Illahee Creek Culvert 1-3-08

This update concerns the Illahee Creek culvert under Illahee Road. Many of us have concluded the culvert has failed and that another major storm could result in a wash out of Illahee Road. We sent the following email to Kitsap County personnel on Tuesday (1/2/08):


We are extremely concerned that the Illahee Creek culvert under Illahee Road has essentially failed as the result of the December 3, 2007 storm. We think this failure is the direct result of the storm and that federal disaster money needs to be applied for to fix the problem.

Another major storm would likely result in the further blockage of the culvert which could result in another major washout along Illahee Road.

The following statement appeared in the recently published Parametrix "Draft Illahee Watershed Characterization and Site Assessment" dated December 2007 which was authored by Erin Nelson and Derek Booth, and provides supporting professional documentation of our concerns.

Along the lower Main Stem and below Illahee Road, the consequences of high sediment loads and nearby base level (i.e., Puget Sound) were manifest in abundant deposition, a braided channel form, and the near-obstruction of the Illahee Road culvert. Based on local reports during the storm, filling of the culvert proceeded from downstream to upstream (i.e., not from an obstruction at the upstream end of the culvert) and almost certainly reflects the rapid delivery of sediment onto the delta of Illahee Creek that built a steepening wedge of sediment into the Sound. Local dredging of the sediment immediately downstream of the culvert has provided temporary relief, but additional high flows would almost certainly deliver sediment more rapidly than a backhoe could remove it. Long-term, a reduction of sediment delivery into Illahee Creek would allow the reestablishment of a reduced gradient between the creek and the Sound, lowering sediment levels in the culvert and recreating free passage. Given the improbability of this scenario absent dramatic efforts to resolve acute and chronic sediment inputs into the channel network, however, emergency maintenance and eventual replacement of the culvert appears almost unavoidable.


The filling of the old stream channel with sediment has significantly altered the stream flow at the mouth such that salmon passage is now questionable .

We have a stream with such a large sediment transport problem, caused by the lack of storm water controls, that it is effectively raising the height of the flood plain up and down the main corridor of Illahee Creek, including the delta at the mouth of the creek.

Some has suggested that the only way to solve the problem is to raise the height of the culvert or put in a bridge structure, which would mean raising the height of Illahee Road in the vicinity of the culvert. We will leave those decisions to the engineers, though they may appreciate some help at this point.

There are no easy solutions and no one has come up with any quick fixes. The recent backhoe work at the culvert outlet increased the opening at the upstream inlet by 3 inches (from a 19 to a 22 inch clear opening). We commend those efforts, but remind the county that the culvert will not likely handle another major storm.

The community needs to be aware of this situation as it is always the local citizens who are most impacted and affected when systems fail. We welcome your thoughts and comments.

Dennis Sheeran & Jim Aho