River flood stage?

[TRIGGER]

The Cumberland river in Clarksville is at 40.1 at the moment. Where does the 40.1 measurement come from? Just curious.

 

[TennSportsman]

I'll take a stab....the hashmarks on the bridge supports?

 

[TRIGGER]

I'll take a stab....the hashmarks on the bridge supports?

Those are a reference for the barges to know how much height they have between the water and the bridge. The higher the water gets the lower that number gets unlike the flood stage numbers.

 

[WTM]

lol posted in wrong thread. providence rd bridge guage going toward ft cambell.
click the link and zoom in on the map and hit river observation.

https://water.weather.gov/ahps/forecasts.php

 

[TennSportsman]

makes sense

 

[TRIGGER]

lol posted in wrong thread. providence rd bridge guage going toward ft cambell.
click the link and zoom in on the map and hit river observation.

https://water.weather.gov/ahps/forecasts.php

I should have been more clear. The river it at 40.1' from what? Where is the 0' measurement taken from?

 

[WTM]

lol posted in wrong thread. providence rd bridge guage going toward ft cambell.
click the link and zoom in on the map and hit river observation.

https://water.weather.gov/ahps/forecasts.php

I should have been more clear. The river it at 40.1' from what? Where is the 0' measurement taken from?

from whatever measurement they decided to set the datum(lowest measured level). i believe there is also a measurement where sea level comes into play.

 

[WTM]

i think TVA reports theirs as ft above sea level as well.

 

[Andy S.]

0' on that gage corresponds to elevation 330.9'. So a 40.1' on the gage corresponds to an elevation of 330.9 + 40.1 = 371.0' water surface elevation at the gage. That is the thing I would want to know, for reference to surrounding elevations and base floor elevations.

 

[TRIGGER]

0' on that gage corresponds to elevation 330.9'. So a 40.1' on the gage corresponds to an elevation of 330.9 + 40.1 = 371.0' water surface elevation at the gage. That is the thing I would want to know, for reference to surrounding elevations and base floor elevations.

Thank you. Do you know why 330.9 was designated as the zero?

 

[Andy S.]

0' on that gage corresponds to elevation 330.9'. So a 40.1' on the gage corresponds to an elevation of 330.9 + 40.1 = 371.0' water surface elevation at the gage. That is the thing I would want to know, for reference to surrounding elevations and base floor elevations.

Thank you. Do you know why 330.9 was designated as the zero?

Not exactly, possibly a historical low water mark or something like that. I'll dig around and see what I can come up with.

 

[catman529]

USGS gage height is measured at various locations, usually bridges, and from what I've seen observing the USGS stations around my area, it's a metal pipe going down the bank into the bottom of the river. I'm assuming the river height is measured off the bottom of the river wherever the pipe goes in. TVA on the other hand does sea level height.


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[WTM]

like i said before, lowest possible point near the river bottom, BUT this may not be true at every gauge. i think some folks got lazy at some guages and just set some arbritary point.

https://water.usgs.gov/edu/qa-measure-streamstage.html

 

[Cardinalskyhawk]

I'm not sure but I do know that some gauges on the Mississippi River will occasionally be negative numbers.

 

[Andy S.]

Some datums (0 on the gauge) have historical significance, like nearby benchmarks and such, while others are more arbitrary in nature. See this NWS link for their explanation:

https://www.weather.gov/ctp/NegativeRiverStages

 

[TRIGGER]

Some datums (0 on the gauge) have historical significance, like nearby benchmarks and such, while others are more arbitrary in nature. See this NWS link for their explanation:

https://www.weather.gov/ctp/NegativeRiverStages

Thank you for all of your information.