Rôle de l'humidité des sols sur les crues en milieu urbain

Role of several variables on the hydrology of a small urban catchment

Centre de Développement des Géosciences Appliquées, Université Bordeaux 1

Abstract

The catchment is the Marly, in Cauderan (Bordeaux, France), area 2.23 ha. It is equiped with a combined sewer, and there is a dry-weather flow we have to deal with. Five three-stoyered buildings are sited on this place. The impermeabilisation ratio is 60% (+ 3%). The total length of the network is 380 m . The average slope on the catchment is 5.6 mm/m.

Measurements were held on this catchment between 1991 and 1994, by the Centre d'Etudes Techniques de l'Equipement du Sud-Ouest. There is a runoff gauge at the outlet, and a rainfall gauge is located on the roof of a 50 m far garage. We retain 43 sequences of rainfall-runoff data.

We show the presence of a permanent runoff in the network, related to the humidity of the soil. But during a rainfall event, this seasonnal humidity aspect has no influence on transfer, nor on production. The production coefficient reaches a constant value for relatively strong events, close to the impermeabilisation ratio.

For weaker events, the coefficient depends on the initial state of the surface in terms of humidity. A high height of the rainfall, and a high intensity accelerate the transfer. It seems that the soil humidity does not have any influence on the rainfall-runoff transformation. This means that quick drainage through soil is negligible on this catchment. The main process in the rainfall-runoff transformation is runoff on impervious surfaces.