**1. Introduction**

52 Studies on Water Management Issues

Xia, J.Q.; Falconer, R.A.; Lin, B.J. & Tan, G.M. (2011). Modelling flash flood risk in urban

http://pubs.usgs.gov/of/2001/ofr-01-0144 Accessed on 02.04.2011

areas. Water Management, Vol.164, No.6, pp. 267–282, doi:

*0144*, Available from:

10.1680/wama.2011.164.6.267, ISSN 1741-7589

Venezuela and strategies for mitigation. *U. S. Geological Survey Open File Report 01-*

The waterworks construction affects the hydrological regime of the flow of groundwater in the river alluvia that is usually in the hydrodynamic relation to the regime of the fluctuation of the surface watercourse level. To elaborate the prognosis of the changes in the regime of groundwater means to determine their sequence in time for the entire period of their creation until the final stable status is reached. It has to be made on the basis of the knowledge of hydrogeological situation within the territory and the contemporary regime of groundwater. The creation of such changes may be invoked by natural changes or also anthropogenic interventions into the water situation within the territory. The above implies this is the unsteady flow task from hydrodynamic point of view. It is natural since groundwater flow has always somehow the character of unsteady flow. It is implied by natural conditions of their supply and drainage. The regime of supply and drainage of groundwater in water-bearing collectors depends upon the factors not changed in time, so in general, the mode of fluctuation of groundwater level is affected by the changes in time as well and therefore it is unsteady. However, if the conditions of supply and drainage of groundwater are changed in time negligibly, or if the area of interest of the water-bearing collector is located in a certain sufficient distance from the source of supply and drainage point, the flow of groundwater may be practically considered to be stable. The time slope of the forecast changes within the determined area of flow then shall, in addition to other conditions, depend upon time changes in surface and groundwater at its edges, i.e. in the areas of supply or drainage of groundwater. The forecast time changes shall then depend upon the character of the peripheral impacts, thus they shall be different in the case of the natural changes in hydrological conditions and different in the case of artificial structural interventions into contemporary hydrological conditions. In particular, the morphological changes in the river bed, contents of suspended sediments in the watercourse and natural colmatage of the watercourse belong amongst the natural changes in the hydrological conditions of the territories affecting the groundwater regime (Velísková, 2010; Gomboš, 2008). All the technical structural measures amending the conditions of supply and drainage

Change of Groundwater Flow Characteristics After Construction of the

*The Patince - Štúrovo section, RK 1751.8 to 1716.0* 

River.

výstavba š.p. Bratislava).

**reparian alluvial aquifer** 

main groundwater flow directions.

**2.1.1 Description of study area** 

of the area 108 – 110m a.s.l. (Fig. 1 and 2).

thereby available data needed for modelling and simulation.

**study area** 

Waterworks System Protective Measures on the Danube River – A Case Study in Slovakia 55

banks and building seepage canals. Protective measures include the construction of drainage channels and pumping stations and channels. Since the Hungarian side does not build up the lower reservoir, the operation will only be the Gabčíkovo waterworks and the protective measures established in the Slovak Republic that have been running for the maintenance of surface and ground water management at each water stage in the Danube

The construction of the underground walls in the Kravany nad Dunajom section RK 1746.6 to 1722.5 and in the Štúrovo section RK 1722.5 – 1716.0 took place in 03/1985 – 06/1996. There are two so called "windows" omitted in the non-permeable underground wall. The entire construction was carried out before 11/2002 (the data provided by Vodohospodárska

**2. Modelling and numerical simulation of groundwater flow in the Čenkov** 

**2.1 The long-term minimal anthropogenic disruption in natural conditions in of the** 

The solution of groundwater flow features assessments, which are due to later anthropogenic investigations into the area are ranked as almost natural, are going out from the evaluation of former groundwater regimes based on observations in the nature, knowledge of geological structure of the area and hydrogeologic conditions, which is serving as a base to the water-level regime assessment and the subsequent assessment of the

The aim of the task to be solved is to create a numerical model for a steady groundwater flow in the reparian alluvial aquifer of the Čenkov plain, and its calibration, verification and obtaining of results by a simulation that is at groundwater level, using filtration velocity vectors, groundwater paths by particle tracking and the water budget. One assumption is that long-term minimal anthropogenics disrupted the natural conditions of the study area. As the date of the simulation was chosen on the day of 29 September 1954, because of the steady state of water flow through the study area, and also of the Danube low stage and because of existence of solving similar task by other methods in the past (Duba, 1964) and

The Čenkov plain is situated in the eastern part of the Danubian lowland, west apart from Štúrovo town. It is the fluvial plain of the Danube, which borders in the south on a 23 kilometre long river section between RK 1722 and 1745 and in the north in an arc stretching across the terrace platform, where on its boundary lies the Moča village, the Búč village, the Júrsky Chlm village, the Mužla village and the Obid village. The fluvial plain is from 2.5 km up to 6 km wide and has an overall area of 66 km2. Its surface is flat. The heights of the terrain vary from 106 up to 108 m a.s.l. The lowest-situated section under the terrace is on height level 105m a.s.l. and the highest situated section in the Čenkov wood is on the middle

of groundwater belong amongst the interventions into the waterworks conditions of the territories affecting the groundwater regime (Šoltész & Baroková, 2004). In many cases, it is necessary to know not only the final condition achieved by the groundwater level after the implementation of any technical measure, but also the time after what the final condition is reached, or the time procedure of settlement of the new groundwater level status. That means, in general, the task regarding the long-term prognosis in the changes in the groundwater regime must be compiled as the task of unsteady flow of groundwater, where the reached final steady condition is the extreme case (Duba, 1964).

