GIS data analytics are a vital component in stormwater management—whether a stormwater manager is incorporating that date into a complete software package such as ArcGIS, or modeling that data within one’s in-house stormwater modelling program. GIS data and stormwater modeling applications are many with one such example is the utilization in mapping potential stormwater and wastewater sources, such as CSO locations.
Modeling Software Systems (Part 1) By Carol Brzozowski
In King County, WA, modeling software is being used to address 19 combined sewer overflow (CSO) locations that are not controlled to the state standard of one event per year, says Bob Swarner, supervisor of the Modeling and GIS group for the Wastewater Treatment Division of the county’s Department of Natural Resources and Parks.
“We’re under a consent decree from EPA and our state Department of Ecology to finish those projects to bring them all under control by 2030,” he says.
The county system’s conveyance pipes total about 355 miles, with about 10 times that amount of pipe draining into them from local systems, Swarner says.
Although there is a separate section in King County’s Wastewater Treatment Division that handles stormwater, Swarner’s group is involved in the combined sewer system section and is responsible for simulating the stormwater as it gets into the combined sewer pipes.
To accomplish the goal of getting the projects finished by 2030, Swarner and his team are using software from DHI to create models to simulate how much rainfall runoff and infiltration from the soil gets into the pipes, and they perform long-term simulations to figure out what size control facilities are needed to control the combined sewer overflows to one event per year at each location.
As a result of the effort, King County has planned two “fairly large” treatment plants for stormwater-related treatment, nine storage projects, one conveyance project, and three green infrastructure projects, one of which is now under construction, Swarner notes.
The city of Seattle also has several CSOs that are not controlled to one event per year and is using stormwater software to help bring those under control, Swarner adds.
“We are using software to simulate what the existing system does, what it would be under our proposed facilities, and what will happen under the city’s proposed CSO projects,” he says.
Historically, King County has been using DHI’s MOUSE, MOdel for Urban SEwers, a computer program designed to model urban wastewater and stormwater collection systems. Presently, the county is moving to MIKE URBAN to keep current with software developments.
MIKE URBAN is an urban water modeling software that is designed to be user-friendly and accommodate workflow, openness, flexibility and GIS data integration, physical soundness, efficiency, and stability of simulation engines. It covers all water in the city, including stormwater drainage systems. It includes two-dimensional overland flow, combined or separate sewer systems, and water distribution systems. MIKE URBAN completely integrates GIS and water modeling. MIKE URBAN modules address such issues as rainfall and runoff, pipe flow, control, overland flow, pollution transport and biological processes.
At one time, King County was using in-house software. “The reason we originally went with the DHI software is because we were applying this to our separated sewer system, and the MOUSE software had a really good ability to characterize inflow and infiltration in a separated system, which is largely long-term and rapid infiltration,” says Swarner. “We’ve had quite a bit of success over the last 10 years of modeling with that, so we’ve decided to apply that same model to our combined system and found we’re getting really good results with that as well.”
Swarner notes that with the software, there is a definite learning curve, especially on the variable infiltration module. “We found it works really well once you come off the learning curve,” he adds.
The ability to simulate varying infiltration rates into pipes is very important, as that “can be the most significant portion of a hydrograph,” notes Swarner. “What’s important is to get good software that can simulate that well if that is a prevalent response to your system,” he says. “It’s also important to find software that has a lot of control flexibility in the way you can control hydraulic structures as well as a good computational engine, which is important for any model.”
