Effect of cut-off walls on submarine groundwater discharge in non-isothermal conditions
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摘要:
温度变化会影响海岸带地下水运移特征，但之前关于截渗工程条件下地下水排泄过程的研究仅限于等温条件，没有考虑非等温过程的影响。文章构建了场地尺度的二维地下水-盐-热耦合数值模型，探究非等温条件下截渗墙对地下水排泄过程的影响，重点关注地下水排泄动态变化特征与温度的关系，采用地下水排海通量（Q）与相对排泄量（Q'）定量评价海水温度对地下水排海通量的影响。研究结果表明：（1）在高温海水条件下，Q'达到平衡的时间显著缩短；（2）海水温度变化会改变截渗墙与咸水楔对地下水渗流的影响程度；（3）低温海水情况下咸水楔对地下水渗流的阻碍作用大于墙体本身，而高温海水条件下截渗墙的阻碍效果更为显著；（4）海水温度高于地下水15 °C时，咸水区内更易产生并维持反向环流，导致咸水区地下水循环加速，进而增加地下水排海总量。研究成果可为截渗工程结构优化和滨海地下水资源可持续利用提供重要技术支撑。
Abstract:Temperature could change the migration characteristics of coastal groundwater. However, research on groundwater discharge processes under the influences of cut-off walls has been limited to isothermal conditions. This study built a two-dimensional numerical model coupling groundwater flow and salt transport in non-isothermal conditions at the site scale to investigate the impact of cut-off walls on groundwater discharge processes, considering the thermal effect. We focused on the dynamic characteristics of submarine groundwater discharge in non-isothermal conditions which are common in reality. This research quantitatively assessed the influence of seawater temperature on groundwater discharge flux (Q) and relative discharge flux (Q'). The results indicate that, under high-temperature seawater conditions, the timescale for Q' to reach equilibrium is significantly reduced. Specifically, higher freshwater temperatures and lower seawater temperatures could result in a greater Q'. However, when the seawater temperature exceeded the groundwater temperature by 15°C, reverse circulation is more likely to develop in the saltwater zone, which accelerates groundwater circulation and increases the total groundwater discharge into the sea, resulting in a corresponding rise in the Q' value. This study is significant for cut-off wall structure optimization and coastal groundwater sustainable utilization.
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Key words:
- seawater intrusion /
- thermal effect /
- coastal aquifer /
- numerical simulation
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图 3 海水温度为20 °C（a）、5 °C（b）和35 °C（c）时，在距离海洋边界70 m处建造26 m高截渗墙后经过0，2，40 a时的渗透系数分布图
Figure 3.
图 6 地下水温度为20 °C（a）、5 °C（b）和35 °C（c）时，在距离海洋边界70 m处建造26 m高截渗墙后经过0，2，40 a时的渗透系数分布图
Figure 6.
模型参数 参数取值 单位 含水层厚度（H） 50 m 含水层长度（L） 400 m 有效孔隙度（n） 0.4 — 水力梯度（dh/dL） 4.0 ‰ 淡水质量浓度（Cf） 0 g/L 咸水质量浓度（Cs） 35 g/L 渗透率（ks） 2×10−11 m2 纵向弥散度（αL） 1.00 m 横向弥散度（αT） 0.1×αL m 多孔介质导热系数（λ） 0.6 J/（m·°C·s） 流体导热系数（λp） 3.5 J/（m·°C·s） 固体骨架比热容（cp,p） 4182 J/（kg·°C） 流体比热容（cp） 840 J/（kg·°C） 固体骨架密度（ρp） 2650 kg/m3 
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