Inflows and Outflows – The Different Patterns of Good and Bad Years

[JFRCalifornia]

It’s sometimes hard to picture how BOR regulates outflows through Glen Canyon Dam, since there’s a whole lot of big numbers always thrown around, and hard to grasp the context compared to inflows. There is a consistent narrative out there that if BOR would somehow just hold back more water, things would be fine. And it’s at this time of year that you’ll often hear that the loudest, because it’s in the winter months that outflows often exceed inflows.

Why don’t they just cut back during the winter months and save more water in Lake Powell?

That’s a question worth exploring. The short answer is that inflow does not happen in linear fashion as the year goes on. A disproportionate amount of inflow occurs during May and June, and in some outlier heavy flow years, even July. And that affects how BOR looks at it when they put together a schedule for releasing water through the dam.

Just to provide some perspective, even in a bad years like 2021 and 2022, roughly 40% of the annual inflow occurs in May and June. In an “average” year like 2016, that proportion is higher—about 53% that year. That’s actually a similar percentage to even better years like 2019 or 2011. The difference in those better years is that they also had a significant amount of inflow in July—around 20% of the annual volume in that month alone. In bad years, July inflow is less than 10% of the annual total.

A quick summary before going on:

Terrible Years (like 2021 and 2022)

May/June inflow – 40% of annual total
July inflow – less than 10% of annual total

Average Years (like 2016)

May/June inflow – 50% of annual total
July inflow – less than 10% of annual total

Very Good to Great Years (like 2011 and 2019)

May/June inflow – 50% of annual total
July inflow – 20% of annual total

In other words, no matter what kind of year it’s going to be, expect 50-70% of the annual inflow to occur in three months—May, June and July. In those months, inflow generally is much greater than outflow, so the lake goes up.

BOR is obligated to deliver 82.3 maf over any 10-year period to the Lower Basin and Mexico. That might change in the future, but that’s what it is right now. That means an annual average of 8.23 maf. If they can deliver more, they can ease up on the gas in later years. And if they deliver less, they eventually have to make up for it in coming years. But no matter what target they choose for a given year, in general, the monthly delivery is fairly consistent—which keeps monthly power generation fairly regular. So whether they deliver 7.0 maf (as they are now), or 9.0, or even more, if you plotted it on a graph, it’s a fairly linear slope as you total the cumulative outflow.

The same cannot be said for inflow, which, as noted, is greatest in late spring and early summer. And so it’s in those months where the lake rises, because inflow greatly exceeds outflow. But from BOR’s perspective, they are mostly focused on where things stand at the end of the water year—September 30. A good year is one in which the aggregate inflow exceeds outflow, and where they are able to deliver at least 8.23 maf. In such years, Lake Powell remains stable or rises. Simple enough.

To help picture all this, it’s useful to see this all on a graph.

First, here’s 2011, a great year—the best of the 21st century. This graph shows the cumulative inflows and outflows that water year:



Here you can see that the year ends with a total inflow of over 16 maf. Outflows were about 12.5 maf. And the lake rose considerably that year. But the key for those looking ahead in 2023 is that cumulative inflow did not exceed outflow until May. When it did, more than half of the ultimate inflow was still ahead.

Now compare that to 2019, another good year.



The pattern of the graph looks similar to 2011. The difference is that total inflow was only about 12.9 maf, and outflow was about 9.0 maf. But as in 2011, the “break even” point happened in May, and at that point, there was still a little over half of the remaining inflow ahead. You see a pattern emerging here. If it’s a good year, the cumulative inflow matches the total outflow sometime in May, and at that point, there’s a little more than half of the year’s inflow still ahead.

Okay, what about an average year? Like 2016? In that year, total inflow ended up at about 9.6 maf, outflow at 9.0 maf.



You can see the pattern looks similar to the better years, with a breakeven point in May. But the difference is that there is not the same mid-summer rise in July. And so only about a third of the annual total inflow happens after the breakeven point.

Now look at two really bad years, 2021 and 2022. In both cases, the cumulative inflow never exceeded the outflow. In 2021, total inflow was about 3.5 maf, compared to 8.23 maf going out. And that is the reason why BOR curtailed releases in 2022 to only 7.0 maf, as low as it has been in recent decades. But even with that, cumulative inflow never exceeded cumulative outflow (6.0 maf for the year), though it came close in June.








The overall takeaway here is that you should expect—it is normal—that cumulative outflow will exceed inflow through April of any year, good or bad. But if the cumulative inflow does not catch up to outflow sometime in May, it’s going to be a very bad year. On the other hand, if it does catch up, the difference between an average year and a good/great one is what inflow looks like in July…

Signposts to watch for in 2023...

