The Sights and the Risks of Inundation in the Agglomeration of Antananarivo: A Concrete Case of the Risk Management related to the Road Infrastructures.

Nowadays, Antananarivo, a hill city of the XVIIth century, becomes a sprawling agglomeration of the plain crossed by the river Ikopa and its three tributaries. Not only is Antananarivo the capital of Madagascar economically speaking, but also its perimeter is about 6000 hectares. It provides several activities on which the economy of the country depends. Several successive measures have been set up in the order to face the almost continuous threat of inundation of the city. Many embankments have been created andreinforced, but the damage of large areas involves a rising of beds and the deposition of alluvial deposits. The extraction of these alluvial deposits requires artificial dredging of beds which can erode the dykes. Due tothe damages of the storm in 1959, some measures of protection have been adopted: infrastructures of protection; regulations so as to prevent the different risks; risk estimation; institutional reinforcement; methods to tackle the plans, and risk management of road infrastructures. New road infrastructures that illustrate this risk management are the Dyke Road and theBy-Pass. For the covering abstract see ITRD E139491.