Cities across the globe historically have viewed stormwater as a public nuisance that causes damaging floods and spreads pollution. This view stands to only worsen in the new age of rising sea levels and increasingly severe and frequent extreme weather events.

That’s because most cities have relied on functional but flawed "gray infrastructure," according to Autodesk’s Brian Young, speaking during a recent GreenBiz Webinar on green infrastructure and the triple bottom line.

"Where it solely used to be about gray infrastructure systems like centralized pipes and tunnels, those worked great in effectively draining cities but did cause some pollution and erosion issues," he said. Autodesk sponsored the webinar.

In an effort to become more resilient in the face of mounting climate change impacts, cities across the globe are changing from gray to so-called "green infrastructure," which includes everything from swales to green roofs and permeable pavement that absorbs, filters and collect stormwater where it falls.

Rather than viewing stormwater as a liability, cities are beginning to treat it as a resource — something to be absorbed, to replenish groundwaters or even reuse. This allows cities to relieve the burden downstream, and also introduces some social and environmental benefits as well.

Stormwater problems in the capital

Stormwater is a particularly tough challenge for older East Coast cities such as Washington, D.C., which rely on combined sewer systems. Heavy rains often cause sewage to overflow and contaminate waterways.

Sustainable DC, the District’s comprehensive sustainability plan, in 2012 established the goal of using 75 percent of its landscape to capture stormwater, as well as increasing wetland acreage around rivers by 50 percent and covering 40 percent of the city with a healthy tree canopy.

But the District also is under a U.S. Department of Justice order to fix it with massive capture tunnels and remediation. The price tag is $1.8 billion for the initial phase, which is being passed on to ratepayers and property owners.

"That’s a major bill for everyone to be able to absorb, but there are a number of incentives and creative ways that the city has been able to help property owners deal with that," said Scott Pomeroy from the Downtown DC Business Improvement Project (BID), which the District has partnered with to implement green infrastructure pilot projects.

Rather than viewing stormwater as a liability, cities are beginning to treat it as a resource — something to be absorbed, to replenish groundwaters or even reuse.

The RiverSmart Rewards Program and the Stormwater Retention Credit Trading Program provide economic incentives for homeowners to invest in green infrastructure such as green roofs and rain barrels.

Autodesk tech helps prioritize projects

Not all of these projects are court-mandated and, with so many green infrastructure options, how can cities and private companies alike know which ones to pursue? Autodesk "has an app for that," so to speak.

BID partnered with Autodesk to revitalize and manage the stormwater runoff in Franklin Park, a dilapidated D.C. greenspace.

Autodesk’s Infraworks 360 combines 3D modeling tools with an analysis dashboard that shows in real time the changes being made, and how it will affect hydrological performance.

Traditional design approaches involve developers and engineers creating a site layout, and then bringing in the stormwater person to make sure it all holds up to code — but this can be expensive and inefficient when the two steps come into conflict.

"Autodesk has tried to combine those steps so with each design decision you can get immediate feedback as to whether you’re getting closer or further from meeting those stormwater regulations, which should lead to less conflict down the line," said Autodesk’s Young.

The tool uses a Google Maps-like interface, where users can type in address and go to an area of interest to model. In five minutes or less, the users are delivered a model that has 3D building data with terrain and road and image data. Anyone who knows how to navigate a map can easily avail themselves of this tool, Young said.

For the Franklin Park project, Autodesk’s tool allowed planners to tinker in real-time with the various options for optimizing stormwater retention in the green space.

"For engineering teams we saw in the Franklin Park example, you can design very quickly, you can sketch a land area, you can sketch a building and immediately see how that affects your performance relative to the local regulations," Young said.

And the tool also is useful on a larger scale, according to Young. Its dashboard allows users to toggle percentage of land area and buildings used for various green options.

"It’s a very simple and easy way to consider what combination of trees or fire retention or green roofs you might be able to consider to be able to accomplish your ambitious goals around stormwater retention at the district scale," he said.

This does not, however, replace the heavy duty civil engineering that needs to take place once projects enter the design phase — it simply makes green infrastructure much more accessible up front in the initial planning phase.

"It is all about integrating the analysis as part of the early stage site layout so this green infrastructure elements are not an afterthought."

Green infrastructure and the triple bottom line

It’s no secret that many cities’ budgets already are stretched thin, which can make it difficult to justify green infrastructure projects using traditional cost-benefit analysis.

This is where "Triple Bottom Line analysis" can help, which quantifies in dollar value the social, environmental and economic impacts associated with projects, according to Impact Infrastructure’s Ryan Meyers during the webinar.

The company has developed a web-based valuation tool called Autocase, which produces risk-adjusted, dollar-based metrics for infrastructure projects and buildings based on their costs, benefits and sustainable design features. The tool can be used as an add-on with Autodesk’s Infraworks 360 to give real-time feedback about how to design a project cost-effectively and how much social and economic benefit it’s creating for the region.

The district used Autocase with a massive project to improve stormwater management on the iconic Capitol Mall. Using the tool, planners were able to come with a design that included an underground parking structure that doubles as a cistern to capture water, and helps with irrigation. Although having a dual purpose led to higher costs, but the triple bottom line analysis showed there were greater long-term benefits.

For the National Mall project, the primary benefits are reduced flood risk, which lead to lower costs from strong storm events, less risk to local business activity and environmental benefits.

"Essentially what this leads to is a project that on the surface would seem more expensive and less appealing, but is actually more beneficial," Meyers said.