## THE GABCIKOVO PART OF THE HYDROELECTRIC POWER PROJECT GABCIKOVO-NAGYMAROS
ENVIRONMENTAL IMPACT REVIEW

#### Igor MUCHA

GROUND WATER Consulting Ltd., P.O.B. 6, 840 00 Bratislava 4, SLOVAKIA

CONCLUSIONS The main measures realised in improving the Danube water quality were the construction of sewage water treatment and industrial waste water treatment plants in Vienna, Bratislava and other upstream sites, and in the 80's refinery waste water treatment plants at the Schwechat refinery in Austria and Slovnaft in Bratislava. Since that time there are no "noticeable continuous coats on the river banks" of oil contaminants.

Based on research, various measures were proposed and realised. Some proposals were realised directly in the reservoir, the other in the river arm system of the floodplain area, all with the goal of improving the surface and ground water quality and to minimise eventual adverse effects. Others measures were realised over the whole Zitny ostrov area with the goal to improve the hygienic and living condition of the inhabitants.

The realisation of the Gabcikovo project mainly changed the following water regime aspects:

- Creation of the reservoir as a new biotope ranging from river conditions at Bratislava to a dynamic through-flowing reservoir with an increased water level in the original Danube river bed at and downstream from Bratislava, in the open river branches, and in the old river arms behind dikes and terrain depressions Rusovecke, Biskupicke, Chorvatske ramena river branches. New water areas and new stretches of the shore have come into existence mainly at Kalinkovo, Samorin, Cunovo. Previous pre(dam shores are no longer in existence, they are covered by water.
- In the floodplain area the discharge and the water level in the river arms have increased, and discharge is ensured continously at the year round. Shores of the river branches have generally moved towards inland. In the main Danube river bed, were the water level decreased, shores and river banks have moved at some places toward the river centre.
- In the inundation area, the ground water level has increased, except in the so called dry triangle and a strip of the old Danube riverbank, where the ground water level has decreased.
- In the upper part of the area the ground water level has recovered (increased( to the position known approximately 30 years ago.

The monitoring review has given an account of the most recent changes in the area influenced by the Gabcikovo hydropower structures. The authors in this issue show competent knowledge of their subjects and propose various measures to improve the development in the area influenced by engineering structures.

#### INTRODUCTION

Human activities, such as those that relate to large scale agricultural use, navigational river training, flood protection, surface and ground water resources, development of water energy potential including dams, and all other human activities such as forestry with planting and the management of forests, parks, the urbanisation of rural territories, traffic, housing, and even making policy, can considerably affect the natural environment, and this in a positive or negative way, according to the point of view and from which position the environment is viewed.

These effects occur during the construction phase, the operational life time of the structure or activity, and in many cases, as with waste disposals sites, may continue long after the primary activities. The consumption of natural resources, resource overexploitation, the generation of lasting waste and pollution, usually lead to a degradation of the urbanised, rural, and natural human environment. Renewable natural resources, such as hydropower and water, are therefore of special interest.

Project evaluation techniques have been evolved over the years stressing various priorities, often mainly the environment in relation to public health and diseases, and also flood, water, air, soil, waste disposal and industry, all as common subjects of hygiene, architecture and engineering. The project evaluation techniques best known at present are the Environmental Impact Assessment.

#### STATE OF THE HUMAN ENVIRONMENT AT THE BEGINNING OF THE PROJECT PREPARATION

Let us briefly review the conditions of human environment at the time of the preparation of the Gabcikovo project from the point of view of hydrobiology, water quality and the public health conditions on the area of Zitny ostrov, long before signing the Treaty in 1977. In this connection we rely on two publications: "Vodo-hospodarsky casopis" (Water economy journal) published by the Slovak Academy of Sciences in 1957 and journal "Nasa veda" (Our sciences) in 1957. In the first one Mucha V., et al. writes: "In 1954(1955 we had the task to find out the indicators and dynamics of pollution and self purification of the Danube water using physical, chemical, hydrobiological and hydromicrobiological methods. Our results should serve technicians, farmers, hygienists and engineers during the construction of hydropower structures."

