Fig. 1: Diagrams of different irrigation drainage systems.

a Traditional decentralized system and b modern centralized system on the district scale. c Four irrigation drainage unit (IDU)-scale management styles within the modern system. The Traditional decentralized system in panel a is drawn based on the Beitang system in China referred to ref. 21, small ponds are scattered in the system and almost all IDUs use small ponds to store drainage water and supply irrigation.