University of Georgia

Managing the ebb & flow of the I-85 corridor

Population growth and development along the “I-85 Corridor”—the roughly 250 miles between Atlanta and Charlotte —have created or exacerbated a host of environmental issues, many of them related to water and waterways. UGA researchers across a number of colleges and research units are studying these phenomena and coming up with strategies to help state agencies, municipalities and even private organizations manage these challenges. (Illustration by Lauren Corcino)

Editor’s note: The data visualizations in the story below were created by Kevin Samples, GIS research analyst with the Institute for Resilient Infrastructure Systems. They are intended to augment the research descriptions, not represent the research conclusions themselves. These visualizations can help viewers understand the environmental trends and phenomena addressed in the research.

U.S. Interstate 85 is a 1,000-mile stretch of freeway running southwest to northeast from Alabama to Virginia. It runs through two of the South’s largest urban centers, Atlanta and Charlotte, and is flanked by dozens of smaller cities, towns, and municipalities.

Since the interstate was first constructed in the 1950s, the area along I-85 has experienced an economic and population explosion—a 1993 article in BusinessWeek magazine labeled the I-85 corridor the “Boom Belt”—that has continued into the new millennium.

But all that growth has a cost, one that could be weighed with water. Every one of those millions of new residents needs water to drink, cook, and wash. They need sewage or septic systems for wastewater. Their homes lie along paved roads that channel rainwater … somewhere else.

Climate change, meanwhile, plays its role in the form of higher temperatures and more intense storms that dump increasing amounts of water on increasingly impervious surfaces.

University of Georgia researchers are investigating challenges like this. Working through the Institute for Resilient Infrastructure Systems (IRIS) and the River Basin Center, UGA scientists from across four schools and colleges have brought their research together to synthesize the water issues facing the I-85 “urban archipelago.”

Many of them co-authored a recent paper in the Journal of the American Water Resources Association that knitted together their various threads of research into a set of recommendations to mitigate the negative impacts of these developments:

  • Increase water-use efficiency.
  • Adopt indirect potable reuse or closed-loop water systems.
  • Allow for water sharing during droughts while regulating inter-basin transfers to protect aquatic ecosystems.
  • Increase nutrient recovery and reduce discharges of carbon and nutrients in effluents.
  • Employ green infrastructure and better stormwater management.
  • Apply the UNESCO Climate Risk Informed Decision Analysis framework into water planning.

The summaries below represent just a few of the projects that informed these recommendations, demonstrating how UGA research is being applied to directly benefit the millions of residents along the I-85 corridor.

Gauging the flow of Southeastern waterways

A few years ago, the Southern Company reached out to IRIS Director Brian Bledsoe with a concern. Waterways across its Southeastern corporate footprint were running lower than in the past—a phenomenon that could have significant business implications—and its leaders wanted some empirical data.

Brian Bledsoe is a UGA Athletic Association Professor in Resilient Infrastructure and director of the Institute for Resilient Infrastructure Systems in the College of Engineering. (Photo by Dorothy Kozlowski)
Brian Bledsoe is a UGA Athletic Association Professor in Resilient Infrastructure and director of the Institute for Resilient Infrastructure Systems in the College of Engineering. (Photo by Dorothy Kozlowski)

Southern Co. uses natural waterways to cool its power plants, especially those with nuclear reactors. It does this in two ways: By piping in stream water to cool reactors, and by releasing heated water back into the waterway. In the first process, low-flowing streams may actually drop below the level of a plant’s intake pipes. In the second, the heat itself acts as a contaminant, as aquatic ecosystems can be greatly affected by shifts in water temperature.

“You’ve heard the saying, ‘Dilution is the solution to pollution,’ right?” asked Bledsoe, UGA Athletic Association Professor in Resilient Infrastructure in the College of Engineering. “If you have more water in the river and you put in a certain load of pollutant, the concentration depends on how much water is there.”

Using data provided by 349 U.S. Geological Survey (USGS) stream gauges across the study area, Bledsoe and former Ph.D. student Timothy Stephens analyzed stream gauge levels going back as far as 100 years. They identified the historical “Q7,” or the lowest-flowing seven-day period each year, at time intervals of 25, 50, 75, and 100 years, then analyzed the comparative data.

