Monthly Archives: January 2009


I got a question from a reader who wants to know what makes a good culvert.  She has some land, and an impaired stream crossing, and a mother with a bulldozer, who is not afraid to use it.  She has been offered a new culvert for Christmas.  I love this.

I don’t know anything about this stream or crossing, and am surely not offering engineering advice here.
A project like this could well require permits, from the Army Corps or from the state Fish and Wildlife department.

But, I can tell you in general what you want from a culvert. What you want from a culvert is that it doesn’t get in the stream’s way. From the upstream side, the culvert should be able to pass a flood’s worth of water. If is too small, or choked with debris, water will back up behind it. You’ll get a big pool behind it, if flood pressure doesn’t wash out the obstruction.

On the downstream side, the worry is whether fish can swim upstream. A too-small culvert is bad news for that. Water constrained through it will act like a fire hose; during wet periods, it can be a velocity barrier, too fast for fish to swim through. There are lots of studies and specs on fish flows. If you want to get precise, you can find out exact velocities for different species at different life stages. If you don’t want to be precise, you can look at nearby reaches with fish. They have small pools upstream of rocks, and eddies near the edges where fish can rest between bursts of swimming against the current. Stillwater refugia. You want that.

Fortunately, the solution to both these problems is the same: big wide culverts, with floors that look like the natural stream. (Here.) As a rough recipe, put in a big section of pipe as wide as the stream, buried about a third deep. “As wide as the stream” is wider than just the water, incidentally. You should look for bankfull width, where the sides start to slope down.

There is another potential problem, one that I hope is not plaguing the reader. It is possible that the streambed below the culvert has been eroding, and the culvert is now the most hardened point along the stream. (The nick point.) The perched culvert is the only thing stopping that waterfall from marching upstream. This is a big problem for fish (because it is hard to leap into a firehose and take off swimming against the flow), and a big problem for fixing the stream. Basically what you have to do then is elevate the downstream section of the stream with a series of weirs. That’s more project than I hope the reader faces.

So, this site is great, with lots of pictures. Another guide, with pictures of failures. Basically, make your culvert really big, as transparent to the stream as you can. 

Good luck!  Send pictures!


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Then, the satellite will call me and tell me to turn off my sprinklers!

Friends, after a day of seminars by several researchers, I feel pretty comfortable telling you that we do not know what effects climate change will have on evapotranspiration. ET is the part of water that goes through the plant (transpiration) or evaporates off the plant surface or dirt. It is a huge part of the water balance, so if you are hoping to know how much water will be in rivers or in groundwater in a few decades, you’d sure like to be able to put a good number for ET into your model. The verdict was that several things will matter:

The growing season will be warmer, and therefore shorter, so crops might use less water from start to finish.
When CO2 is readily available, plants do not need to open their stomata so much to take it in, so less water escapes. Transpiration goes down.
But it will be hotter, so plants will need more water.
If the growing season is short enough, growers might add a second or third crop into rotation, raising the amount of water needed for that acreage.

Basically we don’t know, and we definitely don’t know well enough to settle on a number to put in the big water models.


I have to say, after seeing presentation after presentation, my doubts about the usefulness of large scale models have returned. I do understand that you have to make assumptions to be able to do calculations, or that you dump all your unexplained phenomena into a closure term. But seeing them presented in model after model (because of course the researchers were ethical enough to present them) made me remember that they aren’t remotely close to real life. Then researchers agreed that they have to refine those terms. A part of me just thinks they should skip the model part and present their gut opinions. I think those might be just as good.


Finally, I got to hear a presentation about super high tech laser ET measurements. This guy! I saw these stories about fancy-dancy laser measurement of ET in the news a couple weeks ago. I didn’t pay it much mind. Hmmm, I thought. “It looks like another tool, like soil moisture probes. That could be useful, I suppose.” Then I moved on to contemplating lunch. But that was before I saw pictures, with neato telescope-looking gadgets that shoot lasers a couple kilometers to a receiver and then figure out the water content in the air by refraction or optics or physics or science or something. They can do a good job getting moisture in the air for the transect, but it is expensive to get your fancy-dancy lasers out to the field. BUT GET THIS!

They’re working on calibrating the transects from the lasers to satellite thermal imaging. The satellites come over every couple weeks and take pictures at 30m resolution, but the fancy-dancy lasers can refine that. If those can be calibrated, the Landsat images can cover a lot of ground and the fancy-dancy lasers can improve the resolution and then we’ll know everything about ET everywhere! It’ll be great!

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Happy contemplation.

