Spring Runoff Reality Check - May 7

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Rivered said:
Thanks to JFR for all your time, knowledge, very detailed stories & analysys... I do have a quick question though- what;s your best guess for Lake Mead's peak this year? Having recently moved near there it's interesting to hear some of the local naysayers talk about it dropping another 10-15ft this year. IMO they listen to the NPS too much... as far as running out of gas at Powell recently JFR, blame it on the rental boat!!! Best excuse yet! LOL
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You're welcome... I enjoy all this. As for your question about Lake Mead, I don't have any special insight beyond what's in the latest USBR 24-Month Study, but I will say that what happens in Mead is much more predictable than what happens in Powell. That's because USBR basically controls most of the variables about inflow and outflow for Lake Mead. (For Powell, inflow is largely dependent on snowpack upstream--a highly unpredictable variable.)

Inflow to Lake Mead is almost entirely a function of how much USBR releases from Glen Canyon Dam, with only a very small (and somewhat unpredictable) contribution from the watershed below the dam--notably the input from the Little Colorado and Virgin rivers, plus the many smaller side canyons, including the Paria River, Kanab Creek, and Havasu Creek among others. In all, the expected inflow from all those secondary sources from April through July is only about 0.2 maf--pretty small compared to what's coming through Glen Canyon Dam in that time, which is about 2.5 maf. Keep in mind that the flow through GCD is set relatively low this year--so what benefits Lake Powell hurts Lake Mead, at least as long as the water is stored in Powell.

Outflows are also entirely controlled by USBR, and need to be enough to both deliver Lower Basin water requirements and to generate sufficient power. For April through July, that total is currently set at a little over 3.6 maf.

So when you do the math with 2.7 maf going in, and 3.6 maf going out (plus about another 0.2 maf lost to evaporation), you're guaranteed that Lake Mead will drop during that time.

USBR predicted that Lake Mead would end May at 1067, and that's exactly what happened. They also predict Mead will drop to a little over 1060 by the end of September, and there's no reason to think otherwise, since USBR is at the control of the levers...
 
JFRCalifornia said:
You're welcome... I enjoy all this. As for your question about Lake Mead, I don't have any special insight beyond what's in the latest USBR 24-Month Study, but I will say that what happens in Mead is much more predictable than what happens in Powell. That's because USBR basically controls most of the variables about inflow and outflow for Lake Mead. (For Powell, inflow is largely dependent on snowpack upstream--a highly unpredictable variable.)

Inflow to Lake Mead is almost entirely a function of how much USBR releases from Glen Canyon Dam, with only a very small (and somewhat unpredictable) contribution from the watershed below the dam--notably the input from the Little Colorado and Virgin rivers, plus the many smaller side canyons, including the Paria River, Kanab Creek, and Havasu Creek among others. In all, the expected inflow from all those secondary sources from April through July is only about 0.2 maf--pretty small compared to what's coming through Glen Canyon Dam in that time, which is about 2.5 maf. Keep in mind that the flow through GCD is set relatively low this year--so what benefits Lake Powell hurts Lake Mead, at least as long as the water is stored in Powell.

Outflows are also entirely controlled by USBR, and need to be enough to both deliver Lower Basin water requirements and to generate sufficient power. For April through July, that total is currently set at a little over 3.6 maf.

So when you do the math with 2.7 maf going in, and 3.6 maf going out (plus about another 0.2 maf lost to evaporation), you're guaranteed that Lake Mead will drop during that time.

USBR predicted that Lake Mead would end May at 1067, and that's exactly what happened. They also predict Mead will drop to a little over 1060 by the end of September, and there's no reason to think otherwise, since USBR is at the control of the levers...
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It’s also interesting to know that Lake Powell and Lake Meade are both at 35% capacity right now
 
JFRCalifornia said:
I keep coming back to the CBRFC projection of how much water supply is left in the watershed from April through July. It’s the number that USBR bases its projections on in its monthly report (24-Month Study). USBR’s latest report was based on a May 1 CBRFC forecast of 5.1 maf of unregulated flow into Lake Powell during that period. After May 1, that number rose a bit after some unexpected late season snow. It’s now back down to near 5.1 maf and likely to stay there. The number is updated daily.

