Microdrainge design flow in ungaged basins: Rio Grande do Sul, Brazil

Abstract The design of urban drainage facilities is normally based on intense rainfall data. This data is usually obtained through the intensity-duration-frequency (IDF) relationships or, when they are unavailable, by means of simplified methodologies such as nested intensities, isozones, or synthetic methods such as those proposed by Bell (1969) and Chen (1983). This paper presents an analysis of the applicability of Bell’s (1969) method, with a modification proposed by Back (2009), to estimate intense rainfall in the state of Rio Grande do Sul, and its use in microdrainage design. The results show what the modified Bell methodology is able to correctly estimate intense rainfall and flows (estimated by the rational formula) with a duration lower than 2 hours, where average variations were close to 10%. The exceptions were in Espumoso and Santa Vitória do Palmar, where the variation was over 15%, which makes the methodology an adequate option for the design of microdrainage facilities when IDFs are unavailable.