 

[Richp47]

Since 2010 a huge amount of water above the required volume has been released downstream -- most notably one year when 12 million acre feet was released instead of the required 8+.

What was the rationale for that? Having that extra water in Powell sure would make a difference now.

 

[JFRCalifornia]

Since 2010 a huge amount of water above the required volume has been released downstream -- most notably one year when 12 million acre feet was released instead of the required 8+.

What was the rationale for that? Having that extra water in Powell sure would make a difference now.

A reasonable question. Let's play that one out.

Following the big drought of 2001-04, Lake Powell slowly recovered in the ensuing years, to the point where it reached 3661 in 2011. From 2005 to 2010, releases through Glen Canyon Dam were a steady 8.23 maf, right on target, with the exception of 2008, which was about 9.0 maf. And these relatively modest releases were enough to see Lake Powell rise in 2011 over 100 feet from its low of 3555 in April 2005. Good news in Lake Powell. But at the same time in Lake Mead, things weren't so rosy. From an average of 1214 in 1998, Mead steadily dropped through 2010 to roughly 1100 on average. So while Powell was on its way up, Mead was on its way down, in spite of the nominally decent releases through Glen Canyon Dam. Lower Basin water use was partly to blame in those years, which averaged about 7.4 maf, while Mexico took another 1.5 maf, but the trend there was headed downward, not up.

And so from BOR's perspective as 2011 dawned, Mead needed help, while Powell was looking good. So when there was a big snow year in 2010-11, BOR saw an opportunity, and released 12.5 maf to boost Mead. And it helped--Mead peaked at about 1134 in late January 2012, its highest level in years. And at the same time, Powell did not suffer, but held steady and even rose during that year, peaking, as noted before, at 3661.

It seemed like the smart move at the time. But after two consecutive bad runoff years in 2012 and 2013, that's when questions first started to be asked.

You might ask--how would it have affected Powell if only 8.23 maf was released in 2011 instead of 12.5 maf? It would have added about 35 feet on average that year. Instead of peaking at 3661, it might have peaked closer to 3690, and might have ended the water year at 3685 instead of 3652. But it would have come at the expense of Lake Mead.

In subsequent years, releases through Glen Canyon Dam were relatively high--about 9.0 maf each year from 2015-19. Again, the issue BOR faced was trying to achieve a balance between the two reservoirs, because they knew that releasing 8.23 maf each year in the previous decade was not enough to keep Mead from dropping. Of course in those years after 2010, Lower Basin water use was down significantly, while Upper Basin use was on the rise. Was balance achieved? Sort of. Just at lower levels in each lake than had been the case in 2000. So as drought hit hard in 2018, then again in 2020-22, we're now feeling it in both lakes, and there's not a lot of effective options short of all states reducing their reliance on the water from the basin...

 

[Eagle Rock]

Since 2010 a huge amount of water above the required volume has been released downstream -- most notably one year when 12 million acre feet was released instead of the required 8+.

What was the rationale for that? Having that extra water in Powell sure would make a difference now.

One possible answer - equalizing storage in Powell and Mead. Holding back water in Powell in a wet year means that Mead never experiences a wet year (i.e., a year with inflows well above outflows). Past practice was to try and balance storage in the two reservoirs. That's starting to change because of the further constraint of keeping both reservoirs above minimum power pool, a constraint that was never binding in the past 40 years.

 

[Eagle Rock]

I posted my answer to Richp47 before seeing JFRC's more thorough answer.

 

[Dorado]

Don’t confuse me with the facts

Ultimately, the issue is the “obligation to deliver” a volume of water to the lower basin that is clearly not sustainable.

 

[Bill Sampson]

Thanks for the graphs and the facts. It makes it easier to understand.

 

[Richp47]

Thank you all for the very complete replies.

The thought that immediately comes to mind is that if the lower basin had at a much earlier stage implemented what now are admitted to be necessary conservation measures, a great deal of what is happening now could have been avoided.

 

[scubatim]

It’s sometimes hard to picture how BOR regulates outflows through Glen Canyon Dam, since there’s a whole lot of big numbers always thrown around, and hard to grasp the context compared to inflows. There is a consistent narrative out there that if BOR would somehow just hold back more water, things would be fine. And it’s at this time of year that you’ll often hear that the loudest, because it’s in the winter months that outflows often exceed inflows.

Why don’t they just cut back during the winter months and save more water in Lake Powell?

