138 The Control of Mosquitoes 



In some cases lime mortar and rough stone have 

 been used to advantage, with a small amount of 

 cement mortar for a finishing surface, or the bottom 

 was lined with fiat stone, the interspaces chinked 

 with small stone and sealed with cement mortar. 

 Where it was necessary to line the bottom of the 

 ditch only, the sides were given a slope beyond 

 the angle of repose, and allowed to become 

 covered with grass. As stone is sometimes costly, 

 the quantity used should be reduced to a minimum. 



REINFORCED CONCRETE LINING FOR DITCHES 



Where broken stone "screenings" or gravel can 

 be obtained at a reasonable rate, a reinforced 

 concrete ditch of light section may be the best 

 method of ditch lining. In the Canal Zone, a 

 thickness of about two inches is used for small 

 ditches with two-inch mesh hexagonal poultry 

 netting for reinforcing. In one case where a steep 

 embankment slid, a section of seven feet of this 

 lining was lifted out in one piece. It was only 

 necessary to regrade the ditch and replace the 

 section where it belonged. With most ditches it is 

 sufficient to line the bottoms and a few inches up 

 each side, as we are interested in the flow line of 

 the stream only after the rain has ceased. 



Work of this nature cost about twelve cents per 



