New Sea Level Rise Study Calls Delta Tunnels Into Doubt | KCET
New Sea Level Rise Study Calls Delta Tunnels Into Doubt
California homeowners will know the feeling. You shell out a huge amount of money for a place, and then suddenly you find yourself "underwater" -- owing more than the property's worth.
But it isn't just that metaphorical fiscal water Jerry Brown's California Water Fix project may find itself under. The at-least-$17-billion public works project, intended to divert Sacramento River water around the Delta to the giant pumps that send that water south to farms and cities, may well find its proposed tunnel intakes under three or four feet of seawater by the end of the century.
That's according to a study published in late March in the journal Nature. The study suggested that the West Antarctic ice sheet, which is melting faster than anticipated, will likely cause a meter of sea level rise by the end of the 21st Century. When you add that to other factors causing sea levels to rise, that means California's Bay and Delta may well see sea levels two meters higher in 2100 than they are now -- about six and a half feet of average sea level increase. And that may well push saltwater well past the planned intakes for the California Water Fix's tunnels.
At issue is a recent study by climate scientists Robert DeConto at the University of Massachusetts Amherst and David Pollard at Pennsylvania State University, published in the journal Nature in late March. The study, which examined the little-understood effect of melting surface ice on thinning continental ice sheets, suggested that Antarctic ice sheets could add enough water to Earth's oceans to raise sea levels as much as a meter by 2100, with that rise in sea levels accelerating sharply thereafter.
That boost in sea level is in addition to all the other things causing our planetary ocean to rise: the increase in melting of the Greenland ice sheet, melting of mountain glaciers, and thermal expansion of ocean water chief among them. With the increase in Antartica's estimated contribution to sea level rise, the world's oceans could well be 1.5-2 meters higher in 2100 than they are now, with that rise increasing at a faster pace in subsequent decades.
DeConto and Pollard suggest that by 2500, Antarctica's melting ice might well raise sea levels by 15 meters, or just under 50 feet. Add that to the seven meters of so a melted Greenland would likely contribute by then, and we're looking at sea levels 22 meters higher — 72 or more feet — in the year 2500 than they are today.
That more distant forecast would mean a very different California. A giant inland sea would cover the Central Valley from Yuba City to Merced. Most low-lying cities in the Bay Area would be destroyed, as would much of Long Beach and Orange County, and the Sea of Cortez would extend beyond Interstate 10 near Indio. Millions of people now live in parts of California that would be inundated in sea water if sea levels rise 70 feet by 2500, and the waters would cover important transportation corridors as well.
But we don't need to wait 484 years for this newly projected sea level rise to have a devastating impact on California. That impact may become significant in just a few short decades. And an almost certain casualty of that rise is a project that ironically has pointed to sea level rise as one of the reasons for its existence.
Rising seas threaten the state's existing system for getting fresh water from north to south. As it works now, huge pumps in the south Delta essentially suck water from the Sacramento River through a network of channels and sloughs in the interior of the Delta. When the water reaches the pumps, it's siphoned into aqueducts for the Central Valley Project and the State Water Project, which send the water to farms and cities to the south.
The relevant problem here is that most of those sloughs and channels flow past levees that protect large islands whose surfaces are below sea level. Rising seas threaten to overtop those levees. When they do, or when either earthquakes or simple entropy causes the levees to fail even without rising seas, the resulting floods of those low-lying islands will pull brackish water into the Delta from San Francisco Bay, and that brackish water will likely contaminate the fresh water heading for the pumps.
The much-lauded and much-criticized project currently called California Water Fix by its partisans in government and the Bay Delta Conservation Plan by wonks with a historical memory, but generally called the Peripheral Tunnels by everyone else, is ostensibly intended to solve this problem. Three large intakes along the Sacramento River between Courtland and Clarksburg would shunt Sacramento River water into twin 30-mile tunnels, each of them 40 feet wide, that would be buried 150 feet below the surface of the Delta. The project, which the state estimates would cost $15 billion (though critics charge its cost over the next several decades could be four times that), will be capable of delivering almost five million acre-feet of the Sacramento's water to the pumps each year.
Critics have blasted the project as a way to ensure that water exports from the Delta will continue regardless of the actual amount of water in the Sacramento, to the detriment of species like the Delta smelt and the Sacramento River winter-run Chinook salmon. And this week, the group Public Employees for Environmental Responsibility charged that the state has spent millions of dollars in federal funds on the project that was supposed to go to improving habitat for the Bay Delta's beleaguered wild fish. A federal probe into those allegations is gearing up.
But the new Nature study on sea level rise due to surface melt from the Antarctic ice sheets calls the whole point of the project into question. If sea level can be expected to rise by as much as two meters by the end of this century, with rise speeding up in the decades to follow, the project as described in its official documents would seem to be teetering on the edge of obsolescence before the first shovel of earth is dug.
