SOIL-DENUDATION. 5S5 



Surface-water, or subsoil-water, for instance, may be con- 

 ducted away from above the endangered place by ditches or 

 drains. All quarrying below the threatened hill-side must 

 be stopped. 



(c) The following measures provide against damage by a 

 mountain torrent : 



i. Reafforesting the collecting-area of the stream ; the 

 methods to be adopted for this object are described 

 further on. 



ii. Securing the sides and bed of the torrent by revetments, 

 from its collecting area, downwards. 



iii. Reducing the force of the stream by terracing its bed, 

 and constructing across the stream wattle-work fences or 

 masonry works which keep stones and silt from accumulating 

 in the lower parts of the stream. 



iv. Terracing the slopes of the valley on either side of the 

 stream, and fixing them by means of sowings or plantations. 



4. Remedial Measures. 



When, in spite of every care, landslips or ravines have been 

 caused by abnormally heavy rain, or by melting snow, pro- 

 tective works should at once be constructed. A revetment 

 made of wattle-work, or of logs fixed in position by piles 

 driven into the ground (Fig. 261, A), may prevent the 

 occurrence of further damage. If, however, the landslip is 

 extensive, several such constructions, one above the other, 

 must be made, and the earth between them be brought to a 

 uniform slope and planted up. In certain cases, complicated 

 masonry revetments are required. 



In order to make natural revetments (Fig. 261, B and C) 

 woody growth must be on the spot. The bush is partly cut 

 through, splashed, and pegged down, with its crown uphill. 

 Where there is no woody growth, trellis- work with living 

 branches of willows or dead branches (Fig. 261, D and E) 

 should be employed. Fig. 261, F, shows how these willow 

 trellises may be planted along a slope. Wherever a landslip is 

 feared, adjoining trees should be felled, as they would otherwise 

 fall in and add to the damage. 



