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Smith's team studies impact of urbanization
Researchers hope to determine how - and to what degree—development impacts the natural watershed



A
dead opossum floats by belly-up. A ripe stench rises from leaking sewage pipes beneath the murky water. A demandingly large sign warns passersby “Do NOT touch the water.”

Wow.

Glamorous it may not be, but to James Smith, professor of civil and environmental engineering, this is an exciting place to be. He is certain that anyone stepping foot on this site for the first time would “have to say ‘Wow.’”

Professor Smith and his research team are studying urban watersheds such as this one in Baltimore, Md., trying to understand the hydrology and hydraulics of extreme floods in urban environments.

The project is part of the Baltimore Ecosystem Study, and the National Science Foundation’s (NSF) Long-Term Ecological Research initiative. NSF chose Baltimore as one of two centers (the other being in Phoenix) for a 10-year study on urban environments.

Scientists, policy-makers, environmentalists, and city residents all have many questions about how urbanization impacts the natural environment. Some theories aver that urban development disrupts the

water cycle, lowering water tables, and essentially “drying out” the environment. Some speculate that development disrupts the drainage basins of rivers and streams, damaging watersheds and increasing the severity of floods.

In search of data

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Photo by James Smith

Graduate student Kate Meierdiercks, left, and Hidde Leijnsel, a former student of Professor James Smith, run experiments in a watershed outside Baltimore, Md.

The major purpose of this research is to gather more empirical data that will lead to enlightenment on some of these questions.

Professor Smith’s team of hydrologists mainly studies the river mechanics. Research staff member Peter Nelson ’03 made an intriguing discovery while poring over old topographic maps of the Dead Run Watershed just outside Baltimore.

“The channel meanders around and has a very particular form to it. Peter showed that Dead Run has been remarkably stable over a time scale of about 100 years, when most of the development in the area took place,” Professor Smith said. “That was kind of surprising, because it’s at odds with the standard model of how rivers work in urbanizing watersheds. We would have expected the river to change its form much more, and have more erratic behavior over time.”

To make his point, Mr. Nelson gathered very high-resolution data about the present topography of the area using LIDAR, an instrument capable of supplying a fine-tuned one-meter resolution. He compared those data to that from the old maps, as well as data from hydraulic models, and came up with an idea as to why Dead Run had passed through the last century so unchanged.

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Photo by Frank Wojciechowski

Professor James Smith and his research team are trying to understand the hydrology and hydraulics of extreme floods in urban environments.

“Right now, the working hypothesis is that this particular stream is bedrock-controlled,” Mr. Nelson said. This solid-rock surface protects the stream channel from the drastic alterations that floods cause in most streams. Thus, Mr. Nelson found that the geology of the region can create an “imposed stability” in the stream channel—an important piece of the puzzle when trying to make sense of the watershed.

Another researcher, graduate student Kate Meierdiercks, is researching the human side of the issue, studying the different management practices that rule over the region.

“A lot of the research I’ve done has been uncovering the history of storm water management,” Ms. Meierdiercks said. She explained that prior to the Clean Water Act and other policies that pushed for more environmental management, there really was no storm water management to speak of.

In the 80s, the preferred management practice was the creation of dammed detention basins that hold extra water. Later development practices preferred storm water wetlands.

"All of these areas developed at different times, so they have different methods that affect flooding in very different ways."

Ms. Meierdiercks is studying the region as a whole, piecing together the various local water management systems, and trying to describe how they collectively impact the flood activity of the region.

However, some areas are characterized less by their management and more by their lack thereof. The older areas of the city are defined by the lack of hydrological sophistication available at the time of their development.

Moores Run

The unappealing site described earlier is an area in northeast Baltimore called Moores Run, that were developed in the early 20th century. At that time, part of the meandering stream was paved over. Beneath it were placed large sewer mains that carried a very high volume and were installed at a very high gradient in order to move a great deal of water very quickly.

This high-velocity flux was too much for the small stream and entirely destroyed the structure of the stream channel, leaving leaky sewage pipes exposed and creating a serious public health hazard.

“Moores Run is really a model of the old development worst-case scenario,” Professor Smith said. “Moores Run also has the highest frequency of flood peaks exceeding 100 cfs per square mile in the conterminous United States.”

In plain English, Professor Smith explained that a “flood peak” is the highest level attained by the floodwaters. The benchmark figure used by the United States Geological Survey to identify severe floods is 100 cubic feet per second (cfs) per square mile.

Although regions of Hawaii and Puerto Rico tend to have much higher flood peaks, there is nowhere in the United States that has more floods that reach peaks above that level.

Simply said: a lot of bad floods happen in Moores Run, which is one of the reasons it was chosen for the study.

The research team experienced some of Baltimore’s flooding behavior firsthand while conducting fieldwork over the summer. After several tedious hours of gathering unexciting data in a steady drizzle, the team decided to take a lunch break. But before they finished their meal, research associate Mary Lynn Baeck called from her desk in Princeton, where she was watching real-time weather data of their area. She hustled them out of the restaurant with promises that some serious rain was minutes away.

“We got about 15 or 20 minutes of heavy rain that made the trip worthwhile,” Professor Smith said. “We collected a lot of very useful data.”

Safety first

Traipsing around a flood zone during a storm is not a terribly safe activity, so they kept in touch with Ms. Baeck and each other through cell phones, by working in teams, and following the mantra: if you feel you’re in danger, you probably are, so get out.

In November, three Baltimore residents died in a severe flood, further impressing upon the researchers the importance of their work.

Graduate student Julie Javier is focusing upon possible applications of the research and is attempting to enhance flood forecasting practices and safety procedures.

Despite the danger and the messiness of the work, the team takes it all on with brio.

“I’m inspired by the belief that the urban environment is one of the biggest challenges of the 21st century,” Professor Smith said. “Figuring out how to keep the urban environment livable is a tremendous challenge.

“Also, I was a graduate student at Johns Hopkins University [in Baltimore], and one of my favorite teachers was a fellow named M. Gordon Wolman,” he said. “He took the approach that the urban environment had some of the most exciting scientific challenges.

“I bought into this idea. If you think about it from an experimental perspective, the types of experiments you carry out in natural systems in urban environments are absolutely staggering.”

Curious children

Mr. Nelson was encouraged by the curiosity of local children.

“When we were working out in the streams, elementary and middle-school-aged kids came up and were really curious about what we were doing,” Mr. Nelson said. “Making science more accessible to young people in urban environments is something that can only be positive.”

Ms. Meierdiercks agreed with her research teammates and added that the possible impacts of the research itself were especially invigorating.

“We can answer questions that are going to help a lot of people,” she said. “If we can figure out some way to prevent the destructive flooding in Baltimore, we’ll be helping hundreds of thousands of people.

“Also, people have messed up the hydrology of the natural drainage systems so much that it just seems natural that we should have to go in and try to fix it!”

 

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