Optimal design of wastewater and rainstorm drainage networks

In the paper, a procedure is shown for the optimal design of both wastewater and rainstorm drainage networks which, just adopting a few changes, is also suitable for the sizing of rural drainage networks. The approach proposed is based on the utilization of a Genetic Algorithm (GA), coupled with different analytical/numerical (semi-distributed) models for the evaluation, for given return period T and pre-assigned rainstorm durations d, as of the surface runoff coming from the single parts of the catchments drained by each branch of the network as of the mean flow characteristics in reference cross sections, chosen a-priori on account of their relative importance for subsequent fitness and costs evaluations and distributed along the whole network. The suitability of proposed approach is firstly tested with reference to two different drainage networks taken from the literature. Then, since the hydrologic/hydraulic models proposed in literature which could be utilized for optimized design of drainage networks are more and more characterized by increasing capability level to represent complex phenomena really occurring within the networks they self, such as the flood propagation along distinct reaches, the summation of discharges at nodes of confluence, the development of not of uniform water level profiles (for instance: because of downstream water level boundary conditions and/or interference of flows at confluence nodes), eventual formation and moving of rollings, situation for which pressurized flows may develop within one or more reaches of the network, etc., a discussion is made on the results of the application of a few of them to a specific study case of study