Good Sign - Water Level Equalizing

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JFRCalifornia said:
Just to add more food for thought to the discussion...

Intuitively it seems that more storage is in the top of any lake (like in a martini glass), but I wanted to see how pronounced that was for Lake Powell, because that affects the rate of lake rise. It's interesting. The base elevation of the river below the dam is 3132, so here's the stats for 50-foot intervals (except the first two intervals, since there is no data below 3410):

Elevation Incremental Vol/Total Vol % Capacity Within Interval/Total % of Capacity

3132-3410 1.0 MAF / 1.0 MAF 4.1% / 4.1%
3410-3450 1.3 MAF / 2.3 MAF 5.3% / 9.4%
3450-3500 2.4 MAF / 4.7 MAF 9.9% / 19.3%
3500-3550 3.1 MAF / 7.8 MAF 12.7% / 32.1%
3550-3600 4.0 MAF / 11.8 MAF 16.4% / 48.5%
3600-3650 5.4 MAF / 17.2 MAF 22.2% / 70.7%
3650-3700 7.1 MAF / 24.3 MAF 29.3% / 100.0%

I also did the same exercise in 25-foot intervals, but this illustrates the point just as well. A few things jump out at you right away:

  1. Half of the lake's volume is in the top 100 feet, and the other half is in the lower 458 feet;
  2. The lowest 288 feet of the lake (roughly half the height of the dam) only holds 4% of the lake volume, so the top half of the lake holds 96%;
  3. It takes just as much volume to fill the range 3650-3700 as it does 3500-3600--i.e., it's relatively hard to fill the top 50 feet of the lake.
Many other observations are possible, but indeed the profile of the lake is shaped something like a martini glass...

So how does this relate to actual observed data? Well, let's start with the five years with the biggest elevation rises in the spring (it's never hit 60--someone asked that):

1973 - 58 feet
1979 - 58 feet
1993 - 56 feet
2005 - 53 feet
2011 - 51 feet

How do those correlate to increase in volume during the spring runoff?

1973 - 6.31 MAF
1979 - 7.48 MAF
1993 - 6.67 MAF
2005 - 4.61 MAF
2011 - 5.91 MAF

Notice that even though 1973 and 1979 had the same rise, it took more volume to do it in 1979, because the lake was nearly full. In fact, 1979 was the greatest rise by volume in the lake's history...(one wonders what 1983 would have been like if the releases hadn't been so huge)...

Also notice that even though 2005 and 2011 had a similar rise, it took way less volume to do the slightly larger elevation gain in 2005 because the lake was so much lower that year.

And so what were the five greatest spring runoff rises by volume in the lake's history?

1979 - 7.48 MAF
1995 - 6.78 MAF
1993 - 6.67 MAF
1973 - 6.31 MAY
2011 - 5.91 MAF

Notice 1995 is the second largest increase ever, but the lake only rose 49 feet that spring, because it started at 3645...

Other notable years include:

1997, which had a volume increase of 4.64 MAF but a rise of only 32 feet, because it started at 3663...
2008, which had a volume increase of 4.61 MAF but a rise of 46 feet, because it started at 3588...
1984, which had a volume increase of 4.46 MAF but a rise of only 29 feet, because it started at 3673...
2017, which had a volume increase of 4.33 MAF but a rise of 42 feet, because it started at 3594...

It's notable that the only other years (besides those discussed above) that had a spring volume increase that exceeded 4.0 MAF were 1980 and 1983. None of the years during the time the lake was filling, except 1973, 1979 and 1980 had such a big increase by volume. This tells a larger story: it's often observed that it took 17 years to fill the lake, from 1963-80, which implies that it was a steady rise to fit such a huge volume. But that's not true. By 1970, it was already at 3600, higher than today, and roughly half full. So it took 7 years to fill the first half, but 10 to fill the second half. One reason it took longer in the second half was because of poor years in 1972, 1976, and 1977...which were saved by high years in 1973, 1979 and 1980...

There's also a perception that Powell has been in steady decline since about 2000. Again, untrue. There were five consecutive terrible years from 2000-04, two of which were truly horrific. 2002 and 2004 were the only years in the lake's history that saw next to no spring bump; in the case of 2002, the "bump" for the whole year lasted for only 5 days in late May, with a rise of less than a foot! Starting in summer 2001 and ending in spring 2003, the lake dropped 68 feet and lost over 7 MAF... (!!) A similarly awful overall drop happened in 2004, which also had a negligible spring bump of only 4 feet. The net result of all that was that what was essentially a full lake in July 1999 dropped to 3555 in April 2005 (down 145 feet), a loss of 16 MAF, or about 68% of its volume.

The good news is the since then, the lake has had its ups and downs, but has generally maintained. Three more horrific years (2012, 2013, and 2018) were balanced by several well-above average ones (2005, 2008, 2009, 2011 and 2017...and now 2019), so the net effect of the last 15 years is positive. But it's very true that a short and sharp drought of even 5 years is hard to overcome. It's notable that in order to fill the lake in 1980, we needed two huge years in a row in 1979-80, and also needed to avoid a giant drought from 1963-80. There were bad years in that period, but nothing like we've seen since 2000. Here's the worst years in terms of spring volume increase since 1965. I've included all 10 examples where net spring runoff increase was less than 1.0 MAF:

2002 - 0.02 MAF
2012 - 0.23 MAF
1990 - 0.30 MAF
2018 - 0.31 MAF
2004 - 0.41 MAF
2013 - 0.48 MAF
1981 - 0.51 MAF
1977 - 0.58 MAF
1989 - 0.61 MAF
1966 - 0.84 MAF

Notably, 5 of the top 6 have happened in this century. This trend will likely continue based on consensus scientific climate predictions, so management will become increasingly difficult. But this is somewhat balanced by the fact that many of the years where increases have occurred in this century have been far above average... So the bottom line here is that the annual "norm" is becoming more extreme one way or the other...

