Danubian Lowland - Ground Water Mode

SK98K0043 Ministry of the Environment, Slovak Republic Commission of The European Communities

DANUBIAN LOWLAND - GROUND WATER MODE

PHARE PROJECT NO. PHARE/EC/WAT/1

The Old Danube Final Report

Volume 1 Summary Report December 1995

Danish Hydraulic Institute, Denmark in association with DHV Consultants BV, The Netherlands TNO - Institute of Applied Geoscience, The Netherlands Water Quality Institute, Denmark I Kriiger, Denmark The Royal Veterinary and Agricultural University, Denmark Danish Hydraulic Institute

Danubian Lowland - Ground Water Model Agern Alle 5, DK-2970 Harsholm, Denmark PHARE/EC/WAT/1 Telephone: +45 45 76 95 55 Final Report Telefax: +45 45 76 25 67 Telex: 37 402 dhicph dk

Client Client's representative

Ministry of the Environment, Programme Implementation F. Kelbel, Director, PIU Unit, Slovak Republic

Project Project No

Danubian Lowland - Ground Water Model 92-6828

Authors Date Jens Chr. Refsgaard, DHI December 1 995 Henrik R. Sarensen, DHI DHV-Consultants BV, NL TNO-lnstitute of Applied Geoscience, NL Water Quality Institute (VKI), DK 1. Kriiger Consultant AS, DK Approved by Royal Veterinary and Agricultural University, DK VUVH - Water Resources Research Institute, SK Jens Chr. Refsgaard VU2H - Research Institute of Irrigation, SK /J^0) ecL T eanvpSad e r GWC - Ground Water Consulting Ltd., SK Comenius University, SK t

1 Final Report an 0 Draft Final Report

Revision Description By Checked App. Date

Key words Classification

Danube, integrated modelling, water resources management, • Open numerical modelling, model development, river and reservoir, ground water, unsaturated zone, agriculture, sediment • Internal transport, ground water quality, surface water quality, ecology, geographical information system, field Ix! Proprietary investigations, equipment. FINAL REPORT

VOLUME 1

SUMMARY REPORT

TABLE OF CONTENTS

0 EXECUTIVE SUMMARY 0-1

1 INTRODUCTION 1-1 1.1 Background 1-1 1.2 Project Objectives 1-2 1.3 Project Relation to the Gabcikovo Hydropower Scheme 1-2 1.4 Project Relation to other Water Resources Activities in the Region 1-3 1.5 Purpose and Contents of Report 1-3

2 PROJECT STAFFING 2-1 2.1 Consultant 2-1 2.2 Local Organizations 2-5 2.3 New Project Manager 2-7

3 PROJECT MANAGEMENT ISSUES 3-1 3.1 Project Organizational Framework 3-1 3.2 Steering Committee 3-1 3.3 Project Manager and End User Organisation 3-2 3.4 Project Extension by Six Months 3-3 3.5 Access to Existing Data 3-4 3.6 Support Projects Financed by Slovakian Funds 3-4

4 ESTABLISHMENT OF THE INTEGRATED MODELLING SYSTEM 4-1 4.1 Introduction 4-1 4.2 Equipment 4-1 4.3 Danubian Lowland Information System 4-3 4.4 Modelling Approach 4-4 4.4.1 Further development of modelling systems 4-5 4.4.2 The integrated modelling system 4-6 4.4.3 Approach of model application 4-7 4.5 Ground Water Modelling 4-7

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4.6 Pollution Status of Reservoir Sediments 4-10 4.7 Ground Water Quality 4-11 4.7.1 Geochemical field investigations at Kalinkovo 4-11 4.7.2 Ground water quality model 4-11 4.8 Unsaturated Zone and Agricultural Modelling 4-14 4.9 River and Reservoir Hydrodynamic Modelling 4-16 4.10 River and Reservoir Sediment Transport Modelling 4-19 4.11 Surface Water Quality Modelling 4-21 4.12 Flood plain Ecology and Modelling 4-24

5 SUMMARY OF MODEL APPLICATION 5-1 5.1 Introduction 5-1 5.2 Selected Water Management Regimes 5-1 5.3 Ground Water Flow Regime 5-2 5.3.1 Objectives 5-3 5.3.2 Main conclusions 5-3 5.3.3 Assessment of uncertainties of model predictions 5-5 5.4 Agriculture 5-5 5.4.1 Objectives 5-5 5.4.2 Main conclusions 5-6 5.4.3 Assessment of uncertainties of model predictions 5-6 5.5 Ground Water Quality 5-8 5.5.1 Objectives 5-8 5.5.2 Main conclusions 5-8 5.5.3 Assessment of uncertainties of model predictions 5-9 5.6 Hydrodynamics, Sediment Transport and Water Quality in the Danube . . . 5-12 5.6.1 Objectives 5-12 5.6.2 Main conclusions 5-12 5.6.3 Assessment of uncertainties of model predictions 5-13 5.7 Hydrodynamics, Sediment Transport and Water Quality in the River Branch System 5-16 5.7.1 Objectives 5-16 5.7.2 Main conclusions 5-16 5.7.3 Assessment of uncertainties of model predictions 5-18 5.8 Hydrodynamics, Sediment Transport and Water Quality in the Hrusov Res- ervoir 5-19 5.8.1 Objectives 5-19 5.8.2 Main conclusions 5-19 5.8.3 Assessment of uncertainties of model predictions 5-20 5.9 Ecology 5-20 5.9.1 Objectives 5-20 5.9.2 Main conclusions 5-20 5.9.3 Assessment of uncertainties of model predictions 5-24

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6 CONCLUSIONS AND RECOMMENDATIONS 6-1 6.1 Conclusions Regarding Project Implementation 6-1 6.1.1 Equipment 6-1 6.1.2 Establishment of a generalized integrated modelling system 6-1 6.1.3 Establishment of Danubian Lowland Information System (DLIS) 6-2 6.1.4 Establishment of calibrated and validated models 6-3 6.1.5 Model applications 6-3 6.1.6 Cooperation with Slovakian organisations 6-4 6.1.7 Transfer of technology and know-how 6-4 6.1.8 International workshops 6-5 6.2 Recommendations on future Applications of Modelling System 6-5 6.2.1 Future model applications 6-6 6.2.2 Future modelling group at PRIF UK 6-7 6.3 Recommendations on Water Resources Management in the Danubian Lowland 6-7

LIST OF REFERENCES Ref-1

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0 EXECUTIVE SUMMARY

Background

The Danubian Lowland between Bratislava and Komarno is an inland delta formed in the past by river sediments from the Danube. The entire area forms an alluvial aquifer, which throughout the year receives infiltration water from the Danube in the upper parts of the area and returns it into the Danube via a network of drainage canals in the downstream part. The aquifer is an important water resource for municipal and agricultural water supply.

Various human activities have gradually changed the hydrological regime in the area. In particular a lowering of the water levels in the Danube has been observed between 1960 and 1990. In most of the area the Danube controls the ground water flow regime and hence a lowering of the general ground water level in the area has also been observed.

The Gabcikovo hydropower scheme was put into operation in October 1992. The upstream reservoir and various hydraulic structures related to Gabcikovo have major impacts on the hydrological regime and the ecosystem of the region. The Gabcikovo hydropower scheme is the most important of the man induced impacts of the area and therefore it plays a key role in the project.

Project Objective

The immediate project objective is to develop, test and transfer an integrated mathematical modelling system including the most important aspects for water resources management in the Danubian Lowland. The ultimate project objective is that the transferred modelling system be used as the technical/scientific basis for future management decisions.

Project Framework

The project "Danubian Lowland - Ground Water Model" was defined in 1991 within the PHARE programme agreed upon between the Commission of the European Communities and the Government of the Czech and Slovak Federal Republic. The project was initiated in February 1992. During 1992 the project was executed by the Federal Committee for Environment, Government of the Czech and Slovak Federal Republic. From the beginning of 1993 the project was transferred to the Ministry of the Environment, Slovak Republic.

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The Project Manager is appointed by PRIF UK. Professor Igor Mucha was the Project Manager until the end of 1994. Andrej Cibulka was appointed as new Project Manager in the beginning of 1995.

A Danish-Dutch consortium of six organisations was selected as Consultant for the project. The Consultant is headed by the Danish Hydraulic Institute (DHI) and comprises the following associated partners: DHV Consultants BV, The Netherlands; TNO-Applied Institute of Geoscience, The Netherlands; Water Quality Institute (VKI), Denmark; I Kruger Consult AS, Denmark; and the Royal Veterinary and Agricultural University, Denmark.

Staff members from the following Slovakian organisations have participated actively in the project implementation:

Comenius University (PRIF UK) The Ground Water Consulting, Ltd. (GWC) The Water Research Institute (VUVH) The Irrigation Research Institute (VUZH)

The work of in total 11 persons from these organisations have been funded by various Slovakian organisations and by the Ministry of the Environment. In addition various field- and monitoring programmes have been funded by Slovakian organisations.

Originally, GWC was a part of the Faculty of Natural Science, Comenius University (PRIF UK), but from the beginning of 1994 they established a private firm.

Due to a delayed delivery of about 20 months of the major computer equipment, the project period has been extended with 6 months. The project termination is December 31, 1995.

Equipment

Equipment for almost ECU 600.000 has been procured during the project. This includes various field and laboratory equipment, office equipment and computer hardware and software. The backbone of the computer system is 2 Hewlett Packard Apollo 9000/735 UNIX workstations. The procured equipment has been extensively used during the project and it has fully accommodated the needs of the project. Although, the progress in developing faster computers, more advanced software etc. is tremendous, the procured equipment will be the front end of technology for many years yet to come.

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Establishment of the Integrated Modelling System

In order to address the problems within the project area an integrated modelling system has been established based on the consultants mathematical modelling systems. These are:

MIKE 11 which is a one dimensional river modelling system for hydraulics, sediment transport and morphology and water quality.

MIKE 21 which is a two dimensional modelling system used for reservoir modelling, including hydrodynamics, sediment transport and water quality.

MIKE SHE which simulates the major flow and transport processes within the hydrological cycle. MIKE SHE comprises modules for flow and transport on the ground surface, in rivers, in the unsaturated zone and in the ground water zone

DAISY which is a one-dimensional root zone model for simulation of soil water dynamics and nitrogen transport and transformation.

Although these modelling systems are generalized tools with comprehensive applicability ranges, a few model modifications have taken place within the project, in order to accommodate the very special conditions in the area.

The integrated modelling system is formed by the exchange of data and the feedbacks between the individual modelling system. The structure of the integrated modelling system is illustrated in the figure below.

The Danubian Lowland Information System (DLIS) is a combined data base and geographical information system that has been developed under this project. The DLIS is based on Informix (database) and Arc/Info (GIS) and provides a framework for data storage, maintenance, processing and presentation. In addition, an interface between DLIS and MIKE SHE allowing import and export of maps and time series files in MIKE SHE file formats has been made. Furthermore, an interface that allows loading and storage of river cross-sections in a MIKE 11 file format has been developed. A direct interface to the remaining models has not been developed, but files can easily be transferred from MIKE SHE file format to any other of the applied modelling systems.

Model Setup, Calibration and Validation

The various mathematical models have been established using the three step approach below.

step 1) Model setup step 2) Model calibration step 3) Model validation.

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MIKE 21 Hydrodynamics Sediment transport Water quality Eutrophication

DAISY Unsaturated flow Crop growth Nitrogen transport Nitrogen transformation

MIKE 11 Hydrodynamics Sediment transport Water quality Eutrophication

D LI S

Fig. 0.1 Structure of the integrated modelling system.

The following models have been established:

a MIKE 11 hydrodynamic model for the Danube a MIKE 11 water quality model for the Danube a MIKE 11 sediment transport and morphological model for the Danube. a MIKE 11 hydrodynamic model for the river branch system on the Slovak floodplain. a MIKE 11 eutrophication model for the river branch system. a MIKE 11 sediment transport model for the river branch system.

All the MIKE 11 models have been established in two versions reflecting the situation before and after the damming of the Danube.

a MIKE 21 hydrodynamic model for the reservoir, a MIKE 21 eutrophication model for the reservoir. a MIKE 21 sediment transport model for the reservoir.

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a MIKE SHE regional ground water model for the entire project area (3500 km2 (pre- and post-conditions). a MIKE SHE detailed model for the reservoir area (180 km2). a MIKE SHE detailed model for the river branch system (60 km2) a MIKE SHE geochemical transect model for a geochemical field site. a MIKE SHE geochemical model for the reservoir area (under preparation) a number of DAISY models (profiles) reflecting the different agricultural and hydrological conditions within the area.

Definitions of Scenarios for Model Applications

Phase II has mainly been dedicated to model application. The specific scenarios for which model simulations have been decided jointly by the Slovak Ministry of the Environment and the Consultant.

A framework comprising four Water Management Regimes was chosen. The Water Management Regimes are based on a measured discharge time series at Bratislava for the period 1986 to 1991. This period has an average discharge (2027 m3/s) which is close to the long term average and furthermore contains high flow as well as low flow situations.

Water Management Regime I is a reference situation reflecting the pre-dam situation. Water Management Regime II reflects a post-dam situation where, in average, 400 m3/s are diverted from the reservoir to the Old Danube. Water Management Regime III reflects a post-dam situation where, in average, 800 m3/s are diverted from the reservoir to the Old Danube. Water Management Regime IV reflects a post-dam situation where, in average, 200 m3/s are diverted from the reservoir to the Old Danube.

Results of Model Applications

The main objectives of the model applications were to illustrate the applicability of the established integrated modelling system and to provide modelling results that can support technical decisions and water management policies in the project area.

For the selected water management regimes and scenarios model predictions have been made on the following issues:

Ground water levels, ground water table fluctuations (Pegelweg) and amount of recharge from the river/reservoir to the aquifer.

Ground water quality especially with focus on nitrate, nitrite and redox conditions.

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Crop growth potential, irrigation requirements and nitrate leaching from agricultural areas including their dependence on the location of the ground water table.

Water levels, flow velocities, sedimentation/erosion and oxygen concentrations for the Old Danube. These calculations have been carried out for scenarios with and without underwater weirs.

Flow velocities, sedimentation and eutrophication in the reservoir.

Water levels, flow velocities, sedimentation/erosion and water quality in the river branch system. Furthermore depths, areal extent and duration of surface water inundations as well as ground water depths and fluctuations have been calculated.

On the basis of model predictions of the above hydrological conditions qualitative inferences have been made on possible changes in ecological developments for the reservoir, the Old Danube and the river branch system.

