Mighty MississippEE

Occasionally hydrologists dive too deep into the data.
When that occurs, the inevitably result is the dreaded bad graph.

I can’t even count the number of “bad graph” days I’ve had in my professional career. 

(But now that I think of it – if I had that number, it would make a really good graph!)




Hydrology begins and ends in the United States with the Mississippi River, not to mention here along the Gulf Coast, it’s the freshwater flow source that dwarfs all other comers.

With that in mind, I humbly submit a “bad graph” showing the Mississippi’s flow history going back to 1970, as measured at Tarbert Landing, Mississippi. (Data made available by the Corps of Engineers.)

The gray horizontal bars on the left report the annual flow volume in millions of acre feet per year. Weekly average flow rate is represented on the right side of the graph, in the format of a hydrologic calendar. The large blue dots show extreme high flows, (weeks when average discharge exceeded 1,000,000 cfs). The small red dots show extreme low flows, (weeks when average discharge receded below 200,000 cfs).

I call it a “bad graph” because it’s very busy – which I tend to like because it has lots of information to visually assimilate, but inevitably others will tell me to try again.

So here’s my second offering.

It shows the Mississippi’s annual discharge in equivalent Lake Okeechobee volumes (assuming the Lake at full capacity of 5 million acre feet … around 17 ft above sea level.)

That simplifies the math considerably.

Consider it a big flow year for the Mississippi if it filled up 90 Okeechobee volumes (or more), and a low flow year if it didn’t cap off 60.

Last year was a notch below 90 as a result of a high-flowing April and May.

In conclusion, “bad graphs” are the stepping stones to good ones, and truth be told: 

I like both.
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