That’s a question worth exploring. The short answer is that inflow does not happen in linear fashion as the year goes on. A disproportionate amount of inflow occurs during May and June, and in some outlier heavy flow years, even July. And that affects how BOR looks at when they put together a schedule for releasing water through the dam.

Just to provide some perspective, even in a bad years like 2021 and 2022, roughly 40% of the annual inflow occurs in May and June. In an “average” year like 2016, that proportion is higher—about 53% that year. That’s actually a similar percentage to even better years like 2019 or 2011. The difference in those better years is that they also had a significant amount of inflow in July—around 20% of the annual volume in that month alone. In bad years, July inflow is less than 10% of the annual total.

A quick summary before going on:

Terrible Years (like 2021 and 2022)

May/June inflow – 40% of annual total
July inflow – less than 10% of annual total

Average Years (like 2016)

May/June inflow – 50% of annual total
July inflow – less than 10% of annual total

Very Good to Great Years (like 2011 and 2019)

May/June inflow – 50% of annual total
July inflow – 20% of annual total

In other words, no matter what kind of year it’s going to be, expect 50-70% of the annual inflow to occur in three months—May, June and July. In those months, inflow generally is much greater than outflow, so the lake goes up.

BOR is obligated to deliver 82.3 maf over any 10-year period to the Lower Basin and Mexico. That might change in the future, but that’s what it is right now. That means an annual average of 8.23 maf. If they can deliver more, they can ease up on the gas in later years. And if they deliver less, they eventually have to make up for it in coming years. But no matter what target they choose for a given year, in general, the monthly delivery is fairly consistent—which keeps monthly power generation fairly regular. So whether they deliver 7.0 maf (as they are now), or 9.0, or even more, if you plotted it on a graph, it’s a fairly linear slope as you total the cumulative outflow.

The same cannot be said for inflow, which, as noted, is greatest in late spring and early summer. And so it’s in those months where the lake rises, because inflow greatly exceeds outflow. But from BOR’s perspective, they are mostly focused on where things stand at the end of the water year—September 30. A good year is one in which the aggregate inflow exceeds outflow, and where they are able to deliver at least 8.23 maf. In such years, Lake Powell remains stable or rises. Simple enough.

To help picture all this, it’s useful to see this all on a graph.

First, here’s 2011, a great year—the best of the 21st century. This graph shows the cumulative inflows and outflows that water year:

View attachment 20295

Here you can see that the year ends with a total inflow of over 16 maf. Outflows were about 12.5 maf. And the lake rose considerably that year. But the key for those looking ahead in 2023 is that cumulative inflow did not exceed outflow until May. When it did, more than half of the ultimate inflow was still ahead.

Now compare that to 2019, another good year.

View attachment 20298

The pattern of the graph looks similar to 2011. The difference is that total inflow was only about 12.9 maf, and outflow was about 9.0 maf. But as in 2011, the “break even” point happened in May, and at that point, there was still a little over half of the remaining inflow ahead. You see a pattern emerging here. If it’s a good year, the cumulative inflow matches the total outflow sometime in May, and at that point, there’s a little more than half of the year’s inflow still ahead.

Okay, what about an average year? Like 2016? In that year, total inflow ended up at about 9.6 maf, outflow at 9.0 maf.

View attachment 20299

You can see the pattern looks similar to the better years, with a breakeven point in May. But the difference is that there is not the same mid-summer rise in July. And so only about a third of the annual total inflow happens after the breakeven point.

Now look at two really bad years, 2021 and 2022. In both cases, the cumulative inflow never exceeded the outflow. In 2021, total inflow was about 3.5 maf, compared to 8.23 maf going out. And that is the reason why BOR curtailed releases in 2022 to only 7.0 maf, as low as it has been in recent decades. But even with that, cumulative inflow never exceeded cumulative outflow (6.0 maf for the year), though it came close in June.

View attachment 20302



View attachment 20304


The overall takeaway here is that you should expect—it is normal—that cumulative outflow will exceed inflow through April of any year, good or bad. But if the cumulative inflow does not catch up to outflow sometime in May, it’s going to be a very bad year. On the other hand, if it does catch up, the difference between and average year and a good/great one is what inflow looks like in July…

Signposts to watch for in 2023...

Great analysis - as usual. And the graphs are very "illustrative"!! Given that the starting level will be 3510+- even an average year or 2 will greatly help - provided they do not go back to 8.23 releases?? How would a year like 2016 raise the level this year (also less evap!!)??

