Archive for the ‘oakland hazards’ Category

Pinehaven canyon

4 July 2013

The headwaters of Temescal Creek lie east of route 13 in a steep canyon that has no name on the USGS topo map, so I will feel free to name it Thornhill canyon. The canyon splits at the site of Thornhill Nursery, with Pinehaven Road heading left up its own canyon and Thornhill heading right.

pinehavencynterrain

Pinehaven canyon is heavily wooded with a lot of eucalyptus and is almost entirely underlain by the crumbly Sobrante Formation. It’s a beautiful place, with a nice running stream that helps keep Lake Temescal full.

pinehavencrop

Whenever I visit the high hills I can’t help but think of its hazards, so different from those down below. The risks of landslide and fire, even in the absence of earthquakes, are compounded by the narrow, winding roads as we all know from the 1991 hills fire. Pinehaven canyon has not burned since it was settled, although the 1937 fire came close. Its firefighters are served by a couple of large water tanks, the Swainland tank at the top of Fairlane Drive and another tank above Skyline at the top of Broadway Terrace. If these run dry, a pumping truck is supposed to go halfway up Pinehaven to a spot where the next lower water system can be tapped to replenish the high system.

pinehavenfiresign

Central Reservoir

8 April 2013

Central Reservoir is operated by EBMUD, but it’s much older. It’s the weird-looking steel-covered field north of Sausal Creek. This is a view looking over the reservoir from Ardley Avenue toward the hills.

centralrestop

That’s the Altenheim on the left, across I-580, and of course the LDS temple with Redwood Peak behind it.

The reservoir was built in 1910 by the People’s Water Company, which took the existing valley of a Sausal Creek tributary, hollowed out the top of its watershed and made an earthen dam. Later EBMUD assumed control of it and upgraded things considerably. However, landslides plagued the steep west bank of Sausal Creek directly east of the reservoir starting in the 1930s.

The latest set of slides, in 2006, led to a tangle of lawsuits initially aimed at EBMUD and blaming leakage from the reservoir. The lawsuits were consolidated and went to a jury trial in 2012, with Alameda County as the main defendant and the damaged land owners (two homeowners and a church) as the remaining plaintiffs. The jury found for the County. None of the media that announced the lawsuit bothered to report the outcome, and the City of Oakland hasn’t bothered to clear EBMUD’s name, but the jury dispensed justice as designed.

For 17 MB of geotechnical detail, see EBMUD’s Central Reservoir Seismic Final Report, issued in 2008. As far as engineers can tell, even the Big One on the Hayward fault won’t break the dam. But if I lived downstream, I’d keep a close eye on the dam after a truly major quake and be ready to relocate. And in the aftermath, that emergency water supply may save our lives.


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