DEPARTMENT OF CIVIL ENGINEERING CIV4044S Research Project Investigation of the impact that decentralised groundwater use has on the City of Cape Town’s water demand Prepared by: Raadhiya Perin Prepared for: Prof Neil Armitage and Dr Kirsty Carden 21 November 2016 ii Plagiarism Declaration 1. I know that plagiarism is wrong. Plagiarism is to use another’s work and pretend that it is one’s own. 2. Each significant contribution to, and quotation in, this assignment from the work(s) of other people has been attributed, and has been cited and referenced. 3. This report is my own work. 4. I have not allowed, and will not allow anyone to copy my work with the intention of passing it off as his or her own work. Signature of author: _______________ iii Acknowledgments The author would like to thank her supervisors, Neil Armitage and Kirsty Carden, for their contribution to this study through constructive meetings, their support and advice. John Okedi and Lloyd Fisher-Jeffes kindly provided additional information and data required for this study, and Ben Mauck is thanked for his assistance in the initial stages of this study. The author is grateful to the City of Cape Town for provision of water usage values of suburbs around Cape Town. In addition, Ameen Ghoor and Vincenzo Marchesini kindly assisted with the suburb assessments by driving the author around for more efficient data collection. Lastly, thanks go to Cheryl Wright for forwarding the questionnaire to all academic staff in the UCT Civil Engineering Department, and to all those respondents who participated in completing the questionnaires. iv Abstract This research project investigated the current use of decentralised groundwater in various suburbs around the City of Cape Town, in order to investigate the impact that it would have on the demand of the City’s piped water supply. Due to the rapid increase in Cape Town’s population and the current drought being experienced, the use of an alternative water source, groundwater, needs to be increased to reduce the strain on the potable water supply system. Studies done by Jacobs et al. (2011), Seyler et al. (2016) and Wright (2013) in Cape Town assessed the impact that groundwater use has on the water demand of a household. All three studies found that using groundwater for outdoor use, such as garden irrigation, instead of using potable water, reduced water demand by up to 50%. This study investigated the factors that would contribute to an increase in groundwater usage and therefore the reduction in potable water demand in order to reduce the strain on the Water Supply System. Eight suburbs were assessed around the City of Cape Town. These varied in income levels, elevations above sea level and groundwater yields. It was found that groundwater was mainly used in the dry summer months. The flowrate of the groundwater varied depending on the elevation of the suburb above sea level. For the study area, the higher income areas were situated at a higher elevation levels – these had lower groundwater yields yet the number of properties which made use of groundwater was 30% higher than those in the lower income areas which had a higher groundwater yield. Based on results and comparison of data from the City of Cape Town and the investigations conducted for this study, there was a direct relationship between the income level of the suburb and the use of groundwater. Therefore, the income level of a household is the main factor that contributes to groundwater use, as more money can be saved by not using groundwater for large garden areas and the cost of drilling to the required depth to abstract groundwater is not a problem; the only concerns are the availability of groundwater in the area and the status of water restrictions. v Table of Contents Plagiarism Declaration ii Acknowledgments iii Abstract iv Table of Contents v List of Tables viii List of figures ix Definition of terms x Acronyms and Symbols x Glossary x 1. Introduction 1-1 1.1 Background to study 1-1 1.2 Problem statement 1-1 1.3 Objective of investigation 1-1 1.4 Focus and limitations of the investigation 1-2 1.5 Outline of report 1-3 2. Literature review 2-1 2.1 Groundwater 2-1 2.1.1 Groundwater quality 2-1 2.1.2 Climate change influencing groundwater availability 2-2 2.1.3 Groundwater abstraction points 2-3 2.1.4 Registering GAPs 2-3 2.1.5 Income influencing groundwater use 2-4 2.2 Income groups in South Africa 2-4 2.3 Cape Town’s water supply 2-5 2.3.1 Household water use 2-6 vi 2.3.2 Cape Town water restrictions 2-6 2.4 Water demand 2-7 2.4.1 Factors influencing water demand 2-7 2.4.2 Comparative study – Cape Town and Perth (2001) 2-7 2.4.3 Decentralised groundwater use reducing water demand 2-8 3. Methodology 3-1 3.1 Overview of research process 3-1 3.2 