Tully DH: cool H2O could be exhausted a little earlier this year

[Mike]

With the water temp at the USGS gauge being slightly over 72 F this morning (the target for the dam operator is 68 F at 8 AM) and not having fallen much overnight last night, plus corresponding increase in discharge since yesterday, I could see the reservoir running out of cold water a bit earlier than the more typical July 22 to Aug 1 time period this year.

 

[afishinado]

Thanks for the info, Mike.

Wow! The ACOE made a "cold water" release and the Tully temp went Up! (see charts below)

Put a fork in it! :-(

 

[salvelinus]

I believe when they release after a rain event to maintain the summer pool level, the additional flow does not come from the bottom, hence the temp increase.

 

[afishinado]

salvelinus wrote:
I believe when they release after a rain event to maintain the summer pool level, the additional flow does not come from the bottom, hence the temp increase.

If that's the case, a top-water release when the temps are high wasn't very wise.

 

[Swattie87]

afishinado wrote:

salvelinus wrote:
I believe when they release after a rain event to maintain the summer pool level, the additional flow does not come from the bottom, hence the temp increase.

If that's the case, a top-water release when the temps are high wasn't very wise.

Rock and a hard place type deal. If you release more from the bottom to lower the pool after a Summer rain event, you'll theoretically blow through the cold water reserve faster, and create a longer time period without cold water until temps drop in the Fall. As opposed to running off the top, and temporarily warming temps now, but saving some cool water for later. I don't pretend to know which is overall better for the fish, but you're kind of in a not great situation either way...There's only so much cold water in the bank to spend.

 

[afishinado]

Swattie87 wrote:

afishinado wrote:

salvelinus wrote:
I believe when they release after a rain event to maintain the summer pool level, the additional flow does not come from the bottom, hence the temp increase.

If that's the case, a top-water release when the temps are high wasn't very wise.

Rock and a hard place type deal. If you release more from the bottom to lower the pool after a Summer rain event, you'll theoretically blow through the cold water reserve faster, and create a longer time period without cold water until temps drop in the Fall. As opposed to running off the top, and temporarily warming temps now, but saving some cool water for later. I don't pretend to know which is overall better for the fish, but you're kind of in a not great situation either way...There's only so much cold water in the bank to spend.

No right or wrong answer, but since it's a reality that's it's hot right now, I would choose to cool the water now. No one can predict the conditions later in the summer, it may cool down. If it doesn't you're no better or worse off than you are right now.

Plus Mike, who was interacting with the ACOE until recently believes the cold water is spent.

 

[outsider]

I've seen this happen many times in the past when the flow increased the water temp increased. Then when they dropped the flow they bottom released. This happened a week or so ago when we got a storm here. Hopefully they did not run out of cold water yet.

 

[Mike]

The lowest gate has a volume limitation. I forget what it is, but it is not great. If because of the need to quickly reduce the surface elevation following a summer storm the ACOE needs to release more than the amount that the lower gate is capable of handling, then they release the additional water from the upper gate. There is no mid-level gate, although I was once told by a dam operator that there is a designated location where one could have been installed, but it was considered too expensive. The upper gate is somewhere around 15 ft or so down from the target summer surface level of 290 ft elevation. Outsider is correct in his observation and now you have an explanation that applies to the summer months.

 

[outsider]

It's Thursday 1:40 PM, and the temp is 68 degrees.

 

[afishinado]

As Mike wrote in his OP, late July to early August is normal for the Tully low temp to read over 70*F and the highs in the low to mid 70's.

The high temps this weekend will likely push the temps up to lethal levels for the trout.

Here is 2019 >