What Cities Should Consider When Choosing Stormwater Capital Planning Software
About the Speakers
Marc Leisenring, P.E., is a Senior Principal Water Resources Engineer based in Oregon with more than 20 years of experience focused on stormwater master planning, watershed and storm system modeling, environmental data analysis, regulatory compliance, and water quality management.
Jamie Feldman, P.E., is a stormwater engineer who specializes in hydrologic and hydraulic modeling, as well as geospatial, hydrologic, and water quality data analysis and visualization.
Mike Du Bose, E.I.T., is a water resources professional who specializes in stream restoration, hydraulic and hydrologic model development and calibration, water quality data analysis, stormwater BMP modeling and analysis, and field monitoring.
Let’s start with the basics. How are capital projects typically planned?
A stormwater capital improvement program is often driven by a hydraulic model. This is a computer model that simulates the flow of stormwater through a drainage system. It’s used to evaluate the capacity of the system to handle different size rainfall events.
The hydraulic model is first run using the existing conditions. This helps to identify any capacity issues that may exist during different design storms and the most critical capacity issues within the system.
Once those issues have been identified, the next step is to develop solutions to address them. It’s a very iterative process. The best solution will depend on a number of factors, such as the cost, the feasibility of construction, things like that. And those solutions become the basis for your CIP list.
Outside of what they find through modeling, what do cities consider when planning stormwater capital projects?
Some projects are developed directly from asset management systems that track information, like the condition of the pipes themselves, which are typically determined through TV inspections. There could also be some physical inspections that are done for larger structures where somebody might be able to get down into a pipe. It could also be based on observed flooding, like complaints from residents or from city workers who have identified locations and know where flooding happens during storm events.
A specific CIP project objective that comes to mind for me is reducing the risk of pipe failure. A pipe could fail because it has been overloaded with too much water or is outside of its service life.
Another thing that comes to mind is that ancillary benefits can be achieved through green stormwater infrastructure, both socially and for the ecosystem.
That’s true. And if I can expand on that, Jamie, the benefit of green infrastructure is something that many communities are increasingly looking at, whether it’s ecological uplift, environmental justice, carbon neutrality, climate resilience. All of those things are helping cities meet their larger sustainability and equity goals.
So yeah, I think it goes beyond the conveyance network and what we think of when we talk about green and gray infrastructure. Urban streams are also an important resource for cities, and they are increasingly being included as part of their assets. Not just a natural water body, but a valued City asset.
Going back to modeling, what kind of software and expertise are generally needed to develop a capital improvement program?
The most important piece of software to have for this process is something that can do the hydraulic and hydrologic modeling of the system, so you can quantify the problems and the benefits of the alternatives that you're evaluating. The software that might be used for that is SWMM, whether that's XPSWMM, EPASWMM, or PCSWMM. There's other software too like InfoWorks and various other hydrologic and hydraulic models that are well suited for urban environments.
It sounds like they have a lot of options. How do cities choose among those different modeling software platforms?
Yeah, there are a variety of factors. Could be what software works well with their existing in-house system that manages their assets, what kind integration they have between platforms, and also which is best suited for the long-term maintenance and management of the system data itself.
Money and the type of collections systems you have are big factors, too. For example, smaller municipalities might choose EPASWMM over Infoworks ICM, which is more user friendly but also more expensive and potentially better suited for combined sewer systems.
How do you balance the relative value of these assets against achieving their stormwater goals?
Monetizing the value of these benefits is probably the most challenging part of capital planning. We use a triple-bottom-line analysis to assign monetary value to these factors, like ecological uplift and improvement in air quality.
For example, we recently worked with the City of Calgary to develop a triple bottom line that included different cost factors like the air quality improvement from planting trees. And we had used some data that was able to link the tree canopy and a reduction in a PM 2.5. Those are the very fine particles that that could cause asthma and other health risks to the society.
PM 2.5 are the particles associated with wildfire smoke, right?
That’s right. And so with the triple-bottom-line analysis, we were able look at the health impacts from PM 2.5 to give the trees and other green infrastructure some kind of quantifiable, monetary value.
