Long Island Offshore Sediment Resources
White Paper (Bokuniewicz, Tanski)
•The New York District of the U.S. Army Corps of Engineers is
undertaking a Regional Sediment Management (RSM) program for the
120 mile south shore of Long Island from Coney Island to Montauk Point
known as the Long Island Coastal Planning Project (LICPP).
Objectives of LICPP
•making more effective use of the sediments found along the coast
•enhancing environmental habitat
•improving the collection and dissemination of information on the
movement of sediment in this area.
• The two-day technical workshop was intended to review what is
known, or unknown about the volume of offshore sand reserves, the
potential for onshore transport, and the character of offshore sand
ridges.
Key topics:
1.The quantity, composition and
stratigraphy of the sand resources
seaward of the surf zone to a depth
of 130 feet (40 meters) below sea
level.
2.The nature and role of shoreline
subparallel sand ridges in
nearshore sediment transport rates
and pathways.
3.Influence of sand ridges on
inshore wave energy distribution
and coastal erosion patterns.
Sand Resource Assessments
1. There has been a long history of scientific studies that have been
completed on the shelf south of Long Island.
2. Sand resources have been found in State waters (within three miles of the
coast) along the south shore of Long Island that are of suitable quality for
beach nourishment. Studies show potential sand resources also exist in
federal waters beyond three miles.
Entire Continental Shelf.
“sediment rich” relative to the rest of the mid-Atlantic and
southeastern U.S. coasts.
COASTAL PLAIN STRATA: directly overlying the bedrock are
semi-consolidated Coastal Plain strata of upper Cretaceous or
lower Tertiary age consisting of fine to medium quartz sands
interbedded with lenses of silt and clay. In total, these strata are
about 1800 feet (550 meters) thick under Fire Island, and thicken
to the southeast.
PLEISTOCENE SEDIMENT: Near Fire Island, the Cretaceous
sediments are overlain by a blanket of Pleistocene sediments and
by discontinuous,
HOLOCENE DEPOSITS: Holocene deposits of reworked
Pleistocene sands, including shore-oblique sand ridges.
Pleistocene sediments are composed of sand,
gravel, cobbles, silt and clay from glacial
outwash, and from ground and terminal
moraines deposited (Wisconsinan Glacial).
(shelf = med-coarse sand with gravel)
Thickness = 10-30 m
http://pubs.usgs.gov/of/1999/of99-559/fig5.htm
Holocene Sediments
•Quartzose beach sand, dune sands
and fine-grained lagoonal sediments.
•The blanket of Holocene sands is
generally between 3.3 feet and 10
feet (one meter and three meters)
thick gradually thickening seaward
and eastward from Fire Island.
•They reach a thickness of 33 feet (10
meters) on inlets ebb shoals and in
large scale, linear sand ridges.
3. Estimated sand volume requirements for beach nourishment for
the next 50 years for the Fire Island to Montauk Point Storm Damage
Reduction project are not more than 5% of available volumes based
on most recent geophysical surveys
“Fire Island Inlet to Montauk Point Storm Damage Reduction” (FIMP) project will require about 55
million cubic yards (44 million cubic meters) of sand for beach nourishment over its 50 year lifetime, or
1.1 million cubic yards (0.9 million cubic meters) per year.
Estimates of the volume of beach compatible sand found on the shelf in waters less than 130 feet (40
meters) depth range from about 1.3 billion cubic yards (1.0 billion cubic meters) to 7.3 billion cubic
yards (5.6 billion cubic meters).
4. Accessible sand resources are found all along the coastline but are not
uniformly distributed.
Table 1. Volume of material dredged from inlets.
Extraction
Dredging
Average Annual
Inlet
(cubic yards)
Cycle
Extraction
(years)
(cubic yards/yr)
300,000
2
150,000
East Rockaway
150,000
1
150,000
Shinnecock
350,000
4
87,500
Intracoastal
70,000
5
14,000/
Jones Inlet
640,000
5
128,000
1,500,000
2
750,000
460,000
5
72,000
Moriches
Natural Sand Sources and Transport
Uncertainty and concern with sediment budgets
Montauk Bluffs
Stream Input
Outwash plain of Eastern LI
5. There is geologic evidence that sand is being transported into the surf zone
from beyond the surf zone.
