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National Geographic : 1890 Apr
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56 National GeographicMagazine. flows at various places on the Mississippi and Missouri and Ohio rivers, were tabulated from data given in the reports of the Mississippi and Missouri River Commissions. The tables were largely derived from the results of the measurement of current velocities. As gauge readings were taken at the time of dis charge or outflow measurements, the discharges or outflows can be told approximately at other times when only the river gauge readings are known. The results for the outflow of rivers derived from measurements made under the supervision of these commissions, are of a high order of accuracy, and it is not prob able that the results deduced from the gauge readings are much in error. Of 1881 and 1882, during which years measurements were made, 1881 was a year of great flood in the Missouri river, while the Mississippi river was not flooded. The year 1882, on the other hand, was marked by a great flood in the lower Missis sippi river, with a stage in the Missouri much above the average. The rainfall in the six great valleys of the Mississippi, during the entire years 1881 and 1882, was charted from all observations available, and its amount in cubic miles of water calculated with the aid of a planimeter. In connection with this investigation, and as a matter of value in showing the forces which are in operation to affect the river outflow, the fictitious or possible evaporation of the six great valleys referred to were calculated, in cubic miles of water, from July, 1887, to July, 1888, and also the average amounts of water in the air as vapor, and the amount required to saturate the air in the same valleys during the same period. During the year 1882, the year of great flood in the lower Mississippi valley, the outflow at Red River Landing, La., was 202.7 cubic miles, of which the upper Mississippi river above St. Louis furnished 16 per cent., the Ohio 43, and the whole Missouri above Omaha, 4 per cent. The upper Missouri valley (that is, from the mouth of the Yellowstone up to the sources), and the middle Missouri valley (from the mouth of the Platte to the Yellowstone), each furnished only about 2 per cent. of the entire amount of the water which passed Red River Landing. The lower Mississippi valley, including the Arkansas, etc., furnished 32 per cent. During March, April and May, 1882, the time of highest stage of the water of the lower Mississippi, the outflow at Red River Landing and through the Atchafalya measured 82.7 cubic miles.
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