Aquatic Placement: Successful dredged material management in Long ...
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Aquatic Placement: Successful dredged material management in Long Island Sound
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18
CLIS CS-2 18
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CLIS FVP !
18
CLIS-94
18 17 !
CLIS-86
CS-90-1
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CLIS-91 !
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NHAV-93
CLIS-03 !
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! 18
CLIS SP !
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NWK
CLIS-99 19
! CLIS-88 17
CLIS CS-1
CLIS-02
STNH-N !
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CLIS-87 CLIS-92
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CLIS-90
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CLIS-89
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CLIS-01 ! CLIS-00
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NHAV-74 !
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CLIS-97/98 !
CLIS 04 20
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CLIS 08
19 20 ! CLIS-95/96
MQR ! 19
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NHAV-83 20
STNH-S ! 21
Central Long Island Sound Disposal Site
Drew A. Carey, CoastalVision 21 Christopher Wright; CR Environmental Stephanie Wilson, Aaron Hopkins; AECOM Steven Wolf, 22 Tom Fredette; USACE
Long Island Sound Long Island Sound is an estuary with an ESE‐WNW axis and distinctly different margins. The northern margin has extensive bedrock and glacial deposits drained by river systems that extend as much as 655 km north and discharge fine sediment into small harbors. The southern margin is a glacial moraine with rocky shoreline and very small drainage basins that discharge sand.
Eastern Basin Central Basin Western Basin
The complex geological history of the Sound has left three distinct basins separated by shallow ridges or sills. Each basin contains several important commercial ports and many small harbors that support commercial fishing and recreational boating
Long Island Sound Dredging Needs The region is expected to dredge over 38 million cy of harbor sediments in the next 30 years The majority of the sediments are from Corps Projects located in Connecticut on the northern shore of the Sound. Much smaller volumes of largely non‐federal projects are projected for the coast of Long Island, New York
Dredged Material Management Placement alternatives will be defined through a regional Dredged Material Management Plan (DMMP) including upland, nearshore, beneficial use and aquatic placement.
Central
Western
Upland, Beneficial Use and Dewatering Sites Considered
Ocean Dredged Material Disposal Sites
Ocean Dredged Material Disposal Site: Central Long Island Sound Disposal Site (CLDS)
Disposal Area Monitoring System: DAMOS DAMOS has been monitoring dredged material disposal in the Sound since 1978 and an extensive knowledge base has allowed critical evaluation of placement and capping techniques and physical, chemical and biological responses to placement of dredged material on the seafloor. The program utilizes a formal tiered monitoring protocol to assess potential effects of dredged material placement and guide management actions.
Standard Survey Techniques: Sequential bathymetric surveys to characterize the height and spread of discrete dredged material deposits or mounds. Sediment profile imaging (SPI) surveys to evaluate benthic habitat conditions and recovery from disturbance.
Innovative Survey Techniques: Plan view imaging Side‐scan sonar Towed video Sediment coring Grab sampling for biology and bulk chemistry
What have we learned? Recent advances in acoustic and optical data collection, processing, and analysis have allowed detailed mapping and characterization of dredged material placement sites, including: • the assessment of the stability of silt caps, sand caps, and containment berms; • the spread of dredged material following placement of single barge loads and placement of an entire season of material; • consolidation of dredged material after placement; • and recovery of benthic habitat conditions.
Backscatter
What have we learned? Sites in the Sound have employed a management practice of placing dredged material at taut‐wire buoys and logging disposal activities so that dredged material forms distinctive mounds each season and can be followed through time. This unique time history and spatial distribution of placed dredged material has provided a record of the results of placement techniques, material handling, and environmental responses that spans over thirty years. Well‐selected placement sites and careful management create highly stable mounds on the seafloor • Variations in mound shape and surface texture can be related to placement techniques, dredged material properties (grain size, water content, geotechnical condition) • Variations in seafloor around placement sites can be monitored to assess fluctuations in sediment transport, benthic habitat conditions, hypoxia, organic loading and sediment deposition that may affect site management • Stability of mounds can be inferred from consistent bathymetric expression and evidence of deposition of surface sediment •
Dredged Material: Time Series
Mound stability and presence of dredged material from high resolution bathymetry
Mound stability and presence of dredged material from side‐scan sonar
Sediment texture and presence of dredged material from acoustic backscatter
Mound stability and presence of dredged material from depth difference
What have we learned? •
Benthic habitats converge with reference area conditions within one to two years after material is placed on the seafloor
Less recovery
Recovered
Reference
What have we learned? •
Distinctive properties of dredged material can be identified in some disposal mounds
What have we learned? •
Improved resolution of imaging systems reveal new evidence of seafloor biological processes
Beggiatoa form bacterial colonies in anaerobic sediments. Their characteristic ‘bloom’ on the surface is strong evidence of near bottom hypoxia and organic loading of sediments. Organic‐rich sediments in Long Island Sound have incipient ‘threads’ of Beggiatoa in dredged material and reference area sediments. Monitoring their presence and relative density may provide further insight into biogeochemical processes in surface sediments
Aquatic Placement: Conclusions • Properly selected aquatic placement sites can retain deposits of dredged material for decades with negligible change in volume or surface characteristics • Dredged material that has passed testing supports rapid benthic recolonization • High resolution acoustic and optical imaging of seafloor at placement sites provides insight into large and small-scale processes • Dredged material placement can be closely monitored with imaging of placement patterns and surface textural characteristics • Aquatic placement of dredged material continues to be a viable alternative if managed closely
Aquatic Placement: Successful dredged material management in Long Island Sound
19
18
CLIS CS-2 18
!
