how is lake powell water level decided??

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hidesert cowboy

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I know that 7.5 million acre feet must flow out of lake powell each year to meet some law passed in the 20's or 30's but lake powell has averaged releases of over 9 million acre feet a year. This hasn't been a huge deal for the most part but the problem is it looks like the bullfrog boat ramp is below useable depth. The castle rock cut is closed. Some I am left asking why can't lake powell simply say when the lake is full you get extra water, until that happens you get 7.5 million acre feet. Lake mead does the same. both lakes become more useable and don't suffer problems associated with low water levels. I don't get why this isn't standard practice especially after a year like last year. Why on earth are they letting out more water than they have to? Who is the person that decides how much water is let out so we can complain to them?
 
The official full story has been posted here, but I don't know how to find it and provide the link. For most of the 40 years I have been boating at LP, the annual release was 8.23 million acre feet. A new water compact was agreed upon by the 6 states and Mexico about 8 years ago that for now requires higher releases to balance LP and Mead. I think this year is pegged at 9.0. So, USBR releases water to comply with the compact.
 
why would the upper basin states agree to that? I do think some flexablity needs to be done when it can be, but lake mead is actually higher than at this time last year and the year before. it would seem holding more water in lake powell to aid recreation YET allow the lake to fill more could allow less PITA for recreation but also allow for extra releases later to mead to make up for it when the lake fills more in late may and june. lake mead being higher than its been at this time in 2017 and 2018 doesn't make sense to me.
 
Well, Mead is still really low and not far above levels required to supply water to LV and power generation. We need a couple more winters like this year to get both lakes back to fun levels. It could happen. I remember the 80's. Half a degree of global warming be darned.
 
I think power generation at Lake Mead is a big part of determination of their water level. Hopefully Waterbaby can respond to this thread and clear it up for all of us.
 
Somebody correct me if any of this is wrong, but here goes...

First off, the Colorado River watershed (including both Mead and Powell) is really managed as one unit by the USBR under very strict guidelines that derive from the Colorado River Compact as amended many times, and collectively known as the "Law of the River". In terms of Powell vs Mead, it's not really a case of "our" water vs "their" water, although it certainly plays out that way in the real world, since Mead is the primary storage unit in the lower basin, and Powell in the upper basin. The basic equation under the Compact is 7.5 MAF to the upper basin, 7.5 to the lower basin, and 1.5 MAF to Mexico. Providing the Mexican share is considered to be half the responsibility of the upper and half the lower basin. So in rough terms the upper basin needs to deliver on average 7.5 + 0.75 = 8.25 MAF annually but there is flexibility because this delivery schedule is based on a rolling 10-year period. That is, some years delivery can be higher or lower, but the rolling average needs to be at least that much.

Okay, based on the USBR guidelines, the upper basin has to deliver a minimum of 8.23 MAF and as much as 9.0 MAF each year, and the goal of that is to make sure (among other things) that each reservoir maintains a minimum storage for water and power delivery. But the critical component in this arrangement right now is Mead, not Powell. If you get below 1075 in Mead, then some real changes in the lower basin happen, mostly that not everybody gets their water allocation--specifically, AZ and NV do not get their full share (CA has the senior water right among the three states, a separate topic--CA doesn't have to cut back until it falls to 1025). So there's a very strong effort to keep it above 1075, with especially loud voices in AZ and NV since they'd be affected first. Today we're at 1089, only 14 feet above that critical level.

Powell, on the other hand, is not really tied to any level in terms of upper basin water delivery, because nobody in the upper basin really draws directly from Powell except the City of Page and the Navajo Power Plant (not for much longer in that case). For Powell, it's all about acting as a storage bank for Mead and for power generation through Glen Canyon Dam, and the minimum power pool for Powell is 3490. We're at 3569 right now--not close. So from a management standpoint, Mead is under more stress than Powell, so it makes sense to send as much as possible in the allowed range (8.23-9.0) down to Mead as long as water delivery requirements downstream are in jeopardy. And in a big water year, it makes sense to send as much as possible downstream.

That might not be popular with the Lake Powell crowd, but that's the reality from a legal framework...

Of course, the whole thing is based on the assumption that the river system can deliver 16.5 MAF to all users. The reality is that average flows over the past century are much less than that, more on the order of 13 MAF +/-. So while some years may exceed 16.5, most do not, which means in the long run, water rights exceed supply, and the reservoir levels will inevitably trend downward if everyone exercises their water rights, even with the occasional up years. And the long-term forecast in terms of climate change is that the SW will experience less precipitation in general over the next century, not more. That's why cutting back demand is the critical approach if a sustainable balance is ever going to be achieved, which is hard to do within an established water rights framework... but that's the whole point of the recent agreement among the seven basin states...
 
