[env-trinity] Sinking Delta

Josh Allen jallen at trinitycounty.org
Wed Oct 17 10:04:26 PDT 2007


Sinking Delta


Where tules replace corn, they grow soil. It's no quick fix, but it
could save levees.


By Matt Weiser - Bee Staff Writer


Last Updated 9:20 am PDT Wednesday, October 17, 2007
Story appeared in MAIN NEWS section, Page A1

http://www.sacbee.com/101/story/436685.html 

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Robin Miller of the U.S. Geological Survey checks plant material on
Twitchell Island near Rio Vista last week. An experiment there that
duplicates how soil was originally made in the Sacramento-San Joaquin
Delta could help reverse its decline. Randy Pench/Sacramento Bee

See additional images
<http://www.sacbee.com/101/story/436685.html#more_images> 

 

TWITCHELL ISLAND - A stretch of dirt road cutting through this
3,500-acre island near Rio Vista offers a stark look at two different
futures for the Sacramento-San Joaquin Delta.

One side of the road is a farm field, with corn stretching in orderly
and silent rows across hundreds of acres. It sits at least 5 feet lower
than the road, a result of decaying peat soils that have made many Delta
islands into deep bowls through a process called subsidence.

On the other side is a soggy marsh, its floor nearly level with the
road. The marsh is thick with tules and cattails reaching 10 feet
overhead. Songbirds and waterfowl rise between pockets of open water.
The air is filled with chirping and quacking. 

This side of the road was once a subsided bowl, too, and filled with
corn. But 10 years ago, the U.S. Geological Survey converted it to
marshland, allowing tules and other native plants to grow and die back
with the seasons as they once did.

The experiment has revived the process that created the Delta's peat
soils in the first place. Over 10 years it has slowly raised the ground
surface more than 2 feet in places, and it could restore generations of
decline in the Delta, the West Coast's largest estuary.

"I'm standing on 2 feet of accumulated material, and it didn't just
squish down," said Robin Miller, USGS project chief at the Twitchell
site, as she stepped off a plywood platform into a jungle of tules and
cattails. A decade earlier, she would have dropped into thigh-deep
water.

"When I first started doing this project 10 years ago ... I didn't
expect the reversal to be so startlingly enormous."

Delta islands have been sinking below sea level ever since the first
levees were built. Peat soil is fertile farmland, helping to make farms
the Delta's economic heart.

But conventional farm practices have helped sink many Delta islands,
which now survive only thanks to increasingly fragile levees.

Peat soil slowly decays when drained and exposed to air, especially when
it's plowed over and over for farming, as it has been for more than 100
years.

Many Delta islands are now more than 20 feet below sea level, and
continue to subside up to 1 inch per year. This slowly weakens
surrounding levees, creating what scientists say is at least a 20
percent chance that multiple islands will flood in an earthquake within
the next 25 years.

After such a quake, rebuilding at least some of these islands and
forcing out seawater drawn in from San Francisco Bay could take years.
This would cut off the Delta as a drinking water supply for the 23
million Californians who depend on it, with economic damages to the
state estimated at $40 billion.

Restoring peat soils on some islands could avoid that catastrophe by
raising the ground surface again and bolstering levees.

But it won't be a quick fix.

Roger Fujii, chief of the USGS Bay-Delta Program, will present results
of the Twitchell Island project today at the State of the Estuary
Conference in Oakland. The USGS team learned that it can grow peat soil
an average of 1.6 inches - and up to 4 inches - per year merely by
keeping shallow water on the land all the time.

Two test plots were started in 1997 with a few tules planted in each.
Over time, plants filled the rest of the plots on their own.

One plot was maintained at a water depth of 10 inches, the other 22
inches. This ensures that as tules and other plants die, they accumulate
in the water rather than decaying, drying up and blowing away with the
wind.

New plants grow up through dead plants each year. The cycle repeats,
creating successive layers of dead material.

Scientists working for the state Department of Water Resources estimate
that if seven islands in the west Delta were converted to growing tules,
they could be raised 11 feet by 2050.

"We're interested in moving the technology down the path to see if this
can be implemented on larger scales," said Jerry Johns, DWR deputy
director.

The expensive alternative is to keep building levees taller and wider.
DWR estimates reinforcing levees on seven Delta islands would cost $8
billion.

Growing peat takes longer but looks like a cheaper fix. Converting seven
islands to peat could cost $600 million. But 85 percent of that cost
involves first grading the land flat, which could be avoided if islands
were planted in stages following natural land contours.

Miller said the benefits don't take decades to accrue. Wildlife habitat
improves immediately and grows richer each year. If an island floods
early in the process, marsh plants might buffer waves within the island
that could further damage levees.

There's also potential to reduce global warming by storing carbon
dioxide from the atmosphere in new peat soils. If a market can be
created to sell carbon credits in peat soil, this might cover
restoration costs. 

Researchers plan a larger project on Twitchell Island, which is partly
owned by the state, to simulate growing tules on the scale of a working
farm.

Fujii said Delta farmers could be growing peat soil one day instead of
corn, wheat and tomatoes. They would be paid to store carbon in peat
soil rather than to produce food.

"The vision is to create kind of a blueprint, so a farmer can take a
corn field and convert it," said Fujii.

Some questions still need to be answered. For instance, drain water from
the test plots might put more dissolved organic carbon and mercury into
the Delta. These chemicals create harmful byproducts when water is
treated for domestic consumption.

The potential for storing carbon dioxide in peat soils also needs to be
measured precisely.

Fujii said a larger test project could provide these answers within five
years.

Finally, there is a thornier question: How will growing peat affect the
farm economy of the Delta and the people who live there?

Marci Coglianese, former Rio Vista mayor, acknowledged that farming has
a mixed legacy in the Delta: It has degraded Delta islands, but revenue
from growing food is also the primary source of money to maintain
levees.

Putting farmers to work growing peat "could be a wonderful solution,"
she said, if there is an economy to support that.

"Those of us who are down here physically working and trying to maintain
the Delta cannot stay if there is not a local economy," she said. "So we
have to balance all of that. It is people who are the stewards of the
land down here."

 

 

Robin Miller of the U.S. Geological Survey inspects tules on Twitchell
Island, where scientists are growing peat soil on Delta islands by
letting plants decay in standing water, which stops them from blowing
away. Sacramento Bee/Randy Pench

 

 

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