Tules on Twitchell Island in the Delta. (Photo: Josh Cassidy/KQED)

With thousands of acres of rich farmland, the Delta has a long agricultural legacy. But farming there can be a risky business. Dozens of farms have been flooded over the past half century as aging levees have collapsed.

That became a reality for farmer Rudy Mussi on the morning of June 3, 2004. It was clear, sunny day. "You never expect a flood in the summer months," says Mussi.

Mussi was growing corn and asparagus on lower Jones Tract, an island in the Delta, 10 miles west of Stockton. That morning, he got a phone call. Water was flooding onto his farmland.

"Your heart stops for a second or two and then realism sets in. And you just start moving your equipment and get it to high ground," says Mussi.

How did a flood happen a on a sunny day? It's because of a basic rule of physics. Mussi farmed on an island below sea level, like a lot of the islands in the Delta. The Delta used to be a huge swath of wetlands, where two major rivers met San Francisco Bay. Today, earthen levees hold that water back – most of the time.

"Once a break occurs, you know, there's no way you're gonna stop that, not with 10 feet of water on the other side," Mussi says. Draining the island and repairing the levees around Jones Tract cost about $90 million.

The levee break on Jones Tract in 2004. (Photo: CA Department of Water Resources)

It wasn't an isolated incident. Over the last century, more than 150 levees have failed in the Delta.

Delta Infrastructure at Risk

"This is how we get ourselves in kind of an arms race between the water and the land," says Jeff Mount, professor with the Center for Watershed Sciences at the University of California-Davis.

Levee-building began in the 1850s, when settlers came to the Delta for the rich soil. More than a thousand miles of levees were built. "This network of levees through time had to get bigger and bigger for a very basic reason: the land has been steadily lowering," says Mount.

As farmers exposed the rich peat soil, it started decomposing. The land level dropped; "In some places they talked about four inches per year," says Mount. Today, it's less than an inch per year thanks to better farming practices.

Add up all those inches over the past century and some islands are now 30 feet below sea level. That puts a lot of stress on the levees. There are also other concerns: rising sea levels and extreme floods. "And then the big 800-pound gorilla in the room – we're due for a very large earthquake on the San Andreas system."

Add up all these risks and Mount says there's a two-thirds chance of a catastrophic levee failure in the next 50 years. That, of course, affects farmers and communities in the Delta, but it could also impact California's water supply.

"The raindrops that fall in Mount Shasta are consumed by people in San Diego. Water moves a great distance and this is one of the critical hubs in that system," says Mount.

Fixing the Delta's levees is estimated to cost billions. But on some islands, scientists are experimenting with a new fix.

Farming Carbon

Peat soil samples on Twitchell Island. (Photo: Josh Cassidy/KQED)

On a windy day on Twitchell Island in the Delta, ecologist Lisa Windham-Myers of the US Geological Survey pushes her way through a wetland filled with a tall, reed-like plant known as tule.

"The plant grows… some of these are 16 feet tall. They're just huge," she says. That growth is changing the ground we're standing on. Windham-Myers pulls out a sample of the dark peat soil.

The wetland produces soil at a rapid rate – four inches a year on average. That's huge, says USGS scientist Brian Bergamaschi, in a place where the land is sinking. "These islands are like bowls and the way we see projects like this is you want to fill up the middle of that bowl and help level out the whole island."

Planting wetlands like this one could raise the land level and water table on the inside of levees, relieving some of the pressure. But why would farmers want to replace cash crops with tule? Windham-Myers points to the soil.

"This is basically almost 100 percent carbon. These take up far more than a typical forest environment," she says. California is setting up a market for carbon, as part of the state's effort to cut global warming emissions. Early next year, companies that need to reduce their emissions could pay farmers to store carbon in wetlands like this.

USGS scientist Brian Bergamaschi talks with Delta farmer Al Medvitch. (Photo: Josh Cassidy/KQED)

Today, two farmers are here checking out the project: Steve Mello, a Delta farmer on Tyler Island and Al Medvitch, a farmer in the Montezuma Hills.

"The potential has been demonstrated well. You guys are standing in the middle of it. But in order to move from here to market, we need to develop a lot more techniques so people can come and verify that the carbon is stored," says Brian Bergamaschi, describing how wetland farming might work.

