| Frequently
Asked Questions |
| 1. Where
can I find historical river data for the Mississippi River? |
| |
The
US Army Corps of Engineers is the official record keepers for Mississippi
River Data. You can access their web site at www.usace.army.mil.
We have a limited amount of unofficial Mississippi River data on our
site. Click here
to view. |
| 2.
Where can I find river stages and forecasts for the Upper Misssissippi
River? |
| |
You
can access this data from the NWS's
River Watch site. This asite has forecasts for the Mississippi,
Ohio, Missouri, and Illinois Rivers. |
| 3.
I am curious about how river stages are calculated. Specifically,
what is the point of reference used to determine a height? |
| |
River
stages are calculated from an arbitrary "gage zero" point. The reason
that we get negative levels is because these "gage zero" points
were established decades ago and over time the river has shifted
and scoured. The reason that this is not adjusted is because the
people that live around the river are familiar with the flood stage
and how the current stage compares to it. It takes a vast amount
of planning and education in order to change a "gage zero" which
would also change the flood stage.
Also, all "gage
zero" points are independent of each other. For example, you may
see a stage of -6.7 feet upstream of a 13.5 feet stage even though
the river is higher at the upstream point when compared to mean
sea level. |
| 4.
We hear about all the flooding along the northern Mississippi River.
Why is it we don't see rises expected in the forecast of the Lower
Mississippi and Atchafalaya Rivers? |
| |
The
reason that we do not get a (major) rise on the Lower Mississippi
and Atchafalaya Rivers is because the upper Mississippi (above Cairo,
IL) contributes less percentage of flow to the those rivers. The Ohio
River actually has a much greater impact on the lower Mississippi
and Atchafalaya Rivers. We have a much greater concern for flooding
on the lower Mississippi if the Ohio River goes into flood. |
| 5. How
are the river stage reading determined? Does the sea level of the
adjoining land have anything to do with it? |
| |
The
river stage readings are determined by the agency responsible for
installing and maintaing the gage. This is determined after coordinating
with local agencies and interests and before the gage is installed.
On each of our forecasts we provide the gage's reference to mean sea
level. For example, if the forecast product states "308.54 + Forecast
Stage = Height in FT MSL" and the height of the stage is currently
24.9 feet, then the height of the river level would be 333.44 feet
above mean sea level. |
| 6. (1)
What are "action stage", "flood stage", and "record stage"? (2) Are
the river stages in the forecast seasonally related? |
| |
(1)
Action stage is the stage at which some sort of action is taken for
the river point. This is different for all points depending on the
community's needs. It may be flooding of secondary roads or just a
"heads up" that the river is rising. Flood stage is the stage at which
structures begin to get affected. This may be a road or building.
Record stage is the highest stage that the river point has gotten
to since records were established. (2) None of our action or flood
stages in the LMRFC area are seasonal, but there are some river points
in the US that are seasonal. For example, you may have a lower flood
stage in the summer due to increased outdoor activities by the river. |
weather.gov
NWS River Forecast Process in the Amite/Comite River Basin