Meeting Notes - Knik Arm Bridge and Toll Authority

Meeting Notes 

Subject 

Project 

Number 

Bridge Approach Design Option Agency Meeting 

#2 

21132 

Meeting Date August 26, 2005 Meeting 

Location 

Notes by Terry McConnell Office Anchorage 

Sheet 1 of 7 

4 th Floor Conference Room 

Attendees: 

See List Below 

Topics Discussed Bridge Lengths Abutments Roadway Embankment 

Fill 

Carri Harder U.S. Army Corps of Engineers (COE) 

Skip Joy U.S. Army Corps of Engineers (COE) 

Heather Dean Environmental Protection Agency (EPA) 

Edrie Vinson Federal Highway Administration (FHWA) via teleconference 

Al Ewing Knik Arm Bridge and Toll Authority / Department of Transportation and Public 

Facility (KABATA/DOT&PF) 

Bill Greene Knik Arm Bridge and Toll Authority / Attorney General (KABATA/AG) 

Dale Paulson Knik Arm Bridge and Toll Authority / Department of Transportation and Public 


Henry Springer Knik Arm Bridge and Toll Authority / Department of Transportation and Public 


Michael Allwright HDR Alaska 

Terry McConnell HDR Alaska 

Robin Reich HDR Alaska 

Doug Kenley PND 

Karen Brown URS Corporation 

Jim Glaspell URS Corporation 

Robin Reich (HDR) Introductions 

The purpose of this meeting is to talk about the in-water portion of the Knik Arm Crossing. 

The agencies have requested this focus because of concerns about juvenile fish passage, 

beluga passage, and sedimentation. We want to get feedback from you about these issues. 

Doug Kenley (PND) 

Early on, Kevin presented constraints that gave us the where we could place the crossing. We 

talked with vessel operators for navigation needs and came up with a 50 ft clear height and 

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approximately 200-250 ft opening between pilings. We have looked at several lengths. The 

west side of the bluff is 70-80 ft high and would need fill to approach. The Knik Arm channel 

is approximately 12,500 ft wide. We have looked at a 7,000 ft perpendicular bridge with fill 

on both sides. The skewed option would shorten the road length below the bluff and benefit 

the beluga concerns. Port MacKenzie has been a good example for us. It is filled in at 

approximately 2.1 slope over time. 

The 7,000 ft option has a footprint of about 56 acres with a sediment accumulation of about 

400 acres. The cost of the bridge would be approximately $140 million. The approaches 

would cost approximately $65 million. The total cost would be $205 million. 

The 10,000 ft option has a footprint of about 33 acres with a sediment accumulation of around 

160 acres. The cost of the bridge would be approximately $200 million with the approaches 

costing approximately $35 million. The total cost would be about $235 million. 

The 12,500 ft option has a footprint of about 12 acres with an expected sediment 

accumulation of around 7 acres. The cost of the bridge would be approximately $250 million, 

and the approaches would be approximately $15 million. The total cost would be $265 

million. 

Robin Reich (HDR) 

One of the major reasons to look into the skewed alignment is because NOAA Fisheries 

indicated belugas gather near Six Mile Creek. We have looked at the pros and cons of each 

bridge alignment. Pros for perpendicular include navigation ease. Cons could include 

hydrologic impacts. Pros for skewed include a shorter approach and the greater distance from 

Six Mile Creek. Cons for skewed include navigation impacts and proximity to submarine 

trench. We have not decided which to bring forward. 

Skip Joy (COE) 

If you assume the distance between two banks at Cairn Point caused the submarine trench, 

could the bridge have an impact of increasing trench? 


The hydrologists are doing the modeling now. 


That question must be answered. 


Agencies want us to look at a fully pile supported bridge without embankments. That option 

will be carried forward. We will also consider cost concerns. The 12,500 ft maintains fish 

and beluga passage, but we are also concerned about the amount of time it would take to 

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build. The more pilings that must be drilled, the more noise that could have beluga impacts. 

Another option that came up is including an embankment on only one side. The fisheries 

report will also help determine which side is more important for fish passage. 

Heather Dean (EPA) 

We are concerned about sedimentation impacting other important wetlands in Knik Arm and 

erosion. 


The hydrology work will address that. Heather, are you concerned with wetlands like those at 

the mouth of Eagle River? 


Anywhere in the realm of influence up or down Knik Arm. 


We are interested in the secondary impacts to those wetlands too. 

Jim Glaspell (URS) 

There is a side observation about this. From aerial photos going back 50 years, we see Six 

Mile Creek perpendicular to the bank. From May 18, 2005 until now, we see the channel 

flowing parallel to the bluff. At extremely low tide it seems to have a bump, and even heavy 

flows have not changed it back. It has cut a 4-6 ft channel on the tide lands. 


When we look at fish around Port MacKenzie dock, we saw a fair amount of juvenile salmon. 

We caught fewer around the face than on the two sides. Phil Brna (USFWS) mentioned the 

fish may not be able to get around the dock. That leads us to the abutment topic. We want to 

address concerns so we design to make it easier for fish to get around. 


