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In recent years, the concept of a centralized drainage system that connect an entire city to one single treatment plant is increasingly being questioned in terms of the costs, reliability, and environmental impacts. This study introduces an optimization approach based on decentralization in order to develop a cost-effective and sustainable sewage collection system. For this purpose, a new algorithm based on the growing spanning tree algorithm is developed for decentralized layout generation and treatment plant allocation. The trade-off between construction and operation costs, resilience, and the degree of centralization is a multiobjective problem that consists of two subproblems: the layout of the networks and the hydraulic design. The innovative characteristics of the proposed framework are that layout and hydraulic designs are solved simultaneously, three objectives are optimized together, and the entire problem solving process is self-adaptive. The model is then applied to a real case study. The results show that finding an optimum degree of centralization could reduce not only the network’s costs by 17.3%, but could also increase its structural resilience significantly compared to fully centralized networks.
Structural resilience describes urban drainage systems’ (UDSs) ability to minimize the
frequency and magnitude of failure due to common structural issues such as pipe clogging and
cracking or pump failure. Structural resilience is often neglected in the design of UDSs. The current
literature supports structural decentralization as a way to introduce structural resilience into UDSs.
Although there are promising methods in the literature for generating and optimizing decentralized
separate stormwater collection systems, incorporating hydraulic simulations in unsteady flow, these
approaches sometimes require high computational effort, especially for flat areas. This may hamper
their integration into ordinary commercially designed UDS software due to their predominantly
scientific purposes. As a response, this paper introduces simplified cost and structural resilience
indices that can be used as heuristic parameters for optimizing the UDS layout. These indices only
use graph connectivity information, which is computationally much less expensive than hydraulic
simulation. The use of simplified objective functions significantly simplifies the feasible search space
and reduces blind searches by optimization. To demonstrate the application and advantages of the
proposed model, a real case study in the southwest city of Ahvaz, Iran was explored. The proposed
framework was proven to be promising for reducing the computational effort and for delivering
realistic cost-wise and resilient UDSs.