COASTAL SHORELINE PROTECTION USING HARD STRUCTURES

Robert W. Fairbanks, P.E., President Fairbanks Engineering Corp.

Richard N. St. Jean, P.E., President

St. Jean Engineering, LLC

TYPES OF SHORELINE PROTECTION STRUCTURES

• NON STRUCTURAL PROTECTION

• SEAWALLS • REVETMENT • BREAKWATERS

• GROINS

EXAMPLES OF MANMADE CHANGES TO THE SHORELINE IN

RHODE ISLAND USING SEAWALLS, REVETMENTS,

BREAKWATERS AND GROINS

Quonset Point War Effort

Quonset Point 1939 Before World War II

Quonset Point Today

Allen Harbor, North Kingstown

Allen Harbor Pre World War II Effort

Allen Harbor Today

Quonochontaug Breachway

• 1952 Before State of RI Constructed Breachway

• 1981 Aerial showing Breachway Constructed in 1962, and Sediment Entering Pond

Quonochontaug Pond

• Quonochontaug Today with No Maintenance

Buttonwoods Warwick, RI

• 1962 Timber and Stone Groins Showing Sand Accretion

• Timber Groins Not Maintained Showing Loss of Accreted Sand

Buttonwoods, Warwick RI Section Where Stone Groins Remain

Non Structural Shoreline Protection Vegetated Beach Dune – Portsmouth, RI

Vegetated Shoreline • Portsmouth, Rhode Island

Portsmouth Shoreline Before

Concrete Curbs

Jamestown, Rhode Island Coir Logs

Middletown, Rhode Island Coir Logs on Rocky Shoreline

SEAWALLS Steel Sheetpile Bulkhead, Road Town, BVI

Sheet Pile Dead Men Installation Road Town, Tortola, BVI

Concrete Seawall, Hampton Beach, NH

Salisbury Beach, Massachusetts

Pre-Cast Concrete Seawall Units

Salisbury Beach, Massachusetts

Precast Concrete Units

Re-Entrant Face Seawall, San Francisco

Concrete Seawall, Westerly, RI

Timber Seawall – Portsmouth, RI

Steel Sheet Piles, Quonset Airport

REVETMENTS • Stone placed on an earth slope, Warwick, RI

Revetment Under Construction, Jamestown, RI

Larger Revetment, Portsmouth, RI

Revetment Above Seawall, Westerly, RI

Revetment Above Seawall, Westerly, RI

STONE BREAKWATERS SAUNDERSTOWN YACHT CLUB

Location of Former North Kingstown To Jamestown Ferry Landing – circa 1900

Shoreline Adjacent to SYC Breakwater

North of Breakwater High Energy as Shown by Rocky Shore

South of Breakwater High Energy as Shown by Rocky Shore

Beach Formed On South Side of SYC Breakwater

Breakwater Acting As a Groin, Trapping Sand

GROINS Purpose is to trap sand to create a beach

Buttonwoods, Warwick, RI

Remnants of Groins in Buttonwoods

Typical Groins Along Lake Michigan

Tee Type Groin Standard Groin

Groins Typically Interrupt & Trap Sand Moving Down the Coast Replenishing Beaches but Starve Down Shore Beaches Leading to More Aggressive Erosion.

SHORELINE PROTECTION

• These structures have a place • Many coastal shoreline areas have been protected

adequately by these structures across the country • Ports require deep water at dock faces • Ports require protection from waves to allow cargo to

be loaded and unloaded • Municipalities need to protect infrastructure • Homeowners need to protect property

– However these structures typically protect the shoreline better than they protect the structures behind

Non Structural Measures Pros: Environmentally Friendly Relatively Inexpensive to Construct and Maintain if Vegetative Blends into Natural Shoreline and Provides Essential Habitat Typically Does not Cause Erosion of Adjacent Properties Preferred Method in Low Energy Locations (Coves, Protected Areas) Easy to Permit

Non Structural Measures Cons:

Ineffective for Large Fetch Areas Where Waves are in Excess of Approx. 2 Feet Required Frequent Maintenance After Storm Events Requires a Large Footprint Perpendicular to the Shore

Seawalls Pros: Can Provide Deep Water Adjacent to Quay Walls, Ports Piers Small Footprint Seaward, Providing Additional Room for Navigation Excellent Earth Retention with Little to No Loss of Soil Behind Wall When Maintained When Properly Designed Can Sustain High Surcharge Loads at Piers and Adjacent Railways Can Incorporate Cleats, Bollards and Mooring Bits for Docking Seawall Cons: Large Wave Reflection Which Can Almost Double the Incoming Wave Height If Wave Phases Line Up Causing Damage to Marina Facilities Can Cause Excessive Erosion At Beginning and Ends of Wall Costly to Construct Short Life if not Properly Maintained (30 to 50 years) Possibly Shorter Life if in a Marina Environment Due to Stray Electric Current Permitted in Only Certain Water Types

Breakwater Pros: Provides Excellent Energy Absorption with Little Wave Reflection Durable If Properly Designed With Adequate Stone Sizes & Geometry Provides Fish and Sea Creature Habitat Long Lasting if Properly Designed with Durable Stones Ideal for Creating a Refuge Area for Port Facilities and Quiet Water for Pier Operations

Breakwater Cons: Very Costly to Construct and Maintain Upsets Natural Circulation and Sediment Patterns Possibly for Long Distances Covers a Large Footprint at the Mud Line Requires Frequent Dredging At Harbor Entrances and Within Basin Navigation Hazard if Not Properly Marked Very Difficult to Permit

DESIGN PARAMETERS • 100 Year (1%) Storm Generated Forces (FEMA)