Assessments of Uncertainties of Model Predictions

Assessments have been made of uncertainties related to the specific model predictions. In general, it can be stated that the highest uncertainties exist for predictions of changes in ecology, geochemistry and to some extent sedimentation, while predictions of water levels, ground water levels, flow velocities and surface water quality are less uncertain.

Future Model Applications

The model applications carried out during the last phase of the project serve as illustrations of the type of modelling studies which can be made by using the established integrated modelling system. A large range of further modelling studies may be carried out, and the modelling system is a very suitable tool to support decisions on optimal water resources management in the Danubian Lowland region.

Need for combined Monitoring and Modelling

Due to the large uncertainties related to predictions of geochemical changes, development of ecological systems and sediment transport and morphological developments it is recommended to combine future modelling applications with field monitoring programmes.

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INTRODUCTION

1.1 Background

The Danubian Lowland between Bratislava and Komarno is an inland delta formed in the past by river sediments from the Danube. The entire area forms an alluvial aquifer, which throughout the year receives infiltration water from the Danube in the upper parts of the area and returns it into the Danube and the drainage canals in the downstream part. The aquifer is an important water resource for municipal and agricultural water supply.

Human influence has gradually changed the hydrological regime in the area. Construction of dams upstream of Bratislava together with exploitation of river sediments has significantly deepened the river bed and lowered the water level in the river. These changes have had a significant influence on the ground water regime as well as on the sensitive riverside forests downstream of Bratislava. The hydraulic structures related to the hydropower plant at Gabcikovo have major impacts on the hydrological regime and the ecosystem of the region.

Industrial waste and municipal sewage from Bratislava and its surroundings together with the diffuse sources of agricultural fertilizers and agrochemicals are polluting the rivers, soil and ground water.

These physical and biochemical changes may reduce the atmospheric oxygen transport to the ground water and at the same time increase the supply of organic matter which will change the oxidizing conditions to reducing conditions and thereby seriously deteriorate the ground water quality.

To address these urgent water resources problems in the area the project "Danubian Lowland - Ground Water Model" has been defined in 1991 within the PHARE programme agreed upon between the Commission of the European Communities and the Government of the Czech and Slovak Federal Republic.

To understand and analyze the complex relationships between physical, chemical and biological changes in the surface- and subsurface water regimes requires multidisciplinary expertise in combination with advanced mathematical modelling techniques. The overall project objective is to establish a reliable impact assessment model for the Danubian Lowland area, which enables the authorities to formulate optimal management strategies leading to a protection of the water resource and a sound ecological development for the area.

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1.2 Project Objectives

The objective of the project is to provide technical/scientific based management tools for the Slovakian authorities and through interaction with decision makers to apply - these tools for addressing selected problems. Thus, on the one hand, the role of the project is not to define management objectives nor to establish a management decision framework for water resources. On the other hand, the project shall in accordance with the Terms of Reference prepare expert suggestions for the government to be used for technical decisions as well as for policy making.

The water resources problems in the project area are so complex, the number of relevant studies already carried out so high, and the amount of available data so large that it is not possible within the framework of the project to fully process all these data and provide optimal technical solutions to all the problems. Therefore, a priority of project activities was made during the Inception Phase. This involved that data collection and modelling activities relating to predicting the effects of alternative operation schemes of the Gabcikovo system were given highest priority, while other activities such as data collection and modelling of groundwater pollution from point sources (waste disposal sites etc), analyses of potential pollution connected with navigation, and analyses of the irrigation and drainage canal system in the downstream part of Zitny Ostrov were given lower priority.

However, irrespective of the priorities made during the Inception Phase, the modelling system being established during the project shall be able to address the most important types of water resources problems, the performance of the models shall be verified and the models shall be applied to a selected number of practical problems demonstrating their applicability for the large range of problem types.

The ultimate objective of the project is that the models provided during the project be used as the technical/scientific core for the future management decisions. It is noted that this objective can only be fulfilled through close cooperation with Slovakian specialists, who by the end of the project must be able to fully utilize the models.

1.3 Project Relation to the Gab$ikovo Hydropower Scheme

For a clarification of the role of the present PHARE project in relation to the international political discussions between Slovakia and Hungary on the Gabcikovo hydropower scheme it is noted that the project in accordance with its Terms of Reference is limited to the pure technical and scientific aspects. Furthermore, the following two points may be noted:

The project deals with the water resources problems in the entire Danubian Lowland area (the area between Bratislava to the west and Komarno to the east and between the Danube to the south and the Karpathians to the north). The

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Gabcikovo is only one, although at present the largest, of the man induced impacts which has to be studied.

The project deals with modelling of the water resources on the Slovakian side of the Danube. No recent data is available to the project from the Hungarian side, and the project can therefore only make predictions dealing with the effects of the Gabcikovo scheme for Slovakian areas. Thus, the project cannot address questions regarding e.g. the ecological consequences of the Gabcikovo scheme for Hungarian areas.

1.4 Project Relation to other Water Resources Activities in the Region

Due to the very significant water resources problems in the area comprehensive activities are currently being carried out both with regard to monitoring and to studies. Thus many professional organizations are involved in various aspects of water resources activities in the project area. The purpose of the project is to cooperate with all these activities in order to avoid duplication of work and to ensure maximum dissemination of project outputs to Slovakian organizations.

1.5 Purpose and Contents of Report

According to the Terms of References the results of the project shall be reported in a Final Report.

The Final Report is divided into three volumes, namely the present Summary Report (Volume 1), a report which deals with the setup, calibration and validation of various models (Volume 2) and a report that contains results of the model applications (Volume 3).

The present report summarizes the management aspects, which have been continuously reported in six-monthly Progress Reports. Furthermore, a summary of Volume 2 and Volume 3 is provided.

Chapter 2 contains a summary of the project staffing, both in terms of Consultant staff input and input from Slovakian specialists associated to the project.

Chapter 3 deals with the project management issues, including the Steering Committee, results of an International Workshop and the cooperation with local organizations.

Chapter 4 summarizes how the Integrated Modelling System has been established. This Chapter can be seen as a summary of Volume 2 of the report.

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Chapter 5 provides a summary of the Model Applications and of their main conclusions.

Chapter 6 contains the consultants suggestions and recommendations regarding future use of the Integrated Modelling System.

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SK98K0046

PROJECT STAFFING

2.1 Consultant

The assignment of Consultant staff at the project office in Bratislava during the entire project periode is listed in Table 2.1

Table 2.1 Project staff members working in Bratislava.

Staff member Periods Comments

J.C. Refsgaard 06/02-09/02 92 Team Leader, DHI 04/03-12/03 92 01/04-14/04 92 14/05-27/05 92 03/06-23/06 92 07/07-16/07 92 02/09-11/09 92 25/11 92 21/01-29/01 92 06/03-12/03 93 19/04-26/04 93 03/06-16/06 93 01/09-07/09 93 20/10-04/11 93 19/01-07/09 94 10/02-15/02 94 20/04-26/04 94 24/05-03/06 94 12/07-14/07 94 09/09-16/09 94 23/11-01/12 94 19/06-30/06 95 30/11-08/12 95

B. Storm 22/03-14/04 92 Note 1) Deputy Team Leader 06/05-12/05 92 Chief MIKE SHE 01/06-23/06 92 Modeller, DHI 10/01-28/01 94 24/10-04/11 94

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Staff member Periods Comments

H.R. Serensen 10/02-23/02 94 Deputy Team Leader 07/03-11/05 94 Chief MIKE SHE 24/05-10/06 94 Modeller, DHI 20/06-08/07 94 15/08-02/09 94 07/09-30/09 94 20/10-04/11 94 21/11-01/12 94 16/01-27/01 95 11/02-17/02 95 08/03-10/03 95 27/03-07/04 95 01/05-12/05 95 05/06-15/06 95 19/06-30/06 95 13/08-11/09 95 29/11-08/12 95

P.B. Hansen Geohydrologist, I. Kriiger 30/03-15/04 92 T. Clausen 10/01-28/01 94 MIKE SHE Modeller, 20/06-08/07 94 DHI 15/08-02/09 94 19/09-30/09 94 24/10-04/11 94

A. Refsgaard 11/04-22/04 94 MIKE SHE Modeller, 24/05-02/06 94 DHI

J. Griffioen 12/04-03/05 92 Hydrogeochemist, TNO 03/06-19/06 92 18/08-28/08 92 03/11-11/11 92 12/04-20/04 93 03/08-10/08 93 25/05-03/06 94 25/08-02/09 94 03/03-10/03 95 15/06-23/06 95

P.K. Engesgaard 26/04-03/05 92 Note 2) Hydrogeochemical 08/06-19/06 92 Modeller, VKI 15/01-21/01 94 18/04-26/04 94 20/05-02/06 94 15/08-26/08 94 15/06-23/06 95 07/09-11/09 95

M. Styczen 06/05-19/05 92 Note 3) Agronomist, DHI 06/06-16/06 93 15/09-19/09 94

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Staff member Periods Comments

M. Thorsen 21/11-01/12 94 Agronomist, DHI 14/03-20/03 95 14/06-23/06 95 22/08-01/09 95

S.E. Brierley 10/02-12/02 92 Note 4) Hydraulic/sediment engin- 02/03-12/03 92 eer, DHI 22/03-03/04 92

M. Madsen 01/04-15/04 92 Hydraulic Engineer, DHI 29/04-05/05 92 20/05-27/05 92 19/04-29/04 93 15/07-23/07 93 27/09-30/09 93 07/03-15/03 94

J.T. Kjelds 03/05-30/05 92 Hydraulic/sediment 08/06-13/06 92 Engineer, DHI 10/07-06/08 92 K. Wium Olesen 08/06-13/06 92 Hydraulic/sediment En- gineer, DHI H.Bak Surface Water Quality 16/01-20/01 95 Specialist, VKI J.K. Jensen 24/05-19/06 92 Surface Water Quality 30/08-04/09 92 Specialist, VKI 18/07-23/07 93 22/09-01/10 93 27/05-02/06 94 07/09-16/09 94 21/11-24/11 94 27/02-06/03 95 15/05-19/05 95 19/06-26/06 95 14/08-25/08 95 F. Deckers 04/05-19/06 92 Information System Ana- 07/03-25/03 94 lyst, TNO 14/05-01/06 94 14/11-18/11 94 06/03-10/03 95 26/03-31/03 95

F. Wardenburg 07/03-25/03 94 Information System Ana- 14/05-01/06 94 lyst, TNO 14/11-18/11 94 06/03-10/03 95 26/03-31/03 95

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Staff member Periods Comments

J.L. Fiselier 25/05-14/06 92 Flood Plain Ecologist, 26/05-08/06 94 DHV 25/11-29/11 94 05/04-09/04 95 05/06-09/06 95 20/06-23/06 95 16/08-20/08 95 29/08-01/09 95 M.W. de Haan 25/05-14/06 92 Limnologist, DHV 26/05-08/06 94

J.W. van Sluis, 04/05-02/06 92 Emission specialist, DHV Hans G. Enggrob 24/05-11/06 94 Sediment Transport 09/09-19/08 94 Modeller, DHI 14/11-23/11 94 27/03-07/04 95 14/06-26/06 95 30/08-06/09 95 S. Hansen 19/04-04/05 93 Agricultural Modeller, 07/02-18/02 94 KVL 25/05-03/06 94 14/03-20/03 95

A. Bruun 19/08-26/08 94 Geochemical Modeller, 15/10-20/10 94 VKI 28/11-01/12 94 01/03-08/03 95 06/05-11/05 95 L.C. Larsen 11/05-25/05 92 Computer System Special- 21/01-22/01 93 ist, DHI 31/01-03/02 93 26/04-30/04 93 15/11-18/11 94

Notes : 1) B. Storm was replaced by H.R. S0rensen in February 1994. 2) Temporarily substituted by A. Brun from August 1994 to May 1995 3) M. Styczen was replaced by M. Thorsen in November 1994. 4) S.E. Brierley was replaced by J.T. Kjelds and K.W. Olesen in April 1992

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Table 2.2 Project staff members working outside Bratislava and own home office.

Staff member Work Periods Comments place

B. Storm, DHI NL 27/04-29/04 92

L.C. Larsen, DHI NL 26/04-29/04 92 J. Griffioen, TNO DK 20/06-23/06 93 DK 11/09-15/09 95

F. Deckers, TNO DK 18/09 92 F. Waardenburg, TNO DK 18/09 92 J.L. Fiselier, DHV D 04/10-05/10 94

In addition, some of the Consultant staff members have worked on the project at their respective home offices.

2.2 Local Organizations

Staff members from the following Slovakian research organisations have participated actively in the project implementation:

The Ground Water Consulting (GWC). This group was in 1992 and 1993 part of the Faculty of Natural Sciences, Comenius University (PRIF UK). In 1994 the group established itself as a private firm. The following staff members have received training and subsequently participated in the modelling activities under the project:

Professor, Dr. Igor Mucha RNDr. Eva Paulikova RNDr. Dalibor Rodak RNDr. Zoltan Hlavaty RNDr. Lubomir Bansky

Furthermore, GWC staff members have conducted field studies as well as collected and processed data for the project.

The Water Research Institute (VUVH). The three key persons from VUVH, which have contributed with modelling work for the project are:

Ing. Jelica Klucovska Ing. Jana Topolska Ing. Zdena Kelnarova

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These three modelling specialists have been allocated in total for about 55 man-months during Phase I. Furthermore, other VUVH staff members have conducted field studies and corresponding analyses on hydrodynamics, sediment and water quality aspects for the project. From November 1994 Zdena Kelnarova changed job position from VUVH to Ministry of Environment. In January 1995 Jelica Klucovska and Jana Topolska changed job position from VUVH to GWC.

The Irrigation Research Institute (VUZH). The two key persons from VUZH, which have contributed with modelling work for the project are:

RNDr. Jozef Takac Ing. Vladimir Kosc

These modelling specialists have been allocated in total for about 35 man- months during Phase I. Furthermore, other VUZH staff members have contributed with field studies and corresponding analyses.

The Slovakian modelling specialists have received training abroad under the PHARE project as summarized in Table 2.3.

Table 2.3 Training abroad for Slovakian specialists under the project.

