GENERAL DRAINAGE INFORMATION 



81 



FIG. 28. A system which has been in operation for a number of years. 

 It conforms in plan and efficiency to the requirements of the to- 

 pography of the field. The north section, after having been in 

 service some 15 years, was lowered two feet because of the lowering 

 of the surface from shrinkage from various causes. 



