强降雨条件下含大孔隙土柱水分非平衡运移特性

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

摘要:

为揭示强降雨条件下大孔隙土柱水分非平衡运移特性，基于双重渗透模型与运动波模型，采用有限差分技术编制计算程序，对降雨强度、持时、初始含水率、两域间等效扩散距离、经验参数（rw,n*）等对水分非平衡迁移特性进行分析.结果表明,双重渗透模型计算所得的水分交换峰值比运动波模型计算值大但水分交换深度范围小.双重渗透模型模拟表层水分变化较好，而运动波模型模拟土层下部水分变化较好.两种计算模型得到的体积含水率沿深度范围内呈现双拐点特性.湿润峰深度、水分交换深度范围均随降雨强度、降雨持时的增大呈现变大趋势.随着初始含水率逐渐接近饱和含水率，湿润峰位置下移，水分交换深度范围变大，但峰值骤降.随着两域间等效扩散距离增大，水分交换速率大幅减小，造成比较明显的非平衡流现象；但当两域间等效扩散距离超过5 cm时，湿润峰位置、水分交换速率、基质域剖面含水率相差很小.随着经验参数值rw,n*的增大，湿润峰下降速度变慢，但水流交换速度增大.当rw大于0.4或n*大于2.5，湿润峰下降速度、土壤剖面含水率、水流交换速度与范围变化幅度明显降低，产生非平衡流的几率降低.

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.