Groundwater flow modelling to assist dryland salinity management of a coastal plain of southern Australia

Groundwater flow modelling has been undertaken for an area of 10 500 ha within the regional unconfined aquifer system of a coastal plain of southern Australia, in the vicinity of the town of Cooke Plains, to predict the impact of various land management options (including recharge reduction and discharge enhancement) on the extent of land salinisation caused by shallow saline watertables. The model was calibrated against field data collected over 6 years. Sensitivity analysis was performed to assess the influence of mesh size, boundary conditions, and aquifer parameters, and particularly rates of recharge and evaporative discharge, on groundwater levels. These were varied until the model was shown to be capable of simulating seasonal trends and regional and local flow patterns. The model was then used to predict the impact of the management options on groundwater levels. The results showed that continuing current annual crop–pasture rotations will result in watertable rises of approximately 0·2 m in 20 years (significant in this setting), with a further 50 ha of land salinised. A reduction in the rates of groundwater recharge through the establishment of high water-use perennial pastures (e.g. lucerne) showed the most promise for controlling groundwater levels. For example, a reduction in recharge by 90% would result in watertable declines of 0·6–1·0 m within 5–10 years, with the return to productivity of 180 ha of saline land. Small-scale (say <100 ha) efforts to reduce recharge were found to have no significant impact on groundwater levels. Enhanced groundwater discharge such as pumping from a windmill was found to be non-viable due to the relatively high aquifer transmissivity and specific yield. The modelling approach has enabled a relatively small area within a regional aquifer system to be modelled for a finite time (20 years) and has shown that extension of the boundaries of the model would not have altered the predicted outcomes. Furthermore, the analysis of sensitivity to cell size in an undulating landscape where net recharge areas can become net discharge areas with only small increases in groundwater level is novel, and has helped to build confidence in the model. Modelling has demonstrated that dryland salinisation can be controlled by reducing groundwater recharge over substantial tracts of land, and is not dependent on recharge reduction over an extensive area upgradient, at least over the next 20 years.

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GROUNDWATER FLOW MODELlING USING the FINITE DIFFERENCES METHOD AND the FINITE ELEMENTS METHOD – COMPARATIVE MODEL STUDIES

Biuletyn Państwowego Instytutu Geologicznego ◽

10.5604/01.3001.0012.5057 ◽

2018 ◽

Vol 471 ◽

pp. 201-208

Author(s):

Robert ZDECHLIK ◽

Małgorzata PARTYKA

Keyword(s):

Finite Elements ◽

Groundwater Flow ◽

Finite Differences ◽

Finite Elements Method ◽

Advantages And Disadvantages ◽

Flow Modelling ◽

Hydrogeological Conditions ◽

Groundwater Flow Modelling ◽

Finite Differences Method ◽

The Impact

The filtration of groundwater is a complicated process, which is determined by natural environmental factors (hydrogeological conditions) and anthropogenic impacts. Reliable predictions of the impact of the established extortions on the groundwater environment require the use of an appropriate research method that will allow for a precise representation of groundwater circulation. Such methods include numerical modelling of filtration processes, using a mathematical description of groundwater flow, based on assumed parameters and boundary conditions. For groundwater flow modelling, software based on the finite differences method FDM, using Modflow simulators, is most commonly used. Due to the numerous advantages, mainly in terms of greater precision in the representation of the complex geometry of the aquifers and objects affecting the water circulation, the alternative FEM finite elements method is becoming increasingly important. The article presents characteristic features of modelling using both methods. Based on the established imaginary research site, representing typical valley hydrogeological conditions, the paper presents the methodology of model implementation and numerical calculations of water flow using FDM and FEM methods, each in two variants of grid density. Obtained results are presented, with an attempt to compare the advantages and disadvantages of both methods.

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Approaches for Modelling Transient Unsaturated-Saturated Groundwater Flow During and After Construction

ASME 2009 12th International Conference on Environmental Remediation and Radioactive Waste Management, Volume 1 ◽

10.1115/icem2009-16242 ◽

2009 ◽

Author(s):

Matt White ◽

Jordi Guimera` ◽

Takuya Ohyama ◽

Hiroshi Kosaka ◽

Peter Robinson ◽

...

