Wednesday, October 30, 2013

Tisza River, Hungary

Over three days, from Oct. 7th-9th, the UNL-IGERT group learned about the Tisza River and the Great Hungarian Plain from our hosts/guides/teachers, Péter Balogh, and Béla Borsos. The Tisza River is the basis for a case study of a complex social-ecological system. Here's some more insight into its physical geography, hydrology and geomorphology, and a bit more discussion about the "shadow network's" story to re-connect the floods with the plain.

This post compliments the one previous (Nagykörü, Hungary). 

Béla (left) and Péter (right)

The Tisza River is a large tributary of the Danube River (both are major rivers in Central Europe). The river basin (156,000 km2) covers five countries (Hungary, Slovakia, Ukraine, Romania, and Serbia), but the Tisza is considered to be mostly a Hungarian river ("Hungary is bordered by itself" since the Hungarian Empire was separated after WWI). The shape of the basin is exceptionally important for flooding, since the arc-like shape of the Carpathians causes stormwater flowing from the tributaries to converge on the main river channel after storms in near unison. The mountains receive 3-4 times the amount of rainfall as the plains (2000 vs. 600 mm/yr). These factors make the Tisza "flashy" with flow rates changing by a factor of 50 or more, accompanied by sudden (24-36 hours) and extreme (up to 12 m) rises in river stage.

Geographic setting of the Great Hungarian Plain, surrounded by the Carpathian Mountains to the north and east (image from

Humans have a long relationship with river engineering along the Tisza. Sometime during the Medieval period (c. 1100-1200), a Fok-system of dikes (with sluices) was built to control inundation of floodwaters onto specific areas of the floodplain. In the 1700s, Hungarians used the floods as a means to fight against invading Ottoman soldiers. Also during that time, the Tisza was deepened and shortened (by 400 km) and more dikes were built to prevent flooding of wheat fields and settlements.  From 1860 to 2000, a series of seven construction phases occurred, in which the dikes along the Tisza were expanded and raised as a means of flood defense. Today, the dikes are 4-6 m above the river. The seven phases were required for at least two reasons: 1) The headwater regions in the mountains were largely deforested leading to less storage of water and more runoff; and 2) The floodway (within the dikes) continually aggrades (rises) over time due to sedimentation. The latter process has continued as a positive feedback until the dikes (earth embankments) reached their physical limits and now they cannot be raised any further (as evidenced by dike breaks becoming more frequent). Currently, 2700 km of dikes "protects" 17,300 km2 of land along the Tisza within Hungary. In total, dikes within the Tisza River valley stretch 4500 km, and have reduced the area of the active floodplain by 90%.

Map of historic (c. 1700s) areas inundated by floods within large sections of the Hungarian plain (right) and neighboring Danube River valley (left). Péter is pointing to his village, Nagykörú (big circle). He explains to me that the village would not, in fact, have been inundated by floods during this time since it was built on a high natural terrace (relict of an older floodplain).  

Historically, settlements were situated on high lands—only later with man-made dikes did these areas become inundated by floods. Today ~$39 billion is in risk of damage by floods. Over the past 20 years, rising high waters have been overtopping the dikes. The largest and most damaging flood was in 2010. Therefore, there are real consequences, and the issue of flooding is pressing. 

The rise that the road follows is only 1-2 m higher than the surrounding land, but this is enough to be considered on "high" land, which was historically safe from floods.

Péter explaining the physical geography/geomorphology of the region and the potential for a Fok-polder system. Low elevations on this Digital Terrain Map (DTM) are in dark blue, and high elevations are in red-orange. Polders are natural depressions, or "old river beds" that have been preserved as the meandering river has migrated.

The situation for the Tisza River valley is quite bad now as the potential for devastating floods increases. Also, the river channel has degraded (lowered) its bed, thus lowering the water table during dry periods; but the dikes contain many large flows in the active floodway, and thus raise the water table during wet periods. Because of these processes, and because of the spatially varying capacity of the floodway to transmit water, during any given time there can be areas within the Tisza valley flooded and other areas in agricultural drought. Cash crops continue to be subsidized, and subsistence farming is rare to see (but it still continues to some degree). 

The vision explained to us by Péter and Béla (of the Fok-Polder system), is to adapt human infrastructure and our own desires so they balance with the provisions of the natural environment, and to stop adapting/engineering nature to fit human needs by continuing to protect against floods with dikes alone. All that would be needed are strategically located sluices in the dikes, and appropriate land use changes. 

One last statement offered by Péter: "What do you need to break a dike? ... a dike."

The Tisza River looking downstream (SE) from the ferry on the way back to Nagykörú.

Posted by Nathan Rossman

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