What does the riverstage numbers mean?

Question

i know its a measurement of how high the water is but where do they get the number from? i know in new orleans the flood stage is 17ft. thats 17ft from what? where is 0ft at. and dont say sea level because if that was the case, the river from greenville to memphis would be flowing backwards due to the gauge in greenville says 44ft and in memphis says 25ft.

57 minutes ago - 3 days left to answer.

Additional Details

37 minutes ago

if it were taken from the bottom river, the river would be empty when it gets to 0, ive saw it in the negative before and ships are still able to go up the river.

and there is no lock and d**n on the river in N.O. im a towboat pilot on the mississippi

Answer 1

Here is a good description of River Stages and Flood Stages.

River Stage:

A site-specific measurement of river-level referenced as the height in feet above a designated zero reference point, called the gauge zero, at the site. The zero reference point is sometimes, but not always, chosen as the elevation of the river bottom. Normally, stage values are always positive. Drought conditions could cause the river level to fall below gauge zero, and the stage reading at that time would be negative. Since each gauge was established independently at each location, the stage reading is good for that location only and cannot be compared to other locations. For example, a stage of 30 feet at Fargo, N.D., cannot be compared to a stage of 30 feet at Grand Forks, N.D. The only way direct comparisons between two gauges can be made is by converting river stage to elevation by adding the stage to the gauge zero elevation.

Flood Stage:

The National Weather Service, based on the desires of the local community, establishes the “flood stage” gauge height for any given community. The flood stage gauge height is often the stage where damages begin to occur. Many communities desire to use the flood stage gauge height as an early warning alert, prior to the onset of significant damages. Significant damages may not occur until river levels are several feet above flood stage. Additionally, conditions along some rivers may have changed since the gauge and flood stages were established and reaching the flood stage may or may not result in actual flooding. Again, stages are site-specific, so feet above flood stage at one location can’t be compared to another.

Both these paragraphs are from:

U.S. Army Corps of Engineers in Kansas City District

http://www.nwk.usace.army.mil/Flood2007/...

Answer 2

How do you measure water in lakes and rivers?

→Water levels are read manually by gauge readers or continuously recorded either electronically or on graph paper or in digital form.

→Rate of flow (or discharge) requires multiple measurements of channel depth, width, and flow velocity to yield the average discharge in the stream crossing for a given water level. Measurements can be made electronically from a bridge, by wading into a stream, by boat, or from a cableway strung across the river. In winter, the measurements are made through the ice.

→With sufficient measurements of flow over a variety of water levels (including extreme lows and highs), a water level-discharge relationship is established at each location so that the discharge can be computed from measured water levels.

→Historical records from 5000 active and discontinued sites permit the estimation of streamflow at ungauged locations.



44 feet in Greenville, MS and and 17 feet in Memphis is in relation to the bottom of the river at those two points.  Memphis is 337 feet above sea level.  Greenville is 131 feet above sea level.  Both elevations are way above the the bottom of the Mississippi River.

Memphis - 337 (el) - 17 ft = 320 ft above sea level

Greenville - 131 (el) - 44 ft = 87 ft above sea level

The Mississippi River is still going downhill from Memphis to Greenville by 233 feet.

The "0" could mean the lowest recommended level to safely navigate the river or it could mean the average river bottom point during the year.  River bottoms can fluctuate depending on a variety of reasons such as the volume of water flow or sediment build-up from water alluvium.