Archive for the ‘Other topics’ Category

A new kind of shoreline

5 March 2018

Rising sea level is a threat to the Bay area. Already, king tides are flooding the levees and seawalls built for the last century’s ocean. I touched upon this topic a few weeks ago with my proposed walk around Lake Merritt in 2100, assuming that the Bay will be a couple meters higher than today.

Yesterday, happenstance allowed me to witness a promising project that has built an experimental coastline modeled after a natural one — specifically, a living water filter meant to sit between the low tidal mudflats and the higher levees holding the Bay back. The Northern California Science Writers Association arranged for a group of members to visit the Horizontal Levee Project, on the grounds of the Oro Loma Sanitary District wastewater treatment plant in San Lorenzo.

Let me sketch the idea behind the project. To begin with, the natural coastal landscape has been totally messed up. It used to be a nice grassland plain, gradually sloping down to a series of wetlands that merged organically into the tidal marsh, mudflats and open Bay waters. Water from the hills percolated gently down the streams and through the ground, nourishing a lovely ecosystem full of species. American settlers cut off the top part of this landscape and covered it with buildings, dammed and diverted the streams, then filled in and walled off the lower part with levees. Today the coastal wetlands are cut off from the water and sediment from the hills, and meanwhile the sea is creeping up and washing them away.

The thinking behind the Horizontal Levee Project is to build a new slope on the uphill side of this truncated coast, then restore the groundwater flow that used to be there using treated wastewater. Even compressed to a fraction of its former width, the resulting slope should be a powerful water-scrubbing engine and a vibrant habitat. (Figure from here.)

The wastewater part is crucial because we have lots of it, we can control its flow, and the new slope — scientifically, an ecotone — cleanses the wastewater of nitrates and other hard-to-remove compounds better than treatments costing 10 times as much. All while feeding a splendid tidal marsh that resists storm waves better than concrete walls!

Our visit took place on a brisk, bright day by the bayshore. The Oro Loma Sanitary District treatment plant is mostly clean, stark and Brobdingnagian.

But the operators found space to put up this pilot project on their own land, where they didn’t need so many permits. They built a gently sloping earthwork, installed pipes at the top and drains at the bottom, then raised a mix of plants from local sources to seed it with, using these planter boxes.

Project staff noted that the alkali bulrush is particularly good at resisting storm waves with its tall, stiff stems.

Seeding and planting happened in the rainy season of 2015-16, so this lush jungle of native marsh plants on the ecotone was just two years old. It’s so dense that invasive weeds, even pampas grass, don’t stand a chance.

And the water coming out at the lower end is really clean. (Even so, the water was pumped out through the white pipes on the left and put back into the treatment stream.) Soil bacteria actually convert the nasty nitrate to nitrogen gas, so it isn’t just trapped in the dirt or building up within the plants.

Water treatment agencies all around the Bay have their eyes on this experiment. It looks like the design will be flexible enough to be adapted for as much as 5000 acres of wetlands, a significant fraction of the coastline that’s particularly vulnerable to sea rise.

Awareness of sea-level rise needs to happen faster than the rising sea itself. The speakers yesterday found that the hardest nut to crack in moving things forward is regulations: interpreting them creatively, coordinating the regulators, combating inertia. To envision, scope, design and plan improvements to the shoreline literally takes decades, meaning that we have to aim for a target in the year our children reach our age.

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Care and grooming of rocks and outcrops

5 February 2018

Photographers know that everything about a great shot depends on how you set it up. As I capture images of geological subjects, part of the setup involves prepping the model. Often it’s just a matter of removing a few stray twigs to get a decent picture, like these serpentine stream cobbles in Joaquin Miller Park.

Only rarely does nature present rocks in an untouchably satisfying way — and to tell the truth I might have brushed off a cobweb before I took this portrait of laminated siltstone in Shepherd Canyon.

But around here, as opposed to the Grand Canyon, rock exposures are generally kinda shabby. What are you going to do? Rocks are made underground, and once exposed to surface conditions they start to break down. And vegetation doesn’t care where it sheds things.

In many of my outings, I find myself doing some housecleaning. Whenever I lead a walk, it’s mandatory for me to go over the route beforehand and groom the features I plan to show off, like the splendid exposures of the Oakland Conglomerate in Montclair.

This textbook example of load casts always requires a thorough weeding session, followed by a good sweep with my umpire’s brush. Because shale wants nothing more than to return to clay, and weeds like nothing more than decayed shale.

There’s an outcrop in Dimond Canyon, along the trail, that I always take a minute to groom. The last time I did this I took these before-and-after shots.

This is something that any of you can do too, if the spirit moves you. I know people who routinely carry tools to prune snaggy or undesirable vegetation along the trail in a discreet way. Sometimes I do that, but more often I stick to grooming the outcrops. Because who else will? While one of my principles is to “leave the stone alone,” the stone can use a bit of care here and there. That’s my contribution to the geoparks movement in a country that badly needs it.

