Chapters 1 - U.S. Fish and Wildlife Service

Environmental Consequences
result in only minor changes to the hydrology in Anaheim Bay. These proposals could however
result in localized changes to the existing hydrology within the Refuge warranting additional study
prior to restoration. Specifically, the proposal to restore approximately 20 acres just to the
northeast of Case Road Pond would result in a minor expansion of the tidal prism in the area north
of Bolsa Avenue. This could in turn increase the volume of water flowing through the existing
culverts that connect Case Road Pond to the unrestricted portion of Anaheim Bay, located to the
south of Bolsa Avenue.
To ensure that the rate of flow through these culverts during incoming and receding tides would
not create the potential for erosion around the existing culverts, modeling would be conducted in
conjunction with restoration engineering to determine the anticipated flow rates at the culverts.
This modeling effort would also evaluate the adequacy of the other culverts in the area to handle
the anticipated flows. Should the results of this modeling indicate the potential for erosion,
appropriate measures, such as altering the restoration design to reduce tidal velocities and/or
armoring the areas around the affected culverts to minimize the potential for erosion, would be
incorporated into the final restoration design.
As described in Chapter 4 (Section 4.2.5.1), the culverts that convey tidal flows into the western
portion of the Bolsa Cell from the mitigation channel are in very poor condition, showing
significant signs of deterioration. To correct this problem and address past concerns related to
how much tidal flow should be permitted within the Bolsa Cell, Alternative B proposes to remove
the deteriorated culverts, repair the levee, and rather than replace the existing culverts, install a
new water control structure near the center of the levee.
The replacement of the existing culverts with a new water control structure would eliminate
unregulated fluctuations in tidal flow, as experienced in the Bolsa Cell since 1990. This will enable
Refuge staff to protect habitat for the Belding’s savannah sparrow, while also improving habitat in
the cell for the light-footed clapper rail. It will also allow regulation of water levels during periods
of heavy rainfall and higher high tides to protect existing structures to the east of the Bolsa Cell
from flooding. Prior to the completion of final design for the water control structure, a numerical
model of the tidal hydraulics in the Bolsa Cell under existing conditions and in the future assuming
the construction of a new water control structure will be conducted to establish how best to design
the structure to meet the habitat and flood protection needs of the Refuge. Modeling would also
provide the data necessary to determine if the installation of this structure could affect flows in the
existing culvert that connects the mitigation channel to Anaheim Bay, as well as to assist in the
final design of the water control structure, including the appropriate size and invert elevation of
the inlet.
Installation of the new water control structure would require the use of cofferdams, or the
implementation of other appropriate actions, to prevent tidal exchange through the construction
site while the structure is being installed. The existing culverts would remain in place during this
phase of the project to ensure continued tidal exchange within the Bolsa Cell. Once installed, tidal
flows through the water control structure could be adjusted to maintain tidal elevations in the
Bolsa Cell that would optimize habitat quality for light-footed clapper rails and Belding’s savannah
sparrows, while remaining low enough to ensure that adjacent structures would not be subject to
inundation. This structure would also enable the Refuge Manager to regulate elevations in the
Bolsa Cell in the future as needed to respond to the effects of sea level rise.
The proposal to conduct further analysis, including modeling of proposed actions, prior to
implementing any projects that could affect the hydrology within the Refuge’s coastal wetlands,
Draft Comprehensive Conservation Plan 5-15