Both farmers seem open to the idea. But Mello says ultimately, it depends on the bottom line. "It would absolutely need to cash flow. While it could dovetail with levee stability, it would still need to generate enough to amortize your property value."

Still, Mello says assuming carbon prices are high enough, growing patches of wetlands could be a feasible way to improve the levees and to stay farming.

A map of the Delta created by the US Geological Survey in the 1910s.

As detective stories go, this sunny, spring day in the Delta isn't a typical backdrop. In the distance, tractors move slowly through dry fields of row crops.

"Once he got lost, they were wandering all over," says Alison Whipple of the San Francisco Estuary Institute, a non-profit research group based in Richmond. Her colleague, Robin Grossinger, agrees. "They were all over this place." The two are trying to piece together the path of William Wright, a man who got hopelessly lost somewhere nearby.

I should probably mention: it happened 160 years ago. Whipple and Grossinger are historical ecologists. They use sources like old photos, hand-drawn maps and early land surveys to sleuth out what this landscape looked like before it was dramatically remade by Californians.

The Delta's landscape has been dramatically remade over the last 200 years. Today, it's a crucial part of the state's water system, supplying 25 million people and irrigating millions of acres of farm land. But with this re-engineering, the Delta's ecosystem has collapsed, harming the fishing industry and putting water supplies at risk. Little is known about what it once looked like.

Lost in a Delta Marsh

Standing on a levee about 20 miles south of Sacramento, Whipple and Grossinger are discussing what they found a tattered, yellowing notebook uncovered in a state archive. It contains stories from William Wright, a duck hunter who spent a long, cold night lost in the Delta in 1850.

"On all sides stretched a vast wilderness of tules from ten to fifteen feet in height. The driving storm of sleet was bad, but the pitchy darkness was infinitely worse… Our situation was so miserable that no words can do justice to it."

It's not just the dramatic story they're interested in. It's passages this like one:

"The lakes proved to be from one hundred to three hundred yards in width, as near as we could judge. The water was very cold and often waist‐deep."

When Whipple and Grossinger read his account, they knew they’d found a Holy Grail source document. Its detail reveal a landscape that doesn't exist here today and hasn’t existed for some time.

"The Delta is probably one of the most intensively transformed parts of California and it was also changed really early on because of such fertile land," says Grossinger.

As California's Gold Rush boomed, farmers came to the Delta for its rich soil. Land went for a dollar an acre and settlers turned the wetlands into dry, agricultural land. 97% of the historic marshes were lost.

“We have here maybe one of the most important parts of the state's ecosystem and we don’t actually know how it used to work," Says Grossinger.

Alison Whipple and Robin Grossinger examine historic maps in the Delta.

He and Whipple have layered together thousands of historical sources that reveal an ecosystem of incredible complexity. “We would be in trees right here with a couple winding channels that were dry in the summer but had flowing water in the wintertime," explains Whipple.

Yearly floods from the Sacramento River inundated Delta marshes creating habitat for birds and young salmon. Closer to San Francisco Bay, hundreds of miles of small tidal channels branched out like capillaries in the wetlands. Today, most of those channels have been filled in.

Returning the Delta to this pristine state just isn’t possible, says Whipple, and that’s not the goal of the project. But knowing how the ecosystem once worked could improve the habitat restoration efforts that are happening.

Restoring Habitat

Liberty Island is one place in the Delta that looks as it might have 200 years ago. Not long ago, it was a low-lying expanse of farmland, protected by tall levees.

“The levees broke and it wasn’t financially worth reclaiming,” Says Carl Wilcox of with California’s Department of Fish and Game. The landowners gave up when the island flooded 15 years ago. After that, nature took over. Tules and cattails started sprouting and wildlife followed.

Returning vegetation at Liberty Island in the Delta.

Now, “some of the endangered native fishes, Delta smelt, longfin smelt are using this area,” says Wilcox. They're finding endangered Chinook salmon as well. "These are more productive areas for them, they’re more protected, they’re less prone to predators."

California Considers Ambitious Restoration Plans

California is using the Liberty Island project as a model for a proposal to restore 65,000 acres of Delta habitat. It's part of the Bay Delta Conservation Plan – a major overhaul of the Delta’s water infrastructure.

