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Archive for May, 2009

This report from Reid Fisher, a geologist and board member of the CPOA.  Thanks Reid – great information here.

Hello Everyone,

FYI, as a followup to a field trip with Caltrans personnel. As you probably saw from all the orange shirts and reflective vests in town, Caltrans engineering geologists and geotechnical engineers from around the state are just wrapping up a conference focussing in large part on debris flow and rockfall hazards and mitigation. I was very fortunate in being invited to accompany them on their field day review of Big Sur debris flow and rockfall mitigation sites/issues. I came away very impressed with the energy and dedication of these folks, as we have been by Lance Gorman and Steve Balaban. A couple of subjective observations from an outside-the-agency geologist:

* The speed with which Caltrans hit the ground appears to have been partly a result of early “calls” on the level of disaster, and in establishing a “corridor” within which problems could be anticipated, rather than having to first identify specific sites, then request authorization/funding, etc. The corridor concept is new. There was a lot of creative thinking from bottom to top on this effort, and it really paid off.

* The ability to consider working outside the right-of-way may also be a first in the state. It made a huge difference, dramatically opening up the possible approaches to include work that made much more common sense than strict ROW projects. The early input from the local residents, saying in essence “go for it” helped this to happen. Caltrans really appreciated the positive reception and support they got from locals who are very aware of the issues these projects address from previous fires and wet years.

* It appears that there was strong support by local reps to the state and fed level, which helped in getting agencies to pull in the same direction, and helped in funding.

* Caltrans anticipates a significantly elevated debris flow potential for the next at least 3 to 5 years (this is in line with independent work by USGS and others, who project something in that same 3 to 5 to 10 year time frame, depending on weather). After that time period lapses, Caltrans’ intent is to take down the debris flow barriers, which was news to me (they’ll be reused elsewhere). It will be important for CPOA and others to track debris flow occurrence (and rainfall intensities when these events are triggered), and general slope recovery in order to gage the pace of recovery and know whether 3, 5, or 10 years will be required for substantial recovery. The slopes look amazingly green now, but they are by no means recovered. Caltrans has limited rain gages in place, with mini-dataloggers. They do not provide an alert, but they do permit backcalculation of what it took to generate a debris flow event, thus helping to sharpen and focus forecasts and alerts. At $100 each these instruments could be installed elsewhere in the Big Sur area with volunteers to periodically download and forward data.

* There is a recognition on the part of other agencies that landsliding is a natural, ongoing (though episodic at the human scale) process by which coastal sediment is replenished. Intercepting and interrupting this through landslide mitigation is an alteration of this process, and there is attention being paid into how to reintroduce this material into the drainages in a way that approximates the natural regime (rather than trucking to distant disposal sites).

* Access to debris flow barrier systems for effective, rapid cleanout will be essential in the lifespan of these structures. It’ll be tempting for things to get stored, parked and piled on the ramps and landings that are built into these installations. That’s it for now..

Reid

G. Reid Fisher
PACIFIC GEOTECHNICAL ENGINEERING
16055-D Caputo Drive
Morgan Hill, CA 95037
T 408-778-2818 x 402
F 408-779-6879

CPOA Board
info@cpoabigsur.org
Serving the Big Sur Coast for over 45 years.

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