 

[JFRCalifornia]

Great analysis - as usual. And the graphs are very "illustrative"!! Given that the starting level will be 3510+- even an average year or 2 will greatly help - provided they do not go back to 8.23 releases?? How would a year like 2016 raise the level this year (also less evap!!)??

Thanks--I appreciate the feedback!

So the way to figure out a "what if" scenario like the one you propose is to start with what the lake level was on the first day of the water year--October 1. And on 10-1-22 Lake Powell was at 3529. And so here's your "2016 average inflow" scenario, combined with the BOR's planned release of 7.048 maf for WY2023:

Inflow: 9.6 maf
Outflow: 7.0 maf

Assume about 0.5 maf in evaporation and seepage in Lake Powell, which is a ballpark guess but close.

I won't assume any reduction in Upper Basin water consumption, but more about that in a minute.

That means net inflow to Lake Powell in WY2023 would be 2.1 maf.

And then you look at the bathymetric data for volume vs. lake levels. At 3529, Powell holds about 5.8 maf in live storage. Add 2.1 maf, and you end up with 7.9 maf on 9-30-23. And that corresponds to a lake level of 3563. There's your answer. It might peak at a little over 3565 in the summer, but that's the idea. A net rise of over 30 feet.

That all assumes that Upper Basin diversions are the same as they have been in recent years. But if they cut back, the net inflow to Powell would rise correspondingly. If, for example, they managed to reduce their collective withdrawals next year by 10%--about 0.4 maf--then that water gets added to Lake Powell. And that bump would raise the lake by another 5 feet.

Now let's say you repeat that average inflow scenario in 2024, and keep BOR releases at 7.048 maf, what happens? And let's say the Upper Basin actually does reduce water use by 10%, then what? Well, applying the same methodology, you end up adding a net 2.5 maf to a baseline of 7.9 maf (the 9-30-23 lake volume), and end up at 10.4 maf. In that case, the lake would rise from 3563 on 10-1-22 to 3595 on 9-30-24, with a summer 2024 peak probably around 3600.

Not an unreasonable scenario. And that's just two average years in a row.

So far, this winter is looking promising...

 

[Richp47]

JFR, I can in no way reach your level of analysis on all this, nor do I have your in-depth knowledge. Regrettably, I haven't been able to follow all of the detailed discussions in various threads on this. But at the risk of looking foolish, let me see if I can sketch out something from sort of a layman's point of view.

Take the inflow (and this disregards what diversion may be taking place from the headwaters to the Front Range, although that certainly could be a point of contention and negotiation). Subtract what probably cannot be modified in terms of an obligation to Mexico and tribes. Subtract reasonable estimates of Powell's bank storage and evaporation. Half the remaining number gets delivered to the lower basin.

This would preserve the concept of the original compact, let the lower basin deal with their own bank loss and evaporative problems, honor tribal and Mexico obligations, while presumably leaving a little headroom for the upper basin -- hopefully in the form of a structural increase in Powell's level.

Is that too simple a framework to build on?

 

[JFRCalifornia]

JFR, I can in no way reach your level of analysis on all this, nor do I have your in-depth knowledge. Regrettably, I haven't been able to follow all of the detailed discussions in various threads on this. But at the risk of looking foolish, let me see if I can sketch out something from sort of a layman's point of view.

Take the inflow (and this disregards what diversion may be taking place from the headwaters to the Front Range, although that certainly could be a point of contention and negotiation). Subtract what probably cannot be modified in terms of an obligation to Mexico and tribes. Subtract reasonable estimates of Powell's bank storage and evaporation. Half the remaining number gets delivered to the lower basin.

This would preserve the concept of the original compact, let the lower basin deal with their own bank loss and evaporative problems, honor tribal and Mexico obligations, while presumably leaving a little headroom for the upper basin -- hopefully in the form of a structural increase in Powell's level.

Is that too simple a framework to build on?

You propose an interesting approach, and it has the great virtue of simplicity, which is always good thing. Thanks for starting the discussion. To evaluate that idea, it’s helpful to get a feel for recent actual water use in both basins. These are average water use numbers for the period 2016-20:

Upper Basin - 4.2 maf (does not include about 0.45 maf in evaporation, but it does include about 0.5 maf that is diverted to the front range cities)

Lower Basin - 6.9 maf (does not include about 0.47 maf of evaporation)

Mexico - 1.5 maf

These numbers vary a bit year to year, but if you add it up, the total annual use is something like 12.6 maf, plus another 0.9 maf in evaporation. That’s 13.5 maf, if you count evaporation as "consumption".

Let’s call that the baseline condition.

