What Changes When We Hit 3,525?

Ed_on_WD

Well-Known Member
At the current rate, we're only 2 weeks away from a lake level of 3,525. That is where the lake level drops into the "safety buffer" for power generation, right?

Will the BOR release water from upstream? Will they cut releases from the dam (and make up for it later, once the runoff starts)? Will they cut back on power generation, except for (maybe) "peaking"?

Has anybody heard what the plan is?
 

SDuncan

Active Member
Pure speculation here, but my guess is a reduction in release will be the initial move. The problem with that is it will immediately show up downstream as an increase in the rate at which the level of Lake Mead drops. Mead's up almost 2' from Dec 1st, but has dropped 0.4' in the last two weeks. If releases from Powell are reduced enough to hold the lake steady, then Mead may well start to plummet. For sure, one of them has to give until and unless the spring runoff comes to the rescue - which frankly isn't looking too good as the snowpack is just under 91% of the average for the past 7 years, which itself is below the average since the GCD was completed. I didn't see the releases from the upstream reservoirs make all that much of a dent in Powell last year, so I wouldn't expect much help from there this year but I don't know what else they can do.

I think the situation is rapidly coming to the point that it's all up to nature - there's just not much left, at least in the short-to-medium term, that will allow holding both Powell at 3525 and Mead at 1065

3525 is hard-stop target for Powell, by which I mean the BOR would very much prefer not to let it drop below that. Anybody know what the BOR's equivalent level is for Mead?
 

Colorado Expat

Well-Known Member
When we hit 3525 the lake will just keep on going down. The most recent 24-month study from BOR projected the lake level falling to 3522 by April of this year, and that did not factor in the dry February that we just had. In addition, a recent study from Utah State University found that the Bureau's 24-month studies have tended to be overly optimistic in terms of predicting runoff and lake levels, due to inherent statistical biases. Given the current state of the snowpack at 91 percent of normal, and rivers upstream of Lake Powell running at 55 percent of the long-term 1 March average, it would seem that even 3522 might be optimistic.
 

Neil

Active Member
Mead at 1050. Sets off panic then. I believe the plans is to try to hold Powell at 3525 and keep Mead above 1050, then hope spring runoff starts
 
The dam’s hydroelectric intakes are at 3,470 feet above sea level, but as the reservoir level drops below 3,525 feet the risk of equipment damage increases due to the possibility of air passing through the turbines.
 

Richp47

Active Member
Seems like they would be looking for an engineering solution -- some way to smooth out intake flow to avoid the air problem at these marginal levels.
 

Jr B

Active Member
It sounds like whatever they do with the Executive Services Ramp this year, it still won’t be available this year. Just a guess. My Squirrel brain thinks that the lake would have to rise about 15’ before it will be usable. Thoughts? Sq
Hi Squirrel - Following is what was communicated last week by NPS on the Executive Services ramp extension at Bull Frog: This construction contract includes regrading and permanently extending the Bullfrog North Ramp to potentially reach a lake elevation of 3525 feet. (The amount of extension that is possible will be dependent on the lowest water level reached before spring runoff begins, as no construction will occur in water.)

The way I read this is that they will extend the ramp to the lowest level before it starts to rise, so the ramp should be usable prior to the lake dropping this summer. Now what I don't know is how many feet does the lake need to rise before the ramp to be "usable". For example if you have houseboat being launched/pulled how much concrete needs to be extended in water for the trailer not to get stuck..
 

Eagle Rock

Active Member
The dam’s hydroelectric intakes are at 3,470 feet above sea level, but as the reservoir level drops below 3,525 feet the risk of equipment damage increases due to the possibility of air passing through the turbines.
And yet the dam operated for 8 consecutive months when lake elevations were between 3490' and 3494' (8/16/64 through 6/15/65). Makes me think there is an awful lot of (unnecessary?) caution in the asserted plan to try and hold at 3525'. Further evidence: The 24 month forecast currently shows lake elevations below 3520' for all of Feb-April 2023, and parts of Jan and May 2023 as well (https://www.usbr.gov/uc/water/crsp/studies/24Month_02.pdf), and there have been no anguished press releases about having to shut down the powerplant for 3-4 months less than a year from now.

