Wetenschap - 11 januari 2001

Hungarian comes up with ways to help Danube floodplain

If the Hungarians want to revitalise the floodplains of the River Danube they will have to change the water regime. Changes in land use are not enough, argues Dr Istv?n Zsuffa, who obtained his PhD on January 8th from the Sub-department of Water Resources.

During his research Zsuffa discovered that human intervention in the water regime of the Danube has led to serious disturbances in the ecosystem of the floodplain. The river has been deepened, which has resulted in lower water levels and less flooding of the floodplains alongside the river bed. Wetland vegetation has been replaced by dryland vegetation.

Fish

The meanders of the river have also been cut off, making the river straighter. During periods of high rainfall this means that the flood wave passes through more quickly and that the floodplains dry out faster after inundation. Zsuffa: "Fish like carp and pike lay their eggs in the inundated part of the floodplain, but they have no time to hatch." The eggs can only hatch if the water remains in the area long enough. Zsuffa found however that adjustments to the water regime will improve the ecosystem. This can be done by changing control of the dikes, canals and sluice gates. By closing the floodplain after a flood in some places, the sluices can be used to ensure that water levels are maintained, thus enabling the fish to breed.

Ancient practices

Zsuffa: "It is not enough to simply reduce recreation in the floodplains thereby returning areas to nature. We can only revitalise wet ecosystems by improving water conditions." He points out that during the Middle Ages people managed the Danube better. By digging small channels in the floodplain they ensured that there were areas where fish could thrive. When there were enough fish in these artificially created ponds they would close the channels so that some fish stayed, and thus avoided being caught by fishermen. Restoration of this ancient system of channels would help to make the ecosystem more healthy, and could induce a return to this traditional method of fishing.

Hugo Bouter

Istv?n J?nos Szuffa: Multi-criteria decision support for the revitalisation of river floodplains. Supervisors: Professor Janos J. Bogardi and Professor Jan Leentvaar of the Sub-department of Water Resources, Wageningen University.

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