Theis不稳定潜水井流模型的改进——具入渗补给

地下水的补排主要包括垂向的地面入渗补给、蒸发排泄（蒸发可视为入渗的负值）及侧向的地表水补给、排泄。水文地质学最基本的问题之一——地下水可持续开釆量的评价准则,涉及补给的增量与排泄的减量,因此地下水开采的预测模型必须包含上述两类的补给、排泄因素,否则不能满足要求。然而,经典的Theis不稳定井流模型,即使在傍河抽水,也只有侧边界的补给、排泄作用,而不涉及上边界的地面入渗补给。这样一来,这个解析模型基本上不能够用于预测,而只能在旱季用于井流试验求取含水系统的参数。为此,文章的目标是发展具地面入渗补给的Theis不稳定潜水井流模型。对于潜水流问题,不能再用承压水流的以水头为应变量的方程来建立,应采用第二类线性化方法的势函数来建立潜水流问题。对于既有降雨入渗补给,又有抽水井作用的复杂的水文地质问题所概化数学模型的求解,采取的方法是把它分解成若干个简单的子模型问题求解,然后将其合成为原来复杂数学模型的解。基于质量守恒原理,假定渗流服从Darcy定律并满足Dupuit徦定建立了水流基本微分方程。然后对于两平行河流及一河流平行一隔水边界形成的两类条形区域,具地面均匀稳定入渗补给的井流问题,获得通用水位方程和几类常见的特定条件水位方程及其流量方程。此外,提出并采用“边界对边界的反映法”用以求解一河流平行一隔水边界条形区域的同一问题,减少了许多推导过程。最后,作为上述理论成果的初步应用,也是一个重要的应用,即在河水水质不能满足要求的河流附近,设有一口抽水井,计算该抽水井在不汲取河水的前提下的临界流量方程,获得具重要意义的结构简洁的关系式。该方程也可以用于滨海区的抽水井,在不发生海水入侵前提下的临界抽水流量计算。给出了上述条件不稳定井流过程某时刻的地下水流网图,其流网与文献中常见的傍河井流的流网相比,具显明的特征。     

Groundwater evolution beneath Hat Yai, a rapidly developing city in Thailand

Many cities and towns in South and Southeast Asia are unsewered, and urban wastewaters are often discharged either directly to the ground or to surface-water canals and channels. This practice can result in widespread contamination of the shallow groundwater. In Hat Yai, southern Thailand, seepage of urban wastewaters has produced substantial deterioration in the quality of the shallow groundwater directly beneath the city. For this reason, the majority of the potable water supply is obtained from groundwater in deeper semi-confined aquifers 30–50 m below the surface. However, downward leakage of shallow groundwater from beneath the city is a significant component of recharge to the deeper aquifer, which has long-term implications for water quality. Results from cored boreholes and shallow nested piezometers are presented. The combination of high organic content of the urban recharge and the shallow depth to the water table has produced strongly reducing conditions in the upper layer and the mobilisation of arsenic. A simple analytical model shows that time scales for downward leakage, from the surface through the upper aquitard to the semi-confined aquifer, are of the order of several decades. Electronic Publication     

Sustainable groundwater management on the small island of Manukan,Malaysia

Numerical models are capable of simulating various groundwater scenarios and relate it towards groundwater management. This paper focuses on numerical modeling and water balance approaches in the search for a sustainable management plan in Manukan Island. The impacts of pumping and recharge rates represented by groundwater scenarios were investigated by means of hydraulic heads, chloride concentrations and water balance components. Overpumping and inconsistency in recharge rate are the stresses shown in Scenario A. Scenario B involved with reduction pumping rate by 25% has shown an increase in groundwater levels, chloride concentration and groundwater storage. Scenario C showed the most promising finding compared with Scenarios A and B. Highest hydraulic heads, lowest chloride concentration (1,552.2 mg/L) and positive groundwater storage (254.3 m³/day) were obtained in Scenario C. Chloride concentration in pumping wells still exceeds World Health Organization International Standard limit in Scenario C which illustrates an additional water treatment is needed. Nevertheless, in view of a compromise groundwater management plan in study area, Scenario C is the best plan so far to protect the groundwater resources in the study area. More understanding of the artificial recharge method (percolation tank) and study site by means of modeling studies is needed. Additionally, further progress is needed in obtaining the water usage data from each part to determine the best pumping rate. A sustainable groundwater management plan is crucial to maintain the natural resources and social benefits as well as to protect the ecological balance of Manukan Island.     