Stream Gauge Flow Trends across the U.S. Southeast

This graphic shows stream level data from U.S. Geological Survey gauges located around the Southeast. Going back as far as 100 years, UGA researchers looked for significant drops or increases in stream gauge levels across annual “Q7s,” which refer to the lowest-flowing seven-day period each year. By moving the timeline along the bottom, viewers can see streams showing significant changes at 25, 50, 75, and 100 years ago. (Visualization created by Kevin Samples)

In 80% of the streamflow records, Bledsoe and Stephens found decreasing Q7 levels. They also discovered these trends had accelerated in recent decades; in half the gauge records, an “abrupt shift in low-flow magnitude” occurred around the 1975-85 and 1995-2005 timeframes.

“It’s kind of a paradox,” Bledsoe said. “A lot of these streams and rivers are actually showing higher high flows, too. So they’re not ‘low-flow waterways’—they are waterways that are exhibiting more extreme variability in both directions.”

There are a number of potential causes behind this, Bledsoe said, pointing to colleague Marshall Shepherd’s research on intensifying rainfalls (particularly in the summer months), as well as widespread hardening of landcover due to human development. Both of these direct increasing amounts of water to soils that are unable to absorb all the moisture.

And, regardless of whether a particular stream is flowing lower or higher, this is very much a regional issue. Much like they draw power through the countless nodes of Southern Company’s electrical grid, water users across the region are tapping into a vast, interconnected network of waterways from the mountains to the sea.

“Georgia Power is committed to protecting the environment and our natural resources,” said Jennifer Winn, vice president of corporate sustainability for Georgia Power, Southern Company’s largest operating unit. “Dr. Bledsoe’s research on resilient infrastructure helps inform and improve the industry’s stewardship of our water resources. By pursuing resilient infrastructure, we are able to continue meeting our customers’ needs while simultaneously supporting our natural environments.”

“We may not think our actions affect people who are far away, but they do,” Bledsoe said. “We’ve got to do unto others downstream as we’d have those upstream do unto us. We are all connected.”

Assessing wastewater and sewage challenges

Many cities along the I-85 corridor rely on small rivers for water supply and waste assimilation. However, as populations continue to grow, infrastructure is beginning to strain.

The U.S. Southeast is a global hotspot for freshwater biodiversity, and rivers along the corridor have been likened to “underwater rainforests.” However, rivers face many of the same problems that threaten aquatic animals and human well-being, including low water supply during droughts, seasonally low flows for wastewater dilution, increasing drought and precipitation extremes, and downstream “eutrophication,” a process by which an area of water becomes overly saturated with nutrients, leading to the growth of simple plant life such as algal blooms.

While more populated cities and counties have sewage systems to manage wastewater, many homes along the I-85 corridor rely on septic systems. Aging and failing septic systems are often linked to declining water quality in rivers and lakes, but septic management is largely the responsibility of homeowners. Most communities do not maintain detailed information about septic infrastructure.

Krista Capps is an associate professor in the Odum School of Ecology and the Savannah River Ecology Laboratory. (Photo by Andrew Davis Tucker)

With the anticipation of more population growth, Krista Capps, an associate professor in the Odum School of Ecology and the Savannah River Ecology Laboratory, is just one of the many experts searching for ways to address complex issues associated with septic infrastructure.

“Many communities don’t know where their septic tanks are located, how many systems are in use, or what condition they’re in,” Capps said.

Without proper oversight, even relatively new septic tanks can malfunction and release untreated wastewater into the surrounding environment, possibly affecting downstream communities. Many streams along the I-85 corridor are polluted by gut bacteria such as E. coli, which is often attributed to untreated sewage from septic systems.

After all, Capps pointed out, we all live in watersheds, and water management decisions affect everyone in the region.

“In other words, we are drinking water that has been recycled through other people,” she said. “One of my research goals is to support communities in making informed water management decisions and reduce negative impacts on the quality of water moving downstream.”

