10 July Upper End Report

[Longball22]

I'm working a night shift right now, and have too much time on my hands....

http://conservancy.umn.edu/handle/11299/113341 This is not a good read by the way, haha.

"The water in a river flowing into a reservoir, lake or coastal region is rarely of ~xactly the same density as the ambient water in the waterbody. The density difference may be due to a difference in temperature or in concentration of dissolved or suspended substances. Small density differences can have dramatic effects on the flow patterns that develop in the waterbody. In particular, when the river water is denser than the ambient, I the incoming flow dips beneath the ambient water and flows along the reservoir bottom or beach as a density current. Such flows are termed plunging flows. Figure 1-1 shows a plunging flow situation over a sloping bottom with various aspects of the flow illustrated. The position on the water surface where the flow actually plunges is known as the plunge point or plunge line. It will frequently be delineated by a collection of floating debris held by the reverse current generated in the ambient water by the plunged flow. After plunging, the flow becomes a density current underflow. The dynamics of such currents are reasonably well understood [Ellison and Turner, 1959]."

So, my interpretation is cooler water entering at the river arms is cooler than the water in the main lake, and it is creating the "plunging current" described above. They 84 degree water temps that have been described are definitely warmer, and this could create the reverse current described. If anyone saw open water with an isolated section of debris, this would support this.

This theory would also explain why some of you have seen that the thermocline hasn't broken up. The cooler water is simply moving underneath the warmer water, because it is more dense than the warmer main lake water.

If this is all true, that would mean there could be some highly oxygenated water running deeper in the lake right now. Everyone might be looking too shallow.

I should have paid more attention in my fluid mechanics classes in college.....

[Sore Thumbs]

Good stuff. I learn something new everyday. Today I learned two things. The other was that you could actually spend $35 for four hot dogs,four bags of chips and a Coke at Disneyland. Man what a rip off.

[5bites]

That is very interesting. It doesn't quit explain why it changed from one day to the next but it sure can't be ruled out. That is unless the upper water had warmed up by Sunday.

[merc1997 Bo]

I question the theory of backward current 40 miles or so from the dam. This is a very slow-moving current to begin with, so I don't see how it can "bounce back" 40 miles.

it is not any different that if you take a long narrow trough with water in the bottom and tilt slightly length wise and set back down. how long does that water go back and forth before ever being quiet again?? now, with 40 miles of water, just how much energy is all pushing up to a stop, and then bouncing back in the other direction??

why do all the big boat wakes bounce back all the way across the lake? equal and opposite reactions apply here.

anyway, when i am suspecting to be dealing with current in the main lake, i keep a weighted line, with a piece of light cloth material on it. i can lower it into the water and watch the cloth for water flow direction and amount of current. it works the same for hunting slack water areas to look for bass that want to get out of the current. a mass of water going down an impoundment travels a bit differently than one might think. good reason for the string and cloth. one other thing to consider is direction of retrieve when fishing an area in the current. quite similar to river fishing.

bo

[merc1997 Bo]

I'm working a night shift right now, and have too much time on my hands....

http://conservancy.umn.edu/handle/11299/113341 This is not a good read by the way, haha.

"The water in a river flowing into a reservoir, lake or coastal region is rarely of ~xactly the same density as the ambient water in the waterbody. The density difference may be due to a difference in temperature or in concentration of dissolved or suspended substances. Small density differences can have dramatic effects on the flow patterns that develop in the waterbody. In particular, when the river water is denser than the ambient, I the incoming flow dips beneath the ambient water and flows along the reservoir bottom or beach as a density current. Such flows are termed plunging flows. Figure 1-1 shows a plunging flow situation over a sloping bottom with various aspects of the flow illustrated. The position on the water surface where the flow actually plunges is known as the plunge point or plunge line. It will frequently be delineated by a collection of floating debris held by the reverse current generated in the ambient water by the plunged flow. After plunging, the flow becomes a density current underflow. The dynamics of such currents are reasonably well understood [Ellison and Turner, 1959]."

So, my interpretation is cooler water entering at the river arms is cooler than the water in the main lake, and it is creating the "plunging current" described above. They 84 degree water temps that have been described are definitely warmer, and this could create the reverse current described. If anyone saw open water with an isolated section of debris, this would support this.

This theory would also explain why some of you have seen that the thermocline hasn't broken up. The cooler water is simply moving underneath the warmer water, because it is more dense than the warmer main lake water.

If this is all true, that would mean there could be some highly oxygenated water running deeper in the lake right now. Everyone might be looking too shallow.

I should have paid more attention in my fluid mechanics classes in college.....

i am sure this will apply when a good flowing tributary is entering the main channel. however, when i have observed the current going down stream any place on the lake, and they shut off the water flow, you experience a small slack water period, and then the current starts running upstream that kind of eliminates plunge point current.

at any rate, to be successful, one has to acknowledge and adjust to current whether it is going downstream or upstream. when they have really been running lots of water and then shut the flow off, you will see and experience that same upstream current several miles up a big cove or river arm of the lake.

bo

[glennL]

i believe the wind also happens to play havoc with the current. Many times fishing, i can go around a corner and the water is flowing a whole different way. So, between the current and the wind, that may have something to do with how all the logs end up in one area. But that is just a guess. 40 miles from the dam, sounds like a stretch to be impacting current.

[5bites]

The lake was slick flat calm in the mornings. You're forgetting that beaver pushes water in as well as table rock dumping out. I've seen current lots of times visible on stationary objects and by my bait drifting down stream. This time it happened to be going the wrong way. Why does distance from the dam matter? When water is moving it doesn't matter where the dam is.