Trevor English
Tasked with protecting and maintaining the largest river basin entirely within the state of Texas, the Trinity River Authority (TRA) has its work cut out for them. In the northern region of the Trinity River Basin, TRA operates five major wastewater collection and treatment systems serving municipalities in one of the fastest-growing metropolitan areas in the United States. This responsibility requires a combination of keeping an eye on the future and a firm grip on the development and implementation of operational improvements in the present. One way they do that is by relying on hydraulic models as digital twins of their working systems.
The importance of RDII in wastewater operations
Sanitary sewer systems are, by design, closed systems. This means that, in theory, these wastewater systems shouldn’t be influenced by weather events like rain. However, any water or wastewater professional knows that this isn’t the case. Rainfall Derived Inflow and Infiltration (RDII) can drastically affect wastewater operations.
TRA works directly with their customer cities, providing annual reports of RDII and running near continuous master planning updates across their basins. Each basin is different, of course. For example, one unique issue with RDII is observed in the southwestern Dallas-Fort Worth (DFW) Red Oak Creek sewer basin. Specifically, this basin experiences extremely long wet weather tails or heightened flow rates for an extended period of time after a storm, increasing the overall volume in need of treatment resulting in operational challenges and unpredictability in sewer loading.
Correctly modeling and planning for these prolonged flow rates has been a primary focus of the TRA Planning Design and Construction Administration (PDCA) group. The PDCA works alongside field, treatment and engineering staff to ensure the effective use of funds, efficiency in operations, longevity in capital improvements, and an accurate hydraulic representation of their modeled wastewater systems. In keeping with these goals, the planning team performed an in-house master plan of their Red Oak Basin using InfoWorks ICM.
Holy grail: modeling RDII in real time
“Let’s say it’s been raining for two weeks,” posits TRA Modeling Analyst Andrew “AJ” Czubai. “How big of a storm can we handle right now?” Without a proper hydraulic model, answering this important question involves quite a bit of guesswork. However, by being data-driven with their process, PDCA knows they can answer this question empirically. The team blocked off a few months to tackle the best approach for studying and replicating the RDII issues in these two systems.
The Red Oak Creek Regional Wastewater System (ROCRWS) in the southwestern part of the greater Dallas-Fort Worth area experiences abnormally long rainfall responses. Even in dry conditions, a small 1-inch rain event is enough to elevate average flows up to 20% for up to a week before flows return to their normal average daily flow. The effect is noticeably worse when antecedent conditions are saturated from a previous “soaking event” or heavy storm.
The core of how TRA approached the problem was understanding peak flow rates and accurately modeling flow. “On the collection side, we tend to focus on the peak flow rates a pipe can convey, which is a driver for costing and project sizing,” AJ explains. “However, prolonged elevated flows for a few weeks also impact the overall volume of flow that needs to be treated, which means additional chemical costs, heavier run time on pumps, and potential permit violations if not anticipated. By being able to estimate future wet weather volumes, you’re able to plan for and adjust your treatment strategy.”
The TRA team successfully modeled the ROCRWS system inside InfoWorks ICM and calibrated a model with a simulated duration of 2 months using the InfoWorks ICM Ground Infiltration Model. The team utilized data from the 20 distributed temporary flow meters and made the necessary modifications to match the modeled and observed conditions.
The graph in the image above shows a basin successfully calibrated to a simulated 2-month model duration using a Ground Infiltration Model. The red line represents simulation results with the same input data as the other lines but using only runoff surfaces. While it can match some of the peaks seen throughout the monitoring period, the inflow quickly returns to normal after the peak Inflow and Infiltration (I&I) has subsided. The dark blue line represents the runoff surface simulation results coupled with a ground infiltration event. Many of the peaks match closely to the observed conditions. Still, more importantly, the prolonged flows following rain events are better represented, allowing for observed flow volume versus modeled volume to be within 3% over a simulated 2-month period in some basins. While it is true that not all peaks match, TRA planning is confident that with additional refinement, the model will continue to improve.
With the observed conditions in the model to within 3% of modeled volumes inside of InfoWorks ICM, the planning team could begin to run simulations on current or future network conditions and leverage the model to coordinate with plant operators about anticipated flows in real time, something modelers often strive for but don’t always realize. “I felt like I had witnessed a mythological creature, something modelers only whisper about,” says Assistant Manager of Planning and design Nick Dons on real-time analysis. “Having this kind of capability is something that is often sought after in our industry but rarely found.”
The ROCRWS system is in the process of designing and constructing peak flow storage facilities to mitigate peak wet weather flows. The planning team intends to use the results of the extended wet weather model to determine optimal storage flow diversion and draining and anticipate any need for expansion. Effective wet weather modeling gives TRA the tools needed to plan for and mitigate the impact of current and future wet weather on both the collection and treatment facilities in ROCRWS.
