CONCEPTUAL OVERVIEW OF THE REVITALIZATION OPTIONS FOR THE SIDE-ARM SYSTEM OF VÍZVÁR-BÉLAVÁR

PROJECT PARTNER: Directorate of the Duna-Dráva National Park

SUBCONTRACTOR: Inno-Water Research and Environmental Services Ltd.

APRIL 2014, BUDAPEST

Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

Table of contents 1 Introduction and preliminaries ...... 11 1.1 Introduction ...... 11 1.2 Tasks ...... 12 2 Introduction to the area ...... 14 2.1 General introduction to the area ...... 14 2.1.1 The location of the planning area ...... 14 2.1.2 Relief, geological and soil characteristics ...... 14 2.1.3 Climate ...... 16 2.1.4 Characterization of the Hungarian Dráva stretch ...... 16 2.1.5 Flood control and protection ...... 21 2.1.6 Navigation ...... 22 2.1.7 Nature conservation ...... 23 2.1.8 Ecosystem elements ...... 25 2.2 Regulation of the Dráva River ...... 26 2.2.1 River regulation until 1886 ...... 26 2.2.2 River regulation from 1886 until World War I...... 29 2.2.3 River regulation between the two world wars and during the Second World War 31 2.2.4 River regulations from 1945 until the 1980‘s ...... 32 2.2.5 The results of the river regulation ...... 35 2.3 Presentation of the side-arm system of Vízvár-Bélavár and of the affected Drava section ...... 37 2.3.1 The Lower side-arm of Vízvár ...... 38 2.3.2 The Upper side-arm of Vízvár ...... 38 2.3.3 The Side-arm of Bélavár ...... 39 2.3.4 Gravel-pit lakes of Bélavár ...... 41 2.3.5 Lower Drava (AEP438) water body ...... 42 2.3.6 Land use on the planning area ...... 44 3 Principles of habitat revitalization ...... 46 3.1 Revitalization objectives as determined in watershed management plan ...... 48

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 2 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

3.2 Baselines of the Vízvári-Bélavári side-arm system habitat revitalization conceptual plan 51 4 Options for habitat restoration on the basis of the international literature ...... 53 4.1 Examples from Hungarian and foreign practice for revitalization of rivers with similar geographic characteristics ...... 53 4.1.1 Revitalization of the oxbows of River Morava (Slovakia)...... 53 4.1.2 River restoration and prevention of riverbed-erosion in the Danube Floodplain National Park (Austria) ...... 57 4.1.3 Revitalization of the oxbows of the River Saône (France) ...... 65 4.1.4 Revitalization of River Ain (France) ...... 67 4.1.5 Proposals for the restoration of River Spree (Germany) based on the assessments of zoobenthos habitats...... 73 4.2 Options for managing channel deepening based on international experience ...... 76 5 Analysis of the Drava River water regime and alluvial flow on the project reach ...... 78 5.1 Statistical analysis of the Drava River water regime ...... 78 5.1.1 The methodology and objectives of the analysis ...... 78 5.1.2 The analysis of the water level and velocity data measured at Őrtilos river gauge 80 5.1.3 The analysis of the water level and velocity data measured at Vízvár-Heresznye river gauge ...... 84 5.1.4 The analysis of the water level and velocity data measured at Barcs river gauge 86 5.2 Forecast of water level permanence of the Drava River ...... 90 5.2.1 The Drava River water levels extrapolation at the gauge of Őrtilos ...... 91 5.2.2 The Drava River water levels extrapolation at branch system of Vízvár-Bélavár 92 5.2.3 The Drava River water levels extrapolation at the gauge of Barcs ...... 93 5.3 Description of the sediment conditions on the Drava River ...... 94 5.3.1 Sediment volume based on regular measurements at the gauge of Barcs ...... 94 5.3.2 Sediment volume on the region of Bélavár ...... 95 5.3.3 The rolling sediment samples grain composition at Bélavár ...... 97 5.3.4 The suspended sediment samples grain composition at Bélavár ...... 101 6 Observations and conclusions of the geodetic surveys and the site inspections ...... 105

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 3 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

6.1 Location and time of the geodetic surveys ...... 105 6.2 Geodetic survey results of the important channel alternatives in terms of the side- arm-system revitalization ...... 107 6.2.1 Description of the 1st Channel alternative ...... 108 6.2.2 Description of the 2nd Channel alternative ...... 110 6.2.3 Description of the 3rd Channel alternative ...... 112 6.2.4 Description of the 4th Channel alternative ...... 113 6.2.5 Description of the 5th Channel alternative ...... 115 6.2.6 Description of the 6th Channel alternative ...... 118 6.2.7 Description of the 7th Channel alternative ...... 119 7 Characterization of the state of natural water supply Vízvári-Bélavári branch system . 121 7.1 Methodology used ...... 121 7.2 Analysis of the relation between the Drava water-levels and inflow levels at given frequency ...... 122 7.3 The scientific investigation of the frequency of natural water recharges in 2009- 2013. 123 7.4 The analysis of the long-term changes in natural water recharge frequencies ...... 126 8 Managing the problem of riverbed deepening of the Drava ...... 131 8.1 Prevention of the channel deepening by adding coarse gravel ...... 133 8.2 Prevention of riverbed deepening by slowing the river ...... 138 9 Review of the revitalization opportunities at the Vízvár-Bélavár side-arm system ...... 141 9.1 Implementation of the water supply by the local elevation of Drava water levels . 142 9.1.1 The impact of the water level elevation on the water recharge alternatives .... 144 9.2 Partial dredging of the channel line of water supply ...... 148 9.2.1 Effects of partial dredging to the water coverage of supply channels...... 149 9.3 Simultaneous application of the dredging and water level increasing of the Drava 157 9.4 Summary of potential water supply alternatives and the proposed solution ...... 159 10 The potential impact of the interventions on land-uses and the concerned parties ...... 164 11 Summary ...... 170 12 Bibliography ...... 174 13 Annex of photos ...... 180

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 4 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

Executive summary

In the frame of DANUBEPARKS STEP 2.0 SEE/D/0165/2.3/X/02 tender the Directorate of the Duna-Dráva National Park (DDNPI) is making the preliminary preparations for the revitalization of the Vízvári-Bélavári side-arm system. The subcontractor Inno-Water Ltd. was entrusted to prepare a conceptual plan containing alternatives for the habitat revitalization opportunities. The Vízvári-Bélavári side-arm system area concerned covers the Vízvári and Bélavári side- and dead-arms and includes the Bélavári gravel pit mine lakes as well. The river regulation activities in the past few decades (century) resulted in the shortening of the length of the Drava River by cutting through the curves and ultimately increased the velocity of the water. The hydroelectric power dams constructed on the upper stretch of the Drava since 1918 resulted in a drastic decrease in bed-load transport and this was followed by the increased bed and bank erosion processes. Due to the alternated hydromorphological characteristics of the river and the increased water velocities the sinking rate of the river bed averages at about 2-4 cm/year. This process is also mirrored in the decreasing absolute water levels which tendency will continue in the future. Due to the altered river path and bed-load transport processes the natural dynamics of the floodplains have also be effected. According to this, the water supply of the side-arm system decreased considerably the cut of side-arms developing to dead-arm branches and siltation processes prevail. All of these result in highly undesirable ecological and hydrobiological changes. As the Drava water level is continuously decreasing, the water supply into the highly variable Vízvári-Bélavári side-arm system has also been deteriorated throughout the past decades. For the mitigation of the above described disadvantageous processes the primary aim of the planned habitat revitalization project is to manage river bed erosion (slow down or stop) at the Drava section in question (191-198 rkm) and the restoration of the former floodplain dynamic (water supply into the floodplain areas) and ultimately the improvement of habitat-diversity and restoration thereof. The primary objective of the present study is to determine the theoretical possibilities of the revitalization of the area of concern, evaluate them, and on the basis of the results determine the feasible and sustainable design principles of the floodplain revitalization. Assessment and determination of existent data and information gap was also an objective to pinpoint the necessary studies in future to support decision making processes. According to the baseline principles the choice of the potential mitigation measures is based on the minimal perturbance of the area so that the high nature conservation priority areas

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would be disturbed only at minimal level. This would indicate the preference on those methods that can avoid large volume dredging activities and minimization of operational construction. From this principal priority follows the basic aim of the revitalization project to enhance and upgrade the lateral erosion processes on the area of concern in order to improve and sustain the water supply of the side-arm system form the Drava River. The revitalization should enhance the formation of novel gravel islands, natural banks, littoral zones and enhanced formation of side-arm system in general that would provide ground for the evolution of mosaic pattern, variable habitats that prevails earlier on the area. Apart from the enhancement of natural processes care should be taken on other land uses and priorities of other stakeholders regarding the direct and indirect effects of the future revitalization works. Therefore an analysis was given on these particular impacts and boundary conditions. Data and information available on the natural condition, geography, hydrology, ecology of the area have also been assessed and evaluated in details. Information related to river training activities in the past clearly indicated that the upper section of the Bélavári side-arm has been closed (more than 100 years ago) whilst the lower stretch of the Bélavári side-arm had hydraulic connection to the Drava main arm prior to the cut off the Vízvári curve in 1979-82. Detailed evaluation of the presently prevailing natural conditions and processes provides a solid scientific-technical ground to determine the potential alternatives for revitalization actions. Analyses into the water gauge levels at various Drava sections for a historical period (back up to 1970) prevailed the water level changes (sink) and the rate of the decrease of the level of the riverbed. On the basis of these calculations the determination of the absolute levels above the Baltic Sea level was conducted in order to determine the levels at the inflow points of the side-arm system. Based on the historical data the rapid sinking process of the Drava River bed was evidenced at this particular river section. This would certainly indicate the irreversible process of cutting off the side-arm system from the main river in the near future. By the use of statistically evaluated hydrological data conditions of the water supply of the side-arm systems could be predicted (inflow to the system, water coverage, etc.) that can serve as baseline information for the design of revitalization alternatives and their comparison. There were geodetic survey conducted earlier on the area however, these did not covered the area fully. In the frame of the present project therefore further complimentary geodetic surveys were included. In addition to the geodetic survey on-site inspection through several days were conducted both in Hungarian and Croatian areas in order to map the still existent, residual riverbeds and side-arms. During the on-site inspection additional geodetic measurements were also made. On the basis of the results of these investigations we pin-

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pointed those side-arms and water supply paths that can play vital role in the water supply of the Bélavári side-arm and the upper stretch of the Vízvári side-arm. Via the given path we used the cross-sections of the river bed residues and determined their minimal levels (minimum level of the riverbed at a particular cross-section) and we constructed a longitudinal stretch of these. This was followed by the determination of those elevation levels that enables the Drava water to penetrate into the side-arm system by exceeding the minimum riverbed levels as determined in the side-arm system (inflow levels). Following this, the water could be transported via the determined river paths. On the basis of the results of the geodetic survey and the statistical analyses of the Drava water levels we determined the duration of water supply in terms of number of the days, annually. In summary it can be concluded that the decrease of the number of the flow- through days is on a continuous decrease due to the ever sinking river bed in the period of 1970-2013. It is important to note, that apart from the upper stretch of the Vízvári upper section (which has hydraulic connection to the main arm of the Drave almost across the whole year) the other water supply paths (6 flow through paths investigated) are having only 3-7 occasions annually maximum. Based on this and regarding the data on sinking river bed it can be stated unequivocally that the full closure of the side-arm system from the mother river is expected to occur during the forthcoming 10-15 years. It is also evident that the presently almost continuous hydraulic connection of the Vízvári side-arm upper stretch will also be degraded in the coming 10-20 years. On the basis of the results the development of revitalization alternatives at the conceptual level has paramount importance to mitigate the ongoing deterioration processes and to preserve the presently existent habitat diversity of the area. The aim of the revitalization works should not target the restoration of the conditions prevailed in 40-50 years since the aquatic and terrestrial communities have already been adopted to the changes induced by the closure processes. Revitalization measures should improve the water supply of the area but should not case the full inundation thereof. The calculations conducted during the present study also enlighten the fact that the sustainability of the Vízvári-Bélavári side-arm system requires the slowing down or the stop of the Drava riverbed sinking and erosion processes on this particular river section. In failing to meet this criterion the effect of the measures should be considered as temporary solution for water supply (10-20 years). The river bed erosion of this particular Drava section could be mitigated via two principal measures. Analytical results and earlier literature data concerning the Bélavár location bed-load transport processes indicated that one potential alternative could be for riverbed stabilization the filling up the river bed with crushed stone, gravel, concrete that will not be transported away by the current of the stream. This alternative might be prevented by the high investment cost predominantly. Technical alternatives of the supplementation of the river bed materials has to be assessed by detailed

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 7 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

cost-benefit analyses in future taking into account the available international experiences and project results. An additional problem to be investigated in the future is the fate of the gravel riff and small islands should filling material is provided to prevent river bed erosion processes. The other potentially available technical solution is the artificial decrease of water velocities on this particular river section, so that to prevent the drift and transport of the still existent sediment material. Theoretically this is possible by the use of a series of bed- level elevation structures (low bed-sills). These elevated river bed chains however might results in the translocation of the original river path, so their application requires extreme care and further hydraulic studies in details. To prevent these harmful processes it might be necessary to construct these structures further downstream (191 rkm) as well to control the slope within the side-arm systems. Upon the construction of the bed-sills the minimum and average water levels be elevated – an alteration that can be designed during the calculations of the bed-sill structures. Elevation of water levels on the Drava will improve the water supply of the side-arm systems. On the basis of the results of the geodetic surveys on the area and data of the Atlas it is stated that the artificial elevation of the high flood levels can cause the permanent inundation of the area therefore this should be avoided (this can be mitigated by the careful design of the levels of the bed-sill structures, as these low weirs has no significant effects). This mitigation alternative (construction of a series of low bed-sills) could be implemented at significantly lower investment cost than the filling up of the whole river section (up to 5 km length) with supplementary river bed materials. The disadvantage of this solution is the hampered navigation conditions and the possibility of disadvantageous changes in the dynamics of gravel shoal formation processes. The control or hold up the river bed sinking of the Drava section in question is an indispensable element of the side-arm system revitalization therefore irrespective of the side-arm revitalization project it is suggested to design and to implement. Based on the detailed evaluation of the data and information across the preparation of the present study there are two main technical alternatives of the side-arm revitalization. The first alternative considers the presently prevailing Drava water levels (with some slight artificial elevation) and to address the question of the existent side-arms as water paths for water supply (with local small-scale dredging) and therefore the restoration of the direct hydraulic connection with the Drava main arm by increasing the frequency of flow-through periods. According to the results of the geodetic survey the inflow into the side-arms is limited by the high points of the starting stretches of the side-arms. Suggestion were elaborated in this study to maintain these bed sections and high points. The bed section restoration would primarily improve the water supply of the Bélavári side-arm system at different water paths. The suggested technical mitigation actions however require further investigations for the accurate determination of the paths and length of the water supply system. According to the

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presently available data we know the cross-section of the northern section of the Bélavári side-arm where the bed is at the required depth. For the accurate design of the main channel path the full geodetic survey of the water path is needed in future. Prospectively, the intervention does not make an extensive dredging necessary. The dredged material can be placed into the main channel of the Drava, however, this is not a substantive riverbed stabilization (relatively small volumes and grain sizes). Based on the data collected during the on-site inspection the water supply of the upper stretch of the Bélavári system is made across the abandoned gravel pit mine lakes. This is suggested to preserve in the future for using the lakes as primary sediment traps. This solution might prevent and control the future siltation of the side-arm system, in addition, the accumulated bed material can be supplied to the Drava. The application of the determined inflow levels based on the results of the study can significantly improve the water supply conditions of the side-arm system. For this alternative cross-cuts on the Bélavári side- arm and road reconstruction towards to the gravel pit mines is necessary to implement. The other alternative would solve, or mitigate the problem by the significant increase of the Drava water levels. Without dredging however this might result in highly elevated water levels that will result the permanent and/or more frequent inundation of some lower lying area and the potential of translocation of the main stream to some of the present side-arms. Based on the results of this study the management of the river bed erosion processes and improvement of the water supply conditions of the side-arm system the more attractive and more feasible solution would be the elevation of the low water levels that will stabilize the river bed as well, and the application of small-scale dredging to remove the high points in some river bed residues. Reshaping the uppermost sections of the former side- arms would enable the river to wash out the side-arm system and to reestablish the former bed meanders. Channeling part of the Drava flow into the side-arm system should take into account the siltation processes due to the slowing down of water velocities in the side-arms. The gravel pit mine lakes along the Drava will have settling function regarding suspended solids and bed- load transport materials (provided that this path will be activated in future) that controls the siltation processes in future. Regarding the international experiences however, the detailed assessment of the sedimentation and siltation processes requires further studies that are indispensable for appropriate design and preparations. Based on the results of the study it is concluded that due to the river bed erosion processes of the Drava the water supply conditions of the Vízvári-Bélavári side-arm system will be further deteriorating in the future causing the degradation of the aquatic and terrestrial ecosystem elements in the near future. Therefore it is suggested to continue with detailed modelling and calculations to mitigate the control measures against the further river-bed erosion. The problem of the erosion of the river bed involves the entire Hungarian Drava section (similarly to other rivers having hydropower stations only at the upper sections), requiring control measures independently of side-arm revitalization actions. This mitigation will

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 9 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

require the carful investigation of potentially available international networking opportunities. (An example for cooperation could be the transport of the dredged bed material from the upper river section to the river section where erosion is a prevailing and continuous problem). In this study detailed analysis was given on the results of the baseline studies and formerly established information sources on the basis which the detailed decision support and design works could be commenced under the guidance of the DDNPI. The following technical tasks have to be completed in future: complimentary geodetic survey to fill the information gaps, mapping the details of the river bed conditions of the Drava, high resolution investigation of the sediment conditions, and CBA of the alternatives on bed-load filling actions. Parallel to these, it will be necessary to determine those ecological, hydrobiological and nature conservation priorities that need to be meet and these has to be harmonized with local, regional and international (particularly Croatian) stakeholders. Having addressed the nature conservation values as first priority of the project we should keep in mind the sustainability of other land uses and flood control priorities, navigation concerns have to be harmonized in future. Any mitigation action or technical measures have to be taken with respect to regional interests particularly when national and international tendering is considered as a primary source for financing. National and European political priorities have to be cared of throughout the overall planning and designing process. The Vízvári-Bélavári side-arm system in its present state – irrespective of the disadvantageous processes of the past few decades – still provide highly valued and variable habitat mosaic for many of the protected plant and animal species. Without the mitigation action however, the sustainability of this high priority areas cannot be maintained due to the ever continuing river-bed erosion of the Drava River. Ecological degradation processes could be controlled by the appropriate management of the water supply issues on the side-arm system. Based on the discussed data and information it is evidenced that the conservation of the unique natural values of the area can only be protected by the regulation and control of river-bed erosion processes in the Drava section in question. Budapest, April 30, 2014.

Dr. Anita Szabó Dipl. Eng. Executive Manager, INNO-WATER Ltd. Water Management and Environmental Expert (SZKV-1.3.; SZVV-3.10.; Reg. No: 01-14685)

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 10 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

1 Introduction and preliminaries

1.1 Introduction The nature conservation authorities of the Danube Valley are cooperating with each other on the basis of the results of the fruitful former projects. This cooperation is harmonized from 2007 on by the international network of DANUBEPARKS (Danube River Network of Protected Areas) for the protection of the ecosystems of the Danube Valley and its indirect environs. The primary objective of the cooperation is to harmonize the management of the nature conservation areas, development of joint project planning and the emphasis on international priorities of political platforms aiming nature conservation across Danube watershed management plans. The program continues from 2012 by the support of ETC-SEE in the frame of a DANUBEPARKS STEP 2.0 project. The Directorate of the Danube-Drava National Park (DDNPI) in the frame of the DANUBEPARKS STEP 2.0 SEE/D/0165/2.3/X/02 tender initiated the preparation of the Vízvári-Bélavári side-arm system revitalization plan for the improvement of aquatic habitats and wetland areas. The task of the Inno-Water Ltd. in relation to this was to overview the concepts of the potentially available revitalization options. The Vízvári-Bélavári side-arm system includes the Vízvári and Bélavári side-, and dead-arm systems, and the gravel pit mine lakes near to Bélavár. The Vízvári-Bélavári side-arm system is part of the joint Hungarian-Croatian area of the Drava representing the single large such system along the entire river. It is made of several side-arm having different state of siltation and sediment accumulation with meandering river branches. The fast flowing river water and the characteristic gravel islands and shoals on this particular Drava section presenting habitats for numerous protected species (e.g., little stern - Sterna albifrons, Hungarian zingel - Zingel etc.). Important habitats are also located on the floodplain characterized with variable topography and water coverage. River regulation activities during the past few decades and the drastically dropped river bed- load transport due to the hydropower dams on the upper river section the bed of the Drava started to sink considerably a process that will continue on in future. The artificially altered water path and sedimentation processes (suspended and scrolled sediment) the natural floodplain dynamic is also been altered. The water supply of the side-arm system decreased considerably and the cut off side-arm developed into dead-arms by increased siltation processes. By cutting cross the Vízvár curve of the Drava River the former main channel became the Bélavári side-arm and the upper and lower sections of the Vízvári side-arm was established in its present form. The primary aim of the project initiated by the DDNPI is to restore the former dynamics of the floodplain (primarily by using the natural lateral erosion of the river), and the mitigation of the erosion of the river bed (by slowing down or stopping the process and hence the improvement of habitat diversity and restoration thereof.

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1.2 Tasks The DDNPI entrusted the Inno-Water Ltd. to prepare a report on the conceptual opportunities for the restoration of the side-arm system of the Drava at the Vízvári- Bélavári section in relation to the improvement of habitat diversity. The study was focused primarily on the potentially available techniques to restart the natural floodplain river dynamics, how the lateral erosion processes could be used for the development of new gravel islands and shoals. The study details the questions of sustainability and the investigation of the long-term effects of the mitigation actions. On the basis of the technical appendix of the contract the study has to be focused on the following tasks: 1. „Characterization of the Vízvári Dráva section and morphological description, the summary of the river training activities during the XX. century. 2. Overview on the habitat revitalization methodologies. Overview on the improvement methods of side-arm system water supply and the starting up of the floodplain erosion processes. 3. Investigation of technical opportunities for the control of main river arm erosion processes, and for its control, and if it is possible how this will affect the downstream and upstream located river sections. 4. Assessment of various land uses (navigation, forestry, hunting, flood control) that can be affected by the planned habitat revitalization actions and prepare suggestion for the solution of the potentially occurring contradictions. 5. Overview of the existent international examples in case of similar rivers regarding their revitalization. 6. Preparation of a geodetic overview on the area in question, with particular emphasis on the still existent river-bed residues.” This study first will introduce the planning area (see Chapter 2.), with particular emphasis on relief conditions, geology, soil climatic and hydrological data and the particular stages of the regulation of the River Drava. Following this, an overview is given on the baseline concepts of the planned habitat revitalization and its objectives. This all related to the national watershed management planning process and the points its connection point to the priorities of that (see Chapter 3.). Prior to the detailed analyses of the planning area an overview is given on the international and national case studies that were aiming similar revitalization action under similar environmental conditions (Chapter 4.). Chapter 5. details the hydrology of the Dráva section in question and its bed-load transport conditions. Following the conceptual framework overview (Chapters 2-5) in Chapter 6. details of the results of the geodetic survey of the area are discussed and information obtained by the

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on-site inspection is also evaluated (with the priority of habitat revitalization methodologies). In Chapter 7. analysis is given on the present state of water supply of the side-arm system and the predicted state of the area in the lack of intervention actions in future. The Chapter 8. deals with the possible alternative of mitigation the erosion processes in the main arm of the Dráva that has key importance regarding any revitalization of the side-arm systems. On the basis of the calculation and detailed assessment in Chapter 9. an overview is given on the side-arm system revitalization options and a summary on the potential stakeholders and institutions (Chapter 10.). Summary of the results is given in Chapter 11.

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2 Introduction to the area

2.1 General introduction to the area

2.1.1 The location of the planning area The planning area includes the Vízvári and Bélavári side-arms and dead-arms, and the gravel pit mine lakes at Bélavár, concerning the Dráva section at the 191-198 rkm from the main arm of the Drava until the Pécs-Nagykanizsa railroad line (Figure 2.1.). Part of the area belongs the Hungary and part of it belongs to Croatia. The prime concern area is the Bélavári side-arm, the lower Bélavári side-arm and the upper arm of the Vízvári side-arm on the plains of the Dráva, situated in the Middle Dráva Valley. According to the National Watershed Management Plan it falls to the Drava part watershed and to the No. 3-2 Rinya-side subsystem (VKKI, 2010a, b; VKKI-DDKÖVIZIG, 2010a). The Dráva section in focus (191-198 rkm) is part of the lower Dráva (AEP438) water body. This water body belongs to the 3-2 Rinya-side and 3-3 Black water subsections (VKKI, 2010a,b; VKKI-DDKÖVIZIG, 2010a, b).

Gravel-pit lakes of Bélavár

Side-arm of Bélavár

Lower side-arm of Bélavár Upper side-arm of Vízvár

Lower side-arm of Vízvár

Fig. 2.1. – The location of the planning area

2.1.2 Relief, geological and soil characteristics The Middle-Drava-Valley along the Drava River having 1–4 km width and 60–70 km length alluvial surface, that is divided into deep and high floodplain areas, dead-arms, abandoned

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arms, and dead-arms (Dövényi, 2010). In this middle section the river is characterized by meandering river section, curves, meadows, lowlands and wetlands and terraces. The area is predominantly flat having only few meters differences, although between Berzence and Bélavár the difference can be as high as 30 meters (Dövényi, 2010; DDKÖVIZIG, 2007). The planning area is located between 107-112 m above Baltic Sea level (maB) and next to the Bélavári side-arm there is a high-bank reaching 125 maB that serves as the location for the Pécs-Nagykanizsa railroad track. Areas deeper than 110 maB are the Dráva and the Vízvári side-arms, the Bélavári side-arm and its continuation as an abandoned river bed. This area is practically underneath to the 111 maB level (Figure 2.2.). On the right side of the Dráva, opposite to the planning area the height of the land typically above 110 maB level. The only exception is the area opposite to the Vízvári upper side-arm system where the height is around 108-110 m above the Baltic Sea level.

Fig. 2.2. – Deep lying areas within the planning area

The Rinya-side part watershed is a filled up depression containing the ancient Danube bed. The gravel fraction of the bed is typically occurring at the depth of about 5-10 m. On top of the riverbed materials a Pannonic sandy-clayey layer is dominating. Upon the translocation of the ancient Danubian riverbed the morphology of the surface became characteristically Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 15 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

quicksand. Amongst the sand dunes Holocene marshlands are prevailing: meadows, wetlands, turf and other geological formations. The deeper laying areas are wetlands at present where there is direct connection between the groundwater and surface waters (DDKÖVIZIG, 2007). On the top of the Periglacial sandy formation of the Middle-Dráva-Valley brown forest soils with clay are characteristic and on the Western parts pseudoglei brown forest soil types are predominant. The dominant soil type of the Middle-Dráva-Valley is the floodplain meadow soil but significant portions are covered with raw flood soils as well. (Dövényi, 2010). The side-arm systems on the planning area were belonged to the main arm of the Dráva. On the area of the Vízvári-Bélavári side-arm system the gravel layers are typically occurring near to the surface, provided excellent opportunity to gravel mining (abandoned gravel mine pit lakes at Bélavár).

2.1.3 Climate The climate of the planning area is moderately warm and wet. The annual duration of sunny hours is around 1950, with value of 780 hours in summer and 190 in wintertime (Dövényi, 2010). The average annual mean temperature at the South-East part of the Middle-Dráva-Valley (in the vicinity of Barcs-Drávatamási) is around 10.0-10.2 °C, while at North-West (area of Zákány-Őrtilos) 9.7-9.9 °C. The mean temperature of the vegetation period is 16.5 °C, but slightly less on the NW territories. The multiple year average temperature of the hottest days is 32.5-33.0 °C, and the coldest winter days varies between -17.0-17.5 °C (Dövényi, 2010). The last frost are expected to occur in the middle of April. Climate change affect this area as well. At the vicinity of Vízvár during the past 30 years the maximum summer temperatures increased almost by 3 °C in the past 30 years, this increase can be as high as 5 °C in future (http://esotanc.hu/vizvar). The annual precipitation at Barcs-Drávatamási is about 780-800 mm, of which 450 mm is in summer. The other parts of the region having more precipitation reaching values of 800-840 mm/y, and 460-490 mm values in the vegetation period. The most frequently occurring 24 hours precipitation is (118 mm) at Vízvár. Snow cover is expected to occur at 40 days with maximum cover of about 30-32 cm. The dominant wind direction is NW, N, but other direction can also be observed occasionally Average wind speed is about 2.5-3.0 m/s (Dövényi, 2010).

2.1.4 Characterization of the Hungarian Dráva stretch The Dráva River is one of the longest and largest tributary of the Danube. The river takes its rise in South-Tirol, in the height of 1192 meters. It crosses Austria, Slovenia, Croatia and Hungary and confluences into the Danube at Aljmaš (Almás), Croatia. The total length of the

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river is 733 km, the extent of the watershed area is 43238 km2 (Figure 2.3.; György-Burián, 2005). The Hungarian watershed of the Dráva covers 8431 km2, representing 19.5% of the total watershed area (György-Burián, 2005). The Hungarian stretch of the Dráva is predominantly middle river character from 236.0 rkm (Őrtilos) to 70.2 rkm (Matty).

Fig. 2.3. – The watershed area of the Dráva River (DDVIZIG)

Arriving into Hungarian territory the river 5-6 kms downstream of Őrtilos leaves the national border and proceeds on Croatian territory across about 29 kms. At the area of Őrtilos the common river section runs at about 125 maB. Following this the Dráva reenters to Hungary above Vízvár and from here on proceeds on common boundary (Hungarian-Croatian) via an additional 137 kilometers length Dráva section as boundary river (Dolgosné, 2008). The tributaries on the Hungarian Dráva section on the left side are the Mura, the Dombó- channel, the Babócsai-Rinya, the Barcs-Komlósdi-Rinya, the Korcsina-csatorna and the Black water, and some smaller streams. The river section between Őrtilos-Drávaszabolcs covers around 168 km and can be divided into two characteristically separated sections: the Őrtilos-Barcs section and the section downstream of Barcs. The river was regulated on the upper section only by local implementations (VKKI, 2010b). The Dráva meandering through the borderlines of the Zákányi-elevation from S, with well determined river bed. The valley is wide, 5–7 km and contains lots of dead-arms (Lovász, 1964 – cited in: Dolgosné, 2008). Downstream of Zákány the river is meandering in the Gyékényes-Golai basin. The slightly depressing basin forced the river to change its direction and for intensive accumulation of sediment materials (Dolgosné, 2008). The Dráva is listed as typical alluvial river, as its flowing on its own alluvium (silt). Due to its water discharge and small slope its meandering type river decomposing its concave banks and building up the convex ones. Sandy beaches, shoals and islands are all characteristic (Purger, 2013).

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The river bed of the Drava is in a continuous change. Due to the loss of kinetic energy the river deposits its bed-load transport materials forming shoals and islands. The loss of the energy however effects the river in the cross-sectional direction as well. The loss of energy into the cross-sectional direction forms the riverbed, increases or decreases the number of the shoals. Shoals are predominantly occurring in the area of Őrtilos and Barcs. The shoals downstream of Barcs are mostly characteristic for short river sections (DDNPI, 2014). The river section downstream to Barcs is regarded as a regulated river due to the mutual river training works of the Hungarian and Croatian water authorities (see also Chapter 2.2.). The river bed on this section can be considered as uniform. The Dráva between Barcs and Drávatamási became straighter at the Northern edge of its own alluvium. Arriving to the Ormánsági basin due to geological forces it is cutting through the southern edge of the alluvium. Here the Dráva is meandering on an almost 30 km wide plains, while the characteristic Dráva high banks become elapsed. The elevation level of the river decreases into SE direction: at Drávaszabolcs it is only 80 maB. The dead-arms are presented in large numbers on this (DDVIZIG, 1986; – cited in: Dolgosné, 2008). The present riverbed conditions are characterized by the large number of dead-arms and wetlands (Varga, 2002; – cited in: Dolgosné, 2008). The slope of the Drava shows great differences along it longitude. The average value of the slope on the upper section of the Dráva including Italy, Austria, Slovenia is high averaging 2.0-2.5 m/km. Leaving the mountainous region the slope is halved. At Őrtilos the slope of the river is only 45-55 cm/km, on the Hungarian-Croatian section at Vízvár (191 rkm) then it is further reduced till Barcs 15-20 cm/km, and at Drávaszabolcs it is only 10- 15 cm/km. The characteristic average velocities between Őrtilos and Drávaszabolcs are reduced 0.8-1.0 m/s (VKKI, 2010b; VKKI-DDKÖVIZIG, 2010a). The actual hydrological longitudinal section of the Dráva is depicted on Figure 2.4.

