I have a question about the elevation numbers on the TVA Reservoir Information web page. Below the Discharge Schedule there's a list of "Observed" measurements. The first column in the Observed panel is headed "Upstream Elevation" and the second column is headed "Downstream Elevation". Assuming that the "Upstream" figure represents the impounded water level, my question is this: Where exactly is the "Downstream" level measured?

Is the water measured at the base of the dam or some unspecified distance downstream from the face of the dam?

In the case of Norris, for example, today's chart shows a downstream elevation of 820.78 (feet above mean sea level) immediately prior to generation, and a measurement of 824.61 (feet above mean sea level) at the height of generation. According to yesterday's historical data it will take between six and seven hours for the water level to return to near 820.78 --- where?

I understand this is downstream from Norris Lake, but how far downstream? I'm having a hard time believing that it takes 7 hours for the water at the base of the dam to completely fall out. (Of course I've never stuck around to see how long it takes 'cause I usually bug out and head down to the jail when the siren blows.)

If it is farther downstream, how much farther? A mile? a nautical mile? Does it really take 7 hours to clear out enough to cross the weir dam?

Gerry Romer