498 DIKES OF THE NILE. 



ComlmaUon of Methods. 



Upon the whole, it is obvious that no one of the methods 

 heretofore practiced or proposed for averting the evils resulting 

 from river inundations is capable of universal application. Each 

 of them is specially suited to a special case. But the hydrography 

 of almost every considerable river and its tributaries will be found 

 to embrace most special cases, most known forms of superficial 

 fluid circulation. For rivers, in general, begin in the mountains, 

 traverse the plains, and end in the sea ; they are torrents at their 

 sources, swelling streams in their middle course, placid currents, 

 flowing molli Jhimine, at their termination. Hence in the dif- 

 ferent parts of this course the different methods of controlling 

 and utilizing them may successively flnd apphcation, and there is 

 every reason to beheve that by a judicious apphcation of all, 

 every great river may, in a considerable degree, be deprived of 

 its powers of evil and rendered subservient to the use, the con- 

 venience, and the dominion of man.* 



Dikes of the Nile. 



" History tells us," says Mengotti, " that the Nile became ter- 

 rible and destructive to ancient Egypt, in consequence of being 

 confined within elevated dikes, from the borders of Nubia to the 

 sea. It being impossible for these barriers to resist the pressure 

 of its waters at such a height, its floods burst its ramparts, some- 

 times on one side, sometimes on the other, and deluged the plains, 



which lay far below the level of its current In one of its 



formidable inundations the Nile overwhelmed and drowned a 



* On the remedies against inundation, see the valuable paper of Lombar- 

 DiNi, Sulle Inondazioni awenute in questi uliimi tempi in Francia. Milano, 

 1858. 



There can be no doubt that, in the case of rivers which receive their supply 

 in a large measure from mountain streams, the methods described in a former 

 chapter as recently employed in Southeastern France to arrest the formation 

 and lessen the force of torrents, would prove equally useful as a preventive 

 remedy against inundations. They would both retard the delivery of surface- 

 water and diminish the discharge of sediment into rivers, thus operating at 

 once against the two most efficient causes of destructive floods. See Chapter 

 III., ante, p. 808, et seq. 



