Colockum Creek Bridge Scour Repair

Three Chelan County bridges sustained significant scour and erosion damage during a major flood in September 2013.  The flood was produced by an intense thunderstorm which occurred following a forest fire that burned a large portion of the watershed.  The fire created semi-hydrophobic soil conditions which reduced soil permeability and increased runoff. WSE estimated the flood peak was in the range of 2,000 to 3,000 cfs which is at least five times greater than the stream’s estimated 100-year event.

Role / Services:  WSE was retained as the prime consultant to develop cost effective durable solutions that will protect the bridge from scour, improve bridge waterway hydraulic performance, and reduce impacts to stream morphology and habitat. WSE, working with Sargent Engineers, developed countermeasures to protect each crossing.  County staff led the permit process, which was difficult due to a desire by agency personnel replace rather than repair the bridges.  WSE provided significant technical input to address agency concerns and ultimately the County secured the permits.

Outcome:  Construction of the bridges was completed Spring 2016.