Forensic Modeling: How Building a Detailed Model Revealed Clues to Detroit's Sewer System

Purpose and Background The Detroit Water and Sewerage Department (DWSD) serves more than 230,000 accounts that includes a residential population of nearly 700,000. DWSD's sewer system network consists of nearly 3,000 miles of sewer collection piping within the city of Detroit. In June 2017, DWSD established the Capital Improvement Program Management Organization (CIPMO) project with a mission to coordinate and execute capital project planning and project implementation across the City. CIPMO sewer project's goals are to reduce sinkholes and cave-ins, reduce untreated CSO's and minimize inflow and infiltration. As part of DWSD's CIPMO project DWSD decided to build a systemwide hydraulic model based on its asset management database to prioritize condition assessment work, identify areas of suspected capacity constraints, characterize risk and support capital improvement project creation. The DWSD hydraulic model was built through an accelerated schedule in approximately 1 year and includes over 80,000 nodes and 100,000 line segments that represent the entire sewer system in detail. Through the development and calibration of the model, DWSD was able to identify gaps in its asset management database and obtain a more accurate representation of system connectivity. The use of the model to identify areas for additional review resulted in significant savings by producing precise requests for field verification for an efficient use of field crew time. This paper will discuss examples of the benefits of using a hydraulic model to better understand a utility's sewer system and address challenges normally faced by utilities such as: (a) accurate representation of system connectivity, (b) identify gaps on asset management systems inventory, (c) changes to system operation through abandoned or improved assets, (d) locate areas of the system with undocumented capacity limitations. The presentation will also seek to demonstrate how the improvements to the system representation in the sewer system hydraulic model can yield significant savings in ancillary condition assessment efforts, flow metering and more efficient investment in CIP projects. Primary Topics of Discussion - Accelerated model development strategy - Coordination with asset management database - Overcoming challenges of COVID-19 through virtual collaboration - Network connectivity review through model calibration - Model applications beyond capacity analysis Presentation Benefits This paper and presentation will illustrate how careful and detailed hydraulic modeling can contribute to a municipality's knowledge of their collection system. The presentation will provide specific examples of cases where use of the hydraulic model led to details about the collection system that were not previously known. Specific benefits include: - Providing an overview of pioneering sewer CIP work in the host City of Detroit to showcase how each of the utility CIP objectives align with applications of the sewer system hydraulic model. Explaining the approach implemented by DWSD to overcome challenges of developing hydraulic model on accelerated schedule and review lessons learned from the model development process that can be applied by other utilities pursuing similar projects. - Understanding alternate benefits for investment in development of hydraulic model to help build a business case for spending in development or enhancement of similar planning tools by utilities. - Examining benefits of cross collaboration between condition assessment and planning teams and understand the efficiencies and challenges that result from implementing integrated databases by utilities for both asset management and hydraulic modeling. - Understanding value of additional refinement of hydraulic models that are used as planning tools by utilities and how more accurate models lead to identification of areas with high benefit/investment ratio for evaluation as part of CIP projects. - Sharing lessons learned from working 100% through virtual collaboration including staff collaboration, coordination of field support and staff training to overcome challenges due to COVID-19. Status of Completion The development of the sewer system hydraulic model for DWSD's system was completed in July 2020. However, additional refinement of network connectivity and overall system operation representation will continue as a result of conditions assessment effort, local flow monitoring for CIP projects and additional system calibration. Learning Outcomes / Conclusion This presentation will provide the audience with benefits that are not often considered for investment in hydraulic modeling and model development through the lessons learned as part of the DWSD's Capital Improvement Program Management Organization project. The presentation will also review some of the challenges that are common when developing hydraulic models and will demonstrate the processes that DWSD implemented to address such challenges.