JFRCalifornia
Keeper of San Juan Secrets
Since the beginning of 2020, Lake Powell, like the sun in the late afternoon, sometimes appears to be slowly sinking over the horizon. With all the recent reports of impending doom from continued drought, and just seeing things with your own eyes, it’s easy to believe this trend will go on forever until nothing of the lake is left at all. And yet, it’s just as easy to forget that 2019 was a banner year for Lake Powell, one in which it rose 53 feet that spring. That wasn’t so long ago, but right now it sometimes feels like an eternity.
Rather than focus on the extremes to predict a future outcome, its sometimes helpful to focus on the average. The mundane. The ordinary year. And with that concept in mind, I wanted to figure out the answer to this question: What would it take to make Lake Powell rise again, and then stay there? To make the marinas, launch ramps, the Castle Rock Cut—all of the key recreational infrastructure—usable and viable for the long haul? And practically speaking, that means this: what would it take to keep the lake over elevation 3588? That’s the target elevation identified by Fill Lake Powell that would achieve those goals.
Figuring that out is a tall order, and depends on many factors, some of which can’t be controlled (like the snowpack), but some of which can (like water use). And of course to really solve that puzzle, you’ve got to consider the entire system—not just Lake Powell, but Lake Mead too. And the other smaller reservoirs. Not just water use in the Upper Basin, but all seven states and Mexico too. It’s complicated. But as with any complicated puzzle, it’s best to take it one piece at a time, and eventually you will fill in the blanks. Complete the picture. Solve the problem. Or at least identify what it would take to solve the problem. And from there, you can change the way things have always been done into the way they need to be done.
All that means, for our purposes, starting by focusing on Lake Powell. I’ll save Lake Mead and the Lower Basin for another day.
Where to begin? For all the numbers that can be run, the “what-if” scenarios that can be considered, it’s best just to simplify that challenge.
It’s basically just a simple question of inflow vs. outflow.
Let’s first consider outflow. For Lake Powell, there’s really three important factors to consider, but here’s the only one that really matters: USBR’s releases through Glen Canyon Dam. Sure, there is also a small amount directly used from Lake Powell by the city of Page, and then there are evaporative losses from the lake, but both are orders of magnitude less than what flows through the dam. And then, yes, there is the theoretical drain from future water diversion projects not yet online, and perhaps never will be, such as the proposed pipeline to St. George.
With the exception of evaporative loss, all those are controllable factors.
And then on the inflow side, snowpack (precipitation in general) is by far the most important issue, but unlike outflow through the dam, this is out of anyone’s control. There are also other important considerations: the amount of water diverted to serve the needs of the Upper Basin states, and the amount of water available for release stored in the reservoirs above Lake Powell. Unlike the snowfall, these are controllable factors.
In May 2022 the USBR issued its latest 24-Month Study, which forecasts inflows and outflows for all reservoirs affecting the entire Colorado River watershed. The forecast is based in part on projected long-range precipitation forecasts, historic trends, and projected releases from each reservoir. The forecast extends through May 2024, or roughly midway through Water Year 2024 (WY 2024).
Based on this, and other existing USBR documentation, I developed sixteen scenarios to model what could happen to Lake Powell depending on the various factors described above related to inflow and outflow. The most important of these factors is how much total water would be available in the system before anybody uses or stores it. In a simplified model, this number is possible to reverse engineer from existing reported data:
Total Water Availability = Inflow to Lake Powell + Upper Basin Water Use + Upper Basin Additional Storage + Upper Basin Reservoir Evaporation
My report goes into some detail about what those mean and the assumptions behind them, but I'll leave that to those interested in reading the full report.