Application of Numerical Modeling for Groundwater Flow System Analysis in the Akaki Catchment,Central Ethiopia

A three dimensional steady-state finite difference groundwater flow model is used to quantify the groundwater fluxes and analyze the subsurface hydrodynamics in the Akaki catchment by giving particular emphasis to the well field that supplies water to the city of Addis Ababa. The area is characterized by Tertiary volcanics covered with thick residual and alluvial soils. The model is calibrated using head observations from 131 wells. The simulation is made in a two layer unconfined aquifer with spatially variable recharge and hydraulic conductivities under well-defined boundary conditions. The calibrated model is used to forecast groundwater flow pattern, the interaction of groundwater and surface water, and the effect of pumping on the well field under different scenarios. The result indicates that the groundwater flows regionally to the south converging to the major well field. Reservoirs and rivers play an important role in recharging the aquifer. Simulations made under different pumping rate indicate that an increase in pumping rate results in substantial regional groundwater level decline, which will lead to the drying of springs and shallow hand dug wells. Also, it has implications of reversal of flow from contaminated rivers into productive aquifers close to main river courses. The scenario analysis shows that the groundwater potential is not enough to sustain the ever-growing water demand of the city of Addis Ababa. The sensitivity and scenario analysis provided important information on the data gaps and the specific sites to be selected for monitoring, and may be of great help for transient model development. This study has laid the foundation for developing detailed predictive groundwater model, which can be readily used for groundwater management practices.     

Groundwater flow modelling of Hindon-Yamuna interfluve region, Western Uttar Pradesh

The study area Hindon -Yamuna interfluve region is underlain by a thick pile of unconsolidated Quaternary alluvial deposits and host multiple aquifer system. Excessive pumping in the last few decades, mainly for irrigation, has resulted in a significant depletion of the aquifer. Therefore, proper groundwater management of Hindon-Yamuna interfluve region is necessary. For effective groundwater management of a basin it is essential that careful zone budget study should be carried out. Keeping this in view, groundwater flow modelling was attempted to simulate the behavior of flow system and evaluate zone budget. Visual MODFLOW, pro 4.1 is used in this study to simulate groundwater flow. The model simulates groundwater flow over an area of about 1345 km² with a uniform grid size of 1000 m by 1000 m and contains three layers, 58 rows and 37 columns. The horizontal flows, seepage losses from unlined canals, recharge from rainfall and irrigation return flows were applied using different boundary packages available in Visual MODFLOW, pro 4.1. The river — aquifer interaction was simulated using the river boundary package. Simulated pumping rates of 500 m³/day, 1000 m³/day and 1500 m³/day were used in the pumping well package.The zone budget for the steady state condition of study area indicated that the total annual direct recharge is 416.10 MCM and the total annual groundwater draft through pumping is of the order of 416.63 MCM. Two scenarios were considered to predict aquifer system response under different conditions. Sensitivity analysis on model parameters was conducted to quantitatively evaluate the impact of varying model inputs. Based on the results obtained from the sensitivity analysis, it was found that the model is more sensitive to hydraulic conductivity and recharge parameter. Present study deals with importance of groundwater modelling for planning, design, implementation and management of groundwater resources.     

Impact of climate change on groundwater recharge in a small catchment in the Black Forest, Germany

Temporal and spatial changes of the hydrological cycle are the consequences of climate variations. In addition to changes in surface runoff with possible floods and droughts, climate variations may affect groundwater through alteration of groundwater recharge with consequences for future water management. This study investigates the impact of climate change, according to the Special Report on Emission Scenarios (SRES) A1B, A2 and B1, on groundwater recharge in the catchment area of a fissured aquifer in the Black Forest, Germany, which has sparse groundwater data. The study uses a water-balance model considering a conceptual approach for groundwater-surface water exchange. River discharge data are used for model calibration and validation. The results show temporal and spatial changes in groundwater recharge. Groundwater recharge is progressively reduced for summer during the twenty-first century. The annual sum of groundwater recharge is affected negatively for scenarios A1B and A2. On average, groundwater recharge during the twenty-first century is reduced mainly for the lower parts of the valley and increased for the upper parts of the valley and the crests. The reduced storage of water as snow during winter due to projected higher air temperatures causes an important relative increase in rainfall and, therefore, higher groundwater recharge and river discharge.     

