Five Major Causes of Plum Island Erosion

Slide 1: 

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Unlocking the Mystery Of Beach Erosion At Plum Island : 

Unlocking the Mystery Of Beach Erosion At Plum Island Copyright 2008, Michael Morris

An Investigative Study By Michael Morris… : 

An Investigative Study By Michael Morris… …that applies the principles of Oceanography, Meteorology, & Geology to Observed & Historical events at Plum Island with the goal of better understanding the elements that affect its change.

This study achieves the goals of determining… : 

This study achieves the goals of determining… The direction that sand moves along Plum Island’s shore & why. How this migration is affected by our influences such as beach groins, river jetties, houses & dredging. The causes of current & past major episodes of beach erosion at Plum Island. What might be done to solve beach erosion at Plum Island.

“Nature never deceives us; it is we who deceive ourselves.” : 

“Nature never deceives us; it is we who deceive ourselves.” ~ Jean Jacques Rousseau

“History teaches everything including the future.” : 

“History teaches everything including the future.” ~ Lamartine

Plum Island Beach Sand Erodes & Accretes (gathers), : 

Plum Island Beach Sand Erodes & Accretes (gathers), wind … & water… at the direction of the forces exerted by…

Above the water, wind moves sand that isn’t stored by vegetation, roots, debris, beach fences & dunes… : 

Above the water, wind moves sand that isn’t stored by vegetation, roots, debris, beach fences & dunes…

Between the dunes & the water lies the beach berm, a no mans land for sand… : 

Between the dunes & the water lies the beach berm, a no mans land for sand… With nothing to cling to, wind moves sand back towards the dunes… …along the beach, or into the water. The beach berm is like your checkbook. Sand or money that’s there today isn’t the same sand or money that will be there tomorrow. With constant withdrawals & deposits, we maintain a transient average daily balance. Like unexpected expenses, storms can make large withdrawals from a beach berm, but a healthy barrier dune acts like a savings account, keeping the checkbook in balance when necessary. Erosion occurs when sand withdrawals exceed deposits… …and when the sand reserves of the barrier dune system are depleted.

Between the high & low tide lines and below the water, wave action moves sand… : 

Between the high & low tide lines and below the water, wave action moves sand… Photo: Clark Little, Surfer Magazine This is especially true at Plum Island as it is a wave & tide dominated beach Small waves move sand along the shore but ultimately leave it behind upon the beach. Large waves remove sand from the beach to the near shore shallows & continue to move it along near shore, but underwater.

Slide 11: 

The journey that Plum Island Sand makes today is illustrated in the “Littoral Cell” below… Near Shore Wave Driven Sand Migration Barrier Dune Storage & Release River Current Transport Off Shore Large Ground Swell Transport Back Toward Shore Wave & Current induced Migration from River Delta Bar Return to Shore via Transverse Sand Bars & Bar migration When we add beach groins, river jetties, and dredge river sediments, we alter this system’s balance & flow, and introduce sand deficits & erosion.

Slide 12: 

Plum Island Center, Newbury… River Jetties force sand supply offshore… Creating offshore bars that cause wave refraction & accelerated sand migration near shore. Center Groin halts sand migration, starving the beach to the north. Barrier Dune is compromised by large homes. Jetty Breach passes Ocean beach sand to Plum Island Point Five Man Made Variables Causing Erosion… Wave Approach