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 Summary

Horseneck Beach and the Westport River are in trouble.

  1. Sand is eroding from the beach exposing rocks,
  2. sand is accumulated in the harbor and channel threatening boats and
  3. the build-up of nitrogen in the river is suffocating the ecosystem.

 

The cause appears to be the causeway to Gooseberry Island.

Erosion

If you’ve been to Horseneck Beach recently, then you have witnessed the erosion of sand.  As the sand erodes, the underlying rocks are revealed.  Along the camp ground, the beach is comprised entirely of large stones.  Along the guarded section of State Beach, the stones and sand are mix (pictured below).  The stones are evident at Baker’s Beach and they are expected to make a showing along the town beach in the next few years.

Stones are now prevalent along Horseneck State Beach Reservation

Stones are now prevalent along Horseneck State Beach Reservation

What’s going on?

Sand does not simply evaporate or disappear, it went somewhere.  Evidence suggests that the sand traveled West to the mouth of the river where there are numerous sandbars that appear to be growing.  In fact, several years ago, the sand clogged the mouth of the river and had to be dredged.  Here is an article about the last dredging.

Sand accumulating at the entrance of the Westport River Harbor

Sand accumulating at the entrance of the Westport River Harbor

But that’s not all

In addition to loss of sand on the beach and accumulation of sand in the harbor, there is a very concerning build-up of nitrogen in the Wesport River.  Here is an article on the subject.  Excess nitrogen causes excess algae which consumes more than it’s fair share of oxygen.  This has the effect of starving the marshland ecosystem, crabs, shrimp, and other little critters.  The ecosystem is vital to the food chain because without it, the larger species disappear which impacts our local food supply and economy.

How is the Gooseberry Island Causeway involved?

Gooseberry Island Causeway blocks currents and redirects energy along Horseneck Beach

Gooseberry Island Causeway blocks currents and redirects energy along Horseneck Beach

Have you ever noticed that the water on the West side of the Gooseberry Island Causeway is higher and more active than the water on the East side?

Initial measurements suggest that it is six inches higher on average and peaks at twelve inches.  The study that reveals these measurements will be posted on this site.

Have you ever noticed that when you swim in the water at Horseneck, that a slow current pushes you West and you are always compensating by walking or swimming East?

The current comes from the direction of Gooseberry Island and pushes you toward the harbor.  It seems to be the same current that pushes flotsam like driftwood.  It is very likely to be the force behind the movement of the sand.

But how can the current be coming from Gooseberry Island?

The answer seems to be that Gooseberry Island is redirecting the near-shore currents of the Gulf Stream.  This is a well known effect of a “groyne“.

The textbook groyne creates a circulating current called a "primary eddy"

The textbook groyne creates a circulating current called a “primary eddy”

The Gooseberry Island Causeway creates an unintentional groyne when combined with the island, itself.  This has the effect of circulating a massive current along the beach from East to West.

The Gooseberry Island groyne circulates current from East to West along Horseneck.

The Gooseberry Island groyne circulates current from East to West along Horseneck.

The circulating currents are (1) eroding the sand from the beach, (2) depositing the sand into sandbars at the mouth of the river, and (3) trapping the nitrogen-rich water only to circulate back into the river with each tide cycle.  By removing the causeway, possibly by replacing it with a bridge, the current is expected to flow through into Buzzard’s Bay rather than circulate along the beach.

By removing the causeway, the currents will no longer be circulated but will cross into Buzzard's Bay

By removing the causeway, the currents will no longer be circulated but will cross into Buzzard’s Bay

Returning Gooseberry Island to it’s original state without the causeway is expected to restore equilibrium to the currents thereby (1) causing sand to once again accumulate on the beach, (2) arrest the development of sandbars in the harbor and (3) increase flushing of nitrogen from the river.  East Beach might also benefit.  Prior to construction of the causeway, East Beach was a sandy beach.  Few people are old enough to remember sand on East Beach, however, the few that do remember speculation that the causeway was the culprit.

 

This website is dedicated to discussing these questions and finding a way to restore the sand on Horseneck Beach.

This PDF slide deck provides additional information about Horseneck Sand Erosion.