A Comprehensive Approach to Collection System Capacity Assurance for the City of Columbia


  • Bill Orne, PE - Hazen and Sawyer
  • William H. Davis - City of Columbia

Everyone knows that wastewater flows downhill but how does it flow through more than 1,000 miles of piping within the City’s collection system to the Metro WWTP? The City has recently initiated a project under the Clean Water 2020 program to construct a computer simulation of the wastewater collection system. Known as a hydraulic model, this simulation tool will help the City better understand capacity limitations throughout the system and better plan for capital and operations improvements to ensure sufficient long-term capacity. It is one more component in the Clean Water 2020 program to improve and enhance the operation and function of the City’s wastewater collection system. The City has hired Hazen and Sawyer to develop the hydraulic model and to use the model to evaluate the collection system.

Hydraulic models solve complex mathematical equations to determine flow rates and pressure conditions within piping systems and, thus, allow examination of everything from the capacity of a certain pipe, to where manhole overflows could occur, to how the system will respond after an intense rain storm. As such, the computer-based hydraulic model will allow the City to test different flow conditions and potential changes within the system without actually having to conduct expensive testing in the field. Understanding how the system will perform under various flow conditions and how much capacity is in the existing system will better allow the City to optimize operations and plan for capital improvements to address system limitations.

By using the model to consider both current flows and projected future flow increases, the City will be able to determine required capacity improvements, to develop a sewer system capital improvement plan, and to manage future system capacity. As part of this same project, a Capacity Assurance Program (CAP) will define the process by which the City will assure available system capacity in the future. This program will outline the processes for evaluating and approving additional sewer flows as well as define when improvements are needed to maintain adequate capacity.

Hydraulic model construction, system evaluation, and capacity assurance process development will be completed over the next three years with multiple reports and status updates delivered throughout. This project represents a major investment by the City and the results will help the City achieve the following objectives:

• Develop a comprehensive knowledge-base of the current system capacity
• Develop a sewer system hydraulic model that can be used now and in the future to make system improvement decisions
• Minimize all capacity-related overflows (SSOs)
• Develop a strategic plan for bolstering system capacity and performance
• Define and develop a process to review and approve future system flow requests

For more information, please contact the author at worne@hazenandsawyer.com.

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