DISADVANTAGES FROM UNFAVOURABLE SOIL, &C. 47 



29. Eemedial Measures ; Principles of Drainage. 



In order to counteract excess of moisture, and to succeed in 

 obviating its injurious consequences, the predisposing cause of the 

 wetness must first of all be ascertained. 



Should this be occasioned by the exit of subterraneous springs 

 without any proper channel for the off-flow of the water, these 

 should have proper basins dug round their mouths, and the water 

 should then be drained off by means of ditches. 



If, on the other hand, the wetness is due to impermeable sulsoil, 

 this can also easily be remedied, if the gradient be sufficient, by 

 means of ditches conducting to any lower but not very distant 

 water-level ; should, however, such difference of level not make 

 itself apparent, the task of carrying off the surplus moisture is 

 increased in difficulty, but can still be arranged for by boring a 

 passage for the water through to the subsoil, or by lowering the 

 water level by means of ditches. When the impermeable 

 stratum (of plastic clay, moorpan, ironband, &c.) is only of slight 

 depth, and the swampy tract of moderate extent, the water can 

 be conducted to the subsoil by tapping or boring through the 

 impermeable layer at its deepest point; the hole made should 

 not be too small, and should be covered over with large stones to 

 prevent it being soon choked with silt. In many other places 1 

 the water-level is reduced by digging over the whole area, ditches 

 of sufficient depth, and not too far apart, and allowing the water 

 to collect in them ; and as at the same time the out-throw from 

 the ditches is distributed regularly over the intervening spaces 

 between these, the surface of the soil is thus .artificially raised to 

 a considerable height, and the intended sowing or planting can 

 take place favourably on these raised banks or beds. 



Inundations can be prevented by the facing and banking up of 

 the sides of small brooks and streams, by clearing the river-beds 

 of accumulations of silt, by increasing the gradient through cut- 

 tings and corrections of the water-courses, most of which, how- 

 ever, are works going beyond the proper sphere of the forester. 



The following may be considered the main principles of 



drainage. Only the excess or surplus of moisture should be 



removed from the soil, as too extensive depletion of moisture can 



have injurious consequences, not only for the actual areas in 



1 This is the general method of treatment of moorpan in Hanover. Trans. 



