Evaluation of Rio Grande Management Alternatives Using a Surface‐Water/Ground‐Water Model1

Abstract: Previous investigations observed significant seepage losses from the Rio Grande to the shallow aquifer between Socorro and San Antonio, New Mexico. High‐resolution telescopic modeling was used along a 10‐km reach of the Rio Grande and associated drains and canals to evaluate several management alternatives aimed at improving river conveyance efficiency. Observed data consisted of ground‐water and surface‐water elevations, seepage rates along the Rio Grande and associated canals and drains, and borehole geology. Model calibration was achieved by adjusting hydraulic conductivity and specific storage until the output matched observed data. Sensitivity analyses indicated that the system was responsive to changes in hydrogeologic properties, especially when such alterations increased vertical connectivity between layers. The calibrated model predicted that removal of the low flow conveyance channel, a major channel draining the valley, would not only decrease river seepage by 67%, but also decrease total flow through the reach by 75%. The decreased flow through the reach would result in increased water logging and an average increase in ground‐water elevations of 1.21 meter. Simulations of the system with reduced riparian evapotranspiration rates or a relocated river channel also predicted decreased river seepage, but to a much lesser degree.     

Climate change impacts on groundwater resources in Mekong Delta under representative concentration pathways (RCPs) scenarios

Groundwater is the essential resource for various uses and have a great economic importance especially in the areas like Mekong Delta, which is the home for some 18 million people and produces a half of Vietnam’s rice and contributes substantial part of the country’s gross domestic product (GDP). Sustainable use of the groundwater resource is threatened by its uncontrolled abstraction and climate change. This study assesses groundwater resources in Mekong Delta aquifer system in the context of climate change. A set of models are used for the purpose. Groundwater recharge and its spatial variation are estimated using WETSPASS model, groundwater level and storage are estimated using MODFLOW and future climatic conditions in the area are developed by downscaling the data of five General Circulation Models (GCMs) retrieved from CMIP5 data portal. Two representative concentration pathways (RCPs) scenarios (RCP4.5 and RCP8.5) are considered for projecting future conditions of groundwater resources. Results reveal that the future average annual temperature is projected to increase by 1.5 °C and 4.9 °C by the end of the 21st century under RCP4.5 and RCP8.5 scenarios, respectively. Future rainfall is projected to increase in wet season and decrease in dry season. Groundwater recharge is projected to decline in short-, medium-, and long-terms. As a result, groundwater levels and storage are also projected to decline in future. These findings may help decision-makers and stakeholders for devising sustainable groundwater management strategies in Mekong Delta.     

Visual MODFLOW在露天矿地下水模拟中的应用

用Visual MODFLOW建立了某露天矿地下水数值模型,运用其跟踪模拟(MODPATH)子模块及溶质运移模拟(MT3D)子模块对该露天矿地下水的水质点示踪和三维污染羽进行了模拟,模拟结果有助于识别该矿露天开采对地下水污染的污染源及污染途径,为预测露天矿开采期间地下水位及水质的变化,采用的监测与预保护措施提供了决策依据。     

SIMULATING FLOW IN REGIONAL WETLANDS WITH THE MODFLOW WETLANDS PACKAGE1

ABSTRACT: As part of the Comprehensive Everglades Restoration Plan (CERP), various water supply projects have been proposed in a region located between the Miami metropolitan area and the extensive regional wetland systems that are part of the Everglades or remnant Everglades. A ground water flow model of the surficial aquifer within northern Miami‐Dade County was constructed using MODFLOW to evaluate the effects of these projects on water levels in the wetlands and the underlying surficial aquifer. The new Wetlands package was used to conjunctively simulate overland flow through these wetlands and the shallow ground water system. Comparisons of simulated to measured ground water levels and wetland stages were very satisfactory, where computed and measured water levels agreed within 0.5 ft over most of the period of record at nearly all of the monitoring sites. Temporal trends in water levels were also replicated. It was concluded that the assumptions and methodologies inherent to the Wetlands package were suitable for simulating regional wetland hydrology within the Everglades area.     