Leo Winternitz of the Nature Conservancy says bringing back habitat for declining wildlife could make the state’s water supply more reliable. Restrictions under the Endangered Species Act have limited how much water can be pumped from the Delta in recent years.

There is one big problem with restoration: most of the islands in the Delta are below sea level.

"Just south of here, some of the islands, they're in the 17 to 25 below sea level range. So if their levees broke, what you’d have is a large open body of water. You can’t create tidal marshes in those areas," says Winternitz.

That leaves only a few places where restoration is feasible. Winternitz says in those areas it’s crucial the state look to the past to create the same interconnected habitat that once was.

Governor Jerry Brown's administration is set to unveil the sweeping plan to restore the Delta later this year.

A canal in the Delta, heading to the Central Valley Project.

If you're not familiar with where the Sacramento-San Joaquin Delta is or why it's so important to the state, you're not alone. Polls show most Californians have never heard of it.

This relatively small part of California plays a crucial role in the state's water supply. And, as might be expected, it's become ground zero for a decades-long water war involving cities, farmers and fish. This year, the state is taking on an ambitious planning effort to break that deadlock.

Re-plumbing California

The reason the Delta has this starring role is thanks to a basic geography problem. Almost all of the state's water is found in the top third of the state. Most of the population lives in the bottom two-thirds of the state.

This issue was painfully obvious to state planners a century ago. The Central Valley promised rich soil for farmers, but had little rainfall. They knew for California to grow, they had to move water to drier parts of the state.

The Delta is where California's two largest rivers come together, carrying runoff from the Sierra Nevada Mountains. To water planners, it looked like the perfect place to tap into. California began building water infrastructure at a massive scale.

Water is exported out of the Delta primarily through two large pumping plants near Tracy, about 60 miles east of San Francisco. Each moves millions of gallons of water a minute. From there, the water rushes into concrete canals that reach Los Angeles, Silicon Valley and millions of acres of farmland.

This 700-mile system has made California the state it is today. But it's come with a cost…

An Ecosystem in Decline

On a boat in the western Delta, environmental scientist Julio Adib-Samii and team from California's Department of Fish and Game pull in a long fishing net.

A Delta smelt.

"Well, we have an adult Delta smelt," he says, holding a small, silver endangered fish that smells distinctly like a cucumber.

Fish and Game scientists have done these monthly fish surveys for decades. But starting in 2002, they noticed something strange. Where they once caught a lot of Delta smelt, now, they weren't catching any. The population had crashed, as well as populations of striped bass, threadfin shad, longfin smelt and Chinook salmon. In 2008, the commercial salmon fishery shut down completely for two years.

"Their decline is an indication of a changing environment and place they didn't evolve to be in," says Adib-Samii.

The Delta was once a massive tidal marsh, full of winding channels that spread out like capillaries. After the Gold Rush, settlers put up levees to create low-lying islands for farming. Ninety-seven percent of the historic wetlands were lost.

Multiple Stressors, One Big Question

"We've converted almost every scrap of habitat in the Delta to farmland and we need to return some of that to habitat," says Barry Nelson, senior policy analyst with the Natural Resources Defense Council. The ecosystem has also been hit by pollution, invasive species – and by the pumping plants.

"The pumps in the south Delta are so powerful that they literally reverse the direction of flow. It's very easy for those fish to follow that water and get sucked right into the pumps," says Nelson. A few years ago, federal wildlife agencies issued decisions requiring the pumping to slow down during certain times of year to protect fish.

This brings us to the central debate in the Delta: how much water should be pumped out and how much should be left for fish?

"There's a limit to the amount of water you can pump from the Delta ecosystem and in the last decade it's become incredibly clear that we've exceeded that, and we've exceeded it by a lot," says Nelson.

Not everyone agrees. "There is, you know, always going to be shortages. But there's also a lot of years when we have absolutely plenty of water in the system to meet the reasonable needs that are out there," says Jason Peltier with Westlands Water District, an agricultural area in the San Joaquin Valley that depends on Delta water. He says limits on pumping have hurt the district's farmers.

"You can't get a loan to farm unless you can show the banker what water you have. And they don't have a lot of confidence in going to their bankers," says Peltier.