Fig. 2.4. - The actual hydrological longitudinal section of the Dráva (http://www.dravamonitoring.eu/?module=szelvenyvizrajz)

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The average flow of the Dráva at Maribor is 300 m3/s, while it is 650 m3/s at confluence. The characteristic flows of the Dráva at Barcs are the following (VKKI-DDKÖVIZIG, 2010a): Max.: 3190 m3/s Min.: 114 m3/s Average: 512 m3/s On the Slovenian section the record high flood was registered 1965 at 2600 m3/s water discharge. In November 2012 due to the high precipitation on the Austrian and Slovenian watershed the earlier record was exceeded by 2900 m3/s flow value. In Hungary since 1900 the highest peak flow was experienced in summer of 1972 when the water flow was higher than 3000 m3/s at Barcs (DDVIZIG-Inno-Water Ltd., 2014). In the same time the record water level on the Hungarian-Croatian section was measured at Őrtilos 476 cm, and at Barcs 618 cm, at Drávaszabolcs 596 cm. Following the peak values of 1972 high flood were registered in 1975 when the peak levels were Őrtilos 436 cm, Barcs 579 cm (DDVIZIG-Inno-Water Ltd., 2014) in the past few years high flood were occurred in November of 2012 when at Őrtilos 380 cm, and at Barcs 365 cm was measured. The water level changes of the river are highly affected by the peak operation of the Croatian hydropower dams. The hydropower station at Dubrava located 18 km upstream of Őrtilos (lowest located station) has a discharge capacity of 500 m3/s. This value is around the average flow of the Dráva. Should the natural flow be lower than this value the station will gather (swell) the required water volume and depending on the peak energy requirements will discharge the flow. In this way daily peaks are experienced downstream that are going to be flatted towards to the downstream section. This would mean at the Őrtilos section (236 rkm) about 80-130 cm water level changes in the low water period, and at Barcs (154 rkm) 40-70 cm, at Drávaszabolcs 10-20 cm within a day, or even within a few hours (VKKI, 2010b; VKKI-DDKÖVIZIG, 2010a). From energetic viewpoint the Dráva is fully utilized up from Őrtilos as on the area of the three countries 22 hydropower station were established (see also Figure 2.5.). These hydropower station are significantly affecting the transportation processes of the river bed-load and suspended solid processes.

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 19 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

Fig. 2.5. – Hydroelectric power stations on the Dráva (VKKI, 2010b)

The riverbed of the Dráva upstream of Vízvár is moving and shallow. The river has a great slope and there are many wading hampering the navigation. At average water levels the river depths are about 2-3 but the bed is moving and changes its form and the location of the shoals. Between Babócsa and Vízvár there are critically shallow section occurring and the river cannot be navigated upstream of 198 rkm (VKKI-DDKÖVIZIG, 2010a). Downstream of this, however it is available for navigation and it is a registered second class navigational route. The meandering river frequently changes its position and the former main arms became side-arms. Those rivers beds that are open from their downstream end and functioning in the water transport are considered to be side-arms (These area for example Vízvári upper side- arm opened from both ends and the Bélavári side-arm opened only from the downstream end). In the side-arms there is constantly water even at low water periods and at higher water levels they are playing role in the water transportation as well. Should the side be closed at the in- or outflow points the flow-through is ending and the succession processes start to accelerate. When both of the water discharge points are closed (in- and outflow) one can consider the formation of the dead-arm. Dead-arm became marshes and ultimately will be forested by natural succession processes (Purger, 2013). The riverbed material of the Dráva up to Vízvár is characteristically gravel (average grain size is 16-52 mm), till Barcs sandy gravel (average grain size 0.5-20 mm), and from here on till Drávaszabolcs and towards to the confluence point the sand is the dominant fraction (DDNPI, 2014). The gravel mining at the Dráva was commenced on the upstream section of Barcs. On this river section mining was conducted directly from the river bed. Large scale gravel mining was conducted in the region of Vízvár – Bélavár – Gyékényes. Here the gravel layer was near to surface. Mines were operated till reaching the groundwater table as it was prevented to go

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further down due technical limitations. (VKKI-DDKÖVIZIG, 2010a). According to our recent information no mining activities are recorded on the area nowadays.

2.1.5 Flood control and protection There is no flood protection dam system on the Hungarian side at the river section between Őrtilos-Barcs (including the project planning area Dráva-section), the river bank is high. Floods are rather endangering the Croatian territories on this river section and only the right side of the river there are flood control dams (See Figure 2.6.).

Fig. 2.6. – Flood control dams on the right side of the Dráva on the planning area

The high flood level floodplain on the Hungarian side occasionally occupies agricultural lands (Barcs, Heresznye areas). However, the designation of high water basin and the determination of the required standard flood level is in progress at the time of the preparation of this documentation. On the left side of the river downstream of Barcs at Tótújfalu (142 rkm) starts the Hungarian dam system and commences till Matty, where the river leaves Hungary (VKKI-DDKÖVIZIG, 2010a). The flood protection system of the Dráva includes the floodplain forest as well. On Hungarian territory these are located next to the left side dams between 70.2 – 140.8 rkm. Their primary role is to protect the dams against the waves and possible ice damages. The floodplain is practically covered with plantations. The floodplain width is the smallest between Tésenfa –

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Kémes (20.5 – 21.0 rkm) only about 80 meters. It is widest at Drávasztara where it is 1.8 kms at the section of 48.5 – 49.0 rkm. The average width of the floodplain is 600 – 700 m (DDNPI, 2014). The flood protection system is depicted on Figure 2.7.

Fig. 2.7. – Flood protection system on the Dráva (http://www.ddvizig.hu/hu/arvizvedelmi-rendszerek-1)

2.1.6 Navigation As of today the Dráva is classified as an EGB. II. category navigation route. According to this between the 0-198 rkms (downstream to Bélavár), 400-600 t barges can transport in 130-150 days on the river by day (VKKI-DDKÖVIZIG, 2010a). The prescribed 160 cm draught depth is available on the entire length apart from two wading but the permanence is less than the prescribed 240 days occasionally. On average the water levels are met in the 60% of the year of the navigation requirements (Közlekedés Ltd. et al., 2013). The river is only navigable till Barcs (from the confluence), and only during the daytime. On Hungarian territory the navigation is regulated by national and international rules and by the HU-CR agreement. Maintenance of the navigation route is highly dependent on the international tenders and hence volumes and project are highly fluctuating (Közlekedés Ltd. et al., 2013).

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The navigation on the Dráva presently includes both personal carriers and transportation of goods but at negligible volumes. Characteristically one could one mention the pleasure boating in the area of Drávaszabolcs and Barcs. The Croatian ships are transporting occasionally gravel, sand and woods. The Hungarian traffic/transportation is negligible. Regularly on the Barcs Fire Works, DDNPI, police, Water Directorate and some company (e.g., Sefag Zrt., Dráva Kavics and Beton Ltd., Épex Ltd.) uses small boats and larger ships. Wood transportation is on the decrease and gravel transportation is ended (VKKI- DDKÖVIZIG, 2010a; Közlekedés Ltd. et al., 2013; DDKTVF et al., 2013). From 1991 on the aquatic tourism appeared on the river. Kayaking and canoeing is considered to be significant recently as touristic attraction as well as motor boats for angling (Közlekedés Ltd. et al., 2013). Boat use is only characteristic around and nearby to the harbors which are located at the following sites : Őrtilos (237 rkm), Vízvár (Dráva 191 rkm); Heresznye, boat harbor (185 rkm); Barcs-Drávatamási (167-144 rkm), Felsőszentmárton (126-127 rkm), Zaláta, János-sziget (108 rkm); Vejti, Rév-tisztás (98 rkm); Majláthpusztai outlet (93 rkm); Fekete-víz confluence (82 rkm); Drávaszabolcs (78 rkm); Matty- Keselyősfapuszta (71 rkm) (DDKTVF et al., 2013). For the protection of the undisturbed nature of the area the use of motorboats is limited on the Drava and its tributaries due to nature protection concerns. Motor boating is against the objectives of the National Park therefore motor boating is limited to certain sections according to zones described in 14/1997. (V. 28.) KTM Order. Limitation are both in space and in time. These prescription are for the Dráva 236–70.5 rkm Hungarian sections and part of the angling license (DDKTVF et al., 2013). Infrastructure near to the river is underdeveloped and only serves local requirements. Upstream of Barcs there are no harbors at all (VKKI-DDKÖVIZIG, 2010a). With regards to the minimal use of the navigation channel it is of important to reconsider the further sustainability of the navigation route and its harmonization with nature conservation priorities as it was stressed by the documents related to watershed management planning (pl. VKKI-DDKÖVIZIG, 2010a).

2.1.7 Nature conservation The Dráva between Őrtilos and Barcs makes dynamic processes of deconstruction (high banks), construction (low banks) and shoal forming activities (gravel and sand shoals) resulting in the formation of highly variable riverbed morphological conditions (Závoczky, 2005). These variable morphological conditions at the Dráva are holding many natural or near to natural habitats. This was one of the reason for the establishment of the Danube-Drava National Park in 1996. On the Croatian part of the river a regional park was founded in 2011 (Purger, 2013). The location of the nature conservation areas is shown on Figure 2.8.

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Fig. 2.8. – Nature conservation areas on the Hungarian watershed of the Dráva

The area of the Danube-Drava National established in spring 1996 is located along the banks of the Danube and the Drava rivers on an area about 50 000 hectares. The face of the area is dominated by the presence of the water. The two rivers determine the landscape and its habitats and ecosystems. Almost all of the area is located on floodplains (http://www.ddnp.hu/nemzeti-park-drava-menti-teruletek). The area of the National Park along the Dráva is about 21 251 ha including two counties, namely, Somogy and Baranya. The entire Hungarian river stretch is protected area. According to the 275/2004. (X.8.) Gov. Order some sections of the Dráva are Natura 2000 areas: West- Dráva special bird protection area, East-Dráva, Middle-Dráva, West-Dráva and West-Dráva- Plains high priority nature conservation areas (DDKTVF et al., 2013). The sixth Hungarian biosphere reserve was established in 2012 named as Duna-Dráva-Mura Biosphere Reserve crossing boundaries. This UNESCO biosphere reserve unifies the Mura- Dráva-Danube region 10 protected regions and the riverine system. The area of the biosphere reserve consist of about 260 000 hectares core area and buffer zone and of an approximately 540 000 hectares transient zone. The core area is protected by law consisting of a network of protected landscapes forming the ecological center of the reserve. The zone is primarily made of the river and its floodplains bordered by the flood protection dams. The prime function of the core zone is the protection of natural habitats and protected species and revitalization of degraded areas. The buffer zone is located along the rivers and out to the floodplains. It is a mosaic of arable lands and villages but there are some spots of protected land within it (dead-arms, lakes, etc.) Eco-tourism and extensive landscape management is the prevailing land use pattern.

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2.1.8 Ecosystem elements The Dráva between Őrtilos and Barcs is forming the last unregulated river of Europe where the river can form its path undisturbed destructing its banks and building shoals and supply the side-arms with water. Gravel terraces and shoals are forming important habitats for many protected rare species (VKKI-DDKÖVIZIG, 2010a). The gravel islands are very characteristic to the Drava river that are forming and disappearing continuously wandering around. These are characteristic habitats for the pioneer vegetation. The special cypher species (Myricaria germanica) is only occurring only in these islands in Hungary. The banks is covered by floodplain gallery forests, where white willow, white poplar and black poplar are forming the higher forest level and the shrub zone is formed by blood twig dogwood very frequently. The underwood are consist of protected moorlands. The next stage of the succession is the oak-ash-elm forests on the higher lands. It is noted that many of the protected soft-stemmed plant is prevailing in these zones. (http://www.ddnp.hu/nemzeti-park-drava-menti-teruletek). The Barcsi Borókás is special juniper vegetation avoiding lime-soil on sandy topsoil. On areas with no drainage swamps are prevailing containing lots of protected and rare vegetation elements amongst the soft stemmed plants. (http://www.ddnp.hu/nemzeti-park-drava-menti- teruletek). Downstream to Vízvár the dead-arms and oxbows are occurring frequently. On the area of Vízvár and Bélavár there are many abandoned gravel pit mine forming open surface lake system recently. These are also considered to be as regenerated and having high nature conservation value. The natural vegetation near to Vízvár on the floodplain are represented by willows (Leucojo aestivi, Salicetum albae). In the willow forest lots of protected plant species exists Leucojum aestivum, Peucedanum verticillare, Equisetum hyemale. Alder forests are much less frequent than willows (Alnetum), with the dominancy of the common alder (Alnus glutinosa) and some not frequent other alder species (Alnus incana) is (Závoczky, 2005). On the Dráva Valley belonging to the National Park about 4500 different animal species is listed to be existent (http://www.ddnp.hu/nemzeti-park-drava-menti-teruletek). The Dráva is one of the cleanest river of Hungary and provides a unique habitat for the most vulnerable species. The sensitive caddish-fly species (e.g., dravai caddish-fly – Platyphylax frauenfeldi) only occur in the Drava regarding to its global occurrence (Droppa, 2001). The mayflies and caddish-flies are spending most of the life-time under water and the only non-aquatic function is the reproduction (http://www.ddnp.hu/nemzeti-park-drava-menti-teruletek). The impeccable water quality is indicated by the presence of rare dragon-flies as well (Droppa, 2001). About two thirds of the Hungarian fish species are also occur in the Dráva River. Amongst the rare species the protected huchen (Hucho hucho) to newly appeared ship sturgeon (Acipenser nudiventris) are mentioned. Other protected fish species are the bullhead, the stone loach (Barbatula barbatula), the stone-driller loach (Sabanejewia aurata) and the Hungarian zingel (Zingel zingel). From angling viewpoint the nose-carp stands and other cyprinidae

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species are significant and in the dead-arms and side-arms there are large pike, pikeperch and Prussian carp populations (Závoczky, 2005; Droppa, 2001). The river plays a paramount role in the migration and wintering of the water-birds. The cormorant occur in large flocs, and crane and herons are also frequently appearing (Droppa, 2001). Upon the icing of the stagnant waters thousands of aquatic birds are gathering on the open water surface of the river. In the soft-wood forests the protected bald eagle the black stork, and the brown kite thrives (http://www.ddnp.hu/nemzeti-park-drava-menti-teruletek). Of the ducks there are 20 species on the areas and during the wintertime rare northern species are appearing. In springtime and at fall the fishing eagle is present on the river. Migratory snipe species are also occur (Droppa, 2001). On the nude gravel shoal and islands rare stern species are brooding. The high banks provided nesting ground for the swallow (Riparia riparia), the European bee-eater (Merops apiaster), but kingfishers are also nesting here (Alceo atthis) and hoopoes (Upupa epops) as well as hoopoe (http://www.ddnp.hu/nemzeti-park-drava-menti-teruletek). Other highly protected species are the specific clam (Unio crassus), the Hungarian rainbow butterfly (Apatura metis), and Danubian roach (Rutilus pigus) (Závoczky, 2005).

2.2 Regulation of the Dráva River River training activities commenced on the Dráva together with the other rivers in Hungary. The first written report is from the end of the XVIII. century with local importance (VKKI-DDVIZIG, 2010).

2.2.1 River regulation until 1886 River regulation measures were started during the ruling of Joseph II. In the same time the first military mapping was completed on the river path of the Dráva. The first cut-offs were made in 1784 where the over meandering curves were cut through by digging a main channel (10—15 m width) for the river. The artificial main channel was used to be widened up by the strong current of the river. As the new banks and ends of the cut-offs were not reinforced these were washed away by the current soon. The same fate remained for the other flood protection devices established at the end of the 1780 years (Remenyik, 2005; VKKI- DDVIZIG, 2010). On Figure 2.9. a map from 1779, on Figure 2.10. a water management map of the Dráva in 1820 is depicted.

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Fig 2.9. – Regulation of the Dráva near Vízvár, 1779 (http://keptar.oszk.hu/html/kepoldal/index.phtml?id=000102)

Fig 2.10. – Cut-off design on the Dráva next to Vízvár, 1820 (http://keptar.oszk.hu/html/kepoldal/index.phtml?id=000127)

The river regulation based on unified concept could started on the basis of the more accurate maps made in the XIX. century. The river was surveyed together with the Mura between 1835 and 1846 (VKKI-DDVIZIG, 2010). By the year 1838 the flood protection works have been finished along the Dráva banks (Remenyik, 2005). On the basis of the results of the riverbed surveys the regulation plans were developed that provided technical background for shortening the original length of the river (454 km)

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between Légrád-Almás by 182 kms in the end of 1848. This would represent about 40 % shortening (György-Burián, 2005). Downstream to Eszék the single largest cut-off was located at Bieloborod (VKKI-DDVIZIG, 2010). During the revolution and independence war in 1848-49 no flood protection or river training activities were conducted, but during the fifties this situation remained more or less the same. On Figure 2.11. the map originating from 1850 (OSZK – TK 1851, illustrated in: Viczián and Zatykó, 2011) both the Bélavári side-arm and the Vízvári side-arm is separated from the mainstream. Interestingly enough the Bélavári side-arm did not have direct connection to the Dráva from the upper end.

Fig 2.11. - The Dráva section upstream to Vízvár, 1850 (OSZK – TK 1851, illustrated in: Viczián and Zatykó, 2011)

The 1853 and 1855 floods destroyed a significant part of the earlier primitive protective equipment and large areas are flooded. The lords/landowners established Dam Society, these unions pay attention to strengthening the dikes. The dikes in spite of the fact that there has not constituted a coherent defense line, has significantly increased the level of floods. Established cut-offs were not run parallel with dike building procedures, so the drainage patterns have not improved, the duration of flooding has not changed. Therefore the dikes could not withstand prolonged periods of flooding (Remenyik, 2004). Between Eszék and Volpona made cut-off at 8 places between 1850 and 1860 in order to ensure untroubled sailing. The cut-off curves have not been ruled out, the cut-offs have not been insured, and so over develop in the loose structured rock soon. The river bed was growing wider, shallows and fords were formed. After major flooding has passed, the river returned to its original, degenerate river bed (Remenyik, 2004). The regulatory work has not been effective in the long run, in the years following the Austro- Hungarian Compromise. In 1870, the protection of the Vízvár’s old curve were built 10 pieces groynes with stake and crib work (VIZITERV, 1970 – cited: Remenyik 2004), which was washed away completely by the 1871 flood. In 1872 set up river gauge at Barcs (Révai

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Lexikon, 1934 – cited: Remenyik, 2004), reading it twice a day. The Barcs’s river gauge had a major role in predicting of the floods. Continued the organization of river bed, performed cut-offs at the Drava between 1869-82 at Drávaszentmárton, Detkovác, Tótújfalu and Szarvas. The curve cut-offs were finished at Detkovác between 1873-75, at Tótújfalu between 1880 and 1882 and under Eszék between 1882 and 1885. The river was not embedded in the new river bed and the cut-offs was short- lived. After a major flood has passed, the river returned to its original river bed, or divided into several branches and so flow along meandering. The groynes and river bed blockings, which built in the end of the seventeenth century and in the first half of the nineteenth century, had not were visible at 1882, the river’s mouth of the Danube river had become almost unnavigable (Remenyik, 2004). In order to make navigable the Drava again, new training estuary of the Drava began in 1884, a left bank branch was closed for the first time by 120 meters long. Between 1884 and 1886 a 860 meter long riverbank protection works was built, the dike system protected the double curves cut-off (in 1885) at full length, thus finally the newly formed mouth of river became navigable (Remenyik, 2004).

2.2.2 River regulation from 1886 until World War I. In 1886 the Ministry of Public Works and Transport has ordered the preparation of the lay-out from mouth to Zákány, which aims to provide the maximum opportunity for ship navigation (at full load, barrier-free transportation of barges of 400 tons). In 1886 started the hydrological and hydraulic systematic collection of basic data, the inclusion of river bed geodetic survey. The river bed size was performed by the medium water level. Otherwise navigation was available at the law water, but it was not safe (Remenyik, 2004, 2005). The tracing followed the stream, turned aside from that, where over-developed meander formed. According to the surviving manuscripts of the sizing calculations took the shipping aspects into account only, but did not deal with sediment’s and ice moving problems. The medium flow set at 610 m3/s, average water depth of 2 meters and bottom width of 60 meters has been set, about this rate of flow. Groyne construction were planned in every 200 meters (VIZITERV, 1970 – cited: Remenyik, 2004). The ministry has ordered new entering and preparation of the lay-out from Zákány to mouth, because the river’s flood levels were increased and did not follow the marked major river bed. The Eszék River Engineer Office was commissioned in 1893 with the task to survey the river geometry and to make the Drava navigable. Based on the geographic survey the first contiguous regulation plan was prepared in the Drava section from the river mouth to Zákány (György-Burián, 2005). The regulated Drava section was divided into two parts. In the section below Barcs the main objective was to remove any shipping blockage; in the Barcs-Zákány section the extension of the shipping-season and the improvement of steam-shipping conditions were planned.

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The flood prevention was considered as an already solved problem, but still the riverbed had to be settled for that. The construction work started in 1895 on the lower part of the Drava River, in the first step the river channel from the mouth to Barcs was made navigable. The channel embedding process on lower section moved forward at this time (Remenyik, 2004). To reshape the main channel, it had to be separated from all of the cutoff river curves, by the addition of stone material. In order to minimize the costs, stones were substituted by fascine at the concave banks. During the construction work the major problem was the shortness in suitable building rock material, so it had to be brought to the site with high transportation costs. In 1899 the National Water and Soil Improvement Office supervised the already finished construction work (Kvassay J., 1907 – cited: Remenyik, 2004), and accepted the subsequent plans. During the construction strict order was not followed, the works were executed on more sites at the same time: by the Drava river-mouth; at Eszék; at Donji Miholjac; at Moslavina; at Révfalu; at Budkovác; at the region of Tótújfalu, beneath and below Barcs. The cut off of the old-curve at Vízvár was also started (Mike K., 1991 – quoted: Remenyik, 2004). The first phase of the regulations ended in 1904. According to the first Drava regulation plans, only the overdeveloped river curves were planned to cutoff. However, experience has shown that to the satisfactory regulations cutting off the curves is not enough, other adjusting methods were necessary as well. Until the beginning of the XX. century German regulatory principles were followed, so the water was held between parallel structures in both the concave and convex sides (DDNP, 2014). In 1904 a new river regulation plan was prepared, and it would have made the Eszék-Varasd river section also navigable. The draft was validated by the 1908. XLIX. law, in which the National Water and Soil Improvement Office wanted to solve not only the navigation but also the irrigation and water use problem. (Kvassay J., 1907 – cited: Remenyik, 2004). In that time the ship traffic was so high that it had to be taken into consideration. Therefore the following year’s plan was annually prepared on the base of the general plan, and the working order was defined monthly. The principles laid down by the law served to control the construction works. The specified height of the structures: (DDNPI, 2014):  Zákány – Vízvár section: 0.5 meter above the zero point of the river gauge at Zákány;  Vízvár – Barcs and Barcs – Drávaszabolcs section: 1.30 meter above the zero point of the old river gauge at Barcs;  Drávaszabolcs – Eszék section: 1.80 meters above the zero point of the river gauge at Donji-Miholjaci;  Eszék-Drava river mouth section: 2.20 meters above the zero point of the river gauge at Eszék

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The widths between the river banks (mid-water control latitude) was defined on the basis of the best cross-section dimensions found naturally along the river (DDNPI, 2014):  Zákány – Barcs section 160 m;  Barcs – Drávaszabolcs section 170 m;  Drávaszabolcs – Eszék section 180 m;  Eszék – Drava River mouth 220 m. The plan prepared in 1904 partially dismissed the German regulatory principles, namely on the section from the mouth up to Varasd it only applied parallel structures on the concave side, where the channel conditions and the correct contours absolutely required that. On the convex side, the construction of cross-dams were planned with T-shaped heads (DDNP, 2014). From the planned 86.5 km long planned regulation 32 km was finished until the break out of the WWI: between Barcs-Drávatamási 7.8 km, between Tótújfalu-Felsőszentmárton 11,4 km, between Kémes-Kisszentmárton 12.8 km. By the old river curve at Vízvár the constructions continued, but the Drava could not be regulated at this site (VIZITERV, 1970 –cited: Remenyik, 2004). The works stopped on 27th November 1915 and the navigation route planned in the second regulation phase was not built. The implementation of the full program was greatly hindered by the outbreak of WWI. However the previous constructions were so successful, that the system could withstand the following major floods in 1913 and 1915. The National Water and Soil Improvement Office solved important tasks of the river regulations (Kvassay J., 1907 – idézve: Remenyik, 2004). The restoration of the water balance conditions and the reconnection of the cutoffs with the main channel was delivered. For these tasks more powerful excavator ships were used (Remenyik, 2004). 2.2.3 River regulation between the two world wars and during the Second World War The unified river regulation works come to an end in 1915, only the reservation was continued. After the Treaty of Trianon the Drava have become a boundary river, the government was not able to taking care of the water facilities, risk of the damage by water emerged in the affected villages and on agricultural areas (Remenyik, 2002) Until 1921 the bigger part of the area alongside the Drava occupied by Serbia, the complete evacuation of the parts, which was adjudicated to Hungary was carried out until 1923. However the Treaty of Trianon recorded the Drava as an international water way, the shipping volume become rapidly sinking during this period (Erdősi, 1971 – cited in: Remenyik, 2004). Between 1928 and 1931 the River-engineering Agency of Nagykanizsa made a regulation plan for the section between Old and Barcs. During the preliminary works the affected river section was surveyed again with geodetic tools, the hydraulic data was completed with further water-flow measurement results (Remenyik, 2004).

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The basic principles of the planning were the following:  The line of the regulation should be planned with preserving the original riverbed.  The minimal the radius of the top curvature is 1000 m (upper to Barcs is 500 m).  The line of the regulation adhere closely to the convex side of the curvatures.  The cut offs should be avoided because the risk of the seizing of the riverbed.  The line of the regulation should be adjusted to the established mean length of the river.  The places of the inflexion points should be kept.  On behalf of the appropriate forming of the main current, the regulation line should be passed over with a straight transition from the curvature tops to the tangent line of the inflexion point.  Straight sections in compliance with 1.5 times wider than the bank river can be inserted.  The regulation width should be established so that the necessary 2.5 m wading depth for the sailing were available during 220 days of the year. The finished plans did not came about because the lack of founds (Remenyik, 2004). The works of the Hungarian and the Yugoslavian parts either were aimed to the maintenance of the finished artifacts and the stabilizing of the ruining riverbanks due to the erosion. This state was not changed in all detail until 1958 (György-Burián, 2005).

2.2.4 River regulations from 1945 until the 1980‘s After 1945, the Drava River and the surrounding area became restricted territory. After 1954 the political tense situation started to dissolve, but the sealing of the frontiers remained until 1990. The regulatory work of the World War I broke down and just really continued from 1955, after the conclusion of the The river regulating work stopped by the WWI. and it could continue just after 1955, when the Yugoslav-Hungarian Water Management Convention was concluded. (VKKI- DDKÖVIZIG, 2010a). In 1953 the National Water Management Directorate and was formed and in association with the Baranya and Somogy County Council they repaired the dams that were injured in 1951 as a communal work project. The dyke-height determination was based on the 1951 flood level. The defense line was strengthened by Szaporca and the channel of Egerszeg (Reményik, 2004). As a result of The Drava degeneration a Convention was established between Hungary and Yugoslavia in 1955 to prepare a common plan, so the regulations can be carried out uniformly in the future. From 1957 through the functioning of the Hungarian-Yugoslav Standing Committee on Water Resources the issue of the Drava River regulation got growing emphasis. In the first session

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of the Joint Commission in 1957 the river section from the Mura inflow point into the Drava until the Drava orifice in the Danube was declared a section of the Drava common interest (György-Burián, 2005), where any regulating work should be done only with joint effort and agreement (Reményik, 2004). The need for regulation occurred on the 2. session held by the Commission in 1958. The river bed examination and the execution plans were carried out for the Drava section between the 65-75 river km. In 1959 during the 4th session the Commission accepted the general regulatory plans (VIZIG, 1986 – cited in: Reményik 2004). The regulation processes on the 65-70 rkm section was carried out between 1960 and 1962, and the 70-75 rkm section was reshaped in the 1963-65 period. (DDNPI, 2014; György- Burián, 2005). In 1959 it was already mentioned that the plan for regulating the upper section above the 75 rkm is also necessary. But only in 1967 did the Commission come to the decision of regulating the 75-85 rkm Drava Section, and the work was executed in the 1968-73 period. (VIZIG, 1986 – cited in: Reményik, 2004), During the period 1966-68 in joint implementation of the two countries the Drava river bed survey was completed from the river mouth to Őrtilos (236 rkm) and then in 1970 the first Drava Hydrographic Atlas was published (DDNP, 2014). The atlas contains the site plan and cross sections and longitudinal sections of the 0-237 river km Drava section in Gauss-Krüger projection system. The regulation of the Drava’s common stage was pictured in the early periods with the complete regulation of relatively short, 10 km long segments upstream from the lower border section. Meanwhile it was proved by numerous technical factors that the above mentioned theory is not strictly applicable, because there was necessary implementation on unplanned regions because of the endangered dams and the high-bank facilities by the intensive translocation of the riverbank, otherwise the creation of more prosperous conditions to the ice subsiding, last but not least the improvement of the disadvantageous shipping sections and behalf of the elimination of the developed shallows (Reményik, 2004; DDNPI, 2014). In 1974 the VITUKI and the Hydrometeorological Institute of Zagreb have finished and published together the general regulation plan of the Drava river between the sections of the 0-238 rkm, which was approved on the XIX. session of the Committee in 1975 (György-Burián, 2005). It was the first plan in Hungary that took a stand on the regulation conception bear on a whole river (Reményik, 2004; DDNPI, 2014)). The regulation rules served more purposes, on the one hand it was beneficial to the protection of the riverbank, to the precedence of floods and ice, and on the other hand it improved the quality of the of the shipping ways (VKKI-DDVIZIG, 2010).

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The guiding principles were the following (György-Burián, 2005):  The protection of the concave side of the curvatures in the regulation line had to be done with revetments, and slightly with regulatory work built in the riverbed;  On the convex side should be used cross works, where the narrow of the riverbed is reasonable;  The regulatory work can be built as T-work by the less exposed areas;  The side-arm closures should be built perpendicularly in the lower third of it;  The upper closure of the side-arm should be constructed with regulatory works;  The revetment of the distant riverbank from the regulation line should be constructed with stone bulkheads;  The materials of the regulatory works are the locally exploitable twig and stake as well as the water constructional stone and earth;  The height of the stone works is +120 cm water level at Barcs and +170 cm at Drávaszabolcs. After the general regulation plan, in 1983-85 the 70 rkm long section below Barcs (between the southern border and the 150 rkm (Barcs)) have been made a specified regulation plan which is still valid today (Remenyik, 2004; DDNPI, 2014). The river section below the 107 rkm is can be considered completely regulated regarding. The implementation have been finished in 1985 with the building of the additional works. The regulation works are based mostly on cross-dams, T-works and revetments (DDNPI, 2014). The over-developed left curvature of Zaláta (109 rkm) and the right curvature of Drávasztára (115 rkm) are between 107-118 rkm. The construction of the bend cut-off, with regulation purposes is finished between 1988 and 1991. The over-developed bend of Drávasztára extends completely on Croatian area. The shipping demands have necessitated the regulation works on the river section between 140-150 rkm. The Drava had rather not regulated channel, with shallows divided into several branches in this area. The accomplishment works were uninterrupted done during 1980-1988, based on the modified general regulation plan, which formed the actual line of the main river. The focus point if the implementations was the section below Barcs (DDNPI, 2014). The regulation level of the section between the 150-198.6 rkm (Barcs-Bélavár) is significantly lower than the section below Barcs. General, all-embracing regulation have not occurred until present day, the river does meandering, shoaly, intensive destruction and building work. The only important implementation on this section was the cutting-off the bend at Vízvár (DDNPI, 2014). The railway line nearby have necessitated the cutting-off work, which was executed by the Yugoslavian side during 1979-1982. The formed segment have become oversized, because the Yugoslavians have calculated with the impounded channel of the Barcs- Gyurgyevác hydroelectric power plant which was planned (VIZITERV, 1977 – cited in: Remenyik, 2004).

