GIS-supported mitigation of the impact of hydropower dams on the flood plains of the Drava-Mura Rivers in Croatia/Hungary

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1 178 GIS and Remole Sensing in Hydrology-, Water Resources and Environment (Proceedings of ICGRHWE held at the Three Gorges Dam. China, September 2003). IAHS Publ. 289, 2004 GIS-supported mitigation of the impact of hydropower dams on the flood plains of the Drava-Mura Rivers in Croatia/Hungary ULRICH SCHWARZ 1 & JURG BLOESCH 2 1 FLUVIUS, Floodplain Ecology and Management, Hintzerslrasse 2/9, A-1030 Vienna, Austria ulrich.schwarz@i1uvius.eoit] 2 Sims Federal Institute for Environmental Science and Technology (EAWAG), CH-8600 Diihendorf Switzerland Abstract This paper presents GIS and Remote Sensing applications to produce large scale maps on riverine landscapes and their ecomorphological quality. The overlay ofthe map ofthe planned hydropower plant "Novo Vine" in the Drava River (Croatia) exemplifies the potential of this method, in combination with in situ investigations, to show the expected destruction of riverine habitats and flood plains. This publication is part of the research topics of the International Association for Danube Research (IAD). Key words biodiversity; flood plains; G1S mapping; hydropower impact; river morphology INTRODUCTION 'In the course of centuries, all large European rivers have been massively manipulated and severely damaged by human impact (e.g. Petts et al., 1989; Ward & Stanford, 1995; Tockner & Stanford, 2002; Bloesch & Sieber, 2003). However, the Drava and Mura rivers in Croatia and Hungary were generally much less affected (Danube Pollution Reduction Programme, 1999). While in the upper river reaches they are strongly modified by hydropower dams (Fig. 1) and flood protection constructions, including sediment collection and extraction facilities, the lower river courses were only moderately altered by river engineering as they formed the border between Hungary and the former Yugoslavia (today Slovenia/Croatia and Hungary). Therefore, and despite significant downstream effects of this upstream chain of dams, virtually untouched natural stretches and areas with an amazing diversity of species remained in the lower course of these rivers. The Drava River basin has a size of approximately km 2, a river length of about 750 km and an average discharge of 580 m 3 s" 1 at the confluence with the Danube River. The political and economic situation in Europe and especially in the Danube riparian states have been subject to dramatic changes since In view of the accession to the European Union it is evident that increasing economic pressure threatens the still existing ecological values along the Drava-Mura river system. Already before 1990 plans were prepared to build a chain of hydropower plants along the last free flowing stretches of the lower Mura, Drava and Sava rivers, primarily to satisfy the national energy request and to stimulate the national economy. ' This publication is part of the research topics of the International Association for Danube Research (IAD).

2 GIS-supported mitigation of the impact of hydropower dams on flood plains 179 Fig. 1 Upper Danube River basin (Inn, Enns) and Drava River basin (dark area) with hydropower dams. Nearly 90% of the alpine river systems are irreversibly modified (CIPRA 1992), and the impacts of hydropower generation often reach the downstream river stretches and influence large parts of the river basins. Until now, these discussions have focused not only on promoting hydropower energy, but also on navigation and flood protection. Only very recently have the ecological consequences of new and past interventions on the river ecosystem been given some attention. This is in line with the general trends in river basin management (Boon et al, 2000), but is specifically triggered by international political guidelines, in particular, the European Water Framework Directive (EU-WFD), which requires a holistic approach to the river ecosystems. The projected hydropower plant "Novo Virje" in Croatia is the largest and most recent project. However, an integrated, comprehensive evaluation of the related river stretches, especially its ecological aspects, is still missing. In order to fill this gap we present results based on a study of WWF, EURONATUR (2004) which can be qualitatively extrapolated to other lowland rivers. OBJECTIVES OF AN INTEGRATED ECOLOGICAL EVALUATION In a first step the most important impacts of the proposed "Novo Virje" hydropower plant on the lower river course should be given. Then the general analysis is focused on the habitat structure, with special attention to the river ecomorphology. There is great evidence that the change/loss of habitat structures, induced by dam construction, is followed by a loss of biodiversity (Schiemer, 1999). To prove the standard for possible implementation, the final evaluation of results needs to be compared with the

