Vinyl sheet piles used as an element of flood protection infrastructure of the city of Cracow: the next stage of the project to enhance the flood resilience of the Bieżanów district.

Analyses and experience of recent years have clearly proved that the combination of climate change consequences and rapid urban development with the hydrotechnical infrastructure that cannot keep up with the progress of the first two, is a direct path to the increased flood risk. Intense but short-term rainfalls and violent weather anomalies triggered by climate change, unsustainable urbanization comprised some of the most important factors that contributed to flooding, which we analysed in the article dedicated to the Złocień housing estate in Cracow, which is part of the historic Bieżanów district. As the construction works in the next stage of this project have just been completed, we continue the story about the solution that not only helped enhance the flood resilience of Bieżanów but also generated considerable investment savings.

Fig. 1 Footbridge over the Serafa River during high water on May 25, 2019.

The small Serafa River flowing through Bieżanów was a source of worry to the inhabitants of this quiet district of Cracow, which, like many other attractive suburban areas, was subject to rapid urbanization. Since the great floods in 1997 and 2010, when the river bed was significantly degraded, from spring to autumn the areas adjacent to the Serafa were exposed to flooding as a result of flash floods resulting from heavy rains.

In 2016, the Bieżanów retention reservoir was commissioned in Kraków, as an element of a comprehensive project assuming the construction of five cascading such reservoirs in the Serafa river valley. This large investment, which is still under construction, despite its complexity, is an extremely important element of the flood protection system of the whole Cracow and Wieliczka area.

Unfortunately, even despite the existence of the Bieżanów reservoir, heavy rainfalls in 2019 and 2021 caused greater losses than those recorded in 1997 and 2010.

Fig. 2 Flooding in Bieżanów as a result of rainfall on August 6, 2021.

The "Black Friday" of August 6th, 2021

On August 6, 2021, the rainfall was so intense that it caused widespread flooding in the Bieżanów. Geotechnical measurements and hydrotechnical analysis showed that the culminating water flow in the area of the Złocień estate was about 22 m3/s. Such flow exceeded even the estimated 1% probable water flow.

The consequences of such rapid flow of water, combined with still insufficient flood protection measures, have brought massive damage to the local infrastructure and housing. The catastrophic weather conditions resulted in the overflow of the rainwater from the Bieżanów reservoir. As a result of backwater from the reservoir and the damming of water on the bridge along ul. Rakuś, the streets, bridges and the residential area were heavily flooded.

Actions to improve the safety of Bieżanów residents

The events of 6th of August have brought the attention to the need for further urgent action to improve the safety of residents in the area.

As part of the task "Improvement of flood safety in the Serafa river basin in the XIIth Bieżanów-Prokocim district of Cracow ", the investor, i.e. the state owned Polish Waters, decided to construct  additional flood protection infrastructure and our vinyl sheet piles were used in this project.

As in the case of the Złocień housing estate, also in Bieżanów the same vinyl sheet profile GW-610/9 with an integrated gasket was used, to ensure the tightness of the lock connections along the entire length of the sheet pile immediately at the time of the installation.

The wall made of vinyl sheet piles was intended to raise the maximum level of safe damming of water in the Serafa River bed, but also to extend the water filtration path in the ground. A total of 3 818 square meters of 1.5-2.0 m long sheet piles were used for the entire project.

Fig. 3 One of the typical cross-sections assuming the modernization of the embankment with the EcoLock vinyl sheet piles

The sheet piles were driven into the ground on one side of the riverbed, and in sections where it was deemed necessary according to the geotechnical analyses, on both sides of the Serafa river. In order to additionally reinforce the construction give it a more aesthetic appearance, the structure made of sheet piles was crowned with a system vinyl cap, also delivered by the Pietrucha Group.

Was vinyl worth it?

In this case, the investor had the choice to follow the tradition and use the “notorious” technology, i.e. steel sheet piles. Let us look at the issue of comparing the costs of both solutions and attempt answering the question: Did the non-standard approach to solving the flood problem with the use of an innovative material bring financial benefits?

There is no denying that this project was not demanding in terms of the structural challenges connected with the wall construction. Let us assume that in the case of this investment, the steel sheet pile profiles with the wall thickness of 7mm could be safely used. Such thickness would suffice to reinforce the embankment and the greatest risk affecting the structure was from corrosion that would occur over the years, rather than from periodic water pressures on the structure.

Taking into consideration the application of the wall, the steel would have to be protected against corrosion. A steel sheet pile of this type would weigh approximately 77 kg/m2, so the price per square meter of this profile was approximately approx. EUR 112. After adding the average cost of anti-corrosion protection of the wall on both sides, we would get the value of approximately EUR 135. A quick and simple calculation allows us to estimate that the total cost of 3 818 square meter of steel sheet piling used in this project would cost approximately EUR 514 742.

In the case of vinyl sheet piles GW-610/9 with a seal, the price per square meter of which was EUR 67, which gives the price of the material for the entire project of EUR 253 082. The amount is a mere 50% of the cost of steel sheet piles!

Add to this the savings from more efficient transport, lighter installation equipment and lower maintenance costs, and the end result would be well over EUR 260 K costs saved. We are talking here about a relatively small project of great importance to the local community.

The added value of using vinyl sheet piles in this project

The installation of vinyl sheet piles was much less costly and less time consuming than traditional methods. In addition to a considerably lower price compared to other available technologies, vinyl sheet piles are lightweight, transport-friendly and 100% corrosion-resistant. Thanks to these factors, they allow investors to generate savings not only at the time of purchase, but also during assembly and subsequent use.

In this project, the sheet piles were installed using the most popular method of installation, i.e. using a vibratory hammer. It is worth emphasizing, however, that the assembly took place in sections in a very densely built-up area. That is why, at some spots with limited access, the sheet piles were installed in a narrow excavation.

Thanks to the use of vinyl sheet pile technology with their numerous advantages, the densely developed areas along the Serafa River have been effectively and quickly protected against flooding.

Fig. 4 EcoLock vinyl sheet piles during installation - excavator used to form the embankment

As summary, it should be noted that the vinyl sheet piles made by Pietrucha Group have played a breakthrough role in the struggle to enhance flood resilience of this part of Cracow. Residents of the Bieżanów-Prokocim and Złocień districts can sleep peacefully without worrying about their homes. The use of vinyl sheet piles not only enabled the project to be completed in the shortest possible time and immediately reduced the risk of flooding, but also contributed to generating significant investment savings.

The role of the investor who decided to use vinyl sheet piles instead of traditional materials such as steel or concrete should be emphasized here. The choice of vinyl sheet piles turned out to be a spot on, not only because it helped expedite the construction but also in terms of costs efficiency of this non-obvious solution. The investment has become a true symbol of success in the struggle against floods, in which a lot of EUR was saved compared to more well-known methods.

Fig. 5 The Serafa River bed secured with EcoLock vinyl sheet piles with a vinyl cap

Thanks to solutions such as EcoLock vinyl sheet piles, the inhabitants of Bieżanów and Złocień can enjoy the safety provided by this innovative technology. This example shows that sustainable construction solutions can bring real benefits to both communities and investors. Safety, savings and low environmental impact  - all this has become possible thanks to the Pietrucha vinyl sheet piles.

Link to the previous article, dedicated to the Złocień estate:

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