Hydrostratigraphy of the Malmani Subgroup dolomites within the northeastern escarpment (Limpopo and Mpumalanga, South Africa)

Abstract The Late Archaean to Early Proterozoic Malmani Subgroup comprises of dolomites and limestones forming part of the Chuniespoort Group within the Transvaal Supergroup, outcropping as an arc structure east of the Pretoria Group along the Limpopo and Mpumalanga escarpment. These rocks form a fractured karst aquifer in the area and have a high degree of heterogeneity and anisotropy. The aquifers are unconfined to semi-confined, with compartmentalisation by dolerite dykes being a possible effect (if the dykes are large and extensive enough) due to the dykes acting as aquitards or barriers to groundwater flow. The contact zones between the dolomite formations and dolerite dykes are usually fractured however, and along with any other faults and fractures result in preferential dolomite dissolution and the development of groundwater flow paths in the area. Borehole yields ranges between 2 to 5 l/s and potentially >10 l/s per borehole in the vicinity of large regional fractures or dolerite intrusions. Groundwater from the Malmani Subgroup generally meets the drinking water quality standards for major constituents and it is of Mg-Ca-HCO3 nature. Groundwater development within this particular hydrostratigraphy is linked to potential well field target zones that take cognisance of various surface water-groundwater interaction affecting surface water discharge rates as well as groundwater over-abstraction concerns. Preliminary results have indicated that given a groundwater potential of 44 hm3/a, the aquifer will be able to support abstractions of up to 29 hm3/a if systematically developed adaptively and could be used and managed conjunctively with surface water to alleviate the pressure on the already stressed Olifants Water Management Area.

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Flow and Radionuclide Transport From Rock to Surface Systems: Characterization and Modelling of Potential Repository Sites in Sweden

11th International Conference on Environmental Remediation and Radioactive Waste Management, Parts A and B ◽

10.1115/icem2007-7300 ◽

2007 ◽

Cited By ~ 1

Author(s):

Kent Werner ◽

Emma Bosson ◽

Sten Berglund

Keyword(s):

Surface Water ◽

Groundwater Flow ◽

Water Flow ◽

Exit Point ◽

Flow Paths ◽

Near Surface ◽

Mike She ◽

Mike 11 ◽

Surface Water Flow ◽

Safety Assessments

The safety assessments of potential geological repositories for spent nuclear fuel in Sweden are supported by modelling of groundwater flow in rock, to predict locations (exit points) where radionuclides from the deep repository may enter land, surface waters and associated ecosystems above the rock. This modelling includes detailed rock descriptions, but simplifies the upper part of the flow domain, including representations of meteorological processes and interactions with hydrological objects at the surface. Using the Laxemar candidate site as example, this paper investigates some potentially important consequences of these simplifications. Specifically, it compares particle tracking results obtained by a deep-rock groundwater flow model (CONNECTFLOW) and by MIKE SHE-MIKE 11, which contains detailed descriptions of near-surface/surface water flow. Overall, the models predict similar exit point patterns, occurring as clusters along streams in valleys, at a lake, and in sea bays. However, on a detailed level there are some prediction differences, which may be of importance for biosphere-focused safety assessments. CONNECTFLOW essentially predicts flow paths through the repository that follow fractures and deformation zones, outcropping in valleys. In comparison, MIKE SHE-MIKE 11 provides more detailed information on near-surface water flow paths, including the associated exit points and inputs to assessments of radionuclide retention.

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Integrated Surface Water-Groundwater Modelling

Global NEST Journal ◽

10.30955/gnj.000378 ◽

2013 ◽

Vol 7 (3) ◽

pp. 281-295

Keyword(s):

Surface Water ◽

Groundwater Flow ◽

Mass Conservation ◽

Water Levels ◽

Governing Equations ◽

Physical Processes ◽

Flow Paths ◽

Flow Models ◽

Surface Water Flow ◽

Model Flow

Two Integrated Surface water - Groundwater flow Models (ISGMs) have been developed at the National Technical University of Athens (NTUA), Greece and Cardiff University (CU), UK to investigate surface water-groundwater interactions. The models are based on physical processes and are capable of describing more accurately the recharge and discharge flow paths between surface and ground waters. The NTUA ISGM consists of a 3-D surface water flow sub-model (FLOW-3DL) and a 3-D saturated groundwater flow sub-model. The CU ISGM is based on the 2-D surface water model DIVAST, which has been extended to include 2-D saturated groundwater flow. Both models use the finite difference method and orthogonal grids. The momentum and mass conservation equations are the governing equations for both surface and groundwater flows. The ISGMs have been applied to two simple cases and their results have been compared to computations using only surface water models (FLOW-3DL and DIVAST) to demonstrate the need to use ISGMs for accurate and satisfactory calculations. Furthermore, the results of the two ISGMs are compared for a channel, which fully penetrates an aquifer. The two ISGMs show a similar behaviour; the NTUA ISGM exhibits a slightly slower response of the aquifer water levels to the water level changes in the channel than the CU ISGM.

