Inlet Presentation

falmouthmass.us

Inlet Presentation

Tidal Inlet Modifications

a potential technique to improve estuarine

water quality

Opportunities for Falmouth

John Ramsey, P.E.


Tidal Inlets: A Primer


Tidal Attenuation in Natural Systems

Great River M 2 Ratio = 0.95

Little Sippewissett M 2 Ratio = 0.48

Ellisville Harbor M 2 Ratio = 0.28


Potential Opportunities for Inlet Improvements

1. Oyster Pond (West

Falmouth)

2. Little Sippewissett

Marsh

3. Salt Pond

4. Little Pond

5. Bournes Pond


Tidal Attenuation Caused by Constricted Inlets


Tidal Attenuation – Example of No Restriction


Estuarine Model Development


Bournes Pond

Falmouth

Inlet Widening


Bournes Pond comparison of model average total N concentrations from present loading

and the widened inlet channel (100 ft) scenario with present loading, with

percent change, for the Ashumet Valley systems.

Sub-Embayment

Effect of Flushing Improvements

Tidal Prism Increases ~28%

monitoring

station

present

(mg/L)

Channel

mod,

present

(mg/L)

% change

Bournes Pond - upper B2 0.875 0.829 -7.7%

Bournes Pond - mid B3 0.782 0.569 -42.4%

Israels Cove B5 0.591 0.581 -3.2%

Bournes Pond - lower B6 0.339 0.323 -27.1%


Bournes Pond, Falmouth

present 100 ft-wide inlet Scenario AB Scenario AB

100 ft-wide inlet


Little Pond, Falmouth

Influece of Widened Culvert on Tides

• Tidal Prism

Increase ~38%

• MHHW

Increase ~0.2 ft

• MLLW

Decrease ~0.1

ft

Culvert Design Can Be Optimized to Limit High Tide Height


Existing

Little Pond, Falmouth

20 ft Culvert

20 ft Culvert with Septic

Removal


Channel Shape & Dimensions


Benefits & Concerns

1. Reduce Cost of

Estuarine Clean-up

2. Reduced Need for

Wastewater

Infrastructure

3. Environmental

Concerns

4. Potential Increased

Maintenance

Dredging


Environmental Concerns

1. Barrier Beach

Resources

2. Sediment

Transport

3. Salinity

4. Coastal Erosion

5. Flooding


Barrier Beach Function

Storm Damage Prevention and

Flood Control

Threatened and Endangered

Species Habitat

Protection of Marine Fisheries

and Wildlife Habitat

Environmental Constraints

Salt Marshes and Land Under the Ocean

Generally Less-Restrictive (habitat recovery)

Protection of Marine Fisheries and Wildlife Habitat


Farm Pond, Oak Bluffs

Existing 4 ft Culvert Proposed 16 ft Culvert


Coastal Processes – Shoreline Change

Sediment “Starvation”

(Natural and Anthropogenic)

Tidal Inlet “Efficiency”

Coastal Engineering

Structures


Understanding History

1894


Understanding History


Bournes Pond – Peak Current Velocities

Existing 100 ft Wide Inlet


Existing 100-ft Wide Inlet

Bournes Pond

Tidally Averaged

Salinity


Some Thoughts on Maintenance Dredging…


Questions?

More magazines by this user
Similar magazines