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The operating of the Committee was interrupted because of the disintegration of Yugoslavia, there was raged war in the first half of the 90’s alongside the Drava. After the end of the South Slavic War, in 1994 have established a Convection about the Water Management Collaboration between the Republic of Hungary and the Republic of Croatia, which had drafted the harmonized accomplishment of the works affected to the water management, water quality and quantity (György-Burián, 2005). It have become unambiguous that Croatia wants to carry out the water regulation with building hydroelectric power plants. The Hydroelectric Power Plant of Dubrava was built in 1994 on the Croatian side near to Zákány. The water level of the Drava have decreased due to the impact of the power plant, the operation have effected 50 cm daily fluctuation in the water level, which have made the shipping almost impossible. Therefore the preliminary steps of the building of the Hydroelectric Power Plant in Botovo was done in 1994, but the location was modified already to Novo Virje at the end of the 90’s (Remenyik, 2004). It would have made the upper section of the Drava navigable, and the section between Barcs and Vízvár would have remained unregulated. The environmentalist protested against the possible environmental impacts equally on the Hungarian and the Croatian side, therefore the power plant have not built. At the early 90’s, after the forming of the Danube-Drava National Park the volume of the traditional water regulation works have significantly reduced on the common stage of the Drava (VKKI-DDKÖVIZIG, 2010a). In the 2000s the water regulation primarily focused on the maintaining works. The Permanent Hungarian-Croatian Water Management Committee and its Danube-Drava Reservoir Subcommitee provided for maintenance the water management facilities which are in common interest. It contained the mine clearing of the areas alongside the Drava, and the creating of the Hydrographic Atlas of the Drava (Permanent Hungarian- Croatian Water Management Committee, 2004). The 138 km of the mapped area is longwise between Old (70.2 rkm), Bélavár (198.6 rkm), Gyékényes (228.6 rkm) and Őrtilos (236.0 rkm). The width of it holds to the dams or the definitive flood-level (Burián, 2005)

2.2.5 The results of the river regulation As part of the Drava regulations, longitudinal structures, cross-works, revetments were constructed and the river bed was strengthened in order to stabilize the river bed and to decrease the rate of erosion. The main objective of the regulations was to keep the river channel between the planned shorelines. By the constructions the river channel was narrowed down, and as a result the flow velocity increased (DDNPI, 2014). Cutting off the river curves also resulted growing velocity. In 1982 the Vízvári Drava River curve was cut off, and the latest cutoff was constructed by Zaláta in 1992 (DDNPI, 2014). Dredging was applied along those Drava sections where the river formed way too many sandbanks, and by this means the channel was narrowed down, which induced river bank Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 35 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

erosion on the opposite side. The last time on the Hungarian side dredging was applied at 3 sections by Barcs and Bolhó, and on the Croatian side between 229 – 229.75 rkm on the right side of Drava River (DDNP, 2014). During the accomplished regulation works and cut offs the length of the river was shortened, and the river bed was narrowed, therefore the slope, the flow rate and also the velocity increased. As a result of the altered hydro-morphological characteristics and the accelerated velocity in the main channel the river bed began to deepen. Since 1918 22 hydroelectric power stations have been built along the Drava River: 11 in Austria, 8 in Slovenia, and 3 in Croatia. Because of the constructed dams the river cannot carry ahead the sediment, so the active sediment volume significantly decreased, and this effect was boosted by the gravel and sand extractions. All of these factors induced the excavation of the river bed and the decrease of the water level. In the past 80 years, the Drava riverbed sank about 2 meters at Botovo and 2.5 meters at Terezino Polje and Barcs, and the river channel deepening is still persisting (see Chapter 5.1.). After the interposition in the dynamic river and the floodplain system, due to the water level decrease, desiccation processes started on the wetlands of the Drava-Valley and along the former river flats. The water scarcity leads to the change of the habitats and it increases the rate of the succession processes, especially in case of the side-arms and oxbows. The number and diversity of the habitats continuously decreases, the cutoff side-arms are slowly closing up and transforming into oxbows, which can quickly fill up and then disappear. The interventions unfavorably affected the water management of the former forests. Because of the changing naturally occurring seasonal flood extensions and frequencies, the water quality and the habitat diversity are deteriorating, which has a negative impact on wildlife, living conditions, and the habitats. With the disappearance of the diversified river channel- shapes and their characteristic habitats many species can vanish, which ones were previously preserved thanks to the natural river dynamics (Purger, 2013). In order to reduce the adverse impacts mentioned above and to reverse the harmful processes, the Danube-Drava National Park Directorate has initiated a number of projects which aimed at the revitalization of wetlands and the natural water-supply improvement of the side-arms and oxbows. Such IPA project was the "Water and Life for Drava and Vuka". Within the framework of this project the Dárvatamási upper and lower side-arm, the Tótújfalui side-arm and the Drávapalkonya branch was rehabilitated.

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2.3 Presentation of the side-arm system of Vízvár-Bélavár and of the affected Drava section Revitalization of the wetlands located on the side-arm system of Vízvár-Bélavár, planned within the framework of DANUBEPARKS STEP 2.0 SEE/D/0165/2.3/X/02 project, affects the area between Vízvár and Bélavár ranging from the main channel of Drava to the railway line of Pécs-Nagykanizsa including the side-arms, the oxbows and the gravel-pit lakes of Bélavár. The extension of the affected area should be clarified during the design of the interventions, since these interventions, depending on their nature (e.g., due to flood inundation and impacts to groundwater), may affect a wider area as well. There are two major branches of the Drava near Vízvár, the Lower side-arm and the Upper side-arm of Vízvár. On the border of Bélavár, there is the side-arm of Bélavár and the Lower side-arm of Bélavár flowing into the first one. These are not identified as distinct water bodies by the River Basin Management Plan. In addition to the side-arms, several oxbows and channel remains in different phases of siltation can be found on the area that can be covered with water periodically. The current status of the side-arm system of Vízvár-Bélavár has been obtained as a result of the last channel regulation (curve cut-off at Vízvár) in 1979-1982, which aimed the protection of the railway in the region of Bélavár (DDVIZIG, 2013). In 1979, the present Upper side-arm of Vízvár still belonged to the main channel of Drava and the Lower side-arm of Bélavár was directly connected to the Drava (see Figure 2.12.).

Fig. 2.12. – The bend of the Drava at Vízvár in 1979-ben (picture on the left) and in 2003 (picture on the right) (Andrási, 2014)

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2.3.1 The Lower side-arm of Vízvár The Lower side-arm of Vízvár extends from 191+000 to 192+600 river km on the left side of the Drava, in the administrative area of Vízvár (see Figure 2.13.). With the Drava river it surrounds a small island. Its length is 1.4 km, with an average width of 25 m and a surface area of approximately 3.5 hectares. It forms the property of the Hungarian State, managed by the South-Transdanubian Water Management Directorate. It is conservation area, part of the Danube-Drava National Park. It branches off the Upper side-arm of Vízvár (DDNP, 2014). On the end of the branch, at the point of inflow its width is 12-15 m, lower down it widens up to 30 m. The channel is narrowing in some places and it is characterized by collapsed trees. This side-arm is supplied by fresh water. It is connected to the Upper side-arm of Vízvár by a 2-3 m wide branch, which is also involved in water transport. Its relationship with the main channel is an open systems both at the branching and at the mouth. The area is located partly on Hungarian (the lower section), partly on Croatian (the upper section) territory (DDNP, 2014).

Lower side-arm of Lower side-arm of Vízvár Vízvár

Fig. 2.13. – Location of the Lower side-arm of Vízvár

2.3.2 The Upper side-arm of Vízvár The Upper side-arm of Vízvár is located on the left side of the Drava, between the 192 +600 and 196 +800 rkm, on the administrative area of Vízvár (see Figure 2.14). On this section the river surrounds a large island. The length of the side-arm is 4.0 km, its average width is 50 m, and its surface area is approximately 20 hectares. It forms the property of the Hungarian State, managed by the South-Transdanubian Water Management Directorate. It is conservation area, part of the Danube-Drava National Park. It branches off the Upper side-arm of Vízvár (DDNPI, 2014).

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Upper side-arm of Upper side-arm of Vízvár Vízvár

Fig. 2.14. – Location of the Upper side-arm of Vízvár

The current condition of the side-arm has formed after the bend cut-off at Vízvár in 1981. The branch is 15-20 m wide on the upper inflow point. Approaching the side-arm of Bélavár, it is characterized by embedded blocks and collapsed trees. There is also a small island in the channel. Below the mouth of the side-arm of Bélavár, that is the water section located downsteam from the water house of Vízvár is characterized by calm, 40-50 m wide water surface. By the mouth to the Drava river, a small island can be found (DDNPI, 2014). During medium and high waters, the Upper side-arm of Vízvár transports relatively small amount of water compared to the Drava river, but it is significant compared to the branches, therefore it is able to flush the side-arms in a great extent. Intermittent water flow can be experienced in the smaller branches connecting the side-arm and the Drava as well. These branches are 2-5 m wide, and carry water only in case of medium or high waters. The side- arm is slightly involved in the water transport of the Drava. Its relationship with the main channel is an open systems both at the branching and at the mouth. The main part is located in Croatian territory and the approximately 1.3 km long section under the mouth of the side-arm of Bélavár belongs to Hungary (DDNPI, 2014).

2.3.3 The Side-arm of Bélavár The side-arm of Bélavár is located on the left side of the Drava by the 195+000 rkm, on the administrative area of Bélavár (see Figure 2.15.). It is connected to the Upper side-arm of Vízvár, characterized by a length of 1.4 km, an average width of 25 m and a surface area of approximately 4 hectares. It forms the property of the Hungarian State, managed by the South-Transdanubian Water Management Directorate. It is conservation area, part of the Danube-Drava National Park. It is located on Croatian but mainly Hungarian territory (DDNPI, 2014).

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The current condition of the side-arm has formed after the bend cut-off at Vízvár in 1981. This curved side-arm starts out from the bend located in the central part of the Upper side-arm of Vízvár and breaks into two branches (DDNPI, 2014). The side-arm is about 30 m wide at the outlet section. Its lower half is characterized by open, clean water surface, with 40 to 50 m. The side-arm breaks to two branches in the middle section. The depth of both branches decreases gradually going upwards and aquatic plants appears in the channel. The width varies, the lower branch (the Lower side-arm of Bélavár) is narrower (10 m), the upper branch is wider (20-25 m). The lower branch falls into short branches again at the upper end. The branches come to an end after a few meters, their bed is highly overgrown here. The wider upper branch is also shallow. The upper end of the branch was refilled and a culvert was established on it. Behind the refills the branch continues, being more and more narrow, shallow and overgrown. It does not reach the Drava river (DDNPI, 2014). The side-arm of Bélavár is not taking part in the water transport of the Drava River in its current state, since its upper end is essentially closed. On occasions of mean and high waters it is supplied with fresh water on the lower section by the Drava. It is located on Hungarian and Croatian area, with a greater Hungarian part (DDNPI, 2014). Based on the experiences of the field survey in April 2013 (see also Chapter 6), the channel remains of the upper side-arm and the abandoned gravel-pit lakes located near the Drava bank are directly connected to the Drava River, from where, above a certain water level, they are temporary supplied with water.

Side-arm of Bélavár Side-arm of Bélavár

Lower side-arm of Lower side-arm of Bélavár Bélavár

Fig. 2.15. – Location of the Side-arm of Bélavár and the Lower side-arm of Bélavár

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2.3.4 Gravel-pit lakes of Bélavár The small, oblong-shaped, already uncultivated gravel-pit lakes of Bélavár owned by the Dráva-Kavics és Beton Ltd., are located in the immediate vicinity of the Drava (see Figure 2.16.). The surface of the lakes is about 4.75 hectares, their average water depth is approximately 1.5 m. On the northern gravel-pit lakes of Bélavár being near to the oxbow of Bélavár the fishing is permitted, and there is no ongoing gravel mining either. According to the fishing laws of the Bélavári Szabadidő, Sport és Sporthorgász Egyesület (Leisure, Sport and Sport Fishing Association of Bélavár) it is allowed to use a boat in certain lakes for those who have a valid boating license (in the big pond boats can be used only during the fishing, storage of boats is forbidden). It is forbidden to use the water surface for sport purpose, to construct any structure or pier, to swim, to stay on the ice, to fish with ice hole and to use a boat after dark (http://belavarihe.hu/node/5). Fish like common, grass and crucian carps, pikes, walleyes, catfishes, breams, perches, brown bullheads, smallmouth basses, chubs and pumpkinseeds live in the lakes (http://www.horgasz.hu/page/501/art/246/akt/5/megye/somogy/html/belavari- tavak.html). The cumulated surface of the lakes is about 4.75 hectares, with average depth of 2 m.

Gravel-pit lakes of The northern gravel- Bélavár alongside the pit lakes of Bélavár Drava

Fig. 2.16. - Gravel-pit lakes of Bélavár

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2.3.5 Lower Drava (AEP438) water body The River Basin Management Plan has divided the Hungarian section of the Drava into two water bodies. The planning area includes the upper section (191-198 rkm) of the Lower Drava (AEP438) water body located between the 70 +200 and 199 +040 river km (see Figure 2.17.). The Lower Drava is a heavily modified water body (14 lowland - lime - rough - very large river basin). This water body belongs to the subunits of Rinya riverside (No. 3-2) and to that of Black water (No. 3-3), and to the sub-basin of Drava (No. 3), and its recipient is the Danube (on the territory of Croatia). The extent of the catchment area belonging directly to the water is 331.58727 km2. The full extent of the catchment area above the end section of the water body is 35 000 km2 (VKKI, 2010a).

Fig. 2.17. – Location of the Lower Drava (AEP438) water body (VKKI, 2010a)

The section under Barcs has become entirely regulated as a result of the joint Croatian- Hungarian regulation. Accordingly, the water body of Lower Drava is heavily modified, but it is in good condition in both ecological and chemical terms. Flood protection structures were built on both sides, which form the boundary of the floodplain. Tortuosity of the channel is 129 km/93.996 km. The important hydrographic data of the Drava river were discussed in Chapter 5. The process of riverbed deepening (average 3 cm/yr) and its consequences (detachment and siltation of side-arms etc.) are clearly demonstrable on the Lower Drava water body. The water body is currently recorded as navigable water in its total length in Hungarian- Croatian conventions, which requires review. There are different regulation structures (revetments, cross-works, T-works) on the section affected by the planning (Figure 2.18., and 2.19.). On the section of 197-198.5 rkm, there are no regulation structures according to the Drava Hydrographic Atlas.

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Fig. 2.18. – Regulation structures located on the affected Drava section (191-193 rkm)

Fig. 2.19. - Regulation structures located on the affected Drava section (193-197 rkm)

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2.3.6 Land use on the planning area The area affected by the planned habitat revitalization between the Drava and the railway line of Pécs-Nagykanizsa is typically uncultivated. Many of the Hungarian areas are conservation areas (part of the Danube-Drava National Park) and belong to the Drava and its side- arms/oxbows. The side-arms/oxbows, the gravel-pit lakes, and some paths are surrounded by mostly forested areas. There is no ongoing agricultural production on the area encompassed by the Drava, the Upper side-arm of Vízvár, the Side-arm of Bélavár and the channel remains as its continuation, but close to the side-arm channels there are some cultivated arable lands. The gravel-pit lakes are not currently cultivated, but in the northern lakes fishing is going on with the management of the Bélavári Szabadidő, Sport és Sporthorgász Egyesület (Leisure, Sport and Sport Fishing Association of Bélavár). Otherwise, angling and small-scale fishing is permitted (with fishing tickets and territorial fishing license) on the waters of the Drava and its side-arms. Hunting is taking place on the Hungarian areas between Bélavár and Vízvár, and nearby Vízvár-Zsitfapuszta, there is a hunting land of 6 500 hectares managed by the SEFAG Erdészeti és Faipari Zrt. (SEFAG Forestry and Wood Industry Co.) (Figure 2.20.).

Fig. 2.20. – The location of the hunting land of Vízvár-Zsitfapuszta

Based on the land registry map available of the Hungarian part of the project area (see Figure 2.21.) the principal owners/managers of the area are the DDNPI (forests: 08/, 026/1, 0202/, 0204/1, lands withdrawn from cultivation, settlement, oxbows, Drava), the Dráva-Kavics és Beton Ltd. (mines: 012/1; 016/b; 022/; 024/1; 028/1a; 030/a, forests: 016/a; 028/1a, roads, lands withdrawn from cultivation), the SEFAG Erdészeti és Faipari Ltd. (forests: 042/2; 042/3), the DDVIZIG (oxbows, Drava) and there are some privately owned arable lands (040/; 02/2; 02/3) in the area. The railway line going on the high bank (0175/) is owned by MÁV Ltd..

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042/3

042/2 040/

Railway Mine Arable l. Fore Oxbost wDra v a Fig. 2.21. – Land use patterns on the Hungarian territory

We have no information about the proprietorship of lands on the Croatian area on the left side, based on the experiences of site visits, the area is mostly covered wooded areas with many small side-arms, oxbows and channel remains. There are shooting stands on the glades indicating a hunting area. There are no ongoing agricultural production or lumbering. Over against the section between the upper channel remains of the Side-arm of Bélavár and the inflow point of the Upper side-arm of Vízvár on the right side of the Drava to the Croatian side-arm of the Drava wooded areas and meadows can be found. Plots located to the south of the side-arm, opposite to (and to the east of) the inflow point of the upper oxbow are under agricultural cultivation. In several places, there is cultivation quite close to the bank of the Drava as well. The agricultural areas are typically located above 110 maB. The Hungarian section of the Drava river is a formal waterway of Navigation EGB. II. category although navigation is not typical above Barcs. Water transportation in the affected area is limited to kayak and canoe tourism and use of fishing boats besides the official duties. The water, fishing and hunting tourism of the region continues to developing. Among the objectives indicated in the regional development strategy of Subregion of Barcs (Drava Regional Development Local Government Association, 2009) we can mention the conversion of the abandoned gravel-pit lakes into of beaches (according to the arrangement of mine owners), and the development of fishing tourism on the gravel-pit lakes of Bélavár (after resolving the conflicting interests of gravel mining and fishing), and on the side-arms of Vízvár (with implementation of dredging). Although the primary objective of the interventions is to meet the conservation needs (which are necessary to define very precisely - see Chapter 3) the current and future planned land uses and the interests of the owners should also be taken into account during the planning and foundation of the habitat revitalization.

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3 Principles of habitat revitalization

Prior to the detailed discussion of the habitat revitalization prospects it should be stressed that not even the definitions of the floodplains are unified and does not following a single comprehensive approach. One could mention active floodplains (flood-basins) which is usually representing those areas the will be flooded at 1% probability. Other definition is the area between the mainstream of the river and the flood protection dams (irrespective whether these are natural or man-made). Nevertheless, occasionally the foreshore expression is used, that depicts those are that was gradually silted up and became arable land that can be occasionally flood. There is yet another definition for morphological floodplain that represents areas which could be flooded without flood protection measures the; this would represent about 30% of the total area of Hungary. Apart from these, there are many complex classification systems based on complex geomorphological systems, according to the method of sediment transport processes, on the basis of water course dynamics and river bed types, to name a few. These are all closely related to the definition of the lateral stability which in case of alluvial riverbeds (such as the Dráva River) are determining the bank widening and/or narrowing, the translation or rotation, the degree of side-arm formation, the shoal and island formation processes, and most of all the degree of avulsion processes (riverbed relocation). The theories on river continuum are still incomplete in the sense that we have to take into account not only the main channel of the river but also of the floodplains, side-arm and dead-arm systems along. The flood-pulse concept emphasizes that only the high flood are establishing direct connection between the river and its floodplains when new habitats are opened for the aquatic ecosystem elements. The organisms on the floodplains are highly adopted to the physical characteristic of the floods (timing of floods, duration, water level elevation and decrease scenarios). The regularly occurring floods are resulting in an increase of biological production both in the river and on its floodplains as the ecosystem elements are searching with adaptive strategies the utilization of novel habitats (Bíró and Oertel, 2004). It is evident from research data, that in those river sections where side-arm and dead-arm are abundant the species diversity increases. It is noted, that even the smaller and shorter water kevel fluctuations are also considered as “pulses” as they can modify significantly some physical and morphological features of the given habitat. According to the metastructure theory of the floodplains these areas are the combinations of the floodplain mosaic static and dynamic elements and ecosystem functions are regulated by thereof (Poole, 2002). The geomorphological relations (e.g., the sequencing rows of narrow and wider river sections) classified as static elements, but due to the biological effects can affect some microhabitat changes. The hierarchical patch dynamics, HPD (Wu and Loucks, 1995) theory connects the dynamics of the habitat mosaics with the hierarchical approach. The theory aims to interconnect the terrestrial and aquatic elements in four dimensions, with the surface and groundwater and the dynamics changes of the patch structures.

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Connectivity of the riverine habitats are characterized by the definition of connectivity in relation to the habitat diversity, spatial habitat patterns and hierarchy of the habitats if any (Lang and Blaschke, 2007). The functional connectivity can be assessed on the basis of the ecological, biological elements, particularly to the movement of the animals, and biogeographic connections that connects physically the separated habitats. Similar habitats can be connected into a loose network of habitat sets. From the core area different types of ecological corridors are started that form crossings. The shape of the network mirrors its density and relations of natural and artificial environs. The floodplain structure has to be considered with particular emphasis on functional connectedness. Establishment of hydrological connections paths and points (water paths for the water intake from the main arm into the side-arms) will provide the physical backbone system for connectivity. Evidently the connectivity is only an opportunity and need to be regarded in its statistical sense; the water intake and outlet do not operate on a continuous basis, but rather seasonally and their active period can only be considered as statistical (active periods). It is of paramount importance to keep in mind that during the design and planning of the Vízvári-Bélavári side-arm system the present main arm of the Drava and the side- arms, dead-arms, swamps, and other areas on the floodplain area need to be treat as a single unified natural unit. The primary reason for this is that they are permanently or occasionally forming hydraulic connection with each other and be considered as a single water system. The evaluation of the implementation measures has to take into account that the floodplain area is on a continuous change even recently that is largely governed by the water level fluctuations of the Drava and the construction/deconstruction energy of the river at its banks and riverbed, and finally the sediment transportation processes. Prior to any implementation action and during the preparation of decision making processes one should consider the principles and hydraulic models for predictions (bed- load transport models) piloting experiments and by in-situ „pilot” project it is advised to check the feasibility of the decided method for revitalization. Pilots mean such smaller scale implementation measures where environmental and hydraulic effect can be experienced on a scale of up to a few hundred square meters. (i.e., the effects of the desired lateral erosion processes).

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3.1 Revitalization objectives as determined in watershed management plan The planned revitalization of the Vízvári-Bélavári side-arm system and the riverbed revitalization of the Drava section in question has many connection point to the watershed management planning and implementation actions as prescribed by the Water Framework Directive (WFD) of the EU. The implementation plan of the watershed management program determines the technical, institutional and regulatory actions for reaching the goals and objectives are described in WFD (VKKI, 2010b). The environmental objectives are classified according to the watershed management plans on the basis of their interaction for the reduction of the effects of anthropogenic activities. These are the followings (VKKI, 2010b): 1. Measures for the reduction of nutrient and organic material loads; 2. Prevention of other types of pollution and environmental remediation; 3. Measures for the improvement of the hydromorphological state of watercourses and stagnant waters; 4. Measures serving the execution of sustainable water uses; 5. Measures to provide adequate drinking water quality; 6. Individual measures regarding the aquatic habitats and protected areas; 7. General measures for the solution of environmental problems related to water. On the sub-watershed of the Dráva predominantly the measures for the improvement of the hydromorphological state are occur (VKKI, 2010b). The primary objective of the hydromorphological measures is to mitigate those morphological and hydrological changes or state that prevents to reach the good ecological state (VKKI-DDKÖVIZIG, 2010a). With regards to the fact that the total Hungarian stretch of the Dráva and the design area in within is part of the Danube-Dráva National Park the priorities regarding to the aquatic habitats and of protected areas are prevailing. As it was described in details in the earlier chapters the most important problems of the water dependent aquatic habitats of the Dráva River sub-watershed is the non- sustainable riverbed management, the too high fluctuations of the water levels, sinking of the riverbed and the water supply problems of the side-arms and dead-arms. The various land uses along the river stretch are also enhancing the problem of water shortage (arable land directly till the banks, non-sustainable meadow use (VKKI, 2010b). In case of water courses the natural riverbed development processes have to be maintained and the dredging and artificial regulation is not verified from nature conservation viewpoint. The revitalization of the over-regulated riverbeds is also serving the protection of the habitats partly by counteracting the sinking of the riverbed and by enhancing the mosaic character of

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the habitats. According to this, the riverbed revitalization planned on the 96 % of the watercourses of the area are accounted as habitat protection measure (VKKI, 2010b). The problems of the sinking riverbed cannot be solved by measures only at the Hungarian territory. It is advised to initiate trans-boundary agreements in relation to water issues in order to meet the WFD requirements (VKKI, 2010b). One of the objective of the riverbed revitalization measures is to restore both in cross- sectional and longitudinal direction the natural state of the riverbed by decreasing the degree of the regulation and to enhance mosaic character. In case of large river the decrease of the degree of the regulation means to let the rivers developed freely its riverbed. The opportunities for the decommissioning of the already existent dams and other man-made constructions are very limited and that resulted in the classification of these rivers as heavily modified category in general (VKKI-DDKÖVIZIG, 2010a). The sinking of the riverbed and the constant decrease in water levels resulting in deteriorating water supply of the dead-arms and side-arm system. This can be counteracted by the artificial elevation of the present riverbed (refilling of bed material) or, when it is ecologically reasoned by the dredging of the side-arm (VKKI-DDKÖVIZIG, 2010a). In riverbed revitalization the risk of flood has to be taken into account, the design of the implementation measures should be harmonized with plans and strategies for flood control. The riverbed revitalization might make necessary the modification of the present land uses that should be adopted to conditions of natural water level fluctuations (VKKI-DDKÖVIZIG, 2010a). The littoral zone and the floodplains of the surface waters plays an important role form water quality and ecological viewpoint in the final state of the given water body. Measures related to the littoral zone and the floodplains are aiming to restore the natural state of the floodplains or if this is not possible to approximate this objective by widening up the floodplain area. On flat-plains or in case of large rivers this cannot be executed due to flood control concerns and widening up of floodplains would require costly earthworks. The solution therefore are two faceted: the reshaping of the land use patterns within the present floodplains or the regular water supply of those side-arm, dead-arm and low lying areas that are located on the protected side (VKKI-DDKÖVIZIG, 2010a). The objectives on the floodplain area are the harmonization of the flood control measure with the prevailing nature conservation values: the transition from the conventional agricultural use and the degraded orchards to the floodplain meadow or forestry management, but in some cases arable land use with temporary flood is also accounted for (VKKI-DDKÖVIZIG, 2010a). The set of measures for wetland and aquatic habitats are extremely complex due to nature conservation priorities. The measures aiming to protect and to sustain the water dependent protected habitats are concerning primarily the protection of the nature conservation areas the measures are for the territory and not for the water bodies (VKKI- DDKÖVIZIG, 2010).

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The most important ecological priorities of the design and the measures are (VKKI- DDKÖVIZIG, 2010a).  Conservation of water resources (recycle and re-use of precipitation, retaining high- waters and floods).  The ecological water flow has priority (the volume of water that needed to maintain the protected values) including trans-boundary flows; this would require land uses that taking into account the ecological priorities.  Approximation of riverbed morphology to the natural character and state (letting the natural riverbed development processes to prevails, and revitalization of natural conditions, curves, deep sections, variable water velocities).  Provision of water supply to dead-arms and sodic lakes.  Revitalization of the littoral zones of the water bodies (establishment of plant strips according to the natural, endemic populations, with forest plantation, and meadows, reestablishment of earlier floodplain management practices.  The management and sustainable use of the revitalized conditions (particularly on floodplains) to exclude invasive species. The other group of measure are those ones that aiming to improve the state of water bodies on which aquatic habitats are depending. These are primarily targeting the state of the water bodies but will provide indirectly the ground for the significant improvement of the ecological state of the habitats depending on waters (VKKI-DDKÖVIZIG, 2010a). The most endangering factors for the state of the water dependent ecosystem is the water shortage. Therefore it is concluded that any of the measure aiming to enhance the water supply of a nature protection are that is water dependent can be considered as a nature conservation measure (VKKI-DDKÖVIZIG, 2010a). Objectives related to the improved ecological state of the protected areas should be harmonized by the improvement of water bodies and their sustainable uses according to the WFD. In harmony with this the watershed management plan contains the following priorities for the Dráva, which is a priority water course (VKKI, 2010b):  The ecological effects of the existent river training constructions have to be reconsidered.  The state of the floodplains has to be evaluated on the basis of ecological viewpoints and according to this the necessary actions have to be designed.  Reassessment of the ecologically damaging river training facilities is needed and riverbed dredging and gravel mining has to be minimized and abandoned.  Restoration of hydraulic connection of the side-arm and dead-arm systems with the main river is needed for the better water supply thereof.  The operation of the Croatian hydropower stations has to be modified according to the ecological requirements as needed.  With appropriate design and actions the damages caused by spills has to be mitigated. Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 50 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

3.2 Baselines of the Vízvári-Bélavári side-arm system habitat revitalization conceptual plan The primary objective of the present study is to investigate the opportunities for the improvement of water supply conditions of the side-arm system in question by using natural processes. The chief goal is to slow down or to stop river bed erosion processes on the given section of the Dráva and also to improve the water supply conditions of the still existent side- arm systems with the minimal harmful environmental effects and disturbance. In designing habitat revitalization works the first priority is to cause the least environmental perturbance in the system be rehabilitated and to achieve this goal within the minimal time requirements. The established or restored system has to provide the maximum number of habitat types for the plants and animals thriving on the area. This ambitious goal, however hides a number of open questions that need to be answered in a hard way. What are these question and contradictions in planning? 1. What would be allowed degree and duration of the perturbances? Numerous international and national example have proven that for the sustainability of a given ecosystem a certain degree of regularly occurring disturbances are needed. A good example for this the abandonment of cutting of the meadows on the Bükk Highlands resulted in the gradual increase of weed species. The maintenance of the ecological systems of the floodplains also requires physical disturbances such as the chaotic or stochastic fluctuations of the physical environment (i.e., flood events). These stochastic phenomena are putting a selection pressure on the species of the floodplains by creating occasionally empty ecological niches. In general it is observed that these sudden cataclysmic ever changing environs are advantageous for the invasive species, as they can grow over the emptied habitats (as these are „r strategist” species). In our cases two factors are preferred in the same time: the priority of the protected species and the revitalization of the aquatic habitats. The water supply has to occur more frequently and for longer duration but in the same time this has to be administrated without significant degradation of water quality during flooded (eutrophication processes). To avoid this simple eutrophication modelling is needed along with detailed water balance calculations in order to determine the boundary conditions of water quality parameters (e.g., to avoid anaerobic sediment, ammonium and/or methane production, cyanobacter algal blooms, just to name a few). In any case the implementation actions has to take great care on timing regarding the nesting and reproduction periods and the areal limitations due to nature conservation and protection concerns. The habitat revitalization that is based on the processes of the lateral erosion is considered to be the slightest and “passive” methods but as it was described in the chapters detailing the geodetic conditions of the area some dredging and earth-works might be required. In relation to this some NATURA 2000 based environmental impact assessment study is envisaged in the frame of which it should be demonstrated that where the biotic

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elements are exposed to the least disturbances during implementation works. Possible effects of noise and vibration and construction traffic have to be investigated also. 2. Which habitats of what plants or animals are to be implemented preferentially? As the design area is formed by the mosaic of various areas having different nature protection status one has to prioritize the various implementation alternatives regarding the preferred species. In some of the restored areas species “a”, while in other might be species “b” will find better living conditions. The preferred plant/animals are obviously the high ranked (rare) species which however all have its own ecological valences or tolerance values. The designing process also faces various dilemmas regarding the type of aquatic habitats ones plans to rehabilitate. Predominantly flow-through systems or predominantly stagnant waters or the mosaic thereof, with some terrestrial areas mixed – or to state it simple how many types of habitats one aims to rehabilitate or to recreate. An obvious design criteria could be the maximization of the number of the types of the habitats. This also coins up some theoretically unresolved questions should it be fine grained the mosaic or should it rather be coarse grained habitat. The former one might change at every 10 or 100 meters where in case of the latter one could speak about only 3-4 types of habitats regarding to the whole area. At this point it is important to note that designers and even the client might face contradictions that will not be easy to resolve. One of these could be that should water coverage last too long time that would preferring the increase of the number of the amphibian, reptile species whilst some plant will gradually disappear. Without clearly defined nature conservation priorities the optimization of the design process cannot be maintained. 3. What is the expected average lifespan of the planned implementation actions and at which operating cost? The rivers and the Drava itself is a dynamically changing stochastic natural phenomena. Any of the habitat revitalization action has to take into account this fact, and also we have to remember that whatever is implemented this will be counteracted by the nature of the Dráva (sediment transport processes, sedimentation and siltation, etc.). The river will return sooner or later to its “natural equilibrium”. Therefore irrespective to the type and strength of the given implementation action it has to be regarded as temporarily even if the duration of its effects reaches decades. It has to be investigated via detailed calculations that how much suspended solids are carried by the river into the floodplain areas and will fill up the sediment accumulation zones that need to be maintained regularly. For the checking of these long-term, slow processes it is suggested to design and to maintain a complex monitoring program. It was not our tasks to solve the dilemmas outlined above whilst reviewing the habitat revitalization concepts but it was found to be important to draw the attention that during the forthcoming design and implementation works it is of paramount importance to investigate these questions in details.

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4 Options for habitat restoration on the basis of the international literature

4.1 Examples from Hungarian and foreign practice for revitalization of rivers with similar geographic characteristics To meet flood control and navigation needs the hydro-morphological characteristics of rivers – and hereby the riparian wetlands - have been changed during the past century. Over the past decades, a number of revitalization projects have been implemented, and has been designed to mitigate or reverse the adverse effects of regulatory activity. The revitalization projects are various in terms of local conditions, revitalization goals, the types of implemented interventions, the success of the project, etc. Hereunder we present some examples of which the positive and negative experiences should be taken into consideration when examining the options for the revitalization of the side-arm system of Vízvár-Bélavár.

