13 November 2009

Carbon Canyon Landslide Mitigation Measures

Among the work recently conducted by CalTrans and/or its contractors along Carbon Canyon Road (State Route 142) has been the shoring up of a very steep hillside cut (made years ago when the highway was moved from the canyon bottom along Carbon [Canyon] Creek) on the north side of the highway, just west of Olinda Village in Brea.

The project consisted of attaching netting (what appears to be steel and some fibrous materials) to the hillside to prevent rocks and dirt/mud from sliding down onto the roadway. This is in anticipation of what could be a heavy rain year due to El Niño conditions expected in the Pacific Ocean this winter.

According to the National Oceanic and Atmospheric Administration (NOAA):

Expected El Niño impacts during November 2009-January 2010 include enhanced precipitation over the central tropical Pacific Ocean and a continuation of drier-than-average conditions over Indonesia. For the contiguous United States, potential impacts include above-average precipitation for Florida, central and eastern Texas, and California, with below-average precipitation for parts of the Pacific Northwest.

Obviously, the crucial wording here is "potential", but should heavier than average precipitation occur, there is the factor of last fall's Freeway Complex fire, which burned a considerable portion of the Brea side of the Canyon. With only a limited amount of plant regrowth thus far, it is possible that a major drenching in upcoming months could cause substantial sliding.

Whether the measures taken in this project will work or not, of course, remains to be seen.


Zaphod said...

This sort of bracing has worked well in the steep cuts of Provo Canyon in Utah, but the webbing went up twice as far, almost to the top of the cut. It worked particularly well when there were springs in the hillside, a problem not rampant in Carbon Canyon.

Paul said...

Hello Zaphod, thanks for your comment. Of course, CalTrans has extensive experience in working in slide-prone areas and there is no reason to think that the work in Carbon Canyon would be unsuccessful. My point was that, with the severity of last fall's fires, whatever plant material was there to hinder erosion in heavy rain is largely gone, so we'd just have to see what this will do for mitigation. I have, however, seen some rocks and dirt spill onto the shoulder of the roadway in this exact area and we have only had two very minor days of rainfall thus far. Thanks again!