been managed by the operation of the "Ðerdap" hydro power plant and by the conditions of water inflow to the Danube. However, in the case of the Tisza and the Tamis, the navigation locks and gate system enables the water regime management which suites all users. After completion of a multidisciplinary investigation which proved that forests were dying over a vast space, a project of an experimental regime of the hydrosystem operation on the Tamiš river (the most endangered part) has been designed in order to establish the conditions close to the natural regime. The survey had been carried out during the experimental period, and water regime corrected in accordance with the surveyed conditions.

The problem of forest habitats survival in foreland forests arose after the construction and closing of the HPP "Ðerdap" I reservoir. The forest survival in the Danube foreland, where a natural flooding regime exists, together with the disorder caused by the dam construction and its operation, represents only one aspect of the problem.

Namely, upstream of the HPP "Ðerdap" I dam exists the DTD system - a complete hydro land reclamation and navigation system which encompasses the area from the Hungarian to the Romanian border. The system links the Danube with several big rivers by a navigable canal network which again joins the Danube close to the Rumanian border.

The DTD System has been built before the construction of the HPP "Ðerdap" I, and meant for drainage, irrigation and navigation. The system is constructed as a network of canals the main of which are navigable, with a number of gates and navigation locks which serve for the control of water regime in accordance with the set tasks of the system.

After the construction and closing of the HPP "Ðerdap" I, an additional protection of the DTD had to be built in a form of new gates and navigation locks to annul the negative backwater impact on the operation of the system which, anyway, intakes the water of the rivers Tisza, Begej, Tamiš, Nera and the interior waters from the surface of the system. All this water had previously been drained into Danube by a natural gravitational inflow. The new situation imposed a need for pumping when there is no possibility for the gravitational flow into the Danube.

The pumping has been performed when needed and without any analyses of the negative impact on the foreland woods. A few years after, a drastic yield decrease in the forest has been noticed, as well as dying of trees along a great part of the foreland.

The DTD System has been accused for causing the excessive flooding of the foreland and causes the forest area devastation. In order to find a real cause of the foreland forest devastation, detailed investigations of all parameters have been carried out in the most affected foreland of the Tamiš river, as well as in the other forests of the forelands.

Having in mind that the water regime in this case is very dynamic and applicable due to the impact of the pumping regime and gates system, a complete history of pumping stations operation and water level dynamics, has been made.

The carried out research has shown that the main cause of the foreland forests devastation is an irregular pumping regime which could be called excessive, so that the foreland forest had been exposed to excess drought instead of to flood. A possibility has been discovered to accord the pumping regime with the foreland forest needs, the regime given operation conditions being satisfied. A conceptual design of the gate system operation and the Tamiš System water level maintenance has been made. The design proposes an experimental period of the gate operation and water level maintenance, simultaneously with the research of the newly established regime impact on the woods.

[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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