Holding Back the Flood

A candid conversation with a stormwater expert on the real-world impact of green infrastructure—what works and what doesn’t

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Many developers have increasingly turned to green infrastructure—bioretention ponds, dry wells for roof runoff, and other engineered systems—to support new housing developments without exacerbating runoff and putting nearby properties at risk. But how effective are these solutions?

That question set me on a path that eventually led to the University of Maryland—and to Dr. Adel Shirmohammadi, a professor of water resources and environmental engineering in the Department of the Environmental Science and Technology. A widely respected expert in hydrologic modeling and watershed management, Dr. Shirmohammadi graciously made time for a phone interview with The Joy of Ptap.

His work centers on understanding how stormwater flows through both urban and agricultural landscapes, and on developing decision support tools that help communities make data-informed choices to manage runoff and protect water quality.

He began by saying, 'I have to say, I don’t normally do community extension work, but I try to help if I can find time' which made me all the more grateful that he agreed to do an interview.

You grew up on a farm. Did that influence your path to water resources and environmental engineering?

Well, a lot of it starts with growing up in a poor farming community. Farms in most countries around the world aren’t like those in the U.S. I got my education in Nebraska, where farmers sometimes own 5,000 or 6,000 acres of land. My family had about 24 or 25 acres. At that time, you don’t really think about environmental stuff—you’re more focused on whether you can grow food, basically just trying to survive. That’s the difference between farming in poor or developing countries and farming in the U.S.

I spent 13 years working on watershed monitoring in Frederick County, funded by the US-EPA. I worked with a lot of farmers and served on the Scientific and Technical Advisory Committee (STAC) for the Chesapeake Bay. I’ve also been a member of the National Academy of Sciences’ Committee, which reviewed the Chesapeake Bay’s progress over thirty years and provided recommendations. I just wanted to give you a lay of the land when it comes to my background.

From my understanding, you're serving the community by providing information such as this interview write up. There are people I can put you in touch with—people responsible for watershed restoration in Western Maryland, including Howard County. These are expert agents of our University of Maryland Extension who are on-the-ground people who really know what’s happening in the community—what’s been done and who’s involved. I think speaking with them would be helpful for you.

That’s great. When we’re done, please share their contact information.

Part of why I wanted to talk with you is to better understand how effective solutions like dry wells for roof runoff and bioretention ponds really are when it comes to managing stormwater.

Joy, that’s—how should I say it—a very good question. I get asked that a lot, and honestly, we don’t always have exact answers. But I’ll explain what’s going on.

The Chesapeake Watershed Modeling group has its own office in Annapolis, and I have worked with them closely through the Scientific and Technical Advisory Committee—STAC. They basically run the Chesapeake Watershed Model on background data, and then they say, okay, we need to reduce this much nitrogen, this much phosphorus, this much suspended solids from different states within the Chesapeake watershed. So that includes the state of Maryland. In that regard, they work with state agencies such as the Maryland Department of the Environment, Maryland Department of Agriculture, Maryland Department of Natural Resources, and Maryland researchers to get a good grasp of the effectiveness of what these BMPs are.

(BMPs stands for Best Management Practices. In a watershed these are methods, practices, or structural controls designed to protect water quality and manage stormwater runoff. We have non-structural and structural BMPs that each category and or a combination of them may be implemented to respond to the stormwater management and water quality issues.)

Sometimes you do research on a small scale, so you come up with approximations. Because when land use changes—and with the climate changing, as you know, it’s been changing drastically—you really don’t have exact numbers. However, we’ve done a lot of systems level modeling. We look at those models and say, well, you know, in urban areas, for example, one of the things they’ve started doing is trying to reduce the pollutants going into the Bay by implementing green BMPs (bio-retentions, roof runoff management, etc.).

They also may select to 1) retrofit and modify the existing wastewater treatment plants (a structural BMP), and 2) implement green infrastructure.

For folks who might not be familiar, what are green infrastructures?