Hydrogeology and groundwater management in a coastal granitic area with steep slopes in Galicia (Spain)

Groundwater availability, management and protection are great challenges for the sustainability of groundwater resources in the scattered rural areas of the Atlantic regions of Europe where groundwater is the only option for water supply. This report presents a hydrogeological study of the coastal granitic area of Oia in northwestern Spain, which has unique geomorphological and hydrogeological features with steep slopes favoring the erosion of the weathered granite. The hydrogeological conceptual model of the study area includes: (1) the regolith layer, which is present only in the flat summit of the mountains; (2) the slope debris and the colluvial deposits, which are present in the intermediate and lowest parts of the hillside; (3) the marine terrace; and (4) the underlying fractured granite. Groundwater recharge from rainfall infiltration varies spatially due to variations in terrain slope, geology and land use. The mean annual recharge estimated with a hydrological water balance model ranges from 75 mm in the steepest zone to 135 mm in the lowest flat areas. Groundwater flows mostly through the regolith and the detrital formations, which have the largest hydraulic conductivities. Groundwater discharges in seepage areas, springs, along the main creeks and into the sea. The conceptual hydrogeological model has been implemented in a groundwater flow model, which later has been used to select the best pumping scenario. Model results show that the future water needs for domestic and tourist water supply can be safely provided with eight pumping wells with a maximum pumping rate of 700 m³/day.

     

Optimal Groundwater Development in Coastal Aquifers Near Beihai, China

INTRODUCTIONThe city of Beihai,located on the south coast ofGuangxi,China,relies heavily on groundwater for its potablewater supply and agricultural irrigation.With rapid increasein population (for instance,from 134 0 0 0 in 1987to 47930 0in1995 ) and in developm ent program s,the demand for freshwater has been growing. Approxim ately 170 0 0 0 m3/ d ofgroundwater has been pumped from the productive coastalaquifers in recent years.Contamination of the fresh water inthe coastal aquifers b…     

浅层地下水补给对人类活动影响的响应特征研究

本文通过数据整理分析, 查明滹沱河流域平原区1976-2005年以开采量、灌区引水量和河道过水量为代表的人类活动逐渐增强, 分析了浅层地下水补给在大气降水减少和人类活动逐渐增强背景下大幅减少的响应特征: 综合补给量所占比率由1976-1980年的21.6%下降到2000-2005年的11.3%。随后, 从开采量、河道过水量和灌区引水量三个方面分析了浅层地下水补给响应人类活动的变化特征: 地下水补给量与开采量呈y=65.412x-0.2576模式随降水量增减而负相关变化; 河道渗漏补给量和渠水入渗量在地下水位不同埋深条件下表现出随来水量、引水量增加而增大的态势, 但在不同埋深条件下, 河道渗漏补给量与来水量之间、渠水入渗量和引水量之间关系不同。     

Groundwater resource sustainability in the Wadi Watir delta, Gulf of Aqaba, Sinai, Egypt

The Wadi Watir delta, in the arid Sinai Peninsula, Egypt, contains an alluvial aquifer underlain by impermeable Precambrian basement rock. The scarcity of rainfall during the last decade, combined with high pumping rates, resulted in degradation of water quality in the main supply wells along the mountain front, which has resulted in reduced groundwater pumping. Additionally, seawater intrusion along the coast has increased salinity in some wells. A three-dimensional (3D) groundwater flow model (MODFLOW) was calibrated using groundwater-level changes and pumping rates from 1982 to 2009; the groundwater recharge rate was estimated to be 1.58?×?10⁶ m³/year. A variable-density flow model (SEAWAT) was used to evaluate seawater intrusion for different pumping rates and well-field locations. Water chemistry and stable isotope data were used to calculate seawater mixing with groundwater along the coast. Geochemical modeling (NETPATH) determined the sources and mixing of different groundwaters from the mountainous recharge areas and within the delta aquifers; results showed that the groundwater salinity is controlled by dissolution of minerals and salts in the aquifers along flow paths and mixing of chemically different waters, including upwelling of saline groundwater and seawater intrusion. Future groundwater pumping must be closely monitored to limit these effects.     

