TT 179/02 Commission Water Research Water Future Research Needs Future Current Knowledge and AC Woodford and L Chevallier (Editors) AC Woodford Hydrogeology of the Main Karoo Basin: Hydrogeology of the Main Karoo Basin: AC Woodford and L Chevallier (Editors) Current Knowledge andFuture Research Needs Hydrogeology of the Main Karoo Basin: Current Knowledge and Future Research Needs Prepared for the Water Research Commission by AC Woodford and L Chevallier (editors) Contributers: JF Botha D Cole MR Johnson R Meyer M Simonic GJ Van Tonder B Th Verhagen WRC Report No. TT 179/02 November 2002 Hydrogeology of the Main Karoo Basin: Current Knowledge and Future Research Needs Obtainable from: Water Research Commission Private Bag X03 GEZINA 0031 The publication of this report emanates from aproject entitled: The Preparation of a Handbook on the Hydrogeology of the Karoo Supergroup (WRC Project No. 860) DISCLAIMER This report has been reviewed by the Water Research Commission (WRC) and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the WRC, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. ISBN No 1 86845 851 2 Printed in the Republic of South Africa ii Hydrogeology of the Main Karoo Basin: Current Knowledge and Future Research Needs ACKNOWLEDGEMENTS The Project Team would like to express their gratification to the following instances: • The Water Research Commission for its funding and assistance of the research project, • Members of the Working Group for their time and invaluable input into ensuring the success of the project. The inaugural August 1997 Steering Committee consisted of the following persons: - Mr. A.G. Reynders (Water Research Commission) - Chairman - Mr. K. Pietersen (Water Research Commission) - Chairman - Mr. A. Woodford (Department Water Affairs & Forestry) - Dr. L. Chevallier (Council for Geoscience) - Prof. J.F. Botha (University of the Free State) - Prof. G.J. van Tonder (University of the Free State) - Prof. B. Th. Verhagen (Witwatersrand University) - Mr. M. Simonic (Hydromedia Solutions) - Mr. R. Meyer (CSIR) - Prof. C. Hartnady (Univeristy of Cape Town) - Dr. M.R. Johnson (Council for Geoscience) - Dr. W. Colliston (University of the Free State) - Mr. J. Loock (University of the Free State) - Mr. J.R. Vegter (Consultant) - Mr. N. Andersen (NJB Andersen Consulting) iii Hydrogeology of the Main Karoo Basin: Current Knowledge and Future Research Needs Dedication This manuscript is dedicated to the memory of Tony Reynders, who initiated and enthusiastically guided this project, but was not able to see its fruition. iv Hydrogeology of the Main Karoo Basin: Current Knowledge and Future Research Needs The editors at an exploration site on a dolerite sill in the Victoria West District, during the drilling of an artesian borehole with a drillstem yield of 80 ℓ/s v Hydrogeology of the Main Karoo Basin: Current Knowledge and Future Research Needs vi Hydrogeology of the Main Karoo Basin: Current Knowledge and Future Research Needs TABLE OF CONTENTS Page No. 1. INTRODUCTION 1 1.1 BACKGROUND TO THE PROJECT ……………….……………………...……... 3 1.2 SCOPE ……………………………………………………………………………… 3 1.3 TARGET AUDIENCE ……………………………………………………………... 