Staff member Periods Comments

I. Mucha, GWC PRIF UK 18/09-18/10 92 SHE training at DHI, Denmark E. Paulikova, GWC PRIF 18/09-18/10 92 SHE training at DHI, Denmark UK

D. Rodak, GWC PRIF UK 03/10-25/10 92 Training in geochemical modelling at TNO and Free University of Amsterdam, NL 14/11-05/12 92 Study tour to University of Kassel, Germany

Z. Hlavaty, GWC PRIF UK 19/04-22/04 92 HydroGIS conference, Austria 19/07-03/08 93 GIS training, USA 11/08-25/08 93 GIS training at TNO, Netherlands

L. Bansky, GWC PRIF UK 19/07-03/08 93 GIS training, USA J. Klucovska, VUVH 02/11-30/11 92 MIKE 11/21 training at DHI and VKI, Denmark J. Topolska, VUVH 02/11-30/11 92 MIKE 11/21 training at DHI and VKI, Denmark Z. Kelnarova, VUVH 02/11-30/11 92 MIKE 11/21 training at DHI and VKI, Denmark J. Takac, VUZH 19/10-15/11 92 DAISY training at Agricultural University, Denmark

V. Kosc, VUZH 19/10-15/11 92 Daisy training at Agricultural University, Denmark

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2.3 New Project Manager

Professor Igor Mucha was appointed Project Manager from the beginning of the project. Professor Igor Mucha and his group left PRIF UK in 1994. Therefore, PRIF UK nominated a new Project Manager, Mr. Andrej Cibulka. Mr. Cibulka has been Project Manager since the beginning of 1995.

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PROJECT MANAGEMENT ISSUES

3.1 Project Organizational Framework

The PHARE project was during the first project year, 1992, executed by the Federal Committee for Environment, Government of the Czech and Slovak Federal Republic. From the beginning of 1993 the project was transferred to the Programme Implementation Unit (PIU) at the Ministry of the Environment, Slovak Republic.

The Project Manager is appointed by the Faculty of Natural Science, Comenius University (PRIF UK). From the beginning of the project until the end of 1994 Professor Igor Mucha was the Project Manager. Originally, Professor Igor Mucha and his team of ground water specialists belonged to PRIF UK, but in 1994 they established a private company, Ground Water Consultants Ltd (GWC). Hence, in the beginning of 1995 PRIF UK nominated Mr. Andrej Cibulka in Project Manager.

Important Slovakian contributions to the project are provided by specialist staff from GWC, Water Research Institute (VUVH) and Irrigation Research Institute (VUZH).

A Danish-Dutch consortium of six organizations was selected as Consultant for the project. The Consultant is headed by Danish Hydraulic Institute (DHI) and comprises the following associated partners: DHV Consultants BV, The Netherlands; TNO-Applied Institute of Geoscience, The Netherlands; Water Quality Institute (VKI), Denmark; I Kriiger Consult AS, Denmark; and the Royal Veterinary and Agricultural University, Denmark.

3.2 Steering Committee

In order to facilitate coordination between the project and important cooperation partners as well as key end users of project results a Steering Committee has been established. The committee comprises representatives of the following organizations:

Programme Implementation Unit (PIU), Slovak Ministry of the Environment

Slovak Ministry of the Environment

The Project Manager

Water Research Institute (VUVH)

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Research Institute of Irrigation (VUZH)

Centre of Monitoring, Slovak Hydrometeorological Institute (SHMU)

Faculty of Natural Sciences, Comenius University (PRIF UK)

Ministry of Soil Management

Water Economy Construction (Vodohospodarska Vystavba)

The Danube Catchment Authority (Povodie Dunaja)

Danish Hydraulic Institute on behalf of the Consultant group.

The Steering Committee has held seven meetings during the course of the project, namely on

9 April 1992 27 May 1992 10 March 1993 7 September 1993 26 January 1994 29 November 1994 29 June 1995

The Progress Reports prepared by the Consultant in January 1993, July 1993, January 1994, July 1994 and July 1995 were submitted to the Steering Committee and formed the basis for information and discussions of general project status and work plans. Furthermore, the technical progress and preliminary results were presented and discussed at several of the meetings. The last two meetings were mainly dedicated to discussions regarding the application scenarios presented in Volume 3 of the Final Report.

3.3 Project Manager and End User Organisation

According to the Terms of References the core Slovakian group in the project is the Ground Water Division of the Faculty of Natural Sciences (PRIF UK). This group should provide 6 persons full-time for the project and the group had 3 key functions, namely providing the Project Manager, providing technical input for the project and becoming the future user of the established model, hardware and software. As Project Manager was appointed Professor Igor Mucha. During 1992 and 1993 Professor Mucha and his group received funding for their project activities from the Slovak government. However, from the beginning of 1994 no salaries were paid to the group and the group established a private firm, Ground Water Consulting, Ltd. (GWC) in April, 1994. Throughout 1994 no salaries were made available to GWC

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for providing the project work specified in the Terms of References. During this period GWC provided some work for the project to ensure that the computer system was maintained and running, enabling the project activities to continue. Thus, during 1994 GWC has provided staff input to the project corresponding to on average about 3 persons full-time. This situation with too little input from the core Slovakian group during 1994 has been a major concern and has therefore been subject to many discussions involving the Consultant as well. In November 1994 the following decisions were made in agreement between the involved parties:

PRIF UK nominates a new Project Manager.

GWC continue to provide technical input for the project under direct subcontract with DHL

Formally, all equipment continues to be the property of the Ministry of Environment but in practice PRIF UK becomes the future users.

A new group of Slovak specialists will be established at PRIF UK which after proper training must be able to utilize and further develop the established integrated modelling system.

These conclusions were executed in the beginning of 1995. As new Project Manager PRIF UK appointed Mr. Andrej Cibulka. Training of a new Slovak group is expected to start in January 1996.

3.4 Project Extension by Six Months

The tendering process and delivery of the major computer equipment was after consultation with PIU (Prague) during the Inception Phase estimated to take about seven months. Instead, it turned out to take 15-20 months for the two major computer workstations including the ARC/INFO and INFORMIX data base software systems. This delay has created subsequent delays in many project activities, which were dependent on this equipment.

On this basis the Project Manager and the Consultant had requested that the project period was extended by six months. PIU has approved this request, so that the key timings have been modified as follows:

Phase I: 16 July 1992 - 15 January 1995 Phase II: 16 January 1995 - 15 September 1995 Final Report: 1 December 1995 Project Termination: 31 December 1995.

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3.5 Access to Existing Data

A very large amount of relevant data from the project area exist. The major part of this data is collected by and available through the Centre of Monitoring, which is a separate organization under SHMU specifically responsible for the collection of data for the Danubian Lowland area.

The question of the availability of this data for the project and the associated conditions has been subject to comprehensive discussions at several separate meetings as well as at Steering Committee meetings. Due to considerable efforts by the Project Manager and the Ministry of Environment the project got access to all relevant existing data without costs charged to the project in this regard.

3.6 Support Projects Financed by Slovakian Funds

The PHARE project has been supported in kind by Slovakian financing of associated projects. The key elements in this regard are:

Project input from GWC:

staff input for data collection, data processing, field work, modelling and management, 1992 - 1995; and field work and laboratory analyses for the Kalinkovo geochemical field site, 1994.

The activities in 1992 and 1993 were provided in accordance with the Terms of Reference and funded by the Slovak government. The 1994 staff input amounted to about half the input specified in the Terms of Reference. Since the beginning of 1995 GWC's input for the project has been financed under DHI's PHARE budget. GWC input in 1995 has been about four persons employed full-time.

Project input from VUVH

staff input for modelling work, 1992 - 1994; a sediment transport field programme, 1992 - 1993; and a water quality field programme, 1992 - 1993.

The activities in 1992 were funded by Water Economy Construction, while the 1993 and 1994 activities were funded by the Ministry of the Environment.

Project input from VUZH

staff input for data collection, processing and modelling work, 1992 - 1995.

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The 1992 activities were funded by VUZH, while the activities in 1993, 1994 and 1995 were funded by the Ministry of the Environment.

In addition, the PHARE project has through cooperation with other projects obtained access to field data obtained under other projects. An example in this regard is a major project on reservoir eutrophication conducted by VUVH and financed by the Ministry of the Environment during the second half of 1994. The PHARE project has given recommendations for the field programme, and the measurements have been used in connection with calibration of the reservoir eutrophication model.

These support projects and cooperation with other projects have been very valuable for the PHARE project. Without this support and cooperation it would still have been possible to develop and apply the integrated modelling system as described in the Terms of References. However, with this support it has been possible to establish, calibrate and validate the models to a much higher level of refinement and accuracy than it would otherwise have been possible. Consequently, the direct practical applicability of the project outputs by the end of the project period have improved significantly.

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ESTABLISHMENT OF THE INTEGRATED MODELLING SYSTEM

4.1 Introduction

The Danubian Lowland between Bratislava and Komarno is an inland delta formed in the past by river sediments from the Danube. The entire area forms an alluvial aquifer, which throughout the year receives infiltration water from the Danube in the upper parts of the area and returns it into the Danube in the downstream part. The aquifer is an important water resource for municipal and agricultural water supply.

Various human activities have gradually changed the hydrological regime and affected the ground water quality within the study area. This study mainly concentrates on the man induced impacts on: ground water regime ground water quality surface water regime surface water quality sediment transport agriculture, and flood plain ecology

The Gab?ikovo hydro power scheme is the largest of the man induced impacts within the study area, and hence it plays a central role in this project.

4.2 Equipment

The core of the computer system is two Hewlett Packard work stations (HP Apollo 9000/735). Via a local area network these work stations have been interconnected to a number of personal computers and X-terminals providing a total number of 11 work places.

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In addition various field- and laboratory equipment and a project car have been procured. Table 4.1 provides an overview of the equipment procured under this project.

Table 4.1 Status of Project Equipment by January 1995.

Supply No Description Supplier Price ECU Status Minor supplies

MS 01 Copy machine CZ & CZ 9,200 Delivered, April 1993 + telefax

MS 02 PC equipment BSP 26,130 Delivered, July 1992

MS 03 PC equipment Zecco 6,360 Delivered, July 1992

MS 04 PC equipment APS 12,600 Delivered, July 1992

MS 05 MOOFLOW (software) Scientific 1,200 Delivered, May 1993 Software group

MS 06 Car Kama 10,400 Delivered, Feb. 1994

MS 07 Field equipment - E i jke1karnp 9,123 Delivered, April 1993 tensiometers and cer. cups for sampling of N03 leaching

MS 06 Field equipment - Venika 19,700 Delivered, August 1993 measurements of chemical parameters directly in obs.wells

MS 10 GPS Gravquick 46,900 Delivered, May 1993

MS 11 Laboratory equipment - Eijkelkamp 7,801 Delivered, July 1993 retention curves and gulph hydraulic conductivity

MS 12 Laboratory equipment - Skalar 40,725 Delivered, August 1993 measurements of N-components in soil, water and plants.

MS 13 2 X-terminals OIGIS 10,000 Delivered, August 1994

MS 14 2 X-terminals, DIGIS 30,630 Delivered April-May Computer memory 1995 upgrade, additional hard disk,UPS

MS 15 Arc/Info upgrade, UPS ArcGEO 12,370 Delivered March 1995

International tender - major computer supply

Lot 1 Modelling computer DIGIS 64,246 Delivered, Apr. 1994

Lot 2 Info server system ARC data 239,198 Delivered, Dec. 1993

Lot 4 A1 elstat plotter MATRA 45,541 Delivered, Oct. 1993

Lot 6 Local area network ED I CO 3,816 Delivered and installed, April 1994 GRAND TOTAL 595.940

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4.3 Danubian Lowland Information System

The Danubian Lowland Information System (DLIS) has been developed, providing a central database and Geographical Information System (GIS) with facilities for data storage, maintenance, processing and presentation. In addition, data can be imported and exported in file formats readable for the applied modelling system.

DLIS is based on two software resources, the Informix relational database and the Arc/Info GIS. All non-spatial data is stored in Informix and all spatial data in Arc/I- nfo.

The non-spatial data that is stored in Informix may be any kind of data that is related to a certain location. For instance time series of measurements ground water levels, concentration of oxygen in rivers, river discharge etc. It may also be information on soil horizons in a soil profile in terms of water retention curves and hydraulic conductivities. For all kind of information some additional information may also be stored. It could for instance be a description of soil horizons or name and address of the organisation that owns a certain observation well for ground water observations.

Spatial data stored in Arc/Info (GIS) could for instance be surface topography, geological layer boundaries, cropping and land use, river geometry etc. Spatial data may be displayed together with other spatial data (e.g. cities, roads, rivers etc.) or with point information like location of water supply production wells etc. Some examples on different types of spatial data are given in Fig. 4.1.

An interface between DLIS and MIKE SHE has been developed enabling exchange and presentation of data in MIKE SHE file format. In that way MIKE SHE results may be displayed together with any other data stored in the DLIS. An interface enabling storage of river cross-sections in MIKE 11 file formats has also been developed. A direct interface to the remaining modelling systems has not been implemented. However, data can easily be transferred from MIKE SHE file formats to any other of the relevant modelling systems.

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DLS SFW GLM

project boundary information points infonnatioa points

BCK center lines user contours marker horizon

boundaries grid marker horizon

lakes center lines/ipt overlay layer geometry grid

waterworks boundaries/ipt overlay layer geometry contours

road* GRW/SSL/THM user contours layer property

railways information points layer property grid

grid layer property contours

forestry tin

thicsscn polygons

Fig. 4.1 Different spatial data stored in Arc/Info.

4.4 Modelling Approach

A number of individual modelling systems have been applied within this study:

MIKE 11 which is a one dimensional river modelling system used for hydraulics, sediment transport and morphology and water quality.

MIKE 21 which is a two dimensional modelling system used for reservoir modelling, including hydrodynamics, sediment transport and water quality.

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MIKE SHE which simulates the major flow and transport processes of the hydrological cycle. MIKE SHE comprises the following main components which are fully coupled allowing for feedbacks and interactions between the components:

ID flow and transport in the unsaturated zone 3D flow and transport in the ground water zone 2D flow and transport on the ground surface ID flow and transport in rivers.

DAISY which is a one-dimensional root zone model for simulation of soil water dynamics and nitrogen transport and transformation.

4.4.1 Further development of modelling systems

Although the above mentioned models are generalized tools with comprehensive applicability ranges, some model modifications were needed in order to accommodate the very special conditions in the area. The following model modifications have been made as part of the project:

Daisy

A new crop growth and nitrogen module for maize has been developed.

Coupling of MIKE SHE and MIKE 11

A fully dynamic coupling of MIKE SHE with the hydraulic module of MIKE 11 has been developed. The two modelling systems are running simultaneously exchanging data in the computer memory.

