Groundwater resource assessment aims to obtain fundamental data and information needed to describe the hydraulic and chemical parameters in order to estimate the available groundwater resource which is suitable for drinking. This study was undertaken with the purpose of determining and estimating the groundwater occurrence, groundwater flow parameters, groundwater quality and storage in typical Karoo Main Basin aquifers such as in the Steynsrus study area in South Africa. The field investigations were designed to define and determine the sustainable yields and the properties of the aquifers and the exploitable volumes. The research places emphasis on the appropriate tools and their applications in order to understand the local aquifers so as to optimise the groundwater exploration for town water use and to determine the future water use.
The geophysical surveying methods, particularly the magnetic method, were utilised to investigate and determine borehole drilling targets, and to locate groundwater potential structures, which are often associated with high borehole yields. The quality of the magnetic data utilised for drilling by the external consultant was critically evaluated and was found to be ‘bad data’. Percussion drilling played an important role in providing geological subsurface information; in particular locations of fractures which are often associated with favourable groundwater flow were identified. Seventeen (17) boreholes were drilled in the whole project, seven (7) of the boreholes were sited by magnetometer survey and interpretation, and ten (10) of the drilled boreholes were sited by geological mapping and map interpretation. Twelve of the drilled boreholes were declared ‘unsuccessful’ due to yielding a blow yield below 1.00 L/s; therefore these boreholes were not considered for aquifer pump testing. Blow yields of five (5) of the newly drilled boreholes were between 1.5 and 24 L/s.
Based on these findings, the aquifers in the study were concluded to be a fractured system of alternating layers of sandstone and shale formations, characterised by the favourable groundwater flow characteristics at the dolerite fractures, and in some cases bedding plane fractures of sandstone formations. The study demonstrates the value in the methods and concepts applied in geohydrological studies to understand the local aquifer properties and in order to estimate the sustainable yields and the groundwater balance.
Table of Contents
CHAPTER 1 INTRODUCTION
1.1 RESEARCH FRAMEWORK
1.2 WATER SUPPLY BACKGROUND
1.3 PROBLEM STATEMENT
1.4 METHODOLOGY
1.5 AIMS AND OBJECTIVES
1.6 STRUCTURE OF DISSERTATION
CHAPTER 2 LITERATURE REVIEW
2.1 INTRODUCTION
2.2 OVERVIEW OF GROUNDWATER RESOURCE ASSESSMENT
2.3 GROUNDWATER RESOURCE ASSESSMENT CONCEPTS
2.3.1 Groundwater Occurrence
2.3.2 Groundwater Flow and Storage
2.3.2.1 Borehole sustainability and aquifer parameters
2.3.3 Groundwater Recharge
2.3.3.1 The Chloride Mass Balance Method (CMB)
2.3.3.2 Qualified guesses
2.3.4 Borehole Sustainable Yields
2.3.5 Groundwater Quality
2.3.5.1 Interpretation of chemical data
2.3.5.1.1 Piper and Durov diagrams
2.3.5.1.2 Schoeller diagram
2.3.5.1.3 Groundwater salinity
2.3.5.2 Statistical analysis
2.4 SUSTAINABLE DEVELOPMENT
2.5 GROUNDWATER ASSESSMENT CASE STUDIES
2.6 SUMMARY
CHAPTER 3 SITE DESCRIPTION
3.1 OVERVIEW AND ECONOMIC DEVELOPMENT
3.2 PHYSIOGRAPHY AND DRAINAGE
3.3 RAINFALL AND CLIMATE
3.4 VEGETATION AND LAND USE
3.5 WATER RESOURCES
3.5.1 Surface Water
3.5.2 Local Groundwater
3.5.3 Groundwater Potential
3.5.4 Water Use in the Moqhaka Local Municipality
3.6 GEOLOGY AND GEOHYDROLOGY
3.6.1 General Geology
3.6.2 Geohydrology