Desktop study 3-1 3.2.1 Literature review 3-1 3.2.2 Data obtained from the City of Cape Town 3-1 3.3 Questionnaire Process 3-2 3.4 Study area 3-2 3.4.1 Sub places in Constantia 3-3 3.4.2 Sub places in Grassy Park 3-3 3.4.3 Elevations of suburbs above sea level 3-5 3.4.4 Income levels 3-5 3.5 Suburb assessment 3-5 3.6 Assumptions 3-6 3.7 Analysis of data 3-7 3.7.1 Generating maps 3-7 3.7.2 Data refining 3-7 3.7.3 Groundwater yield 3-9 3.7.4 Groundwater usage during rainfall months 3-9 3.7.5 Income influencing groundwater usage 3-10 3.7.6 Comparison of borehole data available 3-11 3.8 Limitations of methodology 3-11 4. Results and discussion 4-1 4.1 Critical information from questionnaire responses 4-1 4.2 Groundwater use dependent on rainfall 4-3 4.3 Groundwater yield 4-4 vii 4.4 Income influencing groundwater usage 4-9 4.4.1 Groundwater usage per suburb 4-9 4.4.2 Income influence 4-10 4.5 Comparison of GAP datasets 4-13 5. Conclusions and Recommendations 5-1 5.1 Conclusions 5-1 5.2 Recommendations 5-2 6. References 6-1 7. Appendices 7-1 Appendix A: Questionnaire 7-2 Appendix B: Water restriction poster 7-4 Appendix C: Maps 7-6 Appendix D: Summary of results in tabular format 7-9 Appendix E: Ethics form 7-17 Appendix F: ECSA Level Outcomes 7-18 viii List of Tables Table 2-1: Income group brackets 2-4 Table 3-1: Elevations of suburbs above sea level (Citipedia, 2016) 3-5 Table 3-2: Income levels of the study area (2011 Census, 2013) 3-5 Table 4-1: Main results from questionnaire responses 4-1 Table 7-1: Correlation between rainfall and groundwater use 7-9 Table 7-2: Groundwater usage based on signage from the suburb assessment 7-9 Table 7-3: Comparison of flowrates (Ɩ/s) from the City of Cape Town and questionnaire responses 7-10 Table 7-4: AADD (Ɩ/day) for three years 7-10 Table 7-5: Groundwater usage per day (hours), week (days) and yield per day (Ɩ/day) 7-11 Table 7-6: Boreholes and wellpoints used per suburb 7-11 Table 7-7: Comparison of GAP datasets from 3 years 7-12 Table 7-8: 2011 Census Constantia breakdown of boreholes 7-12 Table 7-9: 2012 individual borehole registrations 7-13 Table 7-10: Summary of questionnaire responses 7-16 ix List of figures Figure 2-1: Groundwater is found below the water table (USGS, 2016) 2-1 Figure 2-2: Distribution of household income by income groups in 2011 (Coetzee et al., 2012) 2-5 Figure 2-3: Typical household water use in Cape Town (Aquarista, 2016) 2-6 Figure 3-1: Locality map of the study area (ArcGIS) 3-3 Figure 3-2: Sub places in Constantia (ArcGIS) 3-4 Figure 3-3: Example of groundwater and additional signage found on most property boundaries (Perin, 2016) 3-6 Figure 3-4: Average monthly rainfall data from 2000 to 2012 for Cape Town (World Weather Online, 2016) 3-10 Figure 4-1: Rainfall in Cape Town (2000 to 2012) vs the number of properties using groundwater each month in 2016 4-3 Figure 4-2: CoCT flowrate (l/s) vs measured groundwater abstraction rate (l/s) 4-5 Figure 4-3: AADD (l/day) vs measured yield (l/day) with suburbs placed in order of increasing number of abstraction days per week 4-6 Figure 4-4: AADD (l/day) vs measured yield (l/day) in order of suburbs in increasing income levels 4-7 Figure 4-5: AADD (l/day) vs measured yield (l/day) in order of suburbs in the number of hours’ groundwater is used per day 4-8 Figure 4-6: AADD (l/day) vs measured yield (l/day) in order of increasing flowrate values (l/s) 4-8 Figure 4-7: Income levels influencing groundwater usage 4-11 Figure 4-8: Percentage of properties which have boreholes or wellpoints 4-12 Figure 4-9: Comparison of groundwater datasets 4-14 Figure 7-1: Locality map 7-6 Figure 7-2: Sub places in Grassy Park 7-7 Figure 7-3: Groundwater flowrate from the City of Cape Town (Ɩ/s) 7-8 x Definition of terms Acronyms and Symbols AADD(s) Annual Avergae Daily (water) Demand(s) CoCT City of Cape Town GAP Groundwater Abstraction Point GIS Geographic Information Systems kl kilolitre (1000 litres or 1 cubic meter) kƖ/d kilolitre per day km2 sqaure kilometer Ɩ/s litres per second (flowrate) m metre (distance) m2 square metres m3 cubic metre (1000 litres or 1 kilolitre) Glossary Aquifer A body of permeable rock capable of holding or transmitting groundwater Borehole A deep hole made in the ground to abstract groundwater, usually over 15m deep Cape Metropolitan Area Means Cape Town or cape peninsula City The area of jurisdiction of the municipality of the City of Cape Town DWAF Department of Water Affairs and Forestry Erf Plot of land Flowrate The yield of groundwater per second (Ɩ/s), rate at which groundwater flows per second GAP Any type of abstraction of water from the ground for use on the surface (borehole or wellpoint) Google Maps A web based service that provides information about geographical rgions around the world