The following summary from the paper should give us a picture of the situation when the Gabcikovo-Nagymaros project was in the "larval" stage, the first stage of development after being hatched. It should be stressed that the common subjects of nature, hygiene, architecture and engineering were part of the project preparation and evaluation at that time.

Growth of the microflora and microfauna in the river Danube water is dependent upon a whole set of factors which are very often antagonistic, e.g. oxygen and organic pollutants. This is expressed for example in the composition of bioseston in the river. The high content of oxygen in summer, a rapid and aerated water flow, a relatively low water temperature, all support the survival of stenotopic forms of psychrophilous species, for example Synura uvella, Malomonas sp. div., Chantransia sp., Asterionella formosa, Ceratoneis arcus, Tabelaria fenestrata, these being indicators of clean, oligosaprobic water in the Danube. Long-lasting pollution of the Danube water by communal waste water from Vienna and Bratislava and polluted water from the river Morava, mainly in the autumn, and further the large growth of vegetation in the dead and the non-flowing river arms, gave rise to typical saprobionts such as Colpidium, Cyclidium, Paramecium, Stentor, Vorticella; and from the producents to a whole set of the species of the family Chlamydomonas, these being representatives of water polluted, up to alphamesosaprobic levels.

When evaluating the water quality it is not possible to rely on the benthos and the littoral perifiton as a criterion for the quality of the river bed. The existence of zoobenthos is eliminated by the high water flow velocity and the moving river bed. Littoral is strongly influenced by organic contamination (mineral oils, crude oil, phenols etc.(, which are creating noticeable, continuous coats on the river banks at the water level fluctuation zone. This zone therefore has a permanently alphamesosaprobic character (Cladophora glomerata, Galba truncatula and others). The intense growth of organisms in this zone is therefore not characteristic of the Danube water quality, but characteristic of the decomposition processes of organic matter of contaminants found on the river bank in a compact black(brownish layer. (The situation at that time, in 1957, was similar to that of all the other European rivers.)

In the lentic zones of the Danube river bed there was found a possibility for the growth of floating weeds (e.g. algae) and other organisms. Under the waste water contamination conditions of the Danube (in 1957), it is necessary to take into account, from the hygienic point of view, the permanent decrease in the water quality in the reservoir, after the construction of the hydropower structures, when speaking about the prognosis of the reservoir water quality. This contamination will support the growth of phytoplankton, zooplankton and bacteria(plankton, which will further deteriorate the reservoir water quality and its chemical composition. Anaerobic mineralising of organic sediments, and the decomposition of oil, tar and phenol substances will indirectly do harm to the construction. Therefore we are calling attention to the necessity of realising of preventive measures.

All of the above is from the referenced paper published in 1957, based on the first scientific research done in the framework of the preparation of the Gabcikovo-Nagymaros project.

The main measures realised since that time in improving the Danube water quality were: the construction of sewage water treatment and industrial waste water treatment plants in Vienna, Bratislava and other upstream sites; oil refinery waste water treatment at Schwechat in Austria and Slovnaft in Bratislava (in the 80's). Since then the "noticeable continuous coats on the river banks" of oil contaminants have been eliminated.

And now let us look at the paper published in the instructive journal "Our Science" in 1957, entitled "Sanitation problems in the Zitny ostrov area in connection with the planning of hydropower structures on the Danube" written by V. Mucha. The paper informs us that research done in connection with the Gabcikovo-Nagymaros project had already started in 1953. Scientists from the Czechoslovak and Slovak Academy of Sciences, Comenius University, various research institutions and sanitation institutions took part in the research.

Let us mention some field results which were investigated up until 1957, in order to establish the real situation in the territory at the beginning of the preparation of the Gabcikovo-Nagymaros project, and the problems which were necessary to solve at that time.

