Standing on the creek bank, Amatya points to a gauging station that provides realtime data on stream flow, water levels, and precipitation to an Internet Web site. “We don’t know what’s available in this watershed as surface water,” says Amatya, a research hydrologist with the SRS Center for Forested Wetlands located near Charleston. “We also don’t know what’s available in ground-water.” Long-term monitoring on sites in the national forest—where researchers are also monitoring water quality, testing it for contaminants and dissolved oxygen—will help answer those questions.

General-circulation climate models predict that the Southeast will probably face significant changes in precipitation over the next 50 years. Most climate models show the Southeast becoming wetter, but one model shows it getting drier. Amatya will provide his monitoring data to researchers at the SRS Southern Global Change Team led by project leader Steve McNulty, who are creating computer models of climate change impacts on forests and water use.

The team, which is led by Steve McNulty and includes research hydrologist Ge Sun, has created computer models of 2,100 watershed basins around the United States, addressing potential impacts of climate change, population growth, and land use on forests. “The local watershed information from Turkey Creek will be helpful in validating the regionalscale model of the Southeast that I’m working on,” says Sun.

Water When and Where You Want It

Turkey Creek and nearby watersheds are already relatively wet, receiving on average 52 inches of precipitation annually. Even so, “water can be unavailable where you want it and when you want it because of a combination of climate change, population growth, and development,” says Amatya. “That’s where effective water management comes into play, providing water at the right time and in the right amount.”

Localities and water utilities want more information about water availability, but this will increasingly require an understanding of the interplay between climate change and population pressures.

Amatya and SRS colleagues are collaborating with partners from academia, industries, State and Federal agencies, private landowners, and nonprofit organizations to learn more about how water moves throughout the Turkey Creek watershed’s lowgradient landscape, which ranges from about 10 to 40 feet above sea level. This information can help scientists predict the impacts of climate change on the watershed’s water flow.

“This watershed is becoming a user facility for scientific partners who are interested in understanding various aspects of water quality and availability in the region,” says Carl Trettin, team leader for researchers at the Center for Forested Wetlands. “What we’ll provide is an infrastructure and basic facilities, and encourage partners to come in and participate.”

Amatya has established a costsharing partnership with the U.S. Geological Survey’s Columbia district office to set up and monitor the precipitation-and-flow-gauging station on Turkey Creek. These data are expected to be especially valuable because the creek was previously monitored from 1963 to 1983. By comparing recent and historical data, scientists can learn about the watershed before and after Hurricane Hugo, a category 4 storm that in 1989 destroyed more than 80 percent of the national forest’s tree canopy. The researchers plan to study how Hugo’s destruction of the watershed’s tree cover—which changed a mature forest to one made up of younger trees—has affected long-term water availability and flow dynamics in Turkey Creek. Comparing long-term datasets, the scientists can also examine the rain pattern in the watershed since 1983 to estimate whether there has been any change in precipitation.

“This study could help us understand how climate events will affect the forest and the region’s water balance in the future,” says Amatya.

Water Through Forest

It’s a given among researchers that climate change will alter the water patterns of this region over the next decades. SRS scientists and collaborators are developing information on how water moves today through undeveloped forested areas along the South Carolina Coastal Plain to establish a baseline for comparison purposes.

“In the Coastal Plain you don’t have the dominant force of topography shaping how water moves downhill, as you do in the hills or mountains,” says Trettin. “At first glance, you would not expect to find rapid runoff after heavy rains in the Coastal Plain, but it can happen here. The region has a mixture of soils. Close to the ocean there are sandy soils, which allow precipitation to soak into the ground. But a little farther inland the soil’s more often comprised of heavy clay, which doesn’t allow much moisture to soak in, so at times we can see runoff rates similar to those in the mountains.”

The SRS team plans to study the Turkey Creek watershed as a reference site, comparing it to nearby, geographically similar watersheds that face growing development pressures. As the climate changes in the future, how would the water budget in this reference watershed compare with those of nearby developing watersheds? “If you cut down forests, which are effective water pumps, and build houses in their place,” asks Trettin, “how does that affect the water running through that developed system?”

Sea Levels and Ground Water

Within the national forest, only a few hundred yards from Turkey Creek, SRS scientists have installed shallow ground-water wells that go down to 8 feet. With support from the South Carolina Sea Grant Consortium, Timothy J. Callahan, a geologist at the College of Charleston, in collaboration with SRS researchers, has installed an additional series of deep ground-water wells that range from 15 to 130 feet deep.

Monitored continuously, the wells provide data showing how both shallow and deep ground-water supplies respond to various climate events such as droughts and heavy rains.

“In the natural system, how much precipitation is infiltrating into shallow ground water?” Trettin asks. “How much is infiltrating into deeper ground water? And how much is running off the natural areas into creeks? We have little understanding of all that.”

Over the next decades, climate change is expected to raise sea level, which would drive freshwater tides farther up coastal rivers, potentially creating new wetlands—and changing ground-water levels in areas like the Turkey Creek watershed. Homes built on land that seems high above sea level today could be more vulnerable to flooding in the future.

The scientists have also installed a weather station, which provides data that can be used to calculate evapotranspiration—the process by which plants pump water into the atmosphere. The researchers can then calculate evapotranspiration from the trees in the surrounding woods. “We’re looking at the role of vegetation as a water pump,” says Amatya “How water is drawn out of the forest system and pumped back into the atmosphere is part of the water budget.”

Evapotranspiration in mature trees can store and release up to 85 percent of the water flow in a southern Coastal Plain forest during a very dry period, but only 50 percent when very wet, says Amatya. As a result, heavy rainfall in a wet period can cause damaging floods because forest trees are already saturated with water.

Models for Watersheds

Amatya plans to use monitoring data from the Turkey Creek watershed to create a hydrological model to describe the local area’s “water budget” over time and provide researchers a way to understand today’s water flow condition—and estimate impacts of more intense droughts or floods as the climate changes.

“We want to test whether a hydrological model can predict what’s happening now,” says Amatya. “We’ll calibrate the model to what we measure in the watershed.”

When the model is calibrated, Amatya will incorporate data from the two major global climate models, which predict contrasting scenarios for the Southeast in the future—one wetter, the other dry—into his hydrological model for the Turkey Creek watershed.

“We can then look at how groundwater and surface-water flows would be affected by either scenario,” says Amatya. “For example, isolated wetlands might start disappearing if we see more drying. ”

The model for the Turkey Creek watershed will also be useful for understanding its future hydrological response to both climate and development. SRS scientists will use the results of the model to help regional water managers understand the impacts of future withdrawal rates from ground-water and surface-water resources.

“The South Carolina Coastal Plain is a wet, humid region,” says Trettin. “But water is not available in a limitless supply. There are going to be changes in the forested communities and water supplies as the climate changes, and we need to understand how these systems function now, to estimate how they will function in the future.”