Bottom line, to directly answer the original poster's question as to what changes when we hit 3525': Not much.
 

drewsxmi

Escalante-Class Member
The 3,525' elevation is kind of a warning track for hydroelectric operations, but they have been able to generate power down to 3,490' in the past, as Eagle Rock pointed out above.

The 3,525' elevation is also a "balancing tier" affecting the operations of Lakes Powell and Mead. I'll defer to somebody who understands full USBoR speak, but when Lake Powell stays below that level for some period of time, or is forecast to be below that level, then the USBoR is supposed to "balance" the water storage in Lakes Powell and Mead. Since Lake Mead is around 35% of capacity, that might mean dropping release levels well below the 7.5 maf / year level, and putting the hurt to Lake Mead.
 
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Rainbowbridge

Escalante-Class Member
And yet the dam operated for 8 consecutive months when lake elevations were between 3490' and 3494' (8/16/64 through 6/15/65). Makes me think there is an awful lot of (unnecessary?) caution in the asserted plan to try and hold at 3525'.
I've always wondered when/what elevation did they actually start running the turbines, was it in '63?.....and if/when the levels lower....do they run them slower for less vortex? Does slower work for power generation?

Inquiring minds, ya know.....:unsure:
 

Cookie

Well-Known Member

spidarcus

Active Member
I was just wondering what the lake elevation would be if there wasn't any sediment. 5 feet lower? Need a math wizard to answer this. How much is the sediment currently raising the lake level? (Perhaps the one benefit of sedimentation - during a drought.)
 

Eagle Rock

Active Member
I was just wondering what the lake elevation would be if there wasn't any sediment. 5 feet lower? Need a math wizard to answer this. How much is the sediment currently raising the lake level? (Perhaps the one benefit of sedimentation - during a drought.)
I can give you an upper bound and a lower bound, and the reasons why they are just bounds, with the real number in between.

Lower bound: On 2/27/22 (2 days ago) and on 1/1/68 the lake was at the exact same elevation, but the reported storage differed by 173000 acre-feet (173 KAF; source: http://lakepowell.water-data.com/index2.php?elevation=3527.18). Prior to 1/1/68, a similar comparison shows sediment inflows below elevation 3520' were about 10 KAF/year. So that implies total sedimentation below the current lake level, since the dam began operating in March 1963, has been about 173 + 4.8*10 = 221 KAF. Between 2/23/22 and 3/1/22 the lake dropped exactly one foot, and storage decreased by 62 KAF. So 221 KAF corresponds to a little over 3.5 feet (221/62 = 3.56).

The reason that 3.5 feet is a lower bound is that the relationship between lake elevation and storage stopped being updated for sedimentation after the late 1980s. So that 173 KAF decrease in storage below the 3527' level from 1/1/68 to 2/27/22 is really only the decrease from 1/1/68 to around 1/1/87. An upper bound estimate would assume 173 KAF of sedimentation per 19 years (the 1968-87 rate) and then extrapolate forward to 2022. That would be an upper bound because a lotof the sedimentation post-1987 has ended up in the upper reaches of the lake, above the 3527' contour, so the post-1987 rate of sediment ending up below 3527' has presumably been lower than the pre-1987 rate. So with that warning:

Upper bound: Assume the sedimentation of 173 KAF below 3527' was just for 1/1/1968-1/1/1987. That gives an annual rate of 173/19 = 9.1 KAF/year, which is close to the ~10 KAF/year at below 3520' for the 1964-1968 period. Then 4.8 years of 10 KAF/yr (pre-1968) plus 54.2 years of 9.1 KAF/yr (1/1/68 to March 2022) gives a total of 541 KAF of sediment below 3527'. At 62 KAF per 1 foot of lake elevation at the current reservoir level, that corresponds to 8.7 feet.

Bottom line
(pun intended): If there had been no sedimentation since 1963, but everything else exactly the same, the lakeelevation would currently be 3.6 - 8.7 feet lower. Your 5 foot guess is quite reasonable!!
 
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