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The South Jetty Breach : The South Jetty Breach
The beach was divided into 5 study sectors for satellite image analysis. The period studied was from April 1992 - April of 2007. Square acreage of each study sector was followed over time… : The beach was divided into 5 study sectors for satellite image analysis. The period studied was from April 1992 - April of 2007. Square acreage of each study sector was followed over time… Ocean Beach
Study Sectors PI Point
During the study period, the Ocean Beach Sectors, as a group, lost atotal of 23 square acres of Shoreline…(where did the sand go?) : During the study period, the Ocean Beach Sectors, as a group, lost atotal of 23 square acres of Shoreline…(where did the sand go?) 109 86
During the study period, Plum Island Point gained some 22 square acres of beach… : During the study period, Plum Island Point gained some 22 square acres of beach… 30 53 Clearly sand migrated
from the ocean facing
Beach to Plum Island
Point.
At it’s smallest size (30 Sq. Acres) within the study period, Plum Island Point looked like this in 1998… : At it’s smallest size (30 Sq. Acres) within the study period, Plum Island Point looked like this in 1998… By 2004 it grew to 53 sq acres & has remained at about 50 sq acres in size through 2007…
But how does the sand get around the Merrimack River South Jetty to build PI Point? : But how does the sand get around the Merrimack River South Jetty to build PI Point? The sand passes through an on shore breach in the jetty SE Ground Swell
Constantly Impacts
Jetty Over time,
Rocks topple Waves drive sand
Through breach
The persistent pounding of the SE ground swell coupled with the pressure of the migrating sand, have, over the years, pushed the Jetty granite into the Merrimack River… : The persistent pounding of the SE ground swell coupled with the pressure of the migrating sand, have, over the years, pushed the Jetty granite into the Merrimack River… March 6th 2008
: …about 7200 waves
in 24 hours! Waves push that sand along
every 10 – 12 seconds, as
long as there is a swell …
Gravity returns water, along with some sand, back to its level…in the river. : Gravity returns water, along with some sand, back to its level…in the river.
After passing through the jetty breach, the sand forms a pile, or “wash over terrace”, as it has for decades… : After passing through the jetty breach, the sand forms a pile, or “wash over terrace”, as it has for decades…
Slide 12: Then, smaller ocean waves penetrating the river
entrance scour the sand away… Incoming
Wave Emerging
Reflection
Wave Erosion …transporting it westward to build Plum Island Point… Sand
Transport
Slide 13: Small beach building wavestransporting sand…
Slide 14: On the incoming tide, sea water enters the river through
the breach… The Tide Carries a plume
of sand with it Wave action
kicks up sand