8. Slovak - Hungarian Agreement and the underwater weir

On April 19, 1995, the Governments of the Slovak Republic and the Republic of Hungary signed an "Agreement between the Government of the Slovak Republic and the Government of Hungary about Certain Temporary Measures and Discharges to the Danube and Mosoni Danube" [6].

The specification of water management measures according to the "Agreement" are as follows:

  • Increase the water discharge into the Mosoni Danube from 20 to 43 m3/s via the Čunovo intake structure, under certain assumptions of hydrological and technical conditions specified in the "Agreement".
  • Distribute this water on the Hungarian territory into the river branches on the right side of the Danube, into the protected area, and into the Mosoni Danube.
  • Increase and regulate the discharge into the main Danube downstream from the Čunovo weir, to values between 250 and 600 m3/s - 400 m3/s on average - according to rules specified in the appendices to the "Agreement".
  • Construct an underwater weir in the main Danube at Dunakiliti (Hungary), (river kilometre rkm 1843) to increase the water level in the Danube upstream from the weir, connect the Danube with the Hungarian river armsby openings in the river banks and regulate the supply of the Hungarian river branches with water up to 130 m3/s or even more.
  • Collect and exchange the environmental monitoring data which are necessary for an analysis of the impact of the mentioned measures
  • Prepare National annual reports.
  • Prepare Joint annual reports.

The results of the "Agreement" ensured the following surface water regime:

  • The discharge into the Mosoni Danube increased, is regulated, and is permanently ensured throughout all the year round. Water is distributed into the Mosoni Danube arm, the Zatonyi Danube arm and other Hungarian branches.
  • The Hungarian river branch system in the flood-plain is permanently and sufficiently supplied with water. Water levels and discharges are regulated by the Dunakiliti weir and inside the Hungarian river branch system, similar to the Slovak cascades with culverts.
  • The water level raised in the Danube river bed, upstream from the underwater weir at Dunakiliti, and as far as the Čunovo weir.
  • These measures have also raised the ground water level.

After putting the Gabčíkovo part of the project into operation, a 20 m3/s discharge was released by the Slovak Water Authorities at the Mosoni Danube intake into the seepage canal. From October, 1994, in accordance with the agreement between the Slovak and Hungarian parties, this amount was increased to 40 m3/s. [10, 7]

The underwater weir, constructed in the framework of the joint Slovak - Hungarian Agreement, is situated opposite the already constructed Dunakiliti weir on the Hungarian side. The Dunakiliti weir is the point where the Čunovo structures join the structures and dikes of the original Gabčíkovo-Nagymaros Project. The structures are situated in Slovakia and inside of the original project area. The goal of the Čunovo complex is the same as had been the goal of the Dunakiliti weir, to impound the water, to put the Gabčíkovo hydropower station into operation, and to open a new international navigation corridor via the diversion canal and ship-locks at the Gabčíkovo hydropower station.

From the 23rd of June, 1995, the increased water level caused by the underwater weir and the Dunakiliti weir allowed, in general, a 40 - 130 m3/s discharge of water into the branch system of the Hungarian flood-plain, directly from the Danube. The water level of the main channel of the flood-plain was raised by 1 m on average. Thus, some side branches, formerly totally dry (as a result of long term development and not construction of projected measures), could to some extent be supplied with water again [10,7]. These main channel and side branches are now directly connected with the Danube by openings in the river bank. The water level upstream of the underwater weir is on a level of about 123 m a.s.l. and is regulated by the Dunakiliti weir.

Regular measurement of surface water quality was carried out for many years before damming the Danube [9, 10, 7]. Long term monitoring of the Danube water shows improvement of the Danube water quality, especially in the amount of organic matter, plant nutrients, nitrogen and phosphorus [7].

The water quality alongside the Mosoni- Danube depends on a number of conditions. The most important factor is the water quality of the tributaries Lajta, Rábca and Rába [10], according to the Hungarian report. The quality of the Mosoni Danube water, mainly in the upper part, was substantially improved and resembles the Danube water quality. In the past, before building the intake structure into the Mosoni Danube, water stagnated in the upper part of the Mosoni Danube, and side river branches were without water or only with stagnant water. For most of the year the Mosoni Danube was disconnected from the flow in the Danube.

