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History shows Delta has taken beating through time

Published in the Stockton Record on 12/30/04

History shows Delta has taken beating through time

By Dana Nichols
Record Staff Writer
Published Thursday, December 30, 2004

The story of the San Joaquin-Sacramento River Delta begins 10,000 years ago, at the end of the last ice age, when much of the Earth's water was locked up in great ice sheets.

Back then, ocean levels were hundreds of feet lower than they are today. The Sacramento River flowed through the present-day Delta and San Francisco Bay. It finally met the ocean somewhere east of the Farallon Islands.

Then the ice age ended, and the oceans started rising. What is now the Delta became a freshwater estuary. Tules grew by the billions, living, dying and piling their dead stalks deep in the still water, said Jeffrey F. Mount, a geologist at the University of California, Davis.

Mount said the mass of decaying tules built the peat soils that farmers love. Under water, exposed to little oxygen, the plant matter decayed very slowly.

The plants grew quickly enough to fill the estuary as sea levels continued to rise gradually over the next 6,000 years, eventually depositing a peat soil layer 50 or more feet deep in much of the Delta.

In the Delta, abundant flows from Sierra rivers deposited mud and sand in the maze of channels running between the peat islands the tules created.

By the 1880s, farmers were adding a little extra mud to the berms surrounding the Delta islands and then pumping out the water inside the islands to expose the rich peat soil.

Once exposed to air, the soil changed. Bacteria now had access to plentiful oxygen and began breaking down plant matter. Some of it burned off in periodic peat fires. Some blew away in massive dust storms that sometimes turned the sky black.

Mount calculates that the volume of soil lost in the Delta since 1900 is about 2.5 billion cubic meters, almost half of all that accumulated over 6,000 years. It would require scraping more than 2 feet off San Joaquin County's 1,399 square miles of land area to fill a hole that big.

Mount says all the mud and sediment washed out of the hills and then out to San Francisco Bay by hydraulic miners during the Gold Rush is less than half the volume of the soil that's been lost in the Delta.

Peat-dust storms were especially bad before 1950, when asparagus farmers mounded the light soil around the asparagus stalks to keep them white, said Tod Ruhstaller, curator at Stockton's Haggin Museum. White asparagus was then a popular delicacy.

"When they would pile the peat around the asparagus, it would be picked up by the wind, and anyone who had a white garage door or a white house would find a mess," Ruhstaller said.

Despite the dust and the fires, however, the vast majority of the peat soil simply oxidized away, converted to carbon dioxide gas, Mount said.

Now, some parts of the Delta are as much as 26 feet below sea level and getting up to 4 inches lower every year.

At the same time, sea levels are rising and may be anywhere from a few inches to a half-foot higher 50 years from now, Mount said.

The sinking islands and rising water put ever more pressure on levees, which often are little more than piles of river mud.

Delta islands have flooded 108 times since 1900. Sometimes -- as in the 12,000-acre Jones Tract flood this past June and the 6,000-acre McDonald Island flood in August 1980 -- levees give way on calm summer days, and authorities can't determine exactly why they broke.

Intuitively, people who find themselves in a hole far below sea level might decide they want to refill the hole. But that just isn't possible, at least not within our lifetimes, Mount said.

Even if there were no dams blocking sediment flow and ocean levels stopped rising, it would take more than 1,000 years for rivers to wash enough mud downstream to fill the hole, he said.

The result is that humans must build ever higher and stronger levees if they want to keep water from filling the hole. And that should be done because of dire consequences to the state's water system should the Delta go back to being an inland sea, said Jason Fanselau, chief of public affairs for the Sacramento office of the Army Corps of Engineers.

"My take is this: If you are behind levees, you are at risk right now," Fanselau said. "While the level of risk or the odds of flooding may be increasing, you are at risk right now. And in many places the risk is fairly significant today," he said.

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* To reach reporter Dana Nichols, phone (209) 546-8295 or e-mail dnichols@recordnet.com

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