#### *The protective measures on the Danube River*

The designed waterworks complex consists of Gabčíkovo waterworks and Nagymaros waterworks which are, in terms of hydraulic, navigation, and energy distribution, a single operating system. The multipurpose hydroelectric project was built together with Hungary, according to an interstate Treaty signed in 1977. The waterworks complex on the Danube was designed to have an additional level at Nagymaros, consisting of a reservoir 95 km long and the Nagymaros power plant. This level was to be located between the Hungarian towns of Nagymaros and Visegrad and its purpose was to use the gradient of the reservoir for production of electricity and to allow ships to pass. When the Gabčíkovo Project was 90% completed, Hungary stopped fulfilling its treaty obligations in 1989 and tried to end the Treaty in 1992 (www.gabcikovo.gov.sk).

In 1992, the Slovak party put into operation the Gabčíkovo waterworks using an alternative solution on the territory of the Slovak Republic (so called "C" variant) and it wholly completed the works on the object "Protective measures of the Nagymaros waterworks storage reservoir". The necessity of the construction of the object was implied by the reason of the prevention of an unfavourable impact of the dammed level of the Danube River by the Nagymaros step on the territory of the Slovak Republic. This was the reinforcement of the Danube River dam on the territory of the Slovak Republic, the Váh river dam, the Hron river dam and the Ipeľ river dam. The backwater of the Danube River would prevent the gravitation outflow if the internal waters into the Danube River. The erected underground walls in the protective dams prevent the gravitation outflow of internal waters from the territory of the Slovak Republic in the Komárno - the Ipeľ river estuary section, even when there is no backwater in the Danube River. For that reason the internal waters of the territory must be pumped into the Danube River through the erected pumping stations. The administrator of the river basis incurs increased costs related to the activity without their compensation. At the time of the decision of the Hungarian party on the termination of the works on the Nagymaros waterworks, the majority of the protective measures had already been implemented or in the uppermost stage of progress. Subsequently, their scope was minimised and they completed the objects related to


Protective measures against the level impoundment in the reservoir Nagymaros were built on the Slovak territory during the construction of Gabčíkovo waterworks. These consist of renovation of existing dams with newly built underground sealing walls, reinforcement of banks and building seepage canals. Protective measures include the construction of drainage channels and pumping stations and channels. Since the Hungarian side does not build up the lower reservoir, the operation will only be the Gabčíkovo waterworks and the protective measures established in the Slovak Republic that have been running for the maintenance of surface and ground water management at each water stage in the Danube River.

#### *The Patince - Štúrovo section, RK 1751.8 to 1716.0*

54 Studies on Water Management Issues

of groundwater belong amongst the interventions into the waterworks conditions of the territories affecting the groundwater regime (Šoltész & Baroková, 2004). In many cases, it is necessary to know not only the final condition achieved by the groundwater level after the implementation of any technical measure, but also the time after what the final condition is reached, or the time procedure of settlement of the new groundwater level status. That means, in general, the task regarding the long-term prognosis in the changes in the groundwater regime must be compiled as the task of unsteady flow of groundwater, where

The designed waterworks complex consists of Gabčíkovo waterworks and Nagymaros waterworks which are, in terms of hydraulic, navigation, and energy distribution, a single operating system. The multipurpose hydroelectric project was built together with Hungary, according to an interstate Treaty signed in 1977. The waterworks complex on the Danube was designed to have an additional level at Nagymaros, consisting of a reservoir 95 km long and the Nagymaros power plant. This level was to be located between the Hungarian towns of Nagymaros and Visegrad and its purpose was to use the gradient of the reservoir for production of electricity and to allow ships to pass. When the Gabčíkovo Project was 90% completed, Hungary stopped fulfilling its treaty obligations in 1989 and tried to end the

In 1992, the Slovak party put into operation the Gabčíkovo waterworks using an alternative solution on the territory of the Slovak Republic (so called "C" variant) and it wholly completed the works on the object "Protective measures of the Nagymaros waterworks storage reservoir". The necessity of the construction of the object was implied by the reason of the prevention of an unfavourable impact of the dammed level of the Danube River by the Nagymaros step on the territory of the Slovak Republic. This was the reinforcement of the Danube River dam on the territory of the Slovak Republic, the Váh river dam, the Hron river dam and the Ipeľ river dam. The backwater of the Danube River would prevent the gravitation outflow if the internal waters into the Danube River. The erected underground walls in the protective dams prevent the gravitation outflow of internal waters from the territory of the Slovak Republic in the Komárno - the Ipeľ river estuary section, even when there is no backwater in the Danube River. For that reason the internal waters of the territory must be pumped into the Danube River through the erected pumping stations. The administrator of the river basis incurs increased costs related to the activity without their compensation. At the time of the decision of the Hungarian party on the termination of the works on the Nagymaros waterworks, the majority of the protective measures had already been implemented or in the uppermost stage of progress. Subsequently, their scope was

Protective measures against the level impoundment in the reservoir Nagymaros were built on the Slovak territory during the construction of Gabčíkovo waterworks. These consist of renovation of existing dams with newly built underground sealing walls, reinforcement of

the reached final steady condition is the extreme case (Duba, 1964).

*The protective measures on the Danube River* 

Treaty in 1992 (www.gabcikovo.gov.sk).

minimised and they completed the objects related to

• the flood protection of the territory and

• the diversion of internal waters.

The construction of the underground walls in the Kravany nad Dunajom section RK 1746.6 to 1722.5 and in the Štúrovo section RK 1722.5 – 1716.0 took place in 03/1985 – 06/1996. There are two so called "windows" omitted in the non-permeable underground wall. The entire construction was carried out before 11/2002 (the data provided by Vodohospodárska výstavba š.p. Bratislava).
