Hydrosalinity balance and critical ratio of drainage to irrigation (RDI) for salt balance in Weigan River irrigation district of the Tarim basin (China)

The analysis of the principle of salt mass balance in irrigation districts is the foundation for the rational drainage system design and its effective evaluation. The salt balance of the Weigan River irrigation district is analyzed using annual measured data. Factors affecting the ratio of drainage to irrigation (RDI) and methods for determining this ratio are discussed. The results show that RDI is related to the volume and salt content of irrigation water and drainage water. The critical RDI for the Weigan River irrigation district is 9.29%. It is necessary to achieve a certain level of percolation to maintain the hydrosalinity balance when planning irrigation schedules and managing irrigation and drainage. Moreover, urgent improvement of the current drainage system is required to ensure that the actual RDI is greater than the critical RDI in the irrigation district. From 1994, the irrigation district turned from salt accumulation to desalinization, and the ratio of drainage to irrigation tended to optimal value.