By Robert Leeper

A series of storms fueled by a mild El Nino hit southern California during the week of 17 – 23 January, 2010.  Rain, which was heavy at times, turned canyons that were burned during the recent Station fire into raging torrents of mud and debris.  Mandatory evacuation orders were issued by law enforcement for over two-thousand residents living in the foothills below where the Station fire occurred.  Fortunately, much of the mud and debris that rushed through the upper canyons did not make it to the foothill communities thanks to properly functioning empty debris basins located at the mouths of the canyons.  The debris basins stopped an immense volume of material that ranged from boulders and burned trees to gravel and mud, filling some to capacity before the storms ended.  If the duration of the storms was longer or the intensity of rain that fell on Thursday or Friday been equal to that which fell earlier in the week, the situation could have been much worse; debris flows and mud would have inundated the communities below.

The following photos document the Mullally debris basin and its inlet filling to capacity over the duration of the storms:

For best viewing, open each photo in a separate browser tab and toggle back and forth between them.

Mullally DB - Photo by Robert Leeper, USGS 01/14/10

Mullally DB - Photo by Robert Leeper, USGS 01/20/10

Mullally DB - Photo by Robert Leeper, USGS 01/22/10

Mullally DB Inlet - Photo by Robert Leeper, USGS 01/14/10

Mullally DB Inlet - Photo by Robert Leeper, USGS 01/20/10

Mullally DB Inlet - Photo by Robert Leeper, USGS 01/22/10

By Robert Leeper

The Multi-Hazards Demonstration Project is coordinating the USGS response to the recent Station fire in southern California.  This response includes ash sampling, debris flow monitoring and warning, and the impact on species in the burn area.  As a part of the debris flow monitoring project, we recorded the geomorphic response of several watersheds within the burn area to the storm that occurred 12 – 14 December, 2009.  Responses ranged from minor erosion to hazardous flash flooding and debris-flow.  The following photos document changes in a stream channel that occurred as a result of a debris flow produced during the afternoon of 13 December, 2009.  The photos were collected by Robert Leeper while conducting fieldwork with Jason Kean on 8 December, 2009 and 15 December, 2009.  The debris flow study area was selected by Jason Kean and Dennis Staley.

Mouth of side canyon in Big Tujunga 12/08/09

Mouth of side canyon in Big Tujunga 12/15/09

Farther up from mouth of side canyon in Big Tujunga 12/08/09

Farther up from mouth of side canyon in Big Tujunga 12/15/09

By Janet Zimmerman

” The potential for devastating floods have not garnered the same attention or concern as earthquakes among planners and the public, said Dale Cox, project manager for the U.S. Geological Survey’s Multi-Hazards Demonstration Project, the group behind the drills.”

“The Big One as it relates to a storm is not really there for people. They’re not thinking of 1861 — probably not even of 1986 — and it’s not your water-cooler disaster that you might talk about. In a sense, that’s a problem … these extreme events are, given climate change, more likely in the future.”

Read more:
http://www.pe.com/localnews/inland/stories/PE_News_Local_S_ark11.43eb34a.html