Table Of Content® Environ mental Assessment and
Finding of No Significant Impact
Maintenance Dredging
Cook Inlet Navigation Channel, Alaska
January 2013
FINDING OF NO SIGNIFICANT IMPACT
Maintenance Dredging
Cook Inlet Navigation Channel, Alaska
The U.S. Army Corps of Engineers (Corps) will be conducting test and maintenance dredging of
10 million cubic yards (cy) of sand, gravel, cobbles, occasional rocks and silty sediments that
have accumulated in the Knik Arm portion of the existing Cook Inlet Navigation Channel.
Maintenance dredging of the existing channel to the maximum depth of -43 feet MLLW, width
of 1,100 feet and length of 11,000 feet will consist of hydraulic and or clamshell dredging of
accumulated sediments into a hopper dredge or barge; dewatering during dredging and transport;
and in-water disposal at the existing Fire Island disposal site. Dewatering is necessary to
facilitate the movement of the largest quantity of dredged material per barge load, therefore
minimizing vessel traffic related to the dredging action. The attached NEPA analysis includes the
effects of annual maintenance dredging of the existing Cook Inlet Navigation Channel and in-
water disposal, with a sampling and production test run dredging (50,000 cy) event as needed.
Incorporating the following mitigation measures into the recommended plan will mitigate
adverse impacts to potentially affected fish and wildlife populations including species listed
under the Endangered Species Act (ESA), marine mammals, and Essential Fish Habitat (EFH):
• Juvenile salmon may be present in Knik Arm for more than a month during the dredging
period and feed successfully at the surface during their residence. All dredged material
and overflow water from dredging will be discharged beneath the surface to avoid
impacts on juvenile salmon feeding. Turbidity at the surface will be tested during
dredging to determine whether additional adaptive measures should be incorporated to
protect this resource.
• Sounds generated by dredging and related activities are similar in intensity to those
associated with other harbor activities and most are close to ambient noise levels. To
protect beluga whales, dredging activities will be suspended any time beluga whales are
within 165 feet of the activity.
The Corps believes the maintenance dredging of Cook Inlet Navigation Channel is consistent
with State and local management programs to the maximum extent possible.
This Finding of No Significant Impact’s associated environmental assessment (EA) supports the
Corps’ conclusion that the maintenance dredging project in the Cook Inlet Navigation Channel
does not constitute a major Federal action significantly affecting the quality of the human
environment. Therefore, preparation of an environmental impact statement is not necessary.
_____________________ Date: _______________________
Christopher D. Lestochi
Colonel, Corps of Engineers
District Commander
Table of Contents
ABBREVIATIONS AND ACRONYMS ....................................................................................... v
1.0 Introduction ............................................................................................................................... 1
1.1 Purpose and Need ............................................................................................................. 1
1.2 Project Authority .............................................................................................................. 2
1.3 Project Area Description .................................................................................................. 2
2.0 Alternatives ............................................................................................................................... 3
2.1 No Action Alternative ...................................................................................................... 3
2.2 Proposed Action ............................................................................................................... 3
2.2.1 Dredging Options ...................................................................................................... 4
2.2.2 Dredged Material Placement Options ....................................................................... 5
2.3 Best Management Practices and Monitoring ................................................................... 5
2.4 Conservation Measures .................................................................................................... 6
3.0 Affected Marine Environment .................................................................................................. 7
3.1 Tides, Currents and Circulation ....................................................................................... 7
3.2 Sediment Transport and Water Quality ............................................................................ 8
3.3 Air and Noise Quality ...................................................................................................... 9
3.4 Marine Mammals ........................................................................................................... 20
3.5 Invertebrates ................................................................................................................... 24
3.6 Fish ................................................................................................................................. 26
3.7 Essential Fish Habitat ..................................................................................................... 28
3.7.1 Importance of EFH Species Stocks in Upper Cook Inlet ....................................... 28
3.7.2 Importance of EFH Species to Beluga Whales ....................................................... 28
3.7.3 EFH Species in the Study Area ............................................................................... 28
3.8 Avifauna ......................................................................................................................... 30
3.9 Threatened and Endangered Species .............................................................................. 31
3.9.1 Vegetation. .............................................................................................................. 31
3.9.2 Fish. ......................................................................................................................... 31
