地下水位前兆敏感水力学条件的数值模拟研究

根据弹性孔隙理论,利用数值分析的方法,研究了承压含水层对井水位的映震效果的影响,模拟结果显示：含水层系统的封闭状态对水位的映震效果有很大的影响,侧漏的大小和水头的高低会直接影响水位的观测效果,在系统封闭很好的情况下,观测水位的变化基本与水头的变化呈线性关系,此外,含水层系统的渗透性也是影响水位变化的重要条件之一,渗透性好则水位的映震效果明显。     

两种井孔变径对水位影响试验的解释

井孔变径对井水位固体潮效应影响的试验有两种不同的结果：一种是影响很大，响应幅度与井径的平方成反比；另一种是影响不大。本文用两种模式解释了两种结果，认为这与水井含水层的渗透系数及含水体的大小有关，渗透系数及含水体越大，则井孔变径对井水位固体潮效应影响越大。这主要体现了并孔水柱压力水头与含水层内孔隙压平衡，所以与并径大小无关。当渗透系数与含水体很小时，主要体现了井孔内水量变化与含水层释放、吸收水量平衡。一般情况下是介于两者之间。     

定水头注水引起的含水层水平运动和应变

基于含水层固体颗粒与孔隙水不可压缩的假设，本文导出了单井注水情况下秦斯承压含水层水平运动速度与水头之间的基本关系式。然后利用注水井壁处的应力、应变边界条件，进一步导出了单井定水头注水引起的泰斯承压含水层水平运动速度、位移和应变解析表达式。该水平位移与应变由两部分组成：一部分为由注水压力本身引起的经典弹性力学解项，它仅随半径而变化，与注水时间无关；另一部分为由地下水头变化引起的水动力学位移和应变解项。其中，含水层水动力学水平位移随时间加长呈指数增长特征、水动力学径向应变则表现为近井处拉张、远井处挤压的分区特征，且近井拉张区随时间加长逐渐向外扩展。单井注水含水层水动力学水平位移、应变解的导出，完善和发展了单孔内压经典弹性平面力学问题解。     

永安井数字化水位水温主要影响因素分析

通过对福建永安井自数字化观测以来的水位、水温资料分析,认为该井水位的主要影响因素为降雨和上游水库泄洪的影响;水温的影响因素较为复杂,主要为水位变化、降雨及上游水库泄洪的影响,但影响水温变化的机理不同.水位的趋势变化对水温的影响是由于随着水位的上升或下降,会引起含水层中孔隙压力发生变化,从而引起水温梯度的变化;降雨对水温的影响变化是由于冷水的渗入,在含水层水头不变的情况下,低温水比例增大,高温水比例减小,从而使得水温下降;上游泄洪对水温造成的影响,是由于处于下游的井孔孔内的渗透率增大,导致水位升高引起水温梯度发生变化,从而使得水温升高.     

日本秋田地震(1983年7.7级)引起我国应力场的震时调整变化

本文通过水平分层承压含水层模型,推导出含水层的水头和含水层应力变化之间的定量关系.利用我国在日本秋田地震时有水位阶变的52口井孔的观测资料,通过水井水位的体应变固体潮系数,估算了震时引起我国应力场的调整变化.讨论了这种应力调整时应力增加区和降低区交替出现的可能原因。     

一种估算地震引起应力场调整的新方法

引言 承压含水层内水井水位的变化可反映含水层孔隙压的变化,而含水层孔隙压的变化与含水层所受的压力状态有密切的关系。地壳内的应力变化有时可影响到含水层所受应力状态发生变化。构造地震的发生,一般看作是地壳内应变的积累,岩体裂隙形成演化的结果。所以在大地震发生时会引起大区域应力场的调整变化。这种应力场的调整变化是     

日本秋田地震(1983年7.7级)引起我国应力场的震时调整变化

本文通过水平分层承压含水层模型,推导出含水层的水头和含水层应力变化之间的定量关系.利用我国在日本秋田地震时有水位阶变的52口井孔的观测资料,通过水井水位的体应变固体潮系数,估算了震时引起我国应力场的调整变化.讨论了这种应力调整时应力增加区和降低区交替出现的可能原因.      

冷水源井水温固体潮现象及其机理研究以黄村井为例

该文对黄村冷水源井的水温固体潮现象进行了观测研究,初步解释了冷水源井的水温固体潮汐的形成机理.通过对黄村观测井进行水温梯度的详细观测及不同深度水温的对比观测研究,得到了黄村井水温潮汐现象的观测结果:① 黄村冷水源井的水温固体潮的相位与水位的相位是相反的;② 黄村井水温梯度曲线呈下凹型,特别是在含水层及受含水层进出水影响较大的附近区域下凹程度大,且随着与含水层底板距离逐渐变大,下凹程度也变小;③ 水温传感器的观测值与含水层观测距离存在一定的规律性:距离含水层越远,水温潮汐差越小, 直至潮汐变化消失.这说明冷水源井与热水井的水温潮汐现象是不同的,前者是吸热过程, 后者是放热过程,由此造成二者水-热动力学特征的不同.      

