潮汐对地下水波动影响的数值模拟

本文从经典的Boussinesq方程出发，在考虑浸润面影响的基础上，建立了基于有限差分法的滨海地区一维地下水运动数值模型。通过将潮汐运动概化为正弦波，模拟了滨海地区地下水水位随潮汐波动的变化。结果显示，地下水水位的波动相对于潮汐波动来说具有不对称性、振幅衰减以及相位滞后等特征。通过比较受潮汐影响的地下水平均水位与不考虑潮汐影响的地下水水位发现，实际的地下水平均水位要高于未考虑潮汐影响的地下水水位。最后数值模拟了浸润面的形成和消失的过程。     

An Analytical Solution of Boussinesq Equation to Predict Water Table Fluctuations Due to Time Varying Recharge and Withdrawal from Multiple Basins, Wells and Leakage Sites

Recharging and pumping are the integral part of any scheme of ground water resources development and both processes significantly affect the dynamic behavior of the aquifer system. Leakage from the aquifer’s base, if present, is other process which affects the water table variation. Therefore, an accurate estimation of water table fluctuation induced by recharging, pumping and leakage is pre-requisite to ensure sustainability of groundwater resources. In the present work an analytical solution of a 2-D linearized Boussinesq equation is developed to predict water table fluctuations in the presence of time varying recharge, pumping and leakage from any number of recharge basins, wells and leakage sites of any dimension for any number of recharge and pumping cycles. The rate of time varying recharge (or pumping) is approximated by using a series of linear elements of different lengths and slopes which are dependent on the nature of variation in the recharge (or pumping) rate. Application of the solution in the prediction of water table fluctuation in the presence of time varying recharge, pumping and leakage is demonstrated with the help of a numerical example. These numerical results indicate significant effect of the time varying recharge/pumping rates and leakage on the water table variation. Such information is useful for the proper management of groundwater.     

Impacts of Receding of the Lakes Located in the Arid and Semi-arid Areas on the Coastal Groundwater: Integrated Modeling and Experimental Study

The dropping of the water level of the lakes located in the arid lands leads to salt concentration increase. In this study, a combined experimental-computational method is developed to explore the effect of seawater concentration on the elevation of groundwater table and the rate of saltwater intrusion, while the lake water level is dropping. At the laboratory tank scale, we have collected experimental data by varying the saltwater concentration by 2.0 and 2.5 times its initial value while measuring the height of the groundwater table. Our simulation has shown an unexpected increase in height of groundwater by 5.0 and 13.0% relative to the head difference at the boundaries of the domain. Also, the intrusion rate of saltwater wedge increased by 2.0 and 3.0 times, respectively. We have used the verified model for a field state and found that if density variations are neglected in simulation, the calculated groundwater level is affected more than 2 times in response to fluctuation of lake water level (relative to simulations by including the effect of fluid density changes). Based on the results density variations can counteract; even reverse, the effect of water table changes. Remarkably, our simulations have shown that despite a severe decrease in the water level of a saline lake over time, the saltwater wedge has indeed intruded further because of the substantial increase in the density of the lake water due to the rising salinity. Based on the findings, to reach a reasonable result in the study of interaction between saline water of shrinking lakes with coastal groundwater, saltwater concentration as well as saline water density in the modeling must be considered.

     

TIDAL EFFECTS ON GROUNDWATER DYNAMICS IN COASTAL AQUI-FER UNDER DIFFERENT BEACH SLOPES

The tide induced groundwater fluctuation and the seawater intrusion have important effects on hydrogeology and ecology of coastal aquifers.Among previous studies,there were few quantitative evaluations of the joint effects of the beach slope and the tide fluctuation on the groundwater dynamics.In this article,a numerical model is built by using the software FEFLOW with consideration of seawater intrusion,tide effects,density dependent flow and beach sloping effects.The simulation results are validated by laboratory experimental data in literature.More numerical scenarios are designed in a practical scale with different beach slopes.Results show that the groundwater fluctuation decays exponentially with the distance to the beach,i.e.,,and our simulation further shows that the beach slope influence can be expressed in the form of a logarithm function.While for the same location,the amplitude increases logarithmically with the beach angle in the form,where and are related with the horizontal distance()in the form of a logarithm function.The beach slope has no influence on the phase lag,although the latter increases regularly with the distance from the sea.The beach slope effect on the seawater intrusion is investigated through the quantitative relationship among the relative intrusion length(),the relative enhancement of the tide induced seawater intrusion()and the beach angle().It is shown that the tide effects on a milder beach is much greater than on a vertical one,and both λ and κ can be expressed in logarithm functions of.The tidal effect on the flow field in the transition zone for a particular mild beach is also studied,with results showing that the tide induced fluctuation of is similar to the groundwater table fluctuation while shows a distinct variation along both directions.     