3 1.4 PHYSIOGRAPHY, CLIMATE AND SURFACE HYDROLOGY ….…………….. 4 1.5 GEOLOGICAL OVERVIEW ……………………………………………………… 8 1.5.1 Sediments of the Karoo Supergroup ………………………………………… 8 1.5.2 Karoo Basalt and Dolerite Magmatism ………………………………...…… 12 1.5.3 Kimberlite Intrusives ………………………..….…………………………… 14 1.6 MODERN GEOMORPHOLOGY ...………………………………………….…….. 14 2. GEOLOGY AND HYDROLOGICAL PROPERTIES 15 2.1 LITHOSTRATIGRAPHY AND DEPOSITIONAL HISTORY 15 2.1.1 Dwyka Group ………………………………………………………………... 15 2.1.1.1 Lithofacies .…………………………………….……………………. 15 2.1.1.2 Depositional Environment and Sediment Source ..………………….. 17 2.1.2 Ecca Group ………………………………………………….………...…….. 18 2.1.2.1 Prince Albert Formation (Lower Ecca) ……...………..……...……... 20 2.1.2.2 Whitehill Formation (Lower Ecca) …………...…...………………... 20 2.1.2.3 Collingham Formation (Upper Ecca) …….……...…………………. 22 2.1.2.4 Vischkuil Formation (Upper Ecca) ……………………………..…... 23 2.1.2.5 Laingsburg Formation (Upper Ecca) ……………………….….…... 23 2.1.2.6 Ripon Formation (Upper Ecca) ……………………………………. 24 2.1.2.7 Fort Brown Formation (Upper Ecca) ……………………………….. 24 2.1.2.8 Waterford Formation of the Southern Zone (Upper Ecca) …………. 25 2.1.2.9 Tierberg Formation (Upper Ecca) ……………………………….….. 25 2.1.2.10 Skoorsteenberg Formation (Upper Ecca) …………………………... 26 2.1.2.11 Kookfontein Formation (Upper Ecca) ……...……………………… 26 2.1.2.12 Waterford Formation of Western Zone (Upper Ecca) ……………... 27 2.1.2.13 Waterford Formation of the North-Western Zone (Upper Ecca) …... 27 2.1.2.14 Pietermaritzburg Formation ………………………………………... 28 2.1.2.15 Vryheid Formation ……………………………………………….… 28 2.1.2.16 Volksrust Formation …………………………………………….…. 29 2.1.2.17 Depositional Environment and Source of Sedimentation ………….. 29 2.1.3 Beaufort Group ……………………………………………………………… 30 2.1.3.1 Adelaide Subgroup ..…………………………...…………………… 30 2.1.3.2 Tarkastad Subgroup .………………………………………………... 31 2.1.4 Molteno, Elliot and Clarens Formations …………………………………….. 33 2.1.4.1 Molteno Formation .………………………………………………… 33 2.1.4.2 Elliot Formation …….…………………….………………………… 34 2.1.4.3 Clarens Formation .……………………….…………………………. 36 vii Hydrogeology of the Main Karoo Basin: Current Knowledge and Future Research Needs 2.2 HYDROSTRATIGRAPHY 37 2.2.1 Dwyka Group ………………………………………………………………... 37 2.2.2 Ecca Group ……………………………………...…………………………... 38 2.2.3 Beaufort Group …………………………………………………………..….. 38 2.2.4 Molteno, Elliot and Clarens Formations …………………………………….. 39 2.2.5 Primary Hydraulic Properties of Karoo Rocks …………………………… 40 2.3 KAROO MAGMATISM 46 2.3.1 Extrusives ……………………………………………………………………. 46 2.3.1.1 Drakensberg Lavas .…………………………………………...……. 46 2.3.2 Intrusives …………………………………………………………………….. 48 2.3.2.1 Karoo Dolerites .…………………………………………………….. 48 2.3.2.2 Breccia Plugs and Volcanic Vents .…………………………………. 113 2.3.2.3 Kimberlite and Associated Alkaline Intrusive Complexes .………... 122 2.4 NON-INTRUSIVE TECTONIC FEATURES 133 2.4.1 Regional Lineaments ………………………………………………………... 133 2.4.1.1 Description …….…………………………………………………….. 133 2.4.1.2 Hydrological Properties ……………………….……………………. 135 2.4.2 Folding ………………………………………………………………………. 135 2.4.2.1 Description …………………………………………………….