College of LAS « Illinois


Dredging Up The Past

Bruce Rhoads

Bruce Rhoads has a plan for naturalizing streams that works for farms, city folks, and fish.

Criss-crossing Illinois' midsection like an interstate highway system for fish, are thousands of miles of agricultural drainage ditches. Sleek and unadorned, these mud-bottomed channels whisk water away from farm fields to rivers so that otherwise swampy land can be tilled. Drainage, not fish habitat, is their primary role. Fish are small and few in species.

In marked contrast is a tiny stretch of the Embarras River, a few miles south of UI. Once a drainage ditch, it has escaped the usual dredging and straightening long enough for natural features to have reappeared in the waterway. There are twisting meanders, deep pools, shallow riffles, and the other varied habitat fish need to thrive, which is why fish are packing the place. In this 1/2-mile area are more than 30 species of fish. "That's twice what you will find in most mountain streams," says Bruce Rhoads, a geography professor in LAS.


For the past 15 years, Rhoads and few like-minded individuals, largely from LAS, have been quietly testing techniques for adding nature back into Illinois' vast drainage dragways. The researchers know what fish need to thrive; the challenge has been in incorporating these elements into the ditches in ways that don't conflict with farming practices. Rhoads and his colleagues have a plan. And it appears to be working, in cities as well as on the farm.

As a fluvial geomorphologist, Rhoads studies how streams and rivers shape the landscape. Most of his colleagues run off to exotic locations like the Rockies and Nepal to make their mark on the world, but he chose Illinois because of what he recognized as the opportunity of a lifetime. In few places, other than inner cities, had the landscape been so radically altered from its natural state as in Illinois' farmbelt. If he could find a way to incorporate nature into the landscape here, the impacts could be enormous.


Until the mid-1800s, the 16-county region that became Illinois' prime farmland was dense prairie, 60 percent of which was so swampy that pioneers often traveled by canoe rather than horses. The swamps were the headwaters for many rivers, though, such as the Embarras, Kaskaskia, and Sangamon, which were home to fish and other wildlife.

These swamps vanished during the drainage boom of 1860-1890, during which time farmers underlaid the prairie with a network of clay tiles. The tiles drained into machine-excavated channels that transported water away from the fields into streams, and on downstream. The few existing streams were dredged and straightened, too, to speed the flow of water away from farm fields. The undertaking transformed uninhabitable prairie into the most productive farmland in the world. It also decimated fish populations.

When Rhoads arrived in Illinois in 1986, drainage practices were coming under scrutiny primarily because of their link to flooding. The streamlined channels rush water and sediment away from farms only to deliver them in greater volume and force on the communities downstream. Stacks of scientific studies document these effects and suggest a wide range of alternatives for slowing the movement of water, from restoring streams' natural meanders and planting trees along the banks to adding wetlands at strategic intervals to catch and hold water.

ariel maps

Aerial photos taken in 1936 of this tributary of the Embarras River in southern Champaign County are nearly identical with photos taken 60 years later—evidence that the landscape in this region is remarkably stable. These findings imply that much of the maintenance work now done in agricultural drainage ditches, which damages fish habitat, is unnecessary. The findings also mean that improvements to streams, if done correctly, will be long lasting.

Because these flood-control techniques also offer valuable fish habitat, Rhoads initially planned to trumpet these techniques as ways of naturalizing drainage ditches. But he quickly changed his mind. In 1989, he and Ed Herricks, a stream ecologist in LAS and the College of Engineering, proposed adding meanders to drainage ditches to control flooding in a nearby town. Even though science and the cost-benefit analysis were in their favor, their proposal was flatly rejected. The citizens' committee voted for more dredging and the removal of trees—the very practices responsible for much of the problem in the first place.

" What we failed to recognize was that the rural community has a different view of the streams than we do," says Rhoads. In part, natural features are seen as slowing drainage. But what is more, "farmers have this ‘neat-and-tidy' philosophy in which mowed roadsides and straight, treeless ditches reflect pride in their place and profession. It is the same kind of pressure to conform with your neighbors as you find in the suburbs."

As they learned a few years later, the differences go even deeper. A study by David Wilson, also a geographer in LAS, and Michael Urban, a former student of Rhoads' (now a professor at the University of Missouri), found that while farmers consider themselves stewards of the land, they see their primary role as preserving the productivity of the soil for future generations. Productivity, in this region, is directly tied to drainage. New farming technology that combines soils data and crop yields with Global Positioning Systems show direct correlations between fields with tile systems and higher yields. Thus, the demand for drainage won't go away.

The experience was pivotal to Rhoads, prompting him and Herricks to focus on alternatives that would accommodate drainage while enhancing fish habitat. They knew from other studies by Herricks that fish were rebounding in oases that were far less "pristine" than the Embarras site. One of Herricks's graduate students was practicing his fly fishing at one of these sites, "not catching trout," says Herricks, "but having a lot of fun reeling in chub on a 4 lb. line."
They began examining how fish were using these varied habitats, taking their analyses further than did other scientists. "We wanted to know how the fish used the front of the pool versus the middle and back," says Herricks. "And at what stage in their lifespan, for how long, and which fish."

From these data, there began to emerge identifiable benefits that could be tied to various stream features. Much like architectural plans for buildings, these features could be mixed and matched depending on conditions, budget, and habitat goals for a particular stream. No longer were they talking about restoration, says Rhoads. "We were advocating something more practical on the large scale—naturalization, a compromise between the needs of humans and fish."

Crucial data in support of their idea came from field studies of different streams in east-central Illinois and of aerial photos taken of the Embarras River watershed every few years since the 1930s. The field studies showed that, over time, natural stream features, including meanders, pools, and riffles often develop within drainage ditches when these ditches are constructed in a certain way. The "streams within a ditch" support high-quality fish communities yet do not hinder drainage. From the aerial photos, a clear pattern emerged. Over 60 years, only 12 percent of streams experienced any change. Of those that had, all but 8 percent of the total change was due to human modifications. Says Rhoads: "With few exceptions, the streams are remarkably stable and any changes you make here will remain that way."

These findings meant that any modifications they made to a stream, if done correctly, were going to be long lasting. The data also indicated that much of the dredging and straightening done to contain agricultural drainage ditches within riparian zones and out of farm fields was unnecessary. On the flip side, the findings also meant that damage to streams was equally enduring. Any serious interest in stream improvement required human intervention.

Rhoads and Herricks recently exported their technique to the Chicago suburb of Northbrook, where they added pools and riffles to a degraded stream that runs through the town's commercial center. Two years later, the modifications are intact. Fish biomass and diversity has doubled. The community has embraced their revitalized stream.

In many respects, naturalization is an easier sell in urban areas, where aesthetics and environmental improvement are valued. But Rhoads is making progress in the rural regions. Leon Wendte, a district conservationist for the Natural Resources Conservation Service who brought the Embarras site to Rhoads' attention, believes that the acceptance of naturalization by farmers will come down to economics. The recent findings support the notion that these fish-friendly designs will be cheaper to maintain than traditional drainage channels. Linking environmental benefits to lower operating costs, Wendte says, is what will win converts. "We went through the same thing with no-till farming in the 60s," he says. "It took two to three decades, but now it's everywhere. Rhoads is writing a whole new chapter in how the agricultural community views its streams."

By Holly Korab
April 2003