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Albemarle-Pamlico National Estuary Partnership - Living Shoreline Protections Part II

Albemarle-Pamlico National Estuary Partnership

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November 15, 2017
The 2017 Albemarle-Pamlico Ecosystem Symposium: Eyes on the Horizon

October 16, 2017
From Dust Came Soil Conservation

September 11, 2017
Taking Nature's Pulse

August 18th, 2017
Teaching Teachers to ExPLORE NC

July 13, 2017
Protecting North Carolina's Coastal Habitats with Jimmy Johnson

May 19, 2017
Cypress Trees as Sentinels of the Sounds

April 5, 2017
Becoming the Napa Valley of Oysters

February 28, 2017
Sound Science Guiding Conservation of the Albemarle-Pamlico Region

February 6, 2017
Celebrating Five Years of SciREN Coast

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December 12, 2016 
Proud Shaddys and Shamommas! A "Shad in the Classroom" Tale

November 2, 2016 
Cape Hatteras National Seashore Provides Opportunity for Scientific Discovery

September 19, 2016 
Restoring Estuaries, One Bag of Recycled Oyster Shells at a Time

July 15, 2016
Landscapes Standing Sentinel in Eastern North Carolina

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APNEP's Soundings Blog: A fresh take on the Albemarle-Pamlico region's salty affairs

Living Storm Protections: Part II

How Did Hurricane Florence and Tropical Storm Michael Impact Living Shorelines?

 February 14th, 2019

Read Part I

Part II: Monitoring the Performance and Resilience of Marsh Sill Living Shorelines
Scientists: Mackenzie Taggart and Brandon Puckett (North Carolina Coastal Reserve and National Estuarine Research Reserve)
 
Regular monitoring of eight constructed rock and oyster sills by scientists with the North Carolina Coastal Reserve and National Estuarine Research Reserve (NCNERR) and the Division of Coastal Management (DCM) is part of an ongoing project to assess the performance and resilience of marsh sills over time in coastal North Carolina. The monitoring addresses 1) structural integrity of the sills, 2) erosion reduction and sediment accumulation because of the sills, and 3) repair and maintenance the sills may need to undergo.
 
Monitoring results will be used to advise waterfront property owners, contractors and regulatory partners on the shoreline protection benefits, durability, and potential cost-effectiveness of marsh sills. The sills being monitored are located along the coastline from the Chowan River in Edenton to St. James Plantation in Southport. The marsh sills range in size from 79 feet (Springer’s Point) to 505 feet (St. James Plantation) and age from 3 to 14 years (Figure 1).
 

 Figure 1. List of monitored marsh sills living shorelines.

Post Hurricane Florence
All the monitored sills were visited 1-3 months pre- and post-Hurricane Florence. Data collected during monitoring showed minimal signs of damage to both the rock and oyster sills due to Hurricane Florence. Across all sills, scientists concluded an average loss of 3.5 inches of sediment due to scour on the waterward side of the sills, and an average loss of 1.2 inches on the landward side of the sills (Figure 2). On average, sill width increased by 9.8 inches, whereas sill height decreased by 1.5 inches, which is likely due to slight movement of sill material (rocks or oyster bags) during the high energy storm event (Figure 2).

Behind the sills, the marsh shoreline eroded an average of 11.8 inches with a subsequent loss of 14 percent of marsh vegetation, suggesting most of the marsh was protected and retained after the storm. Only the St. James Plantation Oyster Sill in Southport suffered structural damages in the form of a few displaced oyster bags from the main sill (Figure 2). Overall, the varied sill types proved successful in offering durable shoreline stabilization—by minimizing erosion and protecting marsh vegetation—even after the strength of a hurricane.

Figure 2. Average changes observed at marsh sill living shorelines from before to after Hurricane Florence (Diagram by B. Puckett, NCNERR).

The saying goes that pictures are worth a thousand words, so below we’ve include pre- and post-Hurricane Florence pictures of the sills we monitored. The pictures speak for themselves and illustrate what the monitoring data suggests—marsh sill living shorelines perform well during large storm events, providing a resilient shoreline stabilization option along North Carolina’s estuarine shorelines.

Morris Landing Rock Sill | Holly Ridge, NC 

August 2018 (one month pre-storm)                         October 2018 (one month post-storm)

This 492-foot rock sill was installed in 2005 at the Morris Landing Clean Water Preserve. The photos were taken looking southwest, along the sill. Notice the similar location of the marsh vegetation line from before to after the hurricane. Changes in vegetation color are largely due to changing seasons (summer to fall). Measuring tapes were used during monitoring.

 

Springers Point Rock Sill | Ocracoke Island, NC 

August 2018 (one month pre-storm)                         December 2018 (three months post-storm)

This 79-foot granite rock sill lies on a very exposed shoreline on the Pamlico Sound side of Ocracoke. The photos are taken looking north along the sill. Changes in vegetation color are due to normal seasonal changes. In the photo on left, the NCNERR staff person is using a highly accurate GPS to measure elevations.

 

Teaches Hole Rock Sill | Ocracoke Island, NC 

August 2018 (one month pre-storm)                         December 2018 (three months post-storm)

The Teaches Hole Channel Sill was constructed in 2015 and measures 141 feet. It is sparsely vegetated imediately behind the sill, but the property owners are considering planting marsh grasses. The top row of photos were taken looking south, along the sill. The bottom row of photos were taken looking east, perpendicular to the sill.

 

Silver Lake Harbor Oyster Sill | Ocracoke Island, NC 

August 2018 (one month pre-storm)                         December 2018 (three months post-storm)

This marl rock sill was constructed in 2012 at a length of 105 feet and is located within Ocracoke’s Silver Lake Harbor. The photos were taken along the sill looking northeast. The water level is relatively high in the bottom, right hand picture, so the sill is not as visible.

 

Chowan River Boat Ramp Rock Sill | Edenton, NC 

August 2018 (one month pre-storm)                         October 2018 (one month post-storm)

Measuring 367 feet, this is the northern most sill in the monitoring program and was the least impacted by Hurricane Florence. The photos in the top row were taken looking northwest, along the sill. The photos in the bottom row were taken looking southeast, along the sill. In bottom left photo, the DCM staff person is using a measuring tape to measure the distance from the rock sill to edge of marsh vegetation.

 

St. James Plantation Oyster Sill| Southport, NC 

August 2018 (one month pre-storm)                         November 2018 (two months post-storm)

Measuring 505 feet, this is the longest sill in the monitoring program. First installed in 2007, this oyster bag sill has had several additions to increase its length. The photos in the top row were taken looking west. The photos in bottom row were taken looking east. A few of the oyster bags (oyster shell in plastic mesh bag) at the top of the sill were knocked off of the sill during the storm (not pictured).

 

Kingsley Street Park Sill| Southport, NC 

August 2018 (one month pre-storm)                         November 2018 (two months post-storm)

This 148 foot granite rock sill was installed in 2004 on behalf of the city of Southport. The photos were taken looking northwest, perpendicular to the sill. In the photo on left, the NCNERR staff person is using a quadrat (the large square) to assess marsh vegetation cover.

Read Part I of the Living Storm Protections Series

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