132 



MOSQUITO ERADICATION 



surface, as compared with an expensive ditching project, that it is 

 often well worth while to try it out in favorable areas. 



As a rule, the holes should be lined to prevent clogging up the 

 avenue of escape for the water by erosion. For the same reason, 



it is often desirable to install a drain-head 

 or other device to keep out the coarser 

 material carried along by the water. 



Gorman 1 describes a typical operation, 

 which resulted in the complete drying 

 up of a pond covering nearly an acre, as 

 follows : 



TYPICAL VERTICAL DRAINAGE 

 OPERATION 



"Beginning at a few feet from the water's 

 edge, on shore, at a shallow part of the pond, 

 a hole was dug to the limestone stratum with 

 a post-hole digger. Then, with a long drill, a 

 hole 12 inches deep was made in the lime- 

 stone and a stick of dynamite inserted, well- 

 packed and exploded. The hole was then 

 cleared out, the drill again used and another 

 stick of dynamite exploded. This was con- 

 tinued for three or four times, until drilling 

 had been carried to a depth of 4 feet or more 

 in the limestone. Water from the pond was 

 then directed into the hole. This same 

 thing was done at two or three other places 

 around the pond ... As the water drain- 

 ed and the pond became smaller, other holes 

 Fig. 92.— Sketch of a verti- were dynamited as described above, and, 



after eight holes had been made, the pond 

 was dry. By observing the rapidity with which the different holes 

 drained, it was noticed that four of them were especially effective . . . 

 showing that, in the case of these four, seams in the limestone had been 

 reached. 



"These four effective drains were dynamited several more times and 

 then, at each of them, holes 2 feet in diameter were dug through the 

 clay to the limestone. In these holes, resting on the limestone stratum, 

 12-inch vitrified clay sewer pipes were placed vertically, being built up 

 to a few inches above the ground. The rest of the hole around the pipe 



1 Transactions of the First Annual Conference of Sanitary Engineers, U. S. 

 Public Health Service, 1919. 



/.imeshne. ' 