3.7 SUMMARY
CHAPTER 4 DESKTOP STUDY
4.1 INTRODUCTION
4.2 REMOTE SENSING AND MAP ANALYSIS
4.2.1 Borehole Siting
4.3 BOREHOLE INFORMATION
4.4 SUMMARY
CHAPTER 5 GEOPHYSICAL INVESTIGATIONS
5.1 INTRODUCTION
5.2 MAGNETIC SURVEY
5.2.1 Results and Discussion
5.3 SUMMARY
CHAPTER 6 DRILLING AND GEOLOGICAL CHARACTERISATION
6.1 INTRODUCTION
6.2 PERCUSSION DRILLING
6.2.1 Lithology
6.2.2 Unsuccessfully Drilled Boreholes
6.3 SUMMARY
CHAPTER 7 PUMP TESTING AND AQUIFER PARAMETERS
7.1 INTRODUCTION
7.2 AQUIFER TESTING
7.2.1 Blow Yields
7.2.2 Step Discharge Test
7.2.3 Constant Discharge Test
7.2.3.1 Diagnostic plots
7.2.4 Recovery Test
7.2.5 Aquifer Parameters
7.2.5.1 Cooper-Jacob method
7.2.5.1.1 Validity of Assumptions of Cooper-Jacob method
7.2.5.1.2 Estimation of Transmissivity using Cooper-Jacob method
7.2.5.2 RPTSOLV program
7.3 SUMMARY
CHAPTER 8 EXPLOITABLE GROUNDWATER RESOURCE
8.1 INTRODUCTION
8.2 RECHARGE ESTIMATION
8.2.1 Chloride Mass Balance Method
8.2.2 Qualified Guesses
8.3 GROUNDWATER RESOURCE SUSTAINABLE YIELD ESTIMATES
8.3.1 Borehole Recommended Yields
8.3.2 Water Balance
8.4 SUMMARY
CHAPTER 9 HYDROCHEMISTRY
9.1 INTRODUCTION
9.2 STATISTICAL ANALYSIS
9.2.1 Univariate Statistics
9.2.2 Quality of Inorganic Chemistry Data
9.3 GROUNDWATER QUALITY
9.3.1 Irrigation Suitability
9.4 HYDROGEOCHEMICAL CHARACTERISTICS
9.5 SUMMARY
CHAPTER 10 CONCLUSIONS AND RECOMMENDATIONS
10.1 INTRODUCTION
10.1.1 Geophysics Survey
10.1.2 Geology and Geohydrology
10.1.3 Aquifer Parameters
10.1.4 Groundwater Quality
10.1.5 Groundwater Sustainable Use
10.1.6 Additional Findings
10.2 RECOMMENDATIONS
Research Goals and Topics
The dissertation aims to assess the groundwater resources for water supply to the town of Steynsrus. The primary goal is to investigate whether current and projected future groundwater resources are sufficient to meet the municipal water demands for the year 2030, while ensuring the sustainable use of the aquifer system.
- Assessment of groundwater occurrence using magnetic geophysical methods.
- Geological characterization and analysis of aquifer lithology from drilling logs.
- Evaluation of aquifer hydraulic and storage properties through constant discharge pump testing.
- Estimation of exploitable groundwater resources, including recharge and water balance calculations.
- Analysis of hydrogeochemical characteristics to determine water quality suitability for domestic consumption.
Extract from the Book
2.3 GROUNDWATER RESOURCE ASSESSMENT CONCEPTS
Scientific methods have been used to determine groundwater occurrence, namely remote sensing, magnetic method, aeromagnetic imagery, electrical and electromagnetic methods, and the gravity method (Woodford and Chevallier, 2002).
Remote sensing has been mainly used as method to locate mapped dolerite intrusions and faults (Woodford and Chevallier, 2002). Remote sensing is ideally suited for Karoo conditions due to the relatively simple geology which mainly consists of undeformed sediments intruded by dolerite dykes and sills, the well-known relationship between the groundwater occurrence and dolerite intrusions, and the association of areas of dense vegetation with the shallow groundwater (Woodford and Chevallier, 2002). However, remote sensing is better used in conjunction with a geophysical method to explore for drilling high-yielding boreholes. Some of the commonly used methods are ground magnetic surveys, which measure the variations of the earth’s magnetic field, electrical and electromagnetic methods, which determine the resistivity of various rock types with depth and lateral extent, and gravity methods, which involves measuring natural variations in the force of gravity.
