Biology Reference
In-Depth Information
Carving out a hole in a levee,
whether with a backhoe or dyna-
mite, allows the bay to surge back
into former wetlands and drain
farm fields such as this Bahia res-
toration site in the North Bay. At
one South Bay breach, engineer
Philip Williams rode the first wave
into the Warm Springs restoration
site, 20 feet below sea level, in a
canoe. As such, Williams claims
he's the only person who has ever
ridden a Class III tidal rapid in
San Francisco Bay. (Jude Stalker)
showed that most common flora species established naturally within a 10-
year period at Muzzi—thus allowing marsh restorations to proceed with
local seed, rather than expensive planting programs. “After 35 years of ex-
perimentation, we now think it might take more than 50 years to develop
all functions of a mature tidal salt marsh,” she says.
The final lesson seems to now be not to try to engineer every detail in
advance. Planners now talk of creating “templates” for wetlands—sending
in bulldozers to push the land to the desired elevations relative to sea level,
and perhaps digging out a historic slough or building up an island. Upon
this template, nature is left to work her magic.
Letting the new landscape evolve slowly over time also brought an-
other important ingredient to the recipe—change. Instead of one fixed
type of wetland habitat with set ingredients, designers aimed for evolving
habitats with different ingredients. It was okay, for example, to breach a
levee and create a shallow pond until enough sediment accumulated to
support vegetation, because this provided interim shorebird habitats. Phil
Williams calls this a significant shift in the thinking process: planning for
the evolution of a landscape over 50 years or more.
“We recognize we're no longer creating a snapshot of historical ecol-
ogy, but rather a new trajectory for how the bay will evolve. We have to
decide where we are going to keep the shoreline where it is, where we will
let the shoreline retreat, where we will restore marshes, and where we want
the sediment to come from and go to,” he says.
Sediment may be the most challenging wetland ingredient for plan-
ners to obtain. The bay's sediment supply comes from many sources,
ranging from the sand and silt already lying on the bay floor, to particles
eroded off headlands and coasts, and imported by ocean tides and river
runoff. Once in the bay, sediment is easily moved by wind, waves, and
other disturbances.
In the past, the biggest source of sediment to the system was Central
