Artificial Dune ConstructionEthan Estey

& Doug Piatkowski

Background

-Barrier islands are part of a sand sharing system

-Constant accretion and erosion with longshore transport

-If left alone to natural processes experience shoreline retreat

-However, shape and width is maintained with retreat

So why are we so concerned?

-The problem of erosion is most often not recognizable until people try to define property lines on moving substrate

-The presence of hard substrate on or close to the beach interrupts the natural shoreline retreat

-Natural barrier island flexibility becomes permanent

-Protective measures to prevent erosion are not for the beach, but for the money invested in development

Man Vs. Nature

Why Artificial Construction

-Prevent erosion – wearing away of the land or the removal of beach or dune sediment by wave action, tidal currents, human activities, waves, drainage or wind

-Natural causes of erosion

-climate – drier climate: river sediment/dying vegetation

-tides - drive currents

-relative sea level change: major reasons why islands receding

-storm frequency: two or more high tide cycles

-Maintain access – right to use or enjoy public beaches including the right to free and unrestricted movement to and from the public beach

-access becoming scarce – increased development

-rotation of access points

-construction of boardwalks or walkways

-paving not appropriate: wind erosion/wave erosion

-Maintain buildings/structures and homes

-higher taxes on shorefront property

-property owner’s structures safe from sea

-shoreline recedes leaving both groups unhappy

*taxing entities don’t recognize erosion of shoreline property

Causes of Erosion

-ORV’s

-soil compaction

-wide access routes / wind erosion

-Recreation

-numerous walkways

-trampling vegetation and dunes

-rattlesnakes

-cactuses

-lifeguards

-Coastal development

-leveling of construction sites

-heavy machinery - to and from site

-laying of pipelines

-leads to removal of sediment, destruction of vegetation, destabilization of sediment, wind

erosion

-Hurricanes

-result in massive wind and wave erosion

Causes of Erosion Cont’d

Results of Erosion on Dunes

-Washover

-when wave height exceeds height of depressions along dune ridge

-sand carried to landward side of dune

-widens after continual attacks and allows for greater volume of water and further penetration, thus, damaging vegetation and removing an even greater volume of sand

-Washouts

-similar to washovers but water and sand move seaward

-sediment deposited in ocean rather than estuary

-often occurs with slow moving hurricane/drainage channels are too small

-Blowout

-breach in dune caused by wind erosion

-dune more susceptible

-multiple channels

-low vegetation/damaged vegetation

Strategies for addressing erosion

1-Relocate or set development back

-minimum setback based on average annual erosion rates

2-Stabilize shoreline

-structural

-non-structural

3-No action

-expensive: individual/local government

-leading to abandonment

Ineffective beach stability measures

-Hard substrates reduce the flexibility of the system

-Unable to respond to changes in dynamic environment

-These disruptions in sand sharing system initiate a chain reaction

-Examples:

-Seawalls (New Jersey)

-Groins (New Jersey)

-Jetties (New Jersey)

-Bulkheads (New Jersey)

-New Jersey, therefore, is home to the worst beaches on the east coast

Hard Substrates Cont’d-Hard substrate armors the property landward against erosion

-Effects shoreline erosion elsewhere by disrupting dynamic transport of sand alongshore

-Inhibits natural dune build-up down drift

-Important to maintain habitat for dune dwelling species

-Provide dunes for endangered nesting sea turtles

-prevent lighting effects from inshore housing and development

-impervious structures prevent nest construction

Effects of seawall construction

-Less effective than natural protective dune barriers

-Beach in front of seawall may be eroded by waves rebounding off structure

-Results in undermining (ex: New Jersey)

Erosion protection policies

-Many state policies found within statutes and rules are targeted towards coastal erosion

-NC has a law against the development of hard substrate for erosion protection

-State policies often promote “soft” methods of avoiding erosion vs. “hard” shoreline protection

-Ex: State-The Dune Protection Act (Texas): recognizes importance of coastal sand dunes and their role in erosion protection

Federal-Public Law 71-570: COE – federal agency to study,

Plan and implement shore protection projects

Artificial dune construction

-Dunes are part of the natural sand exchanging environment

-Cyclic sand sharing events dissipate much of wave energy

-Foredunes: first vegetated dune landward of water absorbing and dissipating initial wave energy

-Bar: buildup of sand offshore causing waves to lose energy by breaking further offshore

-Calm season (summer):

-accretion of sand from offshore bars to beach (intertidal zone)

-sand movement from intertidal zone landward (saltation & surface creep)-buildup of foredune

-Heavy wave action season (winter):

-waves flatten beach, erode and undermine seaward dune face and cause dunes to recede

-eroded sand is carried to offshore bars (help dissipate wave energy)

Accretion/Erosion Cycle

More reasons…

-More attractive

-Habitat for flora and fauna

-Serve biological and ecological functions

-Least expensive and most efficient defense

-Flexible to dynamics of the environment

Methods of Building Dunes1-Trees, brush/groundcover

-Disregarded Christmas trees

-Brush

-Seaweed

2-Geo-tube (Texas A&M)

