Modèles pour l'étude du ruissellement urbain

Ingénieur à SOGREAH

Résumé

The problem in urban hydrology is to determine the flows of a given frequency to allow for in ensuring an outlet for rainfall runoff, and also to be able to ascertain the basic data required to control the runoff, which invariably increases the flood flows of rivers running underneath the urban area. Both statistical and deterministic models are available to deal with this problem. Statistical models relate the maximum flows of frequency F to the maximum mean intensity of rainfall of frequency F, IF (tc), tc being a characteristic duration for the considered catchment area : QF = C X IF (tc) X S Simple deterministic models are capable of transforming the net hyetograph for a catchment area into a flow hyetograph at the outlet from the area, with the possibility of relating the constants involved to the physical catchment area features. The use of such models, however, requires a statistical study of representative hyetograph configurations for a given frequency F, which is quite feasible, though it also implies knowing by how much to reduce the gross rainfall in order to obtain the net rainfall, which is a much more complicated matter. The author is of the opinion that the solution of the problem should be obtained by combined use of both types of model. The statistical model provides a satisfactory estimate of QF for a homogeneous catchment area, which can be used to set the rainfall reduction f mm/h, the latter then being adjusted so that the maximum discharge of a representative hydrograph generated by a deterministic model is equal to QF