It was confirmed that, apart from Komarno and some other villages, inhabitants were supplied with water from private, shallow dug wells, which often contained water defective, which was from a hygienic point of view. Treatment of manure and human excrement was not satisfactory, facilities were often thoughtlessly constructed, and the inherent sanitary danger was evident. A proposal for the construction of new, deep, municipal water supply wells was therefore made by F. Stein. According to the plan, 36( of the inhabitants were to be connected to the municipal water supply system by 1962. Sewage canalisation had to be included in the construction. These measures were necessary mainly in the regions where the ground water level had to change a great deal after the construction of hydropower structures. In addition, in 14 villages, close to the construction sites, new flats with a dwelling area of 7200 m2 were proposed to be built. In addition, the construction of modern roads and the creation of green zones in the villages were proposed.

The region of the Zitny ostrov island was defined as an area with endemic hyperthyroidism (enlargement of the thyroid gland), and the Endocrinology Institute proposed proper measures. During the research it was found that there was a high occurrence of helminthoses, bacterioses, leptospiroses, viroses and protozoan human diseases. In the framework of activities against malaria and other insect-borne diseases, water areas and bogs were investigated and it was confirmed that these were breeding and hiding places of mosquitoes, including mosquitoes of the species Anopheles maculipeunis transmitting malaria at that time. Proposals for the protection from insect-born diseases, mainly malaria, were instituted and realised. Specialists from the Faculty of Natural Sciences confirmed 6 species of sheep-tick, and at the Virological Institute it was confirmed that some species transmit the sheep-tick virus encephalitis. It was confirmed that a large infestation of people occured, most with the parasite worms of the species Enterobius vermicularis, and also some with Trichuris trichiura and Ascaris lumbricoides. At some places it was ascertained that there were worms of taenidosis, strongiloidosis and hymenolepidosis. The last two worms are known from tropical countries and were also found in Hungary.

Sheep, cattle, and pigs were infested with parasitic worms. Approximately 70 ( of sheep were attacked by Fasciola hepatica (motolica), of which the intermediate and usual host is the snail Galba truncatula (Bahnatka mala). Pigs were infected by the worm Ascaris suis, from which germs can be transmitted to human lungs. In the area of the project the mouse Apodemus flavicolis (Rysavka lesna) and the domestic mouse Mus musculus are hosts of L. sejrö, which also causes diseases in men. Insectivore hedgehogs, field mice, rats and other small mammals were infested with leptosprosis and were infecting domestic animals. For example, up to 30 ( of pigs and also some butchers and cooks directly working with pork were infected. Because of the sanitary and biological research results, it was only prudent to assume that in the region of the project some groups of the diseases could increase, mainly in the areas with increased moisture.

#### REVIEW OF SOME SCIENTIFIC ACTIVITIES

Limnological aspects of the Slovak stretch of the Danube were comprehensively researched and published in "Limnology of the Czechoslovak stretch of the Danube" prepared by Mucha V. et al. in 1966. The book reviews the following important topics:

- Hydrology and hydrogeology of the Czechoslovak stretch of the Danube, by Dub O., Duba D., Szolgay J.
- Climate of the Danube region, by Koncek M.
- Hydrochemistry of the Czechoslovak stretch of the Danube and its tributaries, by Antonic M. and Jacko R.
- Radiochemistry of the Czechoslovak stretch of the Danube, by Mayer J.
- Hydromicrobiology of the Czechoslovak stretch of the Danube, by Mucha V. and Daubner I.
- Saprobiology of the Czechoslovak stretch of the Danube, by Rothschein J. and Hanzlikova G.
- Ichtyofauna of the Czechoslovak stretch of the Danube, by Balon E. K.

With respect to international co-operation (in the framework of the "Arbeitsgemeinschaft Donauforschung"), the monography entitled "Limnologie der Donau" published by Prof. R. Liepold in the period 1965 to 1967 is of large importance. On the complex limnological research of the Danube in 1961 took part following Slovak institutions: Institute of Experimental Medicine of the Slovak Academy of Sciences (SAV), Water Research Institute, Biological Institute of SAV, Institute of the Hygiene of the Ministry of Health Service, Laboratory of Fishery, and also various institutions of the Czechoslovak Academy of Agricultural Sciences and others. The main topics of the international publication are:

- Climate of the Danube region, by Koncek N.
- Hydrology of the Danube, by Laszlófy W.
- Paleogeography of the Danube, by Fink J.
- The physical and chemical qualities of the Danube water, by Knie K (and Almazov A., M., Antonic M., Ardelean I., Backhaus D., Dragasanu St., Dvihally-Tamas S., Gederin V., Georgiewa-Mateewa E., Hamm A., Huber L., Marki E., Maistrenko J., K., Nümann W., Petrovic G., Reimann K., Rojdestvensky A.V.(
- The radioactivity of the Danube, by Frantz A.
- Metabolism of organic substances of the river Danube, by Knöpp H.
- Biology of the Danube, by Elster H-J., Liepoldt R
- System of fauna and flora, by Dudich E., Szemes G.
- Microbiology of the Danube, by Mucha V.
- The phytoplankton of the Danube, by Szemes G.
- The zooplankton of the Danube, by Enaceanu V.
- The ichthyofauna of the Danube, by Busnita T.
- The phytobenthos of the Danube, by Szemes G.
- The zoobenthos of the Danube, by Weber E.
- Dammed regions, by Weber E.
- The phreatic fauna associated with the Danube stream deposits, by Schwoerbel J.
- The Danube delta, by Rudescu L.
- Zoogeography of the Danube system, by An der Lan H.
- Biological consequences of man's interference, by Libmann H. and Reinbach-Klinke H.
- Fishery and fishery economy, by Busnita Th.
- Energy, by Wagner H.
- Navigation, by Fekete G.
- Industry, by Eckl E.
- Agriculture, by Welev D.
- Forestry in the inundation area, by Wendelberger E. and Wendelberger G.
- Historical and cultural correlation between human beings and stream, by Kaut H.

In 1968 the Slovak Academy of Sciences published a monograph book entitled "Ground water hydrology" written by prof. D. Duba. The book characterises ground water hydrology in river-side areas, hydrological methods used, and some examples of selected experimental modelling solutions, as for example the prognoses of ground water levels after the construction of the Gabcikovo hydropower structures.

The bibliography of zoological publications about the Danubian lowland region and the surrounding country along the Slovak stretch of the Danube, elaborated by Kalivodova et al. for the period up until 1985, contains 1979 works written by 729 authors (see Stepanovicova in this issue(. The basic work dealing with fauna in the Danube is that of Brtek and Rotschein (Ein Beitrag zur Kenntnis der Hydrofauna und des Reinheitszustandes des tschechoslowakischen Abschnittes der Donau, Bio. Prace, 10, 1964(, containing an inventory of species.

Floodplain forests of the Danube lowland have been the object of a number of botanical studies. A privileged place in this respect belongs to "Soil-ecological conditions and forest communities of the Danube lowland" written by Jurko and published by the Slovak Academy of Sciences in 1958.

Based on this research and other research not mentioned here, technical research, and the research carried out up to present, various measures were proposed and realised. Some proposals were realised directly in the reservoir and in the river arm system of the floodplain area, with the goal of improving the surface and ground water quality and minimising eventual adverse effects, and others were realised in the whole Zitny ostrov area, with the goal of improving the hygienic and living conditions of the inhabitants.

#### ENVIRONMENTAL IMPACT REVIEW

Numerous regulations and guidelines for environmental impact assessment (EIA) exist. One of the most important is the Council Directive of the Commission of the European Community (CEC, 1985). The Directive requires a comprehensive environmental assessment of projects. An EIA requires that qualitative and quantitative predictions be made of the impacts of projects on the environment. Such predictions are based on more or less empirical knowledge, on more or less explicit and usually qualitative understanding of how things may work. In hydropower projects and water resource impact assessments, there exists a substantial amount of physically based modelling methods where the understanding of how things really work can be expressed a little bit more quantitatively. In the environmental assessment, much of our quantitative "understanding" is empirical, sometimes based on experience in very different natural conditions.

The long-term pre-dam hydrological monitoring system, the long-term monitoring of forestry, and the monitoring of some other aspects of biota, enable us to present in this issue the Environmental Impacts Review (EIR( after 2 years of Gabcikovo Variant C operation in comparison with pre-dam development. Monitoring and interpretation experts contributed to the knowledge of pre-dam and present conditions, and these views, from their various historical and personal positions in relation to the Gabcikovo-Nagymaros project.