4.1.1 Revitalization of the oxbows of River Morava (Slovakia) The Morava river is lowland meandering river with small slope and a sandy-gravelly riverbed and in its lower reach creates one of the most valuable wetlands in Europe. The most important hydrological characteristics of the river are the followings:  Flood discharge: 1600 m3/s;  Average mean discharge: 265 m3/s;  Low water discharge: 35 m3/s;  River width: 40-200 m (mean: 70 m);  Mean water depth: 2-6 m;  Average mean water velocity: 0.8 m/s;  River slope: 18 cm/km. Natural conditions have been significantly influenced by river engineering and training works. The watercourse was considerably shortened in order to develop navigation and flood protection. Because of an increase in water velocities the original flow regime dynamics and sediment transport have changed. The sediment transport capacity of the river has been doubled. Original floodplain of the river was significantly narrowed by continuous flood dykes. As a result, during floods a large amount of sediment was deposited in the flooded areas. The siltation of the oxbows began and the diversity of habitats decreased. However, the "straightening" of the river and the fluvial gravel mining have caused the incision of the riverbed and the deepening of the bed were up to two meters. The fluvial and alluvial processes have become increasingly separated, lateral migration and the hydraulic connectivity of the main channel with the oxbows was prevented by hard type of bank revetments (Pišt, 2006; CIS, 2006; Holubova – Steiner, 2011; Holubova et al., 2013).

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 53 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

In the early 1990s, to mitigate these negative trends, four meanders were reconnected with the river channel (including inflow and outflow parts) with the direct transfer of a part of the Morava’s flow. The main aim of these measures was the restoration of hydrological connectivity, increasing of flow dynamics and protection of the oxbow system against successive degradation. Proposal and implementation of meander’s reconnection was done with strong emphasis on ecological improvement regardless of present state of flow dynamics, sediment transport and overall functioning of the river ecosystem (CIS, 2006). The following summarizes the results of the revitalization of the meander marked as DVII in the Morava River, whose location is shown on the Figure 4.1..

Fig. 4.1. - The location of the Morava’s oxbows reconnected in 1993 (CIS, 2006)

The initial benefits of reconnection of meander DVII, resulting from increased flow dynamics, induced changes in the community structure of the aquatic fauna. These improvements proved to be short-lived due to successive degradation induced by high sediment supply and insufficient flow dynamics. Subsequently the degree of water supply and ecological conditions have been worsened (CIS, 2006). Figure 4.2. shows the successive degradation of meander DVII between 1995 and 2004.

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 54 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

Fig. 4.2 - Successive degradation of the oxbow DVII of River Morava reconnected in 1993 (1.)(CIS, 2006)

Fig. 4.3. - Successive degradation of the oxbow DVII of River Morava reconnected in 1993 (2.)(Holubova, 2011)

After the interventions, the examination of the abiotic and biotic processes emerging from the local revitalization works and regularization, the followings can be stated (CIS, 2006):  Water discharges transported relatively large volumes of sediments into meanders.  Dividing the flow between the river and the meander bend ensures that flow in the meander is not sufficient to transport the sediment load. Considerable decrease of flow velocity has caused massive sedimentation and the resultant deposits rapidly blocked the entrance to the meander bend.  Flow conditions after the revitalization are worse than those prior to meander reconnection.

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 55 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

The cause of failure of the revitalization project can be explained by the inconsistent preliminary calculations, which did not take into account the characteristics of the river (e.g. sedimentary conditions). Set out from the experiences above Slovakia and Austria launched a joint revitalization preparatory project for the common section of the Morava, in the course of which they tested different versions of revitalization with physical and numerical models (see Figure 4.4) (Holubova – Steiner, 2011; Holubova et al., 2013).

Fig. 4.4. - An example of the application of physical and numerical models designed to analyze different versions of revitalization of the Morava river (Holubova et al., 2013)

Based on the research results the experts proposed two types of restoration measures for this section of the River Morava (CIS, 2006): 1. Full meander integration (all flows diverted into meander) implemented in selected localities of the river. Meander integration would provide the required flow dynamics in the meanders, higher sinuosity and increased channel habitat diversity. This would also enable degraded river bed to be re-established later followed by associated changes in surface and ground water regime (water level increase). 2. Reconnecting of the meanders only from lower part (outflow) would provide partial interaction with the main river channel and higher fluctuation of water levels but this would require continuous maintenance.

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 56 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

Further scenarios of meander’s reconnection (verified by numerical and physical models) included various types of barriers and groyens in the main river channel with the aim to divert higher discharges into the meander and reduce sediment supply. The results of simulations for these scenarios indicated evident deterioration in the reconnected meanders due to low flow dynamics and high volumes of sediment, thus their implementation would require expensive maintenance and would mean further ecological devastation of the oxbow system (CIS, 2006). Based on the studies, it became clear that in the case of rivers such as the Morava (high sediment transport capacity, lowland, meandering) any flow-sharing between the main channel and the re-opened meander is accompanied by strong siltation due to decrease of velocities and hereby the shear forces. These experiences show that in case of the lowland meandering rivers, re-integration of cut-off meanders (transfer of the total water discharge to the bends) means the efficient restoration of natural riverine functions (al Holubova et. 2,013). As the appropriate devices are available for designing revitalization interventions, some necessary analyses and evaluations have to be done prior to the implementation in order to avoid expensive revitalization failures and costly mistakes (CIS, 2006). The case studies above show that careful preparation and planning of habitat restoration projects are needed in order to achieve the desired effects. In the case of rivers with large sediment transport capacity it is critical to know the conditions of sediment balance and hydromorphology, and to develop the appropriate water velocities. Based on the experiences, the restoration of the line of an originally meandering river and the reconnection of former side-arms can improve the ecological state of the river floodplain, but in case of inadequate design it can cause deterioration compared to conditions prior to the revitalization. In some respects the Morava is similar to the Drava, but the water velocities of Drava are typically larger and the amount of suspended sediment is less. However, the example shown points out that the problem of sedimentation caused by decreasing velocities have to be handled when supplying the side-arms with water from the main channel.

4.1.2 River restoration and prevention of riverbed-erosion in the Danube Floodplain National Park (Austria) The Danube River, once famous for its large inundation areas has undergone a fate similar to that of large rivers in temperate Europe and North America. The Danube has been channelized, confined by levees, impounded, and polluted. One of the last remnants of a functional alluvial landscape on the Danube River is the 48 km long floodplain section located between Vienna and the Slovakian border (between the 1895 and 1909 rkm) (Tockner, 1998). The hydrological and hydromorphological situation have been severely altered by river bank regulation in the 19th century and construction of regulation structures for navigation as well as the construction of hydropower plants in the 20th century. Despite being highly influenced by regulation work, this free-flowing section still exerts its major functional attributes associated with the dynamics of water level fluctuations and bed-load transport (Schneeweihs, 2013). Therefore, this section has been designated as a National Park Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 57 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

(National Park Donau-Auen: NPDA, “Danube Floodplain National Park “) in 1996 (Tockner, 1998).

Fig. 4.5.– The Danube section of the Danube Floodplain National Park (National Park Donau-Auen)

Despite these favorable conditions in consequence of the direct effect of the regulation of the Danube, hydrological connectivity and the geomorphological diversity has been reduced and floodplain habitats have been fragmented. One of the major effects of these regulation efforts is the erosion of the riverbed and thus the lowering of characteristic water levels in the Danube of 2-3 cm per year (Schneeweihs, 2013). This causes disintegration between the river and the adjacent floodplains. Lateral erosion is hampered and cut-off side-arms and parts of the floodplains experience siltation. Lowering groundwater levels have impact on the alluvial forests. Figure 4.6. shows the meandering Danube river section rich in side-arms before and the straight channel after the regulation.

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 58 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

Fig. 4.6. – The Danube section between Vienna and Bratislava before and after the regulation (Schneeweihs, 2013)

The management plan of the National Park contains the restoration of the former connection between the river and the floodplain by the reconstruction of the natural side-arm system. A successful conservation strategy for this floodplain area as a sustainable ecosystem must include measures to (a) reduce bed degradation in the main river channel, (b) to improve water quality and habitat heterogeneity, and (c) increase hydrological connectivity between the river and its floodplain area. Within these required management strategies, the restoration of hydrological connectivity is recognized as the most vital step, going well beyond species and habitat preservation. This concept of restoring hydrological connectivity has been developed in strong co-operation with the Federal Waterway Agency (Wasserstrassendirektion Wien, WSD) and the Committee of the National Park, and both scientists and engineers assume responsibility for this project (Tockner, 1998). The Danube river section located between Vienna and the Slovakian border can be characterized as follows:  Free-flowing section;  Low water discharge = 915 m3/s;  Mean water discharge = 1930 m3/s;  Mean water velocity = 1.6-2.0 m/s;  Average bed-load (gravel) diameter = 29 mm;  Bed-load transportation capacity = 350 000 m3/y;  Fine sediment load = 3-5 million t/y;

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 River bed River bed erosion: 1-3.5 cm/y. Restoration projects in the DFNP aim to enable natural processes like sedimentation and erosion, and to foster the formation of different habitat types several projects have been implemented in the National Park including key measures like reconnection of side-arms and removal of bank embankments (Figure 4.7.).

Fig. 4.7. – Revitalization projects in the NPDA

The study area of one of these projects is located 25 km downstream of Vienna on the orthographically right bank of the Danube (Figure 4.8.). This area has been selected on the basis of the following considerations (Tockner, 1998):  Floodplains water bodies and the Danube channel are still dynamically interconnected via groundwater flow (groundwater dynamics would be much more difficult to restore than surface connectivity).  Only minor engineering work is necessary to considerably enhance hydrological connectivity.  An empirical database, including the main functional processes and habitat requirements of the biota, is available.  The land is in the public domain (National Forest Authority) or is held in trust by WWF-Austria.

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 60 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

Fig. 4.8. - Extent of former inundation areas along the Danube River (between the mouth area and Ulm (Germany)). Black line marks the average width of the main river channel. B.) Location of the remaining free flowing section between Vienna and the Slovakian frontier and the restoration site (rectangle) (Tockner, 1998)

The backwater system is dominated by a former river channel that was cut off from the Danube at its upstream end more than 100 years ago (Figure 4.8.). At present, long stagnant periods are interrupted by short-term flood pulses (average duration: less than four days per event) that typically occur one to three times per year. These are caused by upstream connections at high water levels (>4100 m3/s) via former inflow areas in the streamside embankments. In this area of the Danube nutrient concentrations are well above the desired values with a tendency toward slightly higher concentrations. Water quality may influence the success of the restoration scheme. The high nutrient load constrains hydrological restoration to side-arms close to the main river channel. The negative ecological effects of enhanced eutrophication (impoverishment of benthic communities), can be somewhat ameliorated by a simultaneous reduction of the water retention time within this side-arm system.

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 61 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

Averaged over the past 45 years, the annual decrease of the mean water level is about 2 cm per year for the free-flowing section east of Vienna (Tockner, 1998). Bed degradation led to a decrease of the groundwater table, and reduced the frequency of floodplain inundation and the duration of flooding. The restoration project included the improvement of the water quality, instream habitat enhancement and attempts to reduce bed degradation processes. Different species have different requirements therefore the plan had to optimize the management. The side-arm system was reconnected to the Danube by lowering parts of the riverside embankment (length at each site: 30 m) and by the creation of artificial openings (Figure 4.9.). Embankments were lowered at one site down to mean water level (MW), at the two other sites down to MW + 0.5 m. Some surface connections via artificial openings occurred at lower levels (MW – 0.5 m, Figure 4.9). After implementation, the side-arm system was re- integrated in the flow regime of the river for more than half of an average year (before, it was less than 8 day/year). To improve the rate of discharge through side-arms, existing dams crossing side-arms and dividing them into single sections were completely removed and additional outlets were created. The reopening of former inflow areas had major hydrological effects: first, a gradual increase in floodplain water discharge, secondly, an increase in the frequency and duration of lotic conditions in the side-arm system, and finally a rise of the water level, leading to an expansion of shallow waters in the floodplain. The river channel itself benefited from the restoration of connectivity as it is supplied more frequently by non-refractory organic matter from the aquatic-terrestrial transition zones; and riverine communities may utilize main side channels frequently, in particular during the lotic conditions.

Fig. 4.9. - Measures to reconnect side channels by lowering of riverside embankments and creation of openings to reconnect former inflow channels (side channel) with the Danube channel (numbers indicate the duration of surface connectivity, days per year) (Tockner, 1998)

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The project was implemented between 1996 and 1999. The monitoring program combine physiographic and biotic parameters. The main abiotic parameters evaluated are hydrography, geomorphology, flow, water retention, sediment structure and sediment transport. The biotic describers include the distribution pattern of macrophytic vegetation, macrozoobenthos, adult and larval fish and amphibians. Functional limnological properties of the water bodies are assessed by measurements of phytoplankton, primary production, bacterial production and nutrient regeneration (Tockner, 1998). Within the framework of another similar project the hydrological connection of the Orth floodplain with the Danube was restored. A floodplain area of around 5.5 km2 was reconnected with the Danube’s channel by different measures (Figure 4.10.). Surface water connectivity increased from less than 30 days to more than 220 days per year leading to lotic conditions and an enhanced sediment dynamics during more than 50% of the year. To achieve this goal many restoration activities have been carried out like: (i) removal of riverside embankments (former tow path) at three former floodplain channels, (ii) removing a check dam, and (iii) building one culvert in a check dam within the flood- plain system. The increase in surface water exchange has also led to greater nutrient loading from the river being transported into wetland areas (Gumiero, 2012).

Fig. 4.10. – Restoration measures in the floodplain area of Orth. (Gumiero, 2012)

The Pilot Project Bad Deutsch Altenburg (2012-2014, project leader: Viadonau) is the first restoration project that aims to counteract riverbed erosion by adding coarse gravel to the riverbed. The added material is expected to be mixed with the bed-load material thereby reducing the average bed-load transport velocity by 90%. Considering the average mean velocities of the Danube, the grain size of 40 – 70 mm diameter has been found appropriate (Figure 4.11.). During the project, the gravel was monitored by radio tracer, and average transport velocity was measured.

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 63 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

Fig. 4.11. – The size of the gravel needed to stabilize the Danube’s riverbed (Schneeweihs, 2013)

This pilot project also included the reconnection of a side-arm of 1,5 km length with the river at low water level, the reconstruction of bank embankment, and the adaption of low water regulation with structures. The low water regulation meant the deconstruction of existing groynes, construction of new shaped groynes at lower level, achievement of more current towards banks, improvement of connection between groyne fields (Schneeweihs, 2013).

Fig. 4.12. – The pilot project at Bad Deutsch Altenburg (Schneeweihs, 2013)

The effects of the project are investigated by a 5 years pre-monitoring and 15 years long term monitoring program in order to implicate the results in future restoration projects. The monitoring program evaluates abiotic (hydromorphology) and biotic parameters (habitats, species) (Schneeweihs, 2013).

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The Danube is characterized by higher water discharges and slightly higher mean water velocities than the Drava, so the amount of transported sediment and the size of the shifted particles is greater. However, mindful of the ratio of water discharge, velocity and transported sediment, the project at Bad Deutsch-Altenburg can serve as a reference during the revitalization of the Drava as it is facing similar problems, like river deepening.

4.1.3 Revitalization of the oxbows of the River Saône (France) In 1996, proposals were made for the revitalization of a section of River Saône located between Belleville-sur-Saône and Taponas in the Rhône region, in France. The summary of the draft have been published in December 2000, and the impact assessment study in 2003. The draft included the restoration of the oxbows on the section and the planting of riparian vegetation. The work had two parts. The first intervention started in October-November of 2003, on the two locations shown on Figure 4.13, and it was followed by an additional measure in 2004 on the Le Motio oxbow. During the intervention, a total of 1 020 m section of the river had been restored: a section of 350 m at Belleville, 325 m at South Taponas and 345 m at North Taponas (GeoRiv database).

Fig. 4.13. – The location of the two restored oxbows (GeoRiv database)

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 65 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

Characteristics of the watercourse:  Catchment area: Rhône-Méditerranée;  River width: 190 m;  River slope: 0,0296 %;  Annual average discharge: 400 m3/ s (measured at the station of Macon). The oxbows of Belleville and Taponas are greatly interesting areas in terms of ecology, particularly for the fish population of the River Saône, as they provide reproductive zones and habitats being rich in plankton. These branches home the European bitterling which belongs to species of Community interest. Equally significant species are the mixed oak, elm, ash and willow forests of the riverside. For the development of the navigation on the Saône gravel mining occurred earlier, and the largest hydro-morphological and ecological impact was caused by the construction of the dam of Port-Bernalin. The main problem was the siltation of the oxbows. The poplar plantations disrupted the natural dynamics of the forest and facilitated the filling of side branches as well. If the water level of the Saône play a primary role in the siltation, the subsidiary stream Ardières, whose confluence happens at the relevant level, also plays a role on a local scale. In addition, the waves and the bank erosion related to navigation have a significant effect on habitats, particularly on the area of highly decreased fish populations. In the management plan of 2002 the water quality problems of the Ardière and of the Saône were also cited (municipal, agricultural, viticultural water pollution). The two oxbows form part of the Natura 2000 network ("wet meadows and floodplains along the Saône "). They are both protected as Environmentally Sensitive Area, and the island of Taponas is part of the “Espaces Boisés Classés (EBC)” (Ranked Wooded Area). Finally, the sites of Belleville and Taponas are included in the scope of Ranked Landscape of Val de Saône. The purpose of the intervention is the restoration and maintenance of the wetlands of the Saône’s side-arms, the restoration of the diversity on the habitats degraded, dehydrated and silted due to the regulation of the Saône and to the homogenization of the areas. Several preparatory studies preceded the work. The first was made in 1996. It was about the biological significance of the local aquatic habitats and it contained recommendations for the treatment and evaluation. The CREN (Conservatoire Régional des Espaces Naturels) compiled the scenarios in 2000 based on surveys conducted by surveyors. In 2001, the University of Lyons made a study about the importance of the fish population living in the aqueous environment of Val de Saône. The study made proposals for revitalization and for the controlling of the interventions and the monitoring of the impacts. At the same time, in the same year the sediment sampling and analysis was realized. Based on this work, in the management plan of 2002, the CREN proposed the dredging of the riverbed to 50 cm below the low water level, dredging foreseeably 5680 m3 from the oxbow of Taponas, 6270 m3 from

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 66 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

the oxbow of Le Motio. The aim of the revitalization is to enhance the connection between the aquatic and terrestrial environment, and to promote the water supply of the oxbows. The restoration of both locations had begun with deforestation and clearing, i.e. the removal of all vegetation. On the upper section of the oxbow of Taponas the bed material was dredged and was placed on the bank in a sporadic manner. However, the entrance of the oxbow has not been subject to any modification. At the lower sections of the oxbow of Taponas the work consisted of the followings: the areas still under water were connected, lakes have been created that are related to each other by small channels, and islands providing a wide range of habitats have been formed in the inlet side. Gravel from dredging was used in the construction of a footpath. In the case of the Le Motio oxbow the dredging covered the entire length of the branch. This resulted in a total of 14 000 m3 of sediment, much of which was fine sand (6 000 m3 at Le Motio and 8,000 m3 at Taponas). First, the dredged material was stored on site, than poured into the Saône downstream the site, at the height of Montmerle. This was followed by the restoration of the vegetation (GeoRiv database).

Fig. 4.14. - Topographic and bathymetric map of the oxbow of Belleville before and after restoration. (GeoRiv database).

The River Saône is similar to the Drava in terms of size and water discharge. The case study shows that the partial or full-length dredging of the side-arm’s bed, with the consideration of the low water level, is a widespread solution for reconnecting the oxbows to the river. However, it shows also the problem of the final placement of dredged sediment and the costs of maintenance after the restoration.

4.1.4 Revitalization of River Ain (France)

4.1.4.1 Oxbow revitalization The restoration of the oxbows of the French River Ain began in 2002 within the frameworks of a LIFE project. In the project the revitalization of six oxbow was carried out, that of Terre Soldat, Carronnières, Bellegarde, Sables, Sous-Bresse and Bateaux (Figures 4.14-4.15.). The first oxbow restored was that of Sous-Bresse in November 2004 and then the Oxbow of Bateaux in September-November 2005, the first operation on the oxbow of Bellegarde

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occurred in September 2005 and the rest of the work in November-December 2005, the work on the oxbow of Carronnières started in October 2005 and was completed in January-March 2006, the operation on Sables oxbow began in the winter of 2006 and the last restored oxbow was that of Terre Soldat in September 2008. During the project, a total of 4810 m long river section was restored: 1200 m in Terre Soldat, 450 m in Carronnières, 1450 m in Bellegarde, 300 m in Sables, 160 m in Sous-Bresse and 1250 m in Bateaux. This represents a total of 7.86 ha of restored water surface (GeoRiv database).

Fig. 4.15. – Revitalization of the oxbows of River Ain (GeoRiv database)

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 68 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

Characteristics of the watercourse:  Catchment area: Rhône-Méditerranée;  River width: 80 m;  River slope: 1,2546%;  Annual average discharge: 123 m3/ s (measured at Chazey-sur-Ain station).

Fi g. 4.16. - The oxbow of Bateaux before and after restoration

The Lower Ain Valley is an area exposed to different pressures. The main one is caused by the upstream hydroelectric facilities (the last big dam is located in Germany) resulting in artificial flow and interruption of sediment transport. Besides this there is the pressure of groundwater abstraction for collective and agricultural (in the first place irrigational) needs. However, the Lower Valley has a public natural heritage, with three species considered remarkable by the Habitat Directive and nine other protected species, including plant species as floating water plantain (Luronium natans), the Hampshire-purslane (Ludwigia palustris) or the water-violet (Hottonia palustris). From a hydraulic point of view the oxbows allow the expansion of floods thereby alleviating the effects of high-intensity rainfalls. The River Ain also provides a number of social and recreational opportunities for the area's population (GeoRiv database). The side-arms of River Ain have evolved as a result of direct or indirect human actions. The main factors of the changing were the sedimentation of suspended material and bed-load and the riverbed incision. The Sous-Bresse oxbow’s bed was drilled to facilitate agricultural pumping for irrigation purposes. Another problem was caused by the continuous dehydration. Drying which also affected the oxbow of Bateaux, related to the incision of the stream and a first ineffective restoration. The oxbow of Carronnières, like that of Sables, has strongly silted. The oxbow of Bellegarde, which is an old member of the branch system, also suffered of siltation because of the incision and the weak lateral dynamics. The problem of the Terre Soldat oxbow was the afforestation and the succession accompanied by drainage.

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 69 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

The project had ecological and functional goals. These goals included the preservation or the restoration of habitats of species of special importance, and the restoration of relations between the various oxbows and the rest of the water system (the relationship between the oxbows and the groundwater, the oxbows and the river and the oxbows and the riparian area). The aims of the revitalization of Sous-Bresse oxbow was to create a habitat for the growth of the floating water plantain by increasing the water level, restoration of the upstream connection and the achievement of the water flow in the oxbows in the case of floods. For Carronnières oxbow, the task was to recreate an old channel supplied by groundwater in an incised stretch by restoring the connection with the river and the water flows from upstream to downstream. The goal for the oxbow of Bellegarde was to link the remaining water bodies to the two branches, for oxbow Sables it was the restoration of the flows and the slowing of the siltation in order to preserve the outstanding biological values. Concerning the revitalization of the Bateaux oxbow the objective was to restore the old meander system, the connection between the oxbow and the floodplain forests on one side, and the connection between the river and oxbow on the other. For the oxbow of Terres Soldats the water supplementation and restoration of habitats were the problems to be solved. The measures implemented in the six locations were nearly identical: it began with deforestation and the clearing of the vegetation and continued with the dredging of the oxbows. The amount of excavated material was in different at the six locations. In Sous- Bresse 1 400 m3 of fine sediment was dredged out, in case of the oxbow of Sables it was substantially less, 123 m3. The sand was placed on the dams. At the locations of Bateaux and Carronnières, 1 400 m3 of fine sediment and 25 800 m3 of gravel were extracted in each oxbow, while in Bellegarde it was 6 700 m3 of sand and 18,000 m3 of gravel. The measures was similar in the Terre Soldat oxbow, where 25 000 m3 was dredged out and was replaced into the channel (GeoRiv database).

Fig. 4.17. - The dredging in the oxbow of Terre Soldat (GeoRiv database)

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Fig. 4.18. – The oxbow of Bellegarde before and after restoration (GeoRiv database)

4.1.4.2 The sediment recharge of the River Ain As a continuation of the oxbow revitalization project the sediment recharge of the River Ain has been also realized. The River Ain can be characterized by a major sediment deficit, which causes the deepening of the riverbed and reduces the lateral permeability. As a result, benthic invertebrates and fish habitats can disappear, on the other hand, these harmful processes can cause or worsen the loss of connection with the side-arms.

Fig. 4.19. – Sediment recharge of the River Ain with the material dredged from the oxbow of Terre Soldat (GeoRiv database)

The overall goal was the realization of measures against the sediment deficit and the prevention of the deepening of the riverbed. Using the bed material extracted during the revitalization works the river bed could be refilled and the sediment deficit could be reduced. According to the recovery protocol defined within the framework of the LIFE program, 56700 m3 of gravel was required for the charging. The bed material was excavated from the oxbows, it was placed and spread out along the river in order to be drifted by the river itself. The work on the sediment recharge of the River Ain could not be separated from the measures of the hydraulic restoration of the branches as the dredged bed material was the input of the

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recharge. The processes in the six locations were all the same. The preparatory work included the creation of passage ways (cleaning, felling, creation of trails), i.e. the connection of oxbows as mining sites and the river bed as the location of the sediment recharge. The next step was the dredging, when the upper layers of the sediment were extracted and only the large-grained material (gravel) was transported to the river for deposition. The gravel material was laid down to the boundary of the wetted section of the stream, so in case of flooding the river could mobilize them without disturbing the habitats. Near the Bateau and Carronnières oxbows 25 800 m3, at Bellegarde 18 000 m3, and at Terres Soldats 25 000 m3 gravel was placed in the river (GeoRiv database).

Fig. 4.20. - Photo of the sediment recharge of the River Ain with the use of the bed material of the oxbow of Bellegarde

The River Ain can be characterized by significantly smaller water yields than Drava that has to be taken into consideration when comparing alluvia. However, linking the revitalization of oxbows by dredging and the reduction of the channel deepening by sediment recharge can prove to be a useful practice in the further planning and preparation stages.

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4.1.5 Proposals for the restoration of River Spree (Germany) based on the assessments of zoobenthos habitats. River Spree is a typical lowland river flowing through unconsolidated sandy postglacial deposits with a mean gradient of only 0.088 %. It flows through a reservoir and some shallow lakes. During the past 200 years, the river has been straightened, deepened and the banks have been fixed by rip-raps. Some positive economic effects due to flood control and navigation have been accompanied by serious problems concerning sediment erosion followed by self- deepening, drop of groundwater up to 1.3 m, and siltation of the intercalated. The former meanders are to a great extent still present as 70 backwaters, which form an extensive potential for the restoration of the original river morphology by re-meandering (Kozerski, 1998). The investigations were carried out at two sections (Figure 4.21.). First at the "Krumme Spree", a 23 km section of the river about 100 km upstream of Berlin, in a cross section 600 m upstream of the weir at the village of Kossenblatt. The second section was a 400 m long segment of the "Miiggelspree" near the village of Freienbrink, about 11 km upstream of Berlin.

Fig. 4.21. – Location of the investigated river sections (Kozerski, 1998)

The river bed shape was assessed, the current velocity at various points of the cross-section was measured, and the density and composition of macrozoobenthos (macroscopic invertebrate species) was studied (Figure 4.22.).

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Fig. 4.22. - Zoobenthos, current velocity, and sediment composition in a cross section of River Spree (Kozerski, 1998)

The investigations demonstrated that the composition of river-bed sediments is influenced by human impacts on both the river bed and the hydraulics. The natural branching of the river bed with glacial gravel deposits and woody debris was removed. Due to increased and uniformed current velocities, the straightening of the river resulted in large areas covered with moving sands. Obviously, these areas can hardly be colonized by aquatic macrophytes, which would reduce flow velocity and retain sediments. The colonization of running water sediments by benthic invertebrates is largely determined by sediment composition, current velocity, and food supply. Therefore, the reduction of spatio- temporal hydrological variation or morphological diversity by channelization resulted in a significant decrease of invertebrate density and diversity. This is particularly true for mussels which have significant purification effects. As the Spree represents the main water supply for the city of Berlin, and considering the highly eutrophic status of the river, the purification activity of the mussels may have important economic and sanitarian significance. It is hypothesized that in a river section with restored channel morphology invertebrate abundance and diversity is increased, since natural river morphology offers a wider array of possible habitats with unique combinations of controlling environmental factors, as sediment particle size, current velocity, and nutrient supply e. g. by macrophyte stands. This should hold true both for soft-bottom dwellers on the inner sides of river bends, but also for Unionid mussels in compact fine sands, and for hard-bottom dwellers on exposed parts of dead wood. By widening the stream bed, hydraulic roughness is increased and probably the areal extension of uniformly shifting sand is reduced.

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In summary, five major habitats have been identified: 1. The rip-raps, which occupy a strip of 2-4 m, are densely colonized by invertebrates. However, most of the taxa are neozoa not typical for the zoobenthos assemblages of this lowland river. Thus these rip-raps should be stepwise reduced, following the progress of creation of new habitats for hard bottom-dwelling invertebrates. 2. Bars of fine sand are habitats for a typical potamobiontic community. The protection of this endangered community, which was typical for central European lowland rivers, is a target of the regional conservation policy. Significant sand transport is needed for the conservation of existing bars. New ones can be created by increasing the number of bends due to re- meandering. The new inner border of the bends must be maintained unmolested by human activities as natural deposits of fine sand. 3. Fine sand with macrophyte stands are exquisite habitats for filtrating mussels. Prerequisites for these habitats are light for macrophyte growth, and weakened hydraulic traction forces at the stream margin. These habitats could be expanded by widening of the river channel, protection of bars from excavating, and logging of trees that had been planted to fix the river banks. 4. Muddy deposits on fine sand near the bank are scarcely colonized and should be reduced. The management practice of the hydrological regime should be changed to allow natural flood events. These must be strong enough to wash away the mud from dead zones and redistribute it on the floodplain. 5. Uniformly structured medium sand covers large areas of the river bed and is nearly uncolonized by invertebrates and macrophytes. Its share of bottom area must be drastically reduced. Extensive sediment transport is caused by untypically high current velocity. Therefore, the average slope of the river should be diminished either by a prolongation of the river channel due to re-meandering. Meanders minimize net sediment transport rates by a slope reduction and by accumulation of sand at the inner sides of the bends. Re-meandering of the River Spree (Figure 4.23.) covers most of the necessities and should be the basis of a complex habitat restoration. River Spree has a large potential for re-meandering, if the existing backwaters are activated. A "Leitbild" (model) for re-meandering can be derived from oldest maps and color infrared pictures, which reveal old meander structures in the flood plain. As listed above, re-meandering does not meet all requirements and must be accompanied by:  a partial widening of cross sections;  allowing floods more frequently;  reducing stream maintenance actions;  removing rip-raps, and logging of bank trees.

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Fig. 4.23. – Restoring the meanders of the River Spree (Kozerski, 1998)

For River Spree, the termination of the self-deepening process and the re-elevation of the groundwater level in the floodplain are prior restoration aims. Re-meandering is a key method also in this respect. It can be shown that the changes in river morphology, the increase of bed material supply, and the addition of woody debris in order to stabilize sediments and enlarge the different habitats are needed. Additionally, the reinforcements of the river banks should be removed. The combination of these measures will restore the original degrees of freedom that enables self-development of the river’s morphological and ecological diversity (Kozerski, 1998).

4.2 Options for managing channel deepening based on international experience The realization of the revitalization goals of the Vízvár-Bélavár side-arm system necessarily requires the management of the channel deepening of the relevant Drava section. Considering that the negative effects of the channel deepening affect the whole Hungarian section of the Drava, the channel revitalization goals of this study has been put into words in other Hungarian projects as well. Within the framework of the SEE River project (Sustainable Integrated Management of International River Corridors in SEE Countries) being implemented between 2012 and 2014, the South Transdanubian Water Authority launched a sub-project that also concentrates on the treatment of the riverbed deepening of the Drava (with the sample area located between the 80-124 rkm of the Drava). The second meeting of local stakeholders of the project (on 25 March 2014th in Sellye) they summed the intervention options for the prevention of the riverbed deepening. Based on this summary (SEE River Project, 2014) and other international experience the following theoretical and practical solutions may be relevant for the purpose of preventing the deepening of the river bed:

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 The release of the bed-load from the hydroelectric power plants to the downstream river sections;  Increasing the flowing path lengths, and for this, the review and occasional demolition or relocation of the existing regulatory structures where this is possible;  Revitalization of side-arms (and oxbows), if it is possible with more water flow (the side-arm and oxbow revitalization synchronized with land use improves the water balance of the area as well);  Establishment of smaller, not spillover weir line so that they do not rule out the possibility of the reintroduction of the meandering of the section;  Establishment of (one) greater weir with fish-ladder if it’s possible;  Re-meandering the river channel (see Chapter 4.1.5). This provides benefits for nature conservation, fisheries, tourism, water retention, growth of spawning ground, landscape aesthetics, biodiversity, but because of the restoration of the wider floodplain costs of land expropriation and compensation can appear.  The application of large gravel for strengthening the riverbed in order to stop or slow down the erosion, - similar to the implemented pilot interventions on the Austrian Danube (see Chapter 4.1.2.).  Artificial sediment recharge (with dredged material from side-arms or from reservoirs of hydroelectric power plants, with concrete debris from constructions, with melted bed-load, or with break-stone, etc. - see Chapter 4.1.4.) This subject and the design of specific technical solutions has an extensive international literature, the elaboration of which exceeds the scope of this project. However, it is highly important for the protection of hydro morphological and natural conditions of the side-arm system of Vízvár-Bélavár and the entire Hungarian section of the Drava to analyze these experiences and apply them on the entire lower section of the Drava.

