湖泊防渗对湖底及周边土壤水分分布的影响

为研究湖泊防渗对土壤水分分布的影响,采用情景-后果分析法,通过建立水文地质概念模型以及一维和二维包气带水分运移模型,对防渗前后土壤水分分布以及地下水补给强度的变化进行了预测.以圆明园为例,在现场和室内试验的基础上,进行了研究.结果表明,在枯水期湖内无水时,防渗前后,湖底与周边土壤水分分布规律基本一致,湖泊防渗对湖底及周边土壤水分影响不大.在丰水期湖内水深1.0 m情况下,防渗前,潜水位很快上升至湖底,使地下水与湖水形成直接水力联系,湖水对湖底包气带水及潜水的平均补给强度为18.0 mm/d,湖水对植被根系分布区土壤水分分布的最大影响范围118 m;防渗后,湖底原包气带土层基本处于非饱和状态,上述平均补给强度减小为5.8 mm/d,最大影响范围缩小为14 m.因此,在丰水期湖内有水时,湖泊防渗能显著减少湖水渗漏,使湖泊周边大范围内的土壤水分显著减少.

Impacts of Lake Lining on Soil Moisture Variation in Vadose Zone

For studying impacts of lake lining on soil moisture and groundwater recharge intensity, the scenarios analysis method was adopted, with hydrogeological concept modeling and 1D-and 2D-flow modeling for variably saturated porous media, to simulate and predict the variations of soil water content and groundwater recharge intensity before and after lake lining. Through a case of the Yuanmingyuan Ruins Park, the study was performed on the basis of in situ and laboratory experiments. The results showed that, during the low-water-level season, the distributions of soil moisture before and after the lake lining will be basically consistent with each other, and therefore, the lake lining will have little impacts on the soil moisture and groundwater recharge intensity. However, during the high-water-level season with 1 m depth of lake water, the modeling results showed that the groundwater table will rise quickly to the bottom of lake bed with a recharge rate of 18.0 mm/d, and the maximum impact width of the lake on the water content in vegetated zone will be up to 118 m. While after the lake lining, the groundwater recharge rate, and the impact width will decrease to 5.8 mm/d, and 14 m respectively. The vadose zone under the bottom of lake bed will be still unsaturated. Therefore, during high-water-level season, the lake lining will largely decrease the lake leakage, and also greatly reduce the soil moisture in large area.