>Culvert Concerns 1-15-11


Status of Culvert?  We have been asked about the status of the Illahee Creek culvert and whether the emergency clean-out by the county a few weeks ago has improved the situation.  For those who are new to these Updates or the Blog site, many think the culvert is in jeopardy and could fail, and those comments can be found earlier reports.
Saturday Measurements.  We measured the clear opening of the culvert on Saturday morning (1/15/11) before the rains and found essentially the same clear opening that was measured before the emergency clean-out.  In other words the emergency clean-out DID NOT decrease the sediment levels at the inlet end of the culvert.  See photo of culvert inlet.

Limited Measurement Opportunities.  We had to wait until there was a break in the rains as the creek water becomes too murky and too dangerous to measure when the stream is flowing full.  For those interested in actual measurements, there was a maximum of 29 inches of clearance before the clean-out, and today the clear measurements varied between 27 and 30 inches, depending where in the stream we took the measurements.

Large Logs Moving Toward The Culvert!  We received an email on Friday, along with some photos, alerting us the the fact that there are several upstream areas where there are large logs that seem to be moving downstream.  We received permission from the upstream property owner and took the attached photos.

What Happens if Logs Block Culvert?  So what will happen if the logs block the culvert?  First of all it will take a large rain to cause these logs to move, and secondly some of them would go through the culvert as the high velocity of the flow in the culvert would tend to move them quickly downstream.  If they should get lodged inside or in front of the culvert, the upstream basin area would quickly fill.  The increased pressure might be enough to force a blockage on through, but if not, the water would back up until it overflows at the lowest point of Illahee Road.  That point is probably just opposite the Krigsman’s driveway and would likely cause a road washout.

Why Report This?  The reason we are reporting this is because first of all it is a safety issued and secondly, something needs to be done to help resolve the storm surges that ravage Illahee Creek.  The storm surges have been polluting Puget Sound with large amounts of sediment for over 40 years and has been a concern for residents and the Port.  It became an even greater concern when everyone realized the relatively new culvert (installed in 1999) was also filling with sediment as the flood plain kept rising.  

Raised Flood Plains.  There is not much anyone can do with a raised flood plain.  Someone forwarded us the City of Issaquah’s Frequently Asked Questions on Flooding, which answers many of the questions Illahee residents have raised about the flood plain issues including dredging.  The link is:  http://www.ci.issaquah.wa.us/Page.asp?NavID=442 and their first sentences regarding dredging are:

Current Federal and State environmental regulations make it extremely difficult to justify stream channel dredging as a means to control flooding. While it can be done, it is very costly and time consuming to propose such work. …..

Time to Admit Culvert Failure.  We think it is time to admit that while the culvert hasn’t actually failed, it has technically failed.  It is time to look at either a significant culvert extension or a bridge for Illahee Creek.  But an extension or bridge would only resolve the threat to Illahee Road, and not the storm surge problem.

Time to Secure Golf Course.  So concurrently with correcting the failed culvert, it is finally time, after over 40 years of this small stream polluting Puget Sound, that the storm surges be brought under control.  The logical place for this to be done is at Rolling Hills Golf Course, so we would urge the county to finish the paper work to secure the golf course, which would be a good first step.

Please Let Us Know Your Thoughts!

Jim Aho