224 SWAMPINESS, CAUSES AND QENKEAL CtJUE. 



ARTICLE 1. 



Swampiness, its causes and genbkal cuke. 



Swampiness may be due to one or more of the following 

 causes ; — 



I. Flooding hy overflow of a stream or the sea. One or both of 

 two remedies may be adopted : — (1) Throw up a dam to keep 

 out the water, or (2) confine it within a channel or channels cut 

 through the area subject to inundation and having a free outlet. 



II. Situation along the lower outcrop of an inclined impermeable 

 stratum underlying another freely permeable one. The water falling 

 on the higher ground above sinks through the latter until it reaches 

 the lower stratum, by which it is arrested and over which it flows 

 underground until it wells out where that stratum comes out at, or 

 near, the surface. The famous Tarais of India are formed thus. 

 The swamps in the Dehra Dun and the numerous areas of 

 limited extent in the interior of the Himalayas are less striking, 

 but characteristic, instances. Here the cause of swampiness 

 cannot, as in the first case, be removed, but the excess moisture 

 may be got rid of by drainage. 



III. Inadequate outlet for tlie water entering, or falling over, the 

 area in question owing either-^ 



(1) To an msvjlicient fall, in which case special drainage works 

 must be resorted to ; or 



(2) To the natural drainage channels being rendered ineffective 

 either (a) by a rough bottom of rock, boulders or stones which impedes 

 the rapidity of their dischasge or (b) by contractions and irregular 

 bends or a fold of ground running across, whereby the current is 

 obstructed and thrown a long way back. Here the remedy lies in 

 the removal of all obstructions in the bed of the streams, in the 

 widening of the channels at certain points, and in straightening or 

 rounding oS sharp bends. Or 



(3) To an impermeable subsoil. If this impermeable stratum 

 is neither too thick nor too far below the surface, it may be pierced 

 at a sufficient number of points, especially where it forms dejires- 

 gions, in order to let through the superfluous moisture into the 

 stratum below. If the rock is not very hard and the area to be 

 treated is large enough, special boring machines would be em. 

 ployed with economy. If the thickness to be bored through is too 

 great, or the area is small, a system of drainage cuts cannot bs 

 avoided. 