3.9.3 Marine Mammals. ................................................................................................... 32
3.10 Cultural and Historic Resources ................................................................................. 32
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3.11 Subsistence Resources ................................................................................................ 32
3.11.1 Subsistence Fishing ................................................................................................. 32
3.11.2 Subsistence Hunting................................................................................................ 32
3.12 Socioeconomic Resources .......................................................................................... 33
3.12.1 Population ............................................................................................................... 33
3.12.2 Employment and Income ........................................................................................ 33
3.13 Marine Economic Activity ......................................................................................... 34
4.0 Environmental Consequences ................................................................................................. 35
4.1 Marine Environment ...................................................................................................... 35
4.1.1 No Action ................................................................................................................ 35
4.1.2 Proposed Action ...................................................................................................... 35
4.2 Water Circulation Patterns and Sedimentation .............................................................. 41
4.2.1 No Action ................................................................................................................ 41
4.2.2 Proposed Action ...................................................................................................... 41
4.3 Air Quality and Noise .................................................................................................... 41
4.3.1 No Action ................................................................................................................ 41
4.3.2 Proposed Action ...................................................................................................... 41
4.4 Marine Mammals ........................................................................................................... 42
4.4.1 No Action ................................................................................................................ 42
4.4.2 Proposed Action ...................................................................................................... 42
4.5 Fishery Resources and Essential Fish Habitat ............................................................... 44
4.5.1 Fishery Resources ................................................................................................... 44
4.5.2 Essential Fish Habitat ............................................................................................. 46
4.6 Avifauna ......................................................................................................................... 47
4.6.1 No Action ................................................................................................................ 47
4.6.2 Proposed Action ...................................................................................................... 47
4.7 Threatened and Endangered Species .............................................................................. 48
4.7.1 No Action ................................................................................................................ 48
4.7.2 Proposed Action ...................................................................................................... 48
4.8 Cultural and Historic Resources ..................................................................................... 48
4.8.1 No Action ................................................................................................................ 48
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4.8.2 Proposed Action ...................................................................................................... 48
4.9 Subsistence Resources.................................................................................................... 49
4.9.1 No Action ................................................................................................................ 49
4.9.2 Proposed Action ...................................................................................................... 49
4.10 Socioeconomic Resources .......................................................................................... 49
4.10.1 No Action ................................................................................................................ 49
4.10.2 Proposed Action ...................................................................................................... 49
4.11 Navigation .................................................................................................................. 50
4.11.1 No Action ................................................................................................................ 50
4.11.2 Proposed Action ...................................................................................................... 50
4.12 Environmental Justice and Protection of Children ..................................................... 50
4.12.1 No Action ................................................................................................................ 50
4.12.2 Proposed Action ...................................................................................................... 50
4.13 Cumulative Effects ..................................................................................................... 51
4.13.1 No Action ................................................................................................................ 51
4.13.2 Proposed Action ...................................................................................................... 51
