INLAND DRAINAGE 



125 



approximately 29 miles of ditches were maintained at a cost of 

 $0,045 a foot or $241.52 a mile for the season; estimating the 

 season as lasting 6 months, the cost was less than $0,008 a foot or 

 $40.25 a mile a month. These ditches were kept in almost per- 

 fect condition at all times — free from grass and weeds and 

 obstructions of all kinds. 



PERMANENT LINING OF ANTI-MOSQUITO DITCHES 



Anti-mosquito drainage ditches may be lined to advantage, 

 where excessive erosion takes place or where maintenance costs 

 otherwise become excessive. 



Fig. 84. — Section of ditch lined with redwood boards. 



Materials usually employed for lining ditches are concrete, 

 stone set in mortar and planks. While the former are more 

 expensive, they are more permanent and generally give more 

 satisfaction in the long run. 



LePrince 1 says: "Lined ditches are more permanent, easily cleaned, 

 require less inspection and are ultimately less costly. At some of the 

 settlements in the Panama Canal Zone, it was found that a large saving 

 was made by lining certain ditches and parts of ditches with concrete 

 as against repeated regrading, cleaning and oiling of open earth ditches." 



As a rule, the lining should be U-shaped with sloping sides; it is 

 not always necessary, however, to line the whole depth of the 



1 "Malaria Control; Drainage As An Anti-mosquito Measure," U. S. 

 Public Health Service, 1915. 



