Szigetköz - Temporary Water Management Regime, 1993

EXECUTIVE SUMMARY

BACKGROUND

As a follow-up of the 'Special Agreement for Submission to the International Court of Justice of the differences between the Republic of Hungary and the Slovak Republic concerning the Gabcikovo-Nagymaros Project' a Group of Monitoring and Water Management Experts for the Gabcikovo System of Locks (Working Group) was established by the Republic of Hungary, the Slovak Republic and the Commission of the European Communities (CEC).

The tasks of the Working Group fall in two parts:

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On the basis of available data to assess the impacts of the Gabcikovo Project and to prepare recommendations for strengthening the monitoring system in the area.

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Preparation of recommendations for a Temporary Water Management Regime as well as for necessary discharges, water levels and remedial measures.

The present Data Report is the Final Report of the Working Group dealing with the Temporary Water Management Regime. The first aspect was dealt with in the Data Report, finalized in Budapest on November 2, 1993.

The Working Group has obtained all the relevant data and information requested from the two Governments. The report is based on this information.

ELABORATION OF FIVE SCENARIOS

In the present report five scenarios with different characteristics on discharge regime and remedial measures have been elaborated. All the five discharge regimes are dynamic and characterized by the below average values. The five scenarios and their most important impacts can be summarized as follows:

Scenario 0: November 1993 Situation

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Old Danube: 400 m³/s

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Slovakian side branches: 40 m³/s

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Hungarian side branches: 10 m³/s

The key impacts are as also described in the Data Report:

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The environmental conditions on the Hungarian inundation area are bad due to lack of water.

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The flow velocities and water levels in the Old Danube are too low for providing suitable living conditions for typical flora and fauna.

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The lack of connections between the main channel and the side branches prevents migration of wetland species.

Scenario 1: Increased water supply to the Hungarian Side Branches

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Old Danube: 400 m³/s

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Slovakian side branches: 50 m³/s

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Hungarian side branches: 50 m³/s

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1-3 floods of more than 3500 m³/s are expected to occur each year in the Old Danube.

The key impacts as compared to Scenario 0 are:

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Improvements of the environmental conditions for the Hungarian inundation area.

Scenario 2: Increased Discharge in Main River and in Hungarian Side Branches

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Old Danube: 800 m³/s

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Slovakian side branches: 50 m³/s

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Hungarian side branches: 50 m³/s

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1-3 floods of more than 3500 m³/s are expected to occur every year in the Old Danube.

The key impacts as compared to Scenario 1 are:

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Improvements of the main river environment to a level where species requiring higher flow velocities (e.g. fish) have suitable living conditions.

Scenario 3: Construction of some Underwater weirs

Scenario 3 is basically identical to Scenario 2 except for construction of a number of underwater weirs.

The key impacts as compared to Scenario 2 are:

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The connections between the main channel and the side branches on both sides are maintained or even improved as compared to pre-dam conditions.

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For discharge not exceeding 1000 m³/s the flow velocities in the Old Danube are not sufficient for maintaining the typical flora and fauna.

Scenario 4: Fu11 Capacity of Variant C Structures used for Water Supply of the Main River and the Branches

In Scenario 4 as much water as technically possible will be diverted into the Old Danube and the side channels. However, this will technically not be possible until after the summer of 1996.

CONCLUSIONS

None of the described scenarios are free from key environmental problems. Furthermore, different scenarios result in different environmental problems, which are not directly comparable. Scenario 2 and Scenario 3 show that some environmental problems can be reduced by increasing discharge and remedial measures. .

In addition to the environmental aspect also economical aspects should be considered. In this respect it may be noticed that the value of the present electricity production of 2000 GWh/year is in the order of 50 - 100 million ECU/year. For comparison the electricity production will be reduced by about 30 % in Scenario 2 and 3. The costs for implementation of the remedial measures range between 2 and 12 million ECU depending on the scenario.

