US Geophysical Survey has put out a report on the danger of mud flows (links to summary, but a pdf is available at the site). And, says reader Chip Ossman, who alerted us to this document and has been following this story:
Once again, the world has ignored Altadena, reducing us to "three basins east of the Arroyo" - assuming they are referring to Altadena and not points farther east.
UPDATE 11:30 PM: Chip has received a note from Susan Cannon of USGS, after the jump.
Paul Laustsen forwarded your inquiry to me. You are correct, we didn't evaluate the potential debris flow inundation area for the "three basins east of Arroyo Seco." So sadly, your very own Figure 7a does not yet exist. We restricted the assessment to the mountain front west of Arroyo Seco because the topographic information we had indicated that any material generated from basins east of the arroyo would move through a well-defined channel into Devil's Gate Reservoir. As a result, we didn't see the potential for material to impact neighborhoods in that area. However, we have since learned that the topographic data we were using is not particularly reliable, particularly along the mountain front where recent development has changed many drainage systems. As a result, we are planning to re-run the assessment using more recent, and finer-scale topographic data within the next few weeks. I will save this message and let you know when our assessment is available.
So I am sure you would like to have information sooner than the next few weeks. Are you aware that the LA County Department of Public Works is also doing similar assessments for the area, and are making their engineers available to look at neighborhoods and individual homes? If necessary, the engineers will provide information on possible mitigation approaches. This is a tremendous service and should be able to answer your questions down to the number of sand bags you might need! LADPW has a 1-800 number to call to request this service, but I do not have it at hand. Instead, I can recommend the Coordinated Agency Recovery Effort (CARE) website at www.dpwcare.org as a place to start.
I hope this information is helpful, and please don't hesitate to contact me if you have additional questions.
Susan H. Cannon, PhD
US Geological Survey
Box 25046, DFC, MS 966
Denver CO 80225