One of the best platforms we’ve discussed is the flexibility to add those values. Similar to how Jamie was just talking about mortality risk of pipes and capacity risk of the network, you assign a monetary value so it can be an objective that you're tracking for different capital improvement alternatives.
Air quality from wildfire smoke is one thing, but how do cities assign value to the more traditional stormwater improvements?
I’ll turn this to Mike, because he had quite a bit of recent experience with the City of Portland and the tools they developed for looking at the risk of basement sewer backups.
Mike Du Bose
Yeah, so I’ve been working with the City to quantify the capacity issues that can lead to flooded residential basements and manholes in the streets. I worked with some of the City’s modeling tools to track where these flooded basements and streets occur.
The City evaluates basement flooding at the property level for different design storms. We use the City’s cost estimator tools that assign penalties based on the number of backups and the modeled design storm to estimate the capacity risk. If your model is giving you results where a property is having water backing up into it after a 2-year design storm, there's going to be a much higher penalty in the decision-making framework versus a 25-year design storm.
And the reason that a 2-year design storm has a higher risk profile than a 25-year design storm is because its probability of occurrence. So, risk is defined by the probability of occurrence times the consequence of that occurring. The consequence of a basement flooding is going to have the same cost, but the probability differs. And so, the risk profile is much higher when you have those more frequent design storms occurring.
By using a risk-based framework, we can look at this over a longer planning horizon and see the life-cycle costs and risks associated with our decisions. And those decisions are the capital improvement projects. If you feed that kind of risk information into a model like Optimizer, as well as the cost for the improvements, it allows you to balance that risk versus cost in a formulaic, but comprehensive way.
Expanding on this, there were a few key criteria that were used to evaluate Portland’s system. On big arterial streets, the consequence of manhole flooding is assumed to be higher than on small residential streets. Therefore, both the location of flooding and the probability of flooding were considered when estimating the capacity risk.
So, capacity risk was a big concern but so was the pipe mortality risk. The questions became: How do you quantify the benefit of replacing a pipe in a given area that might have been in poor shape and needing rehabilitation? And how does this benefit the system overall in terms of the long-term reduction in risk of any kind of failure for that line?
Those are the things that we were largely considering for the system performance evaluation criteria. And things that informed options for improvements. For example, one improvement the City wanted, was to intercept the stormwater before it even gets into the system. And going back to green infrastructure, green street projects are a great way to do this.
Another way is to work with land and property owners on alternatives that divert stormwater to different areas on their property to infiltrate, as opposed to entering the storm drain system. The City refers to this as their Private Property Retrofit Program.
Taking a step back. Marc, you mentioned running risk information through Optimizer™. What is that?
Optimizer™ is a decision-support platform from a company called Optimatics that uses genetic algorithms and cloud-based computing to evaluate hundreds of thousands of potential solutions to identify capital improvement projects while balancing multiple user-defined objectives. After the platform is set up, it can be used to develop projects, update, and reevaluate after projects have been completed.
It can effectively help cities get away from the 5- to 10-year planning cycle and create a continuous framework for a living CIP program.
I mean, I can imagine the benefit of that given our recent economic climate. Having a kind of living CIP with those costs built-in allows public works staff to be a bit more confident when creating their yearly budget projections.
That’s true. Another benefit is being able to do these things faster and more efficiently. Because if you wanted to balance the number of objectives we mentioned, and you were just using a hydrologic and hydraulic model and you had enough of an understanding of your goals to do some additional processing on your own. But you’d have to run hundreds of models. You might be able to get there eventually, working through different scenarios to narrow in on something that seemed promising, but this just helps you get there a lot faster and get better answers.
So, I think that the sheer computational power of it, in tandem with the sort of genetic algorithm that it uses, is really pivotal.
Yeah, I agree with that. Particularly for the stormwater program at the City of Portland, that has a group of very talented, sophisticated staff. They weren’t starting from zero. When we first started helping them, the City already had a detailed hydraulic model and a robust asset management program, plus all these costing tools like Mike mentioned.