Control of sea-water intrusion by salt-water pumping: Coast of Oman

A shallow alluvial coastal aquifer in the Batinah area of Oman, with sea-water intrusion that extends several kilometres inland, has been studied experimentally, analytically and numerically. The water table is proved to have a trough caused by intensive pumping from a fresh groundwater zone and evaporation from the saline phreatic surface. Resistivity traverses perpendicular to the shoreline indicated no fresh groundwater recharge into the sea. Using an analytical Dupuit-Forchheimer model, developed for the plain part of the catchment, explicit expressions for the water table, sharp interface location and stored volume of fresh water are obtained. It is shown that by the pumping of salt water from the intruded part of the aquifer, this intrusion can be mitigated. Different catchment sizes, intensities of fresh groundwater pumping, evaporation rates, water densities, sea level, incident fresh water level in the mountains and hydraulic conductivity are considered. SUTRA code is applied to a hypothetical case of a leaky aquifer with line sinks modeling fresh water withdrawal and evaporation. The numerical code also shows that pumping of saline water can pull the dispersion zone back to the shoreline.     

Dupuit模型的改进——具入渗补给

Dupuit（1863年）提出的模型是“圆岛状含水层稳定井流模型”,这个模型只有侧向湖海边界条件,而不涉及上边界降水入渗补给条件。因此,Dupuit模型只能在旱季用于地下水井流试验求取含水系统的参数,而不能够用于预测。文章发展Dupuit潜水井流模型,考虑地面均匀稳定入渗补给（蒸发排泄示为其负值）作用。以质量守衡原理为基础,假定渗流服从Darcy定律并满足Dupuit徦定,建立极坐标下的地下水流微分方程,再依边界条件建立相应的流量方程和水位方程。这些方程为具地面入渗补给条件下井流试验求取水文地质参数以及预测相应条件下地下水抽水的效果,提供了基础条件。讨论了引入Dupuit假定对本问题解析研究可以降维（略去z变量）带来好处的同时,在地下水分水岭附近及抽水井附近可能出现偏离Dupuit假定,建议在抽水试验求取含水层参数时,观测孔的部署要尽量回避这些区段。     

Hydrogeology and sustainable future groundwater abstraction from the Agua Verde aquifer in the Atacama Desert,northern Chile

The hyper-arid conditions prevailing in Agua Verde aquifer in northern Chile make this system the most important water source for nearby towns and mining industries. Due to the growing demand for water in this region, recharge is investigated along with the impact of intense pumping activity in this aquifer. A conceptual model of the hydrogeological system is developed and implemented into a two-dimensional groundwater-flow numerical model. To assess the impact of climate change and groundwater extraction, several scenarios are simulated considering variations in both aquifer recharge and withdrawals. The estimated average groundwater lateral recharge from Precordillera (pre-mountain range) is about 4,482 m³/day. The scenarios that consider an increase of water withdrawal show a non-sustainable groundwater consumption leading to an over-exploitation of the resource, because the outflows surpasses inflows, causing storage depletion. The greater the depletion, the larger the impact of recharge reduction caused by the considered future climate change. This result indicates that the combined effects of such factors may have a severe impact on groundwater availability as found in other groundwater-dependent regions located in arid environments. Furthermore, the scenarios that consider a reduction of the extraction flow rate show that it may be possible to partially alleviate the damage already caused to the aquifer by the continuous extractions since 1974, and it can partially counteract climate change impacts on future groundwater availability caused by a decrease in precipitation (and so in recharge), if the desalination plant in Taltal increases its capacity.     

