Transcript Slide 1

Saltwater Barrier: Is it a Restoration
Alternative for the Northwest Fork of
the Loxahatchee River?
Patricia Walker
Loxahatchee River Management Coordination Council Meeting,
January 30, 2012
Loxahatchee
River
Watershed
Northwest Fork of the Loxahatchee River
THE 1975 PROPOSAL
 Jupiter Inlet District (JID) and Florida
Department of Natural Resources (FDNR)
applied to the U.S. Army Corps of Engineers
for a permit to construct a saltwater barrier
weir in the Northwest Fork near River Mile
6.0.
 Construction of a weir at an elevation 4 feet
below mean sea level within the south
boundary of Jonathan Dickson State Park
(JDSP) and near an existing power line
crossing.
THE 1975 PROPOSAL
 The U.S. Fish and Wildlife Service (FWS)
expressed concern that there was no
hydrologic study that could confirm the
effectiveness of such a weir structure in
preventing saltwater intrusion.
 FWS Recommendations Deny the permit
Studies to show other salinity management
alternatives
THE 1986 FEASIBILITY STUDY
 Jupiter Inlet
District (JID)
initiated the
study
 Feasibility of
placing one or
more submerged
weir(s) to limit
the salinity
intrusion
THE 1986 FEASIBILITY STUDY
 The literature search found that “little
published information exists on the use or
performance of submerged weirs for
salinity control.”
 The feasibility report concluded that
design of a submerged structure on the
Loxahatchee River would require
comprehensive study to verify its
performance.
2005 SFWMD MODELING EVALUATION
 Chapter 9 of the
Restoration
Plan
 Using a
calibrated 3-D
hydrodynamic
model (CH3D)
2005 SFWMD MODELING EVALUATION
Barrier Location
2005 SFWMD MODELING EVALUATION
2 Barrier Types
Tide elevation at the Inlet
Tidal elevation (m, NGVD29)
0.8
0.4
0
-0.4
0
10
20
30
Julian day
Crest elevation = 1.0 ft NGVD29
Crest elevation = +0.1 ft NGVD29
Crest elevation = 1.0 ft NGVD29
Surface Elevation (ft NGVD29)
Elevation Change with a Barrier
2
1
0
-1
8
8.4
8.8
9.2
9.6
10
WATER QUALITY CONCERNS
 Nutrient concentrations and possible algal
problems occurring behind the structure.
 A saltwater barrier can cause both a
temperature and dissolved oxygen
imbalance in and around its vicinity.
 Adding a dam structure to the river may
increase the levels of fecal coliform
bacteria as a result of reduced tidal
flushing.
ECOLOGICAL CONCERNS
 The barrier will
have a negative
impact on the
spawning and
nursery areas
for fish.
 Can lose the
entire floodplain
due to
inundation.
2005 SFWMD MODELING EVALUATION
Conclusions
 Type 1 barrier is unlikely to achieve the target
of salinity reduction at River Mile 6.2 (2 ppt)
without violating minimum channel width
guidelines for small craft navigation
 Type 2 barrier is more effective in
reducing/preventing salt intrusion. Given
sufficient crest height, Type 2 barrier can
achieve the salinity target at River Mile 6.2.
 Due to concerns about disruption of navigation
and ecological impacts, saltwater barrier was
not chosen as a viable option by the
Restoration Plan
Saltwater Barrier – Not a Restoration Alternative for the Northwest
Fork of the Loxahatchee River
Thank you for your interest in the
Northwest Fork of the Loxahatchee River!