9 THE IMPROVEMENT OF RIVERS. 



Each extension made is the signal for a further rise of elevation. An instance 

 in point is given by De Mas : * " From the commencement of the eighteenth century 

 the maximum heights given by a gauge near Ferrara have followed an upward march. 

 Before 1729 the highest figures remained under 23 feet; from 1729 to 1809, or during 

 a period of eighty years, the 2 3 -foot mark was often exceeded without the 2 6 -foot 

 mark being reached. Since 1810, that is, during a period equal to the preceding, the 

 26-foot mark was passed five times." 



Many years ago a French engineer stated that the high-water level of the Po had 

 increased 6| feet in two centuries, and that, while the number of breaks in the dikes \v;u 

 only 41 in the eighteenth century it had been 119 in the first seventy-two years of the 

 nineteenth, 36 of which were in the year of 1872 alone. 



On the Theiss, the embankment works of which are not less in importance or in 

 results than those of the Po, there has been a steadily increasing elevation in the heights 

 of floods. These increased levels have not come without bringing disaster. In 1879 

 the city of Szegedin, one of the most important of Hungary, and having a population 

 of 75,000, was almost destroyed by inundation. The levees were repaired, rebuilt, 

 and increased in height so that even higher floods have since passed in safety. In 

 alluding to this the authority just quoted asks: "Will it always be thus? Will not 

 the height of floods continue to increase in a manner dangerous even to dikes thus 

 strengthened? Will not the old river-beds, kept open for the escape of great floods 

 at the location of each of the cut-offs, silt up little by little? Can the surveillance 

 never be relaxed which was made necessary by a disaster still fresh in the minds of 

 all? When we see what happens elsewhere we cannot fail to regard this matter with 

 apprehension, and in rendering due credit to this remarkable work we ought not to 

 overlook the possibilities of the future." 



A similar experience is recorded with the levees of the Loire. The crown, which 

 was originally placed 1 5 feet above low water, was raised to 2 1 feet after the flood of 

 1 706, and even this has been found to be too low, for all the great floods have continued 

 to rise and to surmount the embankments. After the extreme high water of 1846, 

 an additional height of over 3 feet was placed on the levees, but the floods of 1856 and 

 1866 demonstrated that this raising was again insufficient. 



The argument is frequently made, and is almost universally believed, that by 

 confining a river at flood between levees increased scour of the bed and banks will take 

 place and thus give a greater section for discharge and a greater velocity, the result 

 of which will be to reduce not only the elevation of low water but also that of floods. 

 It is quite probable that a reduction of the height of low water will follow the estab- 

 lishment of levees, but this does not necessarily indicate that the high-water line will 

 also be lowered; in fact, it is necessary to give up this doctrine if we are to profit by 

 experience, because each successive exclusion of territory on the Mississippi has been 

 followed by a higher flood-line. In referring to the flood of 1897 Mr. Starling says: 



* Rivers wit'u ,',\ c Cu.rent, Art. 178. 



