LAND DRAINAGE PRACTICE. 



43 



System is the skeleton which may be developed into a 

 more complete system, if afterwards found necessary, 

 provided the size of the drains is proportioned to the 

 area to be finally improved. 



Fig. 4 — Natural System. 



The Grouping System. — This may be applied to 

 such land as has basins or sloughs, and also areas of 

 dry land, or such as it does not seem desirable to 

 drain. The field is divided into small drainage sec- 

 tions so that one outlet will serve for each division, and 

 a main laid in the lowest land of each separate drain- 

 age basin. The drainage may be completed by lateral 

 lines converging toward the main at such distances 

 apart, and having such lengths, as may be adapted to 

 the purpose. The method is shown in Fig. 5. 



The Gridiron System. — This is the old and generally 

 practised system where thorough drainage is carried 

 out. Systematic drainage generally implies the loca- 

 tion of parallel drains at uniform distances over the 

 entire field. Thorough drainage^ however, is so re- 

 moving water from the entire field as to secure uniform 



