Attack by Drainage 139 



linear foot, in place, for ditches a foot wide, with 

 unsatisfactory labor costing ten cents per hour. 

 Reinforced concrete lining should be selected for 



CrosB Section 

 of Key Wall 



Weep Hole 



Plan of Key Wall 

 -Donorete Lining of Dltoh 



-Key WiiU 



Plan and cross section of key wall and position of weep 

 holes. 



ditches near permanent settlements that are 

 possible mosquito producers throughout the 

 greater part of the year. The work should be 

 accompHshed during the dry season, and the ditch 



