Tidal Fluctuation in a Coastal Aquifer System with a Suboutcrop Covered by a Silt Layer
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摘要: 滨海地区社会与经济的发展引发了各种各样的水文地质问题, 因此对滨海地区的水文地质条件, 尤其是地下水与海水之间的水力联系的研究尤为重要.本文考察了海底露头处具有淤泥层的滨海含水层系统中由海潮引起的水头波动.该系统由潜水含水层、承压含水层和介于其间的弱透水层构成.建立了该系统的数学模型, 得到了该模型的解析解.该解析解包含2个无量纲参数: 弱透水层的相对越流系数和淤泥层的相对透水系数.解析解表明, 淤泥层使各处的水头波幅被缩小了一个常数倍(波幅缩减因子), 并使各处的波动相位产生了一个不超过45°的正位移常数(时滞).该时滞对半日潮不超过1.5h, 对全日潮不超过3h.波幅缩减因子和正位移常数只与弱透水层的相对越流系数和淤泥层的相对透水系数有关.当这两个无量纲参数取某些特殊值时, 本次研究的解和前人考虑的几种较简单情形所对应的解一致.承压含水层中水头波幅随着淤泥层的相对透水系数的递增而严格递增, 随弱透水层的相对越流系数的递增而严格递减; 波动相位随着这2个无量纲参数的递增均严格递减.分析表明弱透水层的越流和淤泥层的存在均对承压含水层水头波动有显著影响.Abstract: With the social and economic development in coastal areas, a variety of hydrogeological problems arise.In order to solve these problems, it is necessary to study hydraulic relation between ground water and seawater.This paper explores the tide-induced ground water head fluctuation in a coastal multi-layered aquifer system with a suboutcrop covered by a silt layer.The system consists of an unconfined aquifer, a leaky confined aquifer and a semi-permeable layer in the middle.The mathematical model for describing the system is built and the analytical solution to the model is derived.The analytical solution contains two dimensionless parameters: the leakances of the semi-permeable layer and the silt-layer, respectively.The silt layer reduces the amplitude of the hydraulic head fluctuation by a constant factor, and increases the phase by a positive shift (time-lag), both of which depend on the leakances of the silt layer and the semi-permeable layer.The time lag does not exceed 1.5 h and 3.0 h for semidiurnal and diurnal sea tides, respectively.When the leakance of the semi-permeable layer or the silt layer assumes certain special values, the solutions are in accordance with the ones derived by several previous researchers.The amplitude of the hydraulic head fluctuation in the confined aquifer increases with the leakance of the silt-layer and decreases with the leakance of the semi-permeable layer; while the phase shift of fluctuation decreases with both of them.The solution analysis indicates that both the silt layer and the leakance of the semi-permeable layer influence significantly the hydraulic head fluctuation in the confined aquifer.
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Key words:
- tide /
- coastal aquifer system /
- silt-layer boundary /
- submarine outcrop /
- leakance /
- analytical solution /
- leakance of the silt layer
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图 1 露头处具有淤泥层的滨海含水层系统在垂直于海岸线方向上的横断面示意图
Fig. 1. Schematic of the cross-intersection perpendicular to the coastline of a coastal aquifer system with a suboutcrop covered by a silt layer
图 2 波幅缩减因子Csilt和相位移φsilt分别随着淤泥层的相对透水系数σ在弱透水层的相对越流系数u取不同值时的变化
Fig. 2. Changes of both the amplitude reducing factor Csilt and phase shift φsilt with the dimensionless leakance σ of the silt layer for different values of the dimensionless leakance u of the semi permeable layer
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