Analysis of the Szigetköz inland delta

RÁCZ Tamás, BARDÓCZI Sándor

(From previous issue No.36)

It is necessary to narrow the title immediately, because this publication talks about not the whole Szigetköz area but a smaller and most important and most neuralgic part of that which holds the fate of the entire region. This smaller part is the floodplain of Szigetköz region. This place is a symbol of the Hungarian political system change and the exact place of that drastic human intervention redraw radically the upper section of the Danube in Hungary for a longterm by a Czechoslovak-Hungarian political decisions series (GabcikovoNagymaros System). Slovaks are unilaterally implemented the so-called C variant here by the effect of the contemporary Hungarian civil protests. Since that time the floodplain area is an unresolved complex problem nodule from the viewpoint of nature protection, ecology, hydrology, forestry, ecotourism, shipping and water quality. Nearly fifteen years of our research and planning activities try to find complex landscaping solutions for these problems. Finally it has been demonstrated in 2007 by a physical hydrology model experiment series that there is a better water supply solution for this region. And this solution could be strengthening the historical characteristic of the Szigetköz Inland Delta where the natural, economic and social aspects could be also fulfilled.

Attempt at modelling the meandering

Attempt at modelling the meandering

The Szigetköz floodplain of the Danube is a complex branch system, an inland delta which is not only important as an hydrological and ecological subsystem but also as an strategic drink water resources stockholder in Hungary, a forestry potential and a huge gravel wealth. If we see the whole picture then we must say some words about the land use potentials and the possibility of fishing, ecotourism and tourism opportunities for yachting.

The diversion of the Danube and the realization of C variant (power canal between Hrusov and Gabcikovo) accelerated and amplified the negative processes which was already exist in the Old Danube and the side branches relationship but it was a slowly culminating problem before that. The ecologically negative water management processes of the last century closed the side branches from the main branch of the Old Danube and made a slowenergize, stagnant water conditions inside the side branch system while accelerated a faster water on main branch of the river which dug deep the riverbed. The very intensive gravel mining in the past was further increased the sinking of the main riverbed. This is came up before the C variant and caused by negative trends ecologically means water quality of side brunch system, the qualities and quantities the patterns of aquatic habitats and fish cradles and had a negative impact on freedom of movement for all aquatic organisms and 'blue corridors' existence. Parallel this calmed water in side brunches caused an ecological shifts inside the historical ecotopes of native waterside vegetation.

In 1992 when the Slovak side cut off the path of the water supply in Dunacsúny to load the lake reservoir Hrušov and after then they divert the significant part of the water to the bypass canal the Old Danube find itself in an ecologically emergency situation. While the riverbed threshold wasn't implemented at Dunakiliti and the Inland Delta water supply system wasn't built up, there was a natural successional process with softwoods on the partly dried Old Danube riverbed. It was further reduced the floodplain watercarrying capacity and at the same time created an extremely natural softwood stripe on the banks opposite the artificial and more industrially useful timber woods of the islands. Parallel this an another interesting phenomenon was observed in the succession of the Hungarian part of the Dunakiliti reservoir area where the prepared works of completely cleaning of its vegetation the territory became abandoned as a never-to-track parts. This planed and rough area of anthropogenic effects has became a wetland meadow in a decade where water-loving orchid species have grown and the wild population increased to an unprecedented population size. Paradoxically that drastic human intervention brought something back from the old landscape summoning the preindustrial scale forestry times. (Pastoralism has almost disappeared from the Szigetköz Inland Delta and the grazing reserved meadows became forest.)

However the list of ecologically significant positive changes can be completed and we must register more significant and much deeper negative processes. At the first place series of small closings created which works as "mini cascades" to ensure that the inland delta do not dry up immediately. It was created a riverbed threshold at Dunakiliti by the Hungarian water management, which can elevate the water level to load some water to the hanging side brunch system. At this moment these waterworks ensure the water level on the whole inland delta. However this water is slowly flowing or flat water with very limited refreshing possibilities and this lower water quality adversely impacted to many aquatic organisms and also the groundwater quality. This system is impermeable for many organisms, blocks the aquatic eco-tourism (rowing) land use, it is strengthen the filling up the riverbed of the side-branches and the evolution process of the formation of hanging riverbeds. Simplifying this, thanks to the built-up water supply system there is enough water on the Inland Delta but this water slowly rotating and barely flowing water and therefore the former fish cradles and the habitat complexity gradually almost completely lost. As a local fisherman summarized this transformation, "there is enough water but no fish." This sentence is somewhat need to be completed. Because in the Lower Szigetkoz which has much more valid suction impact on the downstream bypass channel and the Old Danube and prevail in much less positive water substitution effects on the riverbed threshold of Dunakiliti and therefore in the Ásványi brunch system (but especially the Bagaméri- and Pulabranch system) there are neither fish, nor water level at the same time. This ecological tension, of course, could resolve by water control tools or periodically controlled artificial flooding and it is a clear benefit in the extremely high floods when the Szigetkoz looks like a sponge which capable considerable amount of water but this system never can solve the problem of obstaclefree ecological corridor or the ecotourism and small shipping problems.

Since the diversion of the Danube the Gabcikovo (Bős) Lock has became a hardly resolve blockage in the tourismrelated small shipping and recreational rowing segments for the regional Vienna - Bratislava - Budapest aquatic tourist traffic. Currently it is dangerous and not recommended to enter the Lock for small yachts or rowing boats and they can overcome this blockage with terrestrial detours. Meanwhile, the gates of Csúnyi Lock and the Dunakiliti Lock towards to Szigetköz are closed, although this type of boat traffic could use the Old Danube if we solve the water supply problems and make some technical improvements on these locks and of course the conditions of the exist water sharing would change between the Gabcikovo power plant and the Szigetköz Inland Delta.

Between the above-described frames, the uniformity of natural habitats of Szigetköz intensified and it also means degradation process and impoverishment, and invasion of invasive species. The Slovak and Hungarian side of this complex ecosystem interoperability is critically low level. Hungarian side was prepared some ecological findings and it has a good coincidence with Slovakian ecological findings. These two papers described the situation very similar to propose an entire landscape rehabilitation (Meandering proposal and Anabranch proposal) which provides a biological permeability, a great pattern and variety of natural habitat types and restores the traditional fish abundance of side-branch system. To improve all of these catch up with eco-tourism and forestry and shipping as well as flood protection aspects. Both parties suggested reaching a typical 1950s ecological status as a minimum target. But there isn't possible to reach the status of the 1860 (before the strong water regulations) for rehabilitation of the side-branches.

The national border status of the river was a massive blockage for the complex ecological rehabilitation of Szigetköz and Csallóköz unified system for a long time. The complex ecological and water management proposal by ECOPLAN and TÉRTERV (1999-2001) called 'Meandering solution' was made acted as a sacrilege before 2004, the EU accession. The meandering proposal based on the scheme which was developed and implemented in the mid-90s at Blochingen by an ecologically sensitive German hydraulic engineer, prof Klaus Kern (one of the fathers of the European Water Framework Directive). The essence of the Kern-schema was that he reconnected the closed sidebranches to the main river branch again and after that they works as the main characters of the water supply. For this he lifted up the water level in the main branch by riverbed thresholds. The astonishing result of this procedure was that while the river water carrying capacity doubled at least (because the main branch and the side-branches got flowing freshwater), parallel the flood safety is increased and there have been enough water in the riverbed at the periods of dry season, as well. It is a selfregulating system where the riverbed thresholds operate automatically.

/read the rest of this post in issue No.36/

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