HomeMy WebLinkAboutPublic Works July 23 20131
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WHATCOM COUNTY COUNCIL
Public Works, Health, and Safety Committee
July 23, 2013
CALL TO ORDER
Committee Chair Barbara Brenner called the meeting to order at 3:42 p.m. in the
Council Chambers, 311 Grand Avenue, Bellingham, Washington.
ROLL CALL
(3:43:52 PM)
Present: Barbara Brenner, Ken Mann and Pete Kremen.
Absent: None.
Also Present: Carl Weimer.
COMMITTEE DISCUSSION
1. UPDATE ON THE DEBRIS FLOW IN THE UPPER MIDDLE FORK OF THE
NOOKSACK RIVER (AB2013 -275)
John Thompson, Public Works Department, submitted and read from a presentation
(on file). Since 1994, the glacier has retreated more than one - quarter of a mile. As it
retreats, it leaves steep, unsupported slopes. It's steeper than the angle it would typically
lay back to, and it's unconsolidated. It's boulders, sand, and gravel with nothing holding it
all together. The landslide area is probably 150 feet across.
Brenner stated it had to be a big slide, given all the material that was flowing for
many days. Thompson stated that this was a fairly small event compared to what could
happen. It was significant because they could see the impacts downstream. He continued
the presentation on how they know the timing of the slide. At the USGS gage downstream,
there were spikes in flow on May 31, which showed a surge in the flow. The landslide then
blocked the flow, and the flow dropped off until the pond filled, overtopped the landslide
break, and returned to the regular stream flow. They also received turbidity data
downstream that indicated an event on that day. The turbidity spikes were high enough
that they caused problems for cities and the Public Utility District (PUD), which take water
directly from the river. The PUD actually had to shut down due to too much sediment in the
water, which could result in a shutdown at the refineries, but he's not sure if that happened.
The PUD doesn't have a storage tank.
Mann stated that's a big deal. One would think the refineries would invest in a
storage tank. Thompson stated building storage into the system is in the PUD's five -year
plan. They're evaluating ways to do it sooner.
He continued the presentation on turbidity spikes. It takes a while for the sediment
to be processed through the system, resulting in a number of spikes. Evidence of water
moving through the dam created a health and safety concern if there was a catastrophic
failure. In this case, the biggest risk is to hikers crossing the channel downstream to hike
nearby trails. It was unlikely to damage the Mosquito Lake Road bridge. He asked the
forest service to post signs warning hikers. A month later, the pond filled with sediment.
The original spillway was dry. The chance of the dam failing catastrophically is now low
Public Works, Health, and Safety Committee, 7/23/2013, Page 1
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because the pond is gone. The stream will cut through as the flows come up this winter,
which will result in sediment pulses from various spots.
A characteristic of the debris flow is that the channel tends to scour. He showed
photos of the results of the slide and boulders that were moved downstream. The stream
cuts down through the new deposits within a few weeks, which causes the sediment seen in
the bay. As a scientist, this is a good example of the energy that these slides have. That's
information they can use to make decisions. He concluded the presentation on why this is
important and what to do next.
OTHER BUSINESS
There was no other business.
ADJOURN
The meeting adjourned at 4:16 p.m.
ATTEST:
, Council Clerk
- Minutes Transcription
WHATCOM COUNTY COUNCIL
WHATCOM COUNTY, WASHINGTON
Barbara Brenner, Committee Chair
Public Works, Health, and Safety Committee, 7/23/2013, Page 2