Geochemical Model

A geochemical model describing chemical/microbiological processes related to transformations of nitrogen species, organic matter, oxygen and manganese. This model is linked to the solute transport module of MIKE SHE.

Simplified Unsaturated Zone Description in MIKE SHE

A simplified unsaturated zone description only accounting for gravity flow has been implemented in MIKE SHE.

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4.4.2 The integrated modelling system

The integrated modelling system is formed by the exchange of data and the feedbacks between the individual modelling systems. The structure of the integrated modelling system and the exchange of data between the various modelling systems are illustrated in Fig. 4.2.

MIKE 21 Hydrodynamics Sediment transport Water quality Eutrophication

/Sedimentation \in reservoir

DAISY MIKE SHE Unsaturated flow Water movement Water levels Crop growth Ground water transport Discharge Nitrogen transport Water quality Geochemistry Nitrogen transformation

Hydrodynamics Sediment transport Water quality Eutrophication

DLIS

Fig. 4.2 Structure of the integrated modelling system.

The interfaces A-E between the various models are briefly described below:

A) MIKE SHE forms the core of the integrated modelling system having interfaces to all the individual modelling systems. The coupling of MIKE SHE and MIKE 11 is a fully dynamic coupling where data is exchanged after each computational time step.

The remaining modelling systems are coupled in a more simple manner involving a sequential execution of various models and subsequently a transfer of boundary conditions from one model to another. Some examples are listed below.

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B) Results of eutrophication simulations with MIKE 21 in the reservoir are used to estimate the concentration of various water quality parameters in the water that enters the Danube downstream of the reservoir to be used for water quality simulations for the Danube using MIKE 11.

C) Sediment transport simulations in the reservoir with MIKE 21 provide information on the amount of fine sediment on the bottom of the reservoir. This information is used to calculate leakage coefficients which are used in ground water modelling with MIKE SHE.

D) The DAISY model calculates vegetation parameters which are used in MIKE SHE to calculate the actual evapotranspiration. Ground water levels calculated with MIKE SHE act as lower boundary conditions for DAISY unsaturated zone simulations. Consequently, this process is iterative and requires a few model simulations.

E) Results from water quality simulations with MIKE 11 and MIKE 21 are used to estimate the concentration of various species in the water that infiltrates to the aquifer from the Danube and the reservoir. This is being used in the ground water quality simulations (Geochemistry) with MIKE SHE.

4.4.3 Approach of model application

The procedure that has been applied in the model applications involves three steps:

1) Model setup; involves that the geometry of the system and some physical characteristics are implemented in the model. For instance river cross-sections, surface topography, soil physical parameters, land use, vegetation parameters and hydraulic conductivities in the ground water zone.

2) Model calibration; involves that a number of model simulations is carried out and model results are compared with measured data, until a satisfactory correspondence is obtained. All the applied modelling systems are physically- based implying that all input data can be assessed directly from field data. Thus, the model calibration has been limited to adjustment of a few physical parameters within narrow ranges.

3) Model validation; involves that the model demonstrates the ability to reproduce measured data outside the calibration period.

4.5 Ground Water Modelling

Ground water modelling has been carried out at different scales with different objectives. Thus, the following ground water models have been established:

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a regional ground water model for pre-dam conditions, a regional ground water model for post-dam conditions, a local ground water model for an area surrounding the reservoir a local ground water model for the river branch system, and a cross-sectional (vertical profile) model near Kalinkovo.

The regional model area covers about 3000 km2 but the main area of interest is the Zitny Ostrov which is the area between the Danube, the Little Danube and the Vah. The model area is shown in Fig. 4.3 for the regional model as well as for the local models.

The main objectives of the regional ground water modelling are to study the impacts of the damming of the Danube on the hydrological regime within the project area, in particular in terms of ground water levels and dynamics, and to provide reliable boundary conditions for local ground water models.

The objectives of the local ground water model around the reservoir are to provide more accurate results for this area than can be done with the more coarse regional model and to provide boundary conditions for the cross-sectional model.

The objective of the local model for the river branch system area is to provide more accurate results for this area than can be done with the more coarse regional model.

The objective of the cross-sectional model near Kalinkovo is to provide the hydraulic basis for geochemical modelling of the area where comprehensive project field investigations were carried out.

The applied modelling systems are MIKE SHE, MIKE 11 and the coupled version of the two. AH the modules of MIKE SHE have been applied implying that the major flow processes in the hydrological cycle are described.

The model setup is based on information on location of river systems and cross- sectional geometry, surface topography, climatology, land use and cropping pattern, soil physical properties and hydrogeology. The setup for the two regional models reflecting pre- and post-dam conditions is basically the same. The only difference is that the post-dam model includes the Hrusov reservoir and related hydraulic structures and canals.

The ground water flow regime on Zitny Ostrov is to a large extent controlled by the water level dynamics of the river. Time series of ground water levels measured at locations close to the Danube show a high degree of correlation with the water level fluctuations in the Danube. In zones further away from the river the ground water level dynamics is also significantly affected by precipitation.

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CO 1 -J 1 Q i

•&

I PS

Fig. 4.3 Extent of the regional model area, and indication of local modelling scales.

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In order to model the ground water flow regime within the model area it is therefore of the utmost importance that the river models are simulating the water level dynamics in the Danube correctly. The river model that is used in the ground water modelling is identical to the MIKE 11 river model of the Danube, which has been successfully validated.

The regional ground v/ater models apply a horizontal discretization of 500 m and in the vertical the aquifer has been divided into four geologically determined computational layers.

The pre-dam model was calibrated against measured ground water levels, discharge and water levels for the five year period from 1986 to 1991, and validated by demonstrating the ability to reproduce ground water levels measured after the damming of the Danube.

In general the model reproduces measured ground water levels and dynamics quite well. Figs. 4.4 and 4.5 show comparison of measured and simulated ground water levels for the calibration period and the validation period respectively. As seen the ground water dynamics as well as the levels have been changed significantly due to the damming.

The ground water model for the reservoir area is a sub-model of the regional model and the parameter values of the local model are identical to the ones in the regional model with the only change that the local model applies a horizontal discretization of 250 m, and a finer vertical discretization with 7 computational layers.

Similarly, the local model for the river branch area is a sub-model of the regional model. This local model has a horizontal discretization of 100 m.

The local models receive time varying ground water levels from the regional models as boundary conditions.

4.6 Pollution Status of Reservoir Sediments

The data collected and analysed within the present project are not sufficient to provide firm conclusions regarding the status of organic contaminants and heavy metals in floodplain sediments. From the existing data no general pollution has been detected. However, some samples from the flood plain along the Danube river showed relatively high contents of some PAH's, which can be attributed to local pollution. In respect to other processes affecting the migration of contaminants (mixing, sorption, decay, etc.), the identified local contents of PAH's in sediments are not likely to pose significant threats for deterioration of ground water quality. As the heavy metals origin in sulphides, which are rich on heavy metals, and are characteristic and common for the Alpino-Carpathian geologic situation, the relatively high contents for Ni, Cu and Fe might be explained by higher background

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contents in Slovakia. A significant portion of metals may be associated with non- reactive minerals. Potential release of metals follows probably destruction of reactive minerals like Fe-oxides, but other processes may be important as well.

4.7 Ground Water Quality

4.7.1 Geochemical field investigations at Kalinkovo

A geochemical field investigation has been carried out in a cross-section north of the reservoir near Kalinkovo (see Fig. 4.3). This investigation was directed towards the development of ground water quality during infiltration of the Danube river water into the aquifer. It has been suggested that a change in ground water quality may happen after damming the Danube due to enhanced infiltration of dissolved organic matter in the gravel aquifer.

Eleven multi-screen wells were installed forming a 7.5 km long cross-section close to the water supply wells at Kalinkovo. The multi-screen wells have been sampled frequently to investigate the ongoing (bio)geochemical processes during infiltration of the Danube river water into the aquifer.

A seasonal fluctuation in the concentrations of various species with a delay compared to the fluctuation of the Danube river water was observed for the screens that are close to the Danube. Interpretation of collected data indicates slow denitrification by both solid and dissolved organic matter and reductive dissolution of Mn-oxides, possibly manganite. It is not known whether or not the two redox processes interact.

4.7.2 Ground water quality model

A mathematical model has been developed that includes kinetic denitrification by solid organic matter coupled to reductive dissolution of Mn-oxides. The model consists of three components:

1) advective/dispersive transport of all chemical components 2) kinetically-controlled denitrification, and 3) (pseudo) equilibrium-controlled speciation and equilibrium-controlled inorganic chemistry.

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_ (m3/s) Bratislava discharge 7000 60001 5000 4000^ 3000- 2000^ 1000^ ^^ r (m) 1986 1987 1988 1989 1990 124j well 685 123^ 122: 121-i •<\ 120: \ :/ 1 ^> 119 —i—r~i—i—i—i—i—i—r T ~n—rn—T~T—i—r~i—m—i—m—rn—IT i—i—i—i—i—i—r~i—i—i—n—;—r*r" (m) 1986 1987 1988 1989 1990 well 690 125

• • obs — sim 128 T—i—i—n—i—n—rnrT~r~r~T~i—n—n—i i i i i i i—i—i—i—i—j—n—r~i—r~i—r~i—i—r~i—i—n—n—n—i—r~rn—r 1986 1987 1988 1989 1990

Fig. 4.4 Simulated and observed ground water levels in some wells on Zitny Ostrov (calibration period).

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(m) 122 well 685

' JAN^FEB ' MAR rAPR ' MAY1 JUN ' JUL ' AUG ' SEP ' OCT ' NOV ' DEC I JAN1 FEB ' MAR^'APR ' MAYT JUN ' JUL ~ (m) 1993 1994 well 690

JAN""" FEB ' MAR ^APR ' MAY ' JUN ' JUL ' AUG ' SEP ' OCT ' NOV ' DEC I JAN ' FEB ' MAR1 APR ' MAY ' JUN ' JUL (m) 1993 1994 „ „„ we 694 128 "

T 7 JAN ' FEB ' MAR ' APR ' MAY ' JUN ' JUL ' AUG SEP ' OCT NOV ' DEC I JAN ' FEB ' MAR ' APR ' MAY ' JUN ' JUL (m) 1993 1994 , _, 130 Wdl 721°

IOC,. __ _.. 1 ^'J JAN FEB MAR ' APR MAY JUN ' JUL AUG SEP ' OCT NOV DEC I JAN FEB MAR' APR MAY' JUN JUL (m) 1993 1994 133 Wdl 792

• • obs — sim JAN ' FEB ' MAR ' APR ' MAY ' JUN JUL AUG SEP ' OCT NOV ' DEC I JAN ' FEB ' MAR ' APR ' MAY ' JUN ' JUL 1993 1994

Fig. 4.5 Simulated and observed ground water levels in some wells on Zitny Ostrov (validation period).

682804VI/wrd97/)995-12-12/HRSyikn PHARE/EC/WAT/1 - Danubian Lowland Ground Water Model Final Report, December 1995 - Vol.1 4-14

The denitrification module is a simple, empirical first-order denitrification model, having two parameters. These parameters are a rate parameter and an apparent equilibrium constant for the redox couple NO3/NO2. The rate parameter determines the rate of denitrification and the equilibrium constant determines the occurrence of NO2 as intermediate denitrification product. The denitrification model includes also a more complex description where denitrification takes place under consumption of dissolved organic carbon in addition to consumption of solid organic matter.

The model has been tested for a geohydrological system based on geochemical data from Kalinkovo. These tests have shown that the geochemical model behaves qualitatively correct.

Conservative transport of 18O in the Kalinkovo cross-section and reactive transport has been modelled. The setup of a cross-sectional ground water flow model was based on detailed measurement on the cross-section. An example of a model simulation is given in Fig. 4.6 which shows simulated distribution of 618O in the Kalinkovo cross-section in April 1994 and a comparison of measured and simulated 518O in one of the wells at Kalinkovo.

4.8 Unsaturated Zone and Agricultural Modelling

The objectives of the agricultural studies were to evaluate the impact on agricultural potential and nitrate leaching risk on Zitny Ostrov, due to the damming of the Danube.

The applied modelling system is the DAISY model which simulates crop growth, water flow in the unsaturated zone and nitrogen transport and turnover. The model was calibrated on the basis of data from field experiments carried out during the years 1981-1987 at the experimental station in Most near Bratislava. During this process the crop parameters used in the model were adjusted to Slovak conditions.

After the initial setup and calibration, the model performance was evaluated through preliminary simulations using data from a number of plots located on an experimental field site at Lehnice. On the basis of comparisons between measured and simulated values of nitrogen uptake, dry matter yield and nitrate concentration in soil moisture, the model performance under Slovak conditions was considered satisfactory.

Modelling of the pre-dam and post-dam conditions regarding agricultural potential and nitrate leaching risk was carried out using a representative selection of soil units, cropping pattern and meteorological data covering the area of Zitny Ostrov.

682804Vl/wrd97/1995-12-12/HRS/lkn PHARE/EC/WAT/1 - Danubian Lowland Ground Water Model Final Report, December 1995 - Vol.1 4-15

d180(permil) Fluctuation of 180 in Well PZ-1/3 -ao

-10.0

-10.5-

-11.O

-11.5 -12.0 measured simulated -12.& m i w < ST~i at ' < P ' acr ' Wv ' otc | « ' m ' «« 1993 1994

KALINKOVO - modeled distribution of 1B0 on April 5, 1994 136.0

122.O:

108.0-

94.0- 180 (-per mil) ABOVE 11.20 11.10 - 1 1.20 80.0= 11.00 - 1 1.10 10.90 - 1 1.00 10.80 - 10.90 BELOW 10.80 66.0 250 500 750 1000

Fig. 4.6 Model results from the Kalinkovo cross-section, a) Modelled distribution of 5I8O in April 1994 and b) Comparison between measured and modelled 818O in one of the wells in the cross-section.

The simulations were carried out for the period 1986-1991.

The DAISY model uses time varying ground water levels simulated with the regional MIKE SHE ground water model as lower boundary condition, for the unsaturated flow simulations.

Cropping pattern and fertilizer application is included in the model based on measurements and statistical data from the £itny Ostrov.

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4.9 River and Reservoir Hydrodynamic Modelling

The main objectives for the hydrodynamic modelling are to provide calibrated and validated flow models to be used in relation to water quality, eutrophication and sediment transport modelling. Furthermore, water depths and flow velocities are important factors for ecological predictions.