….… 135 2.4.2.2 Hydrological Properties …………………………………………….. 136 2.4.3 Vertical Faulting and Master-Jointing ………………………………………. 143 2.4.3.1 Description ………………………………………..………………… 144 2.4.3.2 Distribution …………………………………………………….…… 144 2.4.3.3 Jointing Mechanisms ….……………………..………..……………. 145 2.4.3.4 Hydrological Properties ……………………………….……………. 146 Case Study: Flooding of the Orange-Fish River Tunnel ….….…….. 149 2.4.4 Bedding-Plane Fracturing …………………………………………………… 153 2.4.4.1 Description ……………………………………………………………. 153 2.4.4.2 Hydrological Properties ………………………………………………. 154 2.5 SEISMICITY, NEOTECTONICS AND UNLOADING 155 2.5.1 Seismo-neotectonic Provinces ………………………………………….…… 155 2.5.2 Uplifting and Erosional Unloading …………………………………….……. 157 2.5.3 Hydrological Implications …………………………………………………... 157 2.6 GEOMORPHOLOGY, FLUVIAL TERRACES AND PEDOCRETES 158 2.6.1 Geomorphology ……………………………………………………………... 158 2.6.1.1 First Order Features …………………………………………………... 158 2.6.1.2 Second Order Features ………………………………………………... 158 2.6.1.3 Hydrological Significance ……………………………………………. 162 2.6.2 Fluvial Terraces and Floodplains ………………………………………….… 162 2.6.2.1 Description ………………………………………………………….…. 162 2.6.2.2 Hydrological Properties ……………………………….…………….… 164 2.6.3 Pedocretes ………………...………………………………….………………… 167 2.6.3.1 Description……………………………………………………….….…. 167 2.6.3.2 Hydrological Significance ……………………………………………. 169 viii Hydrogeology of the Main Karoo Basin: Current Knowledge and Future Research Needs 2.7 DIAGENESIS, PALEO-FLUID MOVEMENTS AND THERMO- METAMORPHISM 170 2.7.1 Description ……………………………..…………………………..…………... 170 2.7.2 Hydrological Implications ……………………………………………………... 170 2.8 WEATHERING 171 2.8.1 Sediment Weathering …………………………………………...……………... 172 2.8.1.1 Dwyka Diamictite ……………………………………….…………….. 172 2.8.1.2 Mudrock ……………………….………………………….…………… 173 2.8.1.3 Sandstone ………………………………………………….…………... 173 2.8.2 Dolerite Weathering ………………………………………………...……….… 173 2.8.3 Hydrological Implications ……………………………………………………... 176 3. PHYSICAL AND CHEMICAL DESCRIPTION OF KAROO AQUIFERS 178 3.1 GROUNDWATER FLOW AND BEHAVIOUR OF KAROO FRACTURED AQUIFERS 178 3.1.1 Introduction …………………………………………………………...…….…. 178 3.1.2 Nature of Groundwater Flow in Fractured Aquifers ……………...……….….. 179 3.1.2.1 General ……………………..…………………………………..…….... 179 3.1.2.2 Fracture Hydraulics …………………………………………………… 182 3.1.2.3 Fracture Mechanics ………………………………………………….… 186 3.1.2.4 Summary …………………………………………………………….… 188 3.1.3 Theoretical Models of Fractured-Aquifers …………………………………….. 189 3.1.4 Flow Regime Characteristics ……………………………………………….….. 193 3.1.4.1 Inner Boundary Conditions …………………………………………… 194 3.1.4.2 Outer Boundary Conditions ………………………………………….... 196 3.1.4.3 Typical Water-level Drawdown Plots …………………………….…... 197 3.1.4.4 Derivative Plots of Water-level Drawdown …………………………... 198 3.1.4.5 Summary of Drawdown Graph Characteristics ……………..……….... 198 3.1.4.6 Characteristics of Derivative Drawdown Graphs …………………...… 200 3.1.4.7 Examples of Drawdown and Derivative Graphs …...……………..…... 204 Case Study: Borehole GR3 at Graaff-Reinet ………………………… 207 3.2 MACRO-CHEMICAL CONSTITUENTS AND WATER QUALITY