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5 Analysis of the Drava River water regime and alluvial flow on the project reach

5.1 Statistical analysis of the Drava River water regime

5.1.1 The methodology and objectives of the analysis The first step of the planned Habitat Restoration Concept development in the area of Vízvár-Bélavár branch system was to examine the hydrological conditions. Therefore, first we analyzed the long-term water level data of three closest river gauges (Őrtilos, Vízvár Heresznye and Barcs) to the concerned area, which was made available by DDVIZIG. Vízvár-Heresznye, the closest river gauge to the introduced Drava section, has been operating since November 2012, so for this location significantly less data is available. In case of the slightly more distant river gauges at Őrtilos and Barcs data is available since the 1970’s. In addition to these three water level data series, the DDVIZIG provided us their water velocity and flow data measured at Őrtilos and Barcs in 2004-2013 and the water velocity and flow data measured in 2013 at Vízvár. Table 5.1 summarizes the dates of the available data for the statistical analysis.

Őrtilos Vízvár-Heresznye Barcs 235.9 rkm 187.59 rkm 154.1 rkm zero point: 125.94 maB zero point: 101.195 maB zero point: 98.14 maB Water level 1970-2013 2012-2013 1970-2013 Water flow 2004-2013 2013 2004-2013 Velocity 2004-2013 2013 2004-2013 Table 5.1. – Available data at the studied river gauges

First we analyzed the water level data of each river gauges separately. As the water level was read off in centimeter units compared to the river gauge’s zero point, for the ease of comparison and further use we transferred the data into the Baltic Sea elevation values [maB]. (So every data was converted from centimeters into meters and it was added to the maB height of the particular river gauge zero point.) In terms of the planned habitat restoration program the water levels of the Drava reach between the upper riverbed remains of the Bélavári branch and the upper inflow point of the Upper side-arm of Vízvár are prevailing. Considering that there are no river gauges in this particular location, we can only estimate (extrapolate) the water-levels based on the known water levels measured at Vízvár Heresznye and Barcsi river gauges.

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For Vízvár-Heresznye river gauge we only have data from the end of the year 2012, so for the preceding period the water level data for this location were determined by extrapolation. Since the river gauge of Barcs is positioned closer to Vízvár, its data was used for the calculation, according to the following methodology:  At the river gauges of Barcs and Vízvár-Heresznye from the water levels in 2013, we singled out the data measured at the same time. These data pairs were used to determine the water level differences between the two points, and these were averaged in every 10 centimeter (difference values vary linearly depending on the measured Barcsi river gauge’s water level).  The past data for the Vízvár-Heresznye river gauge was prepared by using the data series of Barcs. The water levels measured at the river gauge of Barcs was added to the 10 centimeter averages of the differences. Due to the riverbed deepening the extrapolation gives acceptable approximation only for the last 10 years (maximum for 20 years). Since the Vízvár Heresznye river gauge is positioned on a lower level than the inflow points of the investigated side branches, the data obtained by the methodology mentioned above were corrected according to the declivity of the water level. Finally, these extrapolated water-level data to the Vízvári-Bélavári branch system top potential inflow point’s environment were used to examine by given inflow levels whether how many days in a year is the water able to flow through the particular tributary. For every studied year we determined water levels for 90%, 50%, and 10% frequent occurrence, to obtain at the river gauges the given year’s given durable water levels (expressed in maB. heights). In view of that the durable water levels show a linearly decreasing trend due to the channel deepening, in every year until 2050 we predicted the 10-50-90% water levels, assuming that over the next 40 years the water level decrease is continuing with the similar rate. The extrapolation of the water levels for Vízvár-Heresznye river gauge and the branch system was based on the calculation methodology described above on the basis of Barcs data, assuming that the channel deepening by the two river gauges and the area of the planned revitalization will be the same. In addition to the regular water level measurements, between 2004-2013 at Őrtilos and Barcs several times velocity and water level were measured together. On the base of the linear connection between water level and velocity data and using the water velocity data of these points we calculated the medium and maximum water rates for the annual water levels at given frequencies in the 1994-2013 period. This way we could estimate the velocity data for those earlier years, when we did not have water velocity measurement data. On account of the channel deepening this method can not be used to calculate velocity for the period before 1995.

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According to the presented methodology, in the followings we analyze the water-level and velocity data measured at the three river gauges.

5.1.2 The analysis of the water level and velocity data measured at Őrtilos river gauge At the Őrtilos river gauge (235.9 rkm; zero point: 125.94 maB) the Drava water-levels are measured since 1970. Figure 5.1. shows the water levels registered between 1970 and 2013 (according to the data series provided by DDVIZIG). The water levels seems to successively decrease since the 1970’s and the 80’s. On Figure 5.1. both the annual water level maximums (in the70’s 130.5-132 maB, after 2000 129-130 maB), and the annual water level minimums (126 maB in the 70’s, after 2000 124.5-125.5 maB) show decreasing tendency. Considering the directly measured data (water levels in centimeters compared to the zero point) before the 90’s frequently occurred water levels that surpassed 150 cm. While since the 90’s the water levels were hardly ever higher than 150 cm, and water levels lower (with 0.5-1 m) than the zero point 125,94 maB could be noted more frequently. Since 1970 the highest water level (476 cm =130.70 maB) was measured in the summer of 1972. The second highest water level (436 cm = 130.30 maB) was registered in 1975. In the last decade the highest water level occurred in November 2012 (380 cm = 129.74 cm). The lowest water level (168 cm = 124.26 maB) was also measured in 2012 (in January).

Fig. 5.1. – Drava River water levels measured at the Őrtilos river gauge (1970-2013)

In the period 1970-2013 the annual water level data with 90, 50 and 10% permanence is shown on Figure 5.2. The points of the 90% durability (incidence frequency) show the water level values in a given years that the water surpasses more than 90% of cases. It can be seen that water levels with this permanence have lower and lower heights above the Baltic Sea level. Similar tendency can be noted by the 50 and 10% durable water levels as well.

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The negative slopes of the trend lines fitted to the annual water levels with different durability show that at Őrtilos over the studied 40 years the mean water level fell about 1.7 m (= 3.8 cm / year channel deepening). The rate of water level decrease was significant between 1980 and 2000 (from 7.9-8.6 cm / year), but in the last decade (2003-2013) we experienced an average 1.7- 1.9 cm / year decrease of water level. It can be concluded that the channel deepening is proceeding in a slower pace, but still the annual 1.7- 1.9 cm deepening is a very significant value.

Fig. 5.2. – Drava River annual water level data with 10; 50; 90% permanence at Őrtilos river gauge, (1970-2013)

According to the DDVIZIG’s measurements at the Őrtilos river gauge Figure 5.3. shows the water levels and flows in the 2004-2013 period. The connection between the water level-flow data pairs could be approached with linear regression equation y=0.0031 x+124,41. It can be noted that the water flows rarely exceeded 1000 m3/s and the water level usually fluctuated between 125 maB és 127 maB. The greatest flow (1437 m3/s) was measured in November 2012. The highest water level (128.7 maB) occurred at this same time (from among the data- pairs when flow was measured). The lowest water flow (203 m3/s) was registered in October 2006 with the water level of 125.01 maB. Yet in the studied period the smallest water level (124.82 maB) occurred in a different time, in August 2011 (with 235 m3/s flow).

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Fig. 5.3. – The connection of water flows-water levels measured at Őrtilosi river gauge (2004-2013)

On Figure 5.4 the connectivity of water levels and velocities can be seen in the 2004-2013 period. The maximal velocity-water level connection can be described by the y=0.5091 x- 62.33 regression line. The y=0.3421 x-41.847 regression equation properly approaches the relation between mean velocity and water level. In the studied period the water level fluctuated between 124.5 and 127 maB. The mean velocity values varied beneath 1.8 m/s

(fluctuated in 0.8-1.8 m/s range). The maximum velocities (v(max)) varied between 1-3 m/s, characteristically stayed in the range of 1.5-2.5 m/s. The highest rate of the maximum velocities was 2.93 m/s in June 2004, with the water level of maB.

Fig. 5.4. –The connection of water velocities-water levels measured at Őrtilos river gauge (2004- 2013)

According to the water level and velocity data provided by DDVIZIG we estimated the medium and maximum velocities in the river profile for the 1995-2013 period. It can be noted on the basis of the data measured in 2004-2013 that there is a linear connection between the velocity and water level data series, so using the trend line’s equation the given water level

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the mean velocity can be calculated. The following equation describes the connection between Őrtilosi river gauge’s water level and the medium water velocity:

Figure 5.5. shows the annual medium water velocities in the 1995-2013 period connected to the water levels with 10% 50% 90% frequent occurrence. It can be concluded that in the medium velocities for the 10% incidence of water levels, fluctuate between 1.4 and 1.8 m/s in the studied period of time, the data for 50% permanence fluctuates in a narrower band around 1.3 m/s, and the data for 90% durability around 1.0 m/s.

Fig. 5.5. – Calculated medium velocity based on the water level data measured at Őrtilos river gauge (1995-2013)

Figure 5.6. shows the maximum water velocities calculated from the Drava water levels at Őrtilos river gauge. For the calculation we used the H-v curve’s equation for the maximum velocity (as seen on Figure 5.4.):

It can be noted that the maximum velocity values of Drava River exceeded 1.2-1.6 m/s in 90% of the cases, and only in 10% was higher than 2.1-2.5 m/s.

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Fig. 5.6. – Calculated maximum velocity based on the water level data measured at Őrtilos river gauge (1995-2013)

5.1.3 The analysis of the water level and velocity data measured at Vízvár-Heresznye river gauge The river gauge at Vízvár-Heresznye (187.59 rkm; zero point: 101.195 maB) was put in operation in November 2012. The Figure 5.7. shows Drava River water levels registered between 2012 and 2013 at Vízvár-Heresznye river gauge. (The data was provided by DDVIZIG). On the chart, the periodicity of water levels can be observed and floods at the end of autumn (November) and late spring (May). Since only one full year data are available, it is not possible to examine the long-term trends.

Fig. 5.7. – Drava River water levels measured at the Vízvár-Heresznye river gauge (2012-2013)

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As the water level data is rather small in number, we could not illustrate the 10, 50, 90% permanencies properly. For information Table 5.2 shows the water level values for the given frequencies in 2012-2013.

90% permanence 50% permanence 10% permanence Year [maB] [maB] [maB] 2012 104.635 105.215 105.975 2013 104.025 104.715 106.255 Table 5.2. – Drava River water level data with 10; 50; 90% permanence at Vízvár-Heresznye river gauge (2012-2013)

Figure 5.8. represents the water levels and flows measured at Vízvár-Heresznye river gauge in 2013. The connection between the water levels (expressed in meters above the Baltic Sea level) and water flow rates is nearly linear and it can be described with the y=00028x+103.94 regression line. The highest water level was measured (107.74 maB =590 cm) in November 2013 with the highest flow rate (1432 m3/s). The lowest water level was only 104.03 maB (=208 cm) in June 2013 and the related lowest flow was 311 m3/s. Comparing the two extreme values the maximum water level is more than twice as high as the lowest water level and in case of the flow rates the maximum value is more than four times bigger than the minimum.

Fig. 5.8. – The connection of water flows-water levels measured at Vízvár-Heresznye river gauge (2013)

The measured water levels, the water velocity peaks and mean values in 2013 at Vízvár-Heresznye river gauge are shown on Figure 5.9. below. Both the connection between the water level and maximum velocity and the connection between the water level and mean velocity are nearly linear. Higher water level in both cases are linked to higher water velocity. The equation y=0.2404x-23.597 describes the relation of water level and maximum velocity, the y=0.1692x-16.665 regression line shows the water level and mean velocity connection.

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The highest mean velocity value (1.63 m/s) and the highest maximum velocity (2.33 m/s) were registered in November 2013, when the highest water level (107.85 maB; 590cm) occurred. The lowest mean velocity (0.96 m/s) and the lowest maximum velocity (1.44 m/s) were measured together with the lowest water level (104.03 maB; 208cm) in June 2013. According to the limited data available at Vízvár-Heresznye river gauge from 2013, the characteristic medium velocity is 1.0-1.5 m/s and the characteristic maximum velocity varies between 1.5 m/s and 2.0 m/s. These values also concur with the value-range measured at Őrtilos river gauge.

Fig. 5.9. – The connection of water velocities-water levels measured at Vízvár-Heresznye river gauge (2013)

5.1.4 The analysis of the water level and velocity data measured at Barcs river gauge At Barcs, the water level of Drava is recorded since 1970 (rkm 154.1; zero point: 98.14 maB). Figure 10.5. represents the water level data measured between 1970 and 2013 at Barcs river gauge, provided by the DDVIZIG. Looking at the figure, a gradual reduction in average water levels can be observed from the 1970s, '80s, just as in case of the water levels measured at Őrtilos gauge. Both minimum and maximum values, derived from seasonal fluctuations, decreased. In the ‘70s the maximum values of water level have reached levels as high as 102.5-103 maB, while during low water periods the minimum have not fallen below 98 maB. The maximum values measured after 2000 are just reach the level of 102 maB, and the annual minimums are typically below the zero point of the gauge (98.14 maB), in fact there are values below 97,64 maB (-50 cm) as well. After 1970, the highest water level at Barcs was 618 cm (104.32 maB) in the summer of 1972. In 1975 the water level also peaked at an extremely high value, 579 cm (103.93 maB). The water level exceeded the 400 cm several times before 1998, but ever since it was approached

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at only one time in 2005 (397 cm = 101.79 maB). In 2012, the water level of the highest flood at Barcs was only 365 cm (101.79 maB). The lowest water level (LWL), -164 cm (96.5 maB) was measured in November of 2011.

Fig. 5.10. – Drava River water levels measured at the river gauge of Barcs (1970-2013)

Figure 5.11. shows the 90, 50 and 10% permanencies of annual Drava water levels measured between 1970 and 2013 at Barcs. This figure presents even more expressively the negative trend in water levels. While in 1970 the water level of the Drava was 98.7 meters above the Baltic Sea in 90% of the cases, the 90% permanency of water level was only 97 maB in 2012, 97.3 maB in 2013. The 10% permanency, that is the highest water levels of the given year also reflect the deepening of the riverbed and decrease of water levels. , and as a result the water level. The adapted trend lines show that during the studied 40 year the average water level fell about 1.3-1.7 meters at Barcs, which means a decrease of 3.2-3.6 cm/year. The average rate of decrease in water levels (and that of channel deepening) is 3.4-3.9 cm/year calculated for the last decade (2003-2013), which is considered significant.

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Fig. 5.11. – Drava River annual water level data with 90; 50; 10 % permanence at Barcs river gauge (1970-2013)

The DDVIZIG possesses water velocity data of the period 2004-2013 measured at the river gauge of Barcs (approximately on a monthly basis). Pairing the flow data with the water level data the QH curve of the Drava can be drawn (Figure 5.12.). This figure shows that in the range of flow and water level values of the reference period there is a nearly linear correlation between the two sets of data.

Fig. 5.12. – The connection of water flows-water levels measured at the river gauge of Barcs (2004- 2013)

Using again the data measured by the DDVIZIG between 2004 and 2013 we present the relationship of water velocities and water levels on the following chart. Both the maximum velocities and the mean velocities calculated for the given measurement period has been determined, both is indicated on the chart. On the basis of data measured in 2013 the mean velocity and the maximum velocity of the cross section, typical for the region of Barcs are 0.7-1.1 m/s and 1.0-1.5 m/s, respectively, which are significantly lower than the typical values measured at Őrtilos (mean velocity: 0.8-1.8 m/s, maximum velocity: 1.5-2.5 m/s). Looking at Figure 5.13., we can see that there is a linear relation with high correlation between the series. This linear relation allows us to– after defining the equation describing the relationship – calculate water velocities for those years where water level data are available.

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Fig. 5.13. – The connection of water velocities-water levels measured at river gauge of Barcs (2004- 2013)

On the basis of the above we determined the water velocity values for 10, 50 and 90% annual permanence derived from the corresponding water levels for every year. The velocity data were calculated from the measured water level data using the following equation (also indicated on Figure 5.13.)

Figure 5.14. shows the estimated mean velocities corresponding to the water levels of given permanence for the period of 1995-2013. According to the calculations in the last twenty years in 90% of the cases the mean water velocity of Drava was higher than 0.7-0.8 m/s, and in 10% of the cases it was greater than 1.0-1.1 m/s at Barcs. 0.8-1.0 m/s of maximum velocities belonged to water levels with 50% probability of occurrence.

Fig. 5.14. – Calculated medium velocity based on the water level data measured at river gauge of Barcs (1995- 2013)

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The maximum velocity values of the period 1995-2013 was calculated - following a similar methodology to the case of mean velocities – from water level data recorded at river gauge of Barcs using the equation of the linear relation indicated in Figure 5.13.

The calculated water velocities derived from the water level values with 10, 50 and 90% probability of occurrence can be seen on Figure 5.15.. Based on the chart the water velocity of Drava measured at Barcs was higher than 0,9-1,0 m/s in 90% of the cases, and in case of high waters it exceeded the 1.3- 1.4 m/s. The velocity values of 90% permanence fluctuated around 1.0 m/s, that of 50% permanence were around 1.2 m/s and the velocities of 10 % permanence were around 1.45 m/s. The water velocity values with 10% probability of occurrence had the highest standard deviation, while the velocity values with 50 and 90 % probability of occurrence had similar, lower standard deviation.

Fig. 5.15. – Calculated maximum velocity based on the water level data measured at river gauge of Barcs (1995-2013)

Based on the analysis of water velocity data corresponding to water levels with given permanence it can be ascertained that the water velocity in the river section of Őrtilos is higher than that of the section of Barcs (see Chapter 5.1.2.).

5.2 Forecast of water level permanence of the Drava River Using the measured water level data from the past - taking into consideration the currently dominant channel deepening trend - estimated that the section concerning the planning area of the Drava River water levels are expected in the future what. Knowing this, on the one hand established the water supply of the branch system of Vízvár-Bélavár is how it will evolve without interventions (how often there is direct relationship between a given height can be characterized by the Drava River area), on the other hand can be predicted, the impact of specific interventions in what time scale can succeed.

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Using the current trends all three (Őrtilos, Vízvár-Heresznye, Barcs) gauge water level data are forecast until 2050. It was assumed that the average channel deepening trend for the period 1970-2013 remain constant in the coming decades. A detailed analysis of Őrtilos and water levels at Barcs are showed that the channel deepening was slower pace in the last 10 years than in the previous decades. Taking into account the favorable data (for the entire 1970-2013 period) for the benefit of the security.

5.2.1 The Drava River water levels extrapolation at the gauge of Őrtilos The available water level data the Drava water level has been extrapolated at Őrtilos specifying the trend of water level reduction in nearly 40 years ahead to 2050. Description of the trend the water level data (in maB) are used based on the data counted 90, 50 and 10% annual permanency between 1970 and 2013. The measured data reported of the current year 90, 50 and 10% permanency of water level data were fitted to a linear function. The different permanency of water levels proceeded the following equations:  90% permanency: o the equation of the line:

o the slope of the line:  50% permanency: o the equation of the line:

o the slope of the line:  10% permanency: o the equation of the line:

o the slope of the line: The above equations are shown in Figure 5.16. get the water level values for the period between 1970 and 2050. It can be seen that during the extrapolation extended period (1970- 2050) the Drava water level is declined almost five meters. For 2050 the water level will be lower above three meters than the actual water level in case of each permanency (the largest reduction are affect for the low waters).

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Fig. 5.16. – The extrapolation of the Drava water levels at gauge of Őrtilos between 1970 and 2050

5.2.2 The Drava River water levels extrapolation at branch system of Vízvár- Bélavár Similarly to the extrapolate of water levels at gauge of Őrtilos the trend of water level reduction have been determined around the branch system of Vízvár-Bélavár (~ 198 river km) and water levels are expected with this in the future. For this have been used the measured water level data at gauges of Vízvár-Heresznye and Barcs as well as the water level reduction calculation between the gauge and possible influence of the top-side of the branch system. Calculated on the basis of the above, have been extrapolated the water level of 90, 50 and 10% of annual values permanency until 2050. The different permanency of water levels proceeded the following equations:  90% permanency: o the equation of the line:

o the slope of the line:  50% permanency: o the equation of the line:

o the slope of the line:  10% permanency: o the equation of the line:

o the slope of the line: . In Figure 5.17. can be seen the extrapolated point of influence of our study branches water levels for 50% and 90% incidence. The Drava water level would be lower above 2.5 meters than the currently if the trend channel deepening continued as soon as the last few decades.

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Fig. 5.17. – Extrapolated water levels in the investigation branches of point of influence between 2012 and 2050

5.2.3 The Drava River water levels extrapolation at the gauge of Barcs Following the scheme presented above is determined the trend of water level reduction at our disposal water level data of Barcs. Based on these data the water level of Drava River at Barcs was estimated until 2050 (the trend in recent decades, assuming 2050). Based on data reported between 1970 and 2013, have been extrapolated the water level of 90, 50 and 10% of annual values permanency data were used to describe the trend. The different permanency of water levels proceeded the following equations:  90% permanency: o the equation of the line:

o the slope of the line:  50% permanency: o the equation of the line:

o the slope of the line:  10% permanency: o the equation of the line:

o the slope of the line: , which are shown in the diagram on Figure 5.18. It can be seen that during the extrapolation extended period (1970-2050) the Drava water level is declined almost five meters. For 2050 the water level will be lower above three meters than the actual water level in case of each permanency (taking into account the 10, 50 and 90% incidence water level data).

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Fig. 5.18. – The extrapolation of the Drava water levels at gauge of Barcs between 1970 and 2050

5.3 Description of the sediment conditions on the Drava River If we would like to use the energy of the river as driving force of habitat revitalization, we have to know that in the bottom of the river bed developed shear stress is the basis of river surface formation. The river is able to wash away and transport a certain granulation of alluvial when the river throw down it build the floodplain over the certain threshold of shear stress. The shear stress expressible with the river per unit in cross-section of the existing so- called especial (or specific) of amount of energy. This amount of energy dissipate or probably dissipate in river bed which obviously in relation to process of intensity of riverbed migration and proceedings of sediment transport. Considering a given reach the specific energy clearly associated with the dominant grain size (river-wash). Below are the Drava River sediments conditions discussed based on the available data. The knowledge of suspended sediment quantity and quality in the affected area of revitalization is important because we can get an overall picture of the expected quantity (and quality) of suspended matter deposition from supplied sediment led to branches by Drava River. The examination of sediment amount and grain size distribution give information from erosive proceedings of riverbed and bank. Absolutely indispensable knowledge of appertaining to data of rolling sediment for designing of treatment possibilities of proceedings of riverbed (seen Chapter 8.) as well as prognosticate extent of lateral erosion by lead out water for branches.

5.3.1 Sediment volume based on regular measurements at the gauge of Barcs Suspended sediment yield was measured at gauge of Barcs when water flow and water velocity was measured between 2004 and 2013 as in Chapter 5.1. was described. Compared between the measured mass flow of sediment and medium and maximum velocity of river gives Figure 5.19. Can be seen from data that the correlation between water velocity and sediment yield is quadratic/squared. The sediment yield is 0-30 kg/s speed for smaller (0.5-1.0

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m/s), and in addition to the range of water velocities between 1.25 and 1.5 m/s sediment yield of river is very high 40-80 kg/s or just like 110 kg/s. The density of points can be seen that sediment yield was typically between 0 and 30 kg/s from 2004 to 2013.

Fig. 5.19. – Measured sediments yields and water velocities contacts at the Drava River at gauge of Barcs (2004-2013)

Based on the above data the 50% permanency of water level, in case of approximately 1.0 m/s medium velocity yield of suspended sediment value is 15-20 kg/s which is able to reach quantities of sediment up to 600 000 tons per years. These data are consistent with the previous measurement results according to which the Drava River average annual suspended sediment transport fluctuate between 460 000 and 580 000 tons/year (DDVIZIG). This is significant amount, which call attention to detailed design of branch revitalization is necessary a detailed analyze of sediment-balance conditions.

5.3.2 Sediment volume on the region of Bélavár The South-Transdanubian Water Management Directorate and the Hrvatske Vode examined concentration, yield and grain composition of rolling and suspended sediments a part of Drava River approximately 235 km long and partially common Croatian-Hungarian partfor five indicated cross-section (Botovo, Bélavár, Barcs, Drávaszabolcs and area of Belišće, see Figure 5.20.) within the compass of Hungary-Croatia IPA Cross-border Co-operation Programme 2007-2013 (HU-HR) number HUHR/1001/1.1.2/0009 0 project by „Drava morphological monitoring”(Kulcsár, 2013).

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Fig. 5.20. – The location of bed morphology surveys of South-Transdanubian Water Management Directorate

For exploration of rolling and suspended sediments have been carried out series of measurement three times on 05.08.2012., on 14.06.2012. and on 28.08.2012 in the region of Bélavár (Figure 5.21.). Besides the water depth, water flow rate and the current medium speed for indicated cross section has been measured (Table 5.3.).

Fig. 5.21. – The location of investigation of alluvial conditions at Bélavár (South-Transdanubian Water Management Directorate)

Suspended Rolling Middle Mid- Concentration Flow sediment sediment Date Time velocity depth in the medium yield yield [m3/s] [m/s] [m] [kg/s] [g/m3] [kg/s] 08.05. 15:00 491 1.54 2.91 26.273 53 0.502 14.06. 14:36 700 1.60 2.39 48.831 70 5.644 28.08. 12:49 376 1.22 1.67 11.339 30 0.012

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Table 5.3. – In the course of investigations data of the alluvial conditions from the three series of measurements occasion (Bélavár)

It can be determined based on measurement results that volume of suspended sediments are also hundreds of thousands of tons per year in this region. On the basis of a limited number of measurements make no impression order of magnitude divergence the volume of suspended sediments for area of Barcs and Bélavár. The differences between them primarily arise from due to divergent water velocities sediment transport capacity. (The measured data in Barcs during the same measurement campaign in this study did not analyze in detail.)

5.3.3 The rolling sediment samples grain composition at Bélavár In the table 5.4. can be seen the results of particle compositions of rolling sediments from the first measurement series on May. The percentage and mass of certain fraction of rolling sediment by Drava River was determined by quadric sieve and screening machine. At the first set of measurements (08.05.2012.) measured a total of 109.2 m wide cross-section on 5 perpendiculars. During the May survey measured the rolling sediments from the left bank to the following intervals samples were taken: 25, 53, 70, 85 and 106 meters. The rolling sediments were measured at the first three perpendicular which depth one by one are 4.4, 3.1 and 2.1 meters. The first column of table includes the used sieves diameters. The other columns of table include the particles rate of undersize (undergoing mass) and oversize (remaining mass) grain as perpendicular.

The sediment samples rolling particle composition, Bélavár Number of Perpendicular 1 Perpendicular 2 Perpendicular 3 perpendicular: Distance: 25 m 52 m 70 m Remaining Undergoing Remaining Undergoing Remaining Undergoing Diameter mass mass mass mass mass mass [mm] [%] [%] [%] [%] [%] [%] 32 0.00 100.0 0.00 100.0 0.00 100.0 16 10.35 89.6 4.23 95.8 0.00 100.0 8 29.13 60.5 28.59 67.2 7.87 92.1 4 51.79 8.7 61.29 5.9 67.71 24.4 2 8.67 0.1 5.86 0.0 23.36 1.1 1 0.03 0.0 0.01 0.0 0.21 0.9 0.5 0.01 0.0 0.00 0.0 0.24 0.6 0.25 0.01 0.0 0.01 0.0 0.50 0.1 0.125 0.00 0.0 0.01 0.0 0.11 0.0 0.063 0.00 0.0 0.00 0.0 0.00 0.0 Residual 0.00 0.0 0.00 0.0 0.00 0.0 Total: 100.0 100.0 100.0 Table 5.4. – The particle compositions of rolling sediments from the first measurement series (08.05.2012.)

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Figure 5.22. shows the particle compositions of rolling sediments from the first measurement series on May. On the abscissa (horizontal axis) of the graph included in sieves diameter. Thus the column on certain pacing signify the rate of grains which diameters are greater than the certain sieve diameter and smaller than the next (one more greater) sieve diameter. Relying upon these findings the figure shows that the largest percentage (50-70%) of the particles are between 4 and 8 mm in the rolling sediments for each of the three perpendiculars. It is important to note that in this case the rolling sediment contained no particles with a diameter greater than 32 mm and in the perpendicular 3 there were greater than 16 mm either.

Fig. 5.22. – Distribution of rolling sediments grain size from the first measurement series (08.05.2012.)

In Table 5.5. the results of particle compositions of rolling sediments from the second measurement series (14.06.2012.) can be seen. At the second set of measurements on June measured a total of 183.3 m wide cross-section. Measured from the left bank to the following intervals samples were taken: 23, 63, 88, 114 and 160 meters. The rolling sediments were measured at the first three perpendicular which depth one by one are 2.1, 2.5 and 2.8 meters.

The sediment samples rolling particle composition, Bélavár Number of Perpendicular 1 Perpendicular 2 Perpendicular 3 perpendicular: Distance: 23 m 63 m 88 m Remaining Undergoing Remaining Undergoing Remaining Undergoing Diameter mass mass mass mass mass mass [mm] [%] [%] [%] [%] [%] [%] 64 0.00 100.00 0.00 100.00 0.00 100.00 32 28.08 71.9 30.02 70.0 0.00 100.0 16 15.56 56.4 22.45 47.5 23.69 76.3 8 26.84 29.5 21.54 26.0 25.62 50.7 4 14.44 15.1 5.98 20.0 27.49 23.2 2 5.77 9.3 2.59 17.4 21.70 1.5 1 3.83 5.5 2.99 14.4 1.49 0.0 0.5 2.89 2.6 6.98 7.5 0.01 0.0 0.25 1.95 0.6 6.78 0.7 0.01 0.0 0.125 0.59 0.0 0.65 0.0 0.00 0.0

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0.063 0.03 0.0 0.02 0.0 0.00 0.0 Residual 0.010 0.0 0.00 0.0 0.00 0.0 Total: 100.0 100.0 100.0 Table 5.5. – The particle compositions of rolling sediments from the second measurement series (14.06.2012.)

Figure 5.23. shows the particle compositions of rolling sediments from the second measurement series on June. The diagram shows that in samples from perpendicular 1 and 2 the 32-64 mm diameter particles are the largest majority. But such large particles sediments are not occur near the right bank in the perpendicular 3. The sediment samples from the perpendicular 3 distributed rainfall of >16 mm, 8-16 mm, 4-8 mm, 2-4 mm and dimensions of the particles is similar, 22-27% ratio. Overall, considering that the entire cross-section occurs the particles with a diameter between 4 mm and 64 on a large scale. It is important to note that in this case the rolling sediment contained no particles with a diameter greater than 64 mm.

Fig. 5.23. – Distribution of rolling sediments grain size from the second measurement series (14.06.2012.)

At the third set of measurements (28.08.2012.) measured a total of 185.2 m wide cross- section. Measured from the left bank to the following intervals samples were taken: 34, 67, 97, 122 and 159 meters. In Table 5.6. can be seen the particle compositions of rolling sediments from the third measurement series (28.08.2012.). The rolling sediment only the perpendicular 2. was patterned in this time (2 meters depth).

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The sediment samples rolling particle composition, Bélavár Number of Perpendicular 2 perpendicular: Distance: 67 m Diameter Remaining mass Undergoing mass [mm] [%] [%] 32 0.00 100.0 16 4.23 95.8 8 28.59 67.2 4 61.29 5.9 2 5.86 0.0 1 0.01 0.0 0.5 0.00 0.0 0.25 0.01 0.0 0.125 0.01 0.0 0.063 0.00 0.0 Residual 0.00 0.0 Total: 100.0 Table 5.6. – The particle compositions of rolling sediments from the third measurement series (28.08.2012.)

Figure 5.24. shows the particle compositions of rolling sediments from the third measurement series on August. In the simples detection of particles between 4 and 8 mm occurred largest percentage (61.3%). Thereafter gravel 8-16 mm diameter ratio was relatively high (28.6%). There were not presented particles having diameters of more than 32 mm on the measure series of August.

