S i THE IMPROVEMENT OF RIVERS. 



forbidden to cut.* On the Rhone, whore the slope is nearly 1.6 in 2000, steamboats 

 of special power are needed to ascend the current. 



The bars to be acted upon by the current usually appear at the wider places in 

 a stream, and are composed of sand or fine gravel, so that an increase of vel< >city, even 

 in a slight degree, will set some of the lighter portions in motion. If it be greatly 

 increased the bed may be scoured out beyond the depth desired and thus lower the 

 water-surface at points up stream, and expose new obstacles to navigation. 



In rivers with unstable beds the fixing of a permanent passage is difficult and 

 expensive, but when the bottom is of hard material there is usually no reason why a 

 fairly good channel may not be established, and in such cases regularization would 

 seem a very economical method of improving a river were it only necessary to contract 

 the water-way at each offending bar. 



Applicability. The artificial constructions thus indicated are, however, usually 

 not all that is necessary to satisfy the requirements of navigation. The system has 

 its drawbacks as well as its advantages and it is not practicable to apply it in all streams 

 with success. Prof. Engels, a German authority, thus sums up his conclusions in 

 regard to it:f 



" (i) Only rivers, or long reaches of rivers, in which natural erosion is fully 

 developed are adapted to regulation. The navigability of unfinished rivers, still in 

 a state of erosion, can be improved with permanent results only by canalization. 



" (2) The most that can be accomplished by regulation is the desired adjustment 

 of the slope of the low-water line, and this only on reaches of uniform regimen and 

 uniform characteristics. 



" (3) This adjustment of the slope, to be accomplished when the conditions are 

 most favorable, can only be established and brought about by constructive measures 

 after the formation of that part of the channel which rises above low water is com- 

 pleted; that is, after the conditions of the bed have adapted themselves to the change 

 of energy caused by the formation of the mean high-water bed in other words, after 

 the erosion caused by this formation has come to rest. 



" (4) To secure the establishment and permanent preservation of the adjustment 

 of slope, the irregularities of the bed in the longitudinal and transverse profiles are to 

 be adjusted after reinforcing the low-water shore, and the bed is to be strengthened 

 where attacked by the water on account of the ground plan of the channel. Restriction 

 of width alone will not bring about that degree of navigability which may be desired." 



Hagen, the eminent German engineer, in his treatise on river engineering, thus 

 speaks of the value of regularization : 



" In no case will regularization allow the full attainment of the proposed result. 

 The result obtained depends upon the special characteristics of the river in question, 

 and in particular upon the magnitude of discharge and the fall, so that it is usually 



* "Civil Engineering," Law and Burnell. t Transactions Am. Soc. C. E., vol. xxix, p. aao. 



