By Chuck Squatriglia
San Francisco Chronicle
January 27, 2007
Generations of engineers have tried to
keep the sea from robbing Ocean Beach of its sand, but
nothing's ever worked.
Until now.
The Pacific Ocean has at long last ceded, if only slightly, to
engineers who've shown that the forces eroding the shore can
be harnessed to restore it.
Their elegantly simple solution has helped reclaim 3 feet of
San Francisco's coastline and just might stop Ocean Beach from
washing away.
"It looks like it's working," said Patrick Barnard,
a coastal geologist with the U.S. Geological Survey.
"What we hoped would happen is happening."
Stopping the coastal erosion south of Sloat Boulevard has long
challenged the city and the National Park Service.
The vast stores of sand that once backed the beach diminished
as the city crept toward the sea. The Pacific takes more sand
than the shore replaces, an imbalance that has eroded dunes,
crumpled parking lots and threatened to undermine the Great
Highway.
Repairing the damage has cost several million dollars. Trying
to stop it without resorting to a seawall has cost millions
more. The city has shored up bluffs, realigned roads, and
padded the beach with tons of sand, to little avail.
Now the Army Corps of Engineers believes it's found the
answer: creating a sandbar about a half-mile offshore of Ocean
Beach using the 300,000 cubic yards of sand it dredges each
year from the shipping channel outside the Golden Gate. The
sandbar will dissipate some of the destructive energy carried
by the waves, the thinking went, and provide sand to replenish
what is washed off the beach.
It's worked on the East Coast, and the corps thought it would
work in the complex and dynamic marine topography beyond the
Golden Gate.
To test the idea, the corps dropped about 275,000 cubic yards
of sand in June 2005. It dumped another 300,000 cubic yards in
May.
Barnard said tests show about half of the sand dispersed as
expected. Better yet, the 1,000-meter stretch of coastline
targeted in the test has accreted 1 meter.
In other words, the beach is 3 feet wider.
Barnard called the results "promising" but said
further study is needed before he can attribute all that
growth to the sandbar. Still, he is cautiously optimistic the
corps is on the right track.
The Corps of Engineers is far more bullish.
"While Patrick may be cautiously optimistic, I'm very
optimistic," said Peter Mull, the engineer leading the
project for the corps. "We plan to continue this
near-shore placement so it continues to nourish the
beach."
But don't expect a vast expanse of pristine beach anytime
soon. The sea took its time stealing Ocean Beach and will take
its time returning it.
Like, say, 10 or 20 years.
"It's not a quick fix," said Mull, who has surfed
Ocean Beach for almost 20 years. "We're restoring the
natural system."
That's the beauty of it, some environmentalists and coastal
advocates said. It is a green solution.
"It's using material that is out there already,"
said Lesley Ewing, a coastal engineer with the California
Coastal Commission. "If it starts working, there's an
opportunity to go into the area south of Sloat with sand, with
plants and with what you usually think of as a beach and give
that a start."
It's also relatively cheap, because it uses sand that must be
dumped anyway.
The Corps of Engineers needs a new place to drop the sand
pulled from the shipping channel each year because the spot it
has used since 1971 can't take much more. The corps spends
about $2.5 million dredging the channel each year, and doesn't
expect that figure to change significantly with a new drop
zone.
There are still some points to be worked out in the plan, such
as determining the ideal shape and location for the sandbar.
Mull said the corps hopes to expand the test with a dune of
dredged sand that would further nourish Ocean Beach. Congress
appropriated $500,000 in May for further study.
But the city, the Park Service and the corps agree that the
idea works. The rest, officials said, is just details.
"All of the decision-makers who will have to sign off on
it are in agreement," said Frank Filice, manager of
capital projects for the San Francisco Public Works
Department. "This is the solution we're heading to."
E-mail Chuck Squatriglia at csquatriglia@sfchronicle.com.
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