Risk Factors for Septic Systems across Athens-Clarke County

This graphic portrays septic systems around Athens Clarke-County and the potential risks posed by age of the systems and topographical characteristics such as slope and proximity to streams. By using the control buttons, viewers can overlay or remove these factors from the map. (Visualization created by Kevin Samples)

To support more effective management of septic infrastructure, Capps and colleagues are working with local, regional, and state water managers and public health officials to assess how septic system function changes with extreme weather events, including intense precipitation and droughts. They are also working to develop new resources for local governments to support evidence-based septic management decisions.

Mitigating urban climate effects for ‘thermal and flood justice’

Ask the average American about the deadliest weather events and you’ll probably get one of two answers: tornadoes or hurricanes.

“They’re the most telegenic atmospheric forces that draw my colleague Jim Cantore into those dramatic news segments,” joked Marshall Shepherd, Georgia Athletic Association Distinguished Professor in the Franklin College of Arts and Sciences, in reference to the well-known Weather Channel personality. “In reality, [the most dangerous events are] actually heat and flooding.”

Between 2018 and 2020, more than 3,000 people in the U.S. died from heat-related causes, according to the Centers for Disease Control. Flooding, meanwhile, has cost U.S. taxpayers more than $850 billion since 2000, more than two-thirds the cost of all natural disasters.

Research from Shepherd and colleagues has demonstrated that heat, rainfall, and even lightning are more pronounced in urban centers and what he describes as “climate archipelagos,” or urban chains like the one from Atlanta to Charlotte along the I-85 corridor.

Marshall Shepherd is a Georgia Athletic Association Distinguished Professor of Geography and Atmospheric Sciences. (Photo by Andrew Davis Tucker)
Marshall Shepherd is a Georgia Athletic Association Distinguished Professor of Geography and Atmospheric Sciences. (Photo by Andrew Davis Tucker)

It presents unique challenges in areas often marked by already vulnerable populations.

Urban heat islands (UHIs) are a significant part of the discussion. They form as hard surfaces like asphalt, pavement, and roofs absorb solar radiation and re-radiate it in the form of infrared heat. The lack of urban vegetation also reduces cooling, while buildings and surfaces exchange heat, and car engines and other machinery also contribute their own waste heat.

Using data from 1984 to 2007, Shepherd’s lab found a mean UHI magnitude of 1.31 degrees Celsius when comparing Atlanta to the relatively smaller Athens area.

The figure here illustrates the concept with a pair of satellite images taken of Atlanta in 2000, demonstrating temperature variability of up to 12 degrees Celsius in developed urban centers.

The figure here illustrates the concept with a pair of satellite images taken of Atlanta in 2000, demonstrating temperature variability of up to 12 degrees Celsius in developed urban centers.

This figure, taken from a paper co-authored by Shepherd, illustrates the urban heat effect. The top satellite image shows various Atlanta neighborhoods on Sept. 28, 2000. The corresponding heat map below shows temperature variability in these neighborhoods, red being the hottest. Not coincidentally, industrialized areas are significantly hotter than their natural counterparts.

But it isn’t just the heat.

Rainfall also is a major challenge, with increased rainfall totals around Atlanta during the warm season. Lightning prevalence is another; during the period from 2018 to 2021, Shepherd and his former student Jeffrey Burke found increases in total flash rate density (14.3%), flash days (8.3%), and average flashes per day (5.5%) between urban and rural regions.

“It’s driven by a combination of a few factors,” Shepherd said. “Cities are warmer and tend to have more destabilized air. Buildings are taller and surfaces rougher, so air is more convergent at low levels. There tend to be more aerosols, or pollution, in the air.

“We think a combination of these is driving anomalies in rainfall and lightning that we’ve seen.”

Taken in aggregate, each of these factors can have an even larger impact on urban archipelagos.