Based on that, I’d say that USBR’s latest guess that the lake will peak at just over 3583 is still likely accurate. I say that because the upper reservoirs are nearly full, so the water will mostly pass through them. I also say that because of the cool May, inflow to Powell has been unusually even and holding at just over 30,000 cfs. I think this means the runoff will tend to be steady into June, rising a little, but eventually getting to 3583 without a huge peak rise. It’s going to continue to go up because USBR has kept outflows remarkably low for the month of May, and June outflow is only expected to rise by about 5% over May levels.

You can talk about remaining snow at high elevations, or the lack of it depending on where you are, but that’s my best guess with the data we currently have.
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In the high water contest only one person picked less than 3583. No one is swimming this year!
 
Marina Bum said:
What a cruel tease mother nature is this year. 3580, Really? I'll take it but that's a painful number, not as painful as 3525 but cruel all the same.(so close to filling the cut) Oh well, backing the houseboat out at 5:00 am and into the maytag straights early it is. Not the end of the world, Powell is still worth it but I hope they're wrong about the high point
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Maytag straights , lmao, i love that and hate that at same time ahahahha
 
A quick update here, and generally good news... It's been a steady rise in the recent weeks, but as of June 7 the inflow has not yet cracked 40,000 cfs. That's about to change. This year's pattern is a little unusual, because if there's any kind of big runoff in the cards, you tend to see a higher inflow by early June than we've seen so far. But two indicators suggest we may be in for a faster rise in the next few days. The first is that the rivers above Lake Powell are finally running closer to average for this date, with a collective flow of over 46,000 cfs. That's got to hit Lake Powell soon, and when it does, look for a net increase of about about 70,000 af each day that this level of inflow is maintained, which translates to about 10-11 inches of rise per day. If inflow cracks 51,000 cfs (and outflow stays at about 10,000 cfs), then it would rise by just over a foot per day. There's still a chance of that.

The other positive indicator is that the CBRFC estimated unregulated water supply above Lake Powell is now higher than it was when USBR recently predicted the lake would peak at just over 3583. The total April-July estimated water supply above Powell was 5.1 maf on May 1, but as of June 7 with the unexpected shot of moisture in May, it is up to 5.25 maf.


You might be thinking that doesn't seem like much difference, but even that small change is enough to bump the expected peak of Lake Powell by about 2 feet, so now I'm guessing it peaks at just over 3585 (assuming outflows remain as planned). That's the difference between the Cut being barely open (if at all) for just a couple days to instead being open for maybe 2 weeks or even a bit better. That could be very important for those on the lake in early to mid-July...

Of course this is all still up in the air, but the signs are breaking in the right direction for the moment...
 
just got back from tuna trip in the outer banks and was pleasantly surprised when i went over the bridge in rifle the wing dam which i use as my guage is about 1 foot from being topped the eagle was flowing like crazy and i can see snow everywher still hopefully mother nature is hiding water in those hills
 
I've never been to Lake Powell, but I enjoy these discussions.

A little news from upstream. The GoPro Games in Vail cancelled some events (like Stand Up Paddle boarding ) because of dangerously high flows. So I looked at the flows where Gore Creek meets the Eagle River (just downstream fromm Vail).

On this date last year, the Gore was flowing around 900 cu ft/s. Today, it's running at 1700 cu ft/s!