I’m reading my January copy of the Natural Hazards Observer; if you aren’t subscribed to the Natural Hazards Observer, I don’t know why not. In a summary of the International Disaster and Risk conference 2008, the author wrote:

An anticipated outcome of the conference was to be “100 Ideas for Action” generated by the panels or from the experience of the assembled participants. The organizers did seek innovative ideas, but in this ambitious goal the meeting was not entirely successful. As acknowledged at the final session, many of the resulting videoed comments and even more of the solicited “new ideas” were conventional statements of positive intent.

Oh hell yes. This is all we get, all the time. Fucking platitudes. You feel like a grinch resenting statements of positive intent, but when you talk to bureaucrats you hear generic crap about working together and educating the public every single time. And they need more funding. Or, because it is our duty and our desire, we want to bring the public into our decision making. But in some ways, laypeople are the worst. They have just enough information to tell you the basics of your field. I swear, if you ask the broad public what to do in water, I guarantee you will hear one of two themes. If it is agriculture, you get the echoes of Cadillac Desert. If it is urban, you will hear that we should switch to pervious concrete. I’m not quite sure why pervious concrete has captured people’s attention so, but you can count on that recommendation. I love me some concrete, but that is not a new idea.

I’m not sure where to go for new thought. My friend suggests more demanding facilitation at meetings. I have to confess that I want to put a list of the platitudes that we always hear up on the wall, and if someone offers one, we point to it and cut him or her off. We know. Bigger pies, power of collaboration, efficiency, the children are our future. We know. But I am afraid that bureaucrats are so cowed they are afraid to say more than the platitudes that satisfied people last time. I read the comments to newspaper stories hoping that some crackpot will present such a skewed view that it will trigger something new. It is a pretty punishing search. I’ve said before that I’ve enjoyed the transcriptions of public comments for other processes. They aren’t dense, but there is some signal in that noise. I think my best sources for thought right now are the trade journals: Western Farm Press, the Journal of Light Construction, the Natural Hazard Observer or university presentations.*

My favorite recent thought came out of watching testimony to the Blue Ribbon Delta panel. That day, a county supervisor or city councilperson or someone stood up to say that it wasn’t the Delta that was broken, it was the rest of the state. Now that was an interesting prospect. The Delta in its current configuration, sinking peat islands behind shaky levees, is the priority. The remainder of California should act as a vassal state to support the farming lifestyles of a few thousand people farming in an untenable physical circumstance. The purpose of Silicon Valley and Hollywood is to accumulate money to hold back the rising seas in the Delta. I had never seen it like that before, but I got a lot of mileage out of that concept that day. It was way better than hearing another round of conventional statements of positive intent.

*I know you will die of jealousy –I am spending all day tomorrow at seminars on climate change and evapotranspiration. If I can, I will live-blog it for you. Now that is some riveting reading.


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Everyone laughed at my merry wit, but I was only sixty percent kidding.

I was chatting with some people from my agency about how to talk to the press about this drought. (This is not a problem for me, mind you. The press does not contact me.) Reporters keep wanting to know whether we can attribute this drought to climate change. There are a bunch of answers to that, mostly variations on “we don’t know.” One answer is, ‘we’ll know in retrospect’; reporters apparently don’t want to wait a couple decades to know what to call this drought. The problem with attributing this drought to climate change is that Californian hydrology has always had a ton of variance. This is the third worst two-year drought since we’ve been keeping records, but we are still within historical variance. (Shoot. For that matter, historical variance goes way outside the bounds we’re used to. Here’s a write-up of a neat tree ring study that shows paleodroughts that lasted for centuries.) In one sense that is kinda handy. At a talk I went to last summer, the guy from PG&E said that because they had to build their hydropower generation facilities to handle such a wide range of flows, they don’t expect to have to replace their hydropower facilities for about a decade. Even though they’re seeing more high flows, and believe they’ll see floods more often as spring snow turns to spring rains, they’ll still be within the range of flows they designed for. But it does mean that we can’t say for certain that this unusual drought event is from climate change.

The conversation turned to what to say about the concept of “the new normal”. The Planning and Conservation League is promoting the concept that this drought will be “the new normal” under climate change, and what should we say about that? That’s a little rough too. The climate will change steadily for at least a century; we don’t know where it will stabilize. For as long as we can realistically foresee, normal will be continuous change. So when reporters ask if this drought will be the new normal at the end of that? I suggested “Dear god. We hope so.”, but I didn’t see that in the papers this morning. This is why my work doesn’t let me out in public.

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Most people know better.

Dr. Moser’s talk yesterday was remarkable, for her direct, realistic and authoritative claims about how to change people’s behavior on climate change. If you are interested in that stuff, her powerpoint presentation is clear and gives links to the research behind her talk.

