July 25, 1999

Two weeks after a disastrous canal break in Riverdale, experts are a few steps closer to answering the question many flooded home-owners are asking: What caused it?

Environment Specialist John Hollenhorst has exclusive details.

It's possible we'll never know exactly why the canal broke and unleashed a devastating flow of millions of gallons of mud and water. But experts this week ruled out a couple of causes, and turned up some intriguing leads.

By the time news cameras arrived two Sundays ago, much of the geologic evidence had washed away.

But homeowner Norman Farr started shooting home video within the first eight minutes. His pictures have become a valuable piece of evidence for researchers.

Fred May, a geologist with State Emergency Management says, "It's our only view into the past that we've seen so far. "

When May put the video on his computer, he was able to see the wall of the broken canal before it completely washed away.

"Concrete was still there. We can still see plants growing through it, " he says.

Growing plants might have created leaks. But many miles of the canal have similar plant growth.

"To say it's the cause, we'd have to wonder why it hasn't breached farther to the south, the ten miles up the mouth of the canyon, you get the same feature. But it's a troubling image for people like us that look at a canal, " May says.

Geologists and engineers from 10 government agencies scrambled over the site this week. They reached concensus on several key points. There was no evidence of unstable slopes, an earthquake, or massive earth movement before the canal broke.

"We saw no evidence of landslides or slumps. We did see evidence of rodent and root activity around the canal. And that's worrisome," according to May.

The experts also agreed: the soil itself was unsuitable to support a canal.

"It's a fine, silty sand that basically, very low cohesion. You put water on it, it melts. The wind blows across it, it just slides down. And so, we would consider it to be quite a poor foundation for a canal like this, " he says.

The most likely cause: the canal sprung a leak which quickly grew big because of the unstable soil. But did something else happen that triggered the canal's first major failure in 115 years?

Investigators detected a soggy layer of earth under an unbroken part of the canal. Did water leak from nearby storage tanks, or from a nearby pond, weakening the soil? Was the ground shaken by nearby construction work, or even by noisy jets at Hill Air Force Base? Experts have ruled nothing out.

The concrete lining itself is suspect.

It was poured in 1910, in sections, first the bottom, then the sides. Experts say the resulting seams may have been leak-prone.

In the home video, it's clear the concrete broke along those seams.

The head of the canal company declined an on-camera interview tonight, but he did ask a rhetorical question: If the site is geologically unsuitable, how could the canal go 115 years without a disaster?

He says the basic questions remain unanswered. The canal company's insurors are bringing in their own experts tomorrow.