The reason? Barring heroic measures, the area where the project's water intakes are to be built will likely be underwater not too long after 2100, and perhaps well before. The communities of Courtland and Clarksburg each sit on levees on the Sacramento River's east bank, built by the river's natural flow and augmented by human effort, that hold the flow of the Sacramento River a few meters above the surrounding countryside. At Courtland, the Sacramento's surface is around 20 feet above sea level. A thousand feet east in the outskirts of Courtland, the land sits just six or seven feet above sea level, and it drops off to sea level and below in the middle of Randall Island. At Clarksburg, eight miles upstream, the river is a few feet higher, but the surrounding land also dips below sea level.
If we can truly expect sea level to rise two meters by 2100 and keep going, there's a very good chance that California Water Fix's expensive intakes will be surrounded by salt water well before the end of the century.
Here's a screen shot of the northern Delta courtesy the sea level rise mapping engine at firetree.net. The blue overlay shows areas susceptible to flooding assuming a rise in sea level of just one meter:
I've highlighted the stretch of the Sacramento River between Clarksburg and Courtland with a bit of red. As you can see, the potentially inundated lands in the Delta push up against the east edge of that stretch of river pretty hard -- and that's where the three intakes for the Peripheral Tunnels would go.
Here's the same area with two meters of sea level rise:
At two meters of sea level rise, the inundated area has grown to encompass the whole stretch of river where the intakes would be located, aside from one high spot about midway between Clarksburg and Courtland, approximately where the second of those three intakes would go.
Putting the intake in that high spot might not help matters much. For one thing, the intakes' location was chosen based on the assumption that they'd be adjacent to a freshwater river flowing past dry land and seasonal freshwater marshes. But at a meter of sea level rise, salt water would be pushing well into the northern Delta. How far north would that saltwater reach? That depends in part on how much water's flowing out of the new mouth of the Sacramento River, which at one meter of sea level rise would be right around the Yolo Bypass and Interstate 80. In wet years the river might well push the so-called "mixing zone" well to the south of the intakes' proposed location. In dry years, tidal pressure may well push salt water up around the intakes.
As long as the levee containing the river holds up, that's not necessarily an insoluble problem. But increasing inundation will make those levees more prone to failure. Rivers work ceaselessly to take the easiest possible route to the sea, and if the sea is lapping up against the far side of a 50-yard earthen berm, it won't be long before the river decides not to flow past it for 30 or 40 miles.
If sea level rise were to stop there, a highly engineered and intensively maintained solution to keeping those intakes salt-free might be possible. But no one expects sea level rise to stop there. With seas as much as 22 meters higher by 2500, that's an average annual sea level rise of .05 meters — a meter every 20 years, or about two inches per year. It thus might not be too long after 2100 that sea levels have risen three meters above their current levels, which would completely surround the proposed intakes with water of questionable quality:
You may be wondering whether California Water Fix's planners had anticipated the possibility of sea level rise in their analysis of the project. The answer: yes, but only to a limited degree. While this month's Nature paper definitely underscores the increasing likelihood that seas may rise more than we expected, and sooner, DeConto and Pollard aren't the first to suggest the oceans may be more than a meter higher by 2100. In the 2013 Draft Environmental Impact Report /Environmental Impact Statement for California Water Fix, the authors state:
That said, the underlying assumption in that 2013 Draft EIR/EIS seems to be that sea levels will rise about three feet by 2100 — less than a meter.
As we see in the maps above even a meter of sea level rise puts the intakes in jeopardy, unless the project includes a significant investment in earthworks to keep the Sacramento River flowing unsullied by salinity up to and past those intakes. There was some discussion in development of the Draft EIR/EIS of moving the intakes farther north to get them out of the way of the next century or two of sea level rise. But there's a problem: Get a little ways north of Clarksburg and you run into the outskirts of Sacramento, and construction of intakes and tunnels in that congested, high-real-estate-value city would send costs through the roof.
There's a limit to how much time we could buy by moving the intakes north, of course. If we get that 22 meters of sea level rise by 2500, those intakes would have to be up in Glenn County to stay high and dry.
None of this should be seen as a slam dunk dismissal of the California Water Fix tunnels. The maps we use above are necessarily speculative, and inundation of the area surrounding the intakes doesn't necessarily mean those intakes are doomed to suck saltwater. There's the above-mentioned possibility that levees could channel the Sacramento River to the intakes. They would have to be pretty bulletproof as levees go: a failure would mean cutting off water to the southern half of the state.
There's the possibility — though likely a slim one in a warming world with smaller river flows — that the Sacramento's fresh water would hold the intruding salt water at bay well downstream of the intakes, at least for a while.
And there's the possibility that we as a species will suddenly get our act together and halt our emissions of greenhouse gases, to limit sea level rise to the amount we've already locked in, however much that may turn out to be. Though whether that's any more likely than building a series of unbreakable river levees is a matter for conjecture.
And truth be told? If we want to build more secure levees in the Delta, there are a whole lot of existing ones that could use our attention.
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