ABSTRACT
Traditionally drainage systems, whether surface or subsurface, were designed to evacuate excess water within a specified period (2-7 days depending on the climate), with the aim of preventing waterlogging and/or flooding. With the emergence of water shortages and water quality and environmental concerns, cases have emerged where drainage needs to be managed, only discharging when necessary. Such drainage is broadly referred to as controlled drainage. By maintaining high watertables, water savings of up to 40% during the rice-growing season were achieved in Egypt. Controlled drainage prevents unnecessary mobilisation of nitrogen and phosphorous (Figure 1.9), pesticide residues and other toxis elements (i.e., selenium) and helps to maintain downstream water quality.