It is obvious that when interpreting the impact of water management measures according to the "Agreement", ground water has an identification role for estimating impacts upon the natural environment. If the ground water level rises, more water is at nature’s disposal; if the ground water level lowers, less water is at nature’s disposal. A decrease of soil moisture in the inundation area, or flood-plain, is generally considered as a negative impact, an increase as a positive one, especially if the previous pre- dam long- term development demonstrated a long term continuous trend of lowering of ground water level.

The underwater weir at Dunakiliti increased the water level in the Danube riverbed, upstream to the Čunovo structures. Discharges into the Hungarian flood-plain branches via openings in the Danube river bank were usually around 100 m3/s, with the regulation at the Dunakiliti weir ( regulation of water levels) from 30 m3/s or less to 130 m3/s and more. This substantially increased water levels in the whole Hungarian branch system and also supplied previously dry arms. The discharge into the Mosoni Danube of approximately 40 m3/s increased water levels and discharges in comparison with the pre-dam conditions (1992)

The area where there is a visible impact of measures is according to the "Agreement", defined as at least from the river branches lying closest to the Danube up to at least the Mosoni Danube river arm, and from Čunovo downstream to the Mosoni Danube inlet into the Danube at Győr. In reality, impacts exist from the Danube to the area behind the Mosoni Danube. On the Slovak side, the impact of these measures is minimal, usually not measurable, and occurs only on the right side downward from Čunovo village and between the Danube and the reservoir from Čunovo to Dunakiliti. In general, the impact of measures realised according to the "Agreement" is visible in the whole Hungarian flood- plain and on the whole area of Szigetköz.

In the following, we explain changes in the ground water levels in the Hungarian Szigetköz area using jointly exchanged data from the Szigetköz area and using the Hungarian report [14], including the Hungarian inundation river branch area.

Time intervals of jointly exchanged data of ground water levels is shown in Fig. 8.1. The Hungarian data is shown in Tab. 8.1. The exchanged data of the ground water level was chosen for comparable discharges in the Danube, see Fig. 8.1, [7]. The locations of the wells included in the data exchange are shown in Fig. 8.2. Differences between ground water levels for various years can be seen from Table 8. 1. Differences characterise the following changes:

  • 1995 - 1994 changes after the realisation of measures according to the "Agreement",
  • 1994 - 1992 changes after putting the hydropower station into operation,
  • 1995 - 1992 comparison between the state after realisation of the measures with the pre- dam conditions,
  • 1995 - 1991 comparison between the state after realising the measures with the low Danube discharge state in
  • pre-dam conditions,
  • 1994 - 1991 comparison between the state without the measures after damming the Danube and the lowDanube discharge state in pre- dam conditions.

From Table 8.1 it can be seen that, based on the Hungarian data, of the Szigetköz, from the river branch system to the Mosoni Danube, ground water levels rose after realisation of measures according to the "Agreement" ( 1995 - 1994) . Ground water levels, after implementation of measures of the "Agreement", are higher than the low ground water levels in 1991 ( 1995 - 1991) , and mostly higher than the corresponding states in pre-dam conditions ( 1995 - 1992) . This means that the ground water levels in the Szigetköz area are mostly higher than in the pre-dam conditions for the average discharges in the Danube. This is also expressed in profiles on Hungarian territory in Fig. 8.3. There is no tendency of ground water level drop towards the river branches (Fig. 8.3), which means that the river branches are recharging the ground water after implementation of the water management measures. This also means that, if the underwater weirs would be constructed and the Hungarian river branches would be supplied with water from the Dunakiliti weir, according to the original project, ground water levels would not be lowered after putting the Gabčíkovo part of the project into the operation. Comparing the ground water levels after damming the Danube without the "Agreement" measures, to the low Danube discharge state (1994 - 1991) , it can be seen that the average ground water levels after damming the Danube have not dropped below the low ground water levels known in pre-dam conditions (see Tab. 8.1.).

Using the data in Tab. 8.1 [7] and data from report [14], contour lines of ground water levels were constructed. Using the ground water level contour lines maps, coloured maps showing the ground water level changes were constructed. A brown colour means a decrease of the ground water level, a blue colour means an increase of the ground water level.

The following maps were prepared for the entire area on both the Slovak and Hungarian sides of the Danube:

  • Map of ground water level differences between the years 1995 and 1992, showing differences in ground water levels between the state after the implemented measures and the comparable state in pre-dam time (Fig. 8.4).
  • Map of ground water level differences between the years 1995 and 1991, showing the same, but in comparison with the low ground water level state in pre-dam time (Fig. 8.5).