INTEGRATING GEOGRAPHIC INFORMATION SYSTEMS AND MODFLOW FOR GROUND WATER RESOURCE ASSESSMENTS1

ABSTRACT: The Floridan Aquifer is the primary source of water in the coastal area of Santa Rosa County, Florida. In order to optimize well field design and analyze aquifer stress problems, the USGS MODFLOW code (McDonald and Harbaugh, 1988) is applied to develop a numerical computer model of the aquifer. The Geographical Information System (GIS) is the primary tool used in the development of the model grid, performance of the modeling procedure, and model analysis. The GIS is used in generating multiple grids in which to simulate both regional scale and local scale flow. The grid topology is recorded in geographic coordinates which facilitates geo-referencing and orientation of the grid to base maps and data coyerages. The GIS allows data transfer from various coverages to the nodes of the block centered grid where hydrogeologic information is stored as attributes to the grid coverage. From this grid coverage, pertinent information is queried within the GIS environment and used to generate the input files for the MODFLOW simulation. After MODFLOW execution, simulated heads and drawdown are imported into the grid coverage where residual error and recharge rates can be calculated. Contoured surfaces are then created for selected data sets including simulated heads, drawdown, residual error, and recharge rates. Model calibration is conducted utilizing the GIS to generate and process data sets associated with model simulations.     

Development of a Model for Simulation of Solute Transport in a Stream–Aquifer System

A model for simulation of solute transport in a dynamic stream–aquifer system is developed by integrating four existing sub-models. Interface packages are created to link the sub-models. The developed model is successfully used to simulate chloride transport in the stream–aquifer system of the Arkansas River and the Equus Beds Aquifer in Kansas and demonstrates that chloride concentration in the aquifer decreases in the vicinity of the simulated channel over time.     

离柳矿区石炭系薄层灰岩渗透系数空间分布研究

基于矿井涌水量计算及水资源评价需要,首先运用注水试验代替抽水试验,求取了太原组灰岩含水层的渗透系数.根据后期同一含水层井下放水试验资料,利用VISUAL MODFLOW建立了水文地质三维非稳定流数值模型,通过分区拟合调参,获得了含水层各分区的渗透系数.通过对渗透系数及其空间分布规律的对比研究,发现渗透系数随含水层埋深增大而逐渐减小.注水试验比放水试验所得渗透系数值小,前者是后者的35.6％-50.8％.     

沈阳北部污水处理厂出水回用于丁香湖溶质运移预测

通过对北部污水处理厂出水、丁香湖地区水环境质量现状评价,采用Visual MODFLOW数值模拟方法预测北部污水处理厂出水再生回用于丁香湖后研究区水质的变化情况,分析由此可能带来的水环境水质风险,来研究北部污水处理厂出水再生利用于丁香湖方案在水质上的可行性。预测结果显示：在地下水动力场作用下,随着时间的延长,SO4^2-将向下游不断运移并出现了累积现象,污水再生利用到丁香湖后,对地下水环境未来情况有一定的影响。     

DEVELOPMENT AND APPLICATION OF A MODFLOW PREPROCESSOR USING PERCOLATION THEORY FOR FRACTURED MEDIA1

ABSTRACT: The discrete heterogeneity of fracture distribution and hydraulic discontinuity are the primary difficulties in the modeling of flow in fractured media. The equivalent porous medium (EPM) approach, however, which has been frequently applied to simulate flow in fractured media due to its ease of use, ignores this. This practice results in some severe limitations such as hydraulic head averaging and an inability to handle preferred fluid pathways. The PMF package (a Preprocessor to MODFLOW for Fractured media) was developed employing percolation theory to address these limitations and to utilize the simplicity of the EPM approach at the same time. This preprocessor was applied to a fractured rock aquifer around Cranberry Lake in northern New Jersey. The calibration using hydraulic head observations, validation using water balance, and evaluation using residuals show that the model generated by the PMF package can provide a superior simulation of ground water flow to the EPM approach.     

MODFLOW在四川天台滑坡地下水渗流场模拟当中的应用

四川天台滑坡的发展与形成与暴雨期间滑坡体内各种水的作用密切相关,通过MODFLOW三维渗流计算软件对滑坡体内渗流场的变化进行模拟,以期对滑坡的形成机制做进一步的了解,并对滑坡治理工作提供可靠依据。