594 



PROTECTION AGAINST INUNDATIONS. 



It must 



iii. Regulation of the Loirer Course of the Stream, in order 

 that it may, as far as possible, be able to carry away high 

 floods without danger to the surrounding country. A river is 

 said to be regulated when the water is in the middle of the 

 bed and flows away evenly, and the banks are firm. 



In regulating watercourses the following points must be 

 attended to : 



a. The profile of the watercourse must be normal, 

 be deep enough to carry down small debris 



when there is an average quantity of water, 

 and also wide enough to carry off floods 

 without acquiring any great velocity. Too 

 narrow beds must be widened, and too 

 broad beds reduced in width. 



b. The gradient of the bed of the water- 

 course must be so modified that its velocity 

 will not be too great nor too slow. The 

 former is effected by means of weirs, and 

 the latter by shortening its course, as 

 shown in Fig. 265. 



c. Fixation of the. River-banks. * This 

 can be done by plantations, or by special 

 works. 



For a full account of the measures to be taken in the lower 

 part of a stream, see Vol. V., " Forest Utilization," p. 374. 



4. Management of Forests on Land liable to Inundations.* 



The management of forests on land liable to be flooded 

 includes much that is special to the circumstances of the case. 

 Species should be chosen that can withstand a good deal of 

 moisture in the soil and occasional submersion ; such are the 

 pedunculate oak, elms, black alder, willows, black and white 

 poplars, and the ash. In the wettest places the common alder 

 and willows are found ; ash is more sensitive to soil-moisture 

 than poplars and the pedunculate oak. 



Among exotics are, Juglaus nigra, L., Carya alba, Nutt., 

 C. amara, Nutt., Acer calif or nicum, Torr., and Fra.i-inux 



* Rebtnann, "Die Rheinvvaldungen und deren Bcwirthsliaftunjj:. ' Alliro- 

 mine Forst. u. Jagd. Zeitung, 1896, pp. 360381. 



Fig. 26 



