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July 11, 2003

Land development the big source of flooding problems, expert says

WEST LAFAYETTE, Ind. – While recent rains continue to swell waterways, long-term changes in our natural landscapes are more responsible for the current flooding problems in the Midwest, according to Purdue University land-use experts.

Wabash River flooding
Download photo - caption below

"Development and farming practices have reduced the natural buffers around streams by nearly 70 percent nationally," said Brent Ladd, Purdue Extension water quality specialist.

These buffer areas – wetlands and wooded areas that naturally occur adjacent to streams and rivers – act as sponges to soak up excess water, like what has fallen across much of the Midwest in the past week.

Studies show that without the natural buffer areas, water runoff in developed urban areas increases by a factor of up to 16 times, according to Ladd. His own investigation found water runoff in an Indiana watershed containing 80 percent agricultural lands was eight times greater than in naturally buffered areas.

"The natural plants such as trees and prairie grasses, which used to grow in flood plains, have long root systems that can reach up to 20 feet below the surface," said Ladd. These long-rooted plants help soak up excess water that enters the soil. The deeper the water reaches, the more it also feeds underground aquifers that pour water gently back into the streams. Field crops have roots that are typically much shallower.

While the natural beauty of waterways attracts housing developments, businesses and recreational facilities along rivers, the increased development creates big flooding problems.

"Impervious surfaces, such as buildings, roads and parking lots, which don’t allow water to soak into the ground, cause water to run quickly into streams and rivers," said Ladd. "So not only do you get excess flow in the waterway, but also the water is moving more quickly."

When water starts moving faster downstream, that causes greater erosion and starts to straighten out the natural bends in waterways that help to keep the flow rate down. Streams start to become "surface pipes" that transport the water rapidly, causing flooding.

"Any time you build on a flood plain, you inhibit a waterway’s ability to infiltrate excess water," said Robert McCormick, Purdue Extension specialist with the Planning with Power project. "While you may not experience problems locally, you do cause problems for those downstream."

The Planning with Power project emphasizes incorporating land-use planning with watershed planning at the local level. The project is coordinated by the Illinois-Indiana Sea Grant Program and the Purdue University Cooperative Extension Service.

Ladd said tiling farm fields to make them less susceptible to ponding, also contributes to runoff problems. The tiles rush water toward drainage ditches that empty into larger streams. "Perhaps the compromise here is for farmers to tile some fields and leave some natural wetland areas to act as buffers," he said.

Ladd said the makeup of soil has also changed over the years. "Studies show that the numbers and diversity of soil organisms have changed in developed and agricultural soils compared with native vegetation, and this is thought to affect the way the ground soaks up water," said Ladd.

Two hundred or more years ago, the soil in a watershed may have contained up to 25,000 species of bacteria and 8,000 species of fungal organisms. This diversity in soil ecology created high levels of organic matter and larger soil pore spaces that infiltrated rainfall.

Ladd said increased rainfall, while a problem in the short run, doesn’t seem to be the main culprit in causing long-term flooding problems.

"When you study old, pre-settlement watersheds, you notice that the waterways meandered and flowed more slowly," said Ladd. "Now we have a lot of flashiness, a lot of fast-moving water that goes up and down quickly. If we want to reduce our flood risks, we have to restore many of the natural buffers we’ve lost."

More information on watershed planning and development is available at the Planning with Power web site. More information on dealing with floods is available on the Extension Disaster Education Network flood page at or by calling Purdue Extension at 888 EXT-INFO.

Writer: Beth Forbes, (765) 494-2722; forbes@purdue.edu

Sources: Brent Ladd, (765) 496-6331; laddb@purdue.edu

Robert McCormick, (765) 494-3627; rmccormick@fnr.purdue.edu

Ag Communications: (765) 494-2722; Beth Forbes, bforbes@aes.purdue.edu; http://www.agriculture.purdue.edu/AgComm/public/agnews/

PHOTO CAPTION:
Reducing natural buffers around waterways increases the amount of flood damage sustained by communities, according to Purdue University land-use experts. Crops and developments in a river flood plain, like this farmland under the waters of the Wabash River near Lafayette, Ind., will occasionally succumb to flooding and increase problems downriver, according to Brent Ladd, Purdue Extension water quality specialist. (Purdue Agricultural Communications photo/Tom Campbell)


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