In other words, environmentally friendly systems. One of those could be roof runoff management. How do you manage the roof runoff? If there are flat roofs—plantings on the roof, as some of the government buildings in D.C. are doing, for example. That helps reduce runoff so it doesn’t cause I call high peak discharge, which can have a devastating impact—damaging property, eroding soil, and carrying pollutants into the water.

So that’s one of them. Then there's directing roof runoff through the gutters properly into bioretention ponds, dry wells, rain gardens, or simply into tanks—so you can reuse the water for your plants and bushes around the house. The idea is that we want to take that storm-produced excess runoff and, as much as we can, infiltrate it or store it. Whatever’s appropriate for that area, we use that.

So, let’s say you’re directing roof runoff into a dry pit or dry well that’s properly designed and properly directed—you’re taking that much runoff out of the storm drain system, which would otherwise be overwhelmed. You can imagine if the storm drain was blocked. So again, the idea is to harness the stormwater and reduce the peak flow rate, thus helping to minimize the property damage, erosion, and water quality issues.

For example, if we have grass around our yards, rain gardens, mulch, and some bushes—obviously, water infiltrates rather than running off the surface. It’s like a hydrograph: the more you take off the hydrograph, the flatter it becomes. It’s almost like a boxer—(he laughs)—a strong boxer coming at you, but before the punch lands, someone blocks it. It might still reach you, but it won’t have the same force. Same thing with stormwater. With the hydrograph, you try to reduce that peak by any means possible.

If we could hold all that runoff in a pit, that would be almost 100 percent ideal. But with these intense storms, we’d need to design the pit to hold, let’s say, a 100-year storm. And that’s just not feasible. So what do we do? Can we allow for overflow? The idea is to manage as much as we can.

But sometimes—as I teach in my class—we have to examine the feasibility of any practice that’s being installed. What we’re designing—is it actually going to work (i.e., scientific and Engineering feasibility)? Is it going to have side effects? For example, with dry pits or dry wells, we can’t just put them anywhere. You have to consider all aspects. To design for a 100-year storm, you’d need a much, much bigger dry well or pit. That costs money. It takes up land area. So there’s the question of feasibility—economic feasibility.

Then there’s environmental feasibility. What are the actual environmental impacts once it’s implemented? And finally, there’s public acceptance. Do people actually agree with it (i.e., public feasibility)?

You can’t force me, as a private property owner, to put a dry well in my yard. That’s where the work of environmental stewards and community engagement comes in. I can see the role you’re playing as a positive one: educating the community about practices that can help reduce stormwater in ways that don’t cause damage or erosion.

Really, the fifth aspect I usually talk about is what I call the policy—or political feasibility. How many of the practices we’re suggesting actually fit within our current policies? That doesn’t mean our current policies are perfect, but we can’t do things that are illegal. Whatever we do has to fall within existing policy. If we want new policies, then we need to follow the proper steps—base it on science, and convince people and the legislators as to why we need those changes.

Just to give you an example from agriculture—not in every state, but here in Maryland—we have a mandatory Nutrient Management (NM) Program. Each farmer is required to take a composite soil sample from their farm once every three years, send it to a lab, and get the results for nitrogen, phosphorus, and potassium. Then they say, well, I’m going to grow corn, and I expect to get 180 bushels per acre. Based on the data, the Certified Nutrient Managers, tell the farmer that you already have this much nitrogen, this much phosphorus, and this much potassium in the soil and, you only need to apply this much more. Just enough to grow that 180-bushel crop. Anything beyond that is excess—and that’s what runs off and creates problems for our receiving bodies of water. Nutrient Management is based on 4Rs (i.e., right source, right rate, right method, and right timing of the application).

My point is, that the NM practice is mandatory in Maryland.

Now, state also pays farmers to plant winter cover crops after harvest. But that’s not mandatory—it’s voluntary. Still, it’s a very effective practice.

Let’s get back to urban areas and BMPs.

Bioretention ponds in urban areas are excellent, but you always have to maintain them. Infiltration ponds and pits can accumulate fine particles over time, and those particles can block the pores in the gravel or rock—or whatever material is used in the design. That’s why we have to maintain them, flush them out, and so on. Over time, they may not infiltrate as well, and all of a sudden, they can overflow—onto the land surface, into roads—the very thing the pond was supposed to prevent.

