Water quality as design criterion in drainage water management systems

In the past, irrigation and drainage systems were designed and managed as separate entities. As water supplies become scarce and environmental restrictions increase, there will be a demand for the integrated design and management of irrigation and drainage systems. This type of system will make optimum use of existing water supplies and should reduce the impact of return how on the environment. Modifications in current drainage design practice are presented that will facilitate integrated management. Recommended modifications include changing the design minimum water table depth from 1.2 to 0.9 m and the depth of drains from 2.4 to 1.5 m. These changes, coupled with either improved irrigation management or the incorporation of crop water use from shallow ground water, will result in approximately the same drain spacings as calculated using the USER transient design procedure. Adopting the new drain depth criterion should result in less drain water and lower salt loads being discharged. These concepts were demonstrated with simulations using a drainage system designed for a cotton crop growing in the presence of shallow ground water.