This is the final Leo Berk post describing his experiences as an embedded artist with King County (WA) Bridge Division.
Have you heard the one about the biologist, geologist, engineer, and artist who hiked up a relic stream bed together?
I hadn’t either until last November when I headed to the Money Creek Bridge with King County Roads’ Erick Thompson (biologist), Julia Turney (geologist), and Rich Hovde (engineer).
These three were on their way to the Skykomish area to visit this bridge in order to solve a complicated problem together.
Put simply, bridges are made to stay put, and creeks, by nature, don’t.
When the Money Creek Bridge was built, in the 1950s, its two arches spanned over two sections of the creek. Since then, Money Creek has significantly changed its path in the vicinity of the bridge three times.
Originally, the creek split its water through both of the bridge’s openings. Currently, almost all of the water spills through one side causing the bridge footing to be undermined.
Bridge folk call this “scour,” and if they let it continue, the bridge will ultimately fail.
There are lots of ways to fix this problem, but cost and environmental concerns narrow the list quickly.
A typical quick fix is to add some large boulders called riprap (which is currently my favorite Bridge Unit glossary term) around the bridge footings to prevent the water from taking its toll.
However, in this case, everyone agreed that Money Creek’s volume and velocity would make this a very temporary fix. As an added concern to this proposed fix, the addition of riprap to one side might cause water to be forced to the center pier and scour that area.
Another thought was to divert water through the now dried up side of the bridge. Easy to do: drive some big excavators down to the creek’s edge and dig a trench for the water to follow.
Fortunately for the environment, however, there are regulators who frown on any work that will disturb habitat for fish and plants.
Erick Thompson is the guy who gets the permits from the state environmental regulators, ensuring that engineering problems like this can be resolved with the environmental impacts in mind.
Whatever work does happen for the Money Creek Bridge, there will have to be environmental mitigation work, too, to lessen the impact of the intervention. This works in a similar way as carbon offsets—by planting trees in Africa, you offset the impact of your transatlantic flight. By creating salmon spawning pools and planting native species in the area of the work, Erick and the County are able to offset some of the impact to the creek.
While we drove to the bridge at dawn that morning, with the temperature in the teens, the crew thought they knew what the answer to this bridge question would be.
But once we arrived and reviewed the site, nobody had a clear solution. They were trying to balance cost, environmental impact, and the possibility of unintended consequences.
Finally, as we hiked up a relic stream bed where the creek had flowed at the time of the original bridge-building, the idea of diverting some of the current waters into this channel came to the fore – it would solve many of the bridge’s problems.
Of course, an idea like this would require more study back at the office where, fortunately, the temperature is kept in the high 60s.
*To read more about Leo’s experiences, visit 4Culture.org.
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