The battle over the environmental rules went to the courts. "There was lawsuit after lawsuit," says John Laird, California's Secretary for Natural Resources. "It got to the point that it made much more sense to look at the entire Delta as a whole."

A New Attempt at Progress

Laird's agency is trying to reach a compromise with the Bay Delta Conservation Plan. The 10,000-page plan calls for a new way to pump water out of the Delta, through what's commonly known as the peripheral canal. Huge tunnels would take water from further upstream, bypassing the Delta, which supporters say would make the water supply more reliable.

This isn't a new idea. In 1982, California voters defeated a similar plan. "The real debate is not the tunnel itself. It's how much water and when can it flow through the tunnel," says Laird.

The massive project could harm the Delta's endangered species, but Laird says they'll restore thousands of acres of wetlands to compensate. California voters would be on the hook for that cost, while the $12 billion tunnel would be paid for by water users.

It's a tough sell but, according to Laird, a necessary one since climate change will make the state's water supply more unpredictable. The agency will release a full draft of the plan in July.

The 20-foot shake table at the Pacific Earthquake Engineering Research Center in Richmond. Photo by Andrew Alden.

Earthquake engineering is a discipline that uses a wide range of techniques: There's forensics, for diagnosing collapsed structures. There's 3D dynamic computer simulations, to test building designs in silico. And there's the mechanical joy of giving things a good hard shake. The last part, clearly, is the sugar that draws the news flies. It certainly brings out the little boy in me.

There are all kinds of ways to subject things to seismic-style shaking. At a scientific meeting not long ago I watched a contest that took student-designed model buildings and put them on a shake table the size of a large microwave oven. A shake table is outfitted with actuators—pistons pushing in all directions—that "play" a seismogram, the record of an actual earthquake. The students and judges were serious, but somehow gleeful too, as the models began to shed pieces onto the floor.

Photo by Andrew Alden

At the same meeting we could ride in a much larger apparatus as it played the 1989 Loma Prieta earthquake for us. As a veteran of that quake, I found this an uncanny experience but still couldn't keep a smile off my face.

Photo by Andrew Alden

The Pacific Earthquake Engineering Research Center, in Richmond, is a leading institute for this stuff. (If you can get a tour, don't miss PEER's 4 Million Pound Universal Testing Machine, a steel behemoth built in 1932, and the boneyard of broken stuff out back.) It has the biggest shake table in the Bay Area, 20 feet square. That's big enough to subject a full-sized cottage or model house to a realistic earthquake experience.

The University of Buffalo used two of these at once to test a full-sized two-story townhouse in 2006 at its Structural Engineering and Earthquake Simulation Lab. (Both PEER and SEESL share resources as part of the nationwide George Brown Network for Earthquake Engineering Simulation or NEES.) In that experiment, the building danced to the tune of the 1994 Northridge earthquake. . . a break dance, you might say. Videos from the project are uncanny, period.

But when something is too big to put on a shake table—like the Earth itself—we have to use a different approach. There's the equivalent of a submarine's sonar or the doctor's tap on your chest (a technique called auscultation, you should know) called active-source seismology. This has a long history and is best developed by oil companies and geotechnical consultants. The actuator that sends out the seismic signal can be as small as a sledgehammer blow or as large as blowing up a ton of dynamite, but I think that a fleet of Vibroseis trucks, pushing their thick steel baseplates against the ground in unison, may be the most impressive.

Courtesy Wikimedia Commons under CC-BY-SA license

This week a California research project went to the Sacramento Delta, a water source for some 23 million people among other things, and did some shaking experiments to help get a handle on what a Big One might do there. The news people made a point of getting out to Sherman Island, because what could be cooler? There was a big shiny machine with whirling weights, used to shake nuclear plants, mounted on a segment of simulated levee on top of pure Delta peat. It was easy to visualize mayhem.

The test was not a realistic one: the actuator didn't play a seismogram, just a straight eyeball-rattling vibration. The model levee wasn't twice as tall, a hundred years old, or holding back 20 feet of water like the real levees. The point was to do a basic test of the underlying peat soil—something simple, fundamental and not too dangerous. It was just the start of the thorough science we need, but the experiment made great video. Three newspapers gave it coverage and included footage; links below. In its own way it was as cool as Burning Man.

