A Green‐Ampt model for muddy water considering air resistance based on the layered assumption

Abstract Most irrigation areas in the Yellow River Basin widely use muddy water irrigation, and the sand in the water is the main characteristic that distinguishes muddy water irrigation from clear water irrigation, resulting in a significant difference in its infiltration mechanism compared with clear water. This research aims to determine the influence of muddy water properties on the infiltration process and pore air pressure in the presence of air resistance. Indoor soil column infiltration tests were used to examine the infiltration procedure and the process of pore air pressure change under various muddy water sand contents and sediment particle compositions. The hydraulic conductivity, cumulative infiltration per unit area, and frontal matrix suction in the traditional Green‐Ampt (G‐A) model were modified, a saturated layer thickness calculation model was introduced, and an improved G‐A model considering air resistance based on the layered assumption was established. The research results indicated that the change in pore air pressure over infiltration time may be split into two stages: rapid change and stable change. The sand content and the physical clay content were positively correlated with the pore air pressure and negatively correlated with the saturated hydraulic conductivity. After the wetting front reached 20 cm below the soil surface, compared to the traditional G‐A model, the revised model estimated the infiltration time closer to the measured infiltration time. The improved model significantly improves the prediction accuracy and offers theoretical support for the exploration of muddy water infiltration behavior. The higher the sediment concentration and the higher the clay content, the more obvious the superiority of the modified model becomes.