Debris Flood Report from Imus Creek, Stehekin

David Tucker forwarded me a couple of pictures from Stehekin in the central North Cascades that were sent to him by Jon Riedel of the North Cascades National Park. The email came with a "Post This". Thanks David and Jon. The pictures indicate that the flood and/or debris flood came down Imus Creek just behind the small town at the northwest end of Lake Chelan. Apparently the North Cascades Pass road has also been closed for the second time this summer due to debris flooding. 

The storm event that is winding down (2:00 pm, Sept. 6, 2013) was/is a rather unusual event. Very warm and mild with lots of rain. The total rain fall numbers around the state were impressive, but the more critical aspect of this event was the rain came in the form of intense down pours associated with thunderstorms. This storm had the weather folks pretty excited as it was unusual as evidenced by Cliff Mass putting up multiple posts cliffmass.blogspot before during and as it winds down. 

For geologists, these types of events are important. It is these intense rainfall events that shape our landscape particularly in eastern and central Washington State. In the remote mountain areas it is hard to know what the total rainfalls from these events are and for that matter what the return frequency is for that kind of precipitation. Jon reported 1.3 inches of rain at Stehekin in 3 hours.

The images are a reminder that geo hazard folks need to think about unusual weather events when assessing hazards; in central Washington this is particularly true. Based on the appearance if the shed, I suspect this is rather a rare event. 

Imus Creek is a fairly small watershed. The creek is only about two miles long, but has over 4,000 feet of vertical relief and lots of bare rock exposure. High flows in the creek are mostly due to snow melt, but this storm would have generated a very different hydrologic event than the more typical yearly high water events. 

It will be interesting to see what else comes in from various folks out on the landscape after this storm system.