3 180 Ulrich Schwarz & Jùrg Bloesch existing international conventions and European directives. A broad range of GIS and remote sensing applications are necessary and helpful to support this analysis. The results and technical applications of GIS/RS lead to the generalized view of the future river basin management plans required by the EU-WFD. Water quality aspects, quantitative flow and ecomorphology, including the flood plains, are equally important ecological parameters. The hydrological and sedimentological regime, as key factors to characterize rivers, are an especially important part of GIS-based river basin information. TECHNICAL IMPACTS ON THE DRAVA-MURA RIVER SYSTEM, GIS- METHODOLOGY AND RESULTS The planned "Novo Virje" hydropower plant is the lowermost impoundment in a chain of three already existing lowland-reservoirs of the same type (Fig. 2). Based on a thorough environmental analysis (WWF, EURONATUR, 2004) the direct impacts can be summarized as follows: Loss of river dynamics By turning the free flowing river into a reservoir the dynamics of both surface and groundwater levels as well as sediment transportation, as crucial elements of the riparian landscape, would be reduced considerably. Today, the average flow velocity varies between 1 and 1.8 m s" 1, and the variability in flow (between <0.5 m s" 1 during low water discharge and 2.8 m s' 1 during floods) leads to a heterogeneity in river bed structure. After the construction the flow velocity will decrease to 0.1 m s" 1 in the lower parts ofthe reservoir. Today, the water levels vary Prelog Preiog ill Fig. 2 Drava before and after the construction of an existing dam upstreams of the planned dam "Novo Virje" (CORONA picture from 1962, Landsat 1991).

4 GIS-supported mitigation of the impact of hydropower dams on flood plains 181 between 5-6 m during low and high water periods. The delayed groundwater oscillation is evident up to 10 km from the river and will be equalized after the dam construction. Deterioration of groundwater quality The considerable lowering of the groundwater table during the past 50 years has destroyed important benthic and phreatic habitats. This trend, which is closely related to the reduced sediment load from upstream reservoirs by more than 50% and the subsequent bed incision of 1-2 cm per annum, will be enhanced. Sealing of the river bed and embankments along the reservoir with fine sediments would prevent the natural exchange between river and groundwater. Together with reduced groundwater flow dynamics, a decrease of oxygen and an increase of ammonium, nitrite, manganese and ferric iron may occur and thus deteriorate the good quality of drinking water. Loss of typical river habitats River islands, gravel-sand structures and natural banks as some of the ecologically most valuable habitats in the Drava River will disappear in the impounded stretch. Shallow water zones which are vital as breeding grounds for numerous endangered fish species will be drastically reduced. Natural water bodies such as side arms and oxbows will be disconnected from the natural riverine dynamics. Transition zones between aquatic and terrestrial ecosystems (ecotones) which are hotspots of biodiversity will be lost. In summary, the significant loss of river habitats would mean a change of the current "good ecological status" of this river stretch to a "heavily modified" status which is not in accordance with the EU Water Framework Directive. Loss of European endangered habitats and species Presently more than 50 fish species and over 100 breeding bird species are living in the area. The planned reservoir will cause the substantial reduction or disappearance of 10 habitat types (including two priority habitats of European importance), 30 animal species under the EU Flora- Fauna-Habitat Directive, and 26 bird species under the EU Bird Directive. Disruption of the Drava-Mura River continuum Damming the Drava in the middle of the 380-km long river corridor will cause the loss of the ecological integrity and stability of this river system which is shared between four countries. Not only the habitat and species pool would be reduced, but also the fish migration would be stopped or at least hindered. Deterioration of lowland forest and meadow ecosystems Changes of the groundwater regime leads to the deterioration of the semi-natural forest ecosystems