And then there’s the question: what should be considered a baseline “average” year for modeling purposes? Is it the historic average inflow since Lake Powell came into existence? That seems too broad. Or maybe the period USBR focuses on to establish an “average” inflow, which is 1991-2020? Or should it be something more recent, reflecting the observed realities closer to our time? For example, the 5-year period 2016-20 was a very “average” time in the life of the lake. In terms of inflow, it featured two good years (2017 and 2019), two bad years (2018 and 2020), a pretty average year (2016). In all, the average inflow to Lake Powell during that time was about 8.99 maf, which is a little less than the USBR’s reported 1991-2020 average of 9.6 maf. Based on that, it’s reasonable to use the 2016-20 period as a more conservative “baseline average”, because it would tend to produce less optimistic results when projecting percentage increases (or decreases) from that baseline. It’s also a period where we have very detailed and realistic recent water use data for both the Upper and Lower Basins. For all these reasons, the period 2016-20 is what is used as the baseline “normal” for the purposes of this study.
Based on the assumptions described below, the Total Water Availability in the Upper Basin on average from 2016-20 was 13.6 maf.
What went into developing the various modeled scenarios? Were they just arbitrary? Spitting into the wind?
Sixteen scenarios were developed to predict what would happen to Lake Powell’s surface elevation through Water Year 2027 (WY 2027). Each of these varied one or more of the factors discussed above. In general, these scenarios considered a range of future Total Water Availability via snowpack, from 40% less than the 2016-20 average, to 20% more than average (something like what happened from 1996-2000). Within many of those scenarios, consideration was given to reducing existing Upper Basin Water Use anywhere from 5% to 50% in order to test the sensitivity of that variable and its effect on creating more downstream inflow potential to Lake Powell. Or increasing (or decreasing) flows from the upper reservoirs such as Flaming Gorge. Or varying the outflow through Glen Canyon Dam, although in general, I tried to adhere to existing USBR protocols for that. No effort was made to address Lower Basin water use or effects on Lake Mead in general. While those are extremely important considerations in the big picture, I left them for another time. But they are important.
And without getting into how the sausage was made, I'll cut to the key conclusions of the study, some obvious, some less so:
1. The most important factor in maintaining Lake Powell’s volume is total water availability, primarily through snowpack in the Upper Basin.
2. If the next 5-year period (WY 2023-27) matches the total water availability that occurred from 2016-20 (a very modest goal in historic terms), it is possible to achieve the target elevation of 3588 during WY 2025, although it would require a 5% reduction in Upper Basin water use during that time.
3. It is possible to achieve the target elevation of 3588 in WY 2025 even with a 5-year period with 5% less available water than in 2016-20. But it would require a 5-10% decrease in Upper Basin water use, and potentially additional releases from Flaming Gorge and other Upper Basin reservoirs that could further reduce capacity in those lakes.
4. In any scenario, reducing Upper Basin water use by 10% could add 400,000 AF to Lake Powell each year, which would raise the lake annually 5-6 feet by itself.
5. If the watershed sees a 5-year period of water availability similar to what occurred in 2000-04, which was about 40% less than the 2016-20 average, the outlook is grim. Only substantial reductions in Upper Basin water use and releases from upstream reservoirs (particularly Flaming Gorge) would allow Lake Powell to avoid hitting the dead pool elevation of 3370 in WY 2025. With this sort of 5-year flow regime, it would be impossible to avoid dropping below the minimum power pool of 3490, no matter what was done short of drastically reducing outflows through Glen Canyon Dam to the point of jeopardizing water deliveries to the Lower Basin and power production through Hoover Dam.
6. Conversely, with a 5-year period of water availability 20% above the 2016-20 average (similar to what happened in 1996-2000), it would be possible to fill Lake Powell to 3700 by 2027, provided that outflows through Glen Canyon Dam are generally limited to 8.23-9.00 maf, rather than the larger releases that typically occur in such higher flow years in support of increasing the volume of Lake Mead.
What this all says is that the watershed is a highly dynamic system, and very sensitive to what happens in any five-year period. Long-range precipitation forecasts in the southwest are generally not optimistic, and for that reason, we need to prepare with open eyes for what might happen in if we see another period that matches what we saw in 2000-04. On the other hand, it really doesn't take much to turn things around--even a return to the period 2016-20 could work. We just don't know at this point, but need to think ahead to consider different possible outcomes.
