5^14. 



i>R(yn-:ci"iox acjainst inundations. 



iii. Pu'iinUii'um of tli? IjOucv Course of the Stream, in oider 

 that it may, as far as possible, l)e able to carry away liisb 

 floods without danger to the surrounding country. A river is 

 said to be reguUted 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 he 

 attended to : — 



a. The pro/ile of the watercourse must he normal. It must 

 be deep enough to carry down small dehris 

 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. I ; 



h. The (jrddient of the bed of the water- "\ ! | 



course must he so modified that its velocity ; ) ; 



will rj3t be too great nor too slow. The ^^ ■■ \ \ 

 former is effected by means of weirs, and ( . \ \ 



the latter by shortening its course, as ^ "^^~~-~~\V 

 shown in Fig. 265. "^ 



r. Fixation of the River -hank a. This \^^ 



can ho done by plantations, or by special Fig. 2g.j. 



worlis. 



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

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



•J. Maiiaficiiient of lu>rests o)i Land Uolile to Iiniiiddtioiis.* 

 The management of forests on land liable to be flooded 

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

 S[)ecies 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 peduncuhxte oak. 



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

 ('. amara, >Hutt., Acer californienm, Ton'., and Fra.rinns 



"- Itebniann, "Die Rheitiwalduiigen und deren Bevvirlhshaftung.'' Allgo- 

 niiue Kor.st. u. .Jagd. Zcitiuig, IS'.Ki, pp. :<t;u— 3sl. 