Estimating Land Use Impacts on Regional Scale Urban Water Balance and Groundwater Recharge

Anthropogenic activities have exerted increasingly large-scale influences on terrestrial ecological systems from the past century, primarily through agriculture; however, the impact of such changes on the hydrologic cycle is poorly understood. As one of the important land use (LU) in the coastal Dogo Plain of the Seto Inland Sea, Japan, paddy fields have been decreasing with the increase in urbanization in recent decades. As the main source of water in the Dogo Plain, groundwater plays an important role in providing people with fresh water and contributing to stream base flow. The purpose of this study is to analyze the water resource and evaluate the effect of LU change on groundwater table fluctuation in this coastal plain. Firstly, the observations of groundwater table and the investigation of water balance were carried out in this alluvial plain. Then, a distributed four-block three-layer water balance model was employed to analyze the groundwater table fluctuation with response to the change of paddy field area. Moreover, the role of paddy field in recharging groundwater in the basin has been clarified. Results show that groundwater table depends not only on rainfall and discharge from rivers, but also on irrigation water and topology of the study area. The net groundwater recharge was positive in irrigation periods whereas that in non-irrigation periods was nearly equal to zero or negative. The results of this study would be helpful to the urban development policy and land use planning decision.     

基于元数据分析的西北干旱区生态地下水位埋深及其影响因素

综合现有文献研究成果, 基于元数据分析方法研究不同植被的适宜、极限生态地下水位埋深。选择乔木、灌木 和草本等 3 种植被类型中的 13 种植物, 分析适宜、极限生态地下水位埋深的统计分布、生物多样性和丰富度指数, 推求生态地下水位埋深与植物根系和土壤质地的关系, 得出: 西北地区适宜和极限生态地下水位埋深均值分别为 2. 9、5. 5 m, 控制范围分别为 2. 3~ 3. 9、4. 0~ 7. 2 m; 适宜、极限生态地下水位埋深与植物根系具有显著的相关关系, 适宜生态地下水位埋深还取决于植物根系伸展速率与地下水位埋深下降速率的相对关系; 土壤质地控制毛细管上升高度及地下水位埋深以上水分供给能力, 是确定生态地下水位埋深的重要因子。     

Water-table variation in a sloping aquifer due to random recharge

Variation in the level of the water table is closely linked with recharge. Therefore, any uncertainty associated with the recharge rate is bound to affect the nature of the water-table fluctuation. In this note, a ditch-drainage problem of a sloping aquifer is considered to investigate the effect of uncertainty in the recharge rate on water-table fluctuation. The rate of recharge is taken as an exponentially decaying function with its decay constant as a Gaussian random variable. Expressions for the first two moments of the water-table height, i.e. mean and standard deviation, are presented. By using these expressions, the effect of uncertainty in the recharge rate on the water-table fluctuation has been analyzed with the help of a numerical example.     

基于时间序列模型的济南趵突泉地下水位预测

本文对2012年5月至2017年12月济南泉域趵突泉的地下水位波动规律进行了分析,并采用3种灰色时间序列模型,评价了保泉形势,通过模型的拟合效果检验可知:对于存在周期性波动趋势的地下水位观测值,GM(1,1)模型优势未能得到充分体现,ARIMA与Holt-Winters模型的预测结果较为接近,整体精度较高,表现出明显的预测优势。深入比选ARIMA与Holt-Winters模型的8项拟合优度指标,最终确定利用预测效果最优的Holt-Winters模型,从时间序列的角度对趵突泉地下水位进行分析,并预测2018—2019年趵突泉的年平均水位分别为27.734m和27.605m,泉水位波动的峰值为28.215 m,谷值将出现于2019年的6月份,数值仅为27.124m,逼近27.01m的泉水停喷线,为近7年来的最低水位。预测结果表明:现状降雨与开采条件下,2019年6月趵突泉将面临潜在的停喷的危机,保泉形势不容乐观。     

Operational Prediction of Groundwater Fluctuation in South Florida using Sequence Based Markovian Stochastic Model