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one other thing is lake powell is a more efficient place to store the water because it has less evaporation than mead does. I think there needs to be pressure on mead to make sure they aren't releasing extra water either. a few more feet kept in powell means recreation isn't as effected. I think that needs to be a more important factor. I think both needs can be accommodated, a few more feet kept in to help with boat ramps, let the lake come up a few more feet in june, then give the water back. I am surprised the lake hasn't risen hardly at all in the last 3 weeks.
 
hidesert cowboy said:
one other thing is lake powell is a more efficient place to store the water because it has less evaporation than mead does. I think there needs to be pressure on mead to make sure they aren't releasing extra water either. a few more feet kept in powell means recreation isn't as effected. I think that needs to be a more important factor. I think both needs can be accommodated, a few more feet kept in to help with boat ramps, let the lake come up a few more feet in june, then give the water back. I am surprised the lake hasn't risen hardly at all in the last 3 weeks.
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Good thoughts... in terms of why the lake level hasn't risen in the past few weeks, well, it finally bottomed out on April 10. The other most similar years to this one are 2005, 2011, and 2014, all of which hit bottom around April 10. In each case, the lake rose a lot after a big snow season, ranging from 36 to 53 feet. I'd expect similar this year. That said, even in those years there was hardly any rise in April--only 2-8 feet by the end of the month, depending on the year. And looking at the inflow/outflow numbers of those years compared to this one, we look like we're closely tracking with 2011 so far, with inflows in the 15-20K cfs range, and outflows close to 12K cfs (actually outflows were higher in mid-April 2011). The lake rose 51 feet in 2011.

Most of the rise generally came in June, although in 2005 there was a big rise early because the lake was so low to begin with, and they suppressed outflows in April and May to the 7-10K cfs range. But here's the breakdown:

2005:
April - 8 feet
May - 22 feet
June - 21 feet
July - 1 foot

2011:
April - 2 feet
May - 10 feet
June - 27 feet
July - 12 feet

2014:
April - 4 feet
May - 10 feet
June - 21 feet
July - 1 foot
 
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Interesting to see the lake rise in feet per month. In a similar year like this, what is the rate of drop for the next 8 or so months? Any guesses re inflow/outflow and a prediction on what low water is for next April? Thanks, Dave
 
shanewave said:
JFR--

Oftentimes, I scan the water database, but I love the way that you create such magnificent info in a concise, precise format. Amazing to engage the data. Thanks for the informative look at the issues.
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Thanks Shanewave! Well, I like diving into stuff like this...it’s sort of what I do for a living (I’m an environmental planning consultant in CA), but way more interesting and fun to apply it to Lake Powell...
 
Littlesaltwash said:
Interesting to see the lake rise in feet per month. In a similar year like this, what is the rate of drop for the next 8 or so months? Any guesses re inflow/outflow and a prediction on what low water is for next April? Thanks, Dave
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USBR posts their 24 month study (a forecast of lake levels) around the 15th of each month based on data as of the beginning of the month. Here is the link. Click on April to get the pdf of the latest forecast. Scroll through the pdf down to Lake Powell. It is my understanding that levels for the next water year beginning Oct. 1 are based on long term normal snowpack on the watershed.
 
And you can get tons of USBR data from the link posted on the Home page of WW. I forget to go there rather than direct searches
 
JFRCalifornia said:
Thanks Shanewave! Well, I like diving into stuff like this...it’s sort of what I do for a living (I’m an environmental planning consultant in CA), but way more interesting and fun to apply it to Lake Powell...
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I'm curious, what are some of the possible solutions floating around for the Salton Sea? One thing I can't seem to understand is if the sea is now at a higher salinity than ocean water, why they aren't just pumping ocean water in. It's absolutely crazy that we pump fresh clean water into an accidental salty desert lake.
 
Flow said:
I'm curious, what are some of the possible solutions floating around for the Salton Sea? One thing I can't seem to understand is if the sea is now at a higher salinity than ocean water, why they aren't just pumping ocean water in. It's absolutely crazy that we pump fresh clean water into an accidental salty desert lake.
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Another water problem that could be solved with nuclear generation.
 
