HYDROLOGY OF NEW YORK 



427 



cited of this general truth, but, as the object at present is not 

 specially to multiply proof on this point, a single one is sufficient, 

 although it is proper to remark that the same phenomenon has 

 been obserYed on many other streams. 



Torrential and gently flowing rivers. In addition to the classi- 

 fication as to concavity of profile, given on a preceding page, rivers 

 may be divided into two classes; (1) torrential, and (2) gently 

 flowing rivers. The rivers of the first class have considerable 

 fall and usually flow over impermeable strata, while those 

 of the second class flow over alluvium. Many of the 

 streams of Xew York State belong to both classes — in 

 their upper reaches they are torrential, while in their 

 lower they are gently flowing. This distinction is important to 

 bear in mind in treating of the question of floods, because the 

 floods of torrential rivers, while high, are of brief duration. 

 Gently flowing rivers, on the contrary, have lower floods, but they 

 continue for a. longer time and are therefore likely to be much 

 more injurious. In New York State the torrential streams gener- 

 ally flow through deep valleys and in many cases present excellent 

 opportunities for water storage. Usually the valleys of gently 

 flowing streams are not suitable for storage reservoirs — the cost 

 of the necessary barrage would in many instances, at any rate, 

 prove insuperable. 1 



General principles of river regulation as defined by von Weoc. 

 Perhaps as interesting a paper as any is one by Gustav Rifrter 

 von Wex, Privy-Councilor to the Emperor of Austria, in which 

 the governing principles of river regulation are so clearly set 

 forth that one can hardly do better than to give an extended 

 extract therefrom. Yon Wex's memoir is limited to a brief 

 general summary of the first principles requisite to the successful 

 regulation of intractable rivers. The quotation follows : 



In every case, first of all the upper course of the river must 

 be dealt with separately, and then the lower portion of it, to- 

 gether with its mouth, whether it empties itself into an estuary 

 or into the open sea. 



From long experience it has been ascertained that every 

 river or stream, following its natural course through wide tracts 



l The Conservancy of Rivers, by Win. H. Wheeler and Arthur Jacob, 

 Proc. Inst. C. E., Vol. LXVIT. pp. 201 and 233. 



