Urban flooding: the flood-planned city concept

Abstract

Urban flooding can be generated by two different mechanisms. A town or city occupying a part of the flood plain can be flooded by external floods, or else flooding can be generated by internal urban runoff. In this second case, a completely different hydrology occurs, governed by technologies of urban hydrology and hydraulics. The same flooding protection, however, can be applied for both mechanisms. Urban-generated floods are characterized by specific mechanisms resulting from highly impervious urban areas. Urban hydraulics also has particular features. Insufficient storm drainage capacities basically underlie all urban runoff flooding. Nevertheless, the surface drainage system is the key problem in most cases. In this situation, flooding takes place at runoff concentration areas. Urban design for flood protection includes several types of measures, usually termed flood-proofing. This concept of American origin should be generalized for European urban areas which are densely populated. It should encompass the conception of the entire city. A city under flood should be designed as an artificially created differential flood. This urban design concept is illustrated by several examples. Building codes should use appropriate technical standards for foundations, insulation, basements, lifts, etc. Finally, public services and facilities should be treated in such a way that they suffer the least possible damage from flooding. Flood-proofing of a city should be replaced by the concept of a flood-planned city.