582 



CHAPTER I. 



PROTECTION AGAINST DAMAGE BY SWAMPS, 

 FLOODS AND TORRENTS.* 



WATER acts either as a meteoric phenomenon, or as stagnant 

 or flowing water on the surface of the ground, or in the soil ; 

 its effects are partly mechanical and partly physiological. 



The chief mechanical effects consist in soil-denudation, 

 landslips, or floods. Physiological damage is done to plant- 

 life and to the soil hy stagnant water causing hogs and 

 marshes. Damage to forests hy heavy rain has already been 

 dealt with (p. 554). 



SECTION I. SOIL-DENUDATION. 

 1. Description. 



Soil-denudation on steep slopes may be due either to subsoil- 

 water, surface-water, or to mountain torrents. 



Subsoil-water or surface-water on hill-sides may cause land- 

 slips, which bring down the soil with the vegetation growing on 

 it, and expose the subjacent rock ; this may occur either when 

 the slope of the hill-side is excessive, or when there is an 

 impermeable substratum which prevents the further descent 

 of the water into the hill. 



Excavations of pits or quarries at the base of a hill may 

 have a similar effect. 



Mountain torrents may cause soil-denudation, or form ravines, 

 by deepening their beds and by wearing away their banks. 

 The latter effect occurs chiefly at sharp turns in the course of 

 the torrent, when one bank is formed of rock and the other 

 of loose material. The force of the water increases with its 



* Kraft, Gustav., " Beitrage zur forstl. Wasserbaukunde." Hannover, ism 1 . 

 Demontzey-, " Etude sur les Travaux de lleboisemerit et de Gazounement des 

 Montagnes." Paris, 1878. Id. Trait i? Pratique, 1882. Von Scnkendorf. M V-r- 

 bannuug der Wildbache." Vienna, 1884. Landolt, ll Die Biiche, Schneelawiiu-n 

 und Steinschlage." Ziirich, 1886. 