including the common oak of the Koprivnica-Durdevac region (about ha) and the famous Repas forest. Melioration of the extensive cultural landscape around the dam near Molve would lead to further degradation and loss of ecologically valuable lowland meadow ecosystems. Deterioration of river ecosystem downstream the dam including the Hungarian National Park The dam on the Drava at Dubrava impacts the 220-km long downstream stretch from the Mura confluence along the Croatian-Hungarian border and the Hungarian National Park to the confluence with the Danube near the Nature Park Kopacki Rit. Peak mode operation leads to permanent water oscillation of up to 1.8 m twice a day near the dam (Fig. 3), which is reduced to a few cm at the

5 182 Ulrich Schwarz & Jiïrg Bloesch mouth of the Drava River. A data series of 30 years showed a substantial change in frequency and amplitude of discharge which, however, remained the same in total: The discharge during low water periods is increased, whereas the ecologically important small (1-5 year) flood events are reduced due to the water retention in the upstream reservoirs. Increased river bed incision caused by the sediment trapping in the reservoir modified natural habitats and fish populations, lowered groundwater tables, and drained flood plain forests. Through the permanent water oscillations the siltation of gravel bars and islands with fine sediments (suspended load coming from Mura tributary) increased after the construction of the power plants. This disturbs the sensible semi-aquatic part of the river banks and the succession of pioneer habitats, and consequently changes invertebrate community structure to reduced biodiversity. In contrast, the daily water oscillations increased the erosion in the main channel, thus endangering infrastructure such as bridges. The planned dam at Novo Virje just 30 km downstream of Dubrava, would intensify all these negative trends. Furthermore, the average water discharge will be decreased by more than 95% in the 5-km long diversion stretch along the outlet channel, and hence one of the ecologically most important parts of flood plain forests of the National Park would dry out. Loss of natural areas for recreation and ecotourism The pristine and diverse river landscape would turn into a monotonous, exchangeable, man made and controlled landscape with less attraction for sustainable tourist development which is a great economic perspective for this region. These results allow and support the GIS-analysis of the river stretch, where the hydropower plant "Novo Virje" is planned. The habitat structure of this river part is very rich and heterogeneous, varying from highly dynamic pioneer habitats to large River Drava-Level of water Fig. 3 Daily water oscillation 20 km downstream from the hydropower plant at Dubrava.

6 GIS-supported mitigation of the impact of hydropower dams on flood plains 183 oxbow and hardwood habitats (compare with upper part of Fig. 2). The habitat investigation was based on a landscape structure analysis and a detailed vegetation investigation for each of the described habitats. Subsequently a review of water related ornithological research in the area was carried out. For the analysis of the river stretch of 40 km (8500 ha) a Russian KFA 1000 satellite image (Fig. 4) with a ground resolution of 5 m was analysed in combination with three months of field work. The mapping and overlay of different thematic information such as digital elevation model, water tables, forestry data, historical data, zoological data or the planned hydropower station with its barrage and construction area, was easily performed in a GIS-system. The general approach is similar to the new RAMSAR wetland inventory guidelines (Finlayson et al, 2001). The first result was an overall habitat map in the scale of 1: Figure 5 shows the reduced and adapted data set of habitats into the European-wide FFHD (Flora- Fauna-Habitat Directive) classification for the Natura 2000 network, a comprehensive network of areas with a high nature protection value of community interest. Over 80% of the river corridor fulfil the requirements and need to be integrated into a Natura 2000 area. The river ecomorphology was investigated in a scale of 1: based on field investigations, mostly by boat and following GIS analysis. In a first step a special investigation methodology was developed for the main river channel, diverse small water bodies in the flood plain, larger oxbows, and stagnant water bodies. Parts of the European wide methodology to investigate small rivers developed by Werth (1987) or Fig. 4 KFA-satellite map of the projected "Novo Virje" hydropower plant.

