It's actually not supposed to get as hot today but I thought this was interesting. With past couple days of temperatures reaching the low-century mark, folks need to be careful with fires. Wind, low humidity and high temps will increase the danger for what has been a fairly mild fire season for us in Montana. We do have about a dozen fires right now, most of which are in Western Montana but that could all change in a heart-beat. We've been fortunate unlike states like California, Colorado, Arizona, and Idaho.
So what has the heat done for the fishing, you might ask? Well, right before this last heat wave, the fishing was off the charts. Epic trico hatches in the morning were causing fish to look up well past the typical 1pm threshold. That is, up until yesterday. It felt like yesterday was the tipping point where the heat got the best of the fish and they decided to duck for cover. But there could be another reason for that, that goes beyond just the summer heat. Check these charts out.
I don't claim to understand the approach the USGS in coordination with FWP and Northwestern Corporation takes in managing the reservoirs out here in Montana. Like I've said, I think they did as good of job as they could have this spring, although it kind of sucked for the fishing. The up and downs of flows and the early increases really had an impact on dry-fly fishing especially. But at least, one could understand why they were doing it. We had a ton of snow-pack and some really heavy rainfall that had they managed the water more conservatively, folks in Great Falls would have been screwed. There was flooding but it could have been much worse. What I don't understand is 5,000 cfs now.
I know what a lot of you are thinking. "High water in August is great!" Well...
The Missouri River isn't your typical tail-water. A tail-water is essentially just a river that's regulated by a dam. In most tail-waters, the majority of the water comes out of the bottom of the reservoir, keeping the river below the dam at a cold and consistent temperature. Water coming out of the bottom of a deep reservoir could be as cold as the upper 30's or at least lower 40's even into August. That's why those fisheries remain healthy and fish are happy. Bugs are plentiful and life is good. However, the Missouri River is a different beast in that because it's a hydro-electric dam that doesn't really serve that many households, they only need to release around 2,800 cubic feet per second to meet the demand and anything above say, 3,000 cfs comes from the spill-over at the top of the reservoir. In fact, I'm pretty sure the capacity for water flowing out of the bottom of the dam is somewhere in that range. You just can't push anymore water through it.
I did a little research on this and read on the Wikipedia site for Holter Dam, that in 2004, they were only allowing about 3,000 cfs out of the dam. The optimal flow for the health of the river was suggested to be 4,100 cfs. I've seen it as low as 2,900 cfs, I believe in 2014. I tell you what, the fishing was really good that year, even with the low water. I would suggest it was because all of the water supplying the lower river was coming from the bottom third of the reservoir. But what happens in August when the water is relatively high?
When the air-temps reach triple digits for a few days, after being consistently in the 80's for the majority of the last month, the surface water temps on the reservoir have to increase. Now if you remember your geography classes from junior high, you know that water temps remain more consistent than ground temps. As the sun beats down, it has more of an impact on the ground than on the water. What that also means is that as the sun goes down, the ground temps drop more than the water temps. Consequently, as the water temps increase, even with the air temps dropping at night, water retains more of its heat.
Do the math. If you have twenty percent more water coming into the river from the surface of the reservoir that consists of warmer water; water that might be reaching temps into the upper 80's, what do you think that does to the water temps below the dam? If you look at the charts above, you see that as the water levels increase, so too does the water temperature. It might only be a degree on average but that degree has a significant impact on the fishery at 69 or 70 degrees Fahrenheit. In fact, if the temps reach 70 degrees for a few days straight, FWP will start to impose closures.
So back to the question: Why are they increasing the flows right now? I don't know but I would tend to believe that if they want to do what's right for the fishery, they would bring those flow back down to around 4,000 cfs.
Keep 'em where they live...
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