Fig. 5.24. – Distribution of rolling sediments grain size from the third measurement series (28.08.2012.)

The following table (Table 5.7.) was summarized on the occasion of the certain measured series gravel with a diameter particle size ranges moved out of the river at what speed (averaged from the perpendicular different composition). It can be seen that during the measurement in May and August, the largest rolling sediment in the range of 16 to 32 mm.

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During the June measurement in addition to the above, 1.6 m/s velocity ranging between 32 to 64 mm of sediment is moved by water. This data is referred to later in the chapter on the riverbed deepening stopping. First set of Second set of Third set of Pulled particle size measurements measurements measurements [mm] (08.05.2012.) (14.06.2012.) (28.08.2012.) Ratio by weight [%] >64 0.00 0.00 0.00 32.0-64.0 0.00 19.37 0.00 16.0-32.0 4.86 20.57 4.23 8.0-16.0 21.86 24.67 28.59 4.0-8.0 60.26 15.97 61.29 Water velocity [m/s] 1.54 1.6 1.22 Table 5.7. – The pulled maximum grain size and he measured water velocities from the three measurements

5.3.4 The suspended sediment samples grain composition at Bélavár During the three series of measurements by the Drava suspended sediment was modeled and determined the sediment granulometric features with a precipitating apparatus. In Table 5.8. can be seen the particle compositions of suspended sediments from the first measurement series (08.05.2012.).

First series. The suspended sediment samples particle composition, Bélavár Remaining mass Undergoing mass [%] [%] Diameter Perpen Perpen Perpen Perpen Perpen Perpen Perpen Perpen Perpen Perpen dicular dicular dicular dicular dicular dicular dicular dicular dicular dicular 1 2 3 4 5 1 2 3 4 5 [mm] 25 m 52 m 70 m 85 m 106 m 25 m 52 m 70 m 85 m 106 m 0.5 0.0 0.0 0.0 0.0 0.0 100.0 100.0 100.0 100.0 100.0 0.25 0.0 0.0 0.0 0.0 0.0 100.0 100.0 100.0 100.0 100.0 0.125 0.0 0.0 0.0 0.0 0.0 100.0 100.0 100.0 100.0 100.0 0.1 8.6 11.2 14.4 2.9 5.7 91.4 88.8 85.6 97.1 94.3 0.05 20.5 19.6 19.6 20.2 26.4 70.9 69.3 66.0 76.9 67.8 0.02 33.2 34.2 22.8 31.7 35.3 37.7 35.1 43.2 45.2 32.6 0.01 16.1 13.7 11.1 18.9 15.6 21.6 21.4 32.0 26.3 17.0 0.005 5.4 6.2 3.1 8.5 6.9 16.2 15.1 29.0 17.8 10.0 0.001 16.2 15.1 29.0 17.8 10.0 0.0 0.0 0.0 0.0 0.0 Table 5.8. – The particle compositions of suspended sediments from the first measurement series (08.05.2012.)

In Figure 5.25. can be seen the distribution of suspended sediments grain size from the first measurement series. The samples from the perpendicular 1 and 2 which are closer to the left

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bank particles between 0.1 to 0.25 mm were more predominant. In the other perpendiculars were dominant the particles between 0.02 to 0.05 mm. There were not presented particles having diameters of more than 0.125 mm on the measure series of May.

Fig. 5.25. – Distribution of suspended sediments grain size from the first measurement series (08.05.2012.)

The table 5.9. shows the particle compositions of suspended sediments from the second measurement series from the five sampling perpendicular.

Second series. The suspended sediment samples particle composition, Bélavár Remaining mass Undergoing mass [%] [%] Diameter Perpen Perpen Perpen Perpen Perpen Perpen Perpen Perpen Perpen Perpen dicular dicular dicular dicular dicular dicular dicular dicular dicular dicular 1 2 3 4 5 1 2 3 4 5 [mm] 23 m 63 m 88 m 114 m 160 m 23 m 63 m 88 m 114 m 160 m 0.5 0.0 0.0 0.0 0.0 0.0 100.0 100.0 100.0 100.0 100.0 0.25 0.0 0.0 0.0 0.0 0.0 100.0 100.0 100.0 100.0 100.0 0.125 0.0 0.0 0.0 0.0 0.0 100.0 100.0 100.0 100.0 100.0 0.1 11.8 14.6 8.0 13.2 9.2 88.2 85.4 92.0 86.8 90.8 0.05 16.7 31.6 23.4 26.6 27.4 71.5 53.8 68.6 60.3 63.5 0.02 32.5 24.6 33.5 31.6 32.8 39.0 29.2 35.1 28.7 30.7 0.01 15.9 15.3 15.3 13.9 16.1 23.2 13.9 19.8 14.8 14.6 0.005 9.5 7.5 8.2 7.8 7.6 13.6 6.3 11.6 7.0 7.0 0.001 13.6 6.3 11.6 7.0 7.0 0.0 0.0 0.0 0.0 0.0 Table 5.9. – The particle compositions of suspended sediments from the second measurement series (14.06.2012.)

Figure 5.26. shows the particle compositions of suspended sediments from the second measurement series on June. In all of the measured perpendicular incidence of the particles between 0.05 to 0.02 mm had the highest proportion (30-35%) except of perpendicular 2. In

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the samples of perpendicular 2 were dominant the particles between 0.1 to 0.05 mm. There were not presented particles having diameters of more than 0.125 mm on the measure series of June.

Fig. 5.26. – Distribution of suspended sediments grain size from the second measurement series (14.06.2012.)

Table 5.10. summarized the data of third suspended sediments sampling measurements particle composition on the august.

Third series. The suspended sediment samples particle composition, Bélavár Remaining mass Undergoing mass [%] [%] Diameter Perpen Perpen Perpen Perpen Perpen Perpen Perpen Perpen Perpen Perpen dicular dicular dicular dicular dicular dicular dicular dicular dicular dicular 1 2 3 4 5 1 2 3 4 5 [mm] 34 m 67 m 97 m 122 m 159 m 34 m 67 m 97 m 122 m 159 m 0.5 0.0 0.0 0.0 0.0 0.0 100.0 100.0 100.0 100.0 100.0 0.25 0.0 0.0 0.0 0.0 0.0 100.0 100.0 100.0 100.0 100.0 0.125 0.0 0.0 0.0 0.0 0.0 100.0 100.0 100.0 100.0 100.0 0.1 15.8 8.6 4.9 5.6 8.5 84.2 91.4 95.1 94.4 91.5 0.05 15.1 22.7 22.4 20.9 21.8 69.0 68.7 72.7 73.5 69.7 0.02 23.7 29.7 31.6 35.5 27.1 45.3 39.0 41.1 38.0 42.6 0.01 20.5 19.9 20.3 17.5 17.0 24.8 19.2 20.8 20.5 25.6 0.005 10.2 9.6 10.7 9.3 10.0 14.6 9.6 10.1 11.2 15.6 0.001 14.6 9.6 10.1 11.2 15.6 0.0 0.0 0.0 0.0 0.0 Table 5.10. – The particle compositions of suspended sediments from the third measurement series (28.08.2012.)

In Figure 5.27. can be seen that the suspended sediments samples composites in August are similar than the June samples. In all five of perpendicular the largest scale of grain (23-35%) are the diameter 0.02-0.05 mm. There were not presented particles having diameters of more than 0.125 mm.

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Fig. 5.27. – Distribution of suspended sediments grain size from the third measurement series (28.08.2012.)

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6 Observations and conclusions of the geodetic surveys and the site inspections

I order to summing up the revitalization possibilities of the Vízvár-Bélavár side-arm system the knowledge of relief conditions of the affected region is essentially. The main aim of planned habitat-revitalization is to improve the water supply conditions between the actual main-channel of the Drava, the section of the upper Vízvári-side-arm (over the meeting point of the upper Vízvári-side-arm and the Bélavári-side-arm) and the Bélavári- side-arm and its channel remains in the upper region. Based on the available preliminary topographical information about the side-arm-system there are numerous channel remains, smaller oxbow and swamps on the project area. The conditions (alluvial deposition) of the significant part of the channel-remains do not allow the cost-effective and ecological revitalization. In the course of the preliminary site visit and the site inspection in April 2014 we have found such side-arm-remains besides the silted channels, which revitalization will be able significantly improve the water supply conditions of the side-arm-system. We investigated these options during the surveys. The aim of the multi-level geodetic surveys was the description of the relief conditions of the project area with centimeter accuracy hereby provide information in sufficient amount and quality about the riverbed height of the water supplying side-arms and oxbows, or the localization of the position and height of the former channels, which can be the basis of the revitalization process. Knowing these – considering the water level of the Drava (see also in Chapter 5.2) – the overflowing frequency of the side-arms and oxbows of the Bélavári-Vízvári area can be estimated, in addition the characteristic of the connection with the Drava (directions of the water flow, position and number of the connecting channels), which are essential base information by the planning of the implementations.

6.1 Location and time of the geodetic surveys The geodetic information about the relief levels are provided by the former surveys of the South-Transdanubian Water Management Directorate (2011), by actual measurements (March 2014) and the results of additional surveys (03-04.04.2014) measured by the Inno- Water Ltd. The relief measurements focused on the upper Vízvári-side-arm, the Bélavári-side-arm, the gravel quarries and the affected riverbank of the Drava on the Hungarian side (Figure 6.1.). The surveys were made by geodetic leveling instruments with centimeter accuracy and were compared to known base point. During the surveys mostly the typical cross-sections of actually existing channels and the presumed channels were measured (Figure 6.2.), which allows picturing the possible path of the water supplying channels by the investigation of the minimum height values (the lowest

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point of the bottom in a cross section). Longitudinal sections were made in the case where the main aim was the determination of the cross flow imposing height of a well-defined channel.

Fig. 6.1. – Cross sections affected by the geodetic surveys

Fig. 6.2. – Example of a characteristic cross section of a side-arm

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In the course of the data processing the height values of the affected cross-sections were analyzed along the channels of the potential water supplying alternatives in terms of the side- arm/oxbow revitalization processes (Figure 6.2.). The fundamental aim of the investigation was the determination of limiting relief heights along the existing and potential flow directions based on the measured levels. These maximum values (relative top points of the channel) of the potential channels have become the input value (inflow value) in the calculations of the overflow frequencies. Figure 6.3. shows the considerable alternatives of the water supplying channels.

Fig. 6.3. – Possible revitalization alternatives of the side-arm system of Vízvár-Bélavár

6.2 Geodetic survey results of the important channel alternatives in terms of the side-arm-system revitalization The considerable alternatives of the water supplying channels are summarized the Figure 6.3. in the previous chapter. The channels of each alternatives are water-covered in different level, the features of the banks can be significantly different but in numerous cases the channel alternatives have common sections. In the following seven alternatives will be introduced during the results of the geodetic surveys and the experiences of the site visits.

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6.2.1 Description of the 1st Channel alternative The 1st Channel alternative is marked with blue on Figure 6.3. The presumed longitudinal section of the bottom (based on results of the geodetic surveys) is shown on the minimum level diagram of Figure 6.4. It is distinctly visible that the beginning part of the “channel” is on 107-108 maB (locally 109 maB). Channel slope in the affected section is significant: approximately 5-6 m along 6500 m.

Fig. 6.4. - Longitudinal section of the 1st alternative („0” point on the riverbank of the Drava by the upper inflow)

According to the experiences of the site surveys the channel of the affected alternative is fully silted on the initial section, it is not separated from the surrounding ground level (1st picture of Figure 6.5.). The riverbank area on 107-109 maB as a result of the siltation, makes impossible the live connections with the Drava. This conclusion is corroborated by the experiences of the site surveys, because we have not found any signs of permanent or temporary water coverage (1st picture of Figure 6.5.). Later sections of the channel show various character. Parts of the former channel can be found in shorter segments, but these are considerably silted yet, they are arid and covered with plants (2nd picture of Figure 6.5.). Near to the gravel quarries the line of the channel alternative passes along a dirt road which lies on an embankment and crosses it in each time (3rd picture of Figure 6.5.). The bank of the former cannel is more and more discernible on the further stages of the first alternative. From the northern part of the alternative (from the line of the northern gravel quarries) the water covered, permanent channel bank of the upper Bélavári-side-arm can be observed. The water coverage was expressed during the site visit in March 2014 (4th picture of Figure 6.5.). Permanent water coverage and continuously widening channel is the main characteristic of the side-arm. On the northern part of the alternative two culverts can be found connecting up the side-arms water

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under the roads, which provide the approachability of the gravel quarries. From the eastern culvert there is detailed, high resolution geodetic surveys available. On the diagram of the longitudinal section can be seen that the level of the channel bank is significantly lower (the difference reaches the 2 m in some places) but there are still big fluctuations on the minimum level of the bottom. The channel flows in into the upper Vízvári-side-arm, which is connected to the Drava in the whole year (see also the 5-6th alternative). This part of the side-arm is passable with motorboat most of the year (5th picture of Figure 6.5), but there are sand banks which are continuously building up and washed away, therefore the alternation of shallow and deeper parts can be observed on the field and also on the longitudinal section. The experiences of the site visit in March 2014 corroborate the results of the geodetic survey. According these the bigger part of the alternative line has alternative channel, which water coverage is provided in certain part of the year. The beginning part of the 1st alternative cannot be the water supplying way, because it is significantly silted and separated from the Drava (the actual way of the water supplement is introduced at the 2nd alternative).

Fig. 6.5. Characteristic points of the 1st channel alternative based on the site survey (03.04.2014.)

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6.2.2 Description of the 2nd Channel alternative The channel of the 2nd alternative is mostly common with the 1st cannel, but there is a definitive difference – also in aspect of the practice – in the beginning stage of the channel, namely the connection with the Drava. The second alternative follows the presumed way of the actual water supplement. Figure 6.7. shows the longitudinal section of the 2nd alternative. We would like to call the attention that on the longitudinal section diagram contains only the values based on the data of the cross- and longitudinal sections, the level of the lakes (which are part of the alternative line) do not occurs.

Fig.6.6. –Numbering of the gravel quarry lakes alongside the Drava, on the western side of the affected region

The lower level of the 2nd alternative’s channel (compared to the first alternative) is distinctly visible on the longitudinal section diagram. The level of the bottom do not surpass the 107 maB value, with the exception of the narrow connection stages between the I. and III. just as the III. and V. gravel quarry lakes (according to the numbering of Figure 6.6.), which height changes between 107-108 maB. This blockage will be disappear with the occasional connection of the lakes, so the flow imposing level of the channel will be the road the embankment and the 106.5-107 maB level of the northern curve on common track with the 1st alternative.

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Fig. 6.7. - Longitudinal section of the 1st alternative („0” point on the riverbank of the Drava by the upper inflow)

The track of the channel alternative passes through the gravel quarry lakes alongside the Drava. The experiences of the site visit show, that the actual water supplement comes to pass during the gravel quarry lakes. The II. lake is connected permanently with the Drava, which is shown well on the satellite pictures. The lakes are separated with narrow land-bridges. One of these, between the I. and II. lake is already crevassed on a 1.5 m wide segment (2nd picture of Figure 6.8.). At the site visit in March 2014 constant water flow was observed between the two lakes. The widest land-bridge is between the III. and V. quarry lakes (3rd picture of Figure 6.8.). But the way of the water supplement is probably this, because the water can fall over the land-bridge in time of high Drava levels. So the Drava contacts indirectly with the V. lake, from where the water runs in the channel of the 1st alternative probably. The point of the connection is at the upper two-thirds of the western shore of the lake, where the road margining bank is partially missing (4th picture of Figure 6.8.). Thereafter the path of the water is common with the 1st alternative.

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Fig. 6.8. - Characteristic points of the 2nd and 3rd channel alternative based on the site survey (03.04.2014.)

6.2.3 Description of the 3rd Channel alternative The 3rd alternative is a variation of the 2nd channel alternative. The connection of the main channel and the V. quarry lake is the basic difference. In this case the way of the water is between the northern corner of the lake and the channel instead of the gap on the embankment. According to the above, the longitudinal section of the 3rd alternative is very similar to the 2nd version (Figure 6.9.). However the relief elevation on the connecting stage between the channel and the lake is significantly different. The 108.6 maB altitude is the limiting level of the water supplement frequency.

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Fig. 6.9. - Longitudinal section of the 3rd alternative

In the course of the site survey there was not observed channels with permanent or near permanent water coverage between the main channel and the quarry lake. Near to the dirt- road thick vegetation and silted (in different level), not connected channel fragments can be found (Figure 6.8.). Because of the actual relief conditions most of the year the alternative channel does not take apart in the water supplement (depending on the water level of the Drava) of the side-arms.

6.2.4 Description of the 4th Channel alternative The channel of the 4th alternative runs completely separated from the other options, until the reaching the Bélavári-side-arm. There are not available data of detailed geodetic surveys about this section of the channel. During the estimation of the inflow limits the base data were the results of the relief measurements (with geodetic accuracy), which were made in the course of the site survey. By the illustration of the longitudinal sections the values of the complete channel is represented (Figure 6.10.) besides the information of the beginning stage of the channel on behalf of the better lucidity (Figure 6.11.). It is important because according to the comprehensive view of the geodetic survey the further stage of the channel lies lower therefore the beginning section of the alternative will be the limiting factor by the penetration of the water. In relation of the minimum level of the channel bottom significant differences can be observed. Between the cross sections of the beginning stage and the common stage with the Bélavári-side-arm 4-6 m difference is derived on the basis of the measurement results. Because there are not available detailed relief information about the north-south directional channel of the affected area, on behalf of the more accurate prediction of the optional implementation effects, the detailed geodetic survey (~50 m cross section frequency) of the missing part (marked with dotted line on Figure 6.10 and Figure 6.12.) is essential.

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Fig. 6.10. - Longitudinal section of the 4th alternative (I.)

Fig. 6.11. - Longitudinal section of the 4th alternative (II.)

During the site visit we have found channels, which are started from the left side of the Drava in E-NE direction. The channel is continuous and deeper on the beginning stage but it become ever shallow on the further sections. The connection with the Drava and the permanent water flow is restrained because of the high level (higher than 108 maB) of the riverside (1st picture of Figure 6.12.). The channel is highly overgrown with arborescent vegetation, but it is very uniform in considering the relief conditions (2nd picture of Figure 6.12.), with the exception of a sudden sinking of the channel bottom level, which becomes visible on the longitudinal section of Figure 6.11. The channel runs along the track presented on Figure 6.12. based on the information of Drava-atlas and the site survey measurement results. After 500 m the channel turns sharply to

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the north and splits in two parts. From this point the alternative channel becomes more and more shallow, it can be not differentiate from the ground (3rd picture of Figure 6.12.). (On the basis of the site survey observations there is orderly hunting activity on the affected area). After 350-400 m further the channel arms joins together into one canal, and runs in this way until it reaches the Bélavári-side-arm along the western side of the northern quarry lakes.

Fig. 6.12. - Characteristic points of the 4th channel alternative based on the site survey (04.04.2014.)

6.2.5 Description of the 5th Channel alternative The 5th alternative is basically a version of the 6th water supplying alternative (the Vízvári- side-arm), but the connecting information will be introduced - following the order of the numbering from the west to the east – before that. Related to the same consideration as illustrated in the 4th alternative, the longitudinal section of the channel alternative will be represented in two parts. On the longitudinal section diagram of the Figure 6.13. can be seen that the beginning segment of the alternative is 3-3.5 m higher than the bottom level of the

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upper Vízvári-side-arm. It shows clearly that the limiting part of the channel is the beginning segment in terms of the overflow (the whole year connection of the Drava and the upper Vízvári-side-arm corroborates this conclusion, see also in Chapter 6.1.6.). The relief of the beginning stage of the channel have significant fluctuation in short distances, but it can be characterized with decreasing tendency (80 cm in 160 m) (Figure 6.13.). The survey of the stage between the Drava and the upper Vízvári-side-arm did not come about until finishing this study, therefore the geodetic accuracy results of the site survey measurements (in April 2014) were used as base data. The more accurate estimation of the flow through conditions needs the detailed survey of the missing section (marked with dotted line on Figure 6.3.). The survey results of the further stage of the channel will be introduced by the 6th alternative.

Fig. 6.13. - Longitudinal section of the 5th alternative (I.)

Fig. 6.14. - Longitudinal section of the 5th alternative (II.)

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We have found more channel fragments west from the upper Vízvári-side-arm with different level of water coverage during the site survey. The more and less parallel channel fragments begin from the left side of the Drava and further they join together. The 108 maB level of the riverside blocks the permanent connection with the Drava (1st picture of Figure 6.15.). In spite of this water can be found in most of the channels, which is became stagnant in the lower part of the banks because of the absence of the water supplement (2nd picture of Figure 6.15.). Along the further stage of the alternative the channel fragments join together forming a wider, and deeper channel. This bank have constant water coverage in longer segments, but it is stagnant because the channel bank conditions. The smaller local elevation of the channel bank segments are the reason of the stagnant character, which separate the channel into isolated parts in absence of the water supplement (by lower water levels) (3rd picture of Figure 6.15.). Approaching the upper Vízvári-side-arm the channel become wider and more abundant. The actual state of the 5th alternative is suitable for connecting up the water through the affected area however the correct operation needs the formation/preservation of the permanent connection with the Drava.

Fig. 6.15. - Characteristic points of the 5th channel alternative based on the site survey (04.04.2014.)

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6.2.6 Description of the 6th Channel alternative The 6th alternative is equal with the actual channel of the upper Vízvári-side-arm, which has permanent water coverage in the whole year. Among of the optional water supplement channels this alternative has the most detailed geodetic survey: about 2700 measurement point of 76 cross section, the longitudinal section of Figure 6.16. can be presented. It is fully visible that the bottom level of the channel is low, it does not overtop the 106 maB level not either on the highest points. The above mentioned features and the fact that the level of beginning stage of the channel is near to 104 maB makes possible the constant connection between the Drava and the side-arm. The longitudinal section diagram shows that the channel is varied, there are 2-3 m local decreases compared to 105 maB average level.

Fig. 6.13. - Longitudinal section of the 6th alternative

During the site visit in April 2014 – by intermediate water level – the side-arm was passable with boat (we do not went through the 700 m long beginning stage of the side-arm), but the channel of the side-arm is very unsteady and unpredictable because of the constant building and washing away of the sandbanks and shallows (1st picture of Figure 6.17.). Significant daily fluctuation was observed in the water level of the Drava, which affects to the water level of the side-arm. The navigability (with boat) was also feasible during this period. The cause of the fluctuation is the operation of the Dubrava Hydroelectric Power Plant. The side-arm goes to north from the Drava and after taking 200 m it turns to east. There are numerous sandbank and shallow on the east tending stage of the side-arm. Further the channel turns to south and become 2-3 times wider (2nd picture of Figure 6.17.), because it collects together at this point the water of the affected area of the side-arm and oxbow system (the channels of the water supplement alternatives is common). The character of the 2-2.5 km long south tending stage of the side-arm is very similar to the main stream of the Drava (2nd picture of Figure 6.17.).

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Fig. 6.17. - Characteristic points of the 6th channel alternative based on the site survey (04.04.2014.)

6.2.7 Description of the 7th Channel alternative The 7th water supplement alternative is basically the connection of the upper Vízvári-side-arm and the lower Bélavári-side-arm. The alternative includes the east-west derationed stage of the upper Vízvári-side-arm and the whole lower Bélavári-side-arm. Detailed geodetic information is available about both of them. O the longitudinal section based on these results (Figure 6.18.) can be seen that the bottom level of the two side-arms are almost equal, but the channel of the Bélavári-side-arm has more variable character. The level of the side-arm channel do not overtop the 106 maB level but the connecting is on 108 maB based on the information of the Drava Atlas, which blocks the connection between the two stages. Because there are not available detailed geodetic information about this area (except the information of the Drava Atlas), the more precise prediction of the connection alternatives needs the detailed survey of it.

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Fig. 6.13. - Longitudinal section of the 7th alternative

The observations of the site survey corroborate that the upper Vízvári-side-arm and the lower Bélavári-side-arm have permanent water coverage in the whole year (the results of the geodetic survey also ground for it). The connecting stage has Moorish character but there can be observed some channel fragments. The emerging level of the area blocks the connection between the two channels.

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7 Characterization of the state of natural water supply Vízvári- Bélavári branch system

On the basis of the on-site field survey and experience the geodetic surveys (see Chapter 6) significant part of river bed remains is highly charged in Vízvári-Bélavári branch system territory today. The deepest point of this silted river bed is nearly same as 109-111 MaB altitude levels measured in the field, which means that in case of revitalization with Drava water level raising the total area or substantial part would be under water, thus limiting actual land uses. In addition the silted river beds number of branch remains was found, which revitalization can significantly improve the area natural water supply. Location and main characteristics of these branches (natural water supply tracks) presented in Chapter 6. Examine these branches actual state of flow and water supply in the following.

7.1 Methodology used In order to analyze natural water supply conditions, which include detailed branches, oxbows, water bed remains in the previous chapter, determined the river bed levels of possible water routes (flow tracks cases), which are critical to the water passage. Used the available topographic data in the determination of critical river bed levels:  River bed level and ground level data from previously geodetic surveys prepared by South-Transdanubian Water Management Directorate (see Chapter 6.);  Data from additional geodetic surveys prepared under this project by South- Transdanubian Water Management Directorate (see Chapter 6.);  Our measured ground level data from on-site field survey on April 2014 (see Chapter 6.). The analyzed level of influence of natural water supply tracks was included in Table 7.1. Level of influence Name of flow case Color code on the map [MaB] 1st case Blue line 108,887 2nd case Green line 108,277 3rd case Orange line 108,602 4th case Red line 108,137 5th case Yellow line 108,017 6th case Purple line 106,020 7th case Brown line 108,000 Table 7.1. – The individual branches and branch remains (flow cases) characterized by level of influence

Then, the top points of influence in the emerging area of each water routes Drava water levels were determined. Determination of water level used the measured water levels data from

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Barcs and Vízvár-Heresznye. Knowing the data determined Barcs’s river gauge and Vízvár- Heresznye’s river gauge standard connection, and the Drava river km 187.6 to 198.0 typical stages of water level declivity, which value is from 19 to 21 cm/km. Based on these values obtained that belonging to branch system area of influence Drava section (river km 197 to 198) compared to Vízvár-Heresznye river gauge (river km 187.6) water levels are about 200 centimeters higher water level are achieved. Based on the above, the characteristic area of Vízvár-Bélavár water level data was obtained by extrapolation from Barcs’s water level data for the period 1970-2013. In order to forecast without the intervention probable future natural water supply conditions – as in Chapter 5.2. presented – we estimated that permanence of annual water levels in coming decades at influence of section, taking into consideration the experienced river bed deepening trend between 1970 and 2013. In order to further, more detailed analysis of the actual water supply conditions, using extrapolated Drava river level data and each side riverbeds levels of influence dating back to 1970. Determined the number of flow days, which 7 flow case tested river beds upper, section of influence is direct hydraulic connection with the Drava. Note that ignore the silted of branch, because we have not got information in this regard, so we used actual water levels of influence every year.

7.2 Analysis of the relation between the Drava water-levels and inflow levels at given frequency Figure 7.1. shows the water levels with annual 10, 50 and 90% permanence and the critical inflow levels of the studied 7 alternatives (horizontal lines). It can be noted that besides the inflow point of the 6. alternative (the line representing the current hydraulic connection between the Drava River and the Vízvár-upper side-arm) in case of the 50 % and 90% frequencies the Drava water levels could not reach the critical height of the inflow points. According to the presented data, it can be laid down as a fact that the cutoff of all the branches will happen in the next 4-5 years, if the process have not finished already. However the 6th inflow alternative has direct connection with the Drava River by now, if the channel deepening trend will not change, the cutoff of this side-arm will also be complete by around 2040.

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Fig.7.1. – The relation between the inflow levels of the side branches and the extrapolated water levels to their inflow points (2012-2050)

In summary, it can be stated that in the next 10-15 years, as a result of the channel deepening the side branches are going to completely cut off if the current river bed deepening rate is maintained, and it can be expected that the Vízvári upper tributary’s flow conditions are going to worsen as well at considerable extent. In the sight of these data without intervention the proceeding of the current desiccation trends can be expected, and the cut off of the branch system seems inevitable. We emphasize that the present rate of the Drava riverbed deepening is so high that if it continues uninterruptedly it will threaten the long term sustainability of any designed changes on the branch system. The hydraulic connections of Vízvári Bélavári-branch system and the Drava can be improved if we increase the number (permanence) of those times when the Drava water levels are exceeding the critical bed levels of the side-arms so the water can flow uninterruptedly into the branches (inflow days). This can be attained by raising the Drava water levels or by lowering the critical field levels. (see Chapter 9).

7.3 The scientific investigation of the frequency of natural water recharges in 2009-2013. Figure 7.2. shows the Drava water levels interpolated to the inflow points of the side-arms in 2009. Besides the water levels, the critical cross-sections’ height above the sea level (level of inflow) of the different branches and branch remains can also be noted. The water can flow through the studied side-arms if the Drava water level exceeds the critical inflow level. The figure demonstrates whether the inflow days (when the water level is high enough to flow in) occur for a longer unbroken period or just more separated shorter periods in a year. Based on Figure 7.2 it can be noted that only in the 6th flow case (Vízvári upper side-arm’s present line which is under water at the present as well) was continuous flow achieved all year round. In the 1st case the uninterrupted inflow couldn’t happen in any days of the year. In case of the 2nd 5th 4th flow case’s lines the hydraulic connection was made during the summer for rather long contiguous periods.

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Fig. 7.2. – Critical inflow levels of the different flow cases and the Drava water levels interpolated to the inflow points (2009)

According to the data shown on Figure 7.3 in 2010, only the 6th flow case had inflow connection to the Drava River for almost the whole year. In all other cases only for a few and rather short period could the water get into in the side-arms.

Fig. 7.3. – Critical inflow levels of the different flow cases and the Drava water levels interpolated to the inflow points (2010)

As seen on Figure 7.4. in 2011 (as in the previous year, in 2010) in the 6th case the side branch’s connection to the Drava was almost uninterrupted, however the other line’s top sections were practically never under water.

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Fig. 7.4. – Critical inflow levels of the different flow cases and the Drava water levels interpolated to the inflow points (2011)

In 2012 (Figure 7.5) the water levels are generally higher than in the previous years. In the 6th case the continuous flow persisted since April. The rather lower water level between January and March could not provide the uninterrupted inflow into any of the branches. During the time of the highest water levels occurring in July and November besides the 6th case the water could also flow into the 2nd 4th and 5th lines in longer periods. On the 1st track line only a very short period of inflow developed.

Fig. 7.5. – Critical inflow levels of the different flow cases and the Drava water levels interpolated to the inflow points (2012)

According to the data of 2013 the water levels interpolated to the inflow point of the side- arms show more peaks than in previous years (Figure 7.6.). During the highest levels formed in the spring period the Drava water could flow not only into the 6th line but also into the 2nd 4th and 5th traces for longer unbroken periods between April and June. In addition, for a shorter time in November the water level reached again the critical heights and could flow into almost every branch.

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Fig. 7.6. – Critical inflow levels of the different flow cases and the Drava water levels interpolated to the inflow points (2013)

7.4 The analysis of the long-term changes in natural water recharge frequencies In the followings we present how the annual number of inflow days has changed from 1970 to 2013 in each the side branches or branch remains The critical inflow level of each side-arm was determined by the previously introduced methodology according to the data of the geodetic survey. The critical inflow heights for each trace lines are summarized in Table 7.1 The outcomes of the calculations are illustrated in the following figures. The results show that because of the channel deepening (see section 5.2.) the number of the days when water can flow into the branches (inflow days) are significantly reduced in the 1970-2013 period. In the calculations, the fillings of branches were excluded, so the speed and impact of the cut off results may be higher in reality than as presented below. Regarding the side-arms (the lines of each branch cases) the following establishments can be made: 1. inflow case – According to Figure 7.7 in the 1st case the water was typically unable to flow freely through the side-arm’s line in the period from 1970 to 2013. Some years the water level reached the sufficient height to pass through the initial section of the 1st trail but even in these days the number of inflow days was not high enough (the frequency didn’t reach 30 days). In the 1st case’s riverbed line the flow is restrained by a relative high (108,887 maB) point located in the first section of the branch. According to the geodetic survey and the site visits, it can be seen that the studied riverbed’s first section is divided into two parts by a road leading to the relinquished gravel pit lakes. On the basis of the geomorphologic characteristics it is observable that in this first section of the track flowing water is not typical (the river bed is overgrown by wild plants, driftwood can not be seen) nonetheless by higher water levels water coverage can develop (but the road to the lakes prevent that).

