运用地下水对潮汐的响应识别压力传导系数

在地下水扩散方程中,压力传导系数是描述地下水运动的重要参数。传统的方法是通过抽水或注水给地下水系统一个扰动,监测地下水水位的响应,由此计算含水层的压力传导系数。文章提出用潮汐衰减率方法识别含水层压力传导系数,其适用于滨海区承压含水层的参数识别。在推导出解析解的基础上,通过数值拟合、最小二乘法、牛顿迭代法求得含水层的压力传导系数,提出潮汐衰减率的概念,建立余切函数与潮汐衰减率的线性关系,用线性关系中的斜率和截距识别压力传导系数。用潮汐衰减率方法识别出的压力传导系数与其实际值相等,说明该方法是正确有效的。潮汐信号衰减率与海水振荡的余切函数线性相关。数值仿真表明,该方法可以准确地估算出含水层的压力传导系数。潮汐衰减率方法具有少打井,经济高效等优点。潮汐衰减率方法为实际工程应用提供了可靠的理论基础,它可以用于部分实际工程中。该方法的局限性在于需要提供含水层的部分参数,如含水层的长度、海水波动振幅、频率等。     

利用不对称的地下水位潮汐波动确定滨海含水层参数

在滨海地区,地下水水位受潮汐波动影响较大,使得传统的抽水试验、水位回复试验等方法确定含水层参数存在困难且花费较大。通过对广西北海市滨海含水层地下水位动态资料进行分析,发现其上升段和下降段是不对称的。基于海岸带承压含水层正弦潮汐波的传播理论,提出了确定含水层参数的分段法,并与振幅衰减法和滞后时间法进行对比,各种方法求出的储水系数与导水系数之比(S/T)很接近,说明分段法是有效的。对于北海市滨海含水层,上升段求出的S/T值比下降段要大,其成因机理还有待进一步分析。     

利用观测孔中地下水位潮汐效应计算天津滨海新区含水层参数

在沿海地区,尤其是围海造陆工程形成的陆域地区地下水水位受潮汐影响较大,使传统水文地质试验求取含水层参数存在较大误差。因此通过合理概化地下水在潮汐作用下运动规律,建立数学模型,推导解析公式求取沿海含水层参数具有重要意义。分析天津滨海新区两处观测孔地下水位及潮汐波动特征,在滞后时间不明显的情况下,利用观测孔水位变幅数据计算了含水层水头扩散系数,并根据承压含水层储水系数经验值进一步获得含水层渗透系数。通过两个观测孔分别计算,对比计算结果互相验证发现,该方法取得了令人满意的结果。利用地下水潮汐效应计算含水层参数可以广泛应用于沿海地区水文地质工作中。     

用地下水潮汐效应确定潜水含水层水文地质参数

目前对潜水含水层地下水潮汐效应和水文地质参数求解方法的研究相对较少.通过对福建古雷半岛滨海潜水含水层地下水潮汐效应和海水潮汐动态的观测, 运用Fourier频谱分析方法确定了研究区海水潮汐波动方程(波动特征参数), 并以此作为地下水的边界条件, 推导了潜水含水层地下水潮汐效应的波动方程, 利用最小二乘法以地下水水位波动观测值为目标函数对潜水含水层的渗透系数与重力给水度的比值进行了反演识别, 为类似地区水文地质参数的确定提供了借鉴, 也为该区后续地下水中溶质迁移规律的研究奠定了基础.      

