Activities  Danube

Introduction

europe The Gabcikovo-Nagymoros hydraulic scheme was conceived in the 1950's, as a joint Czech and Hungarian project. In the 1980's, the Hungarians renounced to achieve the Nagymaros side and the construction, which continued only on the Czechoslovakian side, was completed and put into operation in October 1992.
The Cunovo Dam has diverted 80 to 90 percent of the Danube's flow from the river to the above ground diversion canal. The water level of the old Danube bed dropped by 3 to 5m below the ground level of the former floodplain. As a result, the contacts among some side arms and the Danube are completely interrupted and the recharge of groundwater is reduced.

The Danube

Rising in the Black Forest of Germany and travelling 2,840 km to the Black Sea, the Danube River is a living ribbon across Europe.
On the border between Slovakia and Hungary, at the break through the Devin Gate, the Danube enters the "Small Hungarian Plain", an extensive depression filled by neocene and quaternary sediments. The extent of the former inland Delta, "Szigetköz", can still be identified on the images by the Danube's numerous side arms and meanders.
The area of this floodplain considerably decreased in the second half of the 19th century when the Danube was made straighter in a canal for improvement of water transport and dikes aimed at flood control were built.

The Floodplain

Floodplains represent the biologically most productive regions of our planet and the inland delta of the Danube was not an exception. Floods did not merely represent an increase in water area in ground water levels but were an important source of nutrients.
The annual yield in softwood forests, cereals or the production of fishes in the inland delta was two times higher than in the adjacent downstream parts of the Danube River where the floodplain is not so developed.
From the biological point of view, the floods have an enormous positive impact. Wetlands act as kidneys of a river system cleansing water and acting as sediment trap. Good water quality requires healthy and properly functioning wetlands.


Landsat ETM image of bands RGB 7,5,3, 21 Oct. 2000


Landsat MSS 1 Nov. 1973 RGB 2,4,1

Changes in water regime

All natural flooding of the inland Delta ceased in 1992.
Although artificial flooding were planned and implemented, the water provided to the bypassed floodplain does not correspond to the natural regimes in terms of timing, duration, area flooded or sediment deposits. This low discharge is unable to maintain the previous habitat diversity, greatly disrupting the once dynamic ecosystem of the river and has a negative impact on the survival and reproduction of plants and animals. Consequently, the mean annual fish catch, calculated for the period after the damming of the river dropped by 87% in comparison with 1961-1972. Only one fish ladder was built, but the migration of fish upstream was never observed.

The construction of the dam, canals and reservoir system directly affected 3900 ha of fields and 5400 ha of floodplain (WWF 1997). The ground 23km long sealed canal has a maximum height of 18m and a width between 267 to 737m.

The loss of vegetation in the forested area has occurred directly around and below the Cunovo dam where major building works took place. Some areas next to the old Danube River are now seen as barren land patches.

The red patches along the former Danube indicate the loss in water covered areas between October 1973 and November 2000.

Some of these surfaces have been covered with new vegetation

No change in the vegetated surface area, but the level of interpretation does not allow assessment of change in vegetation type.

Lowering of the groundwater level

The 3 to 5 m drop in the water table is a threat to the hydrological balance of the floodplain. The specificity and diversity of the remaining forest is affected. The quality and quantity of ground and drinking water reserves suffer from loss of groundwater recharge.

Danube side-arm near Cikolasziget (A)

July 1988

May 1993

July 1995
Side-arm near Asvanyraro (B)

Nov. 1991

Nov. 1993


Cunovo Dam

Cross dikes

Gabcikovo Locks

Wildlife

The species diversity of vertebrates in the inland delta was high in comparison with other regions. 65 species of fishes, 11 species of amphibians, 9 species of birds were repertoriated. Many of them were limited to this ecosystem.

 


Poster Quick Look

Research conducted by: Nicole Strub, GRID-Europe