Le Havre

In 2010, Le Havre metropolitan area was 293 851 inhabitants for 678 km². More than 60% of inhabitants live in Le Havre city (178 769 inhabitants in 47 km²). The surroundings are agricultural areas and scattered settlement (INSEE, 2010).

Located on the Seine estuary, Le Havre metropolitan area has a very restrictive landscape for development. The North coast is a range of sea-cliffs of 90 meters height. On the western part, the estuary is the entrance of a large industrial harbor for oil tankers (Port 2000), composed of numerous industrial and petrochemical plants. On the eastern part, the Seine estuary is a protected natural area (Natura 2000). The axis for territorial development is from North to East and along the Seine River.

A large part of the potential for economic development and urban planning is located in the watershed valley named La Lézarde. It is a 213 km² basin, with important differences in altitudes (medium height is about 100 meters). The basin is steep-sided, i.e. on a 15% gradient.

The Lézarde watershed often flooded the valley during the 2000s. The type of flood is flash flood by streaming due to intense raining on waterproof ground (agricultural business and urbanization). The flood is particularity risky because the bottom of the watershed valley is densely urbanized and industrialized.

During the late 1990s as well  as the 2000s, public policy for flood management has decided to renew and build several small retention basins (around 120 works), but also to elaborate flood reduction strategies at inter-city level (intermunicipal institution).