基于同震水震波的水文地质参数求取方法探讨

井-含水层系统水文地质参数是地下水/含水层水流模型中的关键参数,这些参数通常通过室内实验、野外试验和模型反演获取。基于新10井水位对远场地震的同震响应,通过频谱法分析了该井水震波与地震波的相关性,提出了一种利用水震波信号(主要是瑞利波引起)反演获取承压含水层水文地质参数的方法。结果表明新10井水震波与地震波在变化形态、频谱特征上均具有很好的一致性,估算得到的新10井-含水层系统的储水系数值为1.33×10~(-5)~1.64×10~(-5),渗透系数值为57~87 m/d。提出的承压井-含水层系统水文参数估算法具有很好的实用性,可为地下水管理、地震机理分析等提供一种新的技术方法。     

抽水试验和长观水位联合模拟确定含水层参数

为了更加准确地确定含水层参数,提出了利用地下水流数值模拟软件Modflow耦合大型抽水试验和长观孔水位两个模型的方法,对含水层参数进行了识别与校验。该方法求得的含水层参数避免了只利用抽水试验模型校验所带来的不确定性,同时利用抽水实验数据进行抽水与恢复的全过程曲线拟合,水位降深模拟相对误差小于6%,提高了含水层参数的准确性。     

确定含水层参数的全程曲线拟合法

含水层参数的确定是地下水资源评价、数值模拟、开发利用与保护以及科学管理的重要基础,抽水试验法是确定含水层参数的主要方法。根据含水层抽水试验的泰斯（Theis）公式,运用优化理论,结合计算机技术,提出利用抽水试验数据确定含水层参数的全程曲线拟合法。该方法充分考虑抽水过程中水位快速下降段、水位缓慢下降段和水位恢复段的观测资料,满足计算水位与实测水位之间的误差平方和最小、计算的水位过程线与抽水过程的实测曲线最佳拟合。实例研究表明,该方法速度快、精度高、求参结果最优,既适用于承压含水层求参,又可推广到潜水含水层求参。     

运用水力层析法对含水层裂隙带成像

含水层裂隙带的识别,是准确模拟计算地下水流和污染扩散的前提。本研究通过数值实验,运用近年来发展起来的水力地质层析方法,对含水层裂隙带成像。文章设定一个17m×17m的二维垂直饱和裂隙含水层,含水层有2口斜井。在斜井与裂隙带的交叉点分别进行抽水试验,由感应器收集水位响应数据,运用VSAFT2对裂隙带进行识别。数值实验证明,水力层析法结合地下水流的逆算方法——连续线性算法(SSLE),可以比较准确地识别非均质含水层的参数分布;非稳定流条件下的识别结果好于稳定流的结果;信息齐全条件下的结果好于资料缺乏时的结果。     

基于广义径向流模型的非均质孔隙含水层井流试验分析

Theis模型、Dupuit模型等经典井流模型分析非均质含水层井流试验数据有一定的局限性,获取的参数不适合表征非均质含水层特性。而GRF模型可以获取含水层流动特性的数据。相比于Theis模型、Dupuit模型,GRF模型更能表征非均质含水层特性。以黄石东湖新村棋盘洲长江大桥的抽水试验数据为例,采用Theis模型和GRF模型计算含水层渗透系数,结合实际水文地质条件,对比分析不同方法计算的水文地质参数,并计算含水层水流维数和表观压力传导系数（K_f /S_sf）。结果表明:研究区含水层为细砂夹条带状黏土透镜体的非均质含水层,采用GRF模型计算结果更符合实际情况,渗透系数为 4.09×10?3cm/s;含水层水流维数为1.61,地下水为双线性流动状态,含水层对抽水试验的响应主要受黏土条带控制;观测井和抽水主井的K_f /S_sf呈非线性相关,进一步验证了含水层的非均质性。在非均质孔隙含水层中,应用多孔联合非稳定GRF井流试验方法不仅能确定水文地质参数,并且能丰富对含水层特性的认知。     

多层含水层系统水文地质参数计算

为求取含水层水文地质参数,常用的试验方法是抽水试验。在进行抽水试验时,经常有越流现象,计算时一般采用越流模型计算。越流模型假定非抽水含水层的水位恒定不变,但在实际抽水过程中,抽水含水层和非抽水含水层间通过越流相互影响、相互作用。如果只考虑抽水含水层的水位变化而不考虑非抽水含水层的水位变化,会导致计算的水文地质参数不准确。实际工作中,有时会在非抽水含水层中布置一口观测井来观测抽水含水层抽水时对非抽水含水层的影响。如果采用多层含水层系统模型的方法,即可利用各含水层观测井中的数据计算出每个含水层和相关弱透水层的水文地质参数,提高参数计算精度、节省资金和工作量。     