– Wave Height

– Current Velocity

– Debris Loads

• Water Depth (Bathymetric Survey)

• Shoreline Profile

DESIGN WAVE HEIGHT • FEMA Flood Study & FIRM MAP • Case By Case Study Considering Unobstructed

Fetch (Partially or Fully Developed Seas) and Water Depth Approaching Structure Location

Typical Design Parameters for Critical Structures – 100 yr Return (1%) Stillwater Elevation (SWL) – 100 yr Return (1%) Maximum Wave Crest Elevation (May Use a More Frequent Storm Event for Structures

That Can Sustain Some Damage Without Loss of Life, Can be Readily Repaired, and Small Economic Impact)

DESIGN WAVE HEIGHT

• Significant Wave Height, Hs – Hs = (Max Wave Crest El – SWL) /0.7

• Example for Max Wave Crest El = 12.0 ft & SWL = 9.0 ft

• Hs = 12.0 ft – 9.0 ft/0.7 = 4.28 ft

• Design for H10 = 1.27 Hs

EFFECT OF WAVE HEIGHT

• Forces on vertical walls1 – 4 ft wave = 8000 lbs/lf

– 8 ft wave = 16,000 lbs/lf

– 12 ft wave = 24,000 lbs/lf 1 – Coastal Construction Manual, Figure 11-8

EFFECT OF WAVE HEIGHT • Forces & increased wave height at vertical walls

EFFECT OF WAVE HEIGHT

• Revetment stone size2 – W = (Wr)(H3)/Kd(Sr – 1)3 (Cotan >)

• Stone size required for 1.5H: 1.0V slope; 2 stone armor layer

– 4 ft wave = 2200 lbs (2.4 ft stone) – 8 ft wave= 18,000 lbs (4.8 ft stone) – 12 ft wave = 60,000 lbs (7 ft stone) – 16 ft wave = 142,000 lbs (9.5 ft stone)

2 – US Army Corps of Engineers, Shore Protection Manual, 1984

EFFECT OF WAVE HEIGHT • Typical breakwater section2

2 – US Army Corps of Engineers, Shore Protection Manual, 1984

RI SHORELINE PROJECTS

• Block Island’s Old Harbor Sheetpile Bulkhead – PZC-34 steel sheets; 41 ft long – Bulkhead length is 242 lf

– Cost $732,000 or $3,025/lf

RI SHORELINE PROJECTS

• Matunuck Beach Road Bulkhead & Revetment, South Kingstown – 202 lf of PZ-35 steel sheetpile (45 ft long sheets) – 202 lf of 11 ton armor stone (2 layers)

– Cost $1,000,000 or $4,950/lf

CARRIBEAN SHORELINE PROJECTS

• Tender Pier Anchored Bulkhead Road Town, Tortola, BVI

– 331 lf of PZ-27 Steel Sheetpile (36 ft long sheets) – Buried Concrete Deadman w/ Steel Tie-rods – Cost $1,200,000 or $3,625/lf

RI SHORELINE PROJECTS

• Larkin Road Seawall, Watch Hill – 185 lf of Concrete Seawall (17 ft high) – 18” -30” thick stem & 9 ft wide footing

– Cost $500,000 or $2,700/lf

RI SHORELINE PROJECTS

• Whipple Ave Revetment, Warwick – 100 lf of stone revetment – 5000 to 8000 lb stone, 2 stone armor layer

– Cost $25,000 or $250/lf

RI SHORELINE PROJECTS

• 75 Surfside Ave, Charlestown – 150 lf of stone revetment – 12000 lb stone, 2 stone armor layer

– Cost $150,000 or $1,000/lf

RI SHORELINE PROJECTS

• 89 Surfside Ave, Charlestown – 70 lf of stone revetment – 12000 lb stone, 2 stone armor layer

– Cost $93,000 or $1,330/lf

RI SHORELINE PROJECTS

• Baker Road, Portsmouth – 90 lf of stone revetment – 8000 lb stone, 2 stone armor layer

– Estimated Cost $90,000 Or $1,000/lf

RI SHORELINE PROJECTS

• Watch Hill Lighthouse Revetment, Watch Hill – 1,700 lf+- of existing stone revetment repairs – 20,000 lb stones or larger – 22 ft design wave heights

– Estimated Cost N/A

RI SHORELINE PROJECTS

• Larkin Ave Groin, Watch Hill

– 150 lf+- of existing stone groin repairs – 3,000 to 4,000 lb stones

– Estimated Cost $25,000+- or $170+-/lf

CARRIBEAN SHORELINE PROJECTS

• Tender & Ferry Pier Breakwater Road Town, Tortola, BVI

– 200 lf stone breakwater – 6,000 to 8,000 lb stones (2 stone armor layer)

– Estimated Cost $620,000 or $3,100/lf

Examples of Programs Used for Design

When Things Go Wrong Westerly Town Property After

Tropical Storm Sandy Building was Demolished After Storm

House in Charlestown

Damage caused by hurricane Sandy

House in Anegada, BVI

One of several cottages damaged due to severe shoreline erosion

Jamestown, Rhode Island Shoreline Protection Is Currently Under Re-Construction

Erosion @ Coast Guard House, Narragansett, RI

Forces Under Piers/Bridge Decks

Bridge Across Escambia Bay, Florida Hurricane Ivan 9/16/2004

Biloxi Bay Bridge, Mississippi Hurricane Katrina

U.S. 90 Biloxi Bay Bridge Hurricane Katrina

SUMMARY • Design is complex & requires several design

parameters – Wave height for design – Storm flood depth (SWL) – Water depth (bathymetry) – Affect on littoral transport – End effects – Structure use – Can structure sustain damage – Permit ability – Constructability – Cost