Agricultural Drainage Criteria
The purpose of the Agricltural Drainage Criteria is to provide good drainage for low land crops to survive and thrive, 
The survival of crops depends upon the crop’s roots not being saturated for long periods of time.
The criteria were designed to limit the duration that the crop’s roots are subjected to saturaged soil conditions and provide a water table low enough to allow for good root growth.
Chronic flooding limits the rage of crops that can be grown on farmland, reduces crop yields and in some cases leads to disease and pest management problems. Good drainage is required to ensure that farmers can produce marketable crops.
Explanation of the agricultural drainage criterria are available in a seven-page factsheet from the Ministry of Agriculture.