Evaluation of unconfined aquifer parameters from flow to partially penetrating wells in Tailan River basin, China

Effective evaluation, management and abstraction of groundwater resources of any aquifer require accurate and reliable estimates of its hydraulic parameters. This study, therefore, looks at the determination of hydraulic parameters of an unconfined aquifer using both analytical and numerical approaches. A long-duration pumping test data obtained from an unconfined aquifer system within the Tailan River basin in Xinjiang Autonomous Region in the northwest of China is used, in this study, to investigate the best method for estimating the parameters of the aquifer. The pumping test was conducted by pumping from a radial collector well and measuring the response in nine observation wells; all the wells used in the test were partially penetrating. Using two well-known tools, namely AquiferTest and MODFLOW, as an aid for the analytical and numerical approaches, respectively, the parameters of the aquifer were determined and their outputs compared. The estimated horizontal hydraulic conductivity, vertical hydraulic conductivity, and specific yield for the analytical approach are 38.1–50.30 m/day, 3.02–9.05 m/day and 0.204–0.339, respectively, while the corresponding numerical estimates are 20.50–35.24 m/day, 0.10–3.40 m/day, and 0.27–0.31, respectively. Comparing the two, the numerical estimates were found to be more representative of the aquifer in the study area since it simulated the groundwater flow conditions of the pumping test in the aquifer system better than the analytical solution.     

基于解析法和数值法的非稳定流抽水试验参数反演

含水层的水文地质参数是进行地下水资源计算、地下水污染防控等所必需的基础数据,结合数值模拟技术进行含水层参数反演很有必要.按照1:5万水文地质调查规范在江汉平原仙桃市杨林尾镇复兴水厂不同含水层位开展抽水试验,包括深层含水层单孔抽水试验以及浅层含水层中群孔(2孔)抽水试验.对于单孔抽水试验,应用第1类越流系统井流理论进行参数反演;对于群孔抽水试验,推导了特定综合井函数,并利用特定标准曲线匹配法和直线图解法求解了含水层参数.随后利用FEFLOW软件建立了相应数值模型,拟合了含水层参数.结果表明:浅层含水层的渗透系数变化范围为21.66~54.00 m/d,贮水率变化范围为1.28×10-5~8.00×10-4 m-1;深层含水层渗透系数变化范围为1.27~7.00 m/d,贮水率变化范围为3.90×10-6~5.00×10-6 m-1.对于深层承压含水层而言,越流补给量较大.采用数值模拟方法结合抽水试验数据求参,综合考虑了含水层结构,拟合效果好,所得结果更加可靠.      

Using time series analysis to assess tidal effect on coastal groundwater level in Southern Laizhou Bay,China

Sea water intrusion is an environmental problem cause by the irrational exploitation of coastal groundwater resources and has attracted the attention of many coastal countries. In this study, we used time series monitoring data of groundwater levels and tidal waves to analyze the influence of tide flow on groundwater dynamics in the southern Laizhou Bay. The auto-correlation and cross-correlation coefficients between groundwater level and tidal wave level were calculated specifically to measure the boundary conditions along the coastline. In addition, spectrum analysis was employed to assess the periodicity and hysteresis of various tide and groundwater level fluctuations. The results of time series analysis show that groundwater level fluctuation is noticeably influenced by tides, but the influence is limited to a certain distance and cannot reach the saltwater-freshwater interface in the southern Laizhou Bay. There are three main periodic components of groundwater level in tidal effect range (i.e. 23.804 h, 12.500 h and 12.046 h), the pattern of which is the same as the tides. The affected groundwater level fluctuations lag behind the tides. The dynamic analysis of groundwater indicates that the coastal aquifer has a hydraulic connection with seawater but not in a direct way. Owing to the existence of the groundwater mound between the salty groundwater (brine) and fresh groundwater, the maximum influencing distance of the tide on the groundwater is 8.85 km. Considering that the fresh-saline groundwater interface is about 30 km away from the coastline, modern seawater has a limited contribution to sea-salt water intrusion in Laizhou Bay. The results of this study are expected to provide a reference for the study on sea water intrusion.     

