JFRCalifornia
Keeper of San Juan Secrets
There are high expectations for the coming El Niño winter, but we all know enough not to get too excited until we see the results on the ground. Until then, the persistent narrative on the other side of the coin is that Lake Powell is doomed. So how can we make sense of all this?
We don't know the future. But we do know what USBR published as its "maximum probable inflow" scenario in August. In that report, it suggests the best that Lake Powell might do is to peak at 3601 next July. Is that even remotely possible? Or just a pipe dream?
The way I unravel that question is to look at the data from the past. Specifically, I want to look at the natural flow of the river, and then peel off all the different ways that water is used in order to figure out what might remain in Lake Powell. Since 2000, the natural flow of the river has averaged about 12.1 maf. That's the worst quarter century since accurate records were first kept over 120 years ago, so that doesn't give us much baseline optimism. And yet, here we are, facing one of the most intense El Niño events on record. But as others have pointed out, El Niño doesn't necessary translate to big snowpack and runoff for the river, although sometimes it does, most famously in 1983, when the river's natural flow was about 23.7 maf. Other big El Niño years were a mixed bag. In 1998, the natural flow was 17 maf, not bad, not gigantic, but well above average. But 2016 was a dud at just 13.4 maf. The other four strongest El Niño years since the 1950s produced one winner (1973, at 19 maf) and three big losers (1966, 1988 and 1992). If I were in Vegas, I'm not betting on El Niño.
There were several other large runoff years (1984, 1997, 2011) that were not El Niño events, and in the case of 1984 and 2011, a La Niña, the opposite of El Niño. That's interesting.
So it's best just to look at the long record, no matter whether there was an El Niño or not. What we find is that since 1906, the greatest natural flow of the river happened in 1984, at 24.2 maf. A handful of other years have topped 20 maf, most recently in 2011. But really, those big events are rare. Since 1987 (40 years ago!), it's only happened twice (1997 and 2011). Based on that, it's fair to say it would be a long shot if it happened again this year.
But let's say that it does. Let's assume the natural flow for 2027 ends up at 20 maf. What would that mean for Lake Powell? Let's do the math. Start by peeling off the 4.5 maf the upper basin will use this year, unencumbered by any cutback requirements from the feds. Then let's assume about 1.5 maf in evaporation and seepage from Lake Powell and the river and reservoirs above that point. Also assume the USBR holds back maybe 2 maf in the upper reservoirs. And since it would be a big runoff year, let's assume USBR releases 7.0 maf from Lake Powell (not 6 maf as currently planned). Add it up, and you get a net increase of about 5 maf to Lake Powell. Maybe 6 maf, if they allow more to flow through from the upper reservoirs than I assumed.
So with a net increase of 5-6 maf in Lake Powell, where do you end up? Today (Oct 2), there's about 5.1 maf in live storage at a lake level of 3518. Now if you add 5-6 maf, you end up with 10.1-11.1 maf in live storage by the end of Water Year 2027. In terms of surface elevation, that's a range of 3601-3612. And that happens to be right in line with USBR's best case scenario.
Is that possible? It seems so. Is it likely? The last 40 years of flow data tells us not really. And the fact thst this is an El Niño year doesn't really make a difference.
What all this also says is that anybody hoping to fill Lake Powell this year after a gigantic winter is just dreaming. At best, we end up with a reservoir that's still only in the neighborhood of half full. On the bright side, the lake would rise 80-90 feet, and the surface area of the lake would nearly double, from 86 square miles today to somewhere close to 140-150 sq miles. And yes, the Cut would be open.
Possible. But not likely. We'll know better once we get closer to spring...
We don't know the future. But we do know what USBR published as its "maximum probable inflow" scenario in August. In that report, it suggests the best that Lake Powell might do is to peak at 3601 next July. Is that even remotely possible? Or just a pipe dream?
The way I unravel that question is to look at the data from the past. Specifically, I want to look at the natural flow of the river, and then peel off all the different ways that water is used in order to figure out what might remain in Lake Powell. Since 2000, the natural flow of the river has averaged about 12.1 maf. That's the worst quarter century since accurate records were first kept over 120 years ago, so that doesn't give us much baseline optimism. And yet, here we are, facing one of the most intense El Niño events on record. But as others have pointed out, El Niño doesn't necessary translate to big snowpack and runoff for the river, although sometimes it does, most famously in 1983, when the river's natural flow was about 23.7 maf. Other big El Niño years were a mixed bag. In 1998, the natural flow was 17 maf, not bad, not gigantic, but well above average. But 2016 was a dud at just 13.4 maf. The other four strongest El Niño years since the 1950s produced one winner (1973, at 19 maf) and three big losers (1966, 1988 and 1992). If I were in Vegas, I'm not betting on El Niño.
There were several other large runoff years (1984, 1997, 2011) that were not El Niño events, and in the case of 1984 and 2011, a La Niña, the opposite of El Niño. That's interesting.
So it's best just to look at the long record, no matter whether there was an El Niño or not. What we find is that since 1906, the greatest natural flow of the river happened in 1984, at 24.2 maf. A handful of other years have topped 20 maf, most recently in 2011. But really, those big events are rare. Since 1987 (40 years ago!), it's only happened twice (1997 and 2011). Based on that, it's fair to say it would be a long shot if it happened again this year.
But let's say that it does. Let's assume the natural flow for 2027 ends up at 20 maf. What would that mean for Lake Powell? Let's do the math. Start by peeling off the 4.5 maf the upper basin will use this year, unencumbered by any cutback requirements from the feds. Then let's assume about 1.5 maf in evaporation and seepage from Lake Powell and the river and reservoirs above that point. Also assume the USBR holds back maybe 2 maf in the upper reservoirs. And since it would be a big runoff year, let's assume USBR releases 7.0 maf from Lake Powell (not 6 maf as currently planned). Add it up, and you get a net increase of about 5 maf to Lake Powell. Maybe 6 maf, if they allow more to flow through from the upper reservoirs than I assumed.
So with a net increase of 5-6 maf in Lake Powell, where do you end up? Today (Oct 2), there's about 5.1 maf in live storage at a lake level of 3518. Now if you add 5-6 maf, you end up with 10.1-11.1 maf in live storage by the end of Water Year 2027. In terms of surface elevation, that's a range of 3601-3612. And that happens to be right in line with USBR's best case scenario.
Is that possible? It seems so. Is it likely? The last 40 years of flow data tells us not really. And the fact thst this is an El Niño year doesn't really make a difference.
What all this also says is that anybody hoping to fill Lake Powell this year after a gigantic winter is just dreaming. At best, we end up with a reservoir that's still only in the neighborhood of half full. On the bright side, the lake would rise 80-90 feet, and the surface area of the lake would nearly double, from 86 square miles today to somewhere close to 140-150 sq miles. And yes, the Cut would be open.
Possible. But not likely. We'll know better once we get closer to spring...
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