Groundwater flow modelling of Yamuna-Krishni interstream,a part of central Ganga Plain Uttar Pradesh

Groundwater is a major source of water for agricultural and domestic requirements in western Uttar Pradesh. Due to increasing agricultural requirements the abstraction of groundwater has increased manifold in the last two-to-three decades. The quaternary alluvium hosts the aquifer in the region. The study area forms a part of Yamuna-Krishni interfluve. Although the area hosts potential aquifers these have been adversely affected by poor management. For effective groundwater management of a basin it is essential that a careful water balance study should be carried out. Keeping this in mind groundwater flow modelling was attempted to simulate the behaviour of the flow system and evaluate the water balance. The groundwater flow modelling was carried out. The horizontal flows, seepage losses from unlined canals, recharge from rainfall and irrigation return flows were applied using different boundary packages available in Visual MODFLOW, Pro 4.1. The river-aquifer interaction was simulated using the river boundary package. Hydraulic conductivity values were applied to specific zones and these ranged from 9.8 to 26.6m/day. Recharge due to rainfall and irrigation returns were assigned to respective zones. Pumping rates of 500m³/day, 1000m³/day, 1500m³/day, 2000m³/day and 2500m³/day were applied to appropriate areas of the model to simulate areas of stress. The zone budget shows a water balance deficit for the period June 2006 to June 2007. The total recharge to the study area is 160.21 million m³ (Mcum). The groundwater draft through pumping is of the order of 233.56 Mcum, thus leaving a deficit balance of −73.35 Mcum. The sensitivity of the model to input parameters was tested by varying the parameters of interest over a range of values, monitoring the response of the model and determining the root mean square error of the simulated groundwater heads to the measured heads. These analyses showed that the model is most sensitive to hydraulic conductivity and recharge parameters. Three scenarios were considered to predict aquifer responses under varied conditions of groundwater bstraction.     

Modeling approaches and strategies for data-scarce aquifers: example of the Dar es Salaam aquifer in Tanzania

Management of groundwater resources can be improved by using groundwater models to perform risk analyses and to improve development strategies, but a lack of extensive basic data often limits the implementation of sophisticated models. Dar es Salaam in Tanzania is an example of a city where increasing groundwater use in a Pleistocene aquifer is causing groundwater-related problems such as saline intrusion along the coastline, lowering of water-table levels, and contamination of pumping wells. The lack of a water-level monitoring network introduces a problem for basic data collection and model calibration and validation. As a replacement, local water-supply wells were used for measuring groundwater depth, and well-top heights were estimated from a regional digital elevation model to recalculate water depths to hydraulic heads. These were used to draw a regional piezometric map. Hydraulic parameters were estimated from short-time pumping tests in the local wells, but variation in hydraulic conductivity was attributed to uncertainty in well characteristics (information often unavailable) and not to aquifer heterogeneity. A MODFLOW model was calibrated with a homogeneous hydraulic conductivity field and a sensitivity analysis between the conductivity and aquifer recharge showed that average annual recharge will likely be in the range 80–100 mm/year.     

Numerical simulation of the effect of heavy groundwater abstraction on groundwater–surface water interaction in Langat Basin, Selangor, Malaysia

The paper aims at evaluating the interaction between ground and surface water along the Langat River in Malaysia through the development of a numerical simulation. Malaysia has been experiencing a rapid economic growth since the last few decades, driven by many factors such as agriculture, industry, and the like. The demand for water in these sectors has increased so tremendously that surface water has been utilized in conjunction to groundwater. Approximately 18,184 m³ of water per day is obtained from the aquifer to supply to the steel factory. There are also workshops, petroleum stations, and houses in the area thus causing the water quantity and quality to degrade. In terms of quantity, the pumping activity has altered the interaction between the groundwater and surface water. Therefore, a numerical model was proposed and two aquifer layers were simulated, with the first layer being approximately >20 m in depth and the second layer >100 m. The recharge estimated from the tank model was input into the groundwater modeling. The effects of the surface water to the aquifer were included in the simulation by defining the river conductance, river bed, and river level. The calibrated model (error about 0.9 m) was achieved and applied to predict the flow pattern in its natural state without the pumping and with the pumping states. As a result, in the first scenario, the stream was in an effluent condition influenced by the groundwater from the northeast to the west. A hyporheic flow occurred and was observed from the contour map. The flow system was changed in the second scenario when the pumping activity was included in the simulation. The groundwater lost its original function but received leakage from the stream near the pumping sites. The findings of this study will help the local authorities and other researchers to understand the aquifer system in the area and assist in the preparation of a sustainable groundwater management.     