Now we can debate the intent of the 1922 Compact, but to cut to the chase, there are two conflicting arguments. Was the primary intent to divide the water evenly between the Upper and Lower Basin? That’s the Upper Basin’s argument. Or was it to guarantee the Lower Basin got its share first? That’s the Lower Basin’s perspective. Both issues are discussed in the Compact.

So let’s set that debate aside for attorneys and pundits, and instead focus on practicality and fairness in devising a solution to the problem at hand. A few key points I’d start with in any solution:

1. It seems reasonable that both basins should account for evaporation in their water accounting, or that neither should.
2. In terms of considering cutbacks, it’s reasonable to start with the reality of what’s actually being used in the two basins.

Now let’s talk about your proposal. If I understand it right, your suggestion would be:

1. Keep Upper Basin water use the same as it is now.
2. Preserve Mexico’s share and tribal water use as they are.
3. Account for evaporation in both basins.
4. Half of the remaining inflow to Lake Powell after other issues are accounted for would get sent downstream for Lower Basin use.
5. Thus, all water cutbacks would come from the Lower Basin, which would vary year to year, and be a function of how much water is available to send downstream depending on the inflow to Lake Powell for that year.

So for example, if after the Upper Basin takes its share, inflow to Lake Powell is 10.5 maf in a given year, and evaporation and bank storage in Lake Powell is 0.5 maf, then there is 10.0 maf net to the lake. And that means BOR would release 5.0 maf through the dam, which could be used by the Lower Basin, plus an additional amount to cover Mexican and tribal needs. (Or did you mean, subtract the Mexican and tribal need from the 10.0 maf, then divide the remainder in half--and that's the Lower Basin share?)

And if inflow to Powell in a bad year is only 6.0 maf after accounting for evaporation and Upper Basin use, that means the Lower Basin only gets 3.0 maf, while the Upper Basin still can use its historic 4.2 maf.

In other words, your plan would guarantee that the Upper Basin gets its existing share before the Lower Basin gets its share. Might seem reasonable to many people, and certainly in places like Utah and Colorado, but it’s not something the Lower Basin states would ever agree to, because it is the exact opposite of the way the 1922 Compact is framed right now, where the Lower Basin gets its share first. Probably a non-starter.

Seems to me any viable solution has to make each basin feel a proportional pain in terms of cutbacks in bad years, and that proportion should be applied to some existing baseline water use. Both basins should have to account for evaporation. Ideally, Mexico would have to cutback proportionally too, to the same extent as the two basins. Tribes too.

I don’t think it’s practical (or even reasonable) to think that the two basins should be held to using an equal amount of water, at least in the short term. It’s a debatable point, of course. I do think it might be reasonable that the Upper Basin states help offset the cost of developing alternative long-term water supplies in the Lower Basin, such as desalination in California. Eventually, that would tend to equalize Upper and Lower Basin use of the Colorado River.

I also think it’s important to understand where all that water in the Lower Basin is actually being used, and target those entities where it might make a real difference. For example, I don’t think Nevada is the problem. They use less than 0.3 maf, and have a great return flow concept because of their proximity to Lake Mead. And in CA, the MWD is already actively working on ways to reduce its dependence on Colorado River water, which right now is on the order of about 0.8 maf.

To me, in the Lower Basin it’s the Imperial Irrigation District in CA and the Central Arizona Project where efforts to reduce could be effectively focused. Those are the elephants in the room. Between those two, they consume about 3.9 maf each year. Nearly as much as the entire Upper Basin! And then there are the myriad irrigation districts on either side of the Colorado River, in both CA and AZ.

And just to lay out who the top 10 users in the Lower Basin are:

1. Imperial Irrigation District - 2.49 maf
2. Central Arizona Project - 1.40 maf
3. MWD of So. Cal. - 0.82 maf
4. Coachella Valley Water District - 0.35 maf
5. Palo Verde Irrigation District - 0.35 maf
6. Wellton-Mohawk Irrigation and Drainage District - 0.26 maf
7. Yuma County Water Users Assoc. - 0.24 maf
8. Griffith Water Project (formerly Southern Nevada Water Project) - 0.23 maf (after discounting Las Vegas Wash return flow)
9. Colorado River Indian Reservation - 0.20 maf
10. Yuma Mesa Irrigation and Drainage District - 0.16 maf

Based on this list, a few themes emerge:

1. Ag districts are by far the largest users, on both the CA and AZ side of the river. They use more than the Central Arizona Project and the MWD combined!
2. Most of the primary water users are generally near the Colorado River itself (MWD and the CAP are the major exceptions)
3. In spite of the growth of Phoenix and Las Vegas in the past several decades, the amount of water they use in the context of overall Colorado River water use isn't that much. Phoenix is a subset of Item 2 (the CAP also covers ag use, urban use in several counties and tribal use in its service area), and Las Vegas is more or less Item 8. Significant water use, but even if those cities disappeared, you'd still have a lot of water being used.
4. Southern California MWD has 26 member agencies, but they split up only 0.82 maf--a significant amount, but again, if urban water use in southern California disappeared, that would not solve the problem.

