Risk reduction requires a multifaceted approach; physical protection and land use planning.
Weirs andlevees do not provide absolute safety and often leave significant residual risk. They can also lull people into afalse sense of security and inadvertently increase risk in the long term. Residual risk that such structures mightbe overcome in floods needs to be weighed and publicly discussed. Given the increase of flash flood hazards,raising and reinforcing physical defenses by itself is neither desirable nor cost-effective. Physical protectionshould be complemented with land use planning so that risk areas are kept permanently clear where flood risksare high. Establishing effective regulations and zoning requires cooperation. Multifunctional areas such as parkscan double as retention areas. Watershed assessments should take into account upstream land use, and becombined with careful urban planning. Project URBAS (http://www.urbanesturzfluten.de) highlightscost-effective strategies that consider the overload case.