HugeassCity, Opinion

How High Does The Seawall Need To Be?

By Dan Bertolet, Monday, January 25, 2010 at 4:31 PM
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As projections of the severity of climate change seem to become more dire by the day, planning for Seattle’s seawall is like shooting at a moving target.

Two years ago the Intergovernmental Panel on Climate Change (IPCC) predicted that by 2100, global sea level will rise between 7 and 23 inches. But this past December, a new international study predicted a 2100 sea level rise (SLR) of 4.5 feet, concluding that “the current target for mitigation should be a maximum of 2 meters (6.6 feet).”  These new projections are higher because new data shows faster-than-anticipated rates of ice melt in Antarctica.

The most recent sea level rise projections for the Pacific Northwest can be found in a January 2008 paper published by the Climate Impacts Group at the University of Washington. The “medium” projection for 2100 SLR is 13 inches.

Concerns over the Seattle seawall and climate change are not new, but as of 2008, the new seawall was being designed to handle only an 11-inch SLR. Mayor Mike McGinn, through a spokesman, has said only that there “a lot of environmental factors that we have to take into account,” and that sea level rise “will be one of them.” More recent designs, if they exist, have not yet been made public. But clearly, 11 inches isn’t going to cut it.

Let’s just say that ideally, we’d plan conservatively—for a SLR of six feet. Add to that the increasing frequency and intensity of storm surges that is expected as the planet warms, and you might as well kiss Harbor Island goodbye.

What would a seawall look like that could handle those conditions? Taller than what we have now, it’s safe to assume. And assuming the wall has to be significantly higher than Alaskan Way, there will major impacts on the design of the waterfront street and open spaces.

Many hope that the city will a choose a seawall design that provides enhanced habitat for salmon and other sea life, and that also creates opportunities for people to touch the water. Both of these goals will be complicated by the magnitude of SLR that is now likely. For example, how much will be left of the beach at Olympic Sculpture Park (photo below) in 50 or 100 years?

Welcome to the reality of climate change. As Climate Impacts Group scientist Lara Whitely Binder put it, “There’s always going to be a coastline. It’s just a matter of where it is.”

P.S. I can’t stop myself from pointing out that in this related Times online piece, Benny Peiser, director of the Global Warming Policy Foundation is given an opportunity to express the contrary view, and—no lie—says this: “We look out of the window and it’s very cold. [So] it doesn’t seem to be warming.”

  • morning fizzy
    Best approach would be something that integrates a two-meter taller sea wall with a design that improves the waterfront. Worst approach would be build the current design and assume others can come up with another quarter billion dollars to fix it in a decade or two….

    Building this would increase the cost and create one horrible looking waterfront - design it to easily raise it later. Why would you assume that that we can come up with twice or three times the money now to build the worst case scenario wall? Using your logic, we should build all the transit, schools, etc. now rather than assuming others (meaning future taxpayers) can come up with the money.



    As for length, I think we have to ask ourselves what low-lying areas are affordably defensible: can we actually afford to save the duwamish/sodo area? If so, should the businesses there pay for that defense? .

    Well as I see it the water will come around the wall wherever it ends. If there is no wall in SODO how will the water be kept out of the central waterfront and the tunnel? Why should the businesses pay? What a strange thought.
  • Dan, it's my understanding that the Climate Impacts Group's 13 inches projection was built from earlier numbers. Be interesting to see what the new numbers do to that projection. Also worth noting that even 13 inches means tides and storm waves that are much higher than they are now.

    "Plastic Exploding Inevitable"- if only we had a glacier on our waterfront...

    Seriously, though, it's worth noting that both sea level and storm wave heights are expected to keep rising quickly this century, and any sea wall we build now will be dealing with that soon. Best approach would be something that integrates a two-meter taller sea wall with a design that improves the waterfront. Worst approach would be build the current design and assume others can come up with another quarter billion dollars to fix it in a decade or two...

    As for length, I think we have to ask ourselves what low-lying areas are affordably defensible: can we actually afford to save the duwamish/sodo area? If so, should the businesses there pay for that defense? How about Ballard? West Seattle?