Just some food for thought and discussion for now...

 

[scubatim]

Thanks--I appreciate the feedback!

So the way to figure out a "what if" scenario like the one you propose is to start with what the lake level was on the first day of the water year--October 1. And on 10-1-22 Lake Powell was at 3529. And so here's your "2016 average inflow" scenario, combined with the BOR's planned release of 7.048 maf for WY2023:

Inflow: 9.6 maf
Outflow: 7.0 maf

Assume about 0.5 maf in evaporation and seepage in Lake Powell, which is a ballpark guess but close.

I won't assume any reduction in Upper Basin water consumption, but more about that in a minute.

That means net inflow to Lake Powell in WY2023 would be 2.1 maf.

And then you look at the bathymetric data for volume vs. lake levels. At 3529, Powell holds about 5.8 maf in live storage. Add 2.1 maf, and you end up with 7.9 maf on 9-30-23. And that corresponds to a lake level of 3563. There's your answer. It might peak at a little over 3565 in the summer, but that's the idea. A net rise of over 30 feet.

That all assumes that Upper Basin diversions are the same as they have been in recent years. But if they cut back, the net inflow to Powell would rise correspondingly. If, for example, they managed to reduce their collective withdrawals next year by 10%--about 0.4 maf--then that water gets added to Lake Powell. And that bump would raise the lake by another 5 feet.

Now let's say you repeat that average inflow scenario in 2024, and keep BOR releases at 7.048 maf, what happens? And let's say the Upper Basin actually does reduce water use by 10%, then what? Well, applying the same methodology, you end up adding a net 2.5 maf to a baseline of 7.9 maf (the 9-30-23 lake volume), and end up at 10.4 maf. In that case, the lake would rise from 3563 on 10-1-22 to 3595 on 9-30-24, with a summer 2024 peak probably around 3600.

Not an unreasonable scenario. And that's just two average years in a row.

So far, this winter is looking promising...

From your keyboard to God's ear!! That is about what I guessed from the bathymetry graph. Just hoping Hall's is able to launch BEFORE/IF they extend the ramp!! 74 and holding - may only have a couple seasons left????

 

[Richp47]

JFR, you analytically outgun me by a wide margin.

One clarification -- my starting point would not be with the upper basin retaining any specific amount. Plainly put, each year the two basins would variably, and evenly split what was left after allocations for Mexico and the tribes are subtracted from the inflow.

Admittedly this would ask more of the Lower Basin. Trade-offs involving accounting for Front Range diversions could be on the table, along with factors that I'm not well enough informed to estimate. But if you slide a bit off the guaranteed delivery component of the Compact and plant your flag on equally sharing the pain, then you're down to tinkering around with formulas for thresholds that would allow gradual reaccumulation of water in Powell.

And to no surprise, the entrenched interests of the financially and politically powerful agricultural sector will be there to (I would say) distort the process.

 

[JFRCalifornia]

JFR, you analytically outgun me by a wide margin.

One clarification -- my starting point would not be with the upper basin retaining any specific amount. Plainly put, each year the two basins would variably, and evenly split what was left after allocations for Mexico and the tribes are subtracted from the inflow.

Admittedly this would ask more of the Lower Basin. Trade-offs involving accounting for Front Range diversions could be on the table, along with factors that I'm not well enough informed to estimate. But if you slide a bit off the guaranteed delivery component of the Compact and plant your flag on equally sharing the pain, then you're down to tinkering around with formulas for thresholds that would allow gradual reaccumulation of water in Powell.

And to no surprise, the entrenched interests of the financially and politically powerful agricultural sector will be there to (I would say) distort the process.

I agree the ag interests will have a disproportionately loud voice in any discussion, relative to the questionably unique value of what they bring to the table compared to the amount of water needed to grow their products. Another discussion for another thread, perhaps.