Keyword(s):

Hydraulic Conductivity ◽

Groundwater Flow ◽

Fractured Rock ◽

Energy Agency ◽

Geological Disposal ◽

Flow Equations ◽

Retention Models ◽

Flow Modelling ◽

Groundwater Flow Modelling ◽

The Impact

Construction of underground research laboratories and geological disposal facilities has a significant transient impact on groundwater flow, leading to a drawdown in the water table and groundwater pressures, and groundwater inflow into shafts, access ways and tunnels accompanied by desaturation of the surrounding rock. Modelling the impact of underground facilities on groundwater flow is important throughout the construction and operation of the facilities, e.g. estimating grouting and water treatment facility requirements during construction, and estimating the rate of resaturation of the engineered barrier system and the establishment of steady-state groundwater flow after backfilling and closure. Estimating the impact of these effects requires modelling of transient groundwater flow under unsaturated conditions at large scales, and over long timescales. This is a significant challenge for groundwater flow modelling, in particular because of the non-linearity in groundwater flow equations, which can have a marked effect on suitable timesteps for transient calculations. In addition, numerical grids need to be developed at appropriate scales for capturing the transition between saturated and unsaturated regions of the sub-surface, and to represent the features of complex hydrogeological structures such as heterogeneous fractured rock. The Japan Atomic Energy Agency (JAEA) has been developing modelling techniques to overcome these problems as part of the Mizunami Underground Research Laboratory (MIU) Project in the Tono area of Gifu Prefecture, Japan. An integrated geological and hydrogeological modelling, and visualisation system referred to as GEOMASS has been developed, which allows for transient unsaturated groundwater flow modelling in the presence of dynamic underground excavation models. The flow simulator in GEOMASS, FracAffinity, allows for such modelling by the application of sophisticated gridding techniques, allowing for modification of hydraulic conductivity in key zones, and by suitable modification of water retention models (the relationship between saturation and pressure, and saturation and hydraulic conductivity). The approaches that have been developed in GEOMASS have been tested through a series of models of increasing complexity, and the testing has demonstrated that there is no significant impact on estimates of regional groundwater flows or local estimates of flow into underground excavations. The tools and approaches that are described in this paper are of significance in all geological disposal projects, where a key requirement is to estimate and understand the hydrogeological regime and the transient response of groundwater flow to underground construction. Such understanding is important for construction, operation and post-closure phases of facility development.

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Land Subsidence Estimation for Aquifer Drainage Induced by Underground Mining

Energies ◽

10.3390/en14154658 ◽

2021 ◽

Vol 14 (15) ◽

pp. 4658

Author(s):

Artur Guzy ◽

Wojciech T. Witkowski

Keyword(s):

Environmental Impact ◽

Land Subsidence ◽

Field Data ◽

Underground Mining ◽

Small Scale ◽

Aquifer System ◽

Maximum Value ◽

The Impact ◽

Method Model ◽

Impact Of Mining

Land subsidence caused by groundwater withdrawal induced by mining is a relatively unknown phenomenon. This is primarily due to the small scale of such movements compared to the land subsidence caused by deposit extraction. Nonetheless, the environmental impact of drainage-related land subsidence remains underestimated. The research was carried out in the “Bogdanka” coal mine in Poland. First, the historical impact of mining on land subsidence and groundwater head changes was investigated. The outcomes of these studies were used to construct the influence method model. With field data, our model was successfully calibrated and validated. Finally, it was used for land subsidence estimation for 2030. As per the findings, the field of mining exploitation has the greatest land subsidence. In 2014, the maximum value of the phenomenon was 0.313 cm. However, this value will reach 0.364 m by 2030. The spatial extent of land subsidence caused by mining-induced drainage extends up to 20 km beyond the mining area’s boundaries. The presented model provided land subsidence patterns without the need for a complex numerical subsidence model. As a result, the method presented can be effectively used for land subsidence regulation plans considering the impact of mining on the aquifer system.

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