An old post on new dams

So, like, there’s a drought in California.  And, like, there are big bathtub rings around our northern reservoirs.  So, do we need more dams?  There are a couple being studied now.  What are these two new dams1?  Will they get built?  Do we hate them?  Who supports them and why?  Is more surface storage a necessary investment to support the next thirty million people here?

Everyone on the agriculture side of water use is crying out for more surface storage.  The standard line is that the State Water Project was designed to be much larger, but never got finished, what with that terrible Wild and Scenic Rivers Act and the popular vote against the Peripheral Canal.  Then (usually) Republicans and agricultural water users say that we haven’t built any major water infrastructure for decades while the population of California has shot up and isn’t it self-evident that we need new reservoirs?  Besides, climate change!  Ten years ago, even five years ago, that kind of talk would have been dismissed immediately by everyone in the water field.  It was taken as an absolute that “the era of dam-building is over” and that there was no public support for new dams, largely because of Cadillac Desert.  The prospect of new dams is coming back, though, with some interesting twists2.

I see the vehement editorials calling for new dams and I grin.  Every single time, I wonder.  Suppose your new dams are built, buddy.  What will you put behind them?  Root beer?  The waters of the state are spoken for.  Ag and cities have claimed what is there, and they aren’t getting all they hope for.  In-stream water uses are both increasing and being hardened by the Endangered Species Act.  Most climate projections for California estimate it will be about 10% drier within decades.   The State Board has applications for the next 4.8 million acre-feet of water that miraculously appears.  The act of pouring concrete for a dam doesn’t call water into being.  What are these dams supposed to impound?

Strangely enough, because of climate change, there may be one chunk of water that those dams could usefully capture.  The climate change models predict that we will get less water overall, and they predict that more of the water we do get will fall as rain instead of snow.  This turns out to be really important.  In the era that is ending, the snowpack held water from winter until June and July, releasing it slowly as snowmelt.  Once you knew how big and wet the snowpack was, you knew how much water you had to make last until November and roughly when it would show up at your reservoir.   Rainstorms are going to be a different story.  Rain falls and runs off in the space of days, a big slug of water arriving at the reservoir at once.  Our reservoirs aren’t big enough to catch that water all at once.  Right now they empty all spring while new snowmelt arrives to top them off; that flow-through creates a lot of capacity.  The other problem is that when you get snowstorms, you can add up the snow and know how much water you’ll have to handle later.  When you get a rainstorm in March, you don’t know whether you’ll get another one in April.  You must empty your dam, so it can catch the next storm before it turns into a flood.  That water, the water that you have to empty out so your dam can hold and control later spring rains, is the water that new surface storage could catch.  Without the snowpack to hold it for us for months, we don’t have space to capture that.  It would run out to sea, and if we’re lucky it won’t take out a city on the way.

The alert reader already noticed that this is not new water.  This is the same water that used to be slow snowmelt, moving through the tops of our reservoirs each spring.  California is looking at building two new dams ($3-$4B each) to try to keep some of what we have now.  Makes one’s eyebrows raise, doesn’t it?  Climate change is expensive.  It also makes one wonder who is going to pay for that?  Agriculture tops the voices calling for new dams, but I don’t know if they realize that it won’t get them anything more than they have, if that.  On the other hand, if I were in a sector that everyone agreed would be the first to give up water, I’d probably call for new storage too.  They aren’t offering up money, in any case.

Well, say the dam-haters.  Maybe we still don’t want two new dams anyway.  Maybe we’ll conserve lots and stop growing rice and alfalfa in the desert!!! agriculture will contract considerably and we’ll just make do on two-thirds of the water we have now, even as the population grows to sixty million people in 2050.  Water markets will solve all this!

Maybe.  Considering the reflexive antipathy to dams sowed by Cadillac Desert, that may be how this works out.  But the other interesting perspective is that both of those dams will almost certainly be operated primarily to fulfill environmental demands.  Because salmon runs and the delta smelt are so precarious, the Endangered Species Act is driving water priorities.  Until salmon or smelt go extinct or recover, they dominate where water goes and when.  When water managers talk about Sites Reservoir (the one proposed for the Sacramento Valley), they don’t talk about new water for cities.  They talk about the location.  They get all dreamy-eyed about the flexibility it could provide to manage fish requirements in the Delta.  It takes three days from water to get from Shasta to the Delta, but it would only take one day from Sites.  Doesn’t sound like much, but it can mean cold water and better tuned salinity control in the Delta.  Anything that helps fish means that you can keep the big pumps to L.A. running, and water managers really want that.  No one says this explicitly, because it sounds too much like extortion, but most water behind Temperance Flats will likely go to the San Joaquin River restoration project.  Having that dam would give water managers another dial to turn as they try to keep cold water in that poor river until October.  Maybe those dams don’t happen and that water comes straight out of ag.  But maybe those dams don’t happen and environmental laws yield instead.

So, do we hate these dams?  Should enviros fight them forever?  Well, we don’t love them for the old-school reason.  They won’t produce new water.  The big cities in the south have realized this; they aren’t offering to pay or even lobbying for new dams.  Both dams would destroy a beautiful valley.  They’ll be expensive.  On the other hand, they’ll have downstream environmental benefits in ways that old dams never provided.  We have more of a need to catch floods, because that’s what we’re going to get in the new hydrology.  They may give us a way to keep more of the ag we have now, if that is the goal.

Honestly, I can’t decide whether I’m personally opposed to these new dams.  I know for sure that the arguments don’t line up in the old ways, cities and ag clamoring for more against the enviros.  With climate change unsettling everything we’ve optimized, we’re likely to be grateful for anything that increases operational flexibility.  I’m more intrigued by the idea that there are actually way more valuable water infrastructure projects that you would never predict!!! Since you were sweet enough to read all the way to the end, I promise I’ll tell you what they are someday.

1The new dams being proposed are named Sites Reservoir and Temperance Flats.  Both are off-stream, which means that instead of dams placed across a river and turning the river into a lake, they put a dam in the neck of a valley near a river and sometimes divert water to turn it into a lake.  Sites Reservoir is on the west side of the Sacramento Valley a couple hours north of Sacramento; it would be connected to the Sacramento River .  Temperance Flats is in the Sierras, a little bit south of Yosemite; the waters that would fill it would otherwise drain to the San Joaquin River.

2 It cracked me up that the money for funding the dam studies was listed under the “Conjunctive Use” portion of the water bond.  This, my friends, is not Straight Talk we can believe in.  The term conjunctive use usually means planned switching between your surface water and your groundwater.  So if you have a big water year, you would try to fill your groundwater aquifers, in anticipation of pulling gw out in a dry year.  That’s all conjunctive use means, and everyone approves of conjunctive use, because who doesn’t want to bank supplies and use the best supply for the occasion.  So stashing the prospect of new dams under Conjunctive Use, while not a lie, because conjunctive use does involve switching between stored water sources, is definitely a stretching a innocuous term past all previous uses.

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