Tuesday, January 19, 2010

storm basins

Devil's Gate on Monday around 1 p.m.

By Guy McCarthy

Devil's Gate Dam on the Arroyo Seco is in no danger of overflowing, officials say, in part because it has adequate means of letting water out as the wetland behind it fills with black soup and debris from the Station Fire.

That is not the case with some of the smaller debris basins across the foothills below recent burned areas.

The 29 debris basins intended to protect residents from erosion disasters are facing a severe test this week, and at least one of them is of particular concern as more storms bear down today on the Southland.

Mullally Basin at the end of Manistee Drive just east of Ocean View Boulevard in La Canada Flintridge is considered undersized for the current post-fire conditions, according to Los Angeles County and U.S. Forest Service records, and it has overflowed at least twice since the massive Station Fire denuded 250 square miles of mountain watersheds.

The basin overflowed early Nov. 13 during a sudden deluge from an "uncharted" storm cell, sending mud and debris flowing down parts of Ocean View Boulevard. It overflowed again Monday, contributing to the need for temporary evacuation of more than 60 homes in the Paradise Valley area.

Enlargement of Mullally Basin has been in the planning stages for several years, according to the county Department of Public Works.

Several alternatives for enlarging Mullally Basin were discussed during an October 2008 community meeting, according to county records.

About a year later, while the Station Fire was still smoldering, a Sept. 22 Burned Area Emergency Response report from the U.S. Forest Service stated, "Mullally Canyon Debris Basin was identified as being significantly undersized by L.A. County Public Works.

"If a large debris flow or flooding event occurs, the release is onto Ocean View Blvd., which runs to Foothill Boulevard," a main thoroughfare, the Forest Service stated. "Downstream residences need to heed triggers and warnings established by the National Weather Service."

In September, the Forest Service listed Mullally's capacity at 9,400 cubic yards and estimated the post-fire annual yield at 19,896 cubic yards. The post-fire estimate may already have been exceeded since Nov. 13.

In addition to Mullally Basin, six other basins are considered undersized and are slated for expansion to increase their storage capacities, but implementing those plans is not scheduled to begin until April, according to a public works report delivered to county supervisors in December.

The $5 million project to expand Big Briar, Mullally, Snover, Pickens, Starfall, Pinelawn and Rowley basins was detailed in a Station Fire disaster recovery report delivered to the county board of supervisors by Director of Public Works Gail Farber.



Bellis said...

I can't get the video to work, but I saw it myself on Monday and Tuesday. Why is there no current visible close to the dam? Is it all running under the thick layer of mud?

guy said...

Sorry about the video - it works on Macs and Blackberries but apparently not on p.c.'s

There's another video from that same day here: http://www.facebook.com/#/video/video.php?v=1337717526727&ref=mf