    As a low-lying coastal city, the proper time to start having these debates was about five years ago.
  • westside
    On both the seawall and light rail to West Seattle and Ballard, McGinn seems to just make up numbers without any design. I usually like to know what I am voting for before I vote for it--but that is just me.
  • dutchoven
    Clearly the height of the sea wall isn't the only question that needs to be answered. The choice of exact location is important. Seattle could take this opportunity to cement itself as the crown jewel in Puget Sound by protecting all the communities along the water. I'm asking the voters of Seattle to approve a levy to build a new earthquake resistant, ecologically sensitive, bicycle friendly, global warming-immune, sea wall from Neah Bay to Bellingham.

    As this will coincidentally follow the border with our neighbor to the north, it's possible we could get some Homeland Security money for it, but finding funding sources isn't my job. Making big sweeping unilateral announcements is.
  • morning fizzy
    Besides the question of how high and when, we must also ask how long? The sea wall would have to extend pretty much all around the bay, certainly on the east side to keep the water from the central waterfront. The new design, if the SLR is to be accepted as certain, would need to extend to the cliffs in the north and to the river in the south.
  • DMS, "The best bet is to hedge."
    That would take too much time to wait for the juniper to grow, but it sure would be pretty.

    http://www.ubcbotanicalgarden.org/forums/showth...
  • Plastic Exploding Inevitable
    Of course, nearby in Alaska, sea levels have been falling...

    http://timesofindia.indiatimes.com/home/environ...

    quote ->

    But in Juneau, Alaska, as almost nowhere else in the
    world, climate change is having the opposite effect: As the glaciers here melt, the land is rising, causing the sea to retreat.

    Morgan DeBoer, a property owner, opened a nine—hole golf course at the mouth of Glacier Bay in 1998, on land that was underwater when his family first settled here 50 years ago. “The highest tides of the year would come into what is now my driving range area,” DeBoer said. Now, with the high—tide line receding even farther, he is planning to add another nine holes.
  • Bill B
  • Alex Broner
    Matt the Engineer has the right idea: tip the whole viaduct over into the water and we solve two problems at once ; )
  • Matt the Engineer
    Maybe we can convert the viaduct into a seawall?
  • Hmmmm.....
    Obviously we should wait to build the seawall until sea levels stabilize.
  • Wells
    http://www.seattlechannel.org/videos/video.asp?...

    The link is to Seattle Channel coverage of Monday’s City Council Briefing. It’s 65 minutes. Mayor McGinn lays out his case for quick action on the Seawall and answers questions from the Council. Shoreline habitat is mentioned as a part of the design, and important because it is a corridor for migrating smolts. Watching this briefing is helpful.
  • dutchoven
    How high should we go? Well, if all the ice melts, sea level will rise 200 feet. That'll take a heck of a levy. And a heck of a levy too.

    If you doubt that number, Google "if all the ice on earth melted."
  • DMS
    It seems that "How about a design that allows raising it at a later date?" is a good idea.

    I think that Dan's question is good but any sort of certain answer is bad, The best bet is to hedge.
  • Zander
    How high? High enough to resist the perfect shitstorm which can't be too far off.
  • Seems pretty obvious.
    The seawall must be high enough to keep the spindancing hippies at Hempfest from twirling off the new prominade into the water.
  • Giffy
    One thing I am wondering is how we could possibly build a seawall to deal with such a rise. I mean no matter how high we make it, unless we ring the whole sound won't the water just flow around it?
  • morning fizzy
    How about a design that allows raising it at a later date?
  • Giffy
    Many hope that the city will a choose a seawall design that provides enhanced habitat for salmon and other sea life,

    And they should be ignored. Any attempt to do that will be incredibly costly, and somewhat pointless in an area not at all suited for sea life. Its a working waterfront after all. How about we just build a damn seawall and spend that money better the 99.9999% of the sound where it would make a difference.
  • MadDen
    Okay, so what? Are you arguing that a vote, with no design on the table, is premature? Or should we vote yes and trust the city to get this right?
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