Review of Modeling Approaches to Groundwater Flow in Deformed Carbonate Aquifers

We discuss techniques to represent groundwater flow in carbonate aquifers using the three existing modeling approaches: equivalent porous medium, conduit network, and discrete fracture network. Fractures in faulted stratigraphic successions are characterized by dominant sets of sub-vertical joints. Grid rotation is recommended using the equivalent porous medium to match higher hydraulic conductivity with the dominant orientation of the joints. Modeling carbonate faults with throws greater than approximately 100 m is more challenging. Such faults are characterized by combined conduit-barrier behavior. The barrier behavior can be modeled using the Horizontal Flow Barrier Package with a low-permeability vertical barrier inserted to represent the impediment of horizontal flow in faults characterized by sharp drops of the piezometric surface. Cavities can occur parallel to the strike of normal faults generating channels for the groundwater. In this case, flow models need to account for turbulence using a conduit network approach. Channels need to be embedded in an equivalent porous medium due to cavities a few centimeters large, which are present in carbonate aquifers even in areas characterized by low hydraulic gradients. Discrete fracture network modeling enables representation of individual rock discontinuities in three dimensions. This approach is used in non-heavily karstified aquifers at industrial sites and was recently combined with the equivalent porous medium to simulate diffusivity in the matrix. Following this review, we recommend that the future research combines three practiced modeling approaches: equivalent porous medium, discrete fracture network, and conduit network, in order to capture structural and flow aspects in the modeling of groundwater in carbonate rocks.     

天津地区含水层类型判别与参数分析

根据含水层数学模型的降深-时间双对数和半对数曲线特征,可以确定含水层类型;依据选定的含水层模型,调整其中水文地质参数以拟合抽水试验中观测井降深-时间实测数据,可以反演水文地质参数。将以上方法应用于天津地区6组工程抽水试验,获得试验含水层类型及其水文地质参数。该方法可用于其他相关工程,天津地区和工程建设有关的50m埋深范围内含水层属性及其水文地质参数取值范围,可参考借鉴本文计算结果。     

水温分层型水库铁、锰垂直分布特征

贵阳市主要饮用水源地阿哈水库系水温分层型季节性缺氧水库,由于沉积物含高浓度Ｆｅ,Ｍｎ至使库水受到污染,经多年测定不同季节２０ｍ深垂直水柱结果表明,Ｆｅ,Ｍｎ分布随着季节变化,水库水温分层而变化,呈现明显的垂直分布规律,高浓度Ｆｅ,Ｍｎ主要出现在水温分层期水库中,下层,与库底缺氧,ＰＨ下降沉积物浓度Ｆｅ,Ｍｎ释放造成的二次污染等密切相关,从而为自来水厂实施优化分层取水和污染控制提供了依据。     

An Analytical Approach for Flow Analysis in Aquifers with Spatially Varying Top Boundary

Analytical models of groundwater flow with a spatially varying elevation of a top boundary are widely used. However, a vast majority of previous analytical studies truncated the irregularly shaped top section with little to no analyses of the shortcomings of the approximate solutions for the resulting rectangles or parallelepipeds. We present an analytical approach based on a perturbation technique that treats complete domains. It is especially accurate near the top boundary, where fluid circulation is most pronounced and higher accuracy is typically needed, such as in regional or hyporheic systems flow. The approach is illustrated by analyzing flow for a Tóthian unit basin.     

Tracer Test Analysis of Anisotropy in Hydraulic Conductivity of Granular Aquifers

A simple method of determining the anisotropy ratio of hydraulic conductivity in near-surface granular aquifers using tracer test and piezometer measurements is presented. Depending on the length of time allowed, the test will yield anisotropy ratios that are representative of the distance traversed by the tracer during the test, up to tens of feet from the injection point for some systems. This method is illustrated with an application to a ground water flow system in northern Wisconsin.     

Overexploitation and Deterioration of Aquifers in Venezuela

Approximately 50 percent of the potable, industrial, and agricultural water supply in Venezuela comes from ground water, mined through some 40,000 wells scattered around the country. The majority of the productive aquifers consist of quaternary deposits in mountain valleys and coastal lowlands, all of which are situated in areas with limited or low precipitation. Intensive exploitation of several of these aquifers for the last 30 years has resulted in overdraft conditions and ground water contamination, causing serious socio-economic consequences in various regions of Venezuela. This paper reviews the quality and quantity aspects of overdrafted aquifers in Venezuela, which can he classified into three major categories: (1) aquifers in the coastal lowlands in the stales of Falcon and Zulia of northern Venezuela: (2) the intermontane Carora and Quibor Valley Aquifers: and (3) aquifers in the Lake Valencia Watershed. If current trends of aquifer overexploitation continue, further water deficits and irreversible environmental damage are predicted.     