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A global-scale two-layer transient groundwater model: development and application to groundwater depletion

10.5194/hess-2016-121 ◽

2016 ◽

Author(s):

Inge E. M. de Graaf ◽

Rens L. P. H. van Beek ◽

Tom Gleeson ◽

Nils Moosdorf ◽

Oliver Schmitz ◽

...

Keyword(s):

Surface Water ◽

Groundwater Flow ◽

Global Scale ◽

Groundwater Depletion ◽

Groundwater Model ◽

Confined Aquifer ◽

Flow Paths ◽

Groundwater Head ◽

Aquifer Systems ◽

Confining Layers

Abstract. Groundwater is the world's largest accessible source of freshwater to satisfy human water needs. Moreover, groundwater buffers variable precipitation rates over time, thereby effectively sustaining river flows in times of droughts as well as evaporation in areas with shallow water tables. Lateral flows between basins can be a significant part of the basins water budget, but most global-scale hydrological models do not consider surface water-groundwater interactions and do not include a lateral groundwater flow component. In this study we simulate groundwater head fluctuation and groundwater storage changes in both confined and unconfined aquifer systems using a global-scale high-resolution (5 arc-minutes) groundwater model by deriving new estimates of the distribution and thickness of confining layers. Inclusion of confined aquifer systems (estimated 6 % to 20 % of the total aquifer area) changes timing and amplitude of head fluctuations, as well as flow paths and groundwater-surface water interactions rates. Also, timing and magnitude of groundwater head fluctuations are better estimated when confining layers are included. Groundwater flow paths within confining layers are shorter then paths in the underlying aquifer, while flows within the confined aquifer can get disconnected from the local drainage system due to the low conductivity of the confining layer. Lateral groundwater flows between basins are significant in the model, especially for areas with (partially) confined aquifers were long flow paths are simulated crossing catchment boundaries, thereby supporting water budgets of neighboring catchments or aquifer systems. The two-layer transient groundwater model is used to identify hotspots of groundwater depletion resulting in an estimated global groundwater depletion of 6700 km3 over the 1960–2010, consistent with estimates of previous studies.

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Characterizing Groundwater Interaction with Lakes and Wetlands Using GIS Modeling and Natural Water Quality Measurements

Water ◽

10.3390/w13070983 ◽

2021 ◽

Vol 13 (7) ◽

pp. 983

Author(s):

Brianna Speldrich ◽

Philip Gerla ◽

Emma Tschann

Keyword(s):

Water Quality ◽

Groundwater Flow ◽

Water Table ◽

Grid Cell ◽

Specific Conductance ◽

Hydric Soils ◽

Flow Paths ◽

Water Budgets ◽

Gis Modeling ◽

Discharge Rates

Wetlands provide many benefits, including flood attenuation, groundwater recharge, water-quality improvement, and habitat for wildlife. As their structure and functions are sensitive to changes in hydrology, characterizing the water budgets of wetlands is crucial to effective management and conservation. The groundwater component of a budget, which often controls resiliency and water quality, is difficult to estimate and can be costly, time-consuming, and invasive. This study used a GIS approach using a digital elevation model (DEM) and the elevations of lakes, wetlands, streams, and hydric soils to produce a water-table surface raster for a portion of the Itasca Moraine, Minnesota, U.S. The water-table surface was used to delineate groundwatersheds and groundwater flow paths for lakes and wetlands, and map recharge and discharge rates across the landscape. Specific conductance and pH, which depend on the hydrological processes that dominate a wetlands water budget, were measured in the field to verify this modeling technique. While the pH of surface waters varied in the study area, specific conductance increased from 16.7 to 357.5 μS/cm downgradient along groundwater flow paths, suggesting increased groundwater interaction. Our results indicate that basic GIS tools and often freely available public-domain elevation datasets can be used to map and characterize the interaction of groundwater in the water budgets of lakes and wetlands, as exemplified by the Itasca Moraine region. Combining this with grid cell-by-cell water balance provides a means to estimate recharge and discharge, thereby affording a way to quantify groundwater contribution to and from lakes and wetlands. Applied elsewhere, this cost-efficient technique can be used to assess the vulnerability of lakes and wetlands to changes in land use, groundwater development, and climate change.

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