During floods they pour over their banks upon the surrounding valleys, by a thousand channels which interlace and establish communication between the main streams. After numerous bifurcations they find their way into the sea by three principal mouths.
The purpose was to decrease the floods which sometimes threaten to entirely submerge the city.
For the next sixty years an urgent question was the prevention of floods in the capital.
About the time of the maxima there must be a longer tidal range (that is, a greater rise and fall than the average); the difference between neap tides and spring tides will also be increased, and as results of these conditions there must be great tidal floods breaking over lowlying coasts and producing extensive denudation.
The abundant records by the Mississippi River Commission and the United States Weather Bureau (by which accurate and extremely useful predictions of floods in the lower river course are made, on the basis of the observed rise in the tributaries) demonstrate a num~ bar of interesting features, of which the chief are as follows: the fall of the river is significantly steepened and its velocity isaccelerated down stream from the point of highest rise; conversely, the fall and the velocity are both diminished up stream from the same point.