Shoreline Stabilization and Changes in Sediment Composition Associated with Small-Scale Oyster

Reefs in South Carolina

Michael HodgesNancy Hadley

Loren Coen

Steve Roth

Lindsay Goodwin

Majbritt Bolton-Warberg

The South Carolina Oyster Restoration and Enhancement Program (SCORE)

was established to:• Involve citizens in oyster

restoration activities• Educate the public and

foster environmental stewardship

• Utilize volunteer assistance to recycle shell

• Use volunteer manpower to establish multiple research platforms annually along South Carolinas coast and aid in data collection

In Five Years, SCORE Has

• Established 128 reefs (2,115m2) at 29 sites along 320 km of coastline

• Encompassed a broad spectrum of environmental conditions

• Involved over 2,000 volunteers/over 15,000 hours of service

• Trained weekly water quality monitors at most of these sites

Typical Site Layout

14 m2

A Sites Firmness Can Vary Depending on Sediment Profile

Shell Sand

Fine Sediment

We Monitor Regularly for the Following

1. Marsh erosion

2. Marsh expansion

3. Sedimentation rate and composition

4. Chlorophyll a

5. Water quality (pH, DO, Salinity, Water Clarity, Temp)

6. Utilization by other organisms

7. Population parameters

8. Reef observations

Marsh Erosion• Natural phenomenon caused by

winds, waves, currents, and tides

• Destabilization of fringing marsh is a cause for concern and seriously affected by erosion

• Human activities such as boat traffic, wetland drainage, and dredging increase rates of erosion

• Oysters act as natural breakwaters for fringing marsh to help decrease the rate of shoreline loss

Marsh Erosion

SCORE Erosion Site Results, 2001-7/06SCORE Erosion Site Results, 2001-7/06

Mean Overall ErosionMean Overall ErosionMonthly Mean Erosion RatesMonthly Mean Erosion Rates

Mean monthly rates ranged from 1.3 – 5.5 cm Overall shoreline losses ranged from 40.5 – 331.3 cm.

Numbers in columns indicate total length of assessment, 21 – 59 mo.

Erosion Rates Are Decreasing With Time Behind Reefs

Spartina Expansion• Although marsh edge continues

to retreat, overtime Spartina is growing seaward

• Expansion has been noted at 10 sites, significant expansion at 9 sites

• Generally takes place 2.5-3 years post-construction

• Appears to be associated with the accumulation of soft sediments and stabilization behind reefs

• Has grown seaward as much as 13 meters at some sites

Marsh Expansion These are totals for the original reefs deployed at these sites, negative numbers represent retreat of marsh

Site Mean Expansion

(m)

Max Expansion

at Single Reef

(m)

Length of Deployment

(months)

Kiawah -1.0 0 29

Boy Scout -0.6 3.5 65

Waddell 3.3 6.3 52

Dataw 3.5 6.2 65

Palmetto 4.6 8.5 65

Trask 7.6 13.9 52

Spartina Expansion at Boy Scout

20022002200320042006

2001 2002

Spartina Expansion at Dataw Island20022003200420062006

Port Royal Sound (High Energy) Expansion

2003

2004

2006

Charleston Harbor (High Energy) Expansion

200120042006

Marsh Expansion Along Entire Shoreline

2002

2005

Shoreline Changes at Palmetto I slands County Park 2001-2005

-10

-8

-6

-4

-2

0

2

4

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29

Location of Forward Marsh Edge Relative to Reef (m)

Oyster Reef 2005 2001-02 2003

Oyster reef

Creek

High Ground

Marsh

(m)

Sediment Depth Poles

• Used to measure rate at which sediments settle at reefs

• Poles are 40 cm in length

• Placed behind reefs• Measured quarterly or

bi-annually

Sediment Depth Poles

Sediment Analysis

Sediment Grain Size Analysis

• We wanted to examine pre-construction sediment composition vs. post-construction sediment composition

• There is a significant difference in the sediment composition accumulating behind reefs vs. sediment composition not associated with constructed reefs

(p= .003)

• At all sites monitored , there has been an increase in the amount of fine sediments settling at our reefs.

• The sediment is either washing down from above salt marshes or settling out with reduced flow rates around new reefs

Changes in Sediment Composition

AVG 29% (13 sites)

0

10

20

30

40

50

60

70

80

90

100

pre-

construction

2004 2006

pre-

construction

2004 2006

pre-

construction

2004 2006

Trask Landing Waddell Center Palmetto Park

Changes in Sedimentation Following Reef Construction, Year Two, and Year Four

Mud

Sand%

Co m

posi

tion

Site/Years

Things To Consider When Constructing Reefs

Boat RampSpacing Between ReefsSpacing Between Reefs

Ways to Address Sediment and Shoreline Changes

Elevate Back RowAdd Stumps Behind Reef

Conclusions• Spacing of reefs is important when considering shoreline

protection• Reef deployment aids in marsh expansion• Sediment compositions are changing at sites as reefs are

introduced• Early adaptive management techniques will help to deal

with excessive sedimentation• Using volunteers will help facilitate work load and

increase community awareness on environmental concerns

• Filling knowledge gaps of sheltered coastal systems

Future Objectives

• Continue to intensely monitor erosion behind reefs and areas not associated with reefs to see if they differ significantly

• Continue to monitor changes in sediment composition and marsh expansion

• Use findings to establish oyster restoration metrics

• Construct more reefs in Northern part of SC

Acknowledgements• All SCORE Volunteers• Community Partners• SRS Staff (past and

present)• Jason Comer and Andy

Jennings• Environmental Action

Volunteers• Beaufort Marine Institute• Wesley Willis (RIP)• Mr. T