So, there are lots of caveats when it comes to effectiveness.

We actually asked this question of maintaining the BMPs to the Deputy Secretary of the Maryland Department of Agriculture (MDA) a few years back—around 2009 to 2011—when we were putting together the National Academy of Sciences Report (a book). For example, someone might say, "We installed this many vegetative buffers," or "We put in this much grassed waterway," or "I have diversion dams," or "I built stormwater management ponds," and so on.

Okay—but do you inspect them once in a while to see if they’re actually functioning the way they were designed? Because effectiveness really comes down to how well they’re maintained. And a lot of times, that’s not something people think about. But every green infrastructure practice is effective for stormwater management—some maybe even close to 100 percent at first.

How do you go about restoring streams to withstand the storms?

After an intense storm, the idea is to prevent banks from collapsing and damaging nearby properties. So, how do we retain those streams? How do we direct that water in a way that doesn’t cause erosion and property damage?

In the community, there are different views. Some people don’t want to remove any trees because of the viewshed. But from an ecological engineering perspective, in certain areas you actually have to remove some trees in order to restore the stream properly—to redirect the water in a non-erosive, ecologically safe way. The key is communication between the community groups and watershed protection experts such as the University of Maryland’s Sea Grant Extension Agents.

So again, there are a lot of caveats with these things.

I know in the hearings I attend, the community is very concerned. Ellicott City has been through so many devastating floods. They worry when there’s new development—whether developers are really using the most effective practices to mitigate stormwater runoff. I think there’s also concern that local stormwater regulations might not be aligned with the best practices for medium- or high-density housing environments.

There’s just a lot of concern out there, and I don’t know enough about it—which is one of the reasons I thought it was important to talk with you.

I’ll just say that after Ellicott City flooded, my daughter had a friend who lived in old Ellicott City—going down on that main road, it’s on the left-hand side, sort of on the slope. So her basement was affected, and I went there with my daughter—actually, everyone in the neighborhood came out. We walked almost a mile up and down, looking at the stream behind the houses. The residents all came out.

Ellicott City is a story that, to be honest with you, is so disturbing—as someone who is a die-hard environmental guy and researcher. Ellicott City is a historic old town, as you know. And with the stream behind the houses, initially there was enough stream capacity to basically move the storm runoff without any problems. However, new developments converted lots of land surface into impervious roofs and or parking lots, thus the old stream channel did not have the capacity to accommodate the generated runoff after storms, especially for the intense storms.

Gerald Winegrad, who Dr. Shirmohammadi references below, served as a Maryland state senator and chaired the Senate Subcommittee on the Environment and Chesapeake Bay.

Well, they slowly—despite opposition—I don’t know if you remember, maybe you’re too young, but there was a state senator named Senator Winegrad. He was very much into the environmental health and into high- and low-density development issues. He wanted to prevent that kind of unchecked and unplanned development in areas that were growing so fast in the ’80s and ’90s. Well, money and capital assistance play a big role. And so, the developers have lots of power, and we have a great legal system—but sometimes money finds loopholes. I don’t want to be cynical this morning, but I’ve seen all of it. So slowly, these developers were permitted to develop.

Now, as you know, state , county, and other entities are committing lots of money—they’re building large, several million-gallon stormwater management ponds, and the underground tunnel to direct the water from the upper portions of the city—so it passes through the tunnel and moves without damaging the properties or overwhelming the old stream channel. But it’s a little bit too late, because of all the devastating damage that flood of 2016 and 2018 caused. So I can understand the valid concern that our community is raising. We shouldn’t ignore the concerns and have a definite plan at hand for the new developments, especially in light of climate change impacts that is causing severe storms.

If you go to Ellicott City, you’ll see that behind those houses, there’s that old stream that runs along the back. One side is a huge rock formation, and on the other side (residential side), they started adding rocks and bricks to increase the depth of the stream. But that obviously didn’t hold up the flood of 2016 and 2018, etc.—it was a temporary fix.