• San Jose Mercury News, "Earthquake simulator gives model levee a big shake"
• Sacramento Bee, "UCLA researchers shake model levee, for peat's sake"
• Stockton Record, "Ground rumbles for sake of research"

Four-year-old white sturgeons farmed by Sterling Caviar in Sacramento County. Photo: Jenny Oh

Sturgeons, the fish whose eggs are known as caviar, have been around for about 250 million years. These giants are the largest of the freshwater fish and have been known to grow to over 4,000 pounds and live more than 100 years. But it took us only a couple hundred years to deplete their stocks around the world, to the point where most caviar is now harvested from farmed sturgeon.

Caviar is generally associated with the Caspian Sea, the large land-locked body of water surrounded by Russia, Kazakhstan, Iran, Azerbaijan and Turkmenistan. Sturgeon are such big animals and the females produce so many eggs (in the wild, eggs can make up as much as 25 percent of their bodyweight) that historically they were a great source of protein. The caviar was for royalty, with the lightest-colored, blond caviar being reserved for the tsar, in Russia, and the shah, in Iran. But this year, virtually no wild-harvested caviar came out of that region.

Less known is the fact that in the late 1800s, the United States was a purveyor of wild-harvested caviar to the world.

“Here in California, they were harvesting millions of pounds in the late 1800s. And actually there was a town in New Jersey called Caviar, which was the world-leading exporter of caviar,” said Peter Struffeneger, general manager of Sterling Caviar, one of the two companies in California that farm sturgeon for caviar. “But within a span of 30 years they wiped it out. They closed down all fishing from about 1905 to the 1950s, 1960s, depending on which river, for the stocks to recover. And most of them have only gotten back to a point where there’s a limited sport fish for it.”

Two species of sturgeon are native to California: the white sturgeon and the green sturgeon. The green sturgeon is a threatened species and can’t even be fished by sport fishermen. Anglers in California can only catch three white sturgeon per year and need a special card from the state’s Department of Fish and Game to do so. White sturgeons have been plentiful in the Bay Area in 2011, according to this report. But sturgeon poaching remains a problem.

We filmed the caviar harvest at Sterling Caviar’s processing plant in Sacramento County. Sterling Caviar is one of only two companies in California, and a handful around the country, that are raising sturgeon for caviar and meat. (Sterling Caviar ships most of the meat overseas, though some ends up in Brooklyn, where it’s prized by the Russian community).

If you’ve ever wondered why caviar is so expensive (an ounce of Sterling’s highest-grade caviar goes for close to $90 on its Web site), one reason is that even in the best of circumstances, you can only harvest a small amount of it, said Struffeneger. It takes eight to 10 years for Sterling’s female sturgeons to produce eggs. The other reason for the high price, said Struffeneger, is caviar’s unique flavor.

“Maybe a hint of the ocean to it, but not an overbearing saltiness,” he said. “It should hit your taste buds and it actually explodes and you get this ‘wow’ sensation.”

Working with Serge Doroshov, a University of California, Davis, scientist who pioneered sturgeon farming in California, Sterling Caviar has figured out ways to farm sustainably. When the company started out, in the early 1980s, it got permits from the Department of Fish and Game to take white sturgeon from the Sacramento River. But in 1994 the company figured out how to spawn its own females, and since then it hasn’t taken any fish from the wild. And Sterling’s sturgeons are fed fish meal made from sustainably fished sardines and menhaden from Peru and Chile, he added.

For Struffeneger, who has degrees in marine and fisheries biology, the United States isn't doing enough to encourage aquaculture. As a result, he said, the country imports 82 percent of the fish we eat.

Fish farming is the only way forward, he said.

“You can’t increase the supply out of the oceans without doing what happened to sturgeon, destroying the resource,” he said. “One hundred years from now we’ll look back at this as a very transitional period in which we’ve really changed from a hunting-and-gathering society for our seafood to a farming-and-ranching society for our seafood.”

Click here for a larger version of the Nile Delta.

The Sacramento-San Joaquin Delta has this classic, triangular shape but with a major caveat — it’s inverted. That is, instead of the delta splitting into numerous channels in a downstream direction, it is characterized by numerous channels coming together in a downstream direction. The geologic history of the greater Bay Area helps explain this rather unique delta geometry. Unlike the Nile, Amazon, Mississippi, and other major river systems, the location where the Sacramento-San Joaquin rivers meet sea level is: (1) well inland of the coast and (2) strongly controlled by the topography of the region.

