Only a small fraction of this water enters the product, while the bulk of it is returned to nature, but in a changed, spent polluted state. The living world, however is sensitive to the quality of water.

The water demand of the society and the utilisable water resources are in a very complex interrelationship with each other, that changed and changes in time and in function of the social development and in that of the changes of the biosphere and the environment.

Apart from the Netherlands, Hungary has the most dense canal system (excess water drainage and irrigation canals) in Europe. The total length of Hungarian rivers is more than 2,800 km. The total length of small mountainous and hilly water courses is nearly 24,500 km, while the total length of flatland drainage and irrigation canals is about 40,000 km.

The objective of water regulation activities was first only the drainage of harmful excess waters and the protection against inundation, following the needs of the society. Available technical facilities have always affected the ways and means of water regulation.

In the 19th century and also until about the 1960-ies manual excavation works dominated the regulation of stream channels. In these projects the size and quantity of earth-works were confined to the minimum requirements.

Widespread propagation of earth moving machinery defined the technological options in the next phase. The economic operation of these machines dominated the technical and non-technical objectives. Increase of the excavated earth volume per unit stream length was demanded by the need of keeping the index of machine-utilisation at a desirable high level.

This resulted in relatively large cross section in the smaller streams. Namely, the state support given to local and public works was determined on the basis of the earth volume excavated.

Appearance of the machines brought along the need for the construction of appropriate access roads along the channels and this resulted in the removal of bushes and trees in the vicinity of the channels.

The mechanised maintenance of the channels (removal of grass, weeds and sediments) demanded tree and bush free cross sections and shoreline corridors. In many cases, mainly within the settlements, the stream channels were turned into canals.

As long as water regulation confiscated only small parts of natural land, it did not created hazards to human communities. Today, however, man is eliminating the very last remnants of natural habitats. This means that one has to stop these procedures and review the behaviour and practices of Mankind.

New approaches to water course regulation must be developed. This new concept has to recognise that each watercourse is a special, unique hydrological-ecological-hydraulic system.

Up-to-date, new demand towards water courses stem partly from the recognition of the harmful consequences of traditional ap-proaches and partly from the changes of the society and the ways of living.

A unified water management approach to the regulation of streams is needed in our modern times. The basic principle is that one shall drain only those waters, which cannot be retained and utilised with economically reasonable means.

The keeping of waters on the spot and allowing their infiltration, the storage of water, is an important task, because the retaining of water on the small catchment may help meeting local (small regional) water demands and can substantially reduce the costs of channel regu-lation.

Smaller flood flows will allow the making of smaller stream channels and less intrusion into the environment, keeping the channels in a near-natural condition.

One of the key elements of up-to-date, environmentally sound stream regulation is the establishment of a chain of reservoirs.

In regulating the watercourses one has to establish a grassed zone along the channels. Grass-bush-tree zones along the water courses and the keeping the valley bottoms in the meadow-pasture landuse form directly serves for the protection of the soil and has a favourable effect on runoff conditions and on the microclimate. Shadows of the trees will reduce water temperatures.

The joint effect of these factors will allow the avoiding of the excess growth of aquatic weeds, that unfavourably affected the water conveyance capacity, and the bank-slopes will also remain weed-free.

If the canopy of the trees can close over the stream channel the result is shadow and filtered sunlight. The undergrowth development will be such, which provides habitat for small mammals and birds, near to the water. The access road to the water may be formed among the trees, still allowing the moving of maintenance machinery down to the stream bank.

The interrelation of water and landscape must be strengthened. The channel shall be as near to the natural one as possible. Tree-trunks left in place can help keeping the stream-bank. Refuges of fish and other aquatic species can be provided in this manner.

The planning and implementation of near-natural stream regulation and the selection of the final solution can be made only in several phases. The planning procedure includes the following elements:

• preliminary studies,
• development of alternatives,
• costefficiency analyses and the
• final decision making.

Of the practical aspects of planning one shall underline those demands which necessitates the regulation of the streams. This includes the decreasing of the frequency of high-water inundation, the deepening of the channel, the decreasing of the groundwater level in the flood-berm and the widening of the channel as required by the tributary watercourses. The simultaneous occurrence of these demands can also be encountered.
Dr. Béla Hajós, C.E.

In: Vízügyi Közlemények
Vol. LXXXIII. Number 1/2001

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VÍZÜGYI KÖZLEMÉNYEK
István Hegedüs
H-1453 Budapest, Pf. 27.
E-mail: hegedus@vituki.hu

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