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Is Your Shoreline Eroding?

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Eroded stone armored shoreline heavily impacted by Super Storm Sandy

Shorelines are dynamic in nature and erosion is to be expected. Not all eroding shores need to be protected or stabilized. However, landowners may want to address erosion if the shoreline experiences chronic and intense erosion, and where valuable habitat, or valuable built infrastructure are at risk. The following will provide readers with information to determine whether a shoreline may be eroding and whether this erosion is of concern.

The cause of the erosion must be identified to successfully protect the shore. Erosion can occur because of: hydrological conditions (i.e. waves and currents); stormwater runoff; human interaction (i.e. structure placement or dredging); or various other reasons. Different stabilization solutions are appropriate only for a specific range of conditions and the unique characteristics at each site will dictate the selection of the optimal stabilization treatment.

 

Are large trees falling into the water?

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Tree in danger of falling into a water body

 

 

 Fully developed trees that are extremely close to the waterline can indicate an area which was once stable but is actively eroding. Large root systems exposed during low tide can be another indication of an eroding shoreline.

 

   

Is there evidence of undermining?

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Undermined shoreline exposed at low water

 

During low tide, currents and waves may cause erosion that is not easily visible.  Undermining will quickly result in the further loss of sediment.

 

Are large portions of bank eroding?

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Larger scale shoreline erosion

 

Large breakaway pieces of land indicate a very unstable shoreline. Uneven, sinuous shorelines will develop.

 

 

 

 

Is land loss apparent in historical images?

After

After

Before

Before

 

Historical photos can show how much land has been lost or gained over a period of time. The tide phase or water level must be similar in comparison images.  Google Earth and historic aerials are sources of photos.

 

Reasons for an Eroding Shoreline

Failed or failing structure

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Compromised bulkhead from washout

 

 

The washout of sediment from behind a bulkhead or revetment is a sign of a failed or compromised structure.  Unless addressed, these shorelines will continue to erode.

 

 Wind driven waves (fetch dependent)

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Examples of fetch on the Hudson River

     

 

A fetch is an uninterrupted distance over a surface of water that the forces of wind act upon.  The sizes of the waves reaching the shore are directly related to the fetch length; a longer fetch has the potential to produce larger waves.  Fetch length can reach up to 8 miles long in the wider portions of the Hudson River.

 

Wakes and proximity to navigation channel

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Wakes from recreational boating

Boat traffic can generate wakes that are often several times larger than the waves from the wind at the site.  Predicting wake sizes is vital for the proper design of any shore stabilization method.  Observing the wakes during peak traffic provides insight into the wake energy at the site.

Fast-moving currents

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Model of currents in the Hudson (NYHOPS, http://hudson.dl.stevens-tech.edu/)

 

Currents running parallel to the shore, both from the ebb and flood of tides and downstream flow can erode the shoreline.  Floating debris can further exacerbate erosion.

 

 

Adjacent structures

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Flanking at the end of a bulkhead

 

 

Very often severe erosion will take place where the built structure meets the natural shoreline. The reflection of the waves on the structure can cause erosion both at the ends or flanks of the structure and at the toe.


Ice

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Ice at Norrie Point, Hudson River

   

Large pieces of floating ice, moved by currents, tides and wind, can scour the shoreline.  Ice is difficult to predict but the impacts may be very significant.

 

 

Content Credit: Andrew J. Rella Ph. D. & Jon K. Miller Ph.D. of the Stevens Institute of Technology

Hudson River National Estuarine Research Reserve

New York State Department of Environmental Conservation
NOAA National Estuarine Research Reserve System

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