199 



^Itt. deep and about 8 ins. wide~are cut horizontally into the banks, 

 in which the mosquitos shelter from the wind during the day, when 

 they may be easily destroyed by inserting a torch of flaming straw. 

 In cases where rivers are bordered by dense thickets of tall weeds 

 and brushwood, beneath which pools of stagnant water lie hidden, 

 pathways should be cut through the undergrowth to allow of oihng 

 these dangerous spots. 



In the case of streams it is often necessary to construct dams to 

 provide drinking ponds and washing pools. When the nature of 

 the ground will allow of it, the banks should be straightened and the 

 bed of the stream cleared of vegetation. Stony torrent-beds should 

 be chamielled in summer time when they are nearly dry. a narrow 

 cutting. 6-12 inches deep, being made at the lowest level of the bed, 

 and bordered with stones. Similarly a stream may be deflected into a 

 channel at a lower level, a method simpler than that of straightening 

 its own bed. 



Mill streams, when badly kept, cause sheets of stagnant water to form 

 at the lowest level as the result of infiltration. Remedies suggested 

 for this are : reinforcing the bed of the canal (which must previously 

 have been run dry) with clay well stamped and rolled in after each 

 addition ; the heightening of the banks ; the lowering of the bed ; 

 the widening of the bed if possible, thus diminishing the depth of 

 flow and reducing erosion ; and the planting of vegetable gardens, 

 which are frequently able to absorb much surface-water. 



Useful stagnant waters can be treated in various ways. Wells 

 should be provided with covers, either sohd or formed of a framework 

 covered with fine metallic gauze, such covers to be raised only durmg 

 the drawing of water. The ground surrounding wells should slope 

 downwards by at least as much as one inch in the yard, to allow 

 spilt water to drain away ; or a mosaic-hke pavement of pebbles 

 or stones should be made round the well. Irrigation waters are best 

 rendered harmless by the periodic alternation method [see this Review, 

 Ser. B, V, p. 190]. The borders of drinking ponds should be kept 

 well-trimmed, the beds free from vegetation, and a metalled-road 

 approach should be maintained, these precautions being doubly 

 necessary since oihng is an impossibihty. 



Useless stagnant waters, such as those caused by the feet of animals, 

 and also those of greater extent, should be filled in. In some ponds 

 stagnation is due to the accumulation of sediment at the bottom, 

 or to the presence of a thin layer of clay, the remedy being to perforate 

 the bed of the pond by a crow-bar or by dynamite to allow the water to 

 permeate into the subsoil, the aperture being covered with loose stones 

 to maintain percolation. Cess-pools made of stones and about 5 to 6 

 feet deep and 3 feet in diameter have proved of great utility in the 

 country, in the courtyards of houses, as receptacles for the waste 

 household liquids. The best treatment for surface waters is the 

 suppression of the initial cause of the inundation, and, faihng this, 

 drainage by means of open drains. Cultivation methods also yield 

 good results, crops such as oats and maize being grown on the ridges 

 separating the water- filled furrows. 



Technical instructions for the making of open ditches and faggot 

 drains, formulae for calculating the rate of flow of currents, and 

 instructions for levelhng, conclude this useful paper. 