Post 500

9 October 2017

The experts say the greenhouse gases we’ve put in the atmosphere will affect global climate for the next several centuries. Where will we be 500 years from now, once this pulse of carbon dioxide has been drawn down by the seas and soil? What will the post 500 world look like?

I’m fond of talking about the deep present, the idea that we should run society as if any natural event that’s happened during the last 10,000 years or so, not just recorded history, could happen again tomorrow. But for the greenhouse pulse the deep present is no guide, because the world hasn’t seen its like for millions of years. The greenhouse pulse has shoved us into the Anthropocene age in which, like it or not, humans are a large-scale geological force.

The Anthropocene world will be an ad hoc world. Post 500, the sea will be tens of meters higher than today, but once we have the means to regulate the climate I suspect we’ll keep the sea where it is, for stability’s sake. I don’t see us bringing the glaciers back unless there’s an existential need.

Some aspects of the future are sure things. I am sure we’ll still be scrambling to deal with the damages we’ve done to the natural world we inherited: the ruined aquifers, the risen seas, the climate out of equilibrium, the ecosystems lost or knocked askew by extinctions and invasives, the metal ores depleted, the billions of holes we’ve made in the ground.

It’s harder to imagine the state of human society post 500. Look back 500 years to 1517 — the Portuguese empire was pushing into the Spice Islands and the Magellan expedition, the first to circle the globe, was still being organized in Spain. Modern science was many generations ahead.

It makes me uneasy to say this, but unless the human population can be reduced to Earth’s carrying capacity, perhaps one-tenth its present total, we’ll need to engineer fully artificial living arrangements that don’t affect the rest of creation. If you like, call that a zoo for humans. If you like, call it the terrestrial version of a Moon base. It will have to be so good we’ll want to live that way. We’re already getting there.

We will need to minimize our wasteful, precarious agricultural system based on pesticides, fertilizer and soil. To save the world’s plants and animals from widespread extinction we will need to stop encroaching upon their environment — not just stop, but withdraw.

Surely the post 500 world will differ wildly from ours. But the seeds of that world are sprouting today. In the past 500 years we have mastered matter, and in the next 500 I anticipate that we’ll master biology and recycling. We will no longer use fossil fuels, and we’ll do much less mining on Earth than today, if any. We’ll undam most of the rivers and heal the coral reefs.

Why do I bring up all this in a blog on the geology of Oakland? Because we’re building the post 500 world now. Look at the 50 years just past, and imagine that degree of change and progress over the 50 years to come — even as sea-level rise starts to really kick in. The next 50 years is the first one-tenth of the next 500 years, and the most important part. Progress will require knowledge of the Earth and the confidence to apply it. Thus Earth scientists will be central as we make our way.

And Oakland will endure; it’s too important not to. Mass transit will gain ground as population density increases. As the sea rises, we’ll raise our harbor and airport and rail lines, even if they end up on plateaus. We’ll restore the salmon run up San Leandro Creek, and our building stock will improve as we go through repeated earthquakes, rebuilding higher each time.

Those are sure things, and they can be done right if we insist. What matters is our culture. What we do today, and how we do it, will make all the difference on our way to post 500, the year 2517.

(Yes, this is my 500th post.)

Coring

14 August 2017

With all the construction going on around town, you’ll see lots of drill rigs taking geotechnical cores. This one was at work at 2330 Webster, where the Webster Alexan development will go.

Just a few days earlier, a rig was collecting cores in the parking lot at 20th and Telegraph, slated to become one of two residential towers.

Crews like this are testing the ground to firm up the construction plans. The weight of these buildings requires a foundation that won’t sink, buckle or deform under the expected loads over the building’s life, including earthquake loads. At the Telegraph site two holes were bored, at opposite ends of the lot.

It takes a couple of workers to run the rig and a geologist to log the hole. They look the same — vests, boots, hardhats — except the geologist carries a clipboard and isn’t quite as muddy. The geologist on this job was a young guy, crouched in the sun and processing sediment plugs that looked like this.

It’s nice, clean marine clay from the lower part of the hole. I refrained from nibbling on a piece to gauge its silt content. It was real firm, not sticky. I’d put a house on it, no problem.

The geologist was poking at the plugs with a pocket tool and keeping them properly organized. He told me the hole was around 90 feet deep, with this stuff at the bottom. The top 20 feet was sand and gravel, then about 30 feet of clay, then some more sand and gravel and finally this clay. It’s a common pattern around the Bay, reflecting the changes in sea level over the last few hundred thousand years.

The crew was finished in less than a day, and they tidied up nicely afterward.

The U.S. Geological Survey’s Open-File Report 2014-1127, “Geologic Logs of Geotechnical Cores from the Subsurface Sacramento-San Joaquin Delta, California,” will give an idea of what core logging involves when it’s done right. What seems like painstaking drudgery is essential for building safely, and geologists can get called into court to vouch for the accuracy of their core logs.