Abstract The soil water retention curve (WRC), describing the relation between the soil water content and its corresponding capillary pressure, relies not only on whether drying or wetting occurs but also on the pore scale water flow velocity. Here, we investigated the effects of the watertable fluctuations on the WRC through 28 laboratory experiments covering a wide range of fluctuation amplitudes and periods. Results show that both the response of the capillary pressure and soil water content lag behind the watertable fluctuation, and the vertical capillary pressure distribution in the unsaturated zone is non-hydrostatic, especially for the fluctuations with shorter period. As a consequence of watertable fluctuation, the measured WRC deviates from that under static conditions, depending on both the fluctuation amplitude and period. Moreover, the air-entry pressure under dynamic conditions is considerably larger than that under static conditions, and it first increases and then decreases as the fluctuation period decreases. The effects of the watertable fluctuations on the dynamic capillary coefficient was further examined. It is found that the relation between the dynamic capillary coefficient and saturation is nonunique even for the drying and wetting of a given sand and watertable fluctuation, suggesting a hysteretic dynamic capillary coefficient, and the dynamic capillary coefficient is rate-dependent, decreasing with an increase of fluctuation rate.

中文翻译：

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水位波动引起的保水曲线变异：砂柱实验

摘要 土壤保水曲线（WRC）描述了土壤含水量与其对应的毛细管压力之间的关系，它不仅取决于干燥或润湿的发生，还取决于孔隙尺度的水流速。在这里，我们通过涵盖广泛波动幅度和周期的 28 项实验室实验研究了地下水位波动对 WRC 的影响。结果表明，毛管压力和土壤含水量的响应均滞后于地下水位波动，非饱和带的垂直毛管压力分布是非静水压的，尤其是周期较短的波动。由于地下水位波动，测得的 WRC 与静态条件下的 WRC 有偏差，这取决于波动幅度和周期。而且，动态条件下的进气压力明显大于静态条件下的进气压力，并且随着波动周期的减小先增大后减小。进一步研究了地下水位波动对动态毛细系数的影响。发现即使对于给定的砂和水位波动的干燥和润湿，动态毛细系数与饱和度之间的关系也不是唯一的，表明存在滞后动态毛细系数，并且动态毛细系数与速率相关，随着增加而减小的波动率。进一步研究了地下水位波动对动态毛细系数的影响。发现即使对于给定的砂和水位波动的干燥和润湿，动态毛细系数与饱和度之间的关系也不是唯一的，表明存在滞后动态毛细系数，并且动态毛细系数与速率相关，随着增加而减小的波动率。进一步研究了地下水位波动对动态毛细系数的影响。发现即使对于给定的砂和水位波动的干燥和润湿，动态毛细系数与饱和度之间的关系也不是唯一的，表明存在滞后动态毛细系数，并且动态毛细系数与速率相关，随着增加而减小的波动率。