Lake Hits Bottom on May 2 at 3599.26. Where to now?

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JFRCalifornia

Keeper of San Juan Secrets
Well, the lake appears to finally have bottomed out on May 2 at 3599.26. That level is pretty much in line with what the USBR expected, but it sure took a long time to get there. May 2 is a very late date to bottom out. The lake usually hits bottom sometime in March or April, with the average being somewhere around April 1. Last year was April 10. When the lake keeps dropping into May, that’s usually not a good sign. Here are the years since 1990 where the lake hit bottom on or after May 1:

1990 – May 25 – 3648. Peaked at 3651 on June 19.
1991 – May 13 – 3627. Peaked at 3639 on June 30.
2000 – May 6 – 3676. Peaked at 3683 on July 2.
2002 – May 26 – 3644. Peaked a little over 3644 on May 31. Terrible year.
2003 – May 1 – 3605. Peaked at 3617 on June 23.
2013 – May 8 – 3596. Peaked at 3601 on June 18.
2015 – May 7 – 3590. Peaked at 3614 on July 14.
2018 – May 2 – 3609. Peaked at 3612 on June 10.

In terms of spring net volume increase in those years, here you go:

1990 – 0.30 MAF
1991 – 1.33 MAF
2000 – 1.14 MAF
2002 – 0.02 MAF
2003 – 1.17 MAF
2013 – 0.48 MAF
2015 – 2.37 MAF
2018 – 0.31 MAF

As a point of reference, in 2019 the lake added 4.95 MAF during the spring runoff.

Collectively, those 8 years are among the worst on record for net volume increase in the spring. Here’s where they rank all-time:

1990 – 53 (out of 58)
1991 – 40
2000 – 43
2002 – 55
2003 – 42
2013 – 50
2015 – 32
2018 – 52

In contrast, the net spring volume increase in 2019 ranked 6th all-time.

To be optimistic, we had a good snowpack up until March, and this may still pay dividends in the coming month as it really heats up. But I wouldn’t expect a miracle after the dry April, and if we’re lucky, we’ll see something like 2015, when the lake rose modestly thorough the spring into mid-July, adding about 24 feet, and a roughly average net volume increase. That year we started seeing the lake inflow hit 30,000 cfs on May 22, about 2 weeks after hitting bottom, ratcheting up to 50,000 cfs on June 6. It hit peak inflow rate on June 14 at a little over 53,000 cfs, before slowing down. That was a pretty average year.

On most of those other years, the peak inflow rate ranged from 23-33K cfs, with some outliers on either end. It was especially bad in 2002, with a max of 11K cfs, while it briefly flirted with 40-50K cfs in 2000 and 2003.

So let’s watch the inflow metrics over the next couple of weeks, and we’ll get a better sense of how this will likely play out into the summer.
 
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I appreciate all the nice feedback on the analysis; it's the least I can do considering I'm no help with a fishing pole. :)

Incidentally, just to give you a sense of what the potential lake level rise might be if this spring turns out to be an average of the net volume increases experienced in those 8 similar years listed above, we'd end up with a net 0.89 MAF on top of what we already have. And that would equate to the lake topping out at about 3610. If instead we took the best of those years (2015), and added the volume increased experienced that year (2.37 MAF), we'd end up somewhere around 3622.

So it's reasonable to think that a cautiously optimistic view that splits the difference puts us at somewhere between 3615-3620...
 
Just checked the USBR website, and they updated their lake level projections on 4-30-20. Looks like now their best guess is 3614.87, although they acknowledge a high degree of uncertainty there, saying the range of possible outcomes could be anywhere from 3604 to 3636. Here's a link:


Here's the same thing in graph form:


My hunch is that USBR's best guess is about right, but if it's going to err on one side or another my gut says it's going to be a touch lower than that. But I'm still hoping for 3617.50, as Trix rightly points out...
 
USBR updated flow projections on May 12, downgrading their inflow estimate a bit. They now project an inflow of 4.65 MAF in April-July, which is about 65% of average during this period. Not too good. Given the projected outflow during that period, which would be about 2.65 MAF, you've got a net spring inflow projection of about 2.0 MAF. That would translate to something like a peak of 3615 or so, maybe a touch better if we're lucky, maybe a little worse. This shapes up as something like a year not quite as good as 2015, but better than the terrible years of of 2002, 2003, 2013 and 2018. But below average for sure... Here's the link: Glen Canyon Dam | Water Operations | UC Region | Bureau of Reclamation
 
Yeah after the February March that we had things aren't so great. This is a picture from just outside of Leadville CO this past weekend on Saturday. Yeah most of the snow down low was burned off but they're still quite a bit of high. I guess it'll depend on how quick and warm when he get.
 

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90 degrees and windy in mountains in May isn't helping....We need a wet pattern!

Here in the Upper Green River basin, we had a slightly above average snowpack at the end of April, and April was much cooler than average. I was backcountry skiing until the start of May. But a few warm and windy weeks dried everything out in a hurry. At least we have been getting some moisture to hold off the start of fire season. But runoff is going to be early (again) and slightly below average.....
 
i wish we could have sent some of the rains from here over there! we sure didn't need any more. it went from a dry spell of a few weeks without rain to about six inches of rain over the past four days (with most of the rain hitting on Monday) including blowing out one dam (for Wixom Lake) and threatening another (Sanford Lake Dam). i still haven't been able to verify if the 2nd dam is breached or not. when looking at vids yesterday the water level on either side of the dam was close to the same so it wouldn't have mattered much then, but after a few days of things draining off it will make a difference if they still have some kind of dam for the lake.

um, ok, sorry, wandering... i'd have been happy to send three inches of rain there...

i know that the mere size of Wixom Lake is tiny compared to LP "surface area of 1,980 acres (8.0 km2) and reaches a depth of 40 feet (12 m)". now it looks more like mud flats and the river flowing through it. Sanford Lake is also not that big but the current discharge rate is 60,000 cubic feet per second (measured just below the dam - not sure how accurate that is during flood event like this).
 
One of the key “yardsticks” I look at when trying to guess where the lake will end up is when the inflow rate hits 30,000 cfs, and for how long that lasts. In a really bad year, it never hits 30,000 cfs. That’s what happened in 2002, 2004, 2007, 2012, 2013, and 2018, each of which rank near the bottom in terms of net volume increase in historic terms.

In a great year (like last year), we break 30,000 cfs for an extended period—58 days in 2019—and also see a long time above 50,000 cfs too (30 days last year). I doubt we’ll reach 50,000 cfs this year, but it might still happen for a brief period. Hope so.

This year, we’ve been hovering in the 20-30,000 cfs range for most of May, but have not quite cracked that 30K barrier. That’s not quite cause for alarm yet, but if we don’t see at least a small spike by the first week of June or so, then it’s not looking good.

Right now, the range of most comparable years for what might happen seem to be 1988, 1992, 2001 and 2006. In each case, they all broke 30,000 cfs, but not for long—just 2 days in 1988, 3 in 1992, 18 in 2001, and 23 in 2006. The buildup leading to that point in each of those years looks similar to what we’ve seen so far this year, so a good indication of what might be ahead.

And what happened in those years? The net volume increase during the spring ranged from 1.11 MAF in 1988 to 2.12 MAF in 2006. Each of those years hit a peak lake level in mid-June to early July.

All that to say, my best guess of a mid-range puts us somewhere in the 1.50 MAF net spring rise until peak in late June. If that guess is right, that kind of volume increase would put us at a shade over 3610 at peak.

So watch the inflow over the next week or so, because that will probably tell the story of what to expect in the weeks ahead…
 
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