Environmental Impact Statement - Sonoma Land Trust

California Department of Fish and Game
U.S. Fish and Wildlife Service
Chapter 2. Alternatives
while construction activities are being completed in the remaining areas. The
type of vegetation that would be established by modifying the current flood-drain
water management schedule at the site using a water control structure such as
slides or flapgates to enable intake of bay water to flood and drain the site. (The
water control structure would be removed upon tidal restoration, and could be
subsequently placed at one of the breach locations.) These water management
modifications would favor the establishment of brackish or salt has not been
determined. While it would be preferable to establish salt-tolerant tidal marsh
vegetation such as pickleweed, saltgrass, or alkali-bulrush, or submerged aquatic
vegetation such as wigeongrass,.Other vegetation, such as brass-buttons and
spearscale,would occur in variable proportions. Allit would be difficult to
provide sufficient brackish water for irrigation to ensure the establishment of
tidal marsh vegetation.
Instead, irrigation would be accomplished using water pumped from ditches
and/or onsite wells. Because all types of vegetation would contribute to soil
stabilization and bed roughness; however, becausemeeting the first two
objectives, any pre-vegetation activities would be considered a benefit for the
site.
Because the existing soil surface is subsided below sea level, much of the
primary vegetation would be sacrificial after tides are restored. Marsh vegetation
established at higher elevations (ridges, mounds, etc.) may persist as live plants,
but even the dead, fibrous remains of submergence-killed vegetation would likely
persist for years and contribute to sediment stability and roughness.Initial
flooding of the site prior to the first growing season would occur after completion
of grading, during late fall seed dispersal periods, to introduce brackish and salt
marsh plant seeds to the site. The initial flooding would briefly reach elevations
approaching MHHW during calm weather to salinize soils and disperse tidal
marsh seeds over the full potential tidal wetland elevations. The site would be
drained to shallow depths during winter to minimize potential internal wave
action and erosion, and to create capacity for impounding rainfall and runoff,
reducing salinity.
The site would be reflooded in early spring with low-salinity water, to mix and
dilute with impounded freshwater. Water levels would be raised to temporarily
submerge graded mounds, ridges, and levee slopes during calm weather. Water
levels would be drawn down gradually to promote wetland plant germination and
seedling establishment over a wide range of elevations during the low salinity
spring growing season. After seedling establishment, water levels would again be
gradually raised as alkali-bulrush seedlings grow in height. Pickleweed would
establish on saline soils that alternate between wet and drained conditions at any
elevation. In case of drought (early onset of high salinity during the spring
growing season), alkali-bulrush recruitment would fail, and water management
would instead focus on pickleweed.
During the spring-early summer growing season, water levels would fluctuate
around depths adapted to the height of alkali-bulrush. Some active transplanting
of alkali-bulrush corms at low density may be undertaken to accelerate its
Sears Point Wetland and Watershed Restoration
Project Final Environmental Impact
Report/Environmental Impact Statement
2-20
April 2012