Scientists have checked whether Warsaw is at risk of flooding. These districts are most at risk

In 2021, scientists from the Department of Water Engineering and Applied Geology of the Warsaw University of Life Sciences (SGGW) published a geomorphological map in the Journal of Maps that could significantly impact flood risk management in the capital. The map shows in detail which areas of Warsaw and the surrounding area are most at risk of flooding in the event of a flood embankment breach.

Is Warsaw at risk of flooding?

The researchers’ research, published in the journal, took into account both the terrain and laser scanning data, the accuracy of which reaches several centimeters. The work also took into account analyses of historical floods. The researchers looked for traces of extreme hydrological events that took place in the past, especially on the higher terraces of the valley, which the Vistula formed in the Pleistocene. Based on their analyses, it was possible to determine which areas were most exposed to flooding in the past and what changes in the landscape caused these events.

Wilanów, Wawer and Łomianki are most at risk

A team of researchers from SGGW found that areas located on the right bank of the Vistula, including the Wawerski Bend, are particularly vulnerable to flooding. On the left bank, the most vulnerable point is Łomianki near Warsaw, as well as areas above the Siekierkowski Bridge, including Kępa Okrzewska and Kępa Oborska in the commune of Konstancin-Jeziorna. All these areas are located on the current flood terrace of the Vistula.

“These areas are sensitive because they could be flooded during large floods. They are potential places where flood embankments could break,” explains Dr. Grzegorz Wierzbicki, the lead author of the study.

Dr. Wierzbicki reminds us that during the great floods in the past, connected with ice jams, the waters of the Vistula poured mainly into the areas of the Wawer Bend, heading towards today’s Dworzec Wschodni, through Targówek and Białołęka to the Narew valley. The left-bank Warsaw, on the other hand, is relatively safe due to the higher terrain, which was shaped by glaciers thousands of years ago.

“The left-bank Warsaw, located higher, is not as threatened by flooding, which is why in many places there are no flood embankments – they are simply unnecessary,” emphasises Dr. Wierzbicki.

The Vistula River flowing through Warsaw is characterized by very variable water levels, which causes large differences in flood risk. Particular attention was paid to the possibility of breaking the flood embankments that protect the city from flooding. The area of ​​the Vistula Valley in Warsaw covers about 350 km², and the difference in water levels during floods can be up to 7 meters.

In recent decades, especially after the fall of communism, Warsaw has experienced rapid urbanization, which has significantly increased pressure on natural floodplains. The researchers emphasize in their analysis that intensive development, especially in the city center, where skyscrapers and underground structures are being built, additionally increases the risk of flooding.

One of the most important discoveries of the SGGW team is the indication that the so-called flood terraces, which were previously considered safe, could be flooded in the event of extreme weather conditions. The research showed numerous traces of river erosion in these areas, which indicate that the Vistula water could reach them during floods.

“The water must have poured onto the higher terraces during extreme floods, which means that the flood threat applies to larger areas than previously thought,” explained Dr. Wierzbicki.

Practical conclusions for developers and residents

The map developed by scientists may be useful not only for services responsible for crisis management, but also for developers and residents planning to build houses in the vicinity of the Vistula. Dr. Wierzbicki recommends that in areas prone to flooding, houses should be built without basements and with additional protection against flooding of lower floors.

“Flood embankments are only effective until they break. Our map clearly shows where such a risk exists, and this is important information for both developers and residents,” the expert concluded.

The geomorphological map of Warsaw developed by the team from SGGW is a step forward in better understanding the flood hazards of the capital and may contribute to better spatial planning and increased safety of residents.