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高校地质学报 ›› 2023, Vol. 29 ›› Issue (4): 580-589.DOI: 10.16108/j.issn1006- 7493.2021104

• 水文地质学 • 上一篇    下一篇

降雨引起的非饱和带压力波传播过程及其对地下水快速排泄的影响研究

党 磊1,谢月清1*,汪 钏1,常 勇2,曾献奎1,吴吉春1   

  1. 1. 南京大学 地球科学与工程学院,南京 210023;
    2. 河海大学 地球科学与工程学院,南京 211100
  • 出版日期:2023-08-15 发布日期:2023-08-15

Precipitation-induced Pressure Wave Propagation in Unsaturated Zone and Its Effect on Rapid Groundwater Discharge

DANG Lei1,XIE Yueqing1*,WANG Chuan1,CHANG Yang2,ZENG Xiankui1,WU Jichun1   

  1. 1. School of Earth Sciences and Engineering, Nanjing University, Nanjing, 210023;
    2. School of Earth Sciences and Engineering, Hohai University, Nanjing, 21100
  • Online:2023-08-15 Published:2023-08-15

摘要: 大量基于河流水化学与同位素的研究表明,降雨引起的河流流量增量很大一部分来源于流域内储存的“旧水”,这一现象被称为“旧水悖论”,降雨引起的非饱和带压力波可能是造成这一现象的一个原因。本研究构建了四种不同土壤类型(砂土、壤质砂土、砂质壤土、壤土)的土柱数值实验,重点探讨非饱和带压力波传播过程及其推动地下水快速排泄的可能性,分析“旧水悖论”发生的原因。模拟结果显示,所有土壤中均能观测到压力波现象,第一次强降雨发生后,四种土柱中压力波传播时间分别为1.86、2.84、5.24和7.46天。压力波现象本质上是水力信号的快速传递,并不表示本次降雨的快速流动,实验中当土柱底部对降雨产生响应时,水化学特征还没有同时发生改变,而是分别滞后到6.12、10.33、18.05和30.00天,引起不同土柱压力波波速和土壤水流速的差分别为74.71、51.05、27.08和20.13 cm/d。 研究表明,压力波波速和土壤水流速与土壤特征曲线和饱和渗透系数紧密相关,在所有土壤中砂土中形成的压力波更容易快速传递到地下水。由于流域中非饱和带厚度一般与河流垂直距离成正比,河滨带压力波能够快速传递到地下水,并能够推动土壤水向地下水和河流排泄,这种现象在渗透性较好的土壤中更为明显。本研究为更准确地认识流域水文过程和更好地揭示“旧水悖论”机理提供了重要理论支撑。

关键词: 旧水悖论, 地下水排泄, 非饱和带, 压力波, 溶质迁移

Abstract: A large number of studies, using water chemistry and stable isotopes to conduct hydrograph separation, indicate that majority of stream water during rainfall is derived from ‘old water’ that is stored in the catchment before the rainfall. This phenomenon is known as ‘old water paradox’. Pressure wave in unsaturated zone driven by precipitation is regarded as a potential underlying mechanism. In this study, we established four numerical soil column experiments with different soil types (sand, loamy sand, sandy loam and loam). We attempted to explore pressure wave propagation and the possibility of rapid groundwater discharge driven by the pressure wave with demonstrative experiments. Our results show that after the first intensive rainfall, pressure wave were generated in the four columns and were observed at the bottom after 1.86, 2.84, 5.24 and 7.46 days. In comparison, the relevant soil water arrived at the bottom after 6.12, 10.33, 18.05 and 30.00 days. The differences between celerities and velocities are 74.71, 51.05, 27.08 and 20.13 cm/d. Our study indicates that celerities and velocities are strongly affected by soil hydraulic conductivities and soil retention curves, and pressure waves in sand can be propagated more easily than those in other soil types. As the thickness of unsaturated zone is usually linearly proportional to the distance from river bank, pressure wave generated during precipitation can propagate into groundwater and drive rapid groundwater discharge. This process would be easier in more permeable soils. Overall, this study advances our understanding of catchment hydrology and helps discover underlying mechanisms in a theoretical manner. 

Key words: old water paradox, groundwater discharge, unsaturated zone, pressure wave, solute transport

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