Application of water and salt balance model in Yinbei irrigation district of Ningxia

According to the principle of mass conservation,water and salt balance models for aeration zones and aquifers were established and employed to simulate the variation of soil salt content,groundwater depth and mineralization in the irrigation areas of each canal in the Yinbei irrigation district of Ningxia.In the water balance equation for aquifers,the evaporation coefficient and the specific yield of phreatic water were treated as the variable parameters,and the subsurface exchange flows between the adjacent irrigation areas were considered.An iteration method was proposed with regard to the nonlinearity of the equation.In the salt balance equation for aquifers,the amount of salt carried by the subsurface flows was determined based on their exchange directions.The simultaneous equations of the salt balance between the aquifers and the aeration zones were solved with the conjugate gradient method.Comparison between the simulated results and measured data shows that the relative error is smaller than 8%,and the present models can be applied to the prediction of the water and salt variation the Yinbei irrigation district.