And thanks for the clarification about how you see the Upper Basin's position in terms of future water use. I would say any formula that divides the water in some fashion is complicated by the fact that the Upper Basin takes its water before it ever reaches any major reservoir, while the Lower Basin is completely at the mercy of whatever BOR releases through Glen Canyon Dam. In other words, from a logistics standpoint, the Upper Basin holds cards not available to the Lower Basin, and that makes the calculation of what's "available" in Lake Powell tricky.

I think one way to address that is to base a future year's approach on what happened the previous year. And as an example, let's say the Upper Basin used 4 maf in Year 1, and 8 maf flowed into Lake Powell, that means in rough terms there were 12 maf available prior to diversions. Your concept then would be to set aside 1.5 maf for Mexico, however much for the tribes (let's call it 0.5 maf), assume 1.0 maf for evaporation, and that means the "leftover" would be 9 maf. And do you propose that in Year 2, that 9 maf be evenly split between Upper and Lower Basin? That is, 4.5 maf for each? Is that basically the concept?

 

[Richp47]

Yes, that's it. And your idea of a retrospective scheme would fit into that.

But there's another layer to this that has to at least envision the possibility of a year with extravagent inflow that would make it tempting to have dramatically greater releases downstream. And it's here that the balancing between Powell and Mead would come into play.

The principle I would invoke in that situation would be that in those years, as long as Mead is optimized for power generation, and since consumption in the lower basin presumably already has been calibrated downward for a lower normalized flow regime, most of that extra inflow would be kept in Powell.

Despite the fact that "extra" water kept in Powell would be money in the bank, so to speak, and always will be available to support Mead, I can see that would be a tough sell for the Lower Basin. But the future I envision for California and Arizona necessarily contemplates structural changes that encompass both agricultural and industrial components of the economy, as well as residential. And because they would have re-engineered their baseline use consistent with the aforementioned modulated number (which would maintain Mead at a workable level), putting water in the Powell "bank" could arguably build a reserve against future growth in Arizona and California -- something that could be a selling point for the plan.

Well I started this out saying I just wanted to throw out a framework, and here I am rattling on about details that really only can be finalized through hard negotiation. But I do want to conclude by thanking you, JFR, for the invaluable contribution you've made here in educating people like me who have visited Powell, enjoyed its beauty, understand its unique role in the economy of the Southwest, and look forward to a solution that balances the many complicated needs of that region.

 

[JFRCalifornia]

Yes, that's it. And your idea of a retrospective scheme would fit into that.

But there's another layer to this that has to at least envision the possibility of a year with extravagent inflow that would make it tempting to have dramatically greater releases downstream. And it's here that the balancing between Powell and Mead would come into play.

The principle I would invoke in that situation would be that in those years, as long as Mead is optimized for power generation, and since consumption in the lower basin presumably already has been calibrated downward for a lower normalized flow regime, most of that extra inflow would be kept in Powell.

Despite the fact that "extra" water kept in Powell would be money in the bank, so to speak, and always will be available to support Mead, I can see that would be a tough sell for the Lower Basin. But the future I envision for California and Arizona necessarily contemplates structural changes that encompass both agricultural and industrial components of the economy, as well as residential. And because they would have re-engineered their baseline use consistent with the aforementioned modulated number (which would maintain Mead at a workable level), putting water in the Powell "bank" could arguably build a reserve against future growth in Arizona and California -- something that could be a selling point for the plan.

Well I started this out saying I just wanted to throw out a framework, and here I am rattling on about details that really only can be finalized through hard negotiation. But I do want to conclude by thanking you, JFR, for the invaluable contribution you've made here in educating people like me who have visited Powell, enjoyed its beauty, understand its unique role in the economy of the Southwest, and look forward to a solution that balances the many complicated needs of that region.

That’s a well thought out, reasoned analysis. A few points I’d want to discuss more, or don’t entirely agree with, but it’s great to read another point of view in pursuit of a fair solution to a complex problem. I really appreciate your creative approach to this. I’m always open to good ideas.

And thanks for the shout out. I’m glad you think my posts are educational, but you’ve got to understand I learn as much or more from reading the posts of others on this site, on all kinds of topics I know nothing about…starting with fishing…

A really great forum…

 

[Richp47]

JFR, I appreciate your kind response. The idea of even nibbling around the edges of such a complex issue, when highly knowledgeable folks like you have already engaged the issue so comprehensively, is sort of daunting to an ordinary guy like me.

 

[Eagle Rock]

Thanks--I appreciate the feedback!

