Digging back to future disasters

BY SUSAN KIM | WASHINGTON | January 3, 2000

Floodwaters leave clues, whether they spill from a remote desert river and affect few people, or accompany Hurricane Floyd and submerge thousands of homes.

Dr. Mary Bourke's job is to examine those clues and interpret what they mean.

She's a fluvial geomorphologist. "I drive around and dig holes," she said

the scientist from her headquarters at the National Air and Space Museum.

Right now most of those holes happen to be in the deserts of Australia,

where she is researching age-old catastrophic floods, determining how they

change the landscape, and theorizing what may be affected by future floods.

The sophisticated processes she uses are ones that could help read the face

of floods worldwide for years to come.

In central Australia, where the desert meets the channel of the Hale River,

she is following what she calls a "a detective story" using "the science of


The 35-year-old scientist has traced flood history in that area back 30,000

years --the longest record of floods ever produced in the world. By

examining aerial and satellite photos, taking detailed surveys, noting land

configuration, and analyzing the location and content of sediments, she can

tell you approximately when catastrophic floods occurred. The last one

along the Hale River, she says, happened just 300 years ago.

But can she tell when the next one will be? Not yet, she said. "There's no

pattern that we can establish yet, not a clustering of events. But that

could be because we just don't have enough data yet."

That's why Bourke is gathering more data. She likes to read a handful of

soil the way most people read a mystery novel. For instance, "there are

more pebbles and stones in sand that's been moved by a river, not by wind,"

she said.

Searching for evidence of catastrophic floods is easier in the desert

because rivers flow infrequently, vegetation is sparse, and human impact is


But her findings in Australia impressed people enough that she's been

invited back to talk about flood mitigation. She told people "you live in

an area that had catastrophic floods a thousand years ago, and 300 years


That means it could conceivably happen again in this lifetime. "Some people

dismiss it, saying it's a thousand-year event," she said, but others want

to learn about flood history so they can prepare for the future.

"I'm not sure if we'll ever be able to predict it," she said, "but I can

say we understand phenomena like floods better."

And better understanding means better preparation, and better knowledge of

how to fit dams and other flood control network into nature's existing

system. Her research could be shared with disaster response leaders,

climatologists, engineers, city planners, emergency management departments,

and residents, all who want to live through the next disaster best they can.

That's how research that seems esoteric can impact everyday lives, said

Bourke. "I enjoy the fact that there's a use," said Bourke. "I approach

this from scientific perspective but there is certainly a human element."

Bourke is trying to bring her research techniques to North Carolina in the

wake of flooding caused by Hurricane Floyd, that displaced tens of

thousands in September and killed some 50 people.

Even with as much damage and human suffering as that flooding caused -- and

is still causing -- it wasn't a catastrophic event from a geological

perspective, said Bourke. "It didn't rip up the flood planes or cause

massive landslides like Hurricane Mitch did in Nicaragua."

An added challenge is that the landscape of North Carolina isn't an ideal

one in which to pick up geomorphic evidence. "It's wide and flat so there's

not a lot of river energy to read," she said. "We don't necessarily know

what to look for."

Still, she is sure there will be clues, even if it means "a one-centimeter

film of silt on top of the flood plane. We could compare it to a sample of

silt from 500 years ago."

If Bourke and others receive the funding they're pursuing from the National

Science Foundation, they'll be able to look for more flood fingerprints, or

"signatures" in North Carolina and begin mapping a flood history that could

date back thousands of years.

Flood "signatures" take many forms, said Bourke, and Hurricane Floyd left

unique geomorphic signatures because the ground was already so saturated

before Floyd hit. Floyd's winds blew over trees because the roots couldn't

hold them in the ground.

"That's a signature. That big hole left by the tree becomes a morphological

expression," said Bourke. Thousands of years from now, geomorphologists

would be able to identify that same expression by the high concentration of

vegetation measured in the silt.

"We can already look at certain thickness of sediment and assign it to,

say, Hurricane Fran," said Bourke. "That right there is a fantastic


Studying morphological expressions and signatures can also enhance

understanding of other types of disasters such as drought, she added. An

ongoing severe drought in the middle Atlantic region has farmers facing a

severe winter hay shortage and water supplies running significantly lower

than normal.

The good news is that, climatically speaking, a drought is a short-term

event. The bad news is that, short-term means "a period of up to 30 years

when rainfall is reduced," said Bourke.

As she gathers data and plots the history of disaster, Bourke may seem to

be racing against the occurrence of the next catastrophic event.

Around the world, there are only about 100 other researchers in her field,

and "there is a lot of the planet to cover," she said. Her study areas have

included Australia, Austria, Ireland, New Zealand, the U.S. - and the

planet Mars, where she gathers evidence via satellite photographs.

Wherever her research takes her, Bourke aims to better understand when and

how extreme events occur. "It's not only the top surface -- it's what's

underneath that holds the story," she said.

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