7 184 Ulrich Schwarz & Jùrg Bloesch r- 1 v- Habitats according to the EU Fauna-Flora-Habitat Directive along the Drava River within the area of the projected Hydropower Plant "Novo Virje" WWF F.UKOSATVK HU Main Habitats according to the FFH Directive! : j Pioneer Habitats (FFH-Codes: , 3270) * _T Sott Wood Habitats (FFH-Codes: 31EO. Priority Habitats) M Oxbow and Rood Habitats (FFH-Codes: 3130,3150,3270) Grassland Habitats (FFH-Codes: 6210 (important Orchid Sites), 6510) i Hard Wood Habitats (FFH-Codes: 91F0) Lowland Forest Habitais (FFH-Codes: 9170,91E0)... Drava River (FFH-Codes: 3230,3240,3270) and Other Waters ÏWiê Modified Soft Woods/Plantalions m h Seltisments " State border - - Railways Main roads - Embankments Novo Virje reservoir and dam Tributaries Temporary channels a Main gravel excavations Tree groups Head widows A Scale: 1: (in A3) Map Credit: Ulrich Schwarz/ FLUVIUS FFH Directive Annex I Codes: 3130: Oligotrophia io mesolrophic standing waters with vegetation of the Littoreiletea unlflorae and/or of the Isoeto-Nanojuncetea 3150: Natural eutfophic lakes with Magnopotamton or Hydrochantion type 3230: Alpinsriversand their ligneous vegetation with Myricario germanica 3240: Aipineriversand their ligneous vegetation with Salix eleagnos 3270: Rivers with muddy banks with Chenopodrun rubrl p.p. and Bidentton p.p. 6210: Semi-natural dry grasslands and scrubland fades on calcareous substrates (Festuco-Bfometalia) ("important orchid sits) 6510: Lowland hay meadows (Alopecurus pratensis, Sanguisorba officinalis) 91EO: Alluvial forests with Ainus glutinosa and Fraxinus excelsior (AJno-Padion. Alnion incanae, Salicion albae) ('Priority Habitats) 91F0: Ripanan mixed forests of Quercus robur, Ulmus iaavis and Ulmus minor, Fraxinus excelsior or Fraxinus angustifolia, along the great rivers (Ulmenton minons) 9170: Eastern Galio-Carpinetum oak-hornbeam forests Fig. 5 Habitat types after the FFHD (EC-Flora-Fauna-Habitat Directive, 92/43/EEC). LAWA (2000) were integrated (Table 1 ). The evaluation was focused on easily visible parameters and can be especially applied for monitoring campaigns concerning the river bank development and the pioneer stages of islands and bars. But also temporary channels and the long-term development of the oxbow systems can be monitored. A post investigation ofthe 40-km long Drava stretch in summer 2001 yielded a map (Fig. 6) showing the standardized evaluation in five classes, similar to the water quality mapping in five classes (Bloesch, 1999) and colours from "blue" (best quality) to green, yellow and orange to red (worst quality). Over 80% of the Drava River belongs to the first two classes. In contrast, the large West Gentian rivers showed mostly orange and red colours, featuring highest morphological degradation (Kern et al, 2002). In a synthesis, these two maps were combined with the information of the planned hydropower dam (Schwarz & Mohl, 1998). Thus, a map (Fig. 7) was carried out showing the potential loss of habitats and destruction of the still intact ecomorphology. Along the 40 km of the Drava River 30% of oxbow and reed habitats will be drowned, 70% of grassland habitats, 90% of soft wood habitats, and 95% each of pioneer habitats and free flowing, braided river stretch. Subsequently, the loss of biodiversity and the extinction of several specialized and endangered fish and bird species can be

8 GIS-supported mitigation of the impact of hydropower dams on flood pla 185 Table 1 Comparison of the ecomorphological methodology based on Werth (1987)/LAWA (2000) for small rivers and the methodology for the Drava River (WWF, EURONATUR, 2004). Parameter set WERTH/LAWA WWF-EURONATUR (DRAVA) Fluvial morphology River bed configuration Patchwork water-land River bank Vegetation Smallest river investigation stretch Evaluation River width, depth, drift, river course development, continuum Bed relief, substrates, depth variance, bed constructions Width variability, water vegetation, fish hiding places, bank protection Slope, shape, profile, bank protection Bank and riparian vegetation strip between m Evaluation in seven (fife) classes based on a comparison with