Cost-optimization of hydraulic rehabilitation of an urban drainage network
Assessment of urban drainage networks often reveals that some systems gradually become subject to pressurized flow, or even backups and overflows. The impacts on the balance of the aquatic environment are troubling, and can have serious consequences on the safety of drinking water resources and the recreational use of these environments. These dysfunctions are often due on one hand to the increases in runoff flow caused by urbanization and climate change and, on the other hand, by the reduced hydraulic capacity caused by wear and lack of network maintenance. To overcome these environmental and hydraulic dysfunctions, we have implemented an optimization program for rehabilitation interventions. Potential rehabilitation interventions mainly focus on Best Management Practices (BMPs), but may also include conventional methods of rehabilitation and even the resizing and reconstruction of problematic pipes in order to improve the network hydraulic capacity. The optimization program has been applied both to a real and to a synthetic network, according to several retention and design storm scenarios. The application of this methodology to the synthetic network allowed the illustration of the benefits of integration of BMPs during design in order to optimize construction and management costs in the short term, while avoiding long-term hydraulic and environmental problems. The case study focuses on the network in the borough of Verdun, which is subjected to many environmental and hydraulic dysfunctions. The proposed program has allowed a definition of the best balance between retention, rehabilitation and pipe resizing, leading to the targeted hydraulic and environmental performances at the least cost.