The applied modelling systems are the hydrodynamic module of MIKE 11 and MIKE 21.

The following models have been setup, calibrated and validated:

one-dimensional MIKE 11 model for the Danube from Bratislava to Komarno one-dimensional MIKE 11 model for the river branch system at the Slovak floodplain. two-dimensional MIKE 21 model for the Hrusov reservoir.

The MIKE 11 models have been established in two versions reflecting post- and pre- dam conditions, respectively.

MIKE 11 on the Danube

The setup of the MIKE 11 model for the Danube is based on river cross-sections measured in 1989 and 1991.

The applied boundary conditions were measured daily discharge at Bratislava (upstream) and a Q-h relation at Komarno (downstream).

The model was initially calibrated for two steady state situations reflecting a low flow situation (905 m3/s) and a flow situation close to the long term average (2390 m3/s), respectively. Subsequently, the model was calibrated against water levels and discharges measured at Bratislava, Medvedov and Komarno in 1991.

The model was finally validated by demonstrating the ability to reproduce measured data from 1990. Fig. 4.7 shows the results of the model validation from Medvedov.

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• DISCHARGE m3/sec Medvedbv. 1 1 1 - - -1000 — - -2000 s Vy Y f r - /IIT \ ~7 - - 1 1 - - I - i JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 1990

Fig. 4.7 Validation of MIKE 11 model for the Danube for pre-dam conditions.

For the post-dam model some river reaches were updated with cross-sections measured in 1993. In addition the reservoir and related hydraulic structures and canals were included. As the conditions after damming of the Danube have changed significantly, recalibration for the post-dam model was carried out for the period April 1993 - July 1993. Subsequently, the model was validated against measured data for the period November 1992 - March 1993.

MIKE 11 on river branch system

The Slovak and Hungarian floodplain are at many locations characterized by a complex system of river branches. The area referred to as the river branch system covers about 20 km of the Slovak flood plain between the Old Danube and the hydro power canal. A layout of the river branch system is shown in Fig. 4.8.

This area is of major ecological interest and is one of the key areas for the ecological studies in this project (cf. Section 4.12).

The cross-sections in the river branch system were measured during the 1960's and 1970's.

The pre-dam model was calibrated against data from the 1965 flood.

682804Vl/wrd97/1995-l2-12/HRS/lkn PHARE/EC/WAT/1 - Danubian Lowland Ground WaCcr Model Final Report, December 1995 - Vol.1 4-18

Fig. 4.8 Layout of the river branch system.

In the post-dam situation the branch system is fed by an inlet structure with water from the hydro power canal (on the figure denoted diversion canal). The system consists of a number of compartments separated by small dikes (lines B-I). On each of these dikes combined structures of culverts and spillways are located enabling some control of the water flows in the system.

Only very scarce and not very reliable data on flow and water levels in the river branch system was available. Therefore, a programme comprising measurements of discharges and water levels at a number of locations was carried under this project during the summer 1994. Fig. 4.9 shows results of the model calibration against these data.

KMER LEVEl mder L4 . i i i i i i i 118.20- -

- 117 Wl-

- 117.60- • 117.40- \1\

117.00- 116.80- I- —i 1 1 1 i i I i i i i i i i i i 15/6 20/6 25/6 1994

Fig. 4.9 Comparison of measured and simulated water levels with in the calibration period, at one location in the river branch system.

682804V[/wrd97/I995-12-12/HRS/lkn PHARE/EC/WAT/1 - Danubian Lowland Ground Water Mode! Final Report, December 1995 - Vol.1 4-19

MIKE 21 on the reservoir

A MIKE 21 hydrodynamic model for the Hrusov reservoir has been established based on a reservoir bathymetry measured in 1994.

The model was calibrated against flow velocities measured in the reservoir in the autumn of 1994. The results of the calibration are illustrated in Fig. 4.10.

4.10 River and Reservoir Sediment Transport Modelling

The sediment transport modelling was based on the use of existing data on the sediment transport processes prevailing in the Danube river. Few additional measurements were carried out to complement these data. Different sediment transport models covering both the fine suspended sediment (cohesive sediment and fine sand) and the bed load sediment (coarse sand and gravel) were established.

Measurements of concentration of suspended sediment at different cross-sections showed that the suspended load has decreased significantly from the 50'ties to the 90'ties due to construction of new reservoirs and treatment plants upstream of Bratislava.

Based on these measurements and established sediment rating curves, both one- dimensional and two-dimensional sediment transport models of transport of fine (suspended) sediment were established for the Danube river, the reservoir and for the river branch system on the Slovak flood plain between the hydro power canal and the Old Danube. The period from November 1992, when the reservoir was taken into operation, to August 1993 was simulated in the two-dimensional MIKE 21 model. Sedimentation rates in the correct order of magnitude (approximately 10 cm in the sedimentation areas) was simulated.

Various grain sizes were included in the mathematical model enabling prediction of the grain size distribution of the new sediment deposits in the reservoir. This information was used together with the simulated thickness of the deposited sediment layer to calculate leakage coefficients for modelling water exchange between the surface water in the reservoir and the ground water beneath it. Sediment rating curves were estimated at different cross-sections based on the simulated sediment transport rates. Siltationas function of upstream discharge was subsequently derived. From November 1992 to August 1993, the simulated siltation rate (kg/day) was 42% of the total suspended load at Bratislava. Simulated sedimentation in the reservoir during November 1992 to August 1993 is shown in Fig. 4.11.

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100

20- 60 70 80 90 100 110 120 /130 HO 150 160 170 180 190 200 1990/01/13 00:01:00 7

Current 1 m/s Velocity Above 1.00 Wt 7 1.00 •MH °-o.2o° -- 0.70 H 0.05 - 0.20 am eeiow 0.05 ^1 lord

Calibration of the reservoir model hydrodynamics velocity distribution 1.0

I cross-section 1 simulation results ^ 0.8 measufemeni No.1 measurement No.2,

0.6 \f

0.4

0.2

0.0 100 200 300 400 500 600 dstamce from the left dike [m]

f srrulstion resuHs N 0.20 - fcross-section 2V~ & measurefnent No.2 0.15 - i\

0.10 - I

0.05 / islan d

0.00 - 1 , j ,, j——,-A soo 1000 1500 2000 2S00 3000 cfctenw from the left cite [m]

Fig. 4.10 Comparison of measured and simulated flow velocities in two cross- sections in the reservoir.

682804Vl/wid97/J995-12-12/HRS/tkn PHARE/EC/WAT71 - Danubian Lowland Ground Water Model Final Report, December 1995 - Vol.1 4-21

Alluvial channel bed material was investigated with respect to grain sizes and exhibited significant scatter due to the natural grading of the sediment inside the cross-sections with bars, pools etc. In order to avoid difficulties in determining accurate mean grain sizes for the mathematical model, the change in mean water level over a decade rather than changes in bed elevations was compared between observations and simulations. By using such an approach, perturbations in bed levels from one cross-section to another did not destroy the picture of the overall trends in aggradation and degradation of the river bed. The morphological model predicted the observed erosion downstream Bratislava during the last decades to a very satisfactory degree.

The reach between rkm 1820 and rkm 1840 (the Danube) is, under pre-dam conditions, characterized by a very complex flow pattern because the Danube interacts with the river branch system. These interactions are not properly described in the hydrodynamic model and consequently the simulated morphological development is less accurate in this reach. Simulated and measured erosion of the river bed is shown in Fig. 4.12 which also illustrates the effects of dredging.

Subsequently, the morphological model was used to evaluate the effect of the dredging which has been going on over the years. Also the effect of the Gabcikovo Dam was investigated with respect to changes in bottom elevations and mean water levels in the new course of the river as well as in the Old Danube.

4.11 Surface Water Quality Modelling

The goal of the surface water quality modelling was to establish models describing the water quality in the main stream of the Old Danube before and after damming, in the reservoir, and in the river branches, respectively.

A BOD-DO model (MIKE 11 WQ) has been used to describe the water quality in the main stream of the Danube in the pre-dam situation and in the main stream of the old Danube in the post-dam situation. This model describes oxygen concentration (DO) as a function of the decay of organic matter (BOD), transformation of nitrogen components, re-aeration, oxygen consumption by the bottom and oxygen production and respiration by living organisms.

The river branches were simulated with a eutrophication model (MIKE 11 EU), in which the algae production is the driving force. The algae growth in this model is described as a function of incoming light, transparency of the water, temperature, sedimentation and growth rate of the algae and of the available inorganic nutrients.

682804 V1 /wrd97/1995-12-12/H RS/lkn PH ARE/EC/WAT/1 - Danubian Lowland Ground Water Model Final Report, December 1995 - Vol.1 4-22

(tu OQ 6u!oodspu6)

Fig. 4.11 Simulated sedimentation in the reservoir from November 1992 to August 1993.

682804Vl/wrd97/1995-12-12/HRS/llcn PHARE/EC/WAT/1 - Danubian Lowland Ground Waler Model Final Report, December 1995 - Vol.1 4-23

In the reservoir the driving force is also the algae growth and hence a eutrophication model (MIKE 21 EU) was applied. This model is, in principle, the same as the MIKE 11 EU, but operates in two-dimensional (horizontally) whereas the MIKE 11 EU operates in one-dimensional.

To provide the basis for the modelling existing field data on water quality have been evaluated.

The field measurements show no significant changes in oxygen level in the Danube river from Bratislava to Komarno. The measurement has shown differences in oxygen concentration of up to 1 - 2 mg O2/l in the river. This difference can be ascribed to the diurnal variation created by oxygen production and respiration of the algae in the river water. Oxygen concentration in the outlet canal from the reservoir have been observed to be 4 mg O2/l higher than in the upstream river. This may also be due to oxygen production of the algae.

No vertical stratification of the water masses in the reservoir was observed during August and September 1994. The measured data do not indicate increases in BOD- level through the reservoir.

The BOD-DO model (MIKE 11 WQ) has been calibrated and validated to a satisfactory level both for pre-dam and post-dam condition. The model furthermore describes the diurnal variation satisfactorily. A comparison of simulated and measured oxygen concentrations in the Danube is shown in Fig. 4.13.

The conditions from pre-dam to post-dam have changed significantly, and hence a recalibration of the pre-dam model was necessary to obtain a well calibrated model for the post-dam situation. The pre-dam model was calibrated against data from October 1991 and validated against data from April and August/September 1991 The post-dam situation was calibrated against data from May 1993 and validated against data from June 1993.

Results from the eutrophication model for the river branch system against data from June-August 1993 (MIKE 11 EU) is shown in Fig. 4.14.

The simulated phytoplankton production is at the same level as the measured one and algae concentrations have been simulated correct within a difference of few micrograms chlorophyll. A little to high nutrient concentrations are at the moment simulated. Smaller adjustment through a continued short calibration procedure in the first quarter of 1995 is expected to bring this model to a stage where it is ready to use for simulation of different scenarios.

The EU model for the reservoir has also been satisfactory calibrated.

682804 VI /wrd97/1995-12-12/H RS/Ikn PHARE/EC/WAT/1 - Danubian Lowland Ground Walcr Model Final Report, December 1995 - VoJ. J 4-24

3000

2500 Dredging 2000 from 1974 to 1990, S 1500

1000

500

pff ffl 1 I ' 1 ' 1890 1880 1870 1860 1850 1840 1830 1820 1810 1800 1790 1780 1770 1760 chainage [km] b)

1.00 - 0.50 - 0.00 /- •^ ^^ t . 1 -0.50 / \ - -1.00 A \ / S - -1.50 - observed changes I -2.00 - —- simulated changes WITH dredging .3 -2.50 - ^— - simulated changes WITHOUT dredging -3.00 i 1 1 — i 1 1 i— L " ' 1 ' | 1 1890 1880 1870 1860 1850 1840 1830 1820 1810 1800 1790 1780 1770 1760 chainage [km]

Fig. 4.12 Amount of dredging (a) and the effect of dredging for the morphological development of the river bed (b).

4.12 Flood Plain Ecology and Modelling

The ecological studies mainly put focus on the Hrusov reservoir, the Danube river and the river branch system on the Slovak floodplain between the hydropower canal and the Old Danube.

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An ecological management tool has been developed. It is based on output from the established integrated modelling system and a number of criteria that links model results to a number of different ecotopes.

The integrated modelling system provides data regarding:

water quality and eutrophication sedimentation regime surface water flow regime, and subsurface flow regime

The ecological criteria are directly comparable with processed model results. The criteria are, for instance, expressed in terms of:

frequency, duration and depth of floodings average depth to ground water table variations in ground water table flow velocities in rivers primary production

A detailed model of the river branch system on the Slovak floodplain has been established. This model is based on the coupled version of MIKE 11 and MIKE SHE and describes the complex network of river branches, their interactions with the subsurface flow regime and the Old Danube.

The model setup is based on the MIKE 11 model for the river branch system and the MIKE SHE regional ground water models. The model was setup in a network of 100 m grid squares, and reflect pre- as well as post-dam conditions.

The model has been calibrated against measured discharges in the river branch system. Large amounts of water is lost as infiltration to the ground water on its way through the river branches. Hence, a successful calibration of flow in the branches require that exchange of water between surface- and subsurface flow regimes are simulated correctly.

An example of model results is given in Fig. 4.15 which shows the extent and depth of flooding in the river branch system in July 1993.

682804Vl/wrd97/l995-12-12/HRS/lkn PHARE/EC/WAT/1 - Danubian Lowland Ground Water Model Final Report, December 1995 • Vol.1 4-26

simulated Komarno ***** measured

I I I 1 I I I I I 1 . J_ 1 I 1 I i _ .1 I I I I I 1 1 1 I 14.000-

i—i—i—|—i—i—i—i—|—i—i i i | i—i—i—i—|—i—i—i—i—I— /5 5/5 2°/5 Medvedov

i i l i i t i I i i i i I i i i i. I .i 14.000- 12.000- 10.000- 8.000- i i i i i i 1 I i i i I 1 /5 1993 HROO °

Hrusov

14.000-

l i i iii i r i i [ i r i i l i i i i i i i i 5/5. ._._.„ 10/5 15/5 20/5 25/5 30/5 1993 Rajka

I f f .1 I I I I t I i I I I I I I ( I < I i t t I L 14.000- 12.000- 10.000- 8.000- "I—i—i i—i—[—i—i—i—i—|—i—i—i—i—I—i—i—i—i—I—i—;—i—i [~ 5/5 10/5 15/5 20/5 25/5 50/5 1993

Fig. 4.13 Comparison of simulated and measured oxygen concentrations in the Danube. Post-dam situation. Calibration.

