location: Nagymaros, Dunapart
design: 2012
construction: 2013
client: Nagymaros Municipality
architect: Varga Csaba, Robogány Andrea
hydraulic engineer: Kenesei József
contractor: HÓD Kft.
photos: Varga Csaba
In parallel with the renovation of the city centre, flood protection for the small city has been built. Being on the banks of a major river, life in Nagymaros is influenced by the Danube and its floods.
In the past, flooding and flood defences were different from today. The 1929 flood was a winter flood with ice. In winter, there is not as much water as in a summer thaw, but the ice cannot melt as quickly and therefore builds up, which can cause enormous devastation. At that time, it would form mountains up to 8-10 metres high and everything in its path would be eaten away. Ice-breaker dams were built to avoid this. There was one in Nagymaros, the Dam, which is now a resting place and lookout point on the Danube. Nowadays, there are no more ice floods because, on the one hand, the river rarely freezes over and, on the other, ice-breaking boats are used to prevent ice drift.
In the past, there was no protection against the flood, and the water would creep up into the lower streets, even onto the main road. They built ballast pavements and used boats to travel on them. Then, when the tide had gone out, the water slowly and quietly receded back into the riverbed. People waited for everything to dry, whitewashed again and the case was closed.
In modern times, the major floods started in the early 2000s, and the attitude of the population was different than before. Everybody - rightly so- feared for their property, so protection started with organized sand bagging during floods. The water held back by sandbags came up from the ground due to capillary forces, so another set of dikes and many pumps were set up at the street ends.Forunately there were no rains at the time, otherwise water would drain down from the mountain above the city as well. Nagymaros lies below the Börzsöny, so when it rains the streets running down the valley function as water catchment and drainage areas as well.
The continous pumping caused a water flow loop partially in the ground, causing weakening and slippage of the foundaation of riverside buildings. In the past this was no problem, because there were no pumps used. There was significant damage to the lower buildings in these floods. The inland bank of the Danube in Nagymaros is nearly 3 km long, so it took a lot of work, a great deal of public cooperation and the help of the military to protect it with sandbags. And when the tyde receided, mountains of sandbags soaked in polluted water remained, which took months to clear.
The simplest technical solution would have been to build a new dam on the bank. But this would have cut the town off from the river, so it was out of the question, leaving a mobile dam as the only possible solution.
The almost 3 km of inland sections have been divided into 3 parts. Of these, the central section is the most exciting from an urban planning point of view. The engineering of the mobile barrier was combined with urban development. The idea was to draw this protection line into the fence line, thus using the dam cosntrcution to also tidy up the end garden fences of the plots that form the back wall of the Danube promenade. The affected fences have been demolished and a waterproof slit wall has been constructed in their place, below the terrain, and a waterproof parapet wall above the terrain. Where there were beautiful fence foundations, made of stone or brick before the demolishon, they were rebuilt in front of the parapet wall. And where they were inappropriate fences before, we designed and built new ones instead, mainly of stone and brick from the demolishon. These fences were different plot to plot and we have also kept this feaqture with the new wall, i.e. in this central part we do not see an uniformly continuous structure, here the dam is hidden in the skin of fences that vary from plot to plot.
A groove was made in the top of the new slotted wall for the panels of the mobile dam to be palced into it. They are practically invisible when there is no flooding. We followed the same principle for the streets that run down to the river, where there can be no raised wall. There the same concept is made with larger, stronger posts, a groove runnig along the road and bigger hardwood panels.
At each end of the protection line a gate was made, and at each of the perpendicular streets corners, a strong column of stone and brick was added to house the large galvanized steel columns.
The end result is a mobile barrier system with a varied appearance, in aesthetic alignment with the historic city centre, but at the same time a modern system of mobile barriers that provides safety against flooding.
