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Hydrological studies of rainfall-runoff processes provide the basis for estimating design flows for urban stormwater drainage systems which control floods and the transport of sediments and pollutants. This paper outlines the theory of urban rainfall-runoff processes and describes the development of modelling practice and the current use of computer models. It concludes that rainfall-runoff theory has reached a mature stage, and highlights deficiencies and dilemmas which require further research, including rainfall variability, scale effects and interfacing between models. RESUME L'étude des processus hydrologiques intervenant dans la transformation pluie-débit fournit les elements nécessaires a l'estimation des debits de projets dans les systèmes urbains d'assainissement pluvial. Ces derniers contrólent les inondations ainsi que Ie transfert des flux de sediments et de pollution. Cet article fait le point des connaissances actuelles sur ces processus en zone urbaine. Il présente ensuite les modèles pratiques les plus couramment utilises ainsi que les outils informatiques qui leur servent de support. La principale conclusion est que la modélisation en hydrologie urbaine a atteint une certaine maturité. Malgré tout certaines insuffisances et incertitudes nécessitent des recherches complémentaires. C'est en particulier le cas de la prise en compte de la variabilité spatiale des pluies ainsi que des effets d'échelle qui posent des problèmes d'inter facage entre les modèles.

Urban stormwater runoff has been recognized as a potential major contributor of pollution to receiving waters. However the projected high costs of control have prompted an examination of the extent to which these impacts have been documented. A nationwide search was conducted for case studies demonstrating a cause‐effect linkage between urban runoff and impairment of beneficial uses in receiving waters. The results indicate that numerous definitions of “impacts” are being used and that few substantive data exist to support many of these allegations. Results of a preliminary impact assessment are presented for the 248 urbanized areas of the United States. Then, the results of more recent efforts to assess these impacts in several case studies are described. This assessment demonstrates the critical need for additional short‐term and long‐term sampling programs.