Littlesaltwash said:
Interesting to see the lake rise in feet per month. In a similar year like this, what is the rate of drop for the next 8 or so months? Any guesses re inflow/outflow and a prediction on what low water is for next April? Thanks, Dave
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Yes, the 24-Month USBR forecast that Trix points to is a nice summary of the likely future into 2020. Of course, even in there is a wide variation between their Min and Max scenarios. They show a "maximum" scenario of the lake hitting 3634 in July, then bottoming out at 3619 in March 2020. Their "minimum" scenario has the lake hitting a peak of 3597 in July, then bottoming out at 3570 in April 2020. In terms of inflow/outflow rates, we are tracking a lot like 2011 or 2014 so far, which had a rise of 51 and 36 feet respectively by summer...if that follows for 2019 (and hard to know till we see the May numbers), we end up somewhere in the range of 3605-3620, which is right in the middle of the USBR forecast. So I'd say their prediction seems pretty good. Of course, all depends on the net inflow in May and June, as it always does.

Now in terms what happens in the months that follow the summer peak, that's always a little more predictable, historically speaking. In general, there's always a very gradual drop from about September to March, and it really doesn't depend on snowpack at all--it's all about how much USBR chooses to release through the dam. In Sept-March 2005-06 and 2014-15, for example, the releases in those months averaged about 11.5K cfs, which is consistent with the idea of a total annual release of 8.23 MAF. In 2011-12 it was much higher, about 15K cfs. (FYI-- a rule of thumb is to end up with an 8.23 MAF for the year, you need to average 11.4K cfs per day; for 9.0 MAF for the year, it's 12.4K cfs per day. So you can check the outflow data in the Lake Powell Water Database (http://lakepowell.water-data.com) to see where their thinking is on any given day.)

Average inflows during all three years Sept to March was pretty consistent--about 8-10K cfs per day, plus or minus. Essentially, this inflow is the steady regulated remainder of the previous year's post-peak snowpack, which is used like a bank by the USBR during the winter months.

So what ended up happening in those 3 years from September through March? The lake dropped 14 feet in 2005-06, 20 feet in 2011-12, and 15 feet in 2014-15. Most of the drop happens in December through February, no surprise, as rain turns to snow and stays in place as snowpack until it melts.

It's worth noting that we headed into a short but awful drought in 2012-13, but that was hard to predict from the lake decrease of 2011-12...it only became apparent when we saw there wasn't much snow in winter 2011-12, and next to no runoff in spring 2012 (it only rose 2 feet that spring season). In other words, it's all about what happens in the mountains in winter, and runoff in April-June (not September to March) to predict the future...again, no surprise...

Here's the summary of lake level decrease in Sept-March for the three years:

2005-06 (total drop of 14 feet)
Sept - 1 foot
Oct - gained a foot
Nov - 1 foot
Dec - 4 feet
Jan - 4 feet
Feb - 4 feet
Mar - 1 foot (peak low was on April 8, 2006)

2011-12 (total drop of 20 feet)
Sept - 2 feet
Oct - 3 feet
Nov - 4 feet
Dec - 6 feet
Jan - 3 feet
Feb - 2 feet
Mar - 0 feet (peak low was on March 14, 2012)

2014-15 (total drop of 15 feet)
Sept - 0 feet
Oct - 0 feet
Nov - 4 feet
Dec - 4 feet
Jan - 4 feet
Feb - 2 feet
Mar - 1 foot (peak low on May 7, 2015)

By the way, it's kind of interesting that since 1965, the average lake spring increase is about 24 feet...and the offseason decrease is about 22 feet. So there's your barometer to judge whether something is a good or bad year. But also notable that the average increase in the years since 2005 is actually higher--27 feet (!)... but so is the decrease, about 25 feet. (That's probably because the lake level was lower in those years, so it takes less volume to make for a higher rise.) It's the droughts that kill us. The period of 2000-04 was bad: average spring increase of 7 feet, but offseason decrease of 28 feet... 2012-13 was even worse: annual average increase of 3.5 feet, and decrease of 33 feet!

And that is the story of the future of the lake and the whole river system...planning for the next big drought...
 
JFR one thing to remember is the lower the lake level the less water it takes for it to rise. the fuller the lake gets the larger exponentially the lake is and thus it take more water to raise it in feet. ie the shorelines become bigger. So that is probably what you are seeing and why when the lake is at lower levels the lake rises greater amounts.

where I live, northern utah, we have saturated ground and giant snow pack to melt. a great recipe for runoff. however it looks like the eastern and northern parts of the colorado drainage while above average aren't as insane as where I live. I am not sure how much the western part of the colorado drainage will help provide the extra run off. Where I live, I hear you on the april to july run off numbers. But in years past with this kind of snow to melt our rivers will run higher and you will not see them become normal and reach their base flows until mid august. at that time generally no matter how much snow we got the rivers run about the same. but with this much snow we will see a much longer runoff period. its really too bad we didn't have at least an average year last year. If we did the lake would really be on the move,
 
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