6. The strongest evidence of onshore transport of sediment is from along
western Fire Island and points west.
Outwash lobes and relict ebb shoals (possible reworking into the sand ridges)
Inner Continental Shelf Offshore Sources
•profiles indicate large gains between spring and fall 1995
•Onshore/offshore transport driven by wind-induced coastal upwelling/downwelling
•Storm events largely produce shore parallel movement (offshore movement is
secondary)
5. There is geologic evidence that sand is being transported into the surf zone
from beyond the surf zone.
6. The strongest evidence of onshore transport of sediment is from along
western Fire Island and points west.
•Glauconite grains, non-indigenous to terrestrial glacial deposits, were found in beach sands
along Rockaway Beach, Long Beach and Jones Beach and traced to offshore deposits via
vibracore samples.
•Glauconite was not found onshore east of Jones Beach.
•The occurrence of euhedral quartz crystals linked sediments from offshore glacial outwash
lobes to beach deposits along the western end of Fire Island, especially in the vicinity of
Democrat Point.
7. The published estimates of onshore transport range from 0% to 63% of the
long shore transport estimates.
•Estimates of the longshore transport rate in western Fire Island range between 254,000
cubic yards (Gravens 1999) and 600,000 cubic yards (Panuzio 1969) .
•Updrift beach nourishment
•Erosion
•Uncertainty in data
8. Sand suitable for beach nourishment is found both in ridges and (more
widely distributed) Pleistocene/glacial deposits.
The inner shelf sand
The Pleistocene sediments are thought to be glaciofluvial outwash deposits composed of
gravels to fine sand with the upper few meters composed primarily of fine to medium-grained
sand.
The oblique ridges are made up of sand reworked from these Pleistocene deposits and
Cretaceous outcrops (Schwab et al. 2000).
Topography of the Middle Atlantic Continental Shelf
•Dominated by the shore-subparallel ridges and
swales
•Approximately northwest to southeast in orientation
•They are superimposed on large-scale, shoal-retreat
massifs left by the Holocene transgression
•Inner shelf ridges in water depths of less than 66 feet
•Middle shelf ridges in water depths 66 to 131 feet
•Inner shelf ridges are oriented between 15º and 30º
to the shoreline
•Middle shelf ridges are more nearly shoreparallel
shoal retreat massif A large sand accumulation that is preserved on the continental shelf during and after a marine
transgression. The massifs represent former estuary-mouth sand bars (inlet-associated shoals) or former zones of
longshore-drift convergence (cape-associated shoals).
Hypothesized Ridge & Swale Origins
•Relict: paleo drainage, abandoned ebb shoals, relic barrier islands, drowned shorelines
•8,000 – 14,000 ybp (during still stands)
•Absence of infilling sediments associated with a speculated barrier island 2-7 km offshore of
FI, 8,500 – 9,000 ybp
•Abandoned shoreface attached ridges created through winter storm generated coastal
currents
9. There is active sand transport on sand ridges.
Ripples, megaripples and sand waves: generated by wind-forced currents
Megaripples: dominate November through March, occupy up to 15% of the shelf
Sand waves/ridges: dominate the inner shelf
Bottom Currents
6 – 14/18 sec period wave orbital velocities
Setup/setdown
Geostrophic bottom currents 1.3 ft/sec
Combined flows upwards of 2 ft/sec
Fair weather conditions wave orbitals move sediments to a depth of 69 ft.
During large storms sediments (coarse sands) will be transported or stirred through much of
the shelf.
Thermal breakdown during winter enhances the movement of sediments on the shelf
Hurricanes are not as critical as noreasters (winter storms) when considering the long
term continental shelf transport system.
10. These ridges are actively maintained by hydrodynamic processes in the
coastal ocean. The types of hydrodynamic processes that maintain these
ridges have been identified but their relative importance has not been
quantified.