The Sacramento-San Joaquin Delta is known as a bay-head delta, which is when a delta forms at the head of a large estuary like the San Francisco Bay. When sea level was much lower during the last ice age the river met the sea at the position of the Farallon Islands. As sea level rose and the valleys that are now the Bay flooded, the river mouth moved inland to its current position. The complex topography of the Bay Area — a result of active faulting associated with the San Andreas, Hayward, and other faults — has forced the channels in the delta to come together at Carquinez Strait.

Future sea-level rise will affect the delta region, especially Suisun and Grizzly Bays, significantly. Even a relatively small rise will change the character of these wetland areas. Further east, near Antioch and Lodi, the delta is actively subsiding (sinking), which could exacerbate the negative effects of a rising sea level even more.

Images: (1) Nile River Delta; credit: Wikipedia, (2) Basemap from FlashEarth, annotation by me.

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Suspended Sediment Concentration in the San Francisco Bay, USGS. Click here for a larger version of the image.

Much of the gold extracted from the Sierra foothills during the Gold Rush was in placer deposits. That is, it was mixed with the rest of the sediment naturally eroding from the mountainside. Flecks of gold have a greater density than almost all the other particles and, thus, can be concentrated through natural water movement. A similar process is seen when you go to the beach. When the mixture of minerals and waves are just right you might notice darker grains of sand creating streaks or patches in the wet sand.

Miners had to devise ways to extract the gold because it was still a minor component even in rich placer deposits. Methods like panning and simple equipment like sluice boxes were used with moving water to enhance the natural mineral separation process.

When all this relatively easy-to-get gold was extracted from the streams and rivers prospectors turned to hydraulic mining to obtain the riches. Hydraulic mining was the process of using high-powered water canons to artificially erode gold-bearing hills made of sedimentary deposits. These sedimentary deposits were ancient stream beds that contained gold in placer deposits much like the modern streams did. Essentially, hydraulic mining eroded ancient river sediment from the hillside and diverted the material into the modern river where miners then extracted the gold.

Unsurprisingly, the activity of hydraulic mining devastated the local environment. The landscape was scarred and the mountain streams choked with gravel and sediment. And the effects weren't just local. These rivers and streams flowed into the San Joaquin River and Sacramento River and deposited some of this sediment in the Central Valley causing flooding and navigation problems. Some of the finer sediment was transported even further, to the San Francisco Bay.

The effects of hydraulic mining practices are still measurable in the Bay today. Geologists from the USGS are studying the amount of sediment the Sacramento-San Joaquin Delta delivers to the Bay and are finding that the Gold Rush-induced sediment levels might be diminishing:

"[USGS geologist David Schoellhamer] says all the extra sediment has finally worked its way past the Golden Gate. The bay's water is about 30 percent clearer than it was 10 years ago."

It is taken many decades for this complex sediment delivery system to reach a new equilibrium. However, the readjustment of the estuary to these 'new' conditions might create new problems:

"Less sediment in the bay could spell trouble if scientists' predictions about rising sea levels come to pass. These delicate tidal marshes could be inundated over the next century."

What I find fascinating, yet also extremely challenging, is how the choices we've made as a civilization over the decades and centuries combine and sum to create the issues we face right now. There are no simple answers. Regardless of how well-intentioned some environmental programs may be there will always be some uncertainty about how natural systems respond. Continuing scientific research of these systems will reduce that uncertainty and inform policy decisions of the future.

Images: (1) California Water Science Center; (2) Wikipedia

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Geologic map of central part of California (credit: California Geological Survey)

This brief post is meant to introduce some of the basic and fundamental geologic context for the river. The geologic map above, which shows a simplified distribution of the types and ages of rock at the surface, nicely illustrates the juxtaposition of the river with California’s geology. The full version of the map and an explanation of the colors can be found on the Educational Resources Center page of the California Geological Survey website.

The San Joaquin River traverses two geologic provinces in California that could not be more different — the high mountains and exposed granitic rock of the southern Sierra Nevada (the red and blue areas on the map above) and the topographically flat and sediment-filled Central Valley (the light yellow area in the map above). The headwaters for the San Joaquin River and it’s tributaries to the north are lined up along the 9,000-14,000 ft high spine of the Sierra cutting canyons and gorges from east to west across the mountains (including the Merced River in Yosemite Valley).

