saltwater barrier: is it a restoration alternative for the northwest fork of the loxahatchee river?...

Saltwater Barrier: Is it a Restoration Alternative for the Northwest Fork of

the Loxahatchee River?

Loxahatchee River Management Coordination Council Meeting, January 30, 2012

Patricia Walker

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 permitStudies 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

Crest elevation = 1.0 ft NGVD29Crest elevation = +0.1 ft NGVD29Crest elevation = 1.0 ft NGVD29

0 10 20 30Ju lia n d a y

-0.4

0

0.4

0.8

Tid

al e

leva

tion

(m

, NG

VD

29

)

Tide elevation at the Inlet

Elevation Change with a Barrier

8 8.4 8.8 9.2 9.6 10

-1

0

1

2

Sur

face

Ele

vatio

n (f

t N

GV

D29

)

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!