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 MaintenanceVegetation

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

Referenceswww.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.