Note 376 — Chapter IV · (continued 2)

For the convenience of navigation, and to lessen the danger of inundation by giving greater directness, and, of course, rapidity to the current, bends in rivers are sometimes cut off and winding channels made straight. This process has the same general effects as diking, and therefore cannot be employed without many of the same results.

This practice has often been resorted to on the Mississippi with advantage to navigation, but it is quite another question whether that advantage has not been too dearly purchased by the injury to the banks at lower points. If we suppose a river to have a navigable course of 1,600 miles as measured by its natural channel, with a descent of 800 feet, we shall have a fall of six inches to the mile. If the length of channel be reduced to 1,200 miles by cutting off bends, the fall is increased to eight inches per mile. The augmentation of velocity consequent upon this increase of inclination is not computable without taking into account other elements, such as depth and volume of water, diminution of direct resistance, and the like, but in almost any supposable case, it would be sufficient to produce great effects on the height of floods, the deposit of sediment in the channel, on the shores, and at the outlet, the erosion of banks and other points of much geographical importance.

The Po, in those parts of its course where the embankments leave a wide space between, often cuts off bends in its channel and straightens its course. These short cuts are called salti, or leaps, and sometimes reduce the distance between their termini by several miles. In 1777, the salto of Cottaro shortened a distance of 7,000 mètres by 5,000, or, in other words, reduced the length of the channel more than three miles; and in 1807 and 1810 the two salti of Mezzanone effected a reduction of distance to the amount of between seven and eight miles.—Baumgarten, l. c. p. 38.