CLIS FVP !
18
CLIS-94
18 17 !
CLIS-86
CS-90-1
!
!
CLIS-91 !
18
NHAV-93
CLIS-03 !
!
! 18
CLIS SP !
!
NWK
CLIS-99 19
! CLIS-88 17
CLIS CS-1
CLIS-02
STNH-N !
!
CLIS-87 CLIS-92
!
CLIS-90
!
!
!
CLIS-89
!
CLIS-01 ! CLIS-00
! 16
NHAV-74 !
18
CLIS-97/98 !
CLIS 04 20
19
!
!
CLIS 08
19 20 ! CLIS-95/96
MQR ! 19
!
NHAV-83 20
STNH-S ! 21
Central Long Island Sound Disposal Site
Drew A. Carey, CoastalVision 21 Christopher Wright; CR Environmental Stephanie Wilson, Aaron Hopkins; AECOM Steven Wolf, 22 Tom Fredette; USACE
Long Island Sound Long Island Sound is an estuary with an ESE‐WNW axis and distinctly different margins. The northern margin has extensive bedrock and glacial deposits drained by river systems that extend as much as 655 km north and discharge fine sediment into small harbors. The southern margin is a glacial moraine with rocky shoreline and very small drainage basins that discharge sand.
Eastern Basin Central Basin Western Basin
The complex geological history of the Sound has left three distinct basins separated by shallow ridges or sills. Each basin contains several important commercial ports and many small harbors that support commercial fishing and recreational boating
Long Island Sound Dredging Needs The region is expected to dredge over 38 million cy of harbor sediments in the next 30 years The majority of the sediments are from Corps Projects located in Connecticut on the northern shore of the Sound. Much smaller volumes of largely non‐federal projects are projected for the coast of Long Island, New York
Dredged Material Management Placement alternatives will be defined through a regional Dredged Material Management Plan (DMMP) including upland, nearshore, beneficial use and aquatic placement.
Central
Western
Upland, Beneficial Use and Dewatering Sites Considered
Ocean Dredged Material Disposal Sites
Ocean Dredged Material Disposal Site: Central Long Island Sound Disposal Site (CLDS)
Disposal Area Monitoring System: DAMOS DAMOS has been monitoring dredged material disposal in the Sound since 1978 and an extensive knowledge base has allowed critical evaluation of placement and capping techniques and physical, chemical and biological responses to placement of dredged material on the seafloor. The program utilizes a formal tiered monitoring protocol to assess potential effects of dredged material placement and guide management actions.
Standard Survey Techniques: Sequential bathymetric surveys to characterize the height and spread of discrete dredged material deposits or mounds. Sediment profile imaging (SPI) surveys to evaluate benthic habitat conditions and recovery from disturbance.
Innovative Survey Techniques: Plan view imaging Side‐scan sonar Towed video Sediment coring Grab sampling for biology and bulk chemistry
What have we learned? Recent advances in acoustic and optical data collection, processing, and analysis have allowed detailed mapping and characterization of dredged material placement sites, including: • the assessment of the stability of silt caps, sand caps, and containment berms; • the spread of dredged material following placement of single barge loads and placement of an entire season of material; • consolidation of dredged material after placement; • and recovery of benthic habitat conditions.
Backscatter
What have we learned? Sites in the Sound have employed a management practice of placing dredged material at taut‐wire buoys and logging disposal activities so that dredged material forms distinctive mounds each season and can be followed through time. This unique time history and spatial distribution of placed dredged material has provided a record of the results of placement techniques, material handling, and environmental responses that spans over thirty years. Well‐selected placement sites and careful management create highly stable mounds on the seafloor • Variations in mound shape and surface texture can be related to placement techniques, dredged material properties (grain size, water content, geotechnical condition) • Variations in seafloor around placement sites can be monitored to assess fluctuations in sediment transport, benthic habitat conditions, hypoxia, organic loading and sediment deposition that may affect site management • Stability of mounds can be inferred from consistent bathymetric expression and evidence of deposition of surface sediment •
Dredged Material: Time Series
Mound stability and presence of dredged material from high resolution bathymetry
Mound stability and presence of dredged material from side‐scan sonar
Sediment texture and presence of dredged material from acoustic backscatter
Mound stability and presence of dredged material from depth difference
What have we learned? •
Benthic habitats converge with reference area conditions within one to two years after material is placed on the seafloor
Less recovery
Recovered
Reference
What have we learned? •
Distinctive properties of dredged material can be identified in some disposal mounds
What have we learned? •
Improved resolution of imaging systems reveal new evidence of seafloor biological processes
Beggiatoa form bacterial colonies in anaerobic sediments. Their characteristic ‘bloom’ on the surface is strong evidence of near bottom hypoxia and organic loading of sediments. Organic‐rich sediments in Long Island Sound have incipient ‘threads’ of Beggiatoa in dredged material and reference area sediments. Monitoring their presence and relative density may provide further insight into biogeochemical processes in surface sediments
Aquatic Placement: Conclusions • Properly selected aquatic placement sites can retain deposits of dredged material for decades with negligible change in volume or surface characteristics • Dredged material that has passed testing supports rapid benthic recolonization • High resolution acoustic and optical imaging of seafloor at placement sites provides insight into large and small-scale processes • Dredged material placement can be closely monitored with imaging of placement patterns and surface textural characteristics • Aquatic placement of dredged material continues to be a viable alternative if managed closely
