coastal bank & shoreline erosion control · david lager, netco, lexington, ma. presentation...
TRANSCRIPT
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Plum IslandShoreline Protection & Management
A Review of Current Design & Construction InitiativesBy David Vine, Vine Associates, Newburyport, MA
David Lager, NETCO, Lexington, MA
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PRESENTATION TOPICS• Introduction• Coastal Conditions• Shoreline Changes• Community Response• Design Issues• Construction Progress• Plum Island Coir Envelopes, Anchors
• Other Recent CoirApplications
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INTRODUCTIONCase Study• Short Term Dune
Stabilization• Community Alliance to Deal
With Beach Management• Still Going On
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COASTAL GEOLOGICAL FACTORS
• Jetty Construction
• Active Ebb Tidal Delta (Sandbar)
• “Reversal”Northern Littoral Drift
• Stone Groin Impact
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COASTAL PROCESSES
• Groin Limiting Northern Sand Flow
• Degraded Jetty• Refraction• Funneling into Area
Causing “Hot Spots” per Particular Storm
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COASTAL PROCESSES
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SHORELINE CHANGES• Long-Term Shoreline
Changes Since 1928• About 3 – 4 feet per
Year 1928-1994
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SHORELINE CHANGES• Shorter Term 2000-2007• 13.3 Feet per Year• Most Significant at Town Center • Circa 1995• Order of 100 Foot Shoreline
Erosion• Groin Fully Covered
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FORMATON OF MERRIMACK RIVER BEACH ALLIANCE
• Newbury• Newburyport• Salisbury• State Senators/Representatives• Seaport Bond Council• Department of Conservation &
Recreation• State Regulatory Agencies
DEPCZM
• Federal Regulatory Agencies• Local Citizens Groups• Newspapers• Local Residents• Privately Retained Lobbyist• Monthly Meetings – Totally Open Process
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DESIGN CONSIDERATIONS• Protect Public
Infrastructure• Sand Nourishment• Less than 3 Ton Sand
Bags• Geotube (High Strength
Plastics)• Bio-Degradable Fabrics• Stone/Timber/Steel• Plantings (Limited)REGULATORY REQUIREMENTS• Off Site Sand Source• Must be Bio-Degradable
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LIMITED SOLUTIONS/FUNDS• Design had to be of large Bio-Degradable Sand Bags or
Envelopes• Considered Placement of Fabric Covered in Sand and
Covering it with Fabric• Considered Pre-Fabricated Coir Forms Placing sand and
then stitching together (Netco Product)
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PLUM ISLAND DESIGN• Investigating Past Coir Projects
How Past Designs Evolved• Consider more like Design of
Revetment• 5 Terrace System• Buried First Terrace 4’ Below Grade• Second Terrace 6’ Wide Section 90°
to Dune• Upper 3 Terraces Paralleled to Dune• Helical Anchors• To be Covered with Sand and
Planted
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OCTOBER/NOVEMBER 2008• Design Set• Permit Approvals Received• Bid Project• Award/Fund Project• Start Construction• November 26, 2008 Storm
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NOVEMBER 28 THRU END OF DECEMBER
• Construction Continues (Accelerated)
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CONSTRUCTION COMPLETED• Mid January Construction Completed
(Though tested along the way)
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MARCH/APRIL 2009SAND NOURISHMENT
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DIFFICULT SPRING/SUMMER• Wave Activity• Several Eastern
Storms• Some Damage
Encountered
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THE PRESENT• Presently USACE Sand Nourishment
to start January 2010• Modest Repairs Scheduled for 6’ Bags• Hope for Mild Fall/Winter Awaiting
Nourishment
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LIMITED REPAIR TO APPROXIMATELY TEN SIX FOOT BAGS
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Coir “Soft Technology”
• Biodegradable Material
• Renewable Resource• Relatively High
Tensile Strength• Imported From Far
East• Custom Fabricated
For Each Project In Massachusetts
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Building Block – Matsof Different Weights, Dimensions
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Mats Fabricated In MA Into Different Sizes, Shapes
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Plum Island Application
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Key – Bottom “Foundation”Terrace
• Bottom Terrace Below Beach Face, Avoid Wave, Surf Undercutting
• 4’ Wide Terrace – Add. Mass, Weight
• 2 x Layers Coir Mat, 1 x Layer Jute Liner
• Helical Tie Down Anchors• Continuous Sand Filled
Envelope 500 Feet Long
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Bottom Foundation Terrace
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Plum Island Application – 2nd
Terrace
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2nd Terrace Level
• 3’ x 3’ x 6’ Envelopes• Attached to Bottom
Terrace and to Adjacent Envelopes
• Imported Sand• Slowest Part of the
Project• 2 x Layers Coir Mat,
1 x Layer Jute Liner
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3rd, 4th, 5th Terraces
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3rd, 4th, 5th Terrace Levels• Coir Envelope Tubes• 3’ x 3’ x 500’• Imported Sand• Attached on All Sides
to Form Continuous Envelope
• Minimize Possible Beach Debris
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Upper Level Terraces In Progress
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Completed Project – January, 2009
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Conclusions• Permit Allowed Excavation Below Beach Face
– Minimized Potential for Undercutting By Waves/Surf• Second Terrace Level Used 6’ Envelopes –
Robust/Durable Design, Repairs Easier• Terraced Stepped Back 3 Feet, Natural Slope
Face Maintained, Increase Stability • Helical Tie Down Anchors Installed @ 50’
Spacing, Decrease to 25’ Spacings• No Recent TV News Coverage of Plum Island
Homes Taken By Ocean• Allowed Time To Develop Longer Term Beach
Nourishment Program With U.S.A.C.E. and Local Communities
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Eastham Toe Protection Design(Engineering/Permitting – LEC Environmental)
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Eastham – Existing Conditions –December, 2006
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Coir Envelope Construction
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Coir Envelope Solution - 2006
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Completed Toe Protection –Ready for Vegetation
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Vegetated Bank – Sep., 2009