云南普洱大寨井水位同震响应研究及预测意义

通过研究1990—2019年云南普洱大寨井水位的同震响应特征,分析井水位响应特征的变化与后续中强地震的关系,并探讨含水层渗透性对区域构造活动的影响。结果显示:当同震响应幅度偏离统计关系时,井孔周边区域后续地震活动有所增强;固体潮相位差由负值变为正值,表明观测井孔含水层渗透性参数发生改变,这与区域地震活动的变化可能存在一定的相关性。分析认为,井水位同震响应和含水层渗透性参数变化可作为探索区域构造和地震活动的参考指标。     

利用时序InSAR技术反演邯郸平原区地表形变与含水层参数

邯郸平原区承压地下水长期处于严重超采状态,导致大面积地面沉降,直接威胁到该地区重大基础设施安全.因此,查明地面沉降时空演变特征,厘清承压地下水变化与地面沉降的耦合关系,对预防和治理地面沉降地质灾害具有重要意义.本文利用Sentinel-1A数据进行时间序列分析,获取了2015—2019年邯郸平原区地表形变时空分布结果,并结合水头数据分析了含水系统对水头变化的不同响应.利用谐波函数分离了地表形变及水头变化的季节性变化,并用其估算了邯郸平原区空间差异变化的弹性骨架释水系数;基于顾及弱透水层延迟排水的一维水头变化-形变模型,反演了非弹性骨架释水系数和时间常数.结果表明：(1)邯郸平原区以沉降为主,最大沉降速率可达14 cm·a^-1;通过与水头数据对比发现该地区地面沉降主要是由承压含水层水头下降及弱透水层的延迟排水引起.(2)水头的季节性变化引起了明显的季节性形变,沉降区季节性形变幅度可达25 mm,峰值时间为1—3月.(3)邯郸平原区弹性骨架释水系数介于1.51×10^-3～4.05×10^-3之间,与抽水试验结果较为相符;非弹性...     

Distinguishing Mountain Front and Mountain Block Recharge in an Intermontane Basin of the Himalayan Region

Intermontane basin aquifers worldwide, particularly in the Himalayan region, are recharged largely by the adjoining mountains. Recharge in these basins can occur either by water infiltrating from streams near mountain fronts (MFs) as mountain front recharge (MFR) or by sub-surface mountain block infiltration as mountain block recharge (MBR). MFR and MBR recharge are challenging to distinguish and are least quantified, considering the lack of extensive understanding of the hydrological processes in the mountains. This study used oxygen and hydrogen isotopes (δ¹⁸O and δ²H), electrical conductivity (EC) data, hydraulic head, and groundwater level data to differentiate MFR and MBR. Groundwater level data provide information about the groundwater-surface water interactions and groundwater flow directions, whereas isotopes and EC data are used to distinguish and quantify different recharge sources. The present methodology is tested in an intermontane basin of the Himalayan region. The results suggest that karst springs (KS) and deep groundwater (DGW) recharge are dominated by snowmelt (47% ± 10% and 46% ± 9%) as MBR from adjacent mountains, insignificantly affected by evaporation. The hydraulic head data and isotopes indicate Quaternary shallow groundwater (SGW) aquifer system recharge as MFR of local meteoric water with significant evaporation. The results indicate several flow paths in the aquifer system, a local flow for KS, intermediate flow for SGW, and regional flow for DGW. The findings will significantly impact water resource management in the area and provide vital baseline knowledge for sustainable groundwater management in other Himalayan intermontane basins.     

An analytical method of analysing the oscillatory pressure head measured at any depth in a well casing

When a slug test is conducted in a highly permeable aquifer, a shallow pressure transducer in the well casing produces an oscillatory pressure head that is representative of the water level fluctuation, whereas a deep pressure transducer in the well casing yields an oscillatory pressure head that is different from the water level change. Although the solutions for shallow and deep pressure head are different, it is found that the ratios of the subsequent extremity displacements are in an identical relationship (an extremity can be a maximum or a minimum in the oscillatory pressure head). Based on this relationship, an analytical data analysis method for the determination of the hydraulic conductivity is developed for both shallow and deep pressure transducer data. This analytical method is applied to the pressure head measured at different depths in the well casing of a well partially penetrating an unconfined coarse sand aquifer. Satisfactory results are obtained, validating the applicability of this analytical method for pressure transducer data at any depth in a well casing. Copyright © 2007 John Wiley & Sons, Ltd.     