But for this year, definitely hoping for the best. But it would be unprecedented if we had a lake level rise of 60 feet or more, since that's never happened before, nor has a volume increase been greater than 7.5 MAF (which was 1979). But if a 7.5 MAF rise DID happen this year, we'd be over 3650 as a summer peak... hmm... But to be cautious, that seems unlikely because of the need to release relatively large volumes for Lake Mead, which is really all part of the same management system...

But not too far-fetched to hope for 3610... and yes, 2014 is a good model for that...

And just noticed BOR's March report, which shows the same range of possibilities they reported in January and February, but now says it's more likely to be within the higher end of their predicted range... they predict it will top out at 3592 in July...
Click to expand...

Thank you for that precise scientific explanation and the hard research work that was put in. I would like to present you with the WW Lake level Mathematician Award for 2019. Congratulations!
 
TR. said:
Your number of 3609 is interesting as the current google earth view is for a water level of 3610. Could be helpful for planning this summer.

TR
Click to expand...
I think the current GoogleEarth image is from 4-6-15, when the water level was at 3591... might be different in different parts of the lake...
 
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JFRCalifornia said:
I think the current GoogleEarth image is from 4-6-15, when the water level was at 3591... might be different in different parts of the lake...
Click to expand...
Copy that, where I was looking had a different date. Good information, thanks.

TR
 
Don't want to get anyone's hopes up too early, but the lake inflow on March 14 was 15,057 cfs (after being mostly 6-12,000 cfs since March 1). The last time (actually the only time) there was an inflow of 15K cfs on 3-14 was the period 1983-87... a good sign, especially with all that snowpack potential ahead... and the first measurable gain in lake level this year (could we have hit bottom already? ... now it's at 3570.80...) In 2017, we hit bottom on March 11 at 3594... and peaked on July 11 at 3636, which was a 4.3 MAF net increase... if we got a 4.3 MAF net increase this spring, we'd end up at 3619... but not ready to make that prediction because...

...on the flip side, outflows have been consistently in the 13K cfs range in the past couple weeks, which is relatively high for this date (historically has been 9-12K cfs, but wide variation)... so this is consistent with the idea of keeping the releases up for Lake Mead...and this could suppress the increase for Powell this year...

FYI... the lake has only had a net spring increase of 4.3 MAF or better 10 times out of 55 years... so we'd have to end up in the top 20%... possible, but still too early to tell... the fact that we had a very bad year in 2018 means groundwater is diminished, so surface runoff this year will be suppressed a bit... on the other hand, we had a 4.6 MAF increase in 2005 after an awful 2000-04, and the snowpack in the upper Colorado (not sure about the Green) that year was not as good as this year...and March outflow was similar in 2005 to this year... hmm...

...a lot of things to consider... not sure exactly what goes into BOR's crystal ball, but looks like they are trending conservative in their guess...
 
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Well, the November 2018 flush saw 20-40K cfs released each day from Nov 5-8... otherwise about 8K cfs each day in November. That flush barely made a blip on the surface of Lake Mead... which is currently at 1089, which is about a foot higher than it was on March 14, 2018... hardly any change at all...

Also worth noting that actual lower basin water use in 2018 apparently isn't the problem:

AZ net use was 2.60 MAF (allowed 2.8 MAF)
CA net use was 4.24 MAF (allowed 4.4 MAF)
NV net use was 0.24 MAF (allowed 0.3 MAF)

Of course these figures include credit for return flow, but still, you get the idea...
 
Great Info and research !!! Lets keep hoping for more snow and or rain the Typical date of max snowpack is April 6 I believe so we need 3 more weeks of wet weather for a great snow pack and runoff to follow. I am still sticking to 3610 or better as a SWAG, Of course lots of variables with releases etc.
But that should be a real possibility. Let it snow let it snow in the high country Colorado drainages...
 
Don't forget that Lake Mead will receive some good input from the Little Colorado drainage this year. Currently at 148%.
 
Yeah, the Little Colorado. We used to live on the Little Colorado River back in the seventies; its bank was an easy stone's throw from our back porch just downstream from Springerville, Arizona, right across the blacktop from Becker Lake. The river was clean and pure up that high and gave us some very nice rainbow and brown trout whenever the mood took us. Also, a good number of greenhead mallards and damage control beaver pelts were dragged out of that river just behind our barn. I sure miss that place.

Anyway, someone on this website penned a great description a week or so back of the route the Little Colorado takes across Arizona on its way to the Colorado River and eventually into Lake Mead. I had to chuckle at my own ignorance. The river tumbled past our place and disappeared down a rugged malpais canyon towards the mudhole of Lyman Lake, and the next I remember of it, the Little Colorado was a dusty little bog of wet silt and goo running through Winslow. It never crossed my mind that any of that water would make its way all the way to the Colorado River. I always thought it petered out in the desert somewhere on the Rez northwest of Winslow. It is nice now to realize that the Little Colorado runoff may actually benefit Lake Powell in some fashion. Thanks Sealegs for that reminder.
 
Hard to believe that beaver actually roamed in this arid environment , I was shocked to see otters at Bartlett lake. Wish we had more of these critters in our water ways today.
 
Meatwagon said:
Hard to believe that beaver actually roamed in this arid environment , I was shocked to see otters at Bartlett lake. Wish we had more of these critters in our water ways today.
Click to expand...
Yes that does tell you the environment is good when you see the critters
 
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