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RAMH 2.971 N'eltoproduction Pelcgic system. gC/.T,2/day I I

2.000-

1.000-

0.000 JUN JUL AUG JUN JUL AUG 1993 1993 Chlorophyll a Net Production

RAMH 2.720 RAMH 2.971 IN, g/m3 IN, g/m3

2.00&

JUN JUL AUG JUN JUL AUG 1993 1993 1993 Inorganic Nitrogen

RAMH 2.720 RAMH 2.971 RAMH 4.953 IP, q/m3 IP, g/m3 — IP, g/m3

0.00& I I i 0.006- i I i JUN JUL AUG JUN JUL AUG JUN JUL AUG 1993 1993 1993 Inorganic Phosphorus

Fig. 4.14 Comparison of simulated and measured water quality data for the river branch system, (Baka branch).

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Water depth

160:

15a ua

12a Hydro power canal 110-

100:

6a sa

3a 2 km (cm) ABOVE 500.000 20: 250.000 - 500.000 O 100.000 - 250.000 1a I 25.000 - 100.000 | 1.000 - 25.000 BELOW 1.000 "ib 20 30 40 50 60 70 80 90 id6 ""lib" ""120 ""Ho

Fig. 4.15 Simulated areal extent and depth of flooding on 25 July 1993.

682804V]/wrd97/1995-12-J2/HRS/]kn PHARE/EC/WAT/1 - Danubian Lowland Ground Water Model Final Report, December 1995 - Vol.1 5-1 HI SK98K0049

SUMMARY OF MODEL APPLICATION

This chapter provides a brief summary of the model applications described in Vol- ume III of the Final Report.

5.1 Introduction

In order to illustrate the applicability of the established integrated modelling system a number of application scenarios have been carried out. The results of these scenarios can support technical decisions and management policies in the project area.

The contents of the scenarios have been discussed and approved at meetings of the Steering Committee. It should be emphasized that the selected application scenarios do not imply any preference with regard to water management regime, but have been made with an aim to demonstrate the applicability of the modelling tool. Hence, the presented model calculations should not be considered the final use of the model, but may serve as references of comparison when Slovakian specialists carry out further model calculations in the future.

5.2 Selected Water Management Regimes

In order to serve as a framework for the application scenarios four different Water Management Regimes were identified. The following terminology was used in the scenario simulations:

- A Water Management Regime is defined by the operation rules for the major structures at Cunovo, Dobrohost and Gabcikovo for the post-dam conditions and no regulation for the pre-dam conditions. Thus, given a hydrological time series of Danube inflow at Bratislava, the overall discharge regime can be explicitly calculated. Hence, the selected Water Management Regime defines the water management as far as the overall discharges are concerned.

- Management Options are here defined as options for management of the system under a given Water Management Regime, e.g. all management possibilities except for changes in the prespecified discharges at the three major structures that define the Water Management Regime.

682805Vl/wrd97/1995-I2-12/HRS/Ikn PHARE/EC/WAT/1 - Danubian Lowland Ground Water Model Final Report, December 1995 - Vol.1 5-2

- A Scenario is defined as calculations of conditions for ground water, agriculture or ecology under a given Water Management Regime and one management option.

The following general conditions have been assumed for the management scenarios:

- Scenarios will be limited to areas on Slovak territory.

- The presence of the Gabcikovo-Cunovo structures and the Hrusov reservoir (Variant C) forms the framework for all post-dam scenarios.

- Scenarios should be directed at key areas from an ecological or management perspective.

- The different scenarios should differ significantly from each other in order to show impacts of importance for the decision making.

The following four water management regimes have been chosen in agreement between the Slovak Ministry of the Environment and the Consultant.

/. Pre-dam 1990. The water management regime in 1990 serves as a reference for the pre-dam situation for ground water conditions, agriculture and ecology. This regime is characterized by no regulation at Cunovo, Dobrohost and Gabcikovo and by the river topography from around 1990.

//. Post-dam (400 m3/s). This regime is represented by the water management which has taken place since the filling of the side branches, i.e. since summer 1993. The discharge regime is characterised by an average annual discharge at Cunovo to the Old Danube of about 400 m3/s and an average intake to the river branches at Dobrohost of about 40 mVs.

///. Post-dam (800 m?/s). An allocation of 800 m3/s and 40 m3/s as average annual discharge to the Old Danube and intake to the river branches, respectively.

JY. Post-dam (200 m3/s, and more dynamic inlet to the river branch system) An allocation of 200 mVs to the Old Danube as average annual discharge and 40 m3/s. The inlet into the river branch system is, in average, approximately the same as in Water Management Regimes II and III, but with larger discharge variations.

5.3 Ground Water Flow Regime

The ground water flow was modelled using the MIKE SHE hydrological modelling system coupled with the MIKE 11 hydrodynamic modelling system.

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5.3.1 Objectives

The objectives of application scenarios in relation to ground water flow were:

- to study the regional ground water flow regime on Zitny Ostrov for WMRI, WMRII and WMRIII, mainly in terms of ground water levels and dynamics of the ground water table.

- to study the flow regime around the Hrusov reservoir for WMRI, WMRII and WMRIII, mainly in terms of ground water flow and infiltration from the reservoir.

- to provide ground water flow velocities for simulation of transport and geochemical transformation of solutes on regional scale and on local reservoir scale.

5.3.2 Main conclusions

Regional Ground Water Flow Regime

Comparison of model results of for WMRI (pre-dam) and the two post-dam scenarios WMRII and WMRIII lead to the following conclusions:

The damming of the Danube has lead to an increase in ground water levels in the upstream part of the Zitny Ostrov. In a narrow zone around the reservoir the ground water table has increased with about 4-5 meters, but in general the increase is in the order of 0.5-1 meter. In the central part of the Zitny Ostrov the ground water levels initially decreased with about 0.5-1 meter due to the decreased water levels in the Old Danube. However, when filling the river branch system the ground water levels was brought back to the pre-dam level. Fig. 5.1 shows the calculated differences between WMRI (pre-dam) and WMRII (post-dam, 400 mVs).

A comparison of two post-dam regimes, WMRII (400 nxVs) and WMRIII (800 m3/s), revealed only minor changes. In the upstream part of the Zitny Ostrov ground water levels were slightly lower for WMRIII than for WMRII. The largest difference is about 0.5 meter close to Samorin, but in general the differences is only in the order of 0.10 to 0.20 m. In a narrow zone along the Old Danube ground water levels will be higher in WMRIII than in WMRII due to higher water levels in the Old Danube for WMRIII.

The most significant difference between WMRI and WMRII/WMRIII is in the ground water table fluctuations. The sum of the annual ground water fluctuations (Pegelweg) in WMRII and WMRIII was reduced to about 1/3 of WMRI in most of the upstream part of Zitny Ostrov. However, a management scenario with temporal variations of water levels in the seepage canals indicate that for areas less than about 1.5 km away from the canals it will be possible to establish groundwater dynamics with the same Pegelweg as in WMRI (pre-dam).

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F/g. 5.7 Difference between WMRI (pre-dam) and WMRII (post-dam, 400 rnJ/s) in average ground water levels calculated corresponding to 1987 discharge conditions at Bratislava. (+ .-increase in WMRII, -.'decrease in WMRII).

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Ground Water Recharge

Before the damming of the Danube the major part of the ground water recharge took place in the reach of Danube where the Hrusov reservoir is now located. If siltation of the reservoir bottom takes place this might lead to significant changes in the infiltration pattern and hence also to the entire ground water flow regime on Zitny Ostrov. For WMRII and WMRIII only limited sedimentation takes place in the old river bed, from where most of the ground water recharge takes place. From Bratis- lava to Dobrohost a ground water recharge of just below 30 m3/s was simulated in average for WMRI in 1987. For WMRII and WMRIII a ground water recharge of about twice this amount was simulated. Practically, no difference in infiltration pattern was observed between WMRII and WMRIII. Ground water recharge will only change significantly if sedimentation takes place in the old river bed. Sediment transport simulations does not indicate that such a situation is likely, and hence problems with regard to a reduction of ground water recharge is not to be expected.

5.3.3 Assessment of uncertainties of model predictions

The uncertainties related to model prediction of ground water levels can generally be considered to be within the range 0.5-1 meter. The uncertainties on predictions of differences between ground water levels of two alternative scenarios can be considered to be less than the uncertainty on the absolute level.

The uncertainties related to prediction of ground water flow velocities of importance for transport and geochemical reactions may be large when considering small scales (< 100 m) due to the very significant spatial variability of hydraulic conductivities. However, if considering an area comprising for example 100 model grids the difference between average flow velocities in nature and in the model can be expected to be rather small. Hence, when making solute transport simulations the overall transport patterns and transport times can be expected to be simulated rather precisely.

5.4 Agriculture

The agricultural modelling was carried out using the DAISY modelling system.

5.4.1 Objectives

The main objectives of the agricultural scenario simulations was to assess the influence of the damming of the Danube on:

- crop growth potential on Zitny Ostrov

- irrigation requirements, and

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- nitrate leaching risk

In order to address these issues model simulations were carried out for WMRI and WMRII and the results were compared.

5.4.2 Main conclusions

The changes in agricultural production on Zitny Ostrov due to the damming of the Danube are marginal. The difference in crop yield indexes between pre-dam (WM- RI) and post-dam (WMRII) scenarios was simulated to be less than 1 % for irrigated as well as non-irrigated areas.

About 70-80% of the agricultural areas on Zitny Ostrov require irrigation. The damming of the Danube has not lead to significant changes in irrigation requirements. In areas where the ground water table has increased due to the damming of the Danube the ground water table is located a few metres into the gravel aquifer. The gravel layer forms an efficient capillary barrier and only if the ground water table enters the fine textured top soil irrigation requirements will be different. This has only happened at very few locations within the Zitny Ostrov.

The simulated average nitrate leaching is generally low compared to estimates from some Western European countries (eg Denmark) and appeared to be almost the same before and after damming of the Danube. The area weighted average leaching was 12.0 kg N/ha for WMRI and 12.3 kg N/ha for WMRII. The highest leaching (up to 30-35 kg N/ha) was simulated in areas where the top soil is thin. Fig. 5.2 illustrates the areal distribution of nitrogen leaching on Zitny Ostrov.

5.4.3 Assessment of uncertainties of model predictions

There are considerable uncertainties related to model predictions of the absolute values of crop growth and nitrogen leaching. These uncertainties can be reduced by further investigations, but this would require new field observations combined with modelling studies. In comparison, the uncertainties on estimates of irrigation requirements are less.

The uncertainties on differences between conditions corresponding to two alternative scenarios are, however, significantly smaller. Hence the above conclusions regarding possible changes in agricultural production, irrigation requirement and nitrate leaching can be considered to be reasonably accurate.

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all

2s (3 2

F/g. 5.2 Simulated average nitrate leaching (kg N/ha per year) from non-irrigated soil columns during the winter season in the period 1987-1991 for Water Management Regime II.

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5.5 Ground Water Quality

The modelling system applied was the Advection Dispersion and Geochemical modules of the MIKE SHE modelling system.

5.5.1 Objectives

The main objectives of the ground water quality modelling were:

to study if the presence of the reservoir together with the changes in infiltration of river water and ground water dynamics may induce changes in ground water quality. Fine organic matter may accumulate on the reservoir bottom, thereby creating a reactive sediment layer. The river water recharging the aquifer has to pass through this layer, which may induce a change in the chemical/biological composition of the infiltrating water. An increased infiltration of river water could also affect the quality of the ground water from being oxic or suboxic towards being anoxic, which is undesirable for the drinking water supply plants in the vicinity of the reservoir. Particular attention should therefore be on the likely redox status of the ground water.

to characterize the fate of NO3 leached from the agricultural fields in the inland area of Zitny Ostrov. High NO3 concentrations are observed in some inland wells, resulting from extensive leaching from the surface.

In order to describe the changes in ground water quality due to the damming of the Danube model scenarios were carried out for WMRI and WMRII.

The geochemical modelling is based on a ground water flow field calculated with the regional ground water models and with the local model of the reservoir area.

In order to simulate the fate of nitrate on regional scale time-series of nitrate on Zitny Ostrov was derived from DAISY scenario simulations.

Water quality parameters of the water that recharges the aquifer was estimated based on modelling results with the MIKE 11 Water Quality model of the Danube and the MIKE 21 Eutrophication model of the reservoir.

5.5.2 Main conclusions

The results of the regional model show that denitrification is slow when compared to other areas. This means that the shallow subsurface is susceptible to NO3 contamination from the surface. Minimizing NO3 leaching is therefore desirable for protection of the shallow ground water resources.

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The results for the reservoir model indicate that the change in geohydrological conditions for the reservoir causes a high flux of river recharge to the subsurface together with an increase in the infiltration area. This means that the water works would be more vulnerable to water quality degradation in the Danube river, since both the flow rates are higher and the distance to the infiltration area is shorter. Monitoring of ground water quality in the vicinity of the reservoir and the water works is thus of prime importance. Fig. 5.3 shows NO3 concentrations around the reservoir where some of the major water supply installations are located. The figure also illustrates the importance of including the denitrification process.

5.5.3 Assessment of uncertainties of model predictions

The uncertainties on predictions of ground water quality are significantly larger than uncertainties related to ground water levels and flow velocities due to uncertainties on geochemical processes and parameters. In this context the very large spatial variations of hydraulic and geochemical parameters at small scales (< 1 m) puts limitations to the accuracy which can be expected in the model predictions.

The complex geochemical model is believed to give a good overall description of the ground water quality regime for the Kalinkovo profile where local field data have been used for its calibration. The model can be considered to have predictive capa- bility in this area.

For predictions on localities outside the Kalinkovo area the complex model can not be considered very accurate. However, the developed model code is so general and contains the key processes, that it, after calibration against local data, can be expected to be able to provide accurate predictions. It is therefore strongly recommended to combine future geochemical modelling studies with local field monitoring programmes.

Used on a regional scale to simulate the fate of nitrate the model can provide orders of magnitude of concentrations and can serve as a good tool for assessing e.g. mass balance of nitrate taking influx from the river, leaching from the root zone and denitrification into account.

682805 V1 /wrd97/1995-12-12/HRS/lkn PHARE/EC/WAT/1 - Danubian Lowland Ground Water Model Final Report, December 1995 - Vol.1 Fig. 5.3a Simulations with the reservoir model for WMRII. Distribution of DOC

(dissolved organic carbon) and N03 taking the denitrification process into account.