-$600,000 project

-15 ft wide and 7 ft high

-buried 2 ft beneath sand

-sand pumped inside

-vegetation planted on top

3-Marine mammal stranding

-Inorganic debris (cars, concrete, tires, etc.) are often discouraged

-not biodegradable and safety hazard

Other Methods

Imported Sand

-Beaches with limited sand supply: saturated or restrained

-Natural sand accumulation process is slow

-20 years – 6 ft high dune

-Sources of artificial sand (sand should NOT be taken from beach)

-construction material suppliers

-cement companies

-dredged material (not good source)

-Treatment

-salt content should not exceed 4 ppt (may inhibit plant growth)

-similar size and mineral content as dune-building site

-similar height, slope, width, and shape as natural dunes

Slope requirements

-height – no less than 4 ft

-slope - no more than 45 degrees

(18.5 deg. Preferred)

-initial width – at least 20 ft

-location – landward of fordune

(increase sand supply)

Atlantic City imported dune

Techniques of Dune Maintenance

Vegetation

Common species

Bitter panicum

(Panicum amarum) Marshay cordgrass

(Spartina patens)

Sea oats

(Uniola paniculata)

Bitter Panicum-Very successful

-hardy grower

-high salt tolerance

-Vegetation requirements

-plants used – 2-3 ft. tall

-cut tops off 1 ft. above root to minimize water loss

-Planting

-early winter to early summer

-survival dependent on adequate moisture

-can be planted horizontally or vertically/wind permitting

-protection from grazers / very susceptible

Sea Oats

-Less salt tolerant than Bitter Panicum

-Rapid growth / low burial rate

-More successful with interplanting

Marshhay Cordgrass

-Low growth rate / high burial rate

-For best results

-interplant with Bitter Panicum

-repair more stable part of dune

American beachgrass(Ammophil brevilugulata)

-Tolerant to salt spray

-Heat resistant

-Deep rhizomes and roots to stabilize dune

Vegetation steps

-For three species: (Panicum amarum, Spartina patens, Uniola paniculata)

-If taken from wild:

-select site low in erosion

-remove plants in scattered pattern

-transplant with shovel

-Vegetation area:

-small area / steep slope – done by hand

-large area – machinery (tractor)

Vegetation steps cont’d

-Planting guidelines:

-holes dug 8-10 inches (hand)

-higher success rate after rainfall or watering

-low wind areas:

-hay is most economical

-3000 pounds per acre

-pack hay in soil

-high wind areas

-burlap or screen (biodegradable)

Transplanted Vegetation Maintenance

-Watering only necessary in drought conditions

-Fertilizer only needed the first year

-Area must be fenced or signed off

-kept safe from grazing, vehicles and pedestrians

-Expect a survival rate of 50-80%

-Less than 10% – replant

-Greater than 10 % - re-vegetate from well developed areas after 1-2 years

Sand Fencing

Sand Fencing Sand Pallets

Sand Fencing

-Resistant to shoreline conditions

-Important: sand fencing must be coupled with vegetation for effective dune building

-Uses: wind erosion preventative or dune building structure

-Composition: two inch wide wooden planks held by wire

-Cost: 50 ft rolls - $30-$50

-Location: four ft. high and no more than 20 ft seaward of veg.

-Installation: 2x4 treated lumber posts driven no more than 2 ft into ground

Sand Fence Specifications

Sand fencing cont’d

-Configurations

-Zig-Zag:

-not recommended

-blocks access for public and wildlife

-use 25 ft sections and leave 5 ft gaps at intervals

Sand fencing cont’d

-Parallel:

-recommended by NC Wildlife Resources Commission

-10 ft. sections spaced seven ft. apart

-Benefits:

-excellent erosion control

-vegetation between sections

-access between sections

Sand fencing cont’d

-Straight-line:

-does not allow access

-may not face prevailing winds

Sand Pallets (plastic fencing)

-Advantages:

-constructed from recovered and post consumer material

-strong, durable and reusable

-will not be broken down for campfire

-Disadvantages:

-3X as expensive as wooden fencing

Sand Fencing for Breaches/Blowouts

Sand Fencing for Damaged Foredune

Sand Fencing in Washover/Washout

Maintenance

-Education:

-use signs (keep off dunes)

-reading material

-Walkovers

-structures to prevent trampling

-prevent erosion

References

www.assateague.com/bea-gras.html

www.crcwater.org/issues8/19990812oceanshoreseis.html

www.crystalbeach.com/geotube.htm

www.environment.gov.au/marine/manuals_reports/coast-manual/section5.html

www.epa.gov/epaoswer/non-hw/procure/products/fencing.htm

www.glo.state.tx.us/coastal/dunerules.html

www.hbtownhall.com/2beach101.htm

www.sea-oats.com/images/oats-1

www.surfrider.org/texas/geotube.html

www.topsailbeach.org/programs.htm

www.uncwil.edu/people/hosier

Coooper, S. William. 1958. Coastal Sand Dunes of Oregon and Washington. Boulder, CO: Geological society of America.

Psuty, P. Norbert, 1988. Sediment Budget and Dune/Beach Interaction. Journal of Coastal Research, 3, 1-4.