So, the question for them was how they could still use these tools, all these inputs, be consistent with what they’ve done in the past, and reach these greater objectives. With a platform like Optimizer™, we were able to create a framework with customized scripts specifically for the City that organized their current tools and methods into that living system plan.
It’s a work in progress but they will be able to be far more efficient. They can regenerate their CIP list kind of continuously and not be stuck to a ten-year planning cycle.
Sticking with being a public works official for a moment. Your staff has varying levels of technical expertise, how easy is a platform like Optimizer™ to use?
It is fairly intuitive to use. Very flexible and customizable. But you do need to have a solid foundation in hydraulic modeling to know what those models are doing and how to interpret those outputs. It also helps to have a basic understanding of optimization theory, which is a concept we haven’t quite discussed yet.
Give me your best breakdown.
To work with a platform like Optimizer™, you need to know what the model is doing and how to interpret those outputs. Developing the inputs and setting up the platform for the first time can be challenging, but after you’ve done that, you can develop a decision-making framework that includes your objectives. This is what we’ve been doing with the City of Portland.
Part of that framework is what we call your decision space, which is the realm of alternatives you want Optimizer™ to iterate through. And this is where the platform is very powerful, since it can help you work through tens of thousands of potential solutions or even hundreds of thousands of potential capital projects to meet your objectives.
So, how do you decide on a CIP program, especially when you want to minimize cost and risk? This is where optimization theory comes in. In optimization theory, when you have multiple objectives, you can create a scatter plot called a Pareto frontier, which shows the optimal balance of your objectives. Each point on the Pareto frontier represents a potential solution.
The more objectives you have, the more axes and the more multidimensional the Pareto frontier becomes. But this also gives you more flexibility. You can adjust the importance of different objectives to find the solution that best meets your needs. For example, you might say that minimizing cost is the most important objective. But you might also want to minimize risk. In this case, you could look for a project on the Pareto frontier that has a low cost and a low risk.
Of course, there is no one-size-fits-all solution. The best way to use optimization theory depends on your specific problem. But it can be a powerful tool for making decisions that minimize cost and risk while also considering other potential objectives.
What are some tips or steps that you'd give to cities that are new and interested in capital improvement planning platforms like Optimizer™?
Mike Du Bose
It’s helpful to be able to explain the environmental and financial benefits of green infrastructure projects. You might have the dollar amount of the cost and maintenance of a green street, but it’s better to have a framework for the monetary benefit that you get from the capacity reduction and infiltrating that water directly into the soil.
And some communities may not even have the basic cost information such as unit costs for different pipe diameters and construction depths. Given certain site constraints, having a database of that construction cost information would be extremely valuable. And it doesn’t have to be a city-specific database. You can get that information from bid tabulations of departments of transportation or from subscription-based commercial databases.
The other thing to have, particularly if you’re looking at mortality risk, is an asset management system and having those maintenance costs and the condition of your assets already understood. We didn't mention GIS earlier, but that is a fundamental software that's used here.
Mike Du Bose
That’s true. Having a GIS asset management tool is important to be able to visualize and explain the results from Optimizer. For example, the City of Portland has EMGAATs, which stands for Explicit Model Generator, Analysis, and Alternative Tool Set. It’s an alternative toolbox they developed for ArcGIS. Basically, you extract results from whatever model you are using, whether its XPSWMM or EPASWMM, and see how these decisions affect basement backups, flooded manholes, or other capacity issues that you're looking at. It allows them to very flexible in terms of updating or grouping an entire block of houses to make a decision, as opposed to going to an individual property-by-property decision basis.
One thing that's been really amazing is the support provided by the platform developer, Optimatics. They're absolutely willing to sit down and teach you how something works or how to formulate an optimization problem.
I’d also suggest having workshops with staff. We’ve conducted one for the City of Portland with Optimizer™ and you know, helping people actually step through the tool and understand how to engage and interact with it. It’s a great way for staff to learn about optimization theory as well as the practical application of how to do it.
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