Measures and solutions for flood management Local case - Flash flood in Gdansk 2001

摘要

The number of people inhabiting our globe is constantly increasing. At the same time the amount of people living in the cities is growing very fast. This way in many countries the population of the cities amounts to 80% of the total country's population. Floods in urban areas are more and more frequent. These floods cause considerable economic and social losses mainly because of developed and expensive city infrastructure. This infrastructure goes now very often underground, which is very flood prone in case of inundation of the city. In urban areas measures and solutions for flood mitigation are primarily of engineering character. However, very often it is difficult to find advantageous technical solutions, because existing city infrastructure restricts the introduction of appropriate new constructions. Another important factor in urban areas is considerable speed of floods, which requires earlier, good planning of solutions in case of inundation.rnFlash flood in Gdansk in 2001 can be considered as an example of local case. Gdansk the Polish old city situated at the mouth of the Vistula River (1047 km long) is most flood prone agglomeration in Poland. There are three possible flood directions. First is from the moraine hills, in case of intensive precipitation, second direction is from the Gulf of Gdansk in case of storm surges and the third is from the main Vistula channel in case of very high discharge.rnThe paper presents the description of floods in the area of Gdansk during past centuries. They were caused mainly by ice jams which formed along final section of Vistula River of very complicated layout. In July 2001 a severe flash flood, coming from the moraine hills invaded Gdansk causing considerable economic and social losses. It was caused by very high and intensive rainfall. One of the main objects in this flood was an artificial Radunia Channel, constructed in the XIV century. The main aim of this Channel was the supply of water to the city of Gdansk. In the paper the analysis of this flood is presented. Detailed measurements of all water courses, hydrological and hydraulic analysis were carried out. 1D unsteady flow model of the Gdansk 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 polders. The network of measuring stations was also proposed.