Environmental Impact Statement - Sonoma Land Trust

Sonoma Land Trust
Chapter 4. Consultation and Other Requirements
the perimeter levee lowering would result in an increase in tidal velocities in
downstream Tolay Creek, while midstream areas of the creek would experience a
minor reduction (Moffat and Nichol 2011). Increases in tidal velocities into the
proposed basin could also expose the new levee along the SMART rail line and
the existing levees to erosion from wave forces. Implementation of the erosion
control measures identified in Chapter 3.2 would reduce erosion from windgenerated
waves.
Implementation of the restoration alternativesIf required by adaptive
management, up to two additional breaches along Tolay Creek could be
constructed for either action alternative. Breaches 3 and 4 would increase tidal
range at the Upper Lagoon in Tolay Creek. Increased currents and tidal prism
could over time create down-cutting of the channel upstream of the breach.
Monitoring of the creek and appropriate adaptive management would minimize
this condition. Implementation of Breaches 3 and 4 would relieve pressure on
upstream sites dependent on aging agricultural levees, thereby reducing the flood
risk to agricultural lands and infrastructure located adjacent to San Pablo Bay and
Tolay Creek. In addition, the project would not significantly alter circulation and
sedimentation processes in adjacent tidal areas.
The Project design described in Chapter 2 would provide flood protection.
Measures to address the potential tidal dampening effect of Breaches 3 and 4
would be incorporated into the design of these breaches. If the Full-Tidal
Alternative were to be constructed, HYD-MM -1 would be implemented to avoid
unacceptable levels of tidal muting in Tolay Creek.
If breach/dredge options 1 or 2 are implemented, they would further mute tidal
range in Tolay Creek in addition to the apparent muting resultant from the Tolay
Creek Restoration Project. This would be a cumulatively significant impact that
can be mitigated through adoption of breach/dredge Option 3.
Therefore, the cumulative contributions for the project from surface- water
hydrology and tidal hydraulics would be less than significant with mitigation.
Water Quality
Implementation of any of the restoration alternatives wouldmay result in
potential short term water quality impacts on Tolay Creek and San Pablo Bay
during construction. Water quality impacts would be due to sedimentation
turbidity resulting from breaching of levees and dredging. Dredging and
placement of dredged material. Placement of dredged material for the proposed
project could result in leaching of contaminants from fill and excavated
sediments and selective uptake and biomagnification of contaminants in plants
and animals. Other projects in San Pablo Bay including the Hamilton Wetland
Restoration PlanProject, Bel Main Keys Restoration Project, and maintenance
dredging, and the Napa River Salt Marsh project, among others could also affect
water quality in San Pablo Bay although these effects are expected to be
relatively local effects and are unlikely to occur in the project area.
Sears Point Wetland and Watershed Restoration
Project Final Environmental Impact
Report/Environmental Impact Statement
4-11
April 2012