By taking a TOTEX approach, we focused on analyzing the overall outcome for our client, rather than a single output of a project being successfully delivered on time and on budget. In this vein, we looked to examine standard operating procedures such as the long-term lega- cies, the costs, the impact on future maintenance, and ownership. This strategy informed our approach in building the hydraulic model, where we mapped all water discharge infrastructure within the ter- rain and layered in rainfall data to establish flow data. We then used stochastically generated rainfall events to evaluate system exceedance rather than the traditional approach focused on retention. Combined, this data helped us better understand the system to determine flow trends into sewers, available capacity, and general water movement within the system. Using a hydraulic model to understand both the magnitude of flows and the timing is critical. Individually, these data points represent simple flow conditions, but collectively they represent a complex matrix of interactions that must be understood and managed to create a success- ful outcome.
In the original plan, interceptors had been proposed to help direct flows to the tunnel. With our strategy of optimization, we focused on deter- mining whether aspects of the original system could be reused through minor upgrades to relieve bottlenecks and get flow to the tunnel. The key was making sure the system was able to push flows into the tunnel sooner to create the capacity in the lower reaches. This would then allow flows in the upper reaches to come down, ultimately reducing the need for new infrastructure. This became the biggest single saving in the optimization strategy. Our reevaluation plan was amended to include this optimized design, which was accepted by the Rhode Island Department of Environmental Management in 2017. Using flow control structures in conjunction with real-time controls enable the existing system capacity to be maximized before flows are diverted to the tunnel; these structures are the cornerstone of the solu- tion optimization.
Analytics tools like this enable engineers to make earlier informed decisions to optimize capital solutions. In making our data and model work harder, our team has been able to support NBC in setting this CSO control solution up for success against the rigors of future climate change, while ensuring the project is being used most effectively and meeting project goals. Using flow control structures in conjunction with real-time controls enable the existing system capacity to be maximized before flows are diverted to the tunnel; these structures are the cornerstone of the solution optimization.
By continuously running the model, collecting NBC’s SCADA data, and, in some cases, adding additional flow meters over the course of our five years on this project, the model has become increasingly informed. In seeing this data year over year, our team is looking for trends and changes, making sure that the designed system is standing up to the rigors of this increased implementation via real-time control and adaptation in the face of future impacts like climate change. One of the keys to the considerable optimization of this project was the opportunity to better use the existing assets to manage flows. Once we were able to understand the system, we used the model to determine that NBC could open and close gates to fill the tunnel – which can hold nearly 59 million gallons of water – earlier, and subsequently direct flows to the treatment plants sooner so that NBC could get the most out of their existing infrastructure. Using a hydraulic model to understand both the magnitude of flows and the timing is critical. Individually, these data points represent simple flow conditions, but collectively they represent a complex matrix of interactions that must be understood and managed to create a successful outcome.
NICK ANDERSON is a chief civil networks engineer in Stantec’s water practice. His primary responsibility is to ensure the technical excellence and quality delivery of engineering planning and hydraulic modeling projects across North America, working from the firm’s Atlanta, Georgia, office. MELISSA CARTER is Vice President, Director of Project Management, and has worked on a range of water and wastewater infrastructure projects from Stantec’s Providence, Rhode Island, office. Her focus is currently on wet weather-related projects to reduce or eliminate sewer overflows that impact the water quality of natural waterways.
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