sample stretches of "best ecological quality" Detailed mapping of islands, bars and transects, separate evaluation of fluvial parameters and river course development Single transects, substrates, special attention to large woody debris Bank investigation in several classes, bank protection structures Detailed bank investigation (e.g. different types of cut off banks) Separate vegetation/habitat mapping in the entire flood plain 100 m No evaluation in a first step River Ecomorphology of the Drava River according to the EU Water Framework Directive within the area of the projected Hydropower Plant "Novo Virje" HU Water Quality according to the WFD 1: Unpolluted to very slightly polluted (High) 2: Slightly polluted (Good) 3: Moderately poliuted(moderate) * 4: Heavily polluted (Poor) ~" 5: Excessively poituted (Bad) "Moderate Status"! 25%* * according to the WFD * ' < * River Ecomorphology according to the WFD ' 1: Natural and sltghlty modified (High) 2: Slightly modified (Good) 3: Moderately modified (Moderate) * 4: intensely modified (Poor) " 5: Completely modified (Bad) accofisrtg lo the WFD tor the parameter "Morpftotagtail conrmons" [ U Drava River and Other Waters Settlements - State border Now Virje reservoir and dam ** t Railways - Tributaries * Temporary channels - Main roads - Embankments 5 Kilometers A Scale: 1: (in A3) Map Credit Ulrich Schwarz/ FtUVlUS, 2003 A"f-,.', ), Frankfurt ti X "Ecomorphology" Overview (compare example from Rhine and */.C'jr^w Main rivers in Germany near Frankfurt, V* Darmstadt and Mainz) Fig. 6 Ecomorphological quality according to the EU-WFD.

9 186 Ulrich Schwarz & Jùrg Bloesch Loss of FFH Habitats and valuable River Ecomorphology (according to the WFD) within the construction area ofthe projected Hydro Power Plant "Novo Virje" WWF M.'RO.VATL'K Loss of FFH Habitats and Valuable River Ecomorphology According to the WFD... Novo Vine Reservoir and Oam Tributary Temporary channel 5 "I Settlements State border Railway Main roads - Small Roads A Embankment FLUVKJ5, Km Scale: 1: (in A3) Loss of Valuable River Ecomorphology (percentage of total loss): _ 1 ; Natural and slightly modified (High) (62%) 2: Slightly modified (Good) (25%) 3: Moderately modified (Moderate) (5%) 4: Intensely modified (Poof) (7%) 5: Completely modified (Bad) (1%) 7%1% SEA FFH Habitat Loss jt^<^wilhln the constmction area C V..' (total percentage of loss). -i* 'Loss related to the ( N entireriverinecorridor (30 km), r MPioneerh3baais "95%) ps-i f son wood habitais (39%; '90%) joxbowand reed habitats {2%; *30%) i ;Grassland habitats (20%: *7G%) ; I Free-flowingDrava river system (19%: '95%) '//)RemainingArea (16%) Fig. 7 Loss of habitats and valuable river morphology within the construction area of the planned hydropower dam. predicted, as was experienced after the construction of the darns upstream. The ongoing biomonitoring of the Hungarian Danube-Drava National Park (with sampling stations and areas up- and downstream of the planned dam) underlines the importance and possible loss of the area. Furthermore, the 350-km long Drava-Mura free-flowing river continuum would be disrupted in the middle, which is one of the most valuable parts of this ecosystem. In the study "Drava-Mura natural rivers or hydropower dams" (WWF, EURONATUR, 2004) three variants were analysed: the first deals with the current situation without any management, the second evaluates the planned hydropower dams, and the third proposes a future management strategy to protect and develop the river corridor and to solve the important problem of riverbed incision. Under the viewpoint of several international Conventions signed by Croatia, such as RAMSAR (on wetlands), Bonn and Bern (on biodiversity and habitats), and the ongoing accession negotiations to join the EU, including the Flora-Fauna-Habitat (FFHD) and Birds Directives with the Natura 2000 network, the Water Framework Directive (EU-WFD) stressing a "good" ecological quality, and the Pan-European Biological and Landscape Diversity Strategy (PEBLDS), which is focused on the riverine corridors, the planned dam does not fulfil international and national requirements.