At the end of her talk, someone in the audience raised the issue of population pressures. I’ve now seen this happen a few times. A scientist presents his or her research to the convention and at the end, someone in the audience brings up the elephant in the room. Everyone gets quiet and intent, because it is obviously crucial and no one official can bring it up. I’ve seen a panel sit silent until one guy took the mike and openly laughed at the prospect of answering that question. When there is an answer, it is usually about brown people in a different country and the solution is to educate the ladies. This is nice because obviously we should be on that path anyway and it will coincidentally solve population problems somewhere else. The other not-very-responsive answer is to mention overconsumption and say that we should have kids but ride our bikes too!

Dr. Moser yesterday acknowledged that the topic is taboo, and discussed the experience of solving policy problems without mentioning taboo topics. She talked about being on the climate change adaptation team, where no one ever mentions development. She talked about the fact that everyone automatically takes a growth economy as the baseline, without acknowledging that we are nearing the physical limits of our landscape and ecology. (We should be transitioning to a steady state economy, living off annual yields.) She did not mention meat and diet, another huge taboo. She did not offer a behavioral prescription for addressing California’s population. But she said to be brave and raise the topic. So here goes.

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Not a demographer, or a demographer’s son, but I can crunch your numbers ’til the demographer comes.

California has 39 million people in it. Our arbitrary planning horizon is 2050. In 2050, California is projected to have 60 million people in it. Growth in California is primarily from births (deaths and immigration are roughly even, pg 3). Obviously we value high individual autonomy in decisions as personal as procreation. But here’s something you might not know. A little under half the births in California are from unintended pregnancies (“women got pregnant sooner than they wanted, had not wanted to get pregnant then or in the future, or weren’t sure what they wanted”). Those are live births, not pregnancies.

Most people who do work on this stuff talk about the effects of unintended children on the parents. Here, I am going to speak to the resource costs of that population increase. I’d like to give you some equivalencies.

California has, roughly, 550,000 live births a year.

Of those, roughly, 46% were unintended. You know where this is going.

Every year, this state adds 253,000 kids whose parents did not want them then.

253,000 people is more than the City of Modesto, added every single year. If they follow usual urban water use patterns (which maybe they wouldn’t as young children, but the delay is likely only 15 years or so), that many people would use 63,000 acrefeet of water a year. That is the size of most medium-sized dams in the state (although not the yield of every dam in the state, because dams have a dead pool).  Every single year. For kids whose parents didn’t want to have them at that point.

If you project out to 2050*, the size gets staggering. By 2050, the difference from not having any unwanted children would be about 9 million people. In 2050, I am sure that water managers would be very grateful if they only have to supply water to 50 million people instead of 60 million people. The difference is the population of the Bay Area plus the San Fernando Valley. It is twenty city of Fresnos. Now you are talking water volumes roughly on the order of Oroville Dam, or California’s share of the Colorado River, or what you could get if agriculture shrinks by a third. Addressing population directly is non-trivial.

When you are talking about climate change and emissions, the story is even starker. Every person consumes water and every person causes greenhouse gas emissions, but greenhouse gas emissions have a cumulative effect that matter over time. Greenhouse gases emitted now hurt us more than greenhouse gases emitted in five years. In the year 2050, delayed emissions means less sea level rise, slightly cooler nights, slightly larger snowpacks. Averted people would reduce emissions, but even postponed people would help.

This stuff gets brought up awkwardly at meetings, then we all retreat. But controlling population has profound implications for California’s resource use and climate. We should face it head on.







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Of course, one needs readers before comments are a problem.

The problem with talking about intentional population control is that everyone points and calls you Hitler. Worse, people use it as a vehicle for their nativist sentiments and say the problem is the unwashed brown hordes swarming the border. For the record, both are bullshit. (If you are inspired to leave some racist comment about immigration, please return to the Public Policy Institute of California report, first paragraph.  Birth rate, not immigration, accounts for population growth in California.)

My hope is to avoid some of that by pointing out the scale of the problem of unintended births. As a first cut, simply getting people’s reproduction in line with their own desires would halve our projected population increase. That should not require state coercion. A state policy and real resources* dedicated to that would be beneficial all around.

You could go even farther, and without saying that anyone shouldn’t have children, create policies that delay desired children. Remember, a year or two of delayed emissions are valuable to us. Flattening the growth curve matters at any discrete point in the future. I was more optimistic about his option until I saw the PPIC report and this CDC report saying that mean maternal age at first birth is already pretty high. But you could target programs at communities in which women have children young. You could use the solution everyone offers for less-developed-countries, and educate the ladies. Forgiving student loans for Latina women who haven’t given birth by age 25 might bring their age at first birth up to the general population’s.

My point is that there are non-coercive options and a role for the state (like making birth control free and ubiquitous). The choice isn’t between doing nothing and firing up the sterilization chambers based on eugenics. There are also large environmental costs from maintaining the taboo on openly discussing population. We should be braver. We should bring it up and keep bringing it up.




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