The ecosystem of South Florida is characterized by a vast wetland system, karst surficial hydrogeology, and extended coastal boundary. The ecosystem is poised under risks of: ecological failure due to increased fragmentation by urbanization; groundwater flow disruption because of sinkhole formation; and intrusion of oceanic water with decreasing water table head because of drought or over pumping. It was found important to synthesize the spatiotemporal state of the groundwater hydrology and also develop a forecasting model to support the intensive management and monitoring in place. In this study, an objective was set to develop a stochastic sequence model capable of forecasting groundwater levels on a monthly span at a daily time scale. The groundwater level simulation was conceptualized as a sequence of daily fluctuating states of magnitudes and patterns that has a defined probability of occurrence. The model setup involved representation of daily fluctuation magnitudes in ten states and pattern changes in three states. The sequential occurrence of states of magnitudes and patterns at each time step was used for estimation of the transitional probabilities and employed in a hidden Markov model frame work for ensemble generation and estimation of posterior probabilities. A realization was chosen based on the highest maximum likelihood ratio of 90% and smallest root mean square error of 0.05–0.12 m against the historical data. A monthly forecasting at daily time step was done dynamically incorporating observed data at each time step and revising prior and posterior probability estimation in the hidden Markov model formulation. A case study was conducted at three well sites, which are situated at three different hydrogeologic settings. The model not only reproduced annual groundwater fluctuation patterns but also forecasted preceding monthly fluctuations at maximum likelihood ratio above 90% and root mean square error below 0.15 m. A further study was recommended first to analyze break point parametric estimation for seasonal analysis, and secondly to integrate the approach in other hydrological models for the purpose of synthetic groundwater fluctuation generation.     

南通市第四纪松散沉积层地下水资源评价规划三维数值模型

根据南通市第四纪松散沉积层地下水系统的水文地质机制,构建了地下水运动的三维数值模型,并在模型识别、验证的基础上,针对各含水层地下水位的控制要求,调整了现有地下水的开采布局,以乡镇为单位,确定出各含水层的地下水可开采资源量及最优开采布局,并预测了2006年底至2021年底逐年地下水水位动态变化情况。     

洪水过程对河岸带地下水水位波动的影响

为揭示洪水作用下河岸带地下水的响应过程,利用室内物理模型试验和数值模拟,研究了不同洪峰及洪峰持续时间对地下水水位波动的影响。结果表明:河岸带地下水水位的波动具有不对称性,水位上升快下降慢,沿程地下水水位的波动呈指数形式衰减,并表现出明显的滞后性;随着洪水洪峰增大,地下水水位波动增大,河水和地下水的交换量增大,而地下水水位的滞后变化不明显;洪峰持续时间变长,地下水水位的滞后性显著,内陆地下水水位波动的幅度增大,恢复至初始状态的时间变长。     

潮汐对沿海潜水水位的影响研究

沿海潜水地下水水位受到潮汐海平面的振动影响而上下波动,而地下水水位的位置与沙滩的稳定性和海水入侵有密切的联系。通过潮汐对沿海地下水水位影响的方程形式的概述,综述了在解析解与数值解方面的研究进展,并在此基础上提出了潮汐影响下地下水水位变化的3个特征:振动不对称性、振幅有衰减、相位滞后。     

盐城市地下水资源规划评价三维数值模型

根据盐城市地下水系统的水文地质机制,在概化出盐城市地下水系统水文地质概念模型的基础上,建立了盐城市地下水资源规划评价的三维数值模型,并针对盐城市对各含水层地下水水位的控制要求,给出了各含水层的最优开采量,为合理开发利用盐城市地下水资源提供了科学依据。     

黄河三角洲1961—2000年水资源时空变化特征

采用降水量、径流量、地下水位及埋深4个指标对1961—2000年水资源的时空变化特征进行分析。结果表明:①降水量年内及年际变化均较大,年内降水量集中于夏季,年际呈下降趋势,空间分布呈自南向北逐渐下降的趋势。②黄河入境径流量年内及年际变化均较大,根据趋势分析1986年之前径流量变化较平缓,之后呈线性下降趋势。当地径流量年内变化较大,夏季径流量超过全年的80%;年际变化较小,呈峰-谷-峰的变化趋势。③东营市浅层地下水位年内变化较小,其中广饶县年内及年际变化均较大,自20世纪80年代至21世纪初平均下降了12.78m。④广饶县地下水埋深自70年代至90年代增幅达到14.70m。1975—2000年广饶县地下水埋深呈显著线性增加趋势(R2=0.93),年均增速达到0.72m/a。     

RELATIONSHIP AMONG EVAPORATION FLUX OF GROUNDWATER, DEPTH OF WATER TABLE AND NEGATIVE PRESSURE HEAD IN BARE SOIL

1.　 INTRODUCTIONThe crisis of water resources is a global problem.Compared with other countries,Chi-na relatively falls shortof water resources.The amount of water resources per capita is justone fourth as the world average value. The distribution of water resources is outof balance.81 % ofthe water resources is concentrated in the reach of the Yangtse River and the south-ern areas of China,while only1 9% is in the areas of the north to the Yangtse River,inwhich the population is4 5.3%…     