The main difference between an EIA and an EIR is that an EIR is based on data measured before and after putting the hydropower project Gabcikovo, Variant C, into operation. An EIR can compare pre-dam development with the present one.

However, a river engineering project such as Gabcikovo-Nagymaros, which is certain to have many effects on the surrounding nature, even if mainly positive, requires the analyses of these effects through permanent monitoring. The monitoring of the effects on the surface and ground water quality, in ground water levels in the zone of aeration, and soil moisture levels and treir effects on flora and fauna, yields immediate results. It is certain that if, within a short period, even minor adverse effects start to appear, severely adverse results will be seen and may be expected in later years if no preventive or mitigating measures are taken. But such measures may be taken and may be altered if necessary and many of them were taken during the construction of the engineering project. In addition, the Gabcikovo engineering project includes a wide variety of tools for surface and ground water management and thus also for the management, or optimisation, of the development of agricultural biotopes, inundation biotopes, forest biotopes, management of floods and flooding of some areas, sedimentation and erosion processes, ground and surface water quality, and other environmental effects management.

The assessment of the adverse impact to soil, flora and fauna is almost exclusively premised on the contention that the engineering project would cause a decrease in the ground water level. This contention has no basis. On the contrary, monitoring measurements showing a decrease in the ground water level are of high value, because the identification of proper measures can be made when combined with the specification of impacts on monitored parameters and organisms. A typical example, in nearly all the published contributions in this issue, is the locality Dunajske kriviny. From the ecological point of view the problem is not in the shifting of biotops, as it is in other places of inundation, but the aridisation of a relatively small area and the introduction of species stranger to previous and surrounding biotops. On the other hand, monitoring precisely states the necessary measures, which are in this example the supply of Dunajske kriviny with water from the ready made intake structure at Dobrohost, and the increase in the ground water level by increasing the water level in the old Danube by means, for example, of a submersible weir. By how much the ground water level should be increased is clear from figures by Hlavaty and Cambel - in this issue.

Monitoring of the effects of the engineering structures goes hand in hand with management. Monitoring is realised with the goal of improving development after completion of the project, minimising the negative impacts and optimising all possible outputs of the project, including energy, transport, natural conditions, water supply, agriculture and the others.

Water engineering projects are characterised by changes in the water regime. Usually they change flows in surface waters, surface water levels, the course of floods, ground water levels, etc. The realisation of the Gabcikovo project mainly changed the following water regime aspects:

- The creation of the reservoir as a new biotope ranging from river conditions at Bratislava to a dynamic through-flowing reservoir. This with an increased water level in the original Danube river bed at and downstream from Bratislava, in the open river branches, and in the old river arms behind dikes and terrain depressions. New water areas and new stretches of the shore have come into existence. Previous pre(dam shores are no longer in existence. They are covered by water.
- In the floodplain area, the discharge and the water levels in the river arms have increased. Shores of the river branches generally have moved inland. In the main Danube river bed, were the water level decreased, shores and river banks have moved at some places toward the river centre.
- In the inundation area, the ground water level has increased, except in the so called dry triangle and a strip of the old Danube riverbank where the ground water level has decreased.
- In the upper part of the area the ground water level has recovered (increased( to a position known approximately 30 years ago.

  Monitoring is based on sampling and measuring of data. In general, there are two types of sampling, probability sampling and nonprobability sampling. The probability sampling means that each item in the population has a chance of being chosen. In nonprobability sampling methods not all items have a chance of being included in the evaluation process. This means that the monitoring results may not be representative of the population. Method of stationary plots used in biota monitoring corresponds to the cluster sampling method, based on subdividing the whole monitoring area into primary units named monitoring areas, plots, places, etc. Monitoring areas, plots, stands, etc., are not situated randomly (see a map of monitoring areas, description of monitoring plots and places of sample collections in papers in this issue).

  The method of monitoring using stationary monitoring stands and plots is not very suitable in these cases, because there is generally not an extinction of biotopes, but a shifting of the biotopes according to hydrological changes. Using such monitoring will always result in a negative interpretation if the pre(project or pre(dam state is considered as the original and natural one. Comprehensive monitoring and its interpretation should therefore monitor the long-term pre-project development and should also use, apart from properly distributed stationary stands, moving observation stands which follow the movement of the biotope conditions. In addition, profiling and regional screening and mapping methods should also be used.

