Cost-efficiency analysis of a runoff detention reservoir with integrated hydraulic and structural dimensioning

ABSTRACT In Brazil, urbanization-dominated imperviousness is prevalent, increasing the incidence and magnitude of floods. An alternative to control this impact is an on-site runoff detention reservoir. The choice of reservoir adopted should ideally combine hydraulic/hydrological and structural/economic criteria, although there is a gap in the literature regarding this type of integrated analysis. In this article, a cost-efficiency analysis is conducted to select a reservoir to control the runoff captured by a roof (4,657 m2) using the Puls method for hydraulic dimensioning and based on technical standards for the design of concrete structures. The results indicate that a decrease of approximately 3% in the theoretically ideal efficiency (100%) of the reservoir provided a 36% drop in cost. Such an alternative is more likely to become attractive and economically viable, with virtually the same benefits to the downstream stormwater drainage system. The analysis of different alternatives induced a decision between the level of control of the reservoir output and the cost that emphasized different aspects, focusing on more than the minimization of the cost or the imposition of a pre-defined control level in an arbitrary way.