The result of the combination of high elevations, eroding granite, and rivers is a lot of sediment. Over hundreds of thousands to millions of years, the erosion and transport of sediment from the high country is balanced by deposition of that sediment in the adjacent low and flat Central Valley. In fact, the Central Valley is flat because of these processes. When the rivers naturally flood they overspill their banks and fine, muddy sediment is deposited across broad areas. Over geologic time, the rivers move around incrementally building up sediment and covering the entire valley. The result of these processes is a vast and soil-rich valley that is now one of the world’s most productive agricultural regions.

The Coast Ranges on the western side of the Central Valley essentially force the San Joaquin and its tributaries to take a right-angle turn to the north towards the next available outlet to the sea — the San Francisco Bay. A somewhat similar pattern occurs in the north for the Sacramento River. The two rivers meet at sea level to form the Sacramento-San Joaquin Delta, one of the world’s largest inland deltas. Some of the water and sediment carried by the San Joaquin River ultimately makes it way into the Pacific Ocean through the San Francisco Bay.

In the coming months my blogging here at QUEST will explore more of the geologic background and history of the greater Bay Area. I will also be writing about some of the local “geo-attractions” where you can go see the rocks for yourself and learn more about the fascinating geologic stories of this region firsthand.

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Every year, millions of fish make a strange and harrowing detour through the Skinner Fish Facility, part of the State Water Project's facilities in the Delta.

In my last post, I wrote about my visit to the Banks Pumping Plant, whose giant pumps slurp water from the Delta to help quench California's thirst. As the volumes of water are sucked up, both resident and migrating fish come along for the ride. The Skinner Facility, in operation since 1968, was built to protect fish from being killed at the pumps–an effort that sadly is not as successful as one would hope (more on that below).

I was amazed to learn there is a whole art and science to fish screens, which range from physical barriers–called positive barriers–like perforated plates or wire mesh, to behavioral barriers like sound, light, or other stimuli aimed at keeping fish away. Well-designed screens minimize both entrainment (fish being pulled into the pump or diversion) and impingement (fish being trapped or injured against the screen itself due to water velocity).

Both physical and behavioral barriers are used at the Skinner Facility. Fish being pulled toward the pumps first encounter a trash rack that diverts many bigger fish, along with floating debris. Next, fish encounter a large, v-shaped array of metal louvers. The louvers create turbulence that functions as a behavioral signal, encouraging the fish to swim away into bypass pipes that function, as our tour guide put it, like "a big vacuum system."

From the bypass pipes fish travel to another set of louvers and pipes, concentrating them into a smaller volume of water, and then into holding tanks in a nearby warehouse. Giant, suspended cone-shaped buckets are used to periodically sample the fish, which are identified, counted, and measured. Some 90 species turn up in the facility, including Chinook salmon, steelhead, white sturgeon, and delta smelt. (I asked our guide if delta smelt really do smell like cucumbers. He confirmed it. In fact, when a school of smelt comes through–an event that has become rare–the warehouse smells "like a salad.") When enough fish have been collected, they are loaded into trucks and driven back to the Delta.

Here's the rub. Many fish caught in the pull of the pumps are lost to predation before even reaching the screening facility. Then, the facility does not effectively screen fish smaller than about 1.5 inches, meaning that littler, less powerful species and juveniles are still vulnerable to the pumps. For the fish that make it to the holding tanks, the process is such a trauma–with big and little fish squashed together in the tanks, buckets, and trucks–it's no surprise there are casualties; in fact, the delicate delta smelt often do not survive. And even for fish that make it through the entire process and out the other end, there's a final, fatal hurdle: the trunks routinely dump salvaged fish at the same locations, where more predators have learned to cluster for a free lunch.

Scientists agree that the loss of fish at the huge state pumps–and other pumps and intake pipes throughout the Delta–is a major contributor to plummeting populations. How much water we use makes a difference: The higher the export rates, the more fish are entrained. There also is broad consensus that more state-of-the-art fish screening facilities are needed. That could come with a hefty price tag. But with our fish disappearing, can we afford not to invest in their survival?

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