Gore Creek at Mouth near Minturn
 
JFRCalifornia said:
A quick update here, and generally good news... It's been a steady rise in the recent weeks, but as of June 7 the inflow has not yet cracked 40,000 cfs. That's about to change. This year's pattern is a little unusual, because if there's any kind of big runoff in the cards, you tend to see a higher inflow by early June than we've seen so far. But two indicators suggest we may be in for a faster rise in the next few days. The first is that the rivers above Lake Powell are finally running closer to average for this date, with a collective flow of over 46,000 cfs. That's got to hit Lake Powell soon, and when it does, look for a net increase of about about 70,000 af each day that this level of inflow is maintained, which translates to about 10-11 inches of rise per day. If inflow cracks 51,000 cfs (and outflow stays at about 10,000 cfs), then it would rise by just over a foot per day. There's still a chance of that.

The other positive indicator is that the CBRFC estimated unregulated water supply above Lake Powell is now higher than it was when USBR recently predicted the lake would peak at just over 3583. The total April-July estimated water supply above Powell was 5.1 maf on May 1, but as of June 7 with the unexpected shot of moisture in May, it is up to 5.25 maf.


You might be thinking that doesn't seem like much difference, but even that small change is enough to bump the expected peak of Lake Powell by about 2 feet, so now I'm guessing it peaks at just over 3585 (assuming outflows remain as planned). That's the difference between the Cut being barely open (if at all) for just a couple days to instead being open for maybe 2 weeks or even a bit better. That could be very important for those on the lake in early to mid-July...

Of course this is all still up in the air, but the signs are breaking in the right direction for the moment...
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How does the filling of the reservoirs above Lake Powell enter the equation? The brief peak release from Flaming Gorge has ended and the results of that release has bumped up the inflow to Lake Powell. They, once again, are leaving most of the flow of the Green in Flaming Gorge and that reservoir has plenty of additional capacity to fill until the inflow subsides. The Navajo and Vallecito are taking virtually all of the San Juan flow which is basically finished. They are refilling Blue Mesa which is still very low. I expect they will try to fill that reservoir as much as possible given the reduced flow in the Gunnison.
Certain reservoirs like McPhee are still filling and have lots of room for more water. All the reservoirs on the Colorado are still filling although they don't take a large portion of the flow. Many reservoirs like Strawberry and Starvation on the Duchene are almost full and are still taking a large portion of the flow. There are some small reservoirs like Scofield and Joes Valley that are over 100% filled(how does that work?). The Big Sandy is at 130%!!
All told, I believe over a million acre feet of water that could have, this year, flowed into Lake Powell has been retained by upstream reservoirs and it doesn't look like they are going to reduce the percent of flow going to those reservoirs. Now, I'm not complaining about that since every drop of water held in the reservoirs above Lake Powell has the potential to end up in Lake Powell but I don't see how they will get the cut usable for more than a few days given that the snowpack is now down to about 7 % of what it was at the peak.
 
RobertGosselin said:
How does the filling of the reservoirs above Lake Powell enter the equation? The brief peak release from Flaming Gorge has ended and the results of that release has bumped up the inflow to Lake Powell. They, once again, are leaving most of the flow of the Green in Flaming Gorge and that reservoir has plenty of additional capacity to fill until the inflow subsides. The Navajo and Vallecito are taking virtually all of the San Juan flow which is basically finished. They are refilling Blue Mesa which is still very low. I expect they will try to fill that reservoir as much as possible given the reduced flow in the Gunnison.
Certain reservoirs like McPhee are still filling and have lots of room for more water. All the reservoirs on the Colorado are still filling although they don't take a large portion of the flow. Many reservoirs like Strawberry and Starvation on the Duchene are almost full and are still taking a large portion of the flow. There are some small reservoirs like Scofield and Joes Valley that are over 100% filled(how does that work?). The Big Sandy is at 130%!!
All told, I believe over a million acre feet of water that could have, this year, flowed into Lake Powell has been retained by upstream reservoirs and it doesn't look like they are going to reduce the percent of flow going to those reservoirs. Now, I'm not complaining about that since every drop of water held in the reservoirs above Lake Powell has the potential to end up in Lake Powell but I don't see how they will get the cut usable for more than a few days given that the snowpack is now down to about 7 % of what it was at the peak.
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Yes, what happens in the upper reservoirs enters into the equation. But the question isn't really "how much will USBR hold back in the upper reservoirs?" as it is "will USBR stick with its current plan?" Their estimates for Lake Powell already account for their release schedules from the upper reservoirs, which are already planned out for the rest of the water year and even beyond...

