Aroca catchment’s hydrogeological characteristics are majorly controlled by deeply weathered crystalline rocks of northern Uganda. Groundwater derived from within the medium grained weathered clasts to the base of the unconsolidated regolith in addition to fissures in the underlying saprocks is widely used to supply water to most upcoming towns.
However, in addition to limited reliable data, little is known of the geometry and storage capacity of these aquifers. This study used magnetic resonance sounding (MRS) and complimentary electrical resistivity (VES), lithological logs and hydraulic tests to determine aquifer geometry and hydraulic properties of Aroca catchment. The main aquifer is largely a medium-grained sandy saprolite and exhibits leaky aquifer characteristics. It is supplemented by the saprolite-fissured boundary and the bulk of the fissured secondary aquifers. MRS and VES were useful in delineating the upper surface (up to a mean depth ~5 mbgl) of the aquifer geometry. The mean depth to the bottom of the saprolite and fractured layers was 33 and 70 mbgl respectively. The mean static water level across the catchment ranges from ~1.4 to 30 mbgl (with a median value of 13.7 mbgl). The mean T is 4.3 to 104 m2d-1, K is 7.0 md-1 and Sy is ~0.016 for this aquifer. MRS determined drainable groundwater storage of aquifers with a mean value of 380 mm, which is much lower than the value of 590 mm from similar geological formations of Benin. MRS water content and decay constant of the saturated aquifer had mean values of 6.4% and 156ms, respectively. Just like most geophysical methods, MRS suffers from resolution loss with depth and result into the fissured zone not being well resolved.
MRS complemented by VES and aquifer tests has provided a new insight in aquifer geometry characterization and groundwater storage in the deeply weathered crystalline rock aquifers of Aroca catchment and the region. The geometry and hydraulic properties of these weathered crystalline rock aquifers can further be constrained for better spatial representation by conducting a number of well distributed long duration aquifer tests and MRS measurements across the catchment and region. Hence, more site investigations is recommended to improve on the knowledge of storage capacities of the catchment/region aquifers for better future groundwater abstraction strategies, resource planning and management.
Inhaltsverzeichnis (Table of Contents)
- INTRODUCTION
- Background
- PROBLEM STATEMENT
- OBJECTIVES
- Main Objectives
- Specific Objectives
- Justification and Significance of the study
- Scope of work
- Study Area
- Location and Demography
- Climate
- Drainage and hydrology
- Geology of the Aroca catchment
- Hydrogeology
- LITERATURE REVIEW
- Geology and geological setting
- Regional Geology
- Evolution of weathered crystalline rock aquifers
- Groundwater occurrance
- Geometry of weathered crystalline rock aquifers
- Lithological Logs
- Geoelectrical resistivity
- Principle of electrical resistivity method
- Electrical profiling
- Vertical Electrical Sounding (VES)
- Magnetic Resonance Sounding (MRS)
- Principle of MRS method
- MRS measurements
- MRS parameters and aquifer geometry
- MRS flow related parameters
- MRS storage related parameters
- Hydraulic properties of crystalline rock aquifers
- Lithological logs
- Aquifer tests
- Theoretical estimation of storage
- Determination of aquifer hydraulic parameters
- Derivative analysis
- Hydrogeological conceptual models
- MATERIALS AND METHODS
- Materials
- Methods
- Archived/historical data collection
- Field activities
- Monitoring well construction
- Aquifer tests
- MRS measurements
- Laboratory analyses
- Data analyses
- Litho-stratigraphic analysis
- Use of geoelectrical resistivity (VES) and borehole lithological logs
- Hydraulic parameters analysis
- Laboratory data analysis
- Aquifer test analysis
- MRS data analysis
- Generation of a hydrogeological conceptual model
- PRESENTATION AND DISCUSSION OF RESULTS
- Aquifer characteristics
- Borehole log analysis
- Physio-chemical analysis
- Spatial lithological distribution and basement spatial variation analysis
- Delination of hydrogeologic units using geophysical technique
- Geoelectrical resistivity (VES)
- MRS aquifer geometry
- Comparison of MRS, VES layer model and lithological logs
- Hydraulic properties of aquifers
- Estimates of hydraulic parameters from pedotransfer functions
- Static water level and hydraulic head distribution
- Aquifer tests analysis
- Parameterization of MRS hydraulic parameters
- MRS flow hydraulic parameters
- MRS drainable groundwater storage
- Conceptual hydrogeological model
- DISCUSSION OF RESULTS
- Aquifer Geometry
- Hydraulic properties of aquifers in the region
- Comparison of MRS hydraulic flow parameters
- Conceptual cross-sectional model model
- CONCLUSIONS AND RECOMMENDATIONS
- Conclusions
- Aquifer architecture
- Aquifer hydraulic properties
- Hydrogeological conceptual model
- Recommendations
Zielsetzung und Themenschwerpunkte (Objectives and Key Themes)
This dissertation aims to quantify groundwater storage and assess the geometry of aquifers in weathered crystalline rock formations in northern Uganda. The study uses a combination of geophysical techniques, including magnetic resonance sounding (MRS), electrical resistivity (VES), and borehole lithological logs, to characterize the aquifers and their hydraulic properties.
- Groundwater storage in weathered crystalline rock aquifers
- Aquifer geometry and its relation to groundwater storage
- Hydraulic properties of aquifers, including transmissivity and hydraulic conductivity
- Application of magnetic resonance sounding (MRS) in hydrogeological investigations
- Development of a hydrogeological conceptual model for the study area
Zusammenfassung der Kapitel (Chapter Summaries)
Chapter one introduces the topic of groundwater storage in weathered crystalline rock aquifers and outlines the objectives and significance of the study. Chapter two provides a comprehensive literature review on the geology, hydrogeology, and geophysical techniques used in the research. Chapter three describes the materials and methods used in the study, including the collection of historical data, field activities, laboratory analyses, and data processing. Chapter four presents and discusses the results obtained from the analysis of the collected data, including the characterization of aquifer geometry, hydraulic properties, and groundwater storage. Chapter five summarizes the conclusions drawn from the study and provides recommendations for future research.
Schlüsselwörter (Keywords)
The main keywords and focus topics of the dissertation include: groundwater storage, weathered crystalline rock aquifers, magnetic resonance sounding (MRS), electrical resistivity (VES), aquifer geometry, hydraulic properties, transmissivity, hydraulic conductivity, hydrogeological conceptual model, northern Uganda.
- Citation du texte
- Joseph Okullo (Auteur), 2016, Estimating Groundwater Storage in Weathered Crystalline Rock Aquifers of Aroca Catchment, Northern Uganda using Geophysical Methods and Aquifer Tests, Munich, GRIN Verlag, https://www.grin.com/document/1488069