10 GIS-supported mitigation of the impact of hydropower dams on flood plains 187 CONCLUSIONS Based on simple and cost effective remote sensing and GIS-technologies the documentation of habitats and river ecomorphology of a 40-km long river corridor of the Drava River in Croatia was carried out within two years. Only the overlay with the planned hydropower map impressively documents the loss of biodiversity within the area. In combination with a better digital elevation model and more hydrological and hydraulic data the vegetation succession can be modelled and morphological changes can be quantified. High-resolution satellite data or cheap digital videography can regularly monitor all morphological changes in the riverbed. In conclusion, this GIS modelling leads to a better understanding of the temporal and spatial changes of the riverine landscape and of the analysis of dominant processes in that area. It can help to strengthen the river management towards a more sustainable strategy including solutions for the river bed incision and flood mitigation. Apart from hydropower use, sand and gravel excavation, traditional "hard" bank constructions for flood protection, navigation and river channelization, as well as irrigation and land-use by agriculture and settlements need to considered in an integrated approach of river basin management that aims at limiting increased human pressure. The ecological integrity of the river and its flood plain is not only threatened by pollution and altered flow regime, but also by morphological destruction. REFERENCES Bloesch, J. (1999) The International Association for Danube Research (IAD): its future role in Danube research. Hydrohiol. Suppl. 115/3-Large Rivers 11/3, Bloesch, J. & Sieber, U. (2003) The morphological destruction and subsequent restoration programmes of large rivers in Europe. Arch. Hydrohiol. Suppl. 147/3-4 - Large Rivers 14/3-4, Boon, P. J., Davies, B. R. & Petts, G. E. (eds) (2000) Global Perspectives on River Conservation: Science, Policy and Practice. John Wiley & Sons, New York, USA, 548 pp. CIPRA, Commission Internationale pour la Protection des Alpes (1992) Die lelzten naturnahen Alpenfliisse. Kleine Schriften 11/92,71 pp. Danube Pollution Reduction Programme ( 1999) Evaluation of Wetlands and Floodplain Areas In the Danube River Basin. WWF Danube-Carpathian Programme and WWF-Auen-Institut (WWF-Germany). Finlayson, C. M., Davidson, N. C. & Stevenson, N. J. (eds) (2001) Wetland inventory, assessment and monitoring: practical techniques and identification of major issues. In: Wetlands and Development (Proc. Workshop 4, second int. Conf., 8-14 November 1998 Dakar, Senegal). Supervising Scientist Report, Darwin, Australia. Kern, K., Fleischhacker, T., Sommer, M. & Kinder, M. (2002) Ecomorphological survey of large rivers Monitoring and assessment of physical habitat conditions and its relevance to biodiversity. Arch. Hydrohiol. Suppl. 141/1-2 - Large Rivers 13/1-2, LAWA, Landerarbeitsgemeinschaft Wasser (2000) Gewdsserslrukturgiitekarllerung in der Bundesrepublik Deutschland Verfahren fiir kleine und mille/grosse Fliessgewâsser. Kulturbuch Verlag, Berlin, Germany, 186 pp. Petts. G. E., Môller, H. & Roux, A. L. (eds) (1989) Historical Change of Large Alluvial Rivers: Western Europe. Wiley, Chichester, UK. Schwarz, U. & Mohl, A. (1998) The impact of the Hydroelectric Power Plant Project on the flow of the Drava River between Botovo and Ferdinandovac. In: Sustainable Economic Use of the Lowland Rivers and Protection of Nature and Environment (Proc. Int. Conf.) EURONATUR, Hrvatsko Sumarsko Drustvo, Hrvatsko Energetsko Drustvo, Zagreb, Croatia. Tockner, K. & Stanford, J. A. (2002) Riverine flood plains: present state and future trends. Environ. Consent. 29(3), Schiemer, F. (1999) Conservation of biodiversity in floodplain rivers. Arch. Hydrohiol. Suppl. 115/3 Large Rivers 11/3, Ward, J. V. & Stanford, J. A. (1995) Ecological connectivity in alluvial river ecosystems and its disruption by regulation. Regulated Rivers: Research and Management 11, Werth, W. (1987) Ôkomorphologische Gewâsserbewertung. Oslerreichtsche Wasserwirlschafl Wien, 39(H. 5/6), WWF, EURONATUR (2004) Drava-Mura - natural rivers or hydropower dams (in press). Arch. flow