Why are there still salt ponds in the SF Bay?
December 16, 2010 8:21 AM   Subscribe

Why are levees around decommissioned salt ponds left in place?

In 2003, Cargill sold most of its salt ponds in the San Francisco Bay to create the Don Edwards National Wildlife Refuge and other stuff.

There's still salt production going on in the East Bay, but the ponds in the south and west sides of the bay aren't being used anymore.

Cargill says
While wildlife managers and government scientists live out their dream of designing a wetland mosaic on 16,500 acres of de-activated salt ponds surrounding the South Bay, they won’t be altering the 9,000-acre salt pond system that forms the core of the original Don Edwards San Francisco Bay National Wildlife Refuge.
A civil engineering firm says
Cargill Salt proposed a land transfer of part of the salt evaporation pond system to the National Wildlife Service. As part of the transfer, the evaporation ponds were operated to maintain the existing open water conditions in the ponds on an interim basis until the Service had established long-term plans for the preferred land uses and pond operations
Is it the principle of "first, do no harm?" because scientists don't know what will happen if the levees are removed or is it for flood control? The ponds do support wildlife, but the water is more stagnant than open tidelands. Surely this is altering the ecology.
posted by morganw to Science & Nature (5 answers total)
It looks like the CE firm was retained to do a hydraulic study that explores what would be necessary to maintain the ponds and keep salinity levels within a certain range. My guess would be that the levees will remain and the ponds will only be modified to the point that the natural tidal flows maintain the ponds as a tidal wetland.

So yes, nothing is going to be altered until the studies and/or designs are completed, because you'd be incurring significant expenses without knowing how your changes will affect the ecology of the ponds.
posted by electroboy at 8:40 AM on December 16, 2010

I think a lot of it is that removing them would be grossly expensive, not to mention disruptive.
posted by Chocolate Pickle at 8:43 AM on December 16, 2010

Mechanical operations in a marsh or a mudflat can be very destructive. It's very easy to cause long-term, even permanent damage to a wetland even with just foot traffic, let alone construction vehicles.

Traffic damages plants. Plants, plant root systems, are essential to hold sediment in place. Damage the plants and the sediment can wash away in a matter of weeks or a season. This tends to be a snowballing process. Damaged channels in a marsh cause sediment erosion on the margins, which leads to big open areas, which leads to no wetland at all. It can be very difficult to reestablish a wetland when plants have been damaged and rapid sediment erosion is going on. This is especially important in areas with high water flows like tidal areas (in the DENWR) or river mouths.

No wetlands means no habitat for lots of animals. Migratory birds depend on a series of wetlands on their routes. Fish, frogs and resident bird populations depend on marshes for permanent habitat. There are few second chances with wetland engineering.

It almost certainly is "do no harm" because wetlands are so vulnerable to damage and so hard to repair. It's much better to study thoroughly and make changes gradually than to get the backhoes in an tear down the berms without proper hydraulic controls.

The engineering firm isn't saying that this is permanent. Years worth of engineering and biological studies probably need to be done. A treatment plan will probably take a couple of years to implement, even assuming no budget issues. With the constraints on public spending these days, I am certain that this is delaying the process even further. Given those realities, it's best to leave the existing stable situation alone, even if it's not the prettiest, than rush to remove the berms.
posted by bonehead at 9:31 AM on December 16, 2010

North of the Dumbarton there is a lot of duck hunting, and I'm sure they form a vocal and unified constituency that has a lot to say about anything that impacts their sport.

Not coincidentally, the ponds as they are today form an important part of some major flyways for migratory birds. How can you knock those dikes down without knowing how it will affect those federally protected birds?

Finally, I suspect that there is a diked pond of bittern around Redwood City, where they used to do salt extraction. Bittern has toxic concentrations of potassium chloride, left over from the extraction of the salt, and it must remain sequestered.

There is much more available at southbayrestoration.org.
posted by the Real Dan at 10:34 AM on December 16, 2010

Traffic damages plants.

But much of the levees are reachable without crossing marsh. The water is awfully shallow, though, so a barge and boat-mounted-excavator would have to have a shallow draft.

There are floating dredges around the bay (e.g. Redwood City channel). I saw excavators at work when I rode the bike trail to the end of the Alviso slough.

But I get the point that making changes slowly and after study is important.

Thanks for the South Bay Restoration link. I learned that pond A6 is
UNDER CONSTRUCTION. Levees are scheduled to be breached on this pond in November 2010.
which will
Create approximately 330 acres of tidal salt marsh & tidal channel habitat that will evolve over time.
There's a lot more planned. Ponds A8, A7 and A5 are to be connected.
posted by morganw at 12:43 PM on December 16, 2010

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