DREDGING THE PASS

1999 Ten-Year Permit vs New Proposed Permit

1999 10-Yr Permit, Clam Bay Restoration and Management Plan

The primary objective was environmental restoration of the ecosystem in particular the restoration of approximately 20 hectares of mangroves that died off in the northern end of the system along the strand road and upper clam bay

Today’s Proposed Permit, Clam Pass Maintenance Dredging

The primary objective is inlet maintenance to aid in flushing and improve environmental resources.

1996

Upper Clam Bay

Reminder of where we used to be…

Development Adjacent to Mangroves

Alteration of Natural

Hydrology

Change in Tidal Flow

Increased Freshwater

Runoff

Altered Hydroperiod Reduced Sheetflow

- Extended Surface Water Retention

- Surface Water Levels Increase

- Tidal Circulation in the Mangroves becomes stagnant

Prolonged Stress of

submerged aerial roots

Black Mangrove

Die-off

Below Ground Decay

Subsidence

Change in Avian Species UseDecline in Avian Populations

Decline in Benthic Invertebrate Community

Decline in Fisheries

Conceptual Model of a Black Mangrove Die-off

REMEMBER THIS

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Rain

Rain

Full Moon

Rain

2"

6"

8"

(Reference) Surface Water Fluctuations During the Wet Season: Tidal Influence at a Station Situated Near the Gulf

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Full Moon

Rain Rain

1"

4"

7"

(Die-off) Surface Water Fluctuations During the Wet Season: Muted Tidal Signatures and Predominant Influence of Rain and Runoff

inch

esin

ches

Clam Bay 2002

NEED A COMPREHENSIVE PLAN TO PROTECT THE ESTUARY WHICH CONSISTS OF ENVIRONMENTAL RESOURCES THAT ARE FOUND IN THE PASS, BAYS AND TRIBUTARIES AND THE LANDWARD HABITATS INCLUDING THE MANGROVE FORESTS , SCRUB AND DUNES

Dredging Clam Pass Inlet ALONE is not answer to maintaining the health of the estuarine waterways and mangrove forest

When to Dredge?

Dredging should occur only when the hydrologic exchange between the Gulf and the Clam Bay estuary has been reduced to the point where the biological integrity of the entire system (water and forest resources) are at risk.

Clam Pass

1953

Clam Pass 1962

Cla

m P

ass

1995

Cla

m P

ass

2003

Inlet Dynamics are influenced by a variety of factors such as:

Inlet Current patterns driven by tides, waves, wind, severe weather, etc.

Constantly variable inlet hydrodynamics are influenced by tidal prism, channel and estuary morphology, slope, elevation, sediment type(s) and geological features, fresh water inflow, gross geometric variation, flow velocity, tidal phase and amplitude and phase, shoaling and scouring, etc…..

Clam Pass 2009

Clam Pass 2008

Circumstances that could necessitate dredging:

1)Pass completely closes due to a storm or other natural event

2)Inlet has lost hydraulic efficiency that is not recoverable through natural processes

Tide Gauges, Mangrove, Seagrass and other

Ecological IndicatorsMonitoring Plan

Purpose: To evaluate inlet characteristics and tidal dynamics within the entire Clam Bay system on a comprehensive long-term basis.

CLAM PASS

Proposed Dredging Template

HYDROLOGIC EFFICIENCY OF THE ENTIRE CLAM BAY

SYSTEM

ECOLOGICAL CONDITIONS OF

THE ENTIRE CLAM BAY SYSTEM

THERE IS NO CUT AND DRIED DECISION OF WHEN TO DREDGE

THE DECIESION SHOULD BE BASED UPON THE BEST SCIENTIFIC HYDROLOGIC AND ECOLOGIC DATA AVAILABLE AND BY WEIGHING THE BENEFITS OF DREDGING VS THE DETRIMENTS OF DREDGING IN

RELATION TO THE ENVIRONMENT