dauphin island east end beach and barrier island...

Dauphin Island East End Beach and Barrier Island Restoration Project

Beau BuhringSouth Coast Engineers

Funding

Funded with qualified outer continental shelf oil and gas revenues by the Coastal Impact Assistance Program (AL-28: Dauphin Island Shoreline Stabilization Project), Fish and Wildlife Service, U.S. Department of the Interior

Overview

Physical BackgroundProject Description

Sand Search InvestigationRegulatory Hurdles

Design ConsiderationsConstruction PhaseBeach Monitoring

Background – Project Location

MOBILEBAY

GULF OF MEXICO

MOBILECOUNTY

BALDWINCOUNTY

PROJECTLOCATION

PERDIDOBEACHRESORT

Background – Coastal Processes

Erosion Areas

Accretion Areas

Background – Site Conditions

Project Description – Goals

Reduce saltwater intrusion risk to valuable freshwater lake and maritime forest habitat Restore erosional foraging and nesting

habitat for birds and sea turtles Introduce beach sands into the littoral drift

of the Gulf barrier island Increase longevity of new sand by

concurrent use of rock breakwaters

Project Description – Benefits

Wide beaches provide protection from waves and storm surge to upland properties during tropical events Wide beaches contribute economically,

thanks to visitor spending and taxes

Project Description – Beach

Dredging and placement of ~320,000 cubic yards of beach sand Beach template

widths to vary from ~100 feet to ~350 feet

Beach nourishment: The placement of large

quantities of good quality sand directly

on the beach to widen the beach.

Project Description – Structures

Eight existing, shore-perpendicular, rock groins to be disassembled Three new, shore-parallel breakwaters to

be built from old rocks and new stone Structures intended to better retain sand

at the eastern end of the project

Sand Search – Overview

Extensive sand search investigation undertaken in 2010 to identify potential sources of borrow sand

Borrow Area Concerns and Priorities

Grain size compatibility Free of contaminants

Proximal to site Sufficient sand quantity

Avoid cultural resources and infrastructure

Sand Search – Sampling

Sand Search – Compatibility

Sand Search – Compatibility

Material Source

Mean Grain Size Sorting Silt Dry Color

(mm) (phi) (phi) (%) MunsellValue

Borrow Area I 0.26 1.95 0.63 1.3 7

Borrow Area II 0.23 2.13 0.54 1.4 7

East End Native 0.28 1.86 0.69 3.6 7

Sand Search – Borrow Area

Final Borrow Sub-area

Regulatory – Cultural Resources

Investigation areas filled with historic shipwrecks Magnetometer and

side scan sonar surveying Sub-area identified

to minimize cultural impacts

“Damn the torpedoes! Full speed ahead!”

- Admiral David Farragut, 1864 (paraphrased)

Regulatory – Tribal Concern

Island has ancient Native American burial mounds Project reviewed by

tribal consultant with the U.S. Corps of Engineers

“…j’ay resté a l’isle, queje nomme du Massacre…”

- Pierre Le Moyne d’Iberville, 1699

Regulatory – Wildlife Concerns

Alabama beaches are nesting areas for endangered shore birds and sea turtles Construction activities

avoided nesting seasons Lighting surveys after

constructionPhoto: alabamaseaturtles.com

Regulatory – Monitoring

During construction: dredge position, onsite bird and turtle activity, and turbidity changes due to fill Post-construction: beach profile surveys,

aerial photography, compaction testing, and escarpment surveys

During Construction

Post-Construction Year 1 Year 2 Year 3

Regulatory – Mean High Tide

Alabama state law requires the municipality to establish a mean high tide line before construction Filled waterbottoms seaward of the mean

high tide line are held in trust by the state Identified by survey in a public hearing

Regulatory – Property Concerns

Alabama state law requires the municipality to obtain by conveyance certain rights necessary to fill areas upland of the new MHT line Property owners included quasi-public

entities (Dauphin Island Park & Beach Board and Dauphin Island Sea Lab) and the federal government (U.S. Coast Guard)

Design – Beach Fill

Estimated and permitted ~320,000 cubic yards of new sand to restore the beaches

Design – Beach Fill Profile

Design – Breakwater Layout

Design – Breakwater Profile

Construction – Groin Reclamation

Construction – Breakwater Core

Construction – Breakwater Armor

Construction – Dredge & Pipe

Construction – Beach Fill

Monitoring – Imagery

Before & After

Monitoring – Beach Profiles

Monitoring – Beach Surveys

Monitoring – Shoreline

Monitoring – Compaction

Biological opinion required cone penetrometer testing to ensure that the new beach is appropriate for nesting turtles Test results showed that the beach was not

too compacted for turtles

Monitoring – Escarpments

Biological Opinion required post-construction escarpment surveys to ensure that sea turtles can access the beach First post-construction survey conducted,

no major escarpments found

Award – Best Restored Beaches

Questions

dauphin island east end beach and barrier island...

Documents