If you want to read the entire analysis with all its mundane details, have at it. It's 13 pages long, and that's leaving out all the original spreadsheets. I'm going to guess there's about five of you who will want to read the whole report...
Here it is:
Rather than focus on the extremes to predict a future outcome, its sometimes helpful to focus on the average. The mundane. The ordinary year. And with that concept in mind, I wanted to figure out the answer to this question: What would it take to make Lake Powell rise again, and then stay there? To make the marinas, launch ramps, the Castle Rock Cut—all of the key recreational infrastructure—usable and viable for the long haul? And practically speaking, that means this: what would it take to keep the lake over elevation 3588? That’s the target elevation identified by Fill Lake Powell that would achieve those goals.
Figuring that out is a tall order, and depends on many factors, some of which can’t be controlled (like the snowpack), but some of which can (like water use). And of course to really solve that puzzle, you’ve got to consider the entire system—not just Lake Powell, but Lake Mead too. And the other smaller reservoirs. Not just water use in the Upper Basin, but all seven states and Mexico too. It’s complicated. But as with any complicated puzzle, it’s best to take it one piece at a time, and eventually you will fill in the blanks. Complete the picture. Solve the problem. Or at least identify what it would take to solve the problem. And from there, you can change the way things have always been done into the way they need to be done.
All that means, for our purposes, starting by focusing on Lake Powell. I’ll save Lake Mead and the Lower Basin for another day.
Where to begin? For all the numbers that can be run, the “what-if” scenarios that can be considered, it’s best just to simplify that challenge.
It’s basically just a simple question of inflow vs. outflow.
Let’s first consider outflow. For Lake Powell, there’s really three important factors to consider, but here’s the only one that really matters: USBR’s releases through Glen Canyon Dam. Sure, there is also a small amount directly used from Lake Powell by the city of Page, and then there are evaporative losses from the lake, but both are orders of magnitude less than what flows through the dam. And then, yes, there is the theoretical drain from future water diversion projects not yet online, and perhaps never will be, such as the proposed pipeline to St. George.
With the exception of evaporative loss, all those are controllable factors.
And then on the inflow side, snowpack (precipitation in general) is by far the most important issue, but unlike outflow through the dam, this is out of anyone’s control. There are also other important considerations: the amount of water diverted to serve the needs of the Upper Basin states, and the amount of water available for release stored in the reservoirs above Lake Powell. Unlike the snowfall, these are controllable factors.
In May 2022 the USBR issued its latest 24-Month Study, which forecasts inflows and outflows for all reservoirs affecting the entire Colorado River watershed. The forecast is based in part on projected long-range precipitation forecasts, historic trends, and projected releases from each reservoir. The forecast extends through May 2024, or roughly midway through Water Year 2024 (WY 2024).
Based on this, and other existing USBR documentation, I developed sixteen scenarios to model what could happen to Lake Powell depending on the various factors described above related to inflow and outflow. The most important of these factors is how much total water would be available in the system before anybody uses or stores it. In a simplified model, this number is possible to reverse engineer from existing reported data:
Total Water Availability = Inflow to Lake Powell + Upper Basin Water Use + Upper Basin Additional Storage + Upper Basin Reservoir Evaporation
My report goes into some detail about what those mean and the assumptions behind them, but I'll leave that to those interested in reading the full report.
And then there’s the question: what should be considered a baseline “average” year for modeling purposes? Is it the historic average inflow since Lake Powell came into existence? That seems too broad. Or maybe the period USBR focuses on to establish an “average” inflow, which is 1991-2020? Or should it be something more recent, reflecting the observed realities closer to our time? For example, the 5-year period 2016-20 was a very “average” time in the life of the lake. In terms of inflow, it featured two good years (2017 and 2019), two bad years (2018 and 2020), a pretty average year (2016). In all, the average inflow to Lake Powell during that time was about 8.99 maf, which is a little less than the USBR’s reported 1991-2020 average of 9.6 maf. Based on that, it’s reasonable to use the 2016-20 period as a more conservative “baseline average”, because it would tend to produce less optimistic results when projecting percentage increases (or decreases) from that baseline. It’s also a period where we have very detailed and realistic recent water use data for both the Upper and Lower Basins. For all these reasons, the period 2016-20 is what is used as the baseline “normal” for the purposes of this study.