Groundwater Response to Tidal Fluctuation in an Inhomogeneous Coastal Aquifer-Aquitard System

This paper investigates tide-induced groundwater fluctuation and submarine groundwater discharge (SGD) in a leaky inhomogeneous coastal aquifer system with an upper unconfined aquifer, a lower confined aquifer, and an aquitard between them. The upper left aquifer is formed due to land reclamation. The SGD defined as the groundwater flow from land into the sea is controlled mainly by the hydraulic gradient between land and sea. An analytical expression is developed to discuss and assess the effect of inhomogeneity on the groundwater head fluctuation in the leaky aquifer system. Joint effects of aquifers’ parameters such as leakage and hydraulic diffusivity on the groundwater head fluctuation and SGD are investigated. The predicted results from the analytical expression indicate that the groundwater head fluctuation in both unconfined and confined aquifers is dependent on dimensionless leakages and increases with dimensionless hydraulic diffusivity.     

地热水资源开发的多目标优化管理

以塘沽地热田为例,建立了地热水位模拟的数值模型,并利用1991年11月至1995年4月的水位动态资料进行了模型的识别与验证.针对31眼地热井布局方案不甚合理的现状,以地热田水位降深最小及地热井开采时干扰最小为目标函数,以地热田最大水位降深满足设计降深及地热井开采量满足实际需水量为约束条件,建立了地热田开采的双目标函数优化管理模型,求解模型得到了优化开采方案.通过与现状开采方案的对比,说明所制定的优化开采方案是合理的.     

Understanding groundwater table using a statistical model

In this study, a statistical model was established to estimate the groundwater table using precipitation, evaporation, the river stage of the Liangduo River, and the tide level of the Yellow Sea, as well as to predict the groundwater table with easily measurable climate data in a coastal plain in eastern China. To achieve these objectives, groundwater table data from twelve wells in a farmland covering an area of 50 m × 150 m were measured over a 12-month period in 2013 in Dongtai City, Jiangsu Province. Trend analysis and correlation analysis were conducted to study the patterns of changes in the groundwater table. In addition, a linear regression model was established and regression analysis was conducted to understand the relationships between precipitation, evaporation, river stage, tide level, and groundwater table. The results are as follows:(1) The groundwater table was strongly affected by climate factors(e.g., precipitation and evaporation), and river stage was also a significant factor affecting the groundwater table in the study area( p 0.01, where p is the probability value).(2) The groundwater table was especially sensitive to precipitation. The significance of the factors of the groundwater table were ranked in the following descending order:precipitation, evaporation, and river stage.(3) A triple linear regression model of the groundwater table, precipitation, evaporation, and river stage was established. The linear relationship between the groundwater table and the main factors was satisfied by the actual values versus the simulated values of the groundwater table(R~2 = 0.841, where R~2 is the coefficient of determination).     

郑州黄河“九五”滩大口径管井井组抽水试验分析

对井组抽水试验观测资料的分析表明,在水位降深不大时,开采量与水位降深呈线性关系;开采条件下,黄河与地下水的水力联系十分密切,短时间内黄河水位的涨落距河边线３００ｍ以内的观测孔水位均有明的影响,且水位变化幅度随观测孔距河线距离的增大而减小;抽水试验引起的地下水位下降不会对黄河大堤造成危害,预测今后长期大量开采地下水所引起的地面积沉降亦不致对黄河堤造成危害性影响,用多种方法得到的水文地质参数为：导水系     

A Finite Element Model for the Unsteady Groundwater Flow over Sloping Beds

A numerical solution of the nonlinear two-dimensional unsteady groundwater flow over sloping beds, using the Galerkin finite element method, is presented. The applied differential equation is based on the assumption that the streamlines are parallel to the sloping bed while the conventional differential equation is based on the Dupuit–Forchheimer assumption of horizontal flow. Furthermore, the gradient of the piezometric head is evaluated as a function of the unknown slope of the groundwater free surface and not simply as the absolute slope of the water table. Water table profiles and seepage rates obtained from the model are compared with those obtained by analytical solutions and experimental results for steady one-dimensional flow and for different values of bed slope. Results of the present model compares reasonably well with experimental results and with the results of Childs' analytical solution. The unsteady-state solution for different values of bed slope are compared to the results of a model based on the assumption that the water table slope is equal to the bed slope. The differences in the predicted water table by these two models are insignificant for small slopes but increase with increasing slope.