运用温度示踪法确定稳定入渗补给速率

开展不同水位埋深条件下的地中渗透仪入渗实验,分析包气带温度场变化规律及其控制因素,进而采用多层介质热传导解析方程评价入渗补给速率,探讨了温度示踪法评价包气带入渗补给问题的适用性。结果表明:气温控制包气带温度场整体特征,其对温度场的影响随深度增加逐渐减弱。水位埋深影响土壤含水率,控制包气带介质比热,决定了温度场波动性。灌水改变介质热导率从而影响包气带温度场;灌水量小且灌水温差小,灌水本身的热状态对温度场的影响可以忽略。水位埋深浅时,基于多层介质热传导解析方程的入渗补给速率评价结果更为准确,旱季相对雨季,评价结果准确性整体更高;浅部包气带含水率波动性强是造成评价误差的重要原因,选取更短的评价周期和更深的计算剖面可相对提高评价结果准确性。含水率在时间尺度上的波动是温度示踪法在非饱和带应用的难点及关键。

Estimating stable infiltration recharge rate by temperature tracer method

To discuss the feasibility of temperature tracer method to evaluate the infiltration recharge rate, a lysimeter test was conducted under different water table conditions. The variation of temperature field of unsaturated zone was analyzed; and then the infiltration recharge rate was estimated by using the analytical solution for one dimensional steady heat transfer through a multi-layer unsaturated zone. The results indi-cate that air temperature is the primary control factor of unsaturated zone temperature field, but its influ-ence would be weakened with increasing depth. Water table depth controls the specific heat of unsaturated zone by affecting the soil moisture content; shallow water table would reduce the fluctuation of temperature field. The irrigation event affects the temperature field by controlling the thermal conductivity of the unsatu-rated zone;the influence of the heat state of irrigation event could be neglected when the irrigation amount is small or the temperature difference between the irrigation water and soil water is inapparent. When the water table is shallow, the calculated infiltration recharge rate is more closed to the measured data com-pared with the results in the deep unsaturated zone; and it is more accurate to estimate the infiltration re-charge rate in the dry season than the wet season by using the soil temperature data. The temporal varia-tion of shallow soil moisture content mainly causes the evaluation error;and it limits the application of tem-perature,as a tracer,to evaluate the water flow in the unsaturated zone.