Archive for the ‘oakland water’ Category

Drainage

18 December 2010

Oakland is a fine town unless it rains too much. Then we have to worry about all the water.

drainage

All things considered, Oakland’s landscape would prefer to be steep, forested hills raised by tectonics along the Hayward fault and gentle coastal plains that absorb the sediment washed off those hills. It’s a rich recipe that produces redwoods in the heights and forage and fruit in the vales. But with impervious roads and homes carpeting the upper slopes, we increase the runoff and undermine our own infrastructure. People like the homeowners above Broadway Terrace run flexible plastic lines over the edge of their properties to put the problem out of mind. But if you walk the road, you’ll find fresh gullies that will work their way uphill to the source of the problem regardless. Landslides will probably follow.

Big Rock

27 September 2010

I was at Temescal Regional Recreation Area yesterday—you probably call it Lake Temescal—and was happy to spot one of my favorite places.

big rock

This big hunk of Franciscan something-or-other sits near the head of the lake, displaying the ugly attractiveness that the French call jolie laide. Not a hundred feet away runs the Hayward fault, and there’s a free-running stream here too. Some classic oak trees shade picnic tables, and you can even swim where fish can nibble your toes.

Big Rock is the place I used to illustrate my post “Leave the Stone Alone.” Because for some reason, people seem to respect Big Rock.

San Leandro Creek (3)

25 July 2010

San Leandro Creek supplies almost all of the water in Lake Chabot. Here’s where it enters the reservoir, at its farthest eastern end.

lake chabot

San Leandro Creek is one of only three streams that cross the East Bay hills. The other two are San Lorenzo Creek, which cuts through Castro Valley and Hayward, and Alameda Creek, which traverses Niles and Fremont.

Since Anthony Chabot built the dam in the 1870s, the creek has dumped sediment and filled in about a mile of its course, creating new level land until today it’s slowly encroaching into the lake itself. Willow Park Golf Course is built on that land.

Not much sediment comes into the lake today, now that Upper San Leandro Reservoir has dammed the creek about four miles upstream. The round pads of aquatic vegetation flank the stream channel, which runs between low, muddy banks that were underwater when I visited last month. I think the vegetation traps sediment, which supports more vegetation, so that the patches tend to grow into a circular shape, reminiscent of bacterial colonies on a petri dish.

The first two ridges in this photo are underlain by the Joaquin Miller Formation, which extends along the whole south shore of the lake between here and the park headquarters. It’s mostly shale with a few large sandstone beds, tilted steeply upward. The farther ridges are all Oakland Conglomerate, and they stand maybe 50 meters higher. They look more sparsely vegetated, which may reflect the bedrock but might just as easily be due to historic land uses.

Drains to bay, an Earth Day message

22 April 2010

earth day

Some things are as obvious as gravity: Here’s the drain. There’s the bay. The geologist knows this so well that it never needs to be stated. The earliest thinkers of modern geology, as far back as Nicolas Steno in the 1600s at least, recognized that rocks arise from the everyday process of mud washing downstream to the sea. The signs are obvious in the petrified ripple and current marks, the fossilized sea creatures and the sandstones as clean as the stuff of beaches. “Drains to bay” might as well be written on the geologist’s coat of arms.

The rest of us need occasional reminders. Many of us never gave it a moment’s thought, probably those same Oaklanders who think that bears live in the woods up on Skyline. Earth Day is for them, the ignorant. Ignorant people are not bad people. Indeed, they’re only selectively ignorant, in that they don’t know something I consider important. Surely I’m just as ignorant in terms of what they care about. Anyway, “drains to bay” is a good start and it needs to be pointed out everywhere, even here where it’s obvious on Embarcadero East at the mouth of 14th Street Creek.

Earth Day, too, should always point out the basics. The rest of the year is for learning more and for putting knowledge into daily action—for Earth Life.

“Drains to bay” means that what we throw away doesn’t go away, any more than the ancient ripples and prehistoric creatures are totally lost.

Creek mouths

7 February 2010

Down at the Martin Luther King Shoreline Regional Park, three creeks debouch into San Leandro Bay. I already talked about San Leandro Creek; the other two are Lion Creek, below (more about it here and here), and Elmhurst Creek, bottom.

lion creek

elmhurst creek

Maybe with all our recent rain, they carried some sediment down to the bay, but probably not. Today both creeks are culverted to within an inch of their lives.

Old-fashioned water filtration

16 January 2010

On the path up to Chabot Dam, you pass this row of big tanks (click for big version).

water filtration

They were used to filter the water from Lake Chabot reservoir, and they’re still filled with fine sand plus, I suppose, the decades’ worth of slime and crap they kept out of Oaklanders’ stomachs and food.

This is roughly the same purification method we rely on when we use well water. The fine pores between mineral grains purify groundwater in two ways. First, of course, they physically trap the crap. Second, the minerals themselves chemically attach to many dissolved contaminants. Clay minerals are especially important for that.

The days are long gone when Oakland was served by wells. The water table has been pulled down all over the city by human intervention. The headwaters of Lion Creek were once called Laundry Canyon because there was so much good water coming down. Fruitvale irrigated orchards for many years. The rains we get here can’t keep up, so now we pipe our water in from the Sierra.

One important feature of the new state water compact, if they can ever get it nailed down, will be a new, wide-scale program of monitoring groundwater. We need that to get a handle on the whole resource. Everyone knows, except the statutes, that surface water and groundwater are intimately connected. Western water law is an ass.

Lake Chabot

20 December 2009

Lake Chabot is a reservoir, but geologists still agree with laypeople that it qualifies as a lake.

lake chabot

That said, reservoirs differ from most lakes. They have steep banks and deep middles. This gives them a greater variety of habitats. They have jagged planforms on the map because they intrude up every little tributary valley instead of developing a nice rounded shape. And, of course, they’re temporary by any geological measure.

Around here, most lakes form as a result of tectonic activity or landslides. Lake Temescal started out as a sag pond on the Hayward fault. Clear Lake, farther north, formed when a landslide dammed a fork of the Russian River. It rose until it spilled eastward down Cache Creek, which has captured the watershed. Lake Chabot is about 50 feet short of that level; if Anthony Chabot had built his dam higher, the lake would now spill south into Castro Valley.

The valley of San Leandro Creek is so steep and its walls so high that I can easily picture it collapsing regularly, especially during big earthquakes, to have made ancient Lake Chabots in the past. So today’s lake isn’t so unusual for the region.


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