Meteorological Snapshot of the U.S. Southeast

The data in this graphic, courtesy of NASA, help illustrate the “urban heat island” effect. The Charlanta at Night setting shows nighttime illumination and spotlights the “urban archipelago” concept of the I-85 corridor. Viewers can toggle between the two maps using the controls along the top of the graphic. (Visualization by Kevin Samples)

“If you think about a mountain, it can impact rain or snowfall,” Shepherd explained. “Now think of a range of mountains like the Rockies and the extended spatial impacts of a system of mountains on the rainfall patterns. That’s what we think exists in these urban centers.”

Socially and economically vulnerable populations living along the I-85 corridor feel that burden more acutely, Shepherd said, in the form of things like higher electricity bills for air conditioning. But there are mitigation techniques: increased urban vegetation, more permeable surfaces that allow water to filter to the soil underneath, and an entirely new approach to stormwater management.

“Many of our cities are engineered under the assumption of what my colleague Brian Bledsoe in IRIS calls ‘stationarity’—that storms in 1970 will look like the storms of 2024,” Shepherd said. “That’s not the case—they have grown in intensity. We propose radically reimagining how we plan and design our cities to engineer them for what we call ‘thermal and flood justice.’”

Protecting our lakes and streams

Agriculture is Georgia’s No. 1 industry. The state is a primary producer of goods like cotton, peanuts, onions, pecans, and corn. According to the U.S. Department of Agriculture, farmland comprises some 26.7%—nearly 10 million acres—of Georgia’s overall land.

With all of this comes a challenge, however: Livestock produce manure, and crops require fertilizer and pesticides. Both pose threats to nearby water sources.

It’s something Warnell School of Forestry and Natural Resources Professor Rhett Jackson works to better understand in hopes of offering solutions to Georgia farmers and forest owners.

Jackson (lead author of the Journal of the American Water Resources Association paper cited at the top of this story) examines non-point source pollution, or pollution that is being carried not through an engineered conveyance system—like a pipe—but through natural processes in the ground.

“Agriculture is really all about non-point source pollution,” said Jackson, John Porter Stevens Distinguished Professor of Water Resources and director of the River Basin Center. “Ag streams tend to be highly polluted, but none of it is coming from the ways we usually think about.”

Rhett Jackson is John Porter Stevens Distinguished Professor of Water Resources in the Warnell School of Forestry & Natural Resources. (Photo by Peter Frey)

Instead, agricultural pollution typically derives from excess fertilization, manure, or pesticide application, or livestock access to streams, from which solutes travel through groundwater into streams, lakes, and estuaries. The result may be algal blooms, toxic cyanobacteria growth, fish kills, and poisoning of wildlife.

But Jackson and colleagues study a natural solution that can mitigate this pollution.

Riparian buffers are zones of undisturbed soils and vegetation along streams, usually featuring shallow water tables and copious organic matter. Within these zones, a process called denitrification can cycle nitrates from the ground back into the atmosphere.

Heterotrophic bacteria—bacteria that absorb nutrition through other sources of organic carbon like plant or animal matter—turn the nitrogen into gas and expel it back into the atmosphere, eliminating many of the harmful nitrates that pollute the stream.

Jackson’s team aims to quantify just how effective these riparian zones are. To study them, they overfertilized a pine forest near a stream and identified excess nitrates that contaminated the forest’s groundwater.

“We saw the contamination in the groundwater, but we never saw nitrate in the streams,” he said. “Enough time had elapsed that it should have been there.”

The denitrification rates?

“Over a 90% reduction,” Jackson said.

To Jackson, the takeaway is clear: We should encourage farmers and those who are fertilizing these lands across the state to avoid removing crucial vegetation that provides a buffer between pollutants and nearby streams.

“This,” he said, “is a very cost-effective strategy for reducing non-point source pollution.”

Local Nitrogen Loads in Soil

Agriculture—Georgia’s No. 1 industry—feeds the state, the nation, and the planet, but inputs of farming such as fertilizer and pesticide also carry risks. Fertilizers, for example, can inject nitrogen into water tables, which can cause algal blooms and cyanobacteria growth in nearby water sources. This graphic shows soil nitrogen levels in an area north of Athens and south of I-85. Data source: U.S. Geological Survey. (Visualization by Kevin Samples)