Summary of Chapters
CHAPTER 1 INTRODUCTION: Outlines the research background, the water scarcity problems in Steynsrus, and the primary objectives of the study.
CHAPTER 2 LITERATURE REVIEW: Reviews the fundamental concepts of groundwater assessment, including occurrence, recharge methods, and sustainable development principles in fractured rock aquifers.
CHAPTER 3 SITE DESCRIPTION: Provides a detailed physical and socio-economic overview of the Steynsrus area, including climate, geology, and existing water resources.
CHAPTER 4 DESKTOP STUDY: Details the collection and evaluation of existing reports, geological maps, and satellite imagery to define drilling targets.
CHAPTER 5 GEOPHYSICAL INVESTIGATIONS: Examines the magnetic methods used to locate and verify potential groundwater structures.
CHAPTER 6 DRILLING AND GEOLOGICAL CHARACTERISATION: Documents the percussion drilling of boreholes and the analysis of lithological logs for characterizing the subsurface.
CHAPTER 7 PUMP TESTING AND AQUIFER PARAMETERS: Discusses the execution of aquifer tests and the determination of key hydraulic properties such as transmissivity and storativity.
CHAPTER 8 EXPLOITABLE GROUNDWATER RESOURCE: Presents the estimates for recharge and water balance to evaluate the sustainability of the groundwater supply.
CHAPTER 9 HYDROCHEMISTRY: Analyzes the chemical composition of the groundwater and its suitability for domestic use according to national standards.
CHAPTER 10 CONCLUSIONS AND RECOMMENDATIONS: Synthesizes the study's findings and offers management recommendations for the Moqhaka Local Municipality.
Keywords
Borehole sustainable yield, Geohydrological characterisation, Groundwater assessment, Groundwater flow, Groundwater occurrence, Aquifer parameters, Karoo fractured-rock aquifers, Water balance, Water quality, Steynsrus, Magnetic survey, Lithology, Hydrochemistry, Pump testing.
Frequently Asked Questions
What is the primary focus of this research?
This research focuses on performing a comprehensive groundwater resource assessment to determine if groundwater can reliably supply the town of Steynsrus to meet its projected 2030 water demands.
Which regional water management area does the study cover?
The study area falls within the Middle Vaal Water Management Area, specifically within the quaternary catchment C60E.
What is the main objective regarding the municipal water supply?
The objective is to estimate the sustainable yield of existing and newly drilled boreholes to determine if groundwater is sufficient as a sole or supplementary water source for the town.
What scientific methods were employed to characterize the aquifer?
The study utilized remote sensing, magnetic geophysical surveys, percussion drilling, aquifer pump testing, and hydrochemical analysis of water samples.
What does the literature review establish regarding Karoo aquifers?
The review establishes that Karoo aquifers are primarily fractured-rock systems where groundwater flow is controlled by secondary features such as faults, joints, and dolerite intrusions.
How are the sustainable yield estimates determined in this study?
Sustainable yields are estimated using the FC program, which incorporates pump testing data, drawdown observations, and recovery data to ensure long-term aquifer viability.
Why were the magnetic data from the original consultant questioned?
The magnetic data were evaluated as "bad data" because they showed unrealistic magnetic intensities and single-point anomalies that did not align with conventional geological expectations.
What is the conclusion regarding the town's future water security?
The study concludes that current groundwater resources are insufficient to meet projected 2030 demands, indicating a significant supply deficit that requires further water management strategies.
- Arbeit zitieren
- Lebogang Malefane (Autor:in), 2016, Groundwater Resource Assessment for Town Water Supply in South Africa. The Case of Steynsrus in the Free State Province, München, GRIN Verlag, https://www.grin.com/document/910024
