Tuesday, March 6, 2012

Flood Damage - Bridges

I think the term flood damage is most appropriately applied to the effects on artificial structures that have been intentionally placed in the path of rapidly moving water.  The only structures I’m concerned with are the foot bridges along the trails.  This bridge crossed the tributary I followed to the creek.  I was not surprised to find it a bit out of place.

This bridge acted just as it was designed to do.  One upstream corner of the bridge is cabled to an immovable tree.  When the water rises high enough to float the bridge, the entire structure is pushed out of the current and on to the bank.  It’s a fairly easy operation to lever the bridge back into its proper place.  Each time a bridge is replaced, I elevate it to a point just above the new high water mark.  I keep thinking that we’re unlikely to have a higher flood and the new elevation should mean never again having to reset the bridges, but I’m continually proven wrong.  The storm of 1997 that produced seven inches of rain in 24 hours, was said to be an event likely to occur only once every few hundred years.  I thought that bridges set above that level would be pretty safe, but that record has been broken seven times since then.  The storm that caused this latest flood only produced 1.2 inches of rain, but it fell on already saturated ground within a period of just a few minutes.

This bridge didn’t get washed away, but it also didn’t fare very well in the flood.  When I first saw it, the image reminded me of a giant snake skeleton strung out on the creek bank.

As water from the creek forced the bridge onto the bank, runoff from the hillside tried to push it back toward the creek.

I once tied to a jetty on the north side of Pelee Island that looked much like the remains of the bridge.  This bridge will not be swinging back into place any time soon.

At some point in the action, the bridge support attached to the cable snapped in two.  Fortunately, the bridge had moved far enough over the bank to be caught and held in place only a few feet away.  I’ll have to get out and salvage the deck boards before we have an even bigger flood that carries away the entire structure.

The ruined bridge seems to blend harmoniously with the torn up surroundings.  I’m afraid it will look totally out of place once things green up this spring.  I’ll make it a priority to get all of the bridge parts picked up before the spring wildflowers begin to bloom.

No comments:

Post a Comment