Meeting Notes - Knik Arm Bridge and Toll Authority

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Meeting Notes 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? Doug Kenley (PND) The hydrologists are doing the modeling now. Skip Joy (COE) That question must be answered. Robin Reich (HDR) 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 2
Meeting Notes 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. Robin Reich (HDR) The hydrology work will address that. Heather, are you concerned with wetlands like those at the mouth of Eagle River? Heather Dean (EPA) Anywhere in the realm of influence up or down Knik Arm. Skip Joy (COE) 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. Robin Reich (HDR) 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. Doug Kenley (PND) 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 3
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Meeting Notes - Knik Arm Bridge and Toll Authority

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