4.13.3 Marine Environment ............................................................................................... 51
4.13.4 Biological Resources .............................................................................................. 51
4.13.5 Cultural and Historic Resources ............................................................................. 52
4.13.6 Air and Noise Quality ............................................................................................. 52
4.13.7 Socio-economic Resources ..................................................................................... 52
4.13.8 Cumulative Effects Summary ................................................................................. 52
5.0 Public Involvement, Federal Compliance and Agency Coordination .................................... 53
5.1 Compliance with Laws and Regulations ........................................................................ 53
6.0 Conclusions and Mitigation Recommendations ..................................................................... 54
7.0 Literature Cited ....................................................................................................................... 55
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List of Figures
Figure 1. Cook Inlet Navigation Channel. ..................................................................................... 3
Figure 2. Map of Cook Inlet, Alaska, showing recording locations from 21-24 August 2001. .. 12
Figure 3. Broadband (10 - 20,000 Hz) levels of ambient underwater sound at eight locations in
Cook Inlet and Knik Arm, with varying levels of proximity to industrial activities .................... 13
Figure 4. Narrowband underwater spectra (4 to 20,000 Hz) from typical 8.5-s samples. ........... 15
Figure 5. Broadband (10 - 20,000 Hz) underwater SPLs as a function of distance to sound source
for various large vessels operating in Anchorage Harbor ............................................................. 17
Figure 6. Valuable Habitat Areas (Types 1, 2, and 3) Identified for Cook Inlet Beluga
Whales ......................................................................................................................................... 22
Figure 7. Dredged material disposal trajectory. ........................................................................... 36
List of Tables
Table 1. Marine Invertebrates in Knik Arm Collections .............................................................. 25
Table 2. Fish in Knik Arm Collections ........................................................................................ 27
Table 3. Environmental Compliance Checklist........................................................................... 54
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ABBREVIATIONS AND ACRONYMS
ADEC – Alaska Department of Environmental Conservation
ADF&G – Alaska Department of Fish and Game
AHRS – Alaska Heritage Resources Survey
APE – Area of Potential Effect
BMP’s – Best Management Practices
Corps – U.S. Army Corps of Engineers
CWA – Clean Water Act
cy – Cubic Yards
EA – Environmental Assessment
EFH – Essential Fish Habitat
EPA – U.S. Environmental Protection Agency
ESA – Endangered Species Act
FONSI – Finding of No Significant Impact
HAPC – Habitat Area of Particular Concern
MHHW – Mean Higher High Water
MLLW – Mean Low Low Water
MSFCMA – Marine Sanctuaries Fishery Conservation and Management Act
NMFS – National Marine Fisheries Service
NOAA – National Oceanic Atmospheric Administration
SHPO – State Historic Preservation Act
USFWS – U. S. Fish and Wildlife Service
USACE – U.S. Army Corps of Engineers
v
Environmental Assessment
Maintenance Dredging
Cook Inlet Navigation Channel
Anchorage, Alaska
1.0 Introduction
1.1 Purpose and Need
The proposed Federal action is maintenance dredging of the Cook Inlet Navigation Channel
(CINC) in the Knik Arm Shoal region of Cook Inlet depicted in figure 1. The CINC has not
required maintenance dredging since it was initially constructed. The purpose of the proposed
action is the restoration of channel depth to facilitate safe navigation through the Cook Inlet
Navigation Channel. The U.S. Army Corps of Engineers (Corps) will be conducting test and
maintenance dredging of 10 million cubic yards (cy) of sand, gravel, cobbles, occasional rocks
and silty sediments that have accumulated in the Knik Arm portion of the existing Cook Inlet
Navigation Channel. Maintenance dredging of the existing channel to the maximum depth of -43
feet MLLW, width of 1,100 feet and length of 11,000 feet will consist of hydraulic and or
clamshell dredging of accumulated sediments into a hopper dredge or barge; dewatering during
dredging and transport; and in-water disposal at the existing Fire Island disposal site. The
proposed Federal action includes a production run test dredging of up to 50,000 cubic yards, geo-
technical sampling, laboratory testing as needed, and disposal of sampled sediments as needed.
This EA considers the effects of maintenance dredging for the CINC for years 2013 through
2017; any required maintenance dredging beyond 2017 will be addressed in further NEPA
analyses.
Maintenance dredging has not been necessary since the CINC was created over a decade ago, but
the shoal has been extending into the CINC in recent years, and the reduced depths are affecting
navigation. If shoaling continues without the proposed maintenance dredging, deeper draft
vessels will have a shorter window to access the Port of Anchorage facilities upstream of the
shoal on high tide cycles, and they could eventually lose access to these facilities
Over the 5-year period considered in this EA, approximately 10 million cubic yards would be
dredged from the CINC. The 10 million cubic yard volume is a best estimate, but how that
quantity breaks down over the 5-year period is uncertain given the changeable nature of the
shoal. Since a shoal is, by definition, a changeable area, dredging may occur on an annual basis
or any combination of years that dredging is necessary to achieve the removal of shoaling
sediments.
1
Description:under the Endangered Species Act (ESA), marine mammals, and Essential Fish
Habitat (EFH): • Juvenile salmon may be present in Knik Arm for more than a
