Optimal Positioning and Sizing of Detention Tanks within Urban Drainage Networks

The work describes a procedure for the evaluation of the optimal number, positions, configuration and sizes of detention tanks inside urban drainage networks, aiming at containing expensive and troublesome replacement of existing sewers unable to properly convey runoff discharges. The procedure proposed is based on the use of a Genetic Algorithm (GA), in which the evaluation of the behaviour of each individual (i.e., of the entire drainage system, consisting of both the detention tanks inserted in it in place of one of a few existing sewer pipes and remaining existing sewers) is analyzed by a semi-distributed hydrological model, where the flood routing is carried out using a simplified hydraulic model: the kinematic wave approximation of De Saint-Venant equations. In particular, for each individual, the proposed hydraulic-hydrological model is used within a "variational" procedure, based on the evaluation, by varying the rainfall durations and the cor-responding value of the rainfall depths (whose correspondence is given by an intensity-duration-frequency relationship), of the maximum value of the peak discharges and/or flow depths. The pro-posed approach has been applied, for example, in a specific case study, showing its promising potential and its ability to obtain results of practical interest.