Located in St. Lucie County Mosquito Control District Impoundment
1, south of the Ft. Pierce Inlet, in Sections 12 and 13, Township 35 South,
Range 40 East, St. Lucie County, Class III Waters.
The Mitigation Bank permits
authorize St. Lucie County to establish a 317 acre mitigation bank (Bear Point
Mitigation Bank) on County-owned wetlands adjacent to the Indian River Lagoon.
Mitigation activities include enhancing water quality and wildlife habitat within
St. Lucie County Mosquito Control District Impoundment 1 by installing 24 culverts
through the impoundment levee, removal of exotic plants and modifying current
impoundment management practices.
Work implemented under the Bank permits are to be used as mitigation for future
impacts within the service area, from Sebastian Inlet to the Saint Lucie Inlet
in the Indian River Lagoon, yielding a potential total of 49.8 estuarine mangrove
mitigation bank DEP credits and 43.3 ACE credits.
The basis of the mitigation plan is the enhancement of water quality and hydrology
by adding (24) 36” culverts in the impoundment levee and increasing the volume
of pumped water (using an additional pump station, previously permitted). The
additional gated culverts will allow for significantly increased water, nutrient
and faunal exchange during the open culvert months (generally mid-September
to mid-April), approximating natural conditions with no levee.
During the flooded, pumping period (May-September), approximately 42,000-49,000
gallons per minute will be continuously pumped into the impoundment. After an
initial impoundment “pump-up” period when culvert gates are closed, the volume
of pumped water will be maintained to allow several of the culvert gates to
be opened partially or completely, mimicking the natural tidal exchange volume,
while maintaining desired impoundment water levels
During the pumping period, the target exchange volume of water is 80% of that
which would be naturally exchanged if the levee were not present. Although this
exchange volume will not occur freely in and out of all culverts, several different
types of culvert gates allow various discharge types: bottom waters, surface
waters, outflow only, or open two-way exchange. The setting and adjustment of
these control structures regulates the circulation and water quality in the
impoundment, and will be conducted weekly, based on water level and water quality
data. In addition to the enhanced water exchange, the mitigation plan also calls
for at least one drawdown in the summer for a 2 week period to allow for more
complete flushing of water and to enhance the feeding opportunity for wading
birds.
In addition to the hydrological enhancements, the mitigation bank site will
be treated for exotic vegetation and regularly maintained. Brazilian pepper
that has become established in the impoundment will be treated, and those locations
will be re-visited on a regular basis for follow-up treatment and to inspect
the recovery of native vegetation. Flooding the impoundment with salt water
should help reduce any additional infestation; however, mangrove planting may
be required in some areas to ensure that the success criterion for re-vegetation
is attained. Exotic vegetation on the levee may also include Casuarina and/or
exotic grasses. These areas are currently being treated by the County, but the
permit contains additional conditions for the monitoring, management and success.