•Tidal forcing, infragravity waves, storm currents, surface wave convergence, or internal waves
•A three-layer flow field is thought to exist on the shelf with the boundary layers mostly
influenced by sustained, high energy winds and the middle layer being more steady, controlled
by mean geostrophic flow.
•Hydrodynamic processes vary across the shelf (inner – vs- middle – vs – outer)
Spit Building
Fire Island Inlet
Lecture 8: Field Trip Review
1.
overlapping barrier island formed by spit extension
2.
recurved spits at Democrat Point suggest island continues to grow westward
3.
the barrier is frequently in danger of breaching
Hypothetical Relocation of Fire Island Inlet (Kraus et.al., 2003)
Present Configuration
1.
Navigation Hazard
2.
Minimal bypassing to Cedar Beach
3.
Requires dredging of 400,000 m3/yr (~5 million dollars annually)
Hypothetical Relocation of Fire Island Inlet (Kraus et.al., 2003)
Fill Old
Inlet
New Inlet
Proposed Relocation
1.
8 km east of present location (150 m west of Lighthouse)
2.
Improve bypassing to Cedar Beach (old ebb shoal feed the downdrift
barrier beaches for ~30 years)
3.
Improved tidal flushing, reduce dredging requirement
Hypothetical Relocation of Fire Island Inlet (Kraus et.al., 2003)
Existing
Predicted
Ac = 2.1 x 103 m3
Vs = 3.0 x 107 m3
P = 8.7 x 107 m3
Increase tidal range
Vs = 3.1 x 107 m3
50% bypassing in 60 years
Vs = 3.8 x 107 m3 (Theory)
90% bypassing in 200 years
Hypothetical Relocation of Fire Island Inlet (Kraus et.al., 2003)
Fill Old
Inlet
Benefits and Drawbacks To Relocation ? (Think About)
New Inlet
1.
Cross-sectional Area of the channel, tidal prism, tidal range in bay
2.
Properties along the bay, potential for flooding
3.
Evolution of the ebb and flood shoal, impact on down drift beaches
4.
Impacts on biology in the bay, vegetation (ie. Wetlands), fish, and shellfish
5.
Economics (charter fishing, state beaches, recreational boaters)
Factors Controlling
Observed
Water
Levels
Why Abundant
on Passive
Margins?
Fire Island Inlet Field Trip
Water moves to the right of the wind in the northern hemisphere
Volume of water displaced by the wind depends on
1.
Wind Velocity
2.
Duration
3.
Fetch
Wind direction
ocean response
Wind
Longshore Transport of Sand
The evolution of the ebb and
flood shoals in part depend
on the volume of material
delivered to the inlet by
wave driven currents.
In addition the rate at
which material is bypassed
across an inlet controls the
evolution of the beaches and
downdrift barriers.
Regional Sediment Management: Impact of coastal inlets on the littoral
transport of sediment
From 1920 to 2000, Long Island’s south-shore beaches have been nourished
with over 128 million cubic yards of fill material.
Shore length = 625,370 linear feet (190.6 km)
Nourishment rate = 2.27 yd3/ft/yr (calculated from 1920 to 2000)
Panuzio, 1977
Westward migration rates and littoral transport based
Inlet
Migration (ft/yr)
Littoral Drift (yd3/yr)
Shinnecock Inlet
4.6
300,000
Moriches Inlet
177
350,000
Fire Island Inlet
212
600,000
Jones Inlet
135
550,000
East Rockaway Inlet
172
400,000
Rockaway Inlet
206
400,000
General Coastal Engineering Background
•1923 Coney Island Nourishment Project: first nourishment project in the
United States
•1927 Jones Beach Reclamation and Nourishment Project: over 40 million
cubic yards, one of the worlds largest barrier reclamation projects
•1938 The Great New England Hurricane: killed over 600 people, destroyed
thousands of homes, and produced 10 new inlets in a 30 km reach along
Westhampton Beach.
•1940 – 1956 Jetties constructed at Shinnecock, Moriches, Fire Island, and
Jones inlets.