水力层析法与克立金法估算非均质含水层渗透系数场比较

含水层非均质性空间分布特征的识别,是准确模拟地下水流和污染物运移的前提.基于室内非均质含水层砂箱实验,分别利用水力层析法和克立金插值法刻画了非均质含水层渗透系数场.研究结果表明:(1) 水力层析法与克立金法相比,不仅可以更好地刻画非均质含水层渗透系数场,还可以更高精度地预测地下水流过程;(2) 水力层析抽水实验中,通过增加抽水实验组数可以有效地提高水力层析参数反演的精度,但是抽水实验组数增加到一定程度以后,再增加抽水组数不会显著提升参数反演的效果.后续需要进一步研究水力层析抽水实验合适的组数,进一步对抽水井进行优化布设.      

Large-scale hydraulic conductivity distribution in an unconfined carbonate aquifer using the ocean tidal propagation

The hydraulic conductivity of an unconfined carbonate aquifer at the uplifted atoll of Minami-Daito, Japan, was evaluated by a combination of cross-spectral analysis, analytical solution, and density-dependent groundwater modeling based on observed groundwater levels in 15 wells and at sea level. The island area was divided into 10 subregions based on island morphology and on inland propagation of ocean tides. The hydraulic conductivity was obtained for each subregion using analytical solutions based on phase lags of M₂ constituents of ocean tides at each well by assuming two aquifer thicknesses (300 and 1,800 m) and two effective porosities (0.1 and 0.3). The density-dependent groundwater model evaluated the hydraulic conductivity of the subregions by reproducing observed groundwater levels. The hydraulic conductivity in the subregions was estimated as 3.46?×?10^?3 to 6.35?×?10^?2 m/s for aquifer thickness of 300 m and effective porosity of 0.1, and as 1.73?×?10^?3 to 3.17?×?10^?2 m/s for aquifer thickness of 1,800 m and the effective porosity of 0.3. It was higher in southern and northern areas, and higher in interior lowland than in the western and eastern areas. Fissures and dolomite distributions on the island control differences of the omnidirectional ocean tidal propagation and cause these differences in hydraulic conductivity. The method used for this study may also be applicable to other small islands that have few or no data for hydraulic conductivity.

     

Characteristics of Valadares Island aquifer,Paranaguá coastal plain,Brazil

. Aquifer characterization in terms of geologic–geomorphological considerations, pumping test and hydrochemistry has been carried out to evaluate the groundwater potential of one of the delicate coastal island systems in Parana State, Brazil. The Valadares Island, lying in the Atlantic coastal zone, represents a stabilized beach ridge having a thickness of more than 20 m unconsolidated quartz-rich sand. Field and laboratory investigations suggest that this homogeneous coastal aquifer can partially meet the local domestic demand of fresh water even though it is in hydraulic continuity with the estuarine and tidal systems of Paranaguá bay. Efficiency of the aquifer to hold and release water was determined by conducting a pumping test in one of the partially penetrating wells in the island for 24 h. The physical, chemical and biological analyses of samples from 12 5-cm diameter wells of the area have indicated that groundwater needs purification for drinking purpose. It is advocated that the groundwater potential of the island aquifer is worth considering for sustained but controlled exploitation.     