So it's worth seeing how closely USBR stuck with its release plans in May, in spite of the fact there was a little more precipitation than expected. I'll just focus on the three main reservoirs--Flaming Gorge, Blue Mesa and Navajo.

Here's the projected and actual outflows from those reservoirs in May:

Flaming Gorge

Projected - 132,000 af
Actual - 157,000 af

Blue Mesa

Projected - 237,000 af
Actual - 217,000 af

Navajo

Projected - 22,000 af
Actual - 23,000 af

Total (Flaming Gorge, Blue Mesa and Navajo)

Projected - 391,000 af
Actual - 397,000 af

What all that shows is that USBR stuck pretty closely to their plan. If anything, they released a little more to Lake Powell than what their original plan called for. They held back a little more than planned in Blue Mesa, released a little extra from FG, and Navajo was right on target. And you'll find if you go back to earlier in 2024, USBR was pretty much right on target with what they planned in those months.

So this all means that the upper basins do matter, but there's no real need to watch those too closely day to day, because USBR is following their plan for them--and it's on that plan that their projected likely peak lake level for Lake Powell is based. Now all that to say, it is still worth understanding what they have planned for June for those reservoirs. Here's their projected outflows for June:

Flaming Gorge - 90,000 af
Blue Mesa - 66,000 af
Navajo - 26,000 af

Total - 182,000 af

The main takeaway there is that they plan to release a lot less from both Flaming Gorge and Blue Mesa in June than they did in May. Navajo will be about the same as in May. In all, they plan to release about 200,000 af less to Lake Powell in June than they did in May. And yet for all that, USBR still predicts Powell will peak at just over 3583---they already took that lowered release plan into account. And now, with the CBRFC estimated upper basin water supply up by about 150,000 af, even with the suppressed upper basin reservoir release plans, Powell is likely to peak at just over 3585 now...

It's also fair to say that if they decided to let the June releases match the ones in May, and added 200,000 af more to Powell, the peak level of Powell might top out at about 3588. But that's not gonna happen...
 
Interesting to see what happens over the next couple of weeks. The lake was only 9ft from 3853 as of June 9th. Yesterday was the biggest rise of the season at over 8 inches. It went up 5.25 ft over the last 7 days. So if USBR prediction holds then the flow compared with the last couple of weeks will really have to slow.
 
IronWares said:
Interesting to see what happens over the next couple of weeks. The lake was only 9ft from 3853 as of June 9th. Yesterday was the biggest rise of the season at over 8 inches. It went up 5.25 ft over the last 7 days. So if USBR prediction holds then the flow compared with the last couple of weeks will really have to slow.
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I agree that it seems like with the current rate of lake rise, we should blow past 3583, since we’re less than 9 feet from that right now.

But I keep coming back to the CBRFC, the agency that tends to have the best grasp on remaining water supply upstream of Powell. And they are holding to the line that from April through July, there’s only 5.28 maf total available, which is only a bit over 80% of average. And if that number is right, it means the lake peaks at 3585 or so. You can see that the range of likely outcomes at this point is pretty small—5.16-5.52 maf.

Of course, it’s also possible that number is wrong, but I don’t see any direct evidence of that yet. I will say that if it ends up where 5.52 maf is the right water supply volume, Powell peaks at 3588.

All that to say, best guess is that the higher river flow doesn’t last for more than a few days, and slows dramatically after June 15-20… and we end up at 3585…

I hope I’m wrong, but I tend to believe the data…

Screen Shot 2024-06-10 at 2.15.00 PM.pngScreen Shot 2024-06-10 at 2.14.44 PM.png
 
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