•1965 – 1970 Construction of Westhampton groin field
Reach: section of coastline generally constrained by an inlet or
change in geologic characteristics
East Hampton
Fire Island
Coney Island
Long Beach
Westhampton
Jones Beach
Rockaway
Montauk
Results By Reach, (Kana 1999)
Coney Island
•Represents 3.7% of the shoreline
•Total of 6.6 million yd3 since the 1920’s or ~3.64 yd3/ft/yr
• ~5.2% of total fill material placed on Atlantic coast of NY
Rockaway Beach
•Represents 8.6% of the shoreline
•Total of 25.7 million yd3 since the 1920’s or ~5.94 yd3/ft/yr
• ~20.2% of total fill material placed on Atlantic coast of NY
Results By Reach
Long Beach
•Represents 7.9% of the shoreline
•Field of 60 groins protect the shoreline
•Total of 2.14 million yd3 or ~1.18 yd3/ft/yr
• ~3.7% of total fill material placed on Atlantic coast of NY
Jones Beach
•Prior to 1920 this stretch of coast was a series of small barrier island and
washover deposits
•Represents 13% of the shoreline
•Total of 61 million yd3 since the 1920’s or ~9.5 yd3/ft/yr
•4 million yd3 placed each decade from dredging of Fire Island Inlet
• ~48% of total fill material placed on Atlantic coast of NY
Results By Reach
Fire Island
•Represents 23.3% of the shoreline
•Total of 8.32 million yd3 or ~0.7 yd3/ft/yr
• ~6.5% of total fill material placed on Atlantic coast of NY
Westhampton Beach
•Represents 13.1% of the shoreline
•Receives 4 – 7 million yd3 of nourishment per decade
• ~2.87 yd3/ft/yr
• ~14.7% of total fill material placed on Atlantic coast of NY
•Most of the fill has been associated with the construction, maintenance, and
settlement of the groin field
Results By Reach
Easthampton Beaches
•Total of 2.9 million yd3 or ~0.33 yd3/ft/yr
• ~2.3% of total fill material placed on Atlantic coast of NY
Montauk
•Ronkonkoma terminal moraine abuts the Atlantic Ocean
•Steep coastal bluffs, rocky headlands, gravel beaches
•Considered the initial source of sediment to Long Island south shore
•No recorded nourishment projects
Summary of Nourishment Volumes By Reach
East Hampton
2.3%
Coney Island
5.2%
Long Beach
3.7%
Rockaway
20.2
Fire Island
6.5%
Montauk
0%
Westhampton
14.7%
Jones Beach
48%
Influence of Shelf Width
• Greater shoaling of tidal wave results in increased tidal range from Montauk
Point to New York Harbor
•Larger tidal ranges suggest a greater portion of the beach could be impacted
by waves
•Larger tidal ranges = increase in frequency of inlets
•Inlets that are not in equilibrium will trap littoral sand and starve the down
drift beaches
Sediment Trapping At Inlets
Sediment can be trapped in both the ebb and flood shoal. As this
material is removed from the littoral drift the down drift beaches
begin to erode
Inlet
Ebb Shoal Trapping (yd3/yr)
Shinnecock Inlet
50,000 – 100,000
Moriches Inlet
>100,000
Fire Island Inlet
>500,000
Jones Inlet
>100,000
East Rockaway Inlet
>200,000
Rockaway Inlet
>120,000
•~1.2 million yd3/yr trapped in ebb-shoals
•Over 80 years this represents 96 million yd3
•~75% of the total nourished volume between 1920 and 2000
Sediment Trapping At Inlets
VEe = 10.5 x 10-5 P 1.23 (ft3)
Inlet
Shinnecock Inlet
Vebb (yd3)
VEf = 2.04 x 10
4,500,000
Moriches Inlet
21,000,000
4,900,000
Fire Island Inlet
26,000,000
5,100,000
Jones Inlet
20,000,000
4,800,000
8,700,000
3,900,000
62,000,000
6,300,000
154,000,000
30,000,000
Rockaway Inlet
Total
P 0.296 (m3)
Vflood (yd3)
15,000,000
East Rockaway Inlet
4
•If the entire system was at equilibrium 184 million yd3 of material would be
contained in the ebb and flood shoals.