Water Transport Characteristics of NonEquilibrium Flow on Soil Column with Macropore Under Heavy Rainfall Condition

Abstract:

In order to reveal the water transport characteristics of nonequilibrium flow on soil column with macropore under heavy rainfall condition, the influence law of the factors(i.e., rainfall intensity, duration time, initial water content, the equivalent diffusion distance between two domain, empirical parameter) on the seepage mechanism of nonequilibrium flow were analyzed by using the dual porosity model and the kinematic wave model. The results indicate that the larger peak and smaller depth range of water exchange calculated by dual porosity are larger than those calculated by using the kinematic wave model. The dual porosity model is more suitable for simulating water change of upper soil while the kinematic wave model is more suitable for simulating water change of bottom soil. The volumetric water content calculated by using the two models along the depth presents the characteristics of double knees. The depth of water exchange and wetting front will increase with the increases of rainfall intensity and duration time. With the initial water content gradually approaching to saturation water content, the wetting front moves down and the depth range of water exchange increases, but the peak of water exchange decreases quickly. With the equivalent diffusion distance increaseing, the water exchange rate significantly reduces, resulting in the nonequilibrium flow. There is a little change in wetting front, water exchange rate and water content of the matrix domain when the equivalent diffusion distance between two domains is longer than 5 cm. With the increase of empirical parameters (rw and n*), the wetting front moves down, but the water exchange rate increases. When the rw is more than 0.4 or n* is more than 2.5, the wetting front decline rate, the moisture content of soil’s profile, and the speed and variation range of water exchange slow down obviously, resulting in the lower risk of nonequilibrium flow.

Key words:heavy rainfall; macropore; noneequilibrium flow; dual porosity model; kinematic wave model