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2. inflow case - According to the 1970-2013 water level data, the water could flow through the upper section of the 2nd case’s flow path significantly more times than in the first 1st case (as shown on Figure 7.8.). The site visits confirmed, that into the Bélavári side-arm the water flows through the gravel pit lakes. According to the on-site observations it can be concluded as well that throughout the gaps of the abandoned gangue flows the water into the remained riverbed of the side-arm Many of the dividing land-strips between the parts of the pond system has already been washed out by the water flow of high water level periods, and the lower part of the lake system, due to the erosion of the Drava riverbank, has already a direct connection with the Drava River so this water route can represent a realistic alternative to improve water supply conditions of the area. However the inflow connection lasted just intermittently, before the 1990’s the annual number of inflow days were about 40-100 days, after the 90’s the inflow days significantly decreased, and it does not develop in every year anymore. In 2012-2013 typically only 4-5 times a year and only for a couple of days could the water flow through the longest side-arm. In this case it can also be observed that the number of the annual inflow days significantly decreased as a consequence of the Drava’s channel deepening. 3. inflow case - At this line in most of the studied years the water could not flow through (Figure 7.9). Before the 1980’s the direct hydraulic connection existed for even 80- 100 days long periods, but in the following years the number of inflow days dramatically decreased. In 2000-2013 the annual inflow days were generally less than 20 days, and in some years the inflow entirely failed to go through. In this study we consider this 3rd case as a possible line for restoring the natural water recharge. 4. inflow case - The Figure 7.10. shows how many days a year did the Drava water level exceed the side-arm’s critical inflow height (108.137 maB) on the trace of the 4th case between 1970. and 2014 under the current conditions. It can be read off the figure that in the past 40 years the highest rate of the inflow days has reached the 180 days. Before 1987 more annual inflow frequencies surpassed the 40-100 day/year, and only in 3 years was less than 60 day/year. In the last two decades the number of the inflow days significantly dropped, since 2000 there were more years when the water level couldn’t reach the critical height and did not flow into the side-arm. In the project area this branch represents an independent path for the flowing water, until it reaches the Bélavári side-arm. Therefore we consider the revitalization of this water flow path as a high priority. On the basis of the on-site visit’s experience it has been found that through this route the water flow nowadays also occur, but based on the calculations only 4-5 times a year for a few days. If the Drava channel deepening will continue, this little periodic flow on the 4th case’s line will completely stop in 10-15 years. 5. inflow case – The Figure 7.11. shows the number of inflow days during past 40 years besides the current conditions for the 5th case. We can see that before 1987 most of the years 100 or even higher was the number of inflow days. In the following years it

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decreased significantly (less than 50 days/year at typical value), and several years was not at all in water. This branch is a short section at the beginning of the present Vízvári upper-branch system. However, the revitalization of this small tributary can improve the water supply of the branch system. 6. inflow case – Regarding the current conditions of the 6th case ( Vízvári upper side-arm) we can state that between 1970 and 2013 the water could flow through for almost the entire years (Figure 7.12.). By 1988, the low number of inflow days can be accounted for this year's incomplete measurement data. From 1990 to the present day situation is still very favorable the inflows are over 300 days every year. Based on the calculations and the on-site visit’s experiences this section is currently in a favorable condition even without any intervention. It is important to note that as a result of the channel deepening experienced in this Drava section the cutoff of the Vízvári upper side-arm is also moving on slowly. In case the river bed deepening continues with the current rate (2-4 cm/year), the uninterrupted inflow periods will last shorter, and in 20-30 years the degree of the cutoff will reach that level when only 30-50 annual inflow days can be predicted. 7. inflow case – The reach marked as 7th case sets off from the Vízvári upper side-arm with a 108 maB height and swampy area, then after a short section it joins to the Bélavári side-arm. Until 1987, usually in one third of the years the water was flowing through this branch the longest water-covered period was in 1979 (Figure 7.13.). However since 1987 the number of the inflow days rarely exceeded the 50 days, precisely only in two years, and the average rate of annual inflow days was below 25. In several years (in 2001, 2003, 2007, 2009) the number of inflow days was close to zero.

Fig. 7.7. – The number of inflow days in case of inflow at 108.887 maB critical height, without the elevation of water level (1970-2013)

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Fig. 7.8. – The number of inflow days in case of inflow at 108.277 maB critical height, without the elevation of water level (1970-2013)

Fig. 7.9. –The number of inflow days in case of inflow at 108.602 maB critical height, without the elevation of water level (1970-2013)

Fig. 7.10. – The number of inflow days in case of inflow at 108.137 maB critical height, with the elevation of water level (1970-2013)

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Fig. 7.11. – The number of inflow days in case of inflow at 108.017 maB critical height, without the elevation of water level (1970-2013)

Fig. 7.12. – The number of inflow days in case of inflow at 106.02 maB critical height, without the elevation of water level (1970-2013)

Fig.7.13. – The number of inflow days in case of inflow at 108.00 maB critical height, without the elevation of water level (1970-2013)

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8 Managing the problem of riverbed deepening of the Drava

For the revitalization of the side-arm system of Vízvár-Bélavár it is extremely important to stop the process of deepening on this section of the Drava river so the current sediment could stay on site and could not be eroded by the energy of the river. Below we analyze two potential methods for riverbed revitalization based on international experiences. According to the first method, the river bed material should be adjusted to the present morphological and flow conditions, so the riverbed of the relevant Drava section have to be stabilized by recharge with appropriate sized sediments, which can not be carried away by the shear stress on the riverbed (considering that the power plants on the upper section do not release the required sized bed material from the reservoirs to the sections downstream). The second option propose to set the prevalent water velocity to the riverbed conditions, thus reducing the riverbed erosion. It can be realized by slowing the river to a velocity that cause lower shear being incapable of displacing the bed material. To design the prevention of channel deepening caused by erosion we must be aware of the relations between the erosion-transport-deposition process and the velocity of the river. The Hjulström-diagram (Figure 8.1.) - created on the basis of empirical measurements - provides information about this. The diagram shows that for a given river velocity what size are the grains of the bed material that are carried away by the river (causing riverbed erosion) and what size are those that settle. Recharge the riverbed by specified amount and grain-composition of sediment can slow or prevent the further deepening. Based on the chart, the size of sediment that can not be swept away by the river in the prevalent velocity range if dumped into the river can be determined (Option 1). On the other hand, regarding the chart, the river velocity that carries away the bed material characteristic of the section can be determined, i.e. the extent to which the river should be slowed down in order to prevent erosion (Option 2). In the followings, we examine the boundary conditions of the two types of interventions above

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Fig. 8.1. – The Hjulström-diagram

A vízvári-bélavári élőhely-rehabilitációs lehetőségek koncepcionális áttekintése 132 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

8.1 Prevention of the channel deepening by adding coarse gravel The river velocity of the examined Drava section was measured at gauges of Őrtilos, Vízvár- Heresznye and Barcs and then made available for us by DDVIZIG. Between 2004 and 2014 the water velocities of Drava measured at Barcs were between 80 and 200 cm/s, at Őrtilosnál, between 100 and 300 cm/s. According to the Hjulström-diagram in this velocity range the river can lift gravel with diameter between 15 and 70 mm (Barcs) or between 18 and 400 mm (Őrtilos), larger grains settle out. For Vízvár-Heresznye we have velocity data only for the year of 2013 and 2014. The measured velocity range of 140-230 cm/s the river can transport gravel between 40 and 180 mm. The empirical Hjulström-diagram is constituted of linear sections between the velocity values indicated in table 8.1., so by reading the appropriate grain diameters to these values from the graph and calculating the slope of the linear sections, the gravel diameter that the river can not lift can be calculated to each velocity value in the range of interest. So Table 8.1. contains the diameters of gravels that just can be transported by the river by in a given velocity range.

vwater dgrain [cm/s] [mm] <110 <20 110-175 20-50 175-195 50-70 195-215 70-100 215-260 100-200 260-290 200-400 >290 >400 Table 8.1. – The diameter of grains transportable in each range of river velocity

We examined which range the measured water velocities fall into and in accordance with this we calculated the grain size transportable for the Drava at the three water gauge.

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Drava (Őrtilos)

v dgrain (average) dgrain (min) dgrain (max) [cm/s] [mm] [mm] [mm] 100 110 18.45 18.18 18.73 110 120 32.29 32.00 32.57 120 130 35.32 34.57 36.57 130 140 37.43 37.43 37.43 140 150 41.29 40.00 42.57 150 160 44.31 43.14 45.14 160 170 47.14 46.29 47.71 170 180 55.03 48.86 63.90 180 190 66.32 64.62 67.85 190 200 78.91 68.92 92.09 200 210 95.35 93.49 96.74 210 220 133.18 97.67 167.69 220 230 173.96 170.00 176.15 230 240 180.26 178.46 183.08 240 250 188.46 185.38 191.54 250 260 198.85 198.46 199.23 260 270 365.52 360.00 371.03 270 280 377.59 373.79 383.45 280 290 388.51 386.21 391.72 290 300 403.45 402.76 404.14 Table 8.2. – Diameter of transportable grains at gauge of Őrtilos (2004-2014)

The table 8.2. and the following Figure 8.2. show that, at the gauge of Őrtilos, gravels of 20-405 mm are needed to stabilize the riverbed. Taking into account the maximum velocity values of each permanence shown on Figure 5.2., - the velocity values of 10% permanence for the past two years were around 2,3 and 2.4 m/s – it has been found that pouring gravels with average size between 175-185 mm to the river at Őrtilos can stabilize the bed.

Fig. 8.2. – Diameter of transportable grains on the basis of river velocities measured at gauge of Őrtilos

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Since the gauge of Vízvár-Heresznye was installed at the end of 2012 very little data is available of this section, therefore in the table 8.3. and on Figure 8.3.all the measured values are presented.

Drava (Vízvár-Heresznye)

vwater dgrain date [cm/s] [mm] [dd.mm.yyyy] 144 41.1 06.09.2013 152 43.4 09.08.2013 166 47.4 22.02.2013 171 48.9 04.10.2013 172 49.1 07.02.2014 191 68.6 07.03.2014 206 95.8 08.03.2013 207 96.3 08.11.2013 212 98.6 08.05.2013 225 173.1 10.05.2013 233 179.2 26.11.2013 233 179.2 14.02.2014 Table 8.3. – Diameter of transportable grains at gauge of Vízvár-Heresznye (2013-2014)

Fig. 8.3. – Diameter of transportable grains on the basis of river velocities measured at gauge of Vízvár-Heresznye

The DDVIZIG studied the sediment conditions, bed material, bed-load composition of a Drava section near Vízvár (at Bélavár) in 2012. The results of this survey are described in Chapter 5.3.. As the mean velocity of the river was also measured during this survey, we can tell the sediment grain size shifted by the river at the exact river velocities. Looking at the river velocities measured on the occasion of the sediment survey indicated in table 5.7. and comparing it to Figure 5.9. we can see that the mean velocities measured in 2013 at Vízvár typically do not exceed the 1.6 m/s, which is the value of maximum mean velocity measured during the sediment survey.

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In addition, assuming a linear relation between the water level and water velocity data, according to the water level permanence values of 2012 and 2013 indicated in table 5.2. the mean velocity corresponding to the water level with 10% permanence (105,975 maB in 2012) was approx. 1.4 m/s, i.e. we can state that higher mean velocities typically occur only during floods. The Table 5.7. shows that the largest gravels shifted during the measurements have fallen into the range of 32-64 mm, under mean velocity of 1.6 m/s. This is consistent with the data read from the Hjulström-diagram, that in a river with velocity of 1.6 m/s the gravels of 46 47 mm already settle. Thus, dumping gravels with average grain diameter of 50-60 mm to the riverbed, the river will not carry them away. If we consider the maximum speeds, based on the Hjulström-diagram, much larger gravels are the ones that settle. As shown on the figure, in 50% of the measurements velocities over 2 m/s, in 25% velocities from 2.2 to 2.4 m/s were measured. Under these water velocities even gravels with diameter of 100-200 mm are transported by the river. However, concluding the permanence of maximum water velocities in the same way as for the mean velocities, it can be stated that the maximum velocities higher than 2 m/s are not typical. It is based on the 100 mm size gravel is not likely to be able to take the river. Relying upon these, the river is not likely to be able to transport 100 mm sized gravel. Table 8.4. and Figure 8.4. show the diameter of grains that large enough to settle calculated on the basis of measured water velocities at gauge of Barcs. Accordingly, gravels of 20-70 mm settles on the river section of Barcs. Figure 5.14. presents the values of given permanence of the measured maximum velocities at Barcs. In the past two years the maximum velocity values of 10% permanence were around 1.3 m/s and 1.5 m/s, that is, higher water velocities not specific. On this basis, we can say that pouring gravels with diameter of 40-45 mm can slow down or prevented the riverbed erosion.

Drava (Barcs)

v dgrain (average) dgrain (min) dgrain (max) [cm/s] [mm] [mm] [mm] 80 90 15.89 15.64 16.18 90 100 17.42 17.09 17.82 100 110 19.15 18.36 19.82 110 120 32.76 31.43 34.00 120 130 35.44 34.29 36.86 130 140 38.52 37.14 39.43 140 150 41.38 40.00 42.29 150 160 43.81 43.43 44.29 160 170 47.81 46.86 48.29 170 180 63.54 62.82 64.26 180 190 65.51 64.62 66.41 190 200 68.56 68.21 68.92 Table 8.4. – Diameter of transportable grains at gauge of Barcs (2004-2014)

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Fig. 8.4. – Diameter of transportable grains on the basis of river velocities measured at gauge of Barcs

In summary, according to our estimations based on the values of 10 % permanence of maximum velocities measured at the three river gauges, gravels with the following grain size should be dumped into the river to prevent the further deepening: o At Őrtilos, gravels between 175-185 mm; o At Vízvár 100 mm; o At Barcs 40-45 mm are necessary.

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8.2 Prevention of riverbed deepening by slowing the river The channel deepening can be prevented by developing water velocities on the studied Drava section that do not take away the bed material and do not cause erosion. We possess data of the riverbed composition at Bélavár measured by the DDVIZIG in 2012. The composition of the bed material was examined in the same way as the bed-load (see Chapter 2.3.1.). Table 8.5. summarizes the results of the three measurements (the percentages of remaining mass indicated in the table are the averages of the percentages measured in the 5 perpendicular). Furthermore, the table shows that a sediment larger than a given diameter is what percentage of the whole bed material.

1. measurement 2. measurement 3. measurement Diameter (09.05.2012) (14.06.2012) (28.08.2012) Larger Larger Larger than a than a than a Remaining Remaining Remaining [mm] given given given mass [%] mass [%] mass [%] diameter diameter diameter [%] [%] [%] 64 0,00 0,00 0,00 0,00 0,00 0 32 0,43 0,43 6,11 6,11 9,20 9,20 16 27,61 28,04 35,78 41,89 33,23 42,43 8 41,06 69,09 36,69 78,58 33,26 75,70 4 25,23 94,32 14,14 92,72 13,64 89,33 2 3,09 97,41 4,40 97,12 5,17 94,50 1 0,15 97,56 1,20 98,32 1,83 96,33 0,5 0,07 97,63 0,76 99,08 0,91 97,24 0,25 1,22 98,85 0,56 99,64 2,13 99,37 0,125 0,92 99,77 0,33 99,97 0,56 99,94 0,063 0,18 99,96 0,03 100,00 0,04 99,98 Table 8.5. – Composition of the bed material of Drava river (at Bélavár)

We conclude that 70-80% of the bed material is consisted of grains larger than 8 mm. To achieve that 70-80% of the bed material keep steady, according to the Hjulström-diagram, the river should be slowed down to 0.60-0.65 m/s. However, such an intervention would significantly alter the characteristics of the affected river section, so we recommend to aim the achievement of higher (approximately 0.7-1.0 m/s) velocities. To determine a more precise target value, additional measurements and calculations are required. There are several interventions capable of reducing the river velocity (channel widening, development of artificial branches, construction of weirs, etc.) but the detailed examination of their suitability has not been the subject of this study. Based on our current knowledge, the construction of weirs can provide a suitable solution. The weir is a structure that increases the level of the riverbed by using natural material

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(stones, large grain size gravels). The downstream side of the bed sill is elongated and flat so it ends in a quite stable ramp. The surface of the bed sills shall be designed to allow the aquatic fauna to ascent from the downstream side of structure to the upstream side, even in the case of low water. The bed sills have to be built to be able to conduct the floods with the prescribed safety. Figure 8.5. shows the effects of cross-dams/bed sills to the water level.

Fig. - 8.5. – Effects of cross-dams/bed sills to the water level

The establishment of a greater, spillover weir (see Figure 8.6.) is not recommended, as it can have many negative effects (e.g. the increased energy of the water falling over the underwater weir may enhance the riverbed erosion on the section after the weir or may impede fish migration).

Fig. 8.6.– Spillover weir (sharp-edged weir/dam)

The deceleration of the river is proposed with establishment of a line of smaller, not spillover weirs (see Figure 8.7.). In case of short, properly designed, not spillover bed sills the erosion of the riverbed under the weir and that of the bank is minimal, since high water flow velocities do not occur, as they do in case of spillover weirs. The short weirs have minimal effects on high water levels, while low and mean water levels can be increased by an extent depending ont he morphology of the channel. It should be noted that weirs make impossible any form of navigation.

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Fig. 8.7.– Not spillover weir (low dam with wide sill)

Fig. 8.8.– Effect of bed sill to water levels

When designing a chain of weirs, the induced water level descent should be taken into account as the fundamental aspects of revitalization is to maintain the current main channel. In other words, the presence of too large weirs can transfer the main channel to the side-arms. Choosing and designing the interventions to reduce the flow rate requires a detailed assessment of hydromorphological characteristics of the affected river section. In course of the development of the specific technical solution the upstream and downstream impact area (primarily the extent of the damming effect), the rate of water level increase, the extent of the resulting water velocities, etc. have to be determined.

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9 Review of the revitalization opportunities at the Vízvár- Bélavár side-arm system

As the investigations showed as a result of the river deepening at this section of Drava River the side-arm system is cutting off in extraordinary pace. According to the calculations it has been found that the annual channel deepening is 2-4 cm, which indicates that the absolute water levels can decrease by 1meter in every 25 years. The degree of water supply on the braches fundamentally affects wildlife and ecological status of the area, therefore the in terms of maintenance and improvement of the current state of the area the water supply is essential. If no actions are taken and the river deepening continues with the current rate, except Vízvári upper branch, the water flow in the side-arms will completely disappear in 10-15 years from now. The present study aims to determine the circle of possible revitalization proceedings, which are able to improve the current water flow conditions in the side-arm system (using a solution that does not require long-term follow-up care or operations). The main objective is to develop an intervention that requires the least necessary interference at the branch system (on the behalf of causing as little disturbance as possible to the natural values in the area). Therefore essential to find a solution when nature can forms itself the favorable conditions in the branch system during the implementation. Based on these analyzes it can be observed that the separated revitalization of each branches not synchronized to the Drava River represents only short term solution, because without stopping the channel deepening any action improves only for maximum 10-20 years the water supply of the side-arm system. To stop the cut off processes (going on at a rather rapid pace) is the fundamental key to repair and conservation of the current state. The direct hydraulic connection of the remained side-arms and the Drava River stands for only 4-7 times a year and just for a couple of days (except Vízvári upper side). The side-arm remains selected on the basis of data from the on-site visits, and the geodetic survey can be characterized with the same problem. In order to stop the cut offs caused by the channel deepening, it is worth to consider the local water level elimination of this river section. Raising the level of the small and medium-water level in this section can be a right solution to improve water flow conditions in selected branches, therefore we consider raising the water level at this Drava section as a realistic alternative. The inflow frequency on the possible water-recharge routes (side-arm channels and bed residues) designated according to the on-site visits and geodetic surveys can be increased by deepening the high channel stages or by constructing new main channel at the critical sections so the water itself can broaden the riverbed during the next flow periods. Developing such revitalization options for each flow cases are discussed separately in Chapter 8.

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However to significantly improve the water flow / water supply conditions in the area a combination of the solutions mentioned above is may require so in Chapter 9.1. we present the development of certain flow conditions supposing both the local elevation of Drava water level and the construction of main channels. The improvement of the water coverage of the area can also represent a revitalization possibility but this itself does not create the desired flow conditions it only improves each side-arm channel’s water-coverage intermittently. It can be solved by the retention of the waters flown into the branches at the high water level periods for example by using flood gates. This solution was not examined in detail because of the high operational and maintenance demands.

9.1 Implementation of the water supply by the local elevation of Drava water levels In the followings we present the effect of raising the Drava water level on the water supply of Vízvári Bélavári-branch system. By the determination of the required water level increases, the nearby altitude conditions has to be considered, in order to avoid the induce any possible increase in flood exposure. Besides avoiding any flood situation, with the excessive increase of water level the water supply of the branches would not improve, instead the entire area would be under water cover. Based on the geodetic survey data and the Drava Atlas the height of the non-water-covered areas are typically 109-112 maB (with the exception of local high points and the high banks), so in case of the high Drava water levels, the water level elevation is unnecessary and even destructive for the area (significantly narrowing down land use options). As the results of side channel remains’ geodetic survey showed in terms of the water flow107.5-108.2 maB heights are currently the dominant in the area. These cross-sections are typically located by the upper initial sections of the branches (see Chapter 6). The suitable procedure for water level elevation can be presented by constructing one or more weirs along this Drava section, but besides many other technical solutions could be suitable. At this present study the necessary water level elevations are estimated (Table 9.1.). In course of the planning of the intervention it have to be taken into account that the water levels during high waters should not significantly increase, only the low and mean water levels. This goal can be achieved by appropriately sized bed sills (the water level elevation resulted by the intervention can be calculated knowing the exact channel geometry). Figure 9.1. illustrates the alluded Drava section in terms of the water level raise.

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Fig. 9.1. – The Drava section involved in the water elevation on the behalf of the flow condition improvement of the branches (~191-198 rkm)

River gauge at Inflow point River gauge at Vízvár Barcs Planned Water level Water level Water level Water level elevation [cm] [maB] [maB] [cm] [cm] 100 <106.7 <104,7 <348 <-18 80 106.7-107.7 104,7-105,7 348-448 -18-103 60 107.7-108.1 105,7-106,1 448-488 103-159 50 108.1-108.4 106,1-106,4 488-518 159-202 20 108.4-108.7 106,4-106,7 518-548 202-240 0 >108.70 >106,7 >548 >240 Table 9.1. – Elevation of the water level at the inflow point at Vízvár, and the interventional water level at Vízvár and Barcs

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In order to determine the water level elevation method, detailed geodetic survey is required along this section of the Drava River, and when the all accurate information of the riverbed is revealed thereafter can the next phase, namely the selection and the planning of the applied structures start. The probably emerging effects on the lower section also should take into account during the designing of possibly planned weirs, groins or barrage systems. Supposing weir is applied, as a consequence of the higher velocity local channel deepening can occur on the lower section. To prevent this negative side effect, the riverbed should be stabilized (to cover up the current channel with large-sized rocks). The planning of these structures or other interventions, and the proper definition of any effects they may cause requires reliable knowledge of the Drava riverbed conditions. The structure or intervention should be carried out in a way that it can keep up the specified water levels in spite of the future impact of channel deepening, and it should be durable against the high flow velocity conditions. In the followings we introduce how the annual inflow frequencies would have been in the 1995-2013 period if the water level has been raised. The slopes of the main channel and the side-arms should also be taken into consideration by the planning of the water level elevation, in order to avoid the relocation of the main channel.

9.1.1 The impact of the water level elevation on the water recharge alternatives For the calculations we used the inflow levels introduced in Chapter 7.2. , so only the effects of the water elevation were investigated. To determine the effects of water level increases we used the original water level data from 1995-2013 added to the elevation values in table 9.1. It is important to note that due to the water level increase in the Bélavári side-branch the number of inflow day and the water flows will significantly increase. Therefore it may be necessary to expand the currently applied culverts, and to strengthen the embankments of the roads and the culvert. It is important to keep in sight during the water level elevation planning process that the access to the rehabilitated areas should be ensured in the future as well, so in these point maybe the construction of bridges will be required. Based on the calculation results it can be laid down that as a result of the water level increases the water flow condition of branches significantly improve. The altering effects of the water level elevation on the selected inflow cases are summarized below: 1. inflow alternative - Based on the water level data from 1995-2013 with the water level elevation on the 1st case line no changes happened (Figure 9.2.). The reason is that the road leading to the lakes bisects the initial phase of the river bed. To enable the water flow through this embankment, the water level elevation should be so high that a significant part of the area would sink under water. 2. inflow alternative –According to the on-site visits, and geodetic survey the current water supply of the Bélavári side-arm is attained through the 2nd case’s path. On this side-arm

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the water enters from the Drava through the abandoned gravel pit lakes. As Figure 9.3. shows the number of inflow days significantly increases as the effect of the water level raising by the current river bed conditions ( in 2013 the water could flow in for 36 days in the base case, but with the water level elevation the inflow days could have reached 121 days). It is important to note based on the site visit experience that in those periods when the water can flow through the side-arm the water flow also causes channel erosion. Currently, the number of inflow days is limited, so the water is not able to change the side-arms river bed shape with the same rate as the Drava channel deepening is moving forward. If the water level increase can be attained, it also should be considered that with the increase of the inflow days, the channel erosion will also change the shape of this side-arm more quickly, and the sediment washed away from the bed material at this section will be deposited in the widened part of the branch. The transfer of the Drava River water through the abandoned gravel pit lakes can be beneficial in several ways. If the water flows through this path on the inflow days, a significant part of the floating drift can settle in the lakes so it will not boost the silting of the side-arm. 3. inflow alternative – The water in case of this trail will also flow through the abandoned gravel pit lakes into the Bélavári side-arm. The critical inflow level is higher on the 3. alternative’s line than in the 2nd case so the number of inflow days is also lower. However in this case it is also noticeable how the number of inflow days increased because of the water level elevation. In 2013 the number of the inflow days was 13, but with water level elevation the water would flow through for 44 days (Figure 9.4.). 4. inflow alternative – The trace of the 4th line conducts the water from the Drava River into the Bélavári side-arm. The data of the geodetic surveys, and channel level measurements made on the site visits provides information about the initial section of the 4th line. The inflow point in this case is located about 10-20 centimeters higher than the 2nd alternative’s. In order to the exact determination of the inflow days’ number at the beginning phase of the revitalization project, the geodetic survey of the entire river is required. Based on the data, the planned water level elevation significantly increases the number of inflow days (Figure 9.5.). As the data from 2013 shows only 42 inflow days occurred while as a result of raising the water level the inflow days could reach 135 days. 5. inflow alternative – This alternative represents a short trail at the first section of the Vízvári upper side-arm. However, due to the water level raise even at this the short length the number of inflow days would significantly increase (Figure 9.6.). 6. inflow alternative -. The 6. inflow line resents the Vízvári upper branch itself. Even under the present conditions this side-arm can be characterized by good inflow conditions. However, because of the water level elevation the water flow rate would increase and as a result the side-arm’s of natural erosion would be also more significant.

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7. inflow alternative - The 7th inflow line leads through a 108 maB high swampy area from the Vízvári upper branch into the Bélavári side-arm. Based on the data, the planned water level elevation the number of inflow days would significantly increases (Figure 9.8.).

Fig. 9.2. – The number of inflow days by 108.887 maB critical height, with the elevation of water level (1995-2013)

Fig. 9.3. – The number of inflow days by 108.277 maB critical height, with the elevation of water level (1995-2013)

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Fig. 9.4. – The number of inflow days by 108.602 maB critical height, with the elevation of water level (1995-2013)

Fig. 9.5. – The number of inflow days by 108.137 maB critical height, with the elevation of water level (1995-2013)

Fig. 9.6. – The number of inflow days by 108.017 maB critical height, with the elevation of water level (1995-2013)

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Fig. 9.7. – The number of inflow days by 106.02 maB critical height, with the elevation of water level (1995-2013)

Fig. 9.8. – The number of inflow days by 108.00 maB critical height, with the elevation of water level (1995-2013)

9.2 Partial dredging of the channel line of water supply As follows, we present the possibilities for revitalization with partial dredging of the side-arm river beds that are suitable based on the experiences of site visits and data of geodetic surveys, side of the. The level of dredging of each bed was determined on the basis of data from geodetic surveys, keeping in mind that only short sections should be excavated. According to this conception we recommend the development of main channels on the planned tracks. The water, flowing through these main channels, will form and broaden them. We are dealing with the possibility of designing main channels in the cases of 2-3. 4. and 5. alternatives. Revitalization of the first channel alternative is not recommended, as in course of the site visit it proved to be possible only with serious disturbances of the area (see Chapter 6). Besides, except for the short initial section, this and the second and third channel alternatives are located in the same track. In the case of track No. 6. the Drava and the side-arm are connected almost all year round under the present conditions as well. With the stabilization of the riverbed of the Drava the water supply of the side-arm will show the same image in the future as well. On the 7th track of water supply the water flows through a marshy area at given water levels (over 108 maB). Based on the experiences of field surveys, this swampy area is significantly different from the rest of the environment, thus the deepening of this area, for the conservation of landscape heterogeneity, is not recommended.

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9.2.1 Effects of partial dredging to the water coverage of supply channels In the following chapters we analyze the effects of proposed main channels with selected water paths. The effects of dredging are evaluated by comparing the number of current inflow days and the ones with the new inflow levels resulted by the local dredging The following table lists the proposed inflow levels for each main channel (the ground level, to which the initial phase of the water supply channel trail is recommended to deepen).

Inflow level Inflow alternatives Color code on the map [maB] 2. alternative Green line 106.500 3. alternative Orange line 106.500 4. alternative Red line 106.600 5. alternative Yellow line 107.500 6. alternative Purple line 106.700 Table 9.2. – Minimum recommended height of each trace line of main channels

9.2.1.1 Changes of 2nd and 3rd channel alternative as a result of main channel development As the two tracks diverge only on a short section, the 2nd and 3rd channel alternatives are treated as a whole. For the two tracks the level of the proposed control channel is the same, 106.5 maB. In both cases the water passes through the abandoned gravel-pit lakes to reach the side-arm of Bélavár, but in order to improve the water inflow conditions at the current water levels, the deepening of the channel is needed in some places. If the alternative presented in this chapter will be implemented, further detailed geodesic studies are necessary on the sections marked by dotted line (Figure 9.9.). From the currently available data we know that the track marked by red line has already reached the desired channel levels, but we have no information of the section between the upper part of the gravel-pit lakes along the Drava River and the red marked cross section (Figure 9.9.). Thus, in order to determine the length of the section to be dredged, detailed geodetic surveys should be conducted. The lakes are still connected to the Drava River in a significant part of the year, however, in order to improve the water flow conditions, the abandoned quarry lakes should be opened on the parts marked with circles. Based on the experience gained during the site visit currently these are the points the water flows through the most frequently. The effect of main channels was analyzed using the methodology described in the previous chapter. Figure 9.11. shows the number of inflow days in the cases of water levels measured in the period 1995-2013, and the inflow days resulted by developing a main channel. Due to

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the lower levels of inflow the number of inflow days in the side-arm of Bélavár increases significantly, even with the current water levels.

Fig. 9.9. – The trail of the 2nd and 3rd channel alternative

Fig. 9.10. – The longitudinal section of 2nd channel alternative and the proposed implementation level.

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Fig. 9.11. – Number of inflow days in case of inflow at 106.5 maB and at the current level (1995- 2013)

Fig. 9.12. – The longitudinal section of 3rd channel alternative and the proposed implementation level.

Fig. 9.13. – Number of inflow days in case of inflow at 106.5 maB and at the current level (1995- 2013)

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9.2.1.2 Changes of the 4th channel alternative as a result of main channel development The fourth water supply trail starts out from the Drava River and conduct the water to the side-arm of Bélavár. The geodetic surveys, and measurements of channel level during site visits provide information of the first section of the trail. This side-arm is an almost completely independent route for water flow up to the section where it flows into the branch of Bélavár. Therefore it is very important to rehabilitate this water flow path. Based on the experiences of the site visit we know that sometimes the water flows through this route nowadays as well, but according to our calculations this occurs only 4-5 times a year. In the case of the fourth trail the main channel is proposed to deepen to the 106-107.5 maB. There is no information available about a significant section (1000-1200 m) of the channel alternative No. 4. In order to determine the optimal level of the main channel to construct, the geodetic survey of this remaining section (the dotted line on Figure 9.14.) is essential (in order to improve the water supply of the side-arm system by the least interference, by dredging). Figure 9.18. illustrates the increased number of inflow days resulting from the construction of main channel based on the water level data of the 1995- 2013 period. As shown in the figure, the development of a main channel with 107.5 maB level can significantly improve the flow conditions of side-arms. In the case of a main channel characterized by a channel level of 106.6 maB the number of inflow days in 2013 would be 214 (Figure 9.17.).

Fig. 9.14. – Trail of the 4th channel alternative

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Fig. 9.15. – The longitudinal section of 4th channel alternative and the proposed implementation level (1)

Fig. 9.16. – The longitudinal section of 4th channel alternative and the proposed implementation level (2)

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Fig. 9.17. – Number of inflow days in case of inflow at 106.6 maB and at the current level (1995- 2013)

Fig. 9.18. - Number of inflow days in case of inflow at 107.5 maB and at the current level (1995-2013)

9.2.1.3 Changes of the 5th channel alternative as a result of main channel development This branch is a short section at the fore-part of the side-arm system of upper Vízvár. However, the side-arm’s water supply can be improved by the revitalization of this small branch. Based on current data, the design of the main channel on this section affects a 200- 300 m section near the bank of the Drava. The proposed level of the channel is 106.7 maB. Figure 9.19. illustrates the effect of the construction of a main channel to flow conditions based on the water level data of the years 1995-2013. As shown in the figure, the number of inflow days will significantly increase as a result of the intervention even under the current water level conditions.