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Fig. 5.3b Simulations with the reservoir model for WMRII. Distribution of DOC (dissolved organic carbon) and N03 without taking the denitrification process into account.

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5.6 Hydrodynamics, Sediment Transport and Water Quality in the Danube

The modelling systems applied are the hydrodynamic, sediment transport and water quality modules of MIKE 11.

5.6.1 Objectives

When the hydro power production at Gabcikovo was initiated the Danube water was diverted to the Gabcikovo hydropower plant leaving only a fraction of the water for the Old Danube. Obviously such a change will affect the hydrodynamics of the old river significantly. Reduced flow velocities and water depth in the Old Danube may induce water quality problems. The construction of the upstream reservoir in combination with the altered flow regime in the Old Danube may also change the sediment deposition/erosion pattern undesirably.

The main objective of the hydrodynamic, water quality and sediment transport simulation for the Danube is to predict (quantify) such changes.

Hydrodynamic, water quality and sediment transport simulations were carried out for all four Water Management Regimes.

Management options including construction of underwater weirs in the Old Danube or upheaveling of the river bed by supplying gravel were investigated. The aim of such management options should be to bring the water levels in the Old Danube back to the level before damming of the Danube.

5.6.2 Main conclusions

Hydrodynamics

By introducing eight underwater weirs with heights of about four meters in the Old Danube the water level can be increased in the order of 1 - 3 metres, which for low flow conditions (1000 m3/s) brings the water level close to the pre-dam (WMRI) conditions. For average flow conditions (2000 m3/s) the water levels for WMRI is about 1 - 1V4 m higher than in WMRII. Water levels in WMR III (800 m7s) is about 2 metres higher than WMR IV (200 mVs).

The studied underwater weir solution will make the Old Danube look rather unnatu- ral with a series of cascades, in particular during low flow conditions. The flow velocities between the weirs will be lower (0.5 - 1 m3/s for average flow), while the velocities on the weirs will be higher (2-3 m3/s for average flow). Therefore, it would be required to derive and study a more optimal shape of the weir as well as to accompany it with other measures.

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Sediment Transport

The overall morphological changes in the Old Danube have been assessed by using a one-dimensional model in which redistribution of sediment within a cross-section is disregarded. Due to the low flow velocities in the Old Danube for WMR II, WMR III and WMRIV almost no bed erosion will take place. Moreover, the river bed is not supplied with coarse material due to the trapping effects of the reservoir. Hence, large scale morphological changes in the Old Danube river bed are very modest according to the model. However, significant local changes (which cannot be resolved in the one-dimensional model) in channel forms may take place. If underwater weirs are constructed in the Old Danube transport of bed load and the coarser fractions of suspended load will be stopped at the weirs. Only the finer sediment fractions may be transported over weirs.

Close to the confluence between the outlet canal and the Old Danube bed erosion will take place due to a sudden increase in river discharge.

Water Quality

In general, water quality simulations do not indicate major problems in the Old Danube. For all post-dam scenarios the lowest oxygen concentrations are simulated in the backwater zone close to the confluence between the outlet canal and the Danube. Model results for a worst case situation are presented in Fig. 5.4. This situation corresponds to discharges of approximately 1000 m3/s at Bratislava of which all (WMR I), 400 mVs (WMR II), 800 mVs (WMR III) and 200 m3/s (WMR- IV), respectively, flows in the Danube channel between Cunovo and the downstream confluence with the power canal. Furthermore, respiration rates corresponding to the highest ones observed during the field campaign, i.e. summer periods with high biological activities, have been assumed. The oxygen concentrations have diurnal variations which generally increase with decrease in discharge. The concentrations shown in Fig. 5.4 are the minimum ones occurring early morning between 3 and 6 am. The maximum concentrations occurring late afternoon are typically 2-3 mg O2/l higher. It is seen from the figure that this worst case minimum concentration is 5-6 mg O2/l with the exception of WMR IV with underwater weirs, where it is around 2.5 mg O2/l. Whereas 2.5 mg O2/l in general is a very low concentration critical to fish species, but generally not to benthic faunal, it must be emphasized that this worst case situation will occur very rarely and over only a few km river length. Fur- thermore, this critical situation will have a duration of a few hours, so that the fish may move away and return afterwards. Hence, such rarely occurring worst case situations are not expected to have significant long lasting ecological effects.

5.6.3 Assessment of uncertainties of model predictions

The hydrodynamic models are considered very reliable. The uncertainty of water level predictions are assessed to be in the order of + 20 cm. By far the most

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important uncertainty is the fact that the river cross-sections are subject to continuous changes mainly due to gravel excavation. The consequence of this is that model uncertainties are a function of time. Hence, if the model can predict water levels with an accuracy of ± 20 cm this uncertainty may be + 50 cm in the year 2000. Thus, in order to maintain the predictive power of the model, river cross-sections in the model must be updated as changes occur and as new field surveys provide new cross-sectional data.

Model predictions of sediment transport, bed load as well as suspended load, are much more uncertain than prediction of water levels and velocities. Sensitivity analyses have indicated that the sediment transport predictions are accurate within a factor of 2.

The uncertainties of the oxygen predictions can within the calibration range of the model, i.e. WMR I and WMR III, be estimated to ± 1 mg O2/l. It should be noticed, however, that the very low oxygen concentrations predicted in WMR IV, represent values far outside the regime for which the model was calibrated. Hence, the simulated low oxygen concentrations are subject to larger uncertainties than the oxygen concentrations predicted for WMR I and WMR III. Similarly, it should be emphasized that the model has not been calibrated to conditions with underwater weirs. The higher reaeration due higher velocities over the weirs are incorporated explicitly in the model, but it has not been possible to calibrate this. These uncertainties can be reduced significantly by establishing a proper monitoring programme.

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to 00

Fig. 5.4 Longitudinal profile of a worst case minimum oxygen concentrations (6 a.m.) in the Old Danube for the different Water Management Regimes and Management Options.

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5.7 Hydrodynamics, Sediment Transport and Water Quality in the River Branch System

The applied modelling system was the hydrodynamic-, sediment transport- and eutrophication modules of the MIKE 11 modelling system.

5.7.1 Objectives

Before the damming of the Danube, the river branch system was filled with water and for high flow events the system was flooded and there was connectivity between the river branches and the main channel of the Danube. These connections were only functioning in high flow conditions a few weeks per year. After the damming the water level in the Old Danube decreased significantly and connections between the main river and the river branch system were blocked. In order to prevent the river branches from drying out a hydraulic structure was built at Dobrohost supplying the river branches with water from the hydropower canal. Hence, the flow regime in the flood plain system changed to an artificial regime, mainly controlled by the flow through the inlet structure at Dobrohost. This system provides many management options, namely the structure at Dobrohost, weirs and culverts within the river branch system and finally the water level (flow regime) in the Old Danube.

The main objectives of this chapter are to characterize the flow regime, the water quality regime and the sedimentation regime in the river branch system for the four different water management regimes.

5.7.2 Main conclusions

Hydrodynamics For all post-dam scenarios (WMRII-WMRIV), the water levels in most of the river branch system are higher than in the pre-dam (WMRI) conditions. The simulations, however, also clearly demonstrate that the hydraulic regime has been totally altered after the damming of the Danube. In brief, the post-dam simulations are characterized by branches which are continuously filled with water but in general with very low flow velocities and almost stagnant water in the most downstream compartments. Before the damming many river branches were dry or with stagnant water in the upstream compartments. In the more downstream compartments, the regime was much more dynamic than the post-dam regime, with dry periods and periods with high water levels and flow velocities during floods followed by periods with stagnant water. Although the simulated scenarios do not represent optimized situations, the model application has demonstrated that the flow regime in the river branches can be controlled to a large extent by operation of the Dobrohost weir in combination with operation of the culverts in the system. A more natural flood plain flow regime can only be obtained if the connections to the Old Danube are reestablished and if the water level in the Old Danube is increased. A longitudinal profile of flow velocities at different discharges is shown in Fig. 5.5. Furthermore, the figure illustrates the effects of establishing one connection to the Old Danube river and effects of decreas- ing invert elevations on the culverts in the river branch system.

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8 8 8 8 3 3 3 3

-3-

«1 P, 0°. t «1 P, «> CM N T* ^ »- o o o d o

Fig. 5.5 Longitudinal flow velocity profile in the main branch of the river branch system (+connections : reopening of one connection to the Old Danube, +new inverts: reduction of invert elevations on culverts in the river branch system).

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Sediment Transport

Siltation of suspended sediment in the river branches only takes place in the blind river branches with almost stagnant water. The main river branches in the upstream compartment are not subject to siltation due to high flow velocities. The main river branches in the downstream parts, where the flow velocities are lower, are not subject to siltation either, as practically no sediment reaches the downstream compartments.

Attempts to flush the system may, however, lead to situations where erosion takes place in the main branches in the upstream compartments, but settles again in the downstream compartments where flow velocities fall below the critical velocity for deposition. Thus, flushing of the system should be carefully studied using the model in order to avoid undesirable effects. The flushing simulations also indicate that it is not possible to flush blind river arms, hence, these will be subject to continuous sedimentation. Many blind river arms have been created due to blocking of the connections to the Old Danube. Hence, re-opening of some connections may enable flushing of such branches.

Water Quality

Simulations with the calibrated eutrophication (water quality) model do not indicate any significant eutrophication problems in the river branch system.

5.7.3 Assessment of uncertainties of model predictions

The uncertainty of the water level predictions are expected to be about 10-20 cm. With regard to flow velocities and discharges the uncertainties are relatively larger due to highly non-uniformity of the river branch channels and due to the significant water loss by infiltration.

The sediment transport model can be used for prediction of trends in sediment transport and of the potential sedimentation and potential erosion areas. Thus the model is suitable for qualitative evaluations of the effects of various operation strategies with respect to sedimentation in the flood plain system. For quantitative assessments the uncertainty of the model results is at least of the same order of magnitude as the sedimentation rates predicted by the model.

The water quality model gives most reliable results for the main branches, while there are larger uncertainties related to predictions in the small channels and in particularly in the blind ends of the river branch system, where either macrophytes in shallow areas or stratification of the water column at deep water locations may occur.

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5.8 Hydrodynamics, Sediment Transport and Water Quality in the Hrusov Reservoir

The applied modelling system includes the hydrodynamic-, sediment transport and eutrophication modules of the MIKE 21 modelling system.

5.8.1 Objectives

The objectives of the hydrodynamic simulations of the reservoir are to describe the surface water flow regime in terms of the flow depth and velocity distribution in the reservoir for the two post-dam water management regimes WMR II and WMR III. These regimes are crucial for the reservoir ecology and they create the basis for further sediment transport and eutrophication simulations.

The objective of sediment transport modelling activities is to study the effects of different discharge regimes (WMR II and WMR III) on the sedimentation patterns in the reservoir and thus to the leakage characteristics of the bed layer which may influence the infiltration to the ground water.

The objective of the water quality modelling of the reservoir is to assess whether eutrophication problems in the Hrusov reservoir can be expected or not.

5.8.2 Main conclusions

Hydrodynamics

There are no significant differences between WMR II and WMR III in terms of flow patterns and velocities in the reservoir for medium and high discharges.

Sediment Transport

The small differences in the flow pattern also result in only small differences in deposition patterns between WMRII and WMRIII. From the total suspended sediment inflow of 2.3 million t during a one year period, about 56% for WMR III and 60% for WMR II will deposit in the reservoir. During high flow periods, approximately 30% of the transported material will deposit in the reservoir, mainly in the downstream part. During low flow periods, almost all material settles down, the major portion in the upstream area. Based on the model results a relation between discharge and sediment load for WMR II and WMR III was established. This relation can be used to give a rough estimate of deposition in the reservoir for different discharges assuming reservoir operation rules similar to WMR II and WMR III. Fig. 5.6 shows the deposition patterns after one year of simulation for WMRII and WMRIII, respectively.

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Water Quality

Due to the short retention time in the reservoir no eutrophication problems in the reservoir will occur.

5.8.3 Assessment of uncertainties of model predictions

Although the available data to evaluate the accuracy of the hydrodynamic model are scarce, it is believed that the calculations of flow velocities in general are rather accurate. The largest uncertainties are related to situations with extremely high wind speeds.

The uncertainty of the model predictions for the overall reservoir sedimentation is estimated to be less than 50%. Local differences of a higher order of magnitude may occur due to bed forms which cannot be resolved in the 100x50 m2 computational grid. Continuous monitoring of reservoir sedimentation is required in order to improve the accuracy of the reservoir sediment transport model.

The uncertainties on the eutrophication model predictions cannot be directly estimated on the basis of the existing data. However, sensitivity analyses indicate that the uncertainties on the chlorophyll concentrations are about 20%, which will not affect the above main conclusion.

5.9 Ecology

Predictions of aquatic ecotopes in the Danube, the reservoir and in the river branch system are made on the basis of the results of the application scenarios described above.

Terrestrial ecotopes in the river branch system is predicted based on results of an integrated flood plain model. This model uses the coupled version of the MIKE 11 and MIKE SHE modelling systems.

5.9.1 Objectives

The objectives of the ecological predictions associated to the four Water Manage- ment Regimes are to demonstrate a methodology of combining the quantitative model predictions of hydrological conditions with qualitative ecological inferences.

As no clear ecological objectives have been decided for the area, and as it is outside the Terms of References of the present project to define such objectives, it is not possible to identify species which can be characterized as the most suitable indicators in describing the various ecotopes. Hence the description given below might as well have been based on other indicators.

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88S2; *- — o a i dddd. d d d o < I I I I I I • o o —

(UJ 09 6uioDdspij6) (tu OS BujoodspuB)

Fig. 5.6 Deposition of sediments in the Hrusov reservoir after one year of simulation in WMRII (a) and WMRIII (b).

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5.9.2 Main conclusions

Aquatic Ecotopes in the Danube River System

The conditions in terms of aquatic ecotopes in the river branch system and the Hrusov reservoir are very similar for all the studied post-dam regimes.