  The comprehensive environmental impact review should also look at the positive impact (i.e., environmental improvement in relation to the long term environmental development and immediate positive changes( from the point of public health principles and practices, direct improvement by material substitution, hydropower replacement of fossil fuel, microclimate improvement, improvements in technological needs, e.g. improvements in water supply, irrigation, navigation, etc. It is necessary to include the improvements due to the increased revenues as a consequence of a new development project, e.g. income to the government and county public funds. The most universal, trustworthy and reliable method for the environmental impact review is the interpretation of monitoring. Such interpretation should be compared with pre(project conditions, the so called zero state, and with the long(term pre(project trends in the development of the environment.

  This publication is the first attempt at an environmental impact review after two years of the hydropower structures operation.

  #### INTERCONNECTION BETWEEN HYDRAULIC STRUCTURES AND TERRESTRIAL ENVIRONMENT

  The operation of the water engineering structures has a direct impact on the regime of surface and ground water. This impact is transferred to other components of the environment directly or indirectly via the zone of aeration. The direct impact is the change of the river banks, lakes, creation of the reservoir and new lakes, changes in the discharge and water levels in the river and the river arms. The indirect impact to the terrestrial environment is via the zone of aeration. This zone is delineated between the ground surface and the ground water level. Changes in the soil moisture and the thickness of the zone of aeration as a response to changes in the hydrological regime are responsible for the changes in the biota of terrestrial organisms. Of course there also exist other factors influencing the zone of aeration or the biotopes directly. Among these factors, the most important are the climatic variations, air and water pollution, forest management and harvesting and human disturbances.

  Monitoring of the zone of aeration helps us to identify the real impact of the Gabcikovo structures on biota. The Gabcikovo structures are influencing the adjacent environment through changes in the ground water level in comparison to the ground water level without the impact of the structures. These changes are manifested through changes in the soil moisture in the zone of aeration. If there is an increase in the ground water level due to the construction of hydropower structures, then there is also usually an increase of soil moisture in the zone of aeration, although occasionally the moisture may remain unchanged at some depths, but there is in no case a decrease in the soil moisture caused by the engineering works (when the ground water level increase(. Reciprocally the same is valid. If there is a decrease in the ground water level due to the construction of the engineering structures, then there is also a decrease in the soil moisture in the zone of aeration, or the situation may be unchanged at some depths, but there is in no case an increase in soil moisture caused by the engineering works. Therefore, areation zone impacts of the ingineering works are directly related to changes in ground water levels: a higher levels correspond to equal or greater moisture, a lower level to equal or less moisture. Monitoring of the soil moisture in the zone of aeration can help us to make decisions concerning which measures, and to which extent should be realised.

  Results of monitoring are usually described as statements, corresponding to hypothesis. Such statements should be tested, and this using deterministic criteria and probability theory, to determine whether the monitoring statement based on sampled data is reasonable statement and should be accepted, or is unreasonable statement and should be rejected.

  #### PROPOSALS RESULTING FROM THE MONITORING REVIEW

  The monitoring review has given an account of the most recent changes in the area influenced by the Gabcikovo hydropower structures. At the end of the monograph we would like to review the main proposals expressed in the individual contributions.

  #### Climate

  Evaluation of the climate suggests a small but favourable effect on the local climate conditions, contrary to the progress of the long(term climatic changes. This is a good reason to continue monitoring and studying factors acting against the trend of negative climatic changes. Such monitoring can also help the decision making in other Slovak and European projects.