So the way to figure out a "what if" scenario like the one you propose is to start with what the lake level was on the first day of the water year--October 1. And on 10-1-22 Lake Powell was at 3529. And so here's your "2016 average inflow" scenario, combined with the BOR's planned release of 7.048 maf for WY2023:

Inflow: 9.6 maf
Outflow: 7.0 maf

Assume about 0.5 maf in evaporation and seepage in Lake Powell, which is a ballpark guess but close.

I won't assume any reduction in Upper Basin water consumption, but more about that in a minute.

That means net inflow to Lake Powell in WY2023 would be 2.1 maf.

And then you look at the bathymetric data for volume vs. lake levels. At 3529, Powell holds about 5.8 maf in live storage. Add 2.1 maf, and you end up with 7.9 maf on 9-30-23. And that corresponds to a lake level of 3563. There's your answer. It might peak at a little over 3565 in the summer, but that's the idea. A net rise of over 30 feet.

That all assumes that Upper Basin diversions are the same as they have been in recent years. But if they cut back, the net inflow to Powell would rise correspondingly. If, for example, they managed to reduce their collective withdrawals next year by 10%--about 0.4 maf--then that water gets added to Lake Powell. And that bump would raise the lake by another 5 feet.

Now let's say you repeat that average inflow scenario in 2024, and keep BOR releases at 7.048 maf, what happens? And let's say the Upper Basin actually does reduce water use by 10%, then what? Well, applying the same methodology, you end up adding a net 2.5 maf to a baseline of 7.9 maf (the 9-30-23 lake volume), and end up at 10.4 maf. In that case, the lake would rise from 3563 on 10-1-22 to 3595 on 9-30-24, with a summer 2024 peak probably around 3600.

Not an unreasonable scenario. And that's just two average years in a row.

So far, this winter is looking promising...

There are two problems with the above scenario. The first is the assumption of a 2nd consecutive year of releases at the 7 MAF level. The current BOR 24-month study shows that releases of 7 MAF this year will drop Mead from 1043' at the end of November '22 to 1021' at the end of the water year in September '23. If Powell rises 35' in 10 months (from 3528' to 3563') while Mead drops 22', then releases will not stay at 7 MAF. Indeed, the 24-month study has Powell at only 3533' at the end of the '22-'23 water year, but still shows an increase in releases to 8 MAF in the following year. Since the basis for cutting releases to 7 MAF this year was to keep Powell above 3525', a rise to 3563' this year would definitely cause releases next year to increase.
The second problem is the difference between unregulated and regulated inflow. Powell inflows have been bolstered by drawing down upstream reservoirs. But a rise in Powell to well above 3525' would allow those drawdowns to be reversed. The current 24-month srudy sows unregulated inflow to Powell in 2023-24 of 9.4 MAF, close to your 9.6 MAF scenario. But regulated inflows are much less, only 8,4 MAF. That's almost entirely due to refilling the upstream reservoirs; the 24-month study shows storage increases in 2023-24 of 0.3 MAF at each of Flaming Gorge, Blue Mesa, and Navajo.

TL/DR: A normal rainfall year this year and next can get Powell up to 3563' thi water year, but another 30' rise the next year won't happen.

 

[JFRCalifornia]

There are two problems with the above scenario. The first is the assumption of a 2nd consecutive year of releases at the 7 MAF level. The current BOR 24-month study shows that releases of 7 MAF this year will drop Mead from 1043' at the end of November '22 to 1021' at the end of the water year in September '23. If Powell rises 35' in 10 months (from 3528' to 3563') while Mead drops 22', then releases will not stay at 7 MAF. Indeed, the 24-month study has Powell at only 3533' at the end of the '22-'23 water year, but still shows an increase in releases to 8 MAF in the following year. Since the basis for cutting releases to 7 MAF this year was to keep Powell above 3525', a rise to 3563' this year would definitely cause releases next year to increase.
The second problem is the difference between unregulated and regulated inflow. Powell inflows have been bolstered by drawing down upstream reservoirs. But a rise in Powell to well above 3525' would allow those drawdowns to be reversed. The current 24-month srudy sows unregulated inflow to Powell in 2023-24 of 9.4 MAF, close to your 9.6 MAF scenario. But regulated inflows are much less, only 8,4 MAF. That's almost entirely due to refilling the upstream reservoirs; the 24-month study shows storage increases in 2023-24 of 0.3 MAF at each of Flaming Gorge, Blue Mesa, and Navajo.

TL/DR: A normal rainfall year this year and next can get Powell up to 3563' thi water year, but another 30' rise the next year won't happen.

All good points, and agree with the idea that if Powell rises to 3563, then BOR would not be releasing 7 maf the following year.. not with Mead in its current condition…