Applicability of spectral analysis to determine hydraulic diffusivity

This study is to evaluate the applicability of estimating the one-dimensional horizontal hydraulic diffusivity of an unconfined aquifer with time-dependent fluctuation of lateral head and vertical recharge boundaries using observed water level spectra. Different models of boundary condition are imposed to evaluate the statistical significance between the calculated hydraulic diffusivity (ξ^′) with the given hydraulic diffusivity (ξ). The auto-spectra of the water level in observation wells tapping the same aquifer are closely related to those at the disturbed boundaries. For an aquifer with a constant hydraulic diffusivity, the water level fluctuation in the monitoring wells is linearly related to the water level spectra observed at the boundaries. The spectral density function of aquifer hydraulic head varies inversely with specific yield (S _y) and directly with recharge. Given small variation in water level spectra at the disturbed boundaries, the water level fluctuation in the aquifer is affected by the recharge condition and the aquifer spectral density function is sensitive to S _y. Using an iterative technique to estimate ξ from 1400 sets of given parameters, 99% of the ξ^′/ξ values deviated within only one order of magnitude with the model length (L) being equal to 1 km and 10 km. For L equal to 100 m, approximately 82% of the ξ^′/ξ population falls within two orders of magnitude. Therefore, spectral analysis of aquifer hydraulic head response can be used to estimate the hydraulic diffusivity of an unconfined aquifer which is affected by periodic variations in recharge and head at boundaries.     

Analysis of steady ground water flow toward wells in a confined-unconfined aquifer

A confined aquifer may become unconfined near the pumping wells when the water level falls below the confining unit in the case where the pumping rate is great and the excess hydraulic head over the top of the aquifer is small. Girinskii's potential function is applied to analyze the steady ground water flow induced by pumping wells with a constant-head boundary in a mixed confined-unconfined aquifer. The solution of the single-well problem is derived, and the critical radial distance at which the flow changes from confined to unconfined condition is obtained. Using image wells and the superposition method, an analytic solution is presented to study steady ground water flow induced by a group of pumping wells in an aquifer bounded by a river with constant head. A dimensionless function is introduced to determine whether a water table condition exists or not near the pumping wells. An example with three pumping wells is used to demonstrate the patterns of potentiometric surface and development of water table around the wells.     

Factors Influencing the Stream‐Aquifer Flow Exchange Coefficient

Knowledge of river gain from or loss to a hydraulically connected water table aquifer is crucial in issues of water rights and also when attempting to optimize conjunctive use of surface and ground waters. Typically in groundwater models this exchange flow is related to a difference in head between the river and some point in the aquifer, through a “coefficient.” This coefficient has been defined differently as well as the location for the head in the aquifer. This paper proposes a new coefficient, analytically derived, and a specific location for the point where the aquifer head is used in the difference. The dimensionless part of the coefficient is referred to as the SAFE (stream‐aquifer flow exchange) dimensionless conductance. The paper investigates the factors that influence the value of this new conductance. Among these factors are (1) the wetted perimeter of the cross‐section, (2) the degree of penetration of the cross‐section, and (3) the shape of the cross‐section. The study shows that these factors just listed are indeed ordered in their respective level of importance. In addition the study verifies that the analytical correct value of the coefficient is matched by finite difference simulation only if the grid system is sufficiently fine. Thus the use of the analytical value of the coefficient is an accurate and efficient alternative to ad hoc estimates for the coefficient typically used in finite difference and finite element methods.     

Development and application of an analytical model of stream/aquifer interaction

A mathematical model to simulate stream/aquifer interactions in an unconfined aquifer subjected to time varying river stage was developed from the linearized Boussinesq equation using the principle of superposition and the concept of semigroups. The mathematical model requires an estimate of three parameters to simulate ground-water elevations; transmissivity, specific yield, and recharge. The solution has physical significance and includes terms for the steady-state water level, the steady-state water level as influenced by a change in river stage, a transient redistribution of water levels in the aquifer from the previous day, and a transient change in water level caused by a change in river stage. The mathematical model was tested using observed water table elevations at three locations across a 2-km-wide alluvial valley aquifer. The average absolute deviation between observed and simulated daily water levels was 0.09 m. The difference in river stage over the test year was 4.9 m.     

大震前地下水位异常与应力异常区

利用井口水位对潮汐应力的响应，分析了含水层对强震孕育过程中应力变化的响应。结果显示，当含水层的瞬时应力变化值大于临界值时，水位的异常图像为阶变形态；当含水层的瞬时应力变化值小于临界值，但某一时段的累计值大于临界值时，水位的异常图像为缓变形态。而水位异常图像出现的上升或下降形态，取决于井孔含水层系统在大震孕育过程的应力调整再积累阶段所处的构造部位。水位震前异常的特征，源于地震孕育过程中应力异常区的形成。     

中国地下水潮汐的观测研究和分析

本文简单介绍了中国地下水潮汐的观测研究情况,介绍了对承压水位潮汐机理研究的理论结果,给出了固体潮体应变、气压和海洋潮汐对承压水头影响的偏微分方程,从这些方程的简化解讨论了它们与含水层参数间的关系.并从全国选取了33口有代表性的井孔,对这些井孔的水位和气压观测资料采取反复调和分析的方法,求出了它们的水位固体潮体应变各分波的潮汐系数和位相滞后,也求出了水位气压各分波的系数和位相滞后.