Quality and quantity of pre-drainage methane and responding strategies in Chinese outburst coal mines

The potential sources of recharge of both water and solutes to the Quaternary aquifer in the area between Ismailia and El Kassara canals in northeastern Egypt include seepage from the irrigation canals and conduits, return flow after irrigation in the cultivated fields, local precipitation, and the upward flow of groundwater from the underlying Miocene aquifer system. Water isotopes, solute concentrations, and sulfate isotopes were used to investigate the geochemical sources, reactions, and the impacts of the hydraulic connections among recharge sources. The obtained results indicate a minimal influence of the underlying Miocene aquifer as a water and solute source while old and new contributions from the irrigation canals represent the main sources of recharge. The chemical reactions responsible for the chemical constituents and salinity in the aquifer include silicate weathering, evaporite dissolution, and carbonate precipitation. Most of groundwater samples appear to lie at/or close to equilibrium with montmorillonite, kaolinite, and illite where clay minerals are quite common in the local soils of the Quaternary aquifer.

     

A modeling study of seawater intrusion in Alabama Gulf Coast,USA

A numerical model of variable-density groundwater flow and miscible salt transport is developed to investigate the extent of seawater intrusion in the Gulf coast aquifers of Alabama, USA. The SEAWAT code is used to solve the density-dependent groundwater flow and solute transport governing equations. The numerical model is calibrated against the observed hydraulic heads measured in 1996 by adjusting the zonation and values of hydraulic conductivity and recharge rate. Using the calibrated model and assuming all the hydrogeologic conditions remain the same as those in 1996, a predictive 40-year simulation run indicates that further seawater intrusion into the coastal aquifers can occur in the study area. Moreover, the predicted intrusion may be more significant in the deeper aquifer than the shallower ones. As the population continues to grow and the demand for groundwater pumping intensifies beyond the 1996 level, it can be expected that the actual extent of seawater intrusion in the future would be more severe than the model prediction. Better strategies for groundwater development and management will be necessary to protect the freshwater aquifers from contamination by seawater intrusion.

大庆西部地下水位降落漏斗区水资源人工调蓄方案

对地下水资源的长期大量集中开采形成了区域性地下水位降落漏斗,地下水的超采引发了一系列环境地质问题。利用降落漏斗区腾空的地下储水空间进行水资源的人工调蓄可使地下水位得到恢复。以地下水为主要供水水源的大庆市目前已形成了东西两个大的区域性地下水位降落漏斗,必须进行地下水人工调蓄。设计并模拟了现状开采、逐年压缩分别在现采和压采基础之上进行人工回灌等4种人工调蓄方案,对大庆西部地下水位降落漏斗区进行水资源人工调蓄。结果表明,压缩开采和人工回灌均可加速降落漏斗区地下水位的恢复,在逐年压缩地下水开采量5%的情况下实施人工回灌（0.45×10⁸m³/a）,地下水位恢复效果最明显,到2010年末,漏斗中心地下水位可回升7.7~10.3 m。     

Artificial groundwater recharge to a semi-arid basin: case study of Mujib aquifer,Jordan

Mujib watershed is an important groundwater basin which is considered a major source for drinking and irrigation water in Jordan. Increased dependence on groundwater needs improved aquifer management with respect to understanding deeply recharge and discharge issues, planning rates withdrawal, and facing water quality problems arising from industrial and agricultural contamination. The efficient management of this source depends on reliable estimates of the recharge to groundwater and is needed in order to protect Mujib basin from depletion. Artificial groundwater recharge was investigated in this study as one of the important options to face water scarcity and to improve groundwater storage in the aquifer. A groundwater model based on the MODFLOW program, calibrated under both steady- and unsteady-state conditions, was used to investigate different groundwater management scenarios that aim at protecting the Mujib basin. The scenarios include variations of abstraction levels combined with different artificial groundwater recharge quantities. The possibilities of artificial groundwater recharge from existing and proposed dams as well as reclaimed municipal wastewater were investigated. Artificial recharge options considered in this study are mainly through injecting water directly to the aquifer and through infiltration from reservoir. Three scenarios were performed to predict the aquifer system response under different artificial recharge options (low, moderate, and high) which then compared with no action (recharge) scenario. The best scenario that provides a good recovery for the groundwater table and that can be feasible is founded to be by reducing current abstraction rates by 20% and implementing the moderate artificial recharge rates of 26 million(M)m³/year. The model constructed in this study helps decision makers and planners in selecting optimum management schemes suitable for such arid and semi-arid regions.