RECOMMENDATIONS BY THE EC MEMBERS OF THE WORICING GROUP

None of the described scenarios can be recommended without modifications. Therefore the three EC members of the Working Group will recommend a combination of elements from different Scenarios.

Objectives

The overall objective of the recommended Temporary Water Management Regime is a minimization of any irreversible developments.

The primary objectives are to enable as good environmental conditions as possible within the given discharge constraints, whereas the secondary objective is electricity production.

Discharge regime

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Old Danube: 800 m³/s

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Slovakian side branches: 50 m³/s

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Hungarian side branches: 50 m³/s

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1-3 floods of more than 3500 m³/s are expected to occur every year in the Old Danube.

Remedial measures

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Improvement of the daily discharge capacity of Variant C structures from this present 600 m³/s to 940 m³/s by May 1994.

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For environmental purposes an underwater weir at RKM 1835 enabling direct contact between the main river and the Slovakian side branches at one upstream point of the Slovakian floodplain.

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For operational purposes an underwater weir at RKM 1845.5. This underwater weir will significantly improve the reliability of the day-to-day water supply through the inundation weir and it will ensure water supply to the Hungarian floodplain.

Day-to-day Operation

Improved operation rules for the day-to-day operation of the water management within the above given discharges has be implemented in order to obtain as good environmental conditions as possible.

Environmental Impacts

The recommended Temporary Water Management Regime is believed to ensure that minimum irreversible environmental developments take place during the few years the temporary regime is supposed to last.

It is furthermore recommended to maintain a detailed environmental monitoring including taking the steps to strengthening the present monitoring system as recommended in the Data Report.

Design Review of Spillway of Inundation Weir

The spillway of the inundation weir is a key issue in terms of discharge possibilities, reliability, time schedule and costs. As no comprehensive design exists for its daily use a design review is recommended to be carried out by an independent, specialized institute.


	*	On the basis of available data to assess the impacts of the Gabcikovo Project and to prepare recommendations for strengthening the monitoring system in the area.

	*	Preparation of recommendations for a Temporary Water Management Regime as well as for necessary discharges, water levels and remedial measures.


	*	Old Danube: 400 m³/s

	*	Slovakian side branches: 40 m³/s

	*	Hungarian side branches: 10 m³/s


	*	The environmental conditions on the Hungarian inundation area are bad due to lack of water.

	*	The flow velocities and water levels in the Old Danube are too low for providing suitable living conditions for typical flora and fauna.

	*	The lack of connections between the main channel and the side branches prevents migration of wetland species.


	*	Old Danube: 400 m³/s

	*	Slovakian side branches: 50 m³/s

	*	Hungarian side branches: 50 m³/s

	*	1-3 floods of more than 3500 m³/s are expected to occur each year in the Old Danube.


	*	Improvements of the environmental conditions for the Hungarian inundation area.


	*	Old Danube: 800 m³/s

	*	Slovakian side branches: 50 m³/s

	*	Hungarian side branches: 50 m³/s

	*	1-3 floods of more than 3500 m³/s are expected to occur every year in the Old Danube.


	*	Improvements of the main river environment to a level where species requiring higher flow velocities (e.g. fish) have suitable living conditions.


	*	The connections between the main channel and the side branches on both sides are maintained or even improved as compared to pre-dam conditions.

	*	For discharge not exceeding 1000 m³/s the flow velocities in the Old Danube are not sufficient for maintaining the typical flora and fauna.


	*	Improvement of the daily discharge capacity of Variant C structures from this present 600 m³/s to 940 m³/s by May 1994.

	*	For environmental purposes an underwater weir at RKM 1835 enabling direct contact between the main river and the Slovakian side branches at one upstream point of the Slovakian floodplain.

	*	For operational purposes an underwater weir at RKM 1845.5. This underwater weir will significantly improve the reliability of the day-to-day water supply through the inundation weir and it will ensure water supply to the Hungarian floodplain.