Bridges vs Floods Round 2

Weather related records are being broken at a rapid pace this year. Some of the records stand for only a short time before they are again broken. Setting a record should be a positive experience, but I’ve not experienced much joy in these record breaking events. A recent intensive storm has set a new high flood level that will be very difficult to top. Foot Bridges that survived the previous record flood just last month were torn to pieces by the wild water that accompanied this last event. Evidence of this flood is going to be visible for a long time.

The only sure way to avoid flood damage is to stay out of places that flood. If you do put something in the path of the flood, expect it to be damaged. I’ve always known that any of my bridges could be torn apart by a wild flood. In anticipation of that fact, I designed the bridges so that the resulting pieces were predetermined. Although this six foot section of bridge decking is 600 feet downstream of its original position, it has not received any damage. It is intended to be one of several separate units that can be easily carried back and reassembled in the proper location.

Here’s the rest of the bridge decking, tethered by its safety cable. The logs used as bridge supports are in a tangle of debris downstream. Moving water is a powerful force, but that shouldn’t have been enough to demolish this bridge. Some logs showing in the debris tangle came from a neighboring property somewhere upstream of the bridge site. These logs, carried down the channel by the flood water, would act as battering ram and would have hit the bridge with enough force to take it apart. Had the water been free of debris, the entire bridge would have been sitting comfortably on the far bank as has occurred in the past.

When I constructed foot bridges across the creek, I had to decide just how much damage I was willing to accept and how much I was willing to deviate from my vision of the perfect crossing in order to reduce damage. As a child, one of my greatest joys was peering through the boards of a bridge deck and spying on the aquatic life beneath. My preference would be to have low bridges that provide an intimate nearness to the creek, but this type of bridge would move with every high water. Raising the bridges high enough to avoid any flood impact would result in a much longer span across the creek and a bridge deck far removed from the water. I chose a position in the middle and set the bridges so they would only be damaged by exceptional runoff events which would be expected once every five to ten years. This bridge was moved from its stone supports, but wasn’t really damaged. The path of bright green ground cover indicates the area that was swept clean by the flood.

The bridges will be repositioned when things dry out. I’ll mark the new high water levels and see if any adjustments to the bridge heights can be accomplished to make them a little more secure. I don’t want to get them too high, because there’s always the chance that I’ll fall off of one some day.