Now, after all the damage, the county is thinking. I haven’t looked at their design plans, but I think they’re doing lots of improvement and that should hopefully do some good in managing stormwater in Ellicott City—at least for that city.

And for the other areas, we must really stay on it. We need to implement whatever green infrastructures we think can detain peak flow , subside it, infiltrate stormwater, and so on. But of course, we also must be mindful that certain places we’re trying to infiltrate have septic systems and fields, and that can create a lot of problems. We need to think system-wide—systems-level design and implementation. We must look at all aspects of the relationship. You see what I’m saying?

If I put in a bioretention pond, but the way it’s located causes it to seep into the septic fields—well, all of a sudden, all that nasty bacteria could come to the surface, and people could start getting sick. So, there are lots of caveats—the design, the location, the capacity, the cost, and what kind of storm we’re designing it for.

What do you recommend?

Policy, economics, environmental, and public—all of that has to work in a united manner. Public education is really key to all this.

There are things we can do as individuals. I often tell my students: we can take simple actions that may not bring immediate personal benefits, but they have intangible benefits.

People used to dump everything down storm drains in old days. A long time ago, it was common for some people to change their oil and pour it right down the drain. Now, whether it’s individuals or mechanic shops, they’re required by law to recycle it properly. So, progress happens—slowly—through education, and gradually that education informs policy. Education leads to policy.

And you know, if I see my neighbor has BMPs, neighbors learn from one another. Education plays a major role.

Roof runoff management—dry wells—you really can’t beat it. We all have roofs, and if we don’t direct that runoff in a non-erosive manner into pits or something similar… For example, in my backyard—most of the rainfall infiltrates into the ground and my roof runoff is directed into the forest behind my house and infiltrates into the ground, thus I am not contributing any storm runoff to the sewer drain. My roof runoff goes from vertical gutters into the underground corrugated pipe that empties into the trees in my backyard. You don’t even see it. There’s a rock formation where the water dissipates into the leaves and organic matter. You don’t see any water running on the surface. The only runoff I have is from my driveway—that’s it.

At a recent hearing I attended, it was mentioned that developers are required to submit an environmental concept plan. But it made me wonder—is anyone actually monitoring what’s being discharged from these sites?

Developers do have to get an environmental impact assessment, as you know. They submit a plan explaining how they’ll mitigate any negative environmental effects, and that’s when the county’s engineering division steps in to review it. The engineers analyze the plan, but they don’t typically verify it in the field through on site monitoring. They’re not out there measuring flow rates with flumes or sampling water quality—unless there’s funding for a specific research project.

There’s actually a great example up north—an agricultural site in Frederick County that’s been monitored for over 13 years as a part of an EPA national watershed monitoring project. A couple of PhD and master’s students even graduated from that project.

When it comes to waste management, 80% of the cost for animal manure storage facilities is covered by a cost-sharing program through the Natural Resources Conservation Service program, called EQIP. The farmer only has to pay about 20% of the cost.

At the end of our project there, one of the families actually thanked us. They said, “You taught us not to throw our money into the stream.” What they were doing was selling their stored organic waste to neighboring farms that didn’t have livestock—using it as fertilizer. So instead of dumping it on the land or into the stream, they turned it into income.

Before the start of our monitoring project in 1991, storms would wash most of animal waste into the streams, contaminating the water. But now they have vegetative buffer zones on both sides of the stream. Animals don’t come into the stream anymore. They are shading under the trees rather than going into the water during the summer.

There’s a lot we can do that doesn’t cost much—and you can definitely see the before and after—both in the samples and in the water quality differences that we observed in our watershed in the Frederick County.

You brought up a great point earlier—some developers include green infrastructure in their plans, but I rarely hear who’s responsible for maintenance or what the long-term plans are. These systems require ongoing care, yet it never seems to come up in hearings.

Yeah, indeed! I will put you in touch with someone working with the community.

Thanks again—I really appreciate it.