Tab. 8.1. Ground water levels - Hungarian territory (m a.s.l.)
 
Year: 
Well number
1991
1992
1994
1995
9310
122.42
123.48
123.22
124.16
9312
122.16
123.38
 
124.01
9327
121.27
122.56
 
122.99
9330
121.70
122.89
122.31
123.25
9368
122.07
123.11
122.88
123.68
9379
121.89
122.75
122.58
123.33
9383
120.25
121.04
121.00
121.83
9384
119.80
120.56
120.46
121.12
9385
119.46
120.14
120.05
120.57
9412
118.54
119.87
 
119.76
9413
118.36
119.47
118.82
119.61
9415
118.24
119.17
118.72
119.38
9416
118.02
118.75
118.55
119.11
9417
117.78
118.40
118.44
118.90
9418
117.34
117.95
117.89
118.21
9425
115.68
116.17
116.19
116.35
9430
115.90
 
115.87
116.76
9434
115.57
116.36
115.88
116.26
9435
115.55
116.27
 
116.30
9457
112.40
113.35
112.34
112.94
9458
112.43
113.18
112.52
112.87
9459
112.21
112.82
 
112.72
9460
112.01
112.55
 
112.57
9475
109.35
110.19
110.34
110.55
9480
109.58
109.91
109.98
110.17
9484
109.25
109.74
109.79
109.98
9536
115.63
116.42
115.86
116.33
9555
111.51
111.93
111.84
12.18
9564
109.44
109.66
 
110.16

It is clear that ground water levels corresponding to the approximately average conditions after the implemented measures, in comparison to the low ground water levels in pre-dam conditions (1991) , decreased only near the Danube. In comparison to the average conditions, the ground water levels of the lower part of the Szigetköz decreased in zones next to the Danube river, which is not influenced by the underwater weir in the Danube at Dunakiliti. The underwater weir at Dunakiliti increased the water level in the Danube and the neighbouring ground water level, between Dunakiliti and Čunovo. The results are shown on a series of maps, see Figs. 8.6, 8.7, and Fig. 8.8. Jointly elaborated, in the frame of the Joint monitoring, ground water contour lines and maps showing the ground water level changes in 1998 in comparison with the pre-dam conditions [13] are in Figs. 8.13, 8.14, 8.15, and 8.16.

It is evident that, after the realisation of water management measures according to the "Agreement" [6], ground water levels have increased significantly on the whole Hungarian flood-plain and Szigetköz area. The aim of the measures, according to the "Agreement", have been evidently fulfilled.

8.1. Impact on the natural environment

The impact of the measures realised according to the "Agreement" is transferred to the natural environment via changes in the ground water levels. In the long term pre-dam development, a lowering of the ground water levels had prevailed. Because ground water level rose after the implemented measures and rose in comparison with the pre-dam conditions, this should be recognised as a positive result of the measures. An rising of the ground water level and an increase of soil moisture in all of the Hungarian inundation area and Szigetköz, in comparison with previous stages, and the increase of water areas and lengthening of the river arm banks, is returning the conditions for flora and fauna back to those supporting more hygrophylous species, which are more valuable, more original and more native especially in the inundation area. For the agricultural Szigetköz, an rise of ground water improves agricultural conditions mainly for deeper rooting plants. The construction of some other underwater weirs in the Danube will further improve these changes. Based on monitoring of the impact of these measures, the changes could be optimised.

8.2. Evaluation

The measures implemented according to the "Agreement" fulfilled the assumptions and have improved the regime of surface and ground waters on the Hungarian side and in the agricultural area of Szigetköz have returned the ground water regime to one similar or better to that existing in the pre- dam conditions, and the conditions of future development as they would be without operating the Gabčíkovo structures. The continuous discharge in the Mosoni Danube and in the river branch system in the Hungarian inundation corresponds to the condition when a relatively large part of the Danube water flowed through the Danube branches. The regime of surface and ground water in the Hungarian inundation and Szigetköz can be regulated by the Dunakiliti weir and optimised by some other measures, for example, by shallow underwater weirs and stabilised natural river fords.

An important information from the monitoring is that the self-purifying processes in the reservoir have had a positive impact on the Danube water quality. This impact is also evident on the Danube stretch downstream from Gabčíkovo on Hungarian territory. The reservoir has this positive impact on water quality because it is no more a single water body between strengthened riverbanks. Variability of water body and aquatic vegetation in shallow water and the banks contributes to the self-purification.


| Back to Contents | References | Figures |