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.

Headwater landscaping

26 March 2013

The advantage of living in the highest hills is that there’s no one upstream from you. At the same time, hilltop dwellers may find it easy to forget what it’s like downstream.

gravelwash

This lot sits at the head of a stream valley at the edge of a regional park. The large expanse of impermeable pavement collects rainwater, and the terrace above it discharges more runoff in a large drainpipe. Ordinarily the ground would absorb most of the water and release it gradually, the way that trees are used to. Instead the flow that results here is strong enough to carry away a lot of gravel. Oh well, call in another truckload.

Turn around and track that water and gravel over the property line into the Regional Open Space. With the extra water, the stream is already cutting a deeper channel into its valley. As the years go by, the valley walls will slump into the stream and the trees will fall with them. A big wad of sediment now working its way downstream will clog the habitat below, smothering the bottomland and its ecosystem. Meanwhile the erosion of the stream valley will work its way headward. Eventually, within a lifetime, the spreading collapse will reach the edge of this large lot (and the neighbors’ lots) and whoever owns it will have an expensive problem. This pristine street may disappear from the map, like others before it in the Oakland hills.

I’m not giving a professional opinion here; it’s obvious to common sense. The landscape of the hills is fragile, but expert advice can make living there much more sustainable.

Displacement at the Altenheim

15 January 2013

The Altenheim complex is on top of the northern side of the Sausal Creek valley, just across the freeway from the reservoir near the McKillop slide. There seems to be a little ground displacement here, too.

altenheim-slump

This view shows the downhill side of the property, on MacArthur Boulevard where it takes a leftward jog north of upper Fruitvale Avenue. The more I explore the stream valleys cutting through the Fan, the more of this I see.

Collecting the Orinda

4 July 2012

Lately I’ve been putting together a rock collection for the Chabot Space & Science Center. The last rock I needed was conglomerate, and I slapped my head and said “Duh! Use the Orinda Formation.” So it came to pass that I was on the Gudde Ridge roadcut, east of the Caldecott Tunnel, admiring that distinctive body of rock. But its exposures were off limits due to the construction.

orinda formation

There were two problems. Finding exposures of the conglomerate was difficult. And once I got close to the rock itself . . .

conglomerate

. . . this magnificent stone turned out to be rotten. You may think of conglomerate as a rugged rock, with all that grit and gravel in it. Indeed it can be. But the young, minimally processed conglomerate of the Orinda Formation doesn’t hold up to sun and weather very well. The pebbles work loose and the matrix turns crumbly in a matter of decades. The stuff in that impressive set of stairstep cuts is actually ready to give way, thudding dull under the hammer and totally useless for my purpose.

In connection with the Caldecott Tunnel work, the Fish Ranch Road offramp looks like it may have some fresh exposures. But it’s fenced off.

orinda formation

In the end, I had to find my conglomerate elsewhere. The fresh stone is beautiful, though, and being able to finish the collection made my day.

orinda formation specimen

Did you see it?

11 June 2012

Oakland is peppered with landslides, whether up in the hills like this little earthflow off Grizzly Peak Boulevard or down in the flats.

landslide

Now the U.S. Geological Survey wants to collect them all, the same way it does with earthquakes. By analogy with its “Did you feel it?” earthquake reporting site, the Survey’s Landslide Hazards Program has launched a “Did you see it?” site.

And now I have submitted this landslide to the DYSI page.

Heritage in a dynamic place

10 February 2012

I gave my talk last night to the Oakland Heritage Alliance and I think it turned out well. I tried to talk about our geology not on its own terms, but weighted toward its relevance in Oakland’s general civic life. One of my slides was this lovely digital elevation model that makes the Hayward fault obvious. Click to see the whole thing. Sadly, I can’t recall exactly where I got it.

oakland DEM

Here are my concluding remarks from the talk.

Oakland is situated in an area that falls down every century or so. Today, a repeat of the 1868 earthquake would erase large areas of our city. I don’t see how we can prevent that. How can we hang on to our history in the face of nature? And how can we hang on to our history in the face of human nature? By that I refer to well-known tendencies in cities that are traumatized. Citizens have a strong, almost overwhelming urge to return to normal, and that drive is amplified in their leaders.

We have the example of San Francisco after 1906, which underwent a furious rebuilding and whose leaders had no tolerance for delay. San Francisco was the leading city of the West, and the stakes were very high. Democracy was short-circuited for a time. The development-driven city leaders, led by “mover and shaker” James Phelan, were prepared to obliterate Chinatown before the Asian-American community rallied to save it. There was no heritage community at the time, and who knows how it would have fared had there been one.

After our earthquake—and it’s coming—Oakland will still have all the geographical gifts that I showed you at the start of my talk. We can assume that the seaport and airport and rail lines and highways will be rebuilt as soon as possible. The stakes will again be very high. There will be little conflict with the heritage community over any of that. The hard part will begin once the emergency ends.

Earthquakes are part of our geography. These days we like to talk about sustainable living: in tornado country, for instance, that means everyone has a storm cellar. What does it mean in Oakland? Some of our most beautiful neighborhoods lie along the fault, and they probably will not be reoccupied once destroyed. The city that arises after the next Big One will be very different in some ways.

I think I can foresee a more sustainable Oakland in which more people will live in well designed multi-family buildings and recreate in a long greenbelt where route 13 runs today. On the other hand, much will endure. City Hall should survive thanks to its retrofit after 1989. Landmarks like Tech High, the Camron-Stanford House, Peralta Hacienda, and Dunsmuir will be restored if they survive the tumult. I know that the Oakland Heritage Alliance will be there, doing its utmost to save what can be saved. In the end, much depends on the citizenry at large: the values they hold most strongly, the values we are teaching them today, will be those that prevail.


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