Innovation should include ‘time to learn more’
The outcomes of this project are significant for the operations, maintenance, and planning of wastewater systems. With their workflows defined, TRA is now equipped to build these models for other systems in the Trinity River Basin. None of this would have happened without the forward-thinking, innovation-focused culture that TRA fosters. AJ and his team have fostered an environment of continuous growth and improvement, and leveraging the groundwater modeling capabilities in InfoWorks ICM in this project is the next logical step toward building a more comprehensive approach to building and maintaining meaningful hydraulic models for TRA.
AJ has worked for other government entities and sees something special at TRA. “In other places, you make a model, hand it off, and it’s not your thing anymore. What the planning team at TRA is doing is innovative. We are constantly evolving the methods for building, developing, and maintaining our models and utilizing all available tools to make impactful and real-world decisions.”
This culture of innovation means that taking a month or two to solve an important challenge and invent new workflows is possible. TRA’s management puts a lot of trust in their planning team, and this trust is reflected in these kinds of outcomes. “Many companies would benefit significantly from taking time to allow their teams to learn new ways of working,” AJ believes. Indeed, taking time to learn should be part of every water modeler’s day-to-day work. In the case of TRA, that “time to learn more” resulted in significant operational efficiency improvements, easily justifying the initial effort.
While consistently building, refining, and maintaining their models, TRA continues to monitor how the RDII impacts their systems and make adjustments as new basins come up for planning. Looking forward, they want to utilize their InfoWorks ICM model to maximize their capital planning decisions.
Models aren’t just for initial planning
Before joining Autodesk, Senior Support Engineer Mel Meng actually worked with TRA on this project. In fact, as a former consultant, he helped design their initial model and sees their continued development of their models as a smart move. “Too often, models are built only for planning purposes, usually to size the pipes and for treatment facilities to handle peak flow during large storms,” says Meng. “Planning consultants may look at a model like this as a significant initial investment, but they don’t often think about how the utility can keep realizing value from that investment.”
“What TRA’s in-house team demonstrated is very exciting. With a dedicated small team, they were able to leverage their existing investment to achieve great results helping their treatment plant operators gain more insight into how the system works and making it easier for them to make better decisions.”
While engineering consultants often play a vital role in jump-starting these processes, going deeper with their in-house model is helping TRA not only understand where they are going but also assists in understanding turn-by-turn what to do to get there.
“As a former consultant who worked on this particular model, I feel great. I know my work still matters, years after it was done,” says Meng. “It’s more than just a report collecting dust on a shelf.”
Since he was so familiar with the area, Meng also served as the internal Autodesk liaison to the TRA team during the project. The team undertook the learning process themselves, but they had access to knowledgeable support engineers like Mel.
Delivering impactful outcomes
InfoWorks ICM continues to be an invaluable tool for organizations like TRA, and this project demonstrated a few core outcomes for those who want to get the most out of their hydraulic models:
- Deep modeling can be done in-house: TRA conducted all the work internally, including managing the flow monitoring and modeling, and were able to do so in a relatively short time span. This speaks to the prowess of the team of modelers at TRA, thanks in no little part to the knowledge of the senior staff, most of whom also have modeling skills.
- Planning and operations can stay connected: TRA clearly demonstrated in this project that by creating and leveraging an accurate hydraulic model, modern modelers can rely on this data to make planning and capital planning decisions and help plant workers operate more efficiently and effectively.
- You are in good hands: At no point during the process was TRA alone. They were able to embark into uncharted waters with Autodesk’s industry-experienced support staff, who were able to jump in on the project and work hand-in-hand with the modelers at TRA.
Owing to their commitment to innovation and technology, Trinity River Authority has built a rock-solid process for extending their hydraulic modeling capabilities to ensure they aren’t just using their models for initial planning but anytime they want to answer an internal question about the feasibility or results of proposed operational improvements. They took the time to create a robust digital twin and are reaping the benefits of digital collaboration, which they can apply to additional watersheds.
Will the Texas population keep growing at its rapid pace? Will climate change drop more unexpected 100-year storms on what has long been called Flash Flood Alley? All signs point to increases in nearly every challenging metric that watershed managers like the Texas River Authority will need to stay on top of to meet the challenges of the future, but TRA has expert modelers on staff, access to the best digital twin technologies, and a reputation as innovators. They’re ready.
Go deeper into the story
- Mel and AJ worked on a short study together, Enhancing Treatment Plant Operations with Digital Twin Technologies at Texas Water 2024, with practical use cases of AI and digital twins in water operations and management.
- Digital twins are being used more and more to protect other fast-growing cities in Texas. Read our story Mapping ‘Flash Flood Alley’: LAN built a digital twin hydraulic model for the city of San Marcos.