Frequently Asked Questions and Fact Sheets

 

Please look over the questions below before you email the Webmaster. If you cannot find an answer here, then we will be happy to help you.

 

Fact Sheets
  NWS River Forecast Process in the Amite/Comite River Basin
HTML Version .pdf Version
  NWS Operations to Support Pat Harrison Waterways
HTML Version  

 

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 NGVD 29" and the height of the stage is currently 24.9 feet, then the height of the river level would be 333.44 feet above NGVD 29.
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.

 

 


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