In the river branches conditions are characterized by generally low flow velocities. Due to the absence of flushing, muddy bottom sediments will develop in secondary branches and water vegetation is expected in all shallow reaches, eventually leading to the terrestrialization of narrow and shallow branches. However, for many species that can be considered typical for river branches, being mainly less critical rheophile species, a large variety in living conditions is maintained. Furthermore, it should be noted that detrimentally low oxygen conditions are not expected and that eutrophication as far as it may occur in the dead-end branches will be within the range of natural variation. However, conditions for typical species could be improved further if the weirs could be made passable to these less swift swimmers. Water vegetation typical for the periodical desiccation in former high water branches will disappear, since all branches and all the previously temporary pools have become permanent waters. Overall an increase in primary and secondary aquatic production is expected.

In the Hrusov reservoir less critical rheophile fish species will find suitable living conditions along the path of the former river channel. In addition, species typical for river branches may be expected in adjacent more shallow areas with moderate to slow flowing conditions. Upstream of the Cunovo weir large shallow areas are present where water vegetation will settle.

Because of the presence of weirs at Cunovo and Dobrohost and also those in the river branch system, most species will only be able to migrate upstream from Sap to Bratislava through the ship locks at Gabcikovo. The conditions for migrating species can be greatly improved by making these weirs passable.

Without underwater weirs and with an upheaveled river bed conditions for typical rheophile fish species in the Old Danube are slightly worse in WMR II than in WMRI while WMRIII has slightly better conditions than WMRI. WMR IV renders the Old Danube largely unsuitable for critical species, mainly because of too low flow velocities in the downstream parts. The reduction in flow velocities will, on the other hand, improve conditions for other species as compared to the pre-dam situation with the uniform river channels with very high flow velocities. The limited water level variation may induce the settlement of softwood species and a largely natural succession of softwood forests along shores and upon gravel banks.

With underwater weirs conditions for rheophile fish species in the Old Danube deteriorate in all water management regimes with WMR III being best. WMR IV makes the Old Danube largely unsuitable to most rheophile fish species, for which only suitable conditions may remain downstream of the Cunovo weir and some other

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weirs in the upstream part. However, reduction in flow velocities, will result in improved conditions for other species, and without knowing the ecological objectives it cannot be stated which condition is the most optimal.

Reestablishment of some connections between the river branch system and the Old Danube would be valuable in general.

Terrestric Ecotopes in the River Branch System without Underwater Weirs in the Old Danube

For WMR II (post-dam), flooding is less extensive, less intensive and varies only slightly between different years. Also variations in Pegelweg on a weekly, seasonal and inter-annual basis are less than for pre-dam conditions (WMR I). The Pegelweg variations can most likely be restored by maintaining suitable water level fluctuations in the seepage canal through operation of the hydraulic structures in the seepage canal. Average ground water levels have decreased in a narrow zone close to the Old Danube. In general, there is no significant change in ground water levels in the flood plain area due to the damming of the Danube, leading to very limited effect upon the flood plain forests and especially upon the less sensitive Canadian poplars. In terms of soil moisture regimes, limited effects could be observed for the rainwater dependent regimes (i.e. regimes where vegetation depends on rain rather than on capillary rise from ground water) that dominated already the northern and eastern parts of the modelled flood plain area.

Especially where flooding is less intense, conditions for the herb-layer will have changed substantially. An exception is areas in a limited zone along the river branches in the upper compartments were ground water levels have increased slightly-

Terrestric Ecotopes in the River Branch System with Underwater Weirs and Upheaveled River Bed in the Old Danube

Model results show that when using underwater weirs, average ground water may be restored in large parts of the area, especially in WMR III. For WMR II and even more for WMR IV, drained pockets with lower ground water levels adjusted to the water levels downstream of the underwater weirs can be expected.

Also soil moisture regimes are largely restored, although non-typical flood-rainwater dependent soil moisture regimes remain present in WMR II, and most probably especially in WMR IV. In WMR III also, previously shallow ground water levels (<0.7 m) may be largely restored and, as a consequence, also ground water dependent moisture regimes.

The conclusions regarding terrestrial ecotopes are made on the basis of model results with the integrated flood plain model. Important information has been provided by mapping ground water classes and soil moisture classes based on combinations of

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different model results. An example of a map of different ground water classes is shown in Fig. 5.7

5.9.3 Assessment of uncertainties of model predictions

In general, predictions of ecological changes are more uncertain than model predictions of changes in water levels, flow velocities, sedimentation and surface water quality. In the present case this is reenforced by the lack of suitable data for calibration of the 'ecological model'. Use of data presently being collected as part of a comprehensive ecological monitoring programme can improve the reliability of the ecological predictions.

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I (0 I

Ul 1 u o PHA R I !

00 00

C Q o

c o O

Fig 5.7 Average Ground Water Classes for the growing season of 1989 (WMRII, with under water weirs in the Old Danube).

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CONCLUSIONS AND RECOMMENDATIONS

This chapter provides a brief summary of conclusions with respect to project implementation issues. Furthermore, the chapter contains recommendations on future applications of the modelling system and on water resources management in the project area.

6.1 Conclusions Regarding Project Implementation

The project has been completed in accordance with the Terms of References. In the following some key features in this respect are emphasized.

6.1.1 Equipment

Equipment for almost ECU 600,000 has been procured and installed during the project. Computer hardware and software constituted the main equipment items, but field and laboratory equipment as well as office equipment were also included. The backbone of the computer system is formed by two Hewlett Packard Apollo 9000/735 UNIX workstations.

The procured equipment has been extensively used during the project and it has fully accommodated the needs of the project. Although, the progress in developments of faster computers and more advanced software is tremendous in these years, the procured equipment will technologically be at the front end for years yet to come.

6.1.2 Establishment of a generalized integrated modelling system

An integrated mathematical modelling system suitable to address the water resources problems in the project area has been established. The modelling system is based on the following packages which can be used individually or brought together in an integrated manner:

* MIKE SHE which, on catchment scale, can simulate the major flow and transport processes of the hydrological cycle which are traditionally divided in separate components: 1-D flow and transport in the unsaturated zone 3-D flow and transport in the ground water zone 2-D flow and transport on the ground surface 1-D flow and transport in the river.

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All the above processes are fully coupled allowing for feedbacks and interactions between components. In addition to the above mentioned components, MIKE SHE includes modules for multi-component chemical reactions in the ground water zone.

* MIKE 11, which is a one-dimensional river modelling system. MIKE 11 is used for hydraulics, sediment transport and morphology, and water quality. The modules for sediment transport and morphology are able to deal with cohesive and non-cohesive sediment transport, as well as the accompanying morphological changes of the river bed.

* MIKE 21, which is a two-dimensional hydrodynamic modelling system. MIKE 21 is used for reservoir modelling, including hydrodynamics, sediment transport and water quality.

* Both of the above mentioned models include River/Reservoir Water Quality (WQ) and Eutrophication (EU) modules to describe oxygen, ammonium, nitrate and phosphorus concentrations and oxygen demands as well as eutrophication issues.

* DAISY is a one-dimensional root zone model for simulation of crop production, soil water dynamics, and nitrogen dynamics in crop production for various agricultural management practices and strategies.

The above mentioned models are all generalized tools with comprehensive applicability ranges, they represent state-of-the-art technology, and they are well proven in a large number of international projects. In addition, some model modifications have been carried out during the project in order to accommodate the very special environment and problems observed in the area.

6.1.3 Establishment of Danubian Lowland Information System (DLIS)

An automated system has been developed to support the modelling activities. The integrated modelling system is interfaced to a central information system, called Danubian Lowland Information System (DLIS). DLIS can provide the different models with key input data and comprises post-processing facilities to elaborate further on the modelling results.

The two main components of the DLIS are a geographical information system (GIS), based on the ARC/INFO software package, and a relational data base management system (RDBMS), based on the INFORMIX software package.

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6.1.4 Establishment of calibrated and validated models

On the basis of the generalized integrated modelling system and the DLIS a number of specific models has been established:

* 1-dimensional and 2-dimensional models of the Danube, the Hrusov reservoir and of the complex system of river branches on the Slovak flood plain. These models are able to address hydrodynamic-, water quality- and sediment transport aspects.

* Ground water flow on the Zitny Ostrov on regional and local scales.

* Transport and geochemical transformation of solutes.

* Crop growth, irrigation requirements and nitrate leaching.

These models are specifically calibrated and validated for the project area.

6.1.5 Model applications

The established models have been applied to selected number of practical problems, partly for demonstrating their applicability and partly for assisting the water resources decision makers by providing technical results to specific questions.

The model applications have been performed under a scenario framework comprising four different Water Management Regimes. The specific content of the Water Management Regimes and the associated scenarios have been defined through discussions in the project Steering Committee and through discussions with the Slovak Ministry of the Environment.

The four Water Management Regimes (WMR) are characterized as follows:

* WMRI is a reference situation reflecting the pre-dam situation.

* WMRII reflects a post-dam situation where in average about 400 m3/s are diverted from the reservoir to the Old Danube.

* WMRIII reflects a post-dam situation where in average about 800 m3/s are diverted from the reservoir to the Old Danube.

* WMRIV reflects a post-dam situation where in average about 200 mVs are diverted from the reservoir to the Old Danube.

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6.1.6 Cooperation with Slovakian organisations

During the project the Consultant has cooperated closely with several Slovakian organisations. Most importantly, staff members from the following Slovak organisations have participated actively in, and have made comprehensive contributions to, the project:

Comenius University (PRIF UK) Research Centre for Irrigation (VUZH) Water Research Institute (VUVH) Ground Water Consulting Ltd. (GWC)

PRIF UK is the recipient institution and the end user of the established models.

6.1.7 Transfer of technology and know-how

10 staff members from PRIF UK, VUZH and VUVH have in the beginning of the project received basic training in the applied modelling systems. Subsequently, they have in close cooperation with Consultant staff members established the various models from the first data collection and interpretation to the final model validation. During phase II of the project the Slovakian staff members have gradually taken over the major part of the work and most of the model application scenarios have been done almost independently by Slovakian staff members. These staff members are now fully trained and have obtained sufficient working experience with respect to the applied modelling systems. Hence, in this respect the transfer of know-how and technology has been very successful.

All project equipment, including the established modelling systems and DLIS as well as the specific model setups and data used during the project, have been successfully transferred to a new project office at PRIF UK.

However, as a result of various organisational changes during 1995 7 out of the 10 trained Slovakian staff members changed job from PRIF UK and VUVH respectively to a private firm, Ground Water Consulting Ltd., and one trained Slovakian staff member changed job from VUVH to the Slovak Ministry of the Environment. Thus, the full project know-how has not, as originally intended, been transferred to PRIF UK. Therefore, the Slovak Ministry of the Environment has initiated training of a new group of specialists established at PRIF UK. The training of this group will take place under a separate contract financed through additional funding by the EC. The training started in September 1995 and is to be completed by the end of March 1996.

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6.1.8 International workshops

Two international workshops with participation of invited international specialists as well as Slovakian specialists have been conducted in June 1992 and in June 1995, respectively.

The first workshop, which took place during the Inception Phase, served as a review of the problem assessment, field works, modelling methodology and detailed project plans proposed by the Consultant.

At the second workshop, which took place in the middle of Phase II, the results of the model calibrations, model validations and the first model application results were reviewed.

Both workshops were held in a very positive atmosphere, and both the international and the Slovakian specialists provided constructive criticism and contributed significantly with many ideas and suggestions of considerable value for the project.

6.2 Recommendations on future Applications of Modelling System

The water resources problems in the project area are so complex, the amount of available data so large and the number of possible management options so high that it, in accordance with the Terms of References, has not been possible to fully process all technical data nor to provide optimal technical solutions to all the problems.

The established modelling system has, as a result of the comprehensive model validations and subsequent model applications, proven to be able to address the most important water resources problems in the area. The modelling tool thus established and now transferred to the Slovakian user has comprehensive fields of applications in connection with the future water resources management in the area.

Thus, it is strongly recommended, and in full accordance with the ultimate objectives of the Terms of References, that the modelling system and data bases established during the project be further applied in the coming years.

The following two subsections outline some obvious fields of future model applications and provide recommendations with respect to the new modelling group at PRIF UK.

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6.2.1 Future model applications

On the basis of the model applications carried out during the project it is recommended to use the established modelling tool to carry out, amongst others, the following types of studies:

* Studies of the many possibilities for management in the Old Danube and the river branch system. The model scenarios carried out during this project have illustrated how the models can be used to predict the conditions in this area assuming different flow regimes and different management options such as underwater weirs in the Old Danube. The established models of the Old Danube and the river branch system provide reliable tools for defining management rules and operational practices, for instance in connection with flooding of the river branch system.

* Design studies of shape and type of underwater weirs, including the slope at the downstream side of the weir and including combinations with groynes.

* Studies of sediment flushing possibilities in the reservoir.

* Studies of sediment flushing possibility in the river branch system.

* Studies of alternative reservoir operation scenarios for how to manage situations where one or more of the structures at Gabcikovo or Cunovo are temporarily not fully functioning. This can form the basis for preparation of emergency plans.

* Studies of possible reestablishment of some connections between the river branches and the Old Danube. This would involve optimal location of connections and design and location of underwater weirs and/or establishment of gravel banks. The established models are ideally suited for such studies.

* Studies of possible effects on ground water pollution of point sources of nitrogen from e.g. manure.

* Studies of ground water pollution from point sources due to e.g. landfills and industrial waste dumps. Such studies have not been included in the present project, but the integrated modelling system is very suitable for such applications.

* Studies of possible effects on ground water dynamics of management of water levels in seepage canals.

* Studies of future development of ground water quality. This should be carried out in combination with the recommended future monitoring of ground water quality.

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Studies of ecological effects of different management options in the river branch system, including various flow regimes. This should be carried out in combination with the recommended future monitoring of ecology in the area.

6.2.2 Future modelling group at PRIF UK

At present, the modelling group trained during the project, now working with Ground Water Consulting Ltd, is fully capable of handling the modelling tools.

In order to upgrade the new group of specialists at PRIF UK to the same level, it will be required that the staff members of this group get the following training and working conditions:

* A basic training course, comprising theoretical and practical/operational introductions to the modelling systems as well as introductions to the established models.

* Full time working experience with the models.

6.3 Recommendations on Water Resources Management in the Danubian Lowland

Experiences from other countries suggest that the reservoir and river system may not come into a new equilibrium for the first couple of years. Hence it is strongly recommended to combine future model applications/predictions with a monitoring programme, which should continue for some years, e.g. on aspects related to floodplain ecology, sediment transport/morphology and geochemistry.

It is outside the Terms of References of the present project to define management objectives or to suggest a management decision framework for water resources. In line with strong recommendations from the international specialists at both international workshops it is recommended that the Slovakian authorities give emphasize to these issues.

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