Long answer? Re: The Cause of River Flow


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Posted by Kerry Grissett on September 07, 2006 at 22:53:42:

In Reply to: The Cause of River Flow posted by Driftfishing on September 06, 2006 at 16:13:00:

Dam effect on current flow is more extreme when near either the upper or lower end of a TVA lake.

Current flow at the middle of TVA lakes is harder to predict. In general, the best or most current flow in the middle of a given lake will be when the spillways for both dams are open. However, this would mean flood conditions.

Given only discharge from the turbines at the dams (normal oprations), the best or most current flow in the middle of TVA lakes in Alabama is when both dams are generating (discharging from the turbines) at high levels. This is only for the main river channel(s).

Streams and tributary current flow is even harder to determine. Streams that have a high inflow of water from upstream *may* have good current in all conditions. However, many streams and tributaries, especially during dry or drought periods, are at the mercy of the lake level concerning current flow. That is to say, if the lake is rising, some streams may actually flow backwards. When the lake is falling they will have downstream flow, i.e. Flint Creek.

There is also a "tidal effect" caused by the releases at the dams. This is, in effect, a wave. When the dam at the lower end of a lake starts discharging water, this causes a depression in the water level just above the dam which creates a wave which moves upstream. Similarly, a dam at the upper end of a lake can cause a wave moving downstream. The effect of either of these waves can cause tributary streams to flow or backup, depending on the location of the wave. These waves can take several hours to "smooth out".

Lakeinfo.tva.gov is the link to use for observing the lake levels on all TVA lakes. The main screen for lake levels and discharges has 3 parts.

1. Predicted times for discharges and number of turbines in operation.

2. Observed lake levels and discharge amounts. This is measured below the named dam and above it.

3. Predicted levels: this part tells you not only the predicted schedule of how much discharge this particular dam will have, but it also lists the daily average "inflow". This usually relates directly to the discharge from the next dam upstream. The difference in outflow and inflow along with the predicted downstream levels should help you determine current flow and lake levels.

I said this was the long answer and I am sure I haven't answered all questions about current and lake levels, but it really takes watching the data and being out on the water to get a feel for what you will find given a particular prediction from TVA.

Nothing beats being there, observing and making your own theories.

TVA lake information page: http://lakeinfo.tva.gov

Wheeler Lake info page: http://lakeinfo.tva.gov/htbin/lakeinfo?site=WEH&DataType=All&SUBMIT=View+data

Gunterville Lake info page: http://lakeinfo.tva.gov/htbin/lakeinfo?site=GUH&DataType=All&SUBMIT=View+data

The TVA operating guides are also availble using these links.

Good luck and good fishin'

P.S.

I was working on a reply that may or may not have been better or more detailed, but my dinosaur computer locked up and I lost it all. This is actually a shorter compilation written "under duress" thinking it might happen again. ;(



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