  #### River Danube water levels and morphology

  From the monitoring of the zone of aeration (Hlavaty, Cambel, Sutor in this issue( at stationary monitoring plots at Dunajske kriviny and along the bank of the old Danube, including monitoring of the biota, it is clear that some increase of the ground water is still necessary. At these monitoring places there are various factors acting. First of all there are the river arms, which are supplied by water, and the old river Danube, with regular discharges from 250 to 600 m3/s at present. Other influencing factors are the geological conditions of the soil moisture profiles. When taking into consideration all the results of the monitoring, the goal of increasing the water level from 1 to 2 m at some places in the old Danube is reasonable. This confirms the view of the EU experts, that, at some places, "shallow" submersible weirs or fortified natural fords should be created. Such submersible weirs and fords allow velocities of water flow to be kept in the acceptable range. Weirs and fords could be shaped to allow small ship navigation and compensation navigation, if necessary. This can be successfully solved by modelling. In the area of Istragov this should be combined by interconnection of some river arms with the old Danube. At other places such one or two way interconnections should be created with the help of some shallow submersible weirs. The type of submersible weir as was constructed in rkm 1843 is not acceptable at other places, because the upper and mainly the "airy" side of the weir is too steep. A natural meandering of the old Danube inside of the fortified banks, the natural rising of islands, and new river banks and natural river fords should be supported.

  #### River branch management

  In the upper part of the river branch area at the locality Dunajske kriviny, the small, old, dead river arm should be supplied by water from the intake structure at Dobrohost. This, combined with a submersible weir (see Hlavaty, Cambel(, can successfully solve the present negative situation described by various authors (in this issue).

  In the upper part of the river branches supplied from the intake structure at Dobrohost, the ground water level, from the view point of commercial forestry, is too high (Nesticky). This problem can be solved by constructig some new interconnections between the compartments, which could, at the same time, be suitable fish passages. In the lower part, the last 3 kms of the river branches at the Gabcikovo harbour, the ground water level and water level in the branches is too low. This can be solved by an underwater weir just downstream from the confluence of the old Danube and the main river arm .

  For the ground water boundary conditions the river arms are of mixed type (Cauchy's conditions or conditions of the third type). This should be utilised together with the Danube discharge for evoking sufficient ground water level fluctuation and the seasonal winter decrease of the ground water level.

  According to the monitoring results it is necessary to inundate the area from time to time. Flooding of the inundation area should follow the natural discharge in the Danube. It should be in agreement with the needs of the commercial forestry and the natural forest vegetation and it should be timed to agree with the fishery. Such water management in the inundation area should be proposed and elaborated using modelling methods.

  #### Reservoir

  During the nesting of waterfowl, in the breeding period of May and June, the water level should be kept as constant as possible (Darolova in this issue(. Such a situation is envisaged and can be ensured in spite of natural floods. Nesting places in the shallow water area opposite to Rusovce village are at the neutral point in the reservoir where the changes of water level are minimal (few centmeters( despite large changes in discharge.

  During a low discharge in the Danube and high water temperatures (such that real eutrophication conditions exist), a decrease of water level and a fluctuation of water level in the reservoir could be used. Monitoring of the reservoir water quality and eutrophication during the summer period will give a basis for optimal reservoir water level and velocity control.

  #### Ground water supply

  Monitoring of the ground water quality should continue on all available and reliable observation and water supply wells. Areas of high quality ground water and perspective areas of potable ground water supply should be estimated and properly protected.

  #### Water and insect-borne diseases

  Water, insect, worm and animal borne and transmitted diseases and parasites are of special interest. Possible infecting agents, transmitters and hosts should be carefully monitored together from the point of biota and public health.

  #### Fisheries

  Fish passage facilities should be constructed, where they are likely to be effective, e.g. between the main river bed and river arms. Reservoir fishery management and river branch fishery should be developed. Regulation of fishing should be instituted. (Cerny, Kirka, Holcik in this issue(. Optimal flooding of the area is suggested.

  #### MONITORING AND DEVELOPMENT

  It is important to realise that the monitoring system is certainly no substitute for many time tested methods and models, but should be seen as a complementary method which can improve and test our knowledge and the input and output data of these models. When integrated with database management, graphics, information system and models, monitoring can help to develop new environmentally friendly methods of planing and management in water engineering.

  The aim of this publication is to reconcile the differences of opinion between engineers and environmentalists and, using monitoring results, to show that the progress in environment and in improving the quality of human life can continue to develop only through improvements in wisdom, knowledge, organisation and technical efficiency.

  Figure 1.