Indigenous Fine-Scale Modeling: Innovating Houston's Wastewater Management

Background Metropolitan areas are prone to several challenges in the wake of rapid urbanization and climate change impacts. Aging wastewater infrastructures have been overburdened in many cities globally, causing increase in Sanitary Sewer Overflows (SSOs) under rainfall events mainly due to inflow and infiltration. To overcome this situation, a robust modelling approach is required, enabling exact determination of SSOs and identifying sewers with capacity limitations. Moreover, by simulating various scenarios, the model can suggest optimal configurations of the network, which may include resizing pipes, modifying slopes, or changing operational strategies to enhance system efficiency. Study Area Houston, one of the fastest-growing cities in the USA, is confronted with significant challenges in managing the increasing demands on its wastewater infrastructure. With a population of approximately 2.5 million and a daily wastewater generation of around 250 million gallons, the city relies on 38 wastewater treatment plants owned by the City of Houston (COH) to handle and treat this vast volume. Each plant is assigned to a specific service area, with associated pipe networks collecting the wastewater. However, the growing demands, fluctuating water consumption, variable weather patterns, and evolving land use exacerbate the difficulties in maintaining these collection systems. Methodology Initially, Houston's Wastewater Collection System model in Info-Works ICM software included 10-inches and larger pipes and associated infrastructures. However, overflows in areas served by smaller diameter pipes and redevelopment happening in already stressed areas required attention to more granular level. To address these challenges, COH started using in-house developed customized SWMM model for small diameters pipes in the basin level using City's discharge criteria and generalized derived RTK parameters. Recently, City focused on the development of high-resolution dynamic models capturing the flows at parcel level for sewer basins using Info-works ICM software. These models replicate the physical network infrastructure, including gravity mains, force mains, lift stations, manholes, weirs, etc., based on comprehensive data sources such as as-built drawings, field surveys, engineering estimates, and lidar data. These models employ advanced techniques to enhance wastewater management and system accuracy. They incorporate the Groundwater Infiltration (GWI) model in ICM to accurately assess and quantify infiltration into the sewer network. This methodology is vital for identifying vulnerable points where groundwater enters the system, allowing for targeted infrastructure improvements and maintenance scheduling. Additionally, the model replicates pump operations by leveraging extensive SCADA (Supervisory Control and Data Acquisition) data. This approach ensures that the simulation of pump behaviors closely mirrors real-world conditions, enabling more precise management of flow dynamics within the network. By integrating real-time operational data, our model optimizes the performance and reliability of pump stations, directly impacting overall system efficiency and reducing the risk of overflows and system failures. For sewer basins with potential capacity issues, additional flow monitors are added in the system, and models are updated and re-calibrated to ensure the models reflect the latest data from strategically placed flowmeters, capturing variations in flow under dry, wet, and extreme conditions. Presently, many high-priority sewer basina models are being updated with latest data. Dry weather calibrations focus on flow unaffected by rainfall, while wet weather calibrations are essential for evaluating network capacities by aligning with peak flows and groundwater inflows during rain events. The model results are evaluated against the tolerance limits of +20% and -10% for flow volume, +10% and -10% for baseflow and +25% and -15% for peak flow during rain event. Once calibrated, these models facilitate predictive analysis of future flow scenarios, thereby enhancing the COHs preparedness and resilience. Results The fine-scale ICM modelling offers a fine-grained approach to managing wastewater networks by providing detailed simulations at the individual parcel. This high-resolution modeling enables precise detection of SSOs, identification of surcharged pipes, and comprehensive assessment of system performance under various conditions. By assigning flow directly from each parcel based on specific land use and occupancy data, the model surpasses the capabilities of lower-resolution models, which often rely on aggregated or averaged data inputs. Consequently, these models deliver significant advantages in terms of reliability, predictive accuracy, and the granularity of data available for decision-making compared to more traditional, less detailed models, thereby, playing a pivotal role in proactive infrastructure management and strategic planning to address Houston's growing needs. Future Work For future, these models will be equipped to utilize real-time data, enabling dynamic and responsive management of wastewater systems. By continuously integrating data from sensors and SCADA systems, these models will provide up-to-the-minute simulations of network conditions, allowing for immediate adjustments in operations and emergency responses. Additionally, automated processes for data validation and error checking will be implemented to maintain the integrity and reliability of model outputs. This approach will not only optimize system efficiency but also enhance the predictive capabilities of the models, leading to more informed decision-making and improved system resilience in the future.