We have 4 options for the end of the embankments of the abutments 

(See handout “Knik Arm Bridge Abutment Options.”) 

Option 1 is similar to the 2.1 slope design with sheetpile at the Port of Anchorage. It doesn’t 

need a lot of fill with armor. The footprint is about 5 acres at a cost of $9 million. 

Another option is a 2.1 slope with the armor extending around the abutment. It increases the 

footprint to 10 acres at a cost of $8 million. It has fill out 190 ft from the top of the slope. 

Another option has a 10.1 slope with a footprint of 44 acres and a cost of $44 million with fill 

700 ft out from top of slope 

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Another option is a bench approach with a footprint of 28 acres and a cost of $16 million with 

fill out 450 ft from top of slope. 


Regarding biology, we wanted to find out how fast the current would move around these 

embankments. We wanted to determine whether it would inhibit juvenile salmon? 

Michael Allwright (HDR) 

The standard is one body length per second. Therefore, a 3 inch fish has a sustainable speed 

of 3 inches per second. 


Regarding the bench option, we looked at tide charts to determine when during the tide the 

bench is covered with water a substantial period of time. We determined that the bench 

should be placed at 15 ft because this depth would be wet for a longer period of time. 


When the water is at that 15 ft level it is moving at its fastest. 


Would this design help to reduce scour? 


Jack Colonel (hydrologist for this project) said very little of the flow is on the sides of the 

channel. Most of the water flow is moving in the middle of the channel. 


And you’re only decreasing it the flow at the lowest water. 


The boundary area (the area next no the abutment where the water slows down) doesn’t 

change based on slope. What does change the boundary area is the amount of friction along 

the abutment. The more roughness (bigger armor rock), the bigger the boundary area. The 

higher the friction, the lower the velocity. When we were talking about this in the prior 

agency meeting, NOAA Fisheries and ADNR OHMP (Mark Somerville) were aware of this. 

Jim Glaspell (URS) 

At 2:1 there is less disturbance and fill. NOAA Fisheries appeared to be was satisfied with 

2:1 slope at the last meeting. 

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We haven’t made a decision yet on abutment type. We are looking for feedback. 


The 10:1 abutment slope would decrease the navigation space. It may still be adequate. 


Did you look at the option of combining options 1 and 4, having sheet pile with a 2:1 slope? 


The primary reason to have sheet pile is to reduce the length of the slope. Also, the sheet pile 

would not slow down the current. 


One of the alternatives to get into Anchorage is the below the bluff roadway. It would have 

gravel fill along the bluff with armor rock on the waterside of the alignment. Doug will 

explain the design options for the below the bluff alignment. 


One option would be to have a 4-lane roadway with a 2.1 side slope. This alternative would 

have a footprint of about 32 acres at a cost of $19 million. Roadway fill would extend 175 ft 

from the bluff into the tidelands. 

Another option would be a 4-lane roadway with a 10.1 side slope with a footprint of about 92 

acres at a cost of $73 million. Fill would go out 575 ft from the bluff to the tidelands. 

Another option would be a 4-lane roadway with a 10:2 benched slope. This option would 

have a footprint of about 55 acres and cost $35 million. Fill would extend out 300 ft into the 

tidelands. In Puget Sound the benched option is used to re-create salt marsh habitat which 

does not occur in this area of Knik Arm. 


In British Columbia spur dikes have been used to replace salt marsh. They have a 30% 

increase in net habitat. 


In that example project we looked at, the area between spur dikes grew into green lush 

marshes. They had a different purpose. Here they could be like a lot of little barriers for the 

fish movement. 


The spur dike option doesn’t look good to me. 

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Anther option is to have an elevated structure all the way along the roadway. There is little 

tideland footprint. This option would cost of $160 million. It is eight times more expensive 

than the 2.1 slope option. 


If it access is through the military base, then none of these options are pertinent. 


This is true however, the below the bluff alignment will be one of the alternatives in the Draft 

EIS. Do you have input now? You can also call or email us. 


I think you could drop the spur dike option. 


I agree. 


The Corps would like the longest bridge possible. 


The decision on embankments and abutments should be based on fisheries and beluga studies. 


Modeling and velocity is going to play into the decision. Friction is an important factor. 

Financially, less fill is better, but we like to see the smallest footprint too. Current velocities 

have impacts. 


We heard the smallest footprint is desirable from USFWS, NOAA Fisheries, and ADNR 

OHMP. I believe they also preferred the 2.1 roadway sideslope. 


That’s my first leaning as well, as long as it doesn’t create high velocities. I really don’t see 

that happening here. 


I would defer to the (agencies concerned with) fisheries on determining the best design. 

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We will get a memo to you explaining the options, pros and cons and costs. 

Edrie Vinson (FHWA) 

Please get a copy to USCG too. 

Meeting Adjourned 

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Meeting Notes - Knik Arm Bridge and Toll Authority

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