Mike Dunbar

Mike Dunbar: Could new trees provoke a downstream disaster?

New almond tree plantings along Crabtree Road in Oakdale on Thursday, Oct. 8, 2015.
New almond tree plantings along Crabtree Road in Oakdale on Thursday, Oct. 8, 2015. aalfaro@modbee.com

It’s not smart to bet against scientists. Their minds grasp numbers faster than most and they’re constantly calculating and recalculating the odds.

Vance Kennedy is a scientist, or was before retiring from the U.S. Geological Survey some years back. He studied rivers, the water in them and the stuff in the water – not fish, but sand, silt and clay and how it all moves.

As the hillsides of eastern Stanislaus County have become covered with almond trees, Kennedy has been calculating the odds. He knows the hillsides were graded and ripped before being planted. Then the ground was often left bare without cover to hold the dirt in place. All this, said Kennedy, could add up to disaster.

“The odds may be 1-in-10 or 1-in-100 that we’ll get a Pineapple Express this year,” said Kennedy, 92. “If we do, I’m concerned we’re going to see a lot of property loss or even loss of life.”

Kennedy isn’t worried about mudslides; slopes of less than 30 degrees rarely give way and few hillsides that steep have been planted. He’s worried about all that loose soil that could eventually be washed into our rivers. Once there, the soil – by then called sediment – will drop to the bottom and accumulate. As that happens, flowing water must rise to get over it. If it tops its banks, it’s called a flood.

The last one in Modesto was in January 1997. It snowed hard throughout December; then, a few days before New Year’s, warm rains blew in from Hawaii – aka the Pineapple Express – and melted much of the snow. By New Year’s Day, water was raging into Lake Don Pedro, almost spilling over the dam.

A short time later, it rushed into Modesto, swamping 1,700 homes. Throughout the state, damage from the worst flood of the 20th century topped $2 billion, killed nine people, damaged 23,000 structures and forced the evacuation of 120,000. The USGS reported 24 inches of rain fell that week in some places.

It was highly, uniquely unusual. But “things are unusual” this year, too, said Kennedy, noting higher atmospheric moisture content and predictions of a strong El Niño.

“What I’m saying is if we get the worst of combined situations, we could have really bad flooding because of what they’ve done in loosening the soils,” Kennedy said.

How much rain will it take? A “pure guess,” said Kennedy: maybe 4 inches.

Modesto has never had that much rain in a day, topping out at 2.7 inches on Dec. 11, 1906. And Kennedy hastens to point out that without a singular megastorm, there is very little to worry about. In fact, all that ripped hillside soil could help speed the flow of water from the surface into the aquifers below.

Matt Machado, Stanislaus County’s director of public works, is counting on that. He’s an engineer, and engineers are pretty good with numbers, too.

“We’re not any more concerned than any other given year,” Machado said. “We’ve had El Niños before. And of the last six El Niños, only three resulted in higher than average rainfall. … Last year we had a 200-year (rainfall) event. … We had two storms, three or four days between them, and the first brought an inch and the second almost 2 inches. … It was more rain than we’ve seen in a very, very long time. We weathered them fine.”

He also has confidence in today’s farmers: “The more I get to know these (big) operations, the more advanced I know they are. They’re out there doing high-tech farming; they’re ready.”

As Machado pointed out, planting an acre of almonds costs from $6,000 to $10,000 (not counting land). “They’ve got so much invested in dirt, irrigation systems and trees, they’re not going to leave anything to chance,” he said. “They know winter’s coming.”

So does the Central Valley Regional Water Quality Control Board, and officials there aren’t as sanguine as Machado.

“Yes, we are concerned,” said Andrew Altevogt, the board’s assistant executive officer. “Given the predictions for the wet winter, our concern has been heightened. But it’s something we pay attention to any year, whether there will be erosion problems associated with some of these operations.”

His agency has already issued one abatement order for a farm and makes frequent inspections. If they find an issue that could lead to erosion – which could then muddy the rivers – they order farmers to act. The most effective remedy is a grassy ground cover, but catchment basins at the bottom of the hills or even fabric “fences” also can contain runoff.

Are those big east-side farmers that advanced?

“We had issues when they began,” said Brett Stevens, the board’s senior environmental scientist, “but we identified some problems and they made improvements. Generally, they are doing a good job.”

The best defense against sediment-laden runoff is to stop it at the source, says the state’s water plan. Which is what worries Kennedy, who once led a team that produced ground-breaking research into the nature of storm runoff. That’s why he’s telling his friends who live near low-lying areas to beef up their flood insurance.

That’s always a good idea, according to Mike Mierzwa, the lead flood planner for the Department of Water Resources. And homeowners shouldn’t wait. Mierzwa noted that it takes 30 days for policies to take effect, and they’re just as important in the foothills where the recent burns can loosen rocks and send debris crashing down hillsides. The Butte fire was just as unusual as the coming El Nino.

“Mr. Kennedy is right,” said Mierzwa. “Anytime you change the land cover there will be a watershed response.” But he notes that the El Nino might not be as strong here as in southern California.

But what if it is?

“To my knowledge, nowhere has there ever been a situation where you have deliberate ripping of material and loosening soil to that depth,” said Kennedy, who raises citrus on a small Modesto farm. “Then, if you add heavy rainfall” you have a recipe for disaster.

What are the chances of such a disaster happening? We don’t know, no one does. But do you want to gamble against a scientist?