Montauk Point Lighthouse Museum & Gift Shop

EROSION CONTROL
Montauk Point in 1838 (vertical section, west to east). The lighthouse is 220' from the bluff.
Copied from the 1838 United States Coast Survey.

Montauk Point in 1990 (vertical section, west to east). The lighthouse is 100' from the bluff.

 

200 FEET OF LAND LOST IN 200 YEARS

The planners of the Montauk Point Lighthouse were well aware of erosion. The governments agents noted that "Montauk Point is washed by the sea in storms" and "wastes very fast". They erected the lighthouse at the extreme west end of the Turtle Hill plateau, at a distance of approximately 300 feet from the bluff.

Over the past 200 years approximately 200' feet of montauk point was washed into the Atlantic Ocean. Today the lighthouse stands less than 100 feet from the edge of the bluff.

 

EROSION: Problem
cross section diagram of unprotected bluff

CAUSES OF EROSION
STORM WAVES
Storm waves at the toe of the bluff causing soil to fall.
GROUNDWATER FLOW
Ground water sinks through the layer of sand and flows laterally on the hard layer of clay. A concentrated stream pours from the bluffs face, rapidly carrying soil with it. The top of the bluff is undermined and carried to the beach below.
RAIN
Erosion of the bluff by rain is a slow but steady process.
GROUNDWATER SEEPAGE
Halted by a further layer of clay groundwater seeps from the permeable layer of glacial till (sand, gravel and boulders). Surface particles are gradually carried away.

 

EROSION: Solution
cross section of protected bluff

METHODS OF EROSION CONTROL
PROTECTING THE TOE  
TOE WALL
Beyond the sea wall a TOE WALL buttresses the base of the bluff. A filter cloth lining behind and benaeth the toe wall prevents storm waves from removing soil and undermining boulders.

SEA WALL
The largest boulders form a SEA WALL to break the force of storm waves.

STABILIZING THE SLOPE  
FILTER BOX TERRACING
The slope above the toe wall is reshaped to a more stable angle which is maintained by terracing and vegetation. The terraces constructed of lumber and secured by steel stakes provide a stable surface for vegetation. A filter cloth lining prevents the filter bed from washing away. Beach grass and rosa rugosa planted on the terraces do the most work to hold the bluff face. Their roots hold the soil in place and draw groundwater from the bluff. Their foliage softens the impact of rain and slows water runoff.
   
DRAINAGE SYSTEM
A drainage system is critical to the stability of the bluff. Here a Water Collection Box is set in the bluff face to capture the stream of groundwater flowing on top of the layer of clay. The water is collected in a concrete trough and funneled into a discharge pipe to run out harmlessly onto the boulders of the toe wall. The top of the water collection box is planted in the same fashion as the filter box terraces.

To Save a Lighthouse
by Giorgina Reid

Against All Odds
by Greg Donohue

 


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