Characterization of an island aquifer from tidal response

Growing demand for potable water for various needs has lead to indiscriminate exploitation of groundwater resources, particularly, in the terrain where surface water resources are negligible. One such area is an island where groundwater is the only source of fresh water. Groundwater is the prime source of fresh water on most of the atolls in the world. Groundwater on these islands is in the form of thin fragile floating lens and is often vulnerable to overexploitation, draught, tidal waves, tsunami and cyclone resulting in seawater ingress. Sustainable development of this meager source of fresh groundwater for a longer time becomes a more difficult task on small atolls with a large population depending on this vital resource. To develop a sustainable management scheme and identify the vulnerable part of aquifer, characterization of the aquifer system on islands is imperative. Groundwater on an atoll is extremely vulnerable to seawater mixing through natural as well as human activities. One such natural process is the tides of the ocean. The response of sea tide to the water table on the island offers valuable data as well as cost-effective means to characterize an aquifer system. Such characterization is vital for the management of groundwater resources on an atoll. The obtained results have compared well with the parameters obtained through a conventional pumping test. Therefore, the use of tidal response to the water table, which can easily be recorded, provides a rapid and cost-effective means to characterization of the aquifer system on the island.     

Tidal controls on coastal groundwater conditions: field investigation of a macrotidal system

Previous studies of coastal groundwater resources have not properly explored the hydraulic conditions at coastal and estuarine boundaries, despite recognised influences of oceanic and estuarine water-level fluctuations (e.g. tides and waves) on groundwater near these boundaries. Such influences may have important implications for determining submarine groundwater discharge and seawater intrusion. In this paper, oceanic and estuarine controls on the hydrology of coastal aquifers are characterised for a macrotidal system—the Pioneer Valley coastal plain, northeastern Australia. The tidal water-table over-height (tide-induced increase in average water-table height at the coastline) is quantified at three locations and compared with theoretical estimates, which assume simplified physiographical conditions compared with those encountered at the field sites. The results indicate that local geological conditions, beach morphology and characteristics of tidal forcing control the behaviour of nearshore groundwater within the system. Existing analytical and numerical solutions that are commonly applied as first-pass estimates are found to be insufficient for predicting observed tidal water-table over-height in the Pioneer Valley, due to the sediment heterogeneities, non-uniform beach slopes and large tidal ranges of the system. The study reveals the spatial and temporal variability in tidally influenced hydraulic heads at the estuarine and coastal boundaries of the aquifer, and provides estimates of tidal water-table over-height up to 2.41 m during spring tides. These findings highlight the complexity of coastal groundwater systems, and the need to incorporate appropriate nearshore and near-estuary boundary conditions in models of regional groundwater flow in coastal aquifers.     

Numerical groundwater-flow modeling to evaluate potential effects of pumping and recharge: implications for sustainable groundwater management in the Mahanadi delta region,India

Process-based groundwater models are useful to understand complex aquifer systems and make predictions about their response to hydrological changes. A conceptual model for evaluating responses to environmental changes is presented, considering the hydrogeologic framework, flow processes, aquifer hydraulic properties, boundary conditions, and sources and sinks of the groundwater system. Based on this conceptual model, a quasi-three-dimensional transient groundwater flow model was designed using MODFLOW to simulate the groundwater system of Mahanadi River delta, eastern India. The model was constructed in the context of an upper unconfined aquifer and lower confined aquifer, separated by an aquitard. Hydraulic heads of 13 shallow wells and 11 deep wells were used to calibrate transient groundwater conditions during 1997–2006, followed by validation (2007–2011). The aquifer and aquitard hydraulic properties were obtained by pumping tests and were calibrated along with the rainfall recharge. The statistical and graphical performance indicators suggested a reasonably good simulation of groundwater flow over the study area. Sensitivity analysis revealed that groundwater level is most sensitive to the hydraulic conductivities of both the aquifers, followed by vertical hydraulic conductivity of the confining layer. The calibrated model was then employed to explore groundwater-flow dynamics in response to changes in pumping and recharge conditions. The simulation results indicate that pumping has a substantial effect on the confined aquifer flow regime as compared to the unconfined aquifer. The results and insights from this study have important implications for other regional groundwater modeling studies, especially in multi-layered aquifer systems.