What the Wier!

I was reading the 178 page master plan for Truman lake and found this:
"A submerged rock weir (skimming weir) is present at Harry S. Truman to prevent low dissolved oxygen (D.O.) in hydropower releases during peak stratification periods during summer months. “Skimming weirs” function as an underwater dam which create an impermeable wall to prevent release of low D.O. water from below the thermocline (Figure 4). They have been very successful at Kansas City District hydropower lakes, although all both projects report decrease in temperature and dissolved oxygen of releases when thermocline elevation exceeds the top of the weir. During the flood year of 2019, Truman Lake surface elevation exceeded the multipurpose pool elevation by 34 feet. Consequently, thermocline elevation measured during monthly water quality profiles, exceeded the crest of the skimming weir from June-September with peak 20 feet above the weir in June (Figure 5). During the worst case of low dissolved oxygen release during June 2019, approximately 51% of the water volume flowing over the skimming weir during 60,000 CFS flood release was composed water from the bottom layer. The minimum dissolved oxygen measured below Truman Dam (site HT-1a) in flood year 2019 was 6.4 mg/L in September while temperature measured below Truman Dam from the mixing zone (site HT-1A at fishing access pier) was 1.3°C lower than surface value measured at site HT-1 between skimming weir and dam."
Attachment 480030

Good information. Pretty cool.

Interesting but Help Jake, What's this mean to us? :dono

Interesting read

Very interesting, shame they did not have that tech for Beaver, Table Rock, Bull Shoals and Norfork Dams, would be very beneficial for the trout fisheries below those dams.

Very interesting for sure. Had to read it twice to get a grasp on the idea. Thanks for sharing

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Originally Posted by grizwilson

would be very beneficial for the trout fisheries below those dams.

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I was thinking the same thing, don't help Truman but helping LOZ I guess?

Quote:

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Originally Posted by grizwilson

Very interesting, shame they did not have that tech for Beaver, Table Rock, Bull Shoals and Norfork Dams, would be very beneficial for the trout fisheries below those dams.

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I don't know about the others, but if Table rock had one, the discharge waters would be too warm for the trout. Right?

Am I reading it wrong? I thought it's saying the water was COLDER (by 1.3ºC) at the fishing access pier than between the skimming wier and the dam. That means the trout would be in COLDER water, no?

I thought the fishery BELOW the dam would be oxygen poor, negatively affecting the fish population moreso than the temps? I think the fish can withstand more temperature swings than just 1.3ºC, but lack of oxygen can have a much worse effect, likely on the whole ecosystem.

Or I'm reading it wrong.

Interesting read, never seen this before. Makes sense though, at normal levels with no spillway action to oxygenate the water, any water through the dam would be used for power generation above the thermocline. Wouldn’t think temperature would be much of an issue.


Sent from my iPhone using Crappie.com Fishing mobile app

And all this time I thought it was because they did not want to remove the old roadbed where the bridge was.

I expect a full report by 8pm - Enjoy! :cheers2

The Downside of Dams: Is the Environmental Price of Hydroelectric Power Too High? | Scientific American

According to the Hydropower Reform Coalition (HRC), a consortium of 150 groups concerned about the impact of dams, degraded water quality is one of the chief concerns. Organic materials from within and outside the river that would normally wash downstream get built up behind dams and start to consume a large amount of oxygen as they decompose. In some cases this triggers algae blooms which, in turn, create oxygen-starved “dead zones” incapable of supporting river life of any kind. Also, water temperatures in dam reservoirs can differ greatly between the surface and depths, further complicating survival for marine life evolved to handle natural temperature cycling. And when dam operators release oxygen-deprived water with unnatural temperatures into the river below, they harm downstream environments as well.


Temperature
Water held in reservoirs tends to heat up, increasing the temperature of the river. Salmon and steelhead prefer cool water. However, water on the bottom of the reservoir remains cold through the summer. If cool water is taken from the bottom (some dams cannot do this) it may actually be used to help keep the river cool through the summer.

Total dissolved gas
Falling water, such as from a dam spillway, may mix nitrogen from the atmosphere into the water. Water can only hold a certain amount of nitrogen, when this is exceeded, bubbles form. These bubbles can also form inside the bodies of fish which are swimming in the water causing injury or death.

How Dams Affect Water and Habitat on the West Coast | NOAA Fisheries

Oxygen
Water released from the bottom of the reservoir is often low in oxygen, causing problems for fish downstream. However, water falling over a spillway may actually mix more oxygen into the water.

Toxic substances
Sediment settles out in reservoirs behind dams. Many toxic substances may be trapped in these sediments such as pesticides, or heavy metals from mine tailings. If these sediments are disturbed these substances may be released into the water.

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Originally Posted by Joedog

Am I reading it wrong? I thought it's saying the water was COLDER (by 1.3ºC) at the fishing access pier than between the skimming wier and the dam. That means the trout would be in COLDER water, no?

I thought the fishery BELOW the dam would be oxygen poor, negatively affecting the fish population moreso than the temps? I think the fish can withstand more temperature swings than just 1.3ºC, but lack of oxygen can have a much worse effect, likely on the whole ecosystem.

Or I'm reading it wrong.

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So the deep water with less DO is also much colder. The weir forces the warmer surface water with more DO to be discharged through the dam.
Table rock has no weir and the discharged water is around 50 degree. Seems like they have big concrete rip rap things the froth the water up before it reaches the hatcheries increasing DO.

Even with a Weir I would expect the discharge water to be cooler than the surface temp above the dam, which would account for the 1.3c.

I think :dono