Connecticut College Magazine · Summer 2006


Fluvial geomorphologist gets his feet wet

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Douglas Thompson, associate professor of geology, likes to get his feet wet

Douglas Thompson, associate professor of geology, likes to get his feet wet

The interest began when he was a young boy growing up near the Sudbury River in Eastern Massachusetts, and now, years later, little has changed. A fluvial geomorphologist, Thompson divides his time between the classroom, his major research project in Maine and a multitude of rivers and streams in between.

Geomorphology is the general study of landforms and the natural processes that create them, and fluvial geomorphology is specific to river systems and how they physically change over time.

Thompson stumbled upon the field as an undergraduate at Middlebury College, where he received a B.A. in geography and geology. "Before college," Thompson says, "I didn´t know what geomorphology was. I just knew that I had always been interested in rivers."

Now an expert in the field, Thompson studies how the turbulence of flowing water both creates and influences the physical characteristics of a river system. He focuses especially on the formation of pool and riffle sequences. Pools and riffles, which are the deep and shallow areas of a river, provide some of the most important habitats for aquatic organisms like fish and micro-invertebrates.

Unfortunately, human influence in the form of dam building, deforestation, and urbanization, among others, has disrupted the natural processes present in rivers, with negative effects on the well-being of the species that live in them.

Though Thompson is more interested in understanding the physics of a river system, his research plays an integral role in learning how to protect these organisms. By studying how humans have negatively impacted rivers, Thompson contributes to the success of stream restoration projects, which work to re-establish the characteristics of a river system that best support aquatic habitats.

"I try to understand how rivers have been physically changed by humans," Thompson says, "and to predict what they should look like. However, it is impossible to go back to the time when rivers were untouched." Consequently, his job is to find a way to manage river systems so that important species can survive, while at the same time taking into account the unavoidable constraints that humans will place on them.
Just this year, the Connecticut state legislature responded to the fact that many species of fish are declining in numbers by passing a law that restricts how water can be used in river systems. The Department of Environmental Protection (DEP) asked Thompson to take part in the workgroup charged with creating the scientific guidelines for how rivers should be managed.

Thompson´s primary job will be to predict how the reduction of water flow might influence the channel system in rivers, thus creating changes that would prove detrimental to its inhabitants. His comprehensive knowledge of the physical characteristics of a channel, the effects that altered river systems have on aquatic species, and past and present stream restoration projects will prove invaluable in discovering the most beneficial route of river management.

"We have to be careful," Thompson warns. "Unfortunately, not everything done to improve a river is actually good." He references a type of stream restoration known as the instream structure. Dating back more than 100 years, instream structures are engineered devices that are placed in waterways to artificially create the physical characteristics of rivers. The idea is that the simulation of these features will benefit species like salmon and trout. Despite the popularity of these devices, however, Thompson´s research, along with that of other scientists, now suggests that instream structures are not nearly as helpful as people originally thought.

Along with the work he does for the DEP, Thompson stays busy conducting his own studies. Although he has performed some research in Colorado, where he received his M.S. and Ph.D. from Colorado State University, he mainly works in the New England area.

Thompson spent the past summer working in Downeast Maine with the US Fish and Wildlife Service. Maine´s situation is similar to that of Connecticut. Maine´s wild salmon are experiencing difficulty reproducing in their native river systems. Unlike in Connecticut, however, the Maine rivers where Thompson conducts his research exhibit very little visual damage.

"The human alteration is not that obvious," he says. "In fact, most people who saw these river systems wouldn´t think there was a problem." The reason for this is that the damage actually began a long time ago, during the Maine logging drives that cleared out much of the wooded areas. Though these parts have since been reforested, neither the forests, nor the rivers and streams running through them, are the same.

"The issue is that during historic deforestation, or logging drives, all natural structures were removed from the rivers, so that they could be used to transport cut timber," Thompson explains. This caused a huge change in the channel´s water turbulence, which then resulted in a disruption of the pool and riffle sequences, and consequently, the natural habitat of the Maine salmon. Thompson theorizes that by re-introducing wood debris to the river systems, it might be possible to re-establish or mimic a habitat more conducive to the salmon´s survival.

The catch is figuring out just how much debris to put back. One method is by finding natural instances of downed timber in order to assess its impact on the river system. Much of this fieldwork consists of data collection. With the help of some of his students, Thompson wades from one river system to another, performing tasks like observing channel velocity and turbulence and measuring water elevation. By looking at multiple rivers, Thompson hopes to find patterns between them.

"The basic idea is that processes operate in a number of different locations, so something we´re seeing in one place is probably happening in another," he says. His goal is to discover and analyze these consistencies in order to figure out which physical processes in river systems "work."

When Thompson is not in the field — for instance during the academic year — he continues his research in a laboratory setting. Connecticut College is home to the state´s largest re-circling flume, a machine that is able to simulate rivers indoors. Thompson uses the flume to model various river conditions, isolating variables like debris obstruction, rate of flow and water turbulence, to examine the physical effects they have on river processes, such as the creation of pools and riffles.

Between his job as a professor, his research and his work for the DEP, Thompson already wears a lot of hats. Add to that the fact that he is also a husband, a father, and an avid bicycle racer, and free time becomes very limited. Luckily, however, some of his roles overlap. His wife of 13 years, Rebecca Nash, research coordinator in the Office of College Advancement at CC, is sometimes able to accompany him on his research trips; and over the past eight years, 25 of his students doing honors theses or independent studies have helped out on his projects.

Even so, it is clear that Douglas Thompson is a busy man. "The trick is a disciplined weekly schedule," he says. "I get up early and go to bed late." He doesn´t seem to mind, though. After all, it keeps him in the water.

This article originally appeared in the Spring 2006 issue of Natural New England.

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