Linear Stability of Thermal Convection in Rotating Systems with Fixed Heat Flux Boundaries

Linear stability of rotating thermal convection in a horizontal layer of Boussinesq fluid under the fixed heat flux boundary condition is examined by the use of a vertically truncated system up to wavenumber one. When the rotation axis is in the vertical direction, the asymptotic behavior of the critical convection for large rotation rates is almost the same as that under the fixed temperature boundary condition. However, when the rotation axis is horizontal and the lateral boundaries are inclined, the mode with zero horizontal wavenumber remains as the critical mode regardless of the rotation rate. The neutral curve has another local minimum at a nonzero horizontal wavenumber, whose asymptotic behavior coincides with the critical mode under the fixed temperature condition. The difference of the critical horizontal wavenumber between those two geometries is qualitatively understood by the difference of wave characteristics; inertial waves and Rossby waves, respectively.     

Schemes of Profile Models of Heat and Mass Transfer in Large Lakes

A method is proposed for reducing the dimensionality of the spatial structure of models used for simulating long-term variability of the ecosystem of a large, deep lake. The method is based on averaging the limnological variables along lines collinear to isobath contours. Conventional and special bathygraphic curves are used to construct a two-dimensional vertical geometric model of the lake bed. The potentialities of the method are illustrated by an example where two-dimensional equations of continuity, thermal diffusivity, and mass transport of material components are derived for an ecosystem model of Lake Onega.     

Interpretation of Pumping Tests in Heterogeneous Aquifers with Constant Head Boundary

This paper investigates the impact of heterogeneity of the transmissivity field on the interpretation of steady-state pumping test data from aquifer systems delimited by constant head boundaries such as aquifers adjacent to lakes or rivers. Spatially variable transmissivity fields are randomly generated and used to simulate the drawdown due to a pumping well located at different distances from a constant head boundary. The steady-state drawdown simulated at different observation wells are then interpreted using the Hantush method (Hantush 1959). The numerical simulations show that, in contrast to the case of infinite aquifer domains, the interpreted transmissivity varies depending on well locations and the separation distance between pumping well and boundary relative to the correlation length. The ensemble-averaged estimated transmissivity varies between the geometric mean and the arithmetic mean, and can even exceed the arithmetic mean in a narrow domain adjacent to the boundary. It approaches the geometric mean of the underlying transmissivity field only if the distance between the pumping well is more than 20 times the characteristic length of the transmissivity field.     

Post Processing of Zone Budgets to Generate Improved Groundwater Influx Estimates Associated with Longwall Mining

Impacts of underground longwall mining on groundwater systems are commonly assessed using numerical groundwater flow models that are capable of forecasting changes to strata pore pressures and rates of groundwater seepage over the mine life. Groundwater ingress to a mining operation is typically estimated using zone budgets to isolate relevant parts of a model that represent specific mining areas, and to aggregate flows at nominated times within specific model stress periods. These rates can be easily misinterpreted if simplistic averaging of daily flow budgets is adopted. Such misinterpretation has significant implications for design of underground dewatering systems for a new mine site or it may lead to model calibration errors where measured mine water seepage rates are used as a primary calibration constraint. Improved estimates of groundwater ingress can be made by generating a cumulative flow history from zone budget data, then differentiating the cumulative flow history using a low order polynomial convolved through the data set.     

Impact of Doppler Radar Wind in Simulating the Intensity and Propagation of Rainbands Associated with Mesoscale Convective Complexes Using MM5-3DVAR System

Pre-monsoon rainfall around Kolkata (northeastern part of India) is mostly of convective origin as 80% of the seasonal rainfall is produced by Mesoscale Convective Systems (MCS). Accurate prediction of the intensity and structure of these convective cloud clusters becomes challenging, mostly because the convective clouds within these clusters are short lived and the inaccuracy in the models initial state to represent the mesoscale details of the true atmospheric state. Besides the role in observing the internal structure of the precipitating systems, Doppler Weather Radar (DWR) provides an important data source for mesoscale and microscale weather analysis and forecasting. An attempt has been made to initialize the storm-scale numerical model using retrieved wind fields from single Doppler radar. In the present study, Doppler wind velocities from the Kolkata Doppler weather radar are assimilated into a mesoscale model, MM5 model using the three-dimensional variational data assimilation (3DVAR) system for the prediction of intense convective events that occurred during 0600 UTC on 5 May and 0000 UTC on 7 May, 2005. In order to evaluate the impact of the DWR wind data in simulating these severe storms, three experiments were carried out. The results show that assimilation of Doppler radar wind data has a positive impact on the prediction of intensity, organization and propagation of rain bands associated with these mesoscale convective systems. The assimilation system has to be modified further to incorporate the radar reflectivity data so that simulation of the microphysical and thermodynamic structure of these convective storms can be improved.     

反倾巨厚层状岩体地震滑坡特征分析

针对汶川大地震中产生的在反倾巨厚层状岩体中滑坡的特征,以甘肃武都寨子崖滑坡为实例,通过详细的野外地质调查,结合滑坡区的工程地质环境和面波测试成果,综合分析反倾巨厚层状岩质边坡中形成滑坡的条件,研究其特征和演化机制。不发育结构面、尤其不发育缓倾坡外结构面时此类边坡不具备产生重力滑坡的条件;此类斜坡在仅有水平地震力时同样不易形成滑坡,双向地震力共同作用时易产生地震滑坡。