Measures and solutions for flood management. A local case: Flash flood 2001 in Gdańsk, Poland

Abstract

The population of the globe is constantly growing. At the same time the number of people living in cities is exploding. Today, in many countries the population of the cities amounts to 80% of the total country's population. Floods in urban areas occur more and more frequently; they cause considerable economic and social losses mainly because of developed and expensive city infrastructure. Today, infrastructure goes underground, which is very flood prone in case of inundation. In urban areas measures and solutions for flood mitigation primarily have an engineering character. However, it is quite often difficult to find advantageous technical solutions, because existing city infrastructure restricts the introduction of appropriate new constructions. Another important factor in urban areas is the considerable propagation speed of floods, which requires advanced, good planning of solutions in the case of a (potential) inundation. The flash flood in Gdańsk in 2001 can be considered as an example of an interesting local case with lessons for other cities with medieval downtown areas. Gdańsk, the historic Polish city, is situated at the mouth of the Vistula River (1047 km long), and is the most flood-prone agglomeration in Poland. Here, floods can come from three directions. The first is down from the moraine hills during severe precipitation; the second direction is from the Gulf of Gdańsk during storm surges; the third is from the main Vistula channel when very high discharges come down the river. This paper presents a description of (severe) floods in the Gdańsk area over the past centuries. They were caused mainly by ice jams, which were formed along the final section of the Vistula River, which has a rather complicated layout. In July 2001 a severe flash flood, coming down from the moraine hills, invaded Gdańsk causing considerable economic and social losses. A long and intensive rainfall caused it. One of the crucial objects during this flood was the artificial Radunia Channel, constructed in the 14th century. The main aim of this channel was the supply of fresh water to the city of Gdańsk. In this paper an analysis of this flood is presented. Detailed measurements of all watercourses in the Gdańsk area, together with hydrological and hydraulic studies, have been carried out. AID unsteady flow model of the Gdańsk Water Node was developed. Calculations were carried out to find the best technical solutions to mitigate consequences of a similar flood in the future. It was proposed to construct 18 small retention reservoirs in the catchment of Radunia Channel, 4 additional control discharge structures from Radunia Channel and in addition 2 flood retention polders. A network of measuring stations was also proposed. Copyright © 2006 John Wiley & Sons, Ltd.