Urban Flood Control in Karst Areas: The Case of Rethymnon (Greece)

Abstract

Rainstorms in autumn and winter in the Mediterranean region produce floods and damage of important economic consequence, especially in coastal cities. Examples of damaging floods in urban areas located in the Greek Mediterranean coast are frequent, as in the case of the flood in the city of Rethymnon, Crete Island, on October 1991 and more recently, November 1993, in Athens. The above examples are located in karst areas, where the relation between rainfall and overland flow has a special form, due to the geological characteristics of karst formations and relatively large runoff coefficient. Traditional engineering structures for protection against floods should take into account the specific conditions of karstic terrain, which in Greece represent approximately half of the total area of the country. A relatively low-cost solution for defence from floods in urban areas may be based on the design of flood retention reservoirs. These can be integrated into the urban space and are compatible with environmental requirements. Green areas and sport facilities may be used as flood retention basins, which are designed to contain floods of 1:20 or 1:50 return periods. The case of flood control in the city of Rethymnon, Crete Island, is the subject of this chapter. A computerized conceptual model has been developed in order to assess the hydrological risk of flooding in karst areas, as a function of the volume and location of retention reservoirs. By using the geomorphological, geological and hydraulic characteristics of karst areas, the model was calibrated in order to reproduce the available runoff data.