No more Lake Mead?

[Tim Frank]

Re: No more Lake Mead?

A lake's surface area, relative to its volume, increases exponentially the fuller it is. So, you lose more water to evaporation per acre foot stored when a lake is full. Make no mistake. These behemouth lakes lose HUGE amounts of water to evaporation every year. They lose 12 times more water every year than they get in rainfall. That's 7 vertical feet lost to evaporation.

Not true....necessarily.
It depends entirely, or at least mostly, on the topography of the surrounding area.
Where the lake is constrained tightly like in a sheer-wall canyon, the actual "footprint" won't change that much as it rises....prairie lakes on the other hand are like "pee on a plate".....huge variance in area for small ioncrease in depth.
There might also be a thermal mass influence on evaporation because heat gain is proportional to surface area....heat mass to volume...a square function versus a cubic one.

As QC sAid, it is a complex issue.

 

[Tim Frank]

Re: No more Lake Mead?

Yeah, that's where I started, but I think it is not that simple . . . is the ratio constant at every altitude start point? Are there altitudes where a 20 ft. gain would mean that Mead gained surface area quicker as it rose?

You are right, it is not that simple.
The volume / area relationship will change for any number of reasons, as you say....depth, topography....and does thermal mass influence evaporation significantly in practice?
I am sure the regulatory agency involved would be happy to tell you what factors they consider in their water management plan.

 

[Drowned Rat]

Re: No more Lake Mead?

Not true....necessarily.
It depends entirely, or at least mostly, on the topography of the surrounding area.
Where the lake is constrained tightly like in a sheer-wall canyon, the actual "footprint" won't change that much as it rises....prairie lakes on the other hand are like "pee on a plate".....huge variance in area for small ioncrease in depth.
There might also be a thermal mass influence on evaporation because heat gain is proportional to surface area....heat mass to volume...a square function versus a cubic one.

As QC sAid, it is a complex issue.

Every lake on Earth is wider at the top than it is at the bottom. The relative surface area depends only on the steepness of the walls. But anyway...

 

[Tim Frank]

Re: No more Lake Mead?

Every lake on Earth is wider at the top than it is at the bottom. ...

Are you sure?.... I just always raise my eyebrows a bit when I see the word "Every" ....
Guess if there was one, it wouldn't last long....gravity always wins.

The relative surface area depends only on the steepness of the walls. But anyway...

Yup, in general terms it's proportional to the tangent of the angle of the walls....but at 45 degrees you are at the balance point....steeper than that and volume is the increasing variable, below, and it is area.
But I have no idea how big a factor that volume versus area ratio is when compared to other considerations....just not my area of expertise.

 

[QC]

Re: No more Lake Mead?

But my point was only that from some points to some other higher point that Mead may increase in surface area quicker despite the fact that Powell's surface is larger when they are both full. In this discussion, I was contemplating the various benefits of filling Powell faster or visa versa. My contention that filling Powell first allowed for longer storage as it was higher and could be used twice is offset by the potential for higher evaporation rates. However . . . If Mead was nearing full pol, and Powell was relatively lower, then there are points where continuing to fill Mead may result in higher overall system evaporation rates . . . So again, as Tim noted, very complex. I believe Power Generation makes the case for filling Powell while Mead even drops a little.

And who pisses on a plate? Honestly?

 

[cheburashka]

Re: No more Lake Mead?

and global warming has recently been replaced by the notion that it is getting colder......russian scientists are calling for an ice age......

so i guess youll need a set of sno skis to pull behind a dry lake wind surfer..........

Ugh! The things you guys say in the name of "truth." AFAIK there's one Russian scientist calling for an ice age and no one gives him much credence. Yet you describe it as "global warming has recently been replaced by the notion that it is getting colder. . ." How does one crackpot from Russia equate to a replacement of the entire theory? Next you'll be telling me that the Creation Museum has replaced the notion of evolution!