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Fig. 9.19. – Trail of the 5th channel alternative

Fig. 9.20. – The longitudinal section of 5th channel alternative and the proposed implementation level (1)

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 155 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

Fig. 9.21. – The longitudinal section of 5th channel alternative and the proposed implementation level (2)

Fig. 9.22. – Number of inflow days in case of inflow at 106.7 maB and at the current level (1995- 2013)

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9.3 Simultaneous application of the dredging and water level increasing of the Drava Significant effects can be achieved in the enhancement of the water recharging processes with simultaneous using of the optional technical tools (Chapter 7. and 8.) of the side-arm-system revitalization. Increasing the low- and middle water levels of the Drava and the dredging of the beginning stages of the channels (or making main channels if it is necessary) have drastic effect to the water balance of the side-arms and oxbows, because instead of the 3- 7 day long periods of the water coverage the side-arms become a permanent connection with the Drava. The effect (sinking or moving of the riverbed) of a fundamental change in the water regime on the affected area cannot be predicted precisely on the basis of the actually available data. Therefore the detailed geodetic survey (with 50 m maximal distance between the cross sections) along the whole length of the affected channel sections is essential before the simultaneous implementation of the dredging and the water level raising. Detailed calculations should be done based on the results of these surveys on behalf of the prediction of the flow conditions due to the implementations. By the results of the Chapter 9.1. and Chapter 9.2. can be seen that the raising of the Drava’s water level and the dredging of the side-arms channel have already significant effect by itself on the increasing number of periods with water overflow. The introduced, combined alternative contains two types of implementations with synergic effect, because in case of the higher level of the Drava the higher channel can be covered with water, while through the channel bed dredging and consturcting of main channels Drava can connect with the channels by lower water level. Accordingly to these, in case of the simultaneous implementation lower water level raising or dredging can be enough, depending on the required water coverage. Figures 9.23.-9.26. are representing the flow through conditions as a combined effect of the defined water level raising (Chapter 9.1.) and the and the dredging (Chapter 9.2.) of the relevant channels. Figure 9.23. that the frequency of the water coverage would have reached the 365 days/year in the whole considered period presumed the conditions of the implementation results. The sharp effect of the implementations to the flow through frequency is more well- marked by the evaluation of the 3rd water recharging alternative (Figure 9.24.). The whole year water coverage also would have exist during the investigated period, but the growth is significantly compared to the base values. Two implementation alternatives are introduced by the 4th channel alternative because the lack of the detailed relief information. The channel would partially covered with water as a result of the water level increasing in case of the dredging to the level 107.5 maB. The degree of it depends significantly on the water level changes of the Drava. The numbers of the flow through days would have reached the 50-200 days based on the former data (Figure

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9.25.). If the dredging reaches the 106.6 maB level, the channel of the 4th water recharging alternative would have 365 day long water coverage.

Fig. 9.23. – Number of inflow days in case of inflow at 106.5 maB critical height, with dredging and water level elevation (1995-2013)

Fig. 9.24. – The number of inflow days in case of inflow at 106.5 maB critical height, with dredging and water level elevation (1995-2013)

Fig. 9.25. – The number of inflow days in case of inflow at 107.5 maB critical height, with dredging and water level elevation (1995-2013) Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 158 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

Fig. 9.26. – The number of inflow days in case of inflow at 106.6 maB critical height, with dredging and water level elevation (1995-2013)

9.4 Summary of potential water supply alternatives and the proposed solution On the basis of analyses branch system in the area is cut off in quick time in consequence of experienced channel deepening in relevant section of Drava River. Based on the calculation results it can be ascertained that Drava channel is deepen approximately 2-4 centimeters per year on stretch around the Vízvár-Bélavár. Which means that newly emerging absolute water levels will be reduced by approximately 1 meter in every 25 years. Water supplies of certain branches and oxbows essentially have an effect on area flora and fauna. Therefore assure satisfactory water coverage of certain side-arms from the point of view of maintenance and improvement of area actual condition. If no intervention is in the area and the tendency of currently experienced channel deepening continues, water supply relation of side-arms systems of Vízvár-Bélavár continue to deteriorate and branch of Bélavár upper replacement of water (direction of second respectively fourth flow route) lay off within 10-15 years (and water exchange of side-arm of Vízvár-upper is limited also). This study aims to determine the possible of revitalization proceedings which suitable to improve the current water flow conditions in branch system and to look for a long-term sustainable and after-care or operate not requiring solution. Based on previous analyses and literature experiences shows that separated revitalization of certain side-arms independently of River Drava can indicate a periodic solution. Namely, without stopping the channel deepening of River Drava, impact of any intervention may be maintained for a limited time only (it depends on intervention water supply of branch system can be improved only within 10 to 20 year period). The River Drava channel deepening stops on the basis of current information two alternative have taken into account (see Chapter 8).

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 159 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

Based on first alternative current riverbed stabilization can be achieved in such a way that on the basis of data of water velocity the riverbed have been covered with stones with size specified. The principle of intervention that stones which get to the riverbed are in a size range which river cannot carry away beside maximum and average flow rate characteristics for certain reach. In order to be able to determine the amount of material required for the stabilization of river, the affected section of the riverbed needed a detailed geodetic survey (detailed knowledge of longitudinal section, cross-section and channel falls), then numerical modeling of the river by the use of data. The purpose of the calculations to be made in future to determine that in addition to the current channel shape where to find a possibly local flow zones which are characterized by significantly different from the measured rate of flow velocities. Based on local experiences it can be proved that the Drava riverbed of the given section varies considerably from year to year due to the current sediment flow characteristics, so past data of riverbed to perform accurate calculations are not suitable. The disadvantage of this alternative is the high costs of investment taking into account the relevant, about 5-6 km long stretch of the main riverbed (see Figure 9.27.).

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 160 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

Fig. 9.27. – Location of the main channel section to stabilize

On the basis of the second alternative the current flow rate of the river has been slacken the riverbed erosive processes have been able to decrease. Based on the available data the maximum flow rate of necessary for significant sediment stabilization is about 0.7-1.0 m/s. To reach this velocity in principle be suitable for building a line of smaller, not spillover weirs. In order to can be exactly designed the structures required position and shaping, necessary for a detailed survey of the relevant section of the Drava River. If this information is available, an opportunity presents itself to calculate detailed the effects of planned series of bed sills. Using the results of numerical model calculations can be determine the result of series of bed sills developed water velocities on the upstream and downstream reaches, the water-level falls

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and height of damming for the given water-levels etc. On the knowledge of this data can be accurately planned revitalization of branches in the area. In case of the last-mentioned alternative must be designed the series of bed sills that due to the water-level elevation by bed sills the value of water-level falls on the involved each of Drava River in the main riverbed is not less than the bypass side-arms, otherwise the main riverbed can transfer to the actual side-arms in the course of time, which is not a purpose. In order to meet this criterion is necessary for detailed geodetical survey (at least in every 50 meters) of the affected reach of the Drava River and appointed branch for the purpose of revitalization interventions, with the help of this data is possible making a detailed model of results of proposed interventions. Considering the above, based on currently available data, two different alternatives are proposed for the purpose of revitalization of the affected area. The first option after the riverbed stabilization of Drava River (the current riverbed has covered appropriate size range material) the main channel has shaped with dredging (see Chapter 9.2.) on the beginning reach of certain side-arms. The advantage of this method that near current water-levels has maintained (without changing the typical water- levels of the given reach of Drava River and the side-arms system) in the residual riverbed of branch increase the number of annual flow days without the land-use has significantly limited. Required a detailed survey of marked side-arms for supposing this solution and thereafter numerical modelling of effects of water inflow. Change of current water flow conditions in the affected branches may be required additional interventions in order to should not be limited to (designed roads on side-arm system of Bélavár and culvert reconstruction or replacement of bridges) the existing land use (for instance the accessibility of quarries). The local interventions do not require the dredging of large amounts of sediment. The dredged material can be placed into the main channel of the Drava river (if it is allowed by the Hungarian and Croatian legislation). However, given the relatively small amount of dredged material and its small particle size, its supplementation to the main channel will not affect the processes of erosion in merits (that is the additional stabilization of the riverbed is necessary). The second option is the riverbed stabilization of relevant reach of Drava River (and the low water levels of relevant reach of Drava River facultative increase) for building a line of smaller, no spillover weirs then may be necessary to the main channel has shaped with dredging on the initial reach of certain side-arms. The first step of this alternative to design to be built planned series of bed sills because of this primary aim to stabilization of current riverbed and at the same time it can be occasion of the increase of low and middle water levels of point of influence for the branches in the Drava section (depends on size and localization). After series of bed sills design, when we know the exact effect on the water level, it is necessary to determine further steps of revitalization of certain side-arms. On the strength of this study can be ascertained that improve significantly the overflow conditions of branches possible only the water level increasing of the given Drava section also, therefore in that case determine the altitude conditions of necessary main channels are

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possible knowing the effects of only series of bed sills. It is important to note that in consequence of design too large bed sills effect of water-level falls the main channel of river can be transferred to the current side-arms, of this reason we recommend a detailed modelling of flow conditions of this alternative and series of bed sills are planned based on modelling results. If current water flow and water covered conditions change in the affected side-arms, it may require additional interventions in order to not to limit the current land use (if Drava River water-level is increased, the flooding frequency of low-lying areas of current branch system is increase). Following the establishment of bed sills the navigation will be very limited in affected section. It can be seen on the basis of presented calculations and results that more possibility is exist for revitalization of side-arms which can be selected based on opinion of affected organizations and cost-benefit analyses of certain interventions.

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10 The potential impact of the interventions on land-uses and the concerned parties

The property owners and users; the businesses concerned in the utilization of the Drava section and the branches, the competent regional water authority (South-Transdanubian Water Management Directorate) and the competent nature protection agency (Danube-Drava National Park) in the affected areas can be regarded as a direct target group in terms of the implementation of the proposed habitat restoration project. Among these key stakeholders are the followings:  The Hungarian state, as the owner of Drava River and side-arms, and as the responsible party for the interventions involving the Drava, as country border water;  The Croatian state as the other responsible party for the interventions involving the country border water;  The managing organizations of the streams and branches (the South-Transdanubian Water Management Directorate, Danube-Drava National Park);  The managing organization of natural values (Danube-Drava National Park);  Entities concerned in shipping along the Drava River;  The Dráva-Kavics és Beton Inc. owning the mining right and properties in the affected area  SEFAG Forestry and Wood Industry Co. Ltd.;  Individual property owners in the affected area;  The association of owning fishing / angling exploitation rights (Bélavári Leisure, Sport and Sport Fishing Association);  The hunting organizations in the area (especially on the Croatian side);  Licensing public authorities (National Environment and Nature Protection Inspectorate; South Transdanubian Environmental Protection and Nature Conservation Inspectorate, South-Transdanubian Water Management Directorate;. Danube-Drava National Park, the South-Transdanubian Water Management Directorate, National Transport Authority, etc.). The directly affected local governments at Bélavár and Vízvár, and the local entrepreneurs may be interested in the implementation of potential beneficiaries as well. The surrounding villages, the potential tourists (rural, eco, water, cycling etc.) and the entire population of the wider sub-region can be considered as indirect beneficiaries who can take in the future services possibly available, due to improving natural conditions as a result of the better water supply. It is expedient to involve into the preparation of the developments those associations and organizations of the cities in the affected are who are already working for the regional developments (e.g. Small Region Association of Barcs).

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The preparation involve developments in the region have been working to develop organizations and of municipalities in the region. Stakeholders may be more local and regional civil society organizations national NGOs, environmental organizations, tourism businesses, fishing, sports and community development relevant potential business. The land-use types in the concerned area are the followings (with the indication of their main stakeholders):  Preserved Area (stakeholder: Danube –Drava National Park);  Stream, side-arms, oxbows (stakeholders: Danube-Drava National Park, South- Transdanubian Water Management Directorate concerned tourism organizations, local residents, tourists);  Gravel mining / quarry (stakeholders: Dráva-Kavics és Beton Ltd., organizations interested in tourism, local residents, tourists);  Fishing (stakeholders: Bélavári Leisure, Sport and Sport Fishing Association, anglers, local residents, tourists, Dráva-Kavics és Beton Ltd.);  agricultural land (arable) (stakeholders: owners, tenants);  Forestry (Danube-Drava National Park, SEFAG Co.);  Roads (all interested sector organization);  Boating (stakeholders with an interest in shipping companies);  Tourism (stakeholders with an interest in tourism organizations, local residents, tourists). In terms of the planned interventions those procedures should be handled separately, which conclude the raising of the Drava water level from those that do not alter the water level at all. The Table 10.1. illustrates which lot numbers are located in the affected areas of each flow alternatives, with mentioning whom they belong and what land use type is defined on the property. It can be noted from the table that the most of affected area is owned by the Drava Dráva-Kavics és Beton Ltd. (Pécs), and the South-Transdanubian Water Management Directorate. Under the jurisdiction of the South-Transdanubian Water Management Directorate mostly those areas belong that are mainly oxbows and the Drava River itself. The Dráva-Kavics és Beton Ltd. owns mainly terrestrial areas such as forests, mining sites and roads and lanes taken out of cultivation. The table shows that the interventions affect the widest area in case the 1. 2. 3. inflow alternatives. The 4., 6. and 7. inflow alternatives affect just the oxbows and the Drava River itself.

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Type of land- Alternatives Lot Number Land-usage Owner use 028/1b forest forest 028/1a mine 022/ checked out Dráva-Kavics és Beton Ltd., Pécs 1.inflow 021/ road case 018/3 forest forest 015/ oxbow South Transdanubian Water 09/ checked out Drava River Management Directorate 0203/ 028/2 checked out checked out 024/2 028/1b forest forest Dráva-Kavics és Beton Ltd., Pécs 022/ mine 2-3. inflow checked out 021/ road case 018/3 forest forest 015/ oxbow South Transdanubian Water 09/ checked out Drava River Management Directorate 0203/ 015/ oxbow 4. inflow South Transdanubian Water 09/ checked out case Drava River Management Directorate 0203/ 5. inflow No data available case 6. inflow 09/ South Transdanubian Water Drava River checked out case 0203/ Management Directorate 015/ oxbow 7. inflow South Transdanubian Water 09/ checked out case Drava River Management Directorate 0203/ Table 10.1. – The affected areas, land owners and land-uses in each inflow alternatives

Figure 10.1. shows the location of the possible inflow alternatives and affected areas in the event of realization. As we mentioned earlier, interventions that would affect the majority of land area are the 1. 2. 3. inflow cases. The other inflow alternatives would only affect the existing channel residues, oxbows, and the Drava itself during implementation works.

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Fig. 10.1. – Affected areas and the inflow alternatives

On Figure 10.2., the marked areas are considered low-lying (under 108.5 maB height) which could be flooded as the water level elevation is implemented. These affected areas are mainly owned by the Dráva-Kavics és Beton Ltd., and the National Park and some wetlands.

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Fig. 10.2. – Low- areas along the involved Drava section (located under108.5 maB)

In the future planning work - in compliance with the applicable national and EU standards - the potential impact of the interventions should be examined in environmental impact studies and analyzed in detail. Because of the Natura 2000 areas are involved the impact assessment must comply with the specifications for such areas. As it can be seen in the tables and on the figures, in the affected area wide range of land use types occur, but they can be synchronized with the nature conservation goals. In any planned intervention alternatives we have to face a special challenge, namely that some parts –not negligible parts- are located in Croatian territory. Thus the Croatian party(s) also has to be involved into the implementation of the revitalization project. Forest management and recreational uses (hunting, fishing, small scale eco-tourism etc.) are already operating under natural protection control so in the course of the future revitalization projects the "normal operation order" would not change in the area. The contradictions are much more likely to appear within the fact that we are trying to artificially reverse a process that is induced also artificially (water power station) but it occurs as a natural process in this section, namely the channel deepening along the Drava, the weakening and complete stop of the sediment transport and the side-arm desiccating. The current stochastic nature of the river cannot be change in all detail (e.g. water levels frequency of flooding occurrence, a seasonal rhythm of the river hydrology, etc.) however the technical interventions according to the nature conservation standards on a given statistical level (probability) will change the water supply of branch system. Although it is expected to maintain a shallow water coverage in a particular area (e.g. following the protected amphibian reproductive cycle) but the Drava hydrological conditions in that period does not allow the water supply (because of the gravitational system). Shortly said in addition to any intervention alternative presented in this study only one single "operation order", it is more appropriate to consider the frequencies of natural overflows and water recharges. The current conditions could also be explained by using the suitable statistics, which we want to change in the future. Adapting the former hydrological statistics of the area, an aquatic and terrestrial biocoenosis has been developed that was slowly driven to adaptation in the last century, and many species are under high-level environmental protection. Effects of interventions are likely to slowly appear (over several decades) in the living structure of the biocoenosis in the affected area. To predict this gradual transformation process – could be defined as secondary succession (or even reverse succession) – would be very difficult, if not impossible on the basis of present knowledge. Therefore it is essential to decide within the sphere of interest of the nature conservation, which are the relevant target species in the area, and which species’ abundance do we plan to increase and which others’ do we plan to decrease.

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At once to the same extent we cannot clear the situation of all (protected) species merely by improving the conditions of the water supply in the area. This imposes the claim for substantial scientifically sound preparatory work (in this case it includes the collaboration of hydrology, flood control, forestry, and regional development policy and nature protection research fields). Moreover the arrangements should be easy to track down, and control and if necessary it could be reversed. In other words, due to the statistical nature of the river, those interventions are preferred which will be able to adapt to the future potentially changing natural conditions as well as to the possible changes in the nature protection legislation and expectations.

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11 Summary

The purpose of the habitat revitalization on the area of the side-arm system of Vízvár- Bélavár designed by the Danube-Drava National Park (DDNP) is the slowing or stopping of riverbed erosion on the relevant Drava section (191-198 river km) and the restoration of former floodplain dynamics (improvement of current water supply of the side-arm system) and thereby the improvement and restoration of habitat diversity. The Inno-Water Ltd. was responsible for the conceptual overview and preliminary evaluation of the opportunities for habitat restoration. In the course of the development of side-arm revitalization options in the area we used the following data:  Data of the river gauge of Őrtilos, Vízvár-Heresznye and Barcs (1970-2013, and 2012- 2013);  Mean and maximum river velocities measured on certain sections of the Drava;  The results of analysis of sediment conditions and bed material of the relevant Drava section  Data from the geodetic survey;  The information of the Drava Atlas about terrain conditions and the relevant river section;  The measured terrain and riverbed elevation data and experiences gathered during the field survey;  Historical information about the area;  International and Hungarian case studies and information about revitalization projects of side-arms dealing with similar problems The following calculations and analysis was performed using the data above:  Using data of each river gauge, rate of channel erosion processes of the sections concerned were determined in order to estimate the rate of disconnection of the branch system if the interventions are not performed.  Based on data from the geodetic survey and water levels measured during the site visit the inflow levels of each water supply trail were determined.  Knowing the interpolated water levels to the given section and the levels of inflow we retrospectively determined the number of days per year when the water flowed through the given branch, assuming the current channel conditions  Given the current situation there was an opportunity to define the boundary conditions allowing the development of the revitalization options.  Using the available sediment and bed material test results we determined the sediment and bed-load composition on the affected section that can be carried away or rolled by the river with a given speed. The results of the calculations were consistent with the relations stated in the literature.

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 Based on the above results and literature data the conditions and possibilities (sediment composition, water rates) of the deceleration of the river bed erosion processes were determined.  We developed the conceptual possibilities of revitalization of the side-arm system (taking into account that the goal is to promote natural processes). According to the evaluation of data processed during the preparation of the study there are two technical options for the revitalization of the side-arm system. The first alternative contains the development of main channels (with local dredging) on the initial sections of the remaining branches (possible water supply trails) while keeping the current water levels of Drava (or with very small elevations) thus providing direct hydraulic connection between the selected channels and the Drava. Based on the geodetic survey the inflow into the side-arms or side-arm remains is limited by the high points of the initial channel section. We have developed proposals for the levels of main channels for each channel remain and trail. The involved channels would basically improve the water supply of the side-arm of Bélavár on various traces. However, the proposed conversion requires further examination in order to determine the exact track and length of the main channel. In order to determine where to begin exactly the development of a main channel, it is necessary to conduct a detailed geodetic survey for the entire channel. Based on the data collected during site visits, the water supply of the side-arm of Bélavár is currently done through the abandoned gravel-pit lakes along the Drava. This is recommended to keep in order to let the large amounts of sediment transported by the Drava settle before the side-arm, slowing the siltation processes of the branch (quarries can more or less serve as an artificial sedimentation basin from which the accumulated sediment can be removed from time to time). Developing the inflow levels as defined in this study the water supply conditions of the side-arm system can be significantly improved. In that case, establishment of culverts on the branch of Bélavár and the reconstruction of a road towards the northern quarries may be necessary. The other alternative is based on the water level raising of the affected Drava section. However, without dredging, the creation of a water level increase necessary for direct hydraulic connection can cause the increasing of flooding frequency of low-lying areas or possible repositioning of the main channel to the current side-arms. According to the analyzes presented in this study the solution seemingly more suitable for the treatment of riverbed erosion and for the improvement of water supply conditions of the side-arm system is the achievement of a slight increase in water level, which also provides the stabilization of riverbed, and the implementation of local dredging to remove the height points of channel remains. The development of main channels on the initial, upper section of the water supply paths is expected to be sufficient to enable the river to develop the side channels with its shear force. When planning to conduct a part of the Drava water into the side-arms, sedimentation due to the decline in flow velocity should be taken into account. The abandoned gravel-pit lakes along the Drava have a settling function as well (considering this path for the flow), which reduces the amount of suspended sediment reaching the side-arm, and thus slow down

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the pace of siltation. Learning from the international experience, the detailed assessment of flow and sedimentation conditions require further investigations, which are essential for the proper preparation and planning of interventions. For the further elaboration of the revitalization opportunities (concepts) outlined in the study the following surveys and analyzes should be performed:  Detailed geodetic survey of the riverbed of the affected Drava section (on sections above and below the side-arms as well).  Detailed geodetic survey of the missing sections of the affected branches.  Preparation of detailed hydraulic calculations in order to accurately forecast the effects of the interventions planned to stop the deepening of the Drava’s riverbed.  Forecast of sediment conditions (sediment movements) on the relevant section based on the planned intervention for the prevention of riverbed deepening.  Detailed calculation of water velocities and water volumes in the side-arms in the light of proposed interventions.  Accurate calculation of the processes of sediment movements and riverbed erosion emerging after the revitalization - based on the hydraulic conditions of the side-arm - in order to avoid siltation of the branch.

The results of the study showed that due to processes of riverbed erosion on the affected Drava section, further worsening of the water supply of the side-arm system of Vízvár- Bélavár, and thereby its ecological conditions is expected in the near future. Therefore, we suggest to carry out detailed calculations starting out from the results of tests presented here to make possible the design of interventions for the prevention of channel deepening process. The problem of channel deepening affects the entire Hungarian section of the Drava (similar to other rivers regulated in their upper section), the treatment of which is required independently of the goals of side-arm revitalization. To this end, besides the interventions with local effects presented in this study, other options might as well requiring international cooperation should be examined (e.g., returning the sediment accumulated in the power plant reservoirs upstream or dredged from the sections above the reservoir in course of maintenance to the river). This recent study described and evaluated the results of the foundational studies on which the future detailed planning and decision-making process can begin by the management of DDNPI. The forthcoming technical tasks include additional geodetic surveys, the detailed and updated measurement of riverbed conditions of the affected Drava section, the large-scale examination of sediment conditions and the cost-benefit analysis of possible alternatives for sediment recharge. Simultaneously, it is necessary to clarify and define the ecological, hydro-biological and conservation priorities that are needed to harmonize in consultation with Hungarian and international (mainly Croatian) partners and involved organizations. Despite the nature conservation being reserved as first priority we can not disregard the sustainability of other land use, and during the future work and discussions, the aspects of

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flood control and navigability should be considered. Any interventions or revitalization measures may only appear in regional level, especially if the national and international tendering opportunities, and the national and EU policy priorities, formulated in the meantime, are considered. The side-arm system of Vízvár-Bélavár - despite the cut-off processes of the recent decades – provides valuable and diverse habitats for many protected plant and animal species. Without interventions, due to the continuous deepening of the main channel of the Drava, the current water supply and ecological conditions of the area can not be sustainable for long (significant degradation is expected in the coming decades). Based on the results presented herein, the key action to preserve the unique natural values is the prevention of channel deepening processes of the affected Drava section.

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12 Bibliography

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Mike K. (1991) Magyarország ősvízrajza és felszíni vizeinek története (Historical hydrography and history surface waters of Hungary, in Hungarian), Budapest (Quoted: Remenyik, 2004). Pišt, P. (2006) Evolution of meandering lower Morava River (West Slovakia) during the first half of 20th century. Geomorphologica Slovaca, 1/2006, pp. 55-68. Poole, G.C. (2002) Fluvial landscape ecology: addressing uniqueness within the river discontinuum. Freshwater Biology 47. 641-660. Purger J. (edit.) (2013) A Dráva négy magyarországi mellékágának élővilága és rehabilitációja (Wildlife and revitalization of four Hungarian side-arm of the Drava, in Hungarian), Pécs. Remenyik B. (2002) A Dráva szabályozása és hajózása (Regulation and navigation on the Drava, in Hungarian), In: Földrajzos Doktoranduszok VII. Országos Konferenciája (VII. National Conference of Geographer PhD Students), ELTE Földrajzi Tanszékcsoport (Eötvös Loránd University, Department of Geography), Budapest, http://geogr.elte.hu/PHD_konferencia_ELTE_2002/doktori_konferencia_anyagai_2002/reme nyikbulcsu.pdf (date of downloading: 08.04.2014.). Remenyik B. (2004) A Dráva szabályozása a XVIII. századtól a XX. század végéig (The regulation of the Drava from the eighteenth century until the end of the twentieth century, in Hungarian), In: II. Magyar Földrajzi Konferencia (Hungarian Geographical Conference), Szeged, 2-4. September 2004. http://geography.hu/mfk2004/mfk2004/cikkek/remenyik_bulcsu.pdf (date of downloading: 08.04.2014.). Remenyik B. (2005) Adatok a Dráva-szabályozás történetéből (Data on the regulation history of the Drava, in Hungarian), Földrajzi Értesítő 2005. (Geographic Report 2005) Bulletin LIV. Number 1-2., pp. 183-188. Révai Lexikon I.-X. (1934) (Quoted: Remenyik, 2004). Sallai, Z. (edit.) (2004) Mit veszíthetünk a Drávára tervezett horvát erőművel? A Drávai táj természeti értékei. (What can we loose with the Croatian power plant planned on the Drava River? Natural values of the Drava’ environs. in Hungarian) Nimfea Természetvédelmi Egyesület (Nimfea Conservation Association), Túrkeve, Nimfea tanulmánykötetek 3 (Nimfea volume of essays 3): 1-220. Sarudi Cs., Szakály Z., Máthé A., Vadász G., Zarándy Á. (2009) A Drávamenti Területfejlesztési Önkormányzati Társulás Fejlesztési Programja (Barcsi kistérség) (Drava Development Program of the Regional Development Self-Government Association for the Subregion of Barcs, in Hungarian). SEE River Projekt (2014) Summary of the second local stakeholder meeting at Sellye in 25 of March 2014 with the title of A SEE River Projekt Dráva folyókorridor problémái és azok megoldása (The problems of the Drava river corridor in the SEE River Project and their solutions, in Hungarian), Manuscript, Pécs.

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Schneeweihs, S. (2013) Pilot-project Bad Deutsch Altenburg: River restoration and prevention of riverbed-erosion in the Danube Floodplain National Park, Mohács. Tockner, Klement; Fritz Schiemer & James V. (1998) The Restoration Concept for a River- Floodplain System on the Danube River in Austria. In: River Restoration ’96 - Session Lectures Proceedings. International Conference arranged by the European Centre for River Restoration. National Environmental Research Institute. Varga D. (2002) A Dráva-völgyi szakasz rövid jellemzése (Brief description of the Drava Valley Section, in Hungarian), In: Iványi I., Lehmann A. (editor.): Duna–Dráva Nemzeti Park (Danube-Drava National Park). Mezőgazda Kiadó, Budapest, pp. 126–132. (Quoted: Dolgosné, 2008). Viczián I., Zatykó Cs. (2011) Geomorphology and environmental history in the Drava valley, near Berzence - Földrajzi Értesítő - Hungarian Geographival Bulletin 60:(4) pp. 357-377. VIZIG (1986) A Magyar- Jugoszláv vízügyi együttműködés 50 éve (The Hungarian-Yugoslav water management cooperation for 50 years, in Hungarian), Manuscript, Budapest (Quoted: Remenyik, 2004). VIZITERV (1970) A Dráva folyó hidrológiai, hidraulikai és potamológiai vizsgálata (The hydrologic and hydraulic analysis of the Drava, in Hungarian), Manuscript, Budapest (Quoted: Remenyik, 2004). VIZITERV (1977) Közösérdekű Dráva-szakasz komplex hasznosítása (Complex utilization of the Drava section of common interest, in Hungarian), Manuscript, Budapest (Quoted: Remenyik, 2004). VIZITERV (1979) Djurdevac- Barcsi vízlépcsőrendszer (River barrage system of Djurdevac- Barcs, in Hungarian), Manuscript, Budapest (Quoted: Remenyik, 2004). Vízügyi és Környezetvédelmi Központi Igazgatóság (VKKI) (Ministry of Environment and Water) – Dél-dunántúli Környezetvédelmi és Vízügyi Igazgatóság (DDKÖVIZIG) (South- Transdanubian Water Management Directorate) (2010a) A Víz Keretirányelv hazai megvalósítása – Vízgyűjtő-gazdálkodási terv – 3-2 Rinya-mente vízgyűjtő (National implementation of the Water Framework Directive - River Basin Management Plan – 3-2 Rinya riverside river basin; in Hungarian), Budapest. Vízügyi és Környezetvédelmi Központi Igazgatóság (VKKI) (Ministry of Environment and Water) – Dél-dunántúli Környezetvédelmi és Vízügyi Igazgatóság (DDKÖVIZIG) (South- Transdanubian Water Management Directorate) (2010b) A Víz Keretirányelv hazai megvalósítása – Vízgyűjtő-gazdálkodási terv – 3-3 Fekete-víz vízgyűjtő (National implementation of the Water Framework Directive - River Basin Management Plan – 3-3 Black water river basin; in Hungarian), Budapest. Vízügyi és Környezetvédelmi Központi Igazgatóság (VKKI) (Ministry of Environment and Water) (2010a) A Duna vízgyűjtő magyarországi része vízgyűjtő-gazdálkodási terve (The River Basin Management Plan of the Hungarian Danube section, in Hungarian), Budapest.

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Vízügyi és Környezetvédelmi Központi Igazgatóság (VKKI) (Ministry of Environment and Water) (2010b) A Víz Keretirányelv hazai megvalósítása – Vízgyűjtő-gazdálkodási terv – Dráva részvízgyűjtő (National implementation of the Water Framework Directive - River Basin Management Plan - Drava sub-basin; in Hungarian), Budapest. Wu, J. & Loucks, O.L. (1995) From balance of nature to hierarchical patch dynamics: a paradigm shift in ecology. Quaterly Review of Biology 70. 439-466. Závoczky Sz. (2005) Vízlépcső vagy nemzeti park…? (River barrage or national park…?; in Hungarian), Hidrológiai tájékoztató 2005 (Hydrological Reviewer of 2005) pp. 35-36.

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13 Annex of photos

Photos 1-2. - The gravel-pit lake No. V. (on the left) and the path to approach the lakes (on the right)

Photo 3. –The accumulated water in the low-lying areas (in the channel remains)

Photos 4-5. – Permanent water transport between the gravel-pit lakes No. I. and No. II. (on the left) and the gravel-pit lake No. III. (on the right)

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 180 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

Photo 6. – The accumulated foam alongside the gravel-pit lake No. III.

Photos 7-8. – The erosion of the Drava’s bank near the gravel-pit lake No. I.

Photos 9-10. – The port of Vízvár (on the left) and the Upper side-arm of Vízvár (on the right)

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 181 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

Photo 11. – The Upper side-arm of Vízvár

Photos 12-13. – The undercut of the Drava’s bank (on the left) and rip-raps for bank protection (on the right)

Photos 14-15. - Accumulated foam in the Drava near the initial section of the 4th channel alternative (on the left) and the picture of the channel (on the right)

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 182 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

Photos 16-17. - The 5th channel alternative

Photos 18-19. – The initial section of the 5th channel alternative

Photos 20-21. – The channel remains on Croatian territory and their environment

Conceptual overview of the revitalization options for the side-arm system of Vízvár-Bélavár 183 Inno-Water Kutató és Környezetvédelmi Szolgáltató Ltd.

Photos 22-23. – The Upper side-arm of Vízvári

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