FINAL REPORT Increase of Water Supply Safety by Managed Aquifer Recharge along the North-South Carrier – A pre-feasibility study ANDREAS LINDHE, LARS ROSÉN, PER-OLOF JOHANSSON, TOMMY NORBERG Department of Civil and Environmental Engineering Division of GeoEngineering Research Group of Engineering Geology CHALMERS UNIVERSITY OF TECHNOLOGY Göteborg, Sweden 2014 Report 2014:2 