Based on the assumptions described below, the Total Water Availability in the Upper Basin on average from 2016-20 was 13.6 maf.
What went into developing the various modeled scenarios? Were they just arbitrary? Spitting into the wind?
Sixteen scenarios were developed to predict what would happen to Lake Powell’s surface elevation through Water Year 2027 (WY 2027). Each of these varied one or more of the factors discussed above. In general, these scenarios considered a range of future Total Water Availability via snowpack, from 40% less than the 2016-20 average, to 20% more than average (something like what happened from 1996-2000). Within many of those scenarios, consideration was given to reducing existing Upper Basin Water Use anywhere from 5% to 50% in order to test the sensitivity of that variable and its effect on creating more downstream inflow potential to Lake Powell. Or increasing (or decreasing) flows from the upper reservoirs such as Flaming Gorge. Or varying the outflow through Glen Canyon Dam, although in general, I tried to adhere to existing USBR protocols for that. No effort was made to address Lower Basin water use or effects on Lake Mead in general. While those are extremely important considerations in the big picture, I left them for another time. But they are important.
And without getting into how the sausage was made, I'll cut to the key conclusions of the study, some obvious, some less so:
1. The most important factor in maintaining Lake Powell’s volume is total water availability, primarily through snowpack in the Upper Basin.
2. If the next 5-year period (WY 2023-27) matches the total water availability that occurred from 2016-20 (a very modest goal in historic terms), it is possible to achieve the target elevation of 3588 during WY 2025, although it would require a 5% reduction in Upper Basin water use during that time.
3. It is possible to achieve the target elevation of 3588 in WY 2025 even with a 5-year period with 5% less available water than in 2016-20. But it would require a 5-10% decrease in Upper Basin water use, and potentially additional releases from Flaming Gorge and other Upper Basin reservoirs that could further reduce capacity in those lakes.
4. In any scenario, reducing Upper Basin water use by 10% could add 400,000 AF to Lake Powell each year, which would raise the lake annually 5-6 feet by itself.
5. If the watershed sees a 5-year period of water availability similar to what occurred in 2000-04, which was about 40% less than the 2016-20 average, the outlook is grim. Only substantial reductions in Upper Basin water use and releases from upstream reservoirs (particularly Flaming Gorge) would allow Lake Powell to avoid hitting the dead pool elevation of 3370 in WY 2025. With this sort of 5-year flow regime, it would be impossible to avoid dropping below the minimum power pool of 3490, no matter what was done short of drastically reducing outflows through Glen Canyon Dam to the point of jeopardizing water deliveries to the Lower Basin and power production through Hoover Dam.
6. Conversely, with a 5-year period of water availability 20% above the 2016-20 average (similar to what happened in 1996-2000), it would be possible to fill Lake Powell to 3700 by 2027, provided that outflows through Glen Canyon Dam are generally limited to 8.23-9.00 maf, rather than the larger releases that typically occur in such higher flow years in support of increasing the volume of Lake Mead.
What this all says is that the watershed is a highly dynamic system, and very sensitive to what happens in any five-year period. Long-range precipitation forecasts in the southwest are generally not optimistic, and for that reason, we need to prepare with open eyes for what might happen in if we see another period that matches what we saw in 2000-04. On the other hand, it really doesn't take much to turn things around--even a return to the period 2016-20 could work. We just don't know at this point, but need to think ahead to consider different possible outcomes.
If you want to read the entire analysis with all its mundane details, have at it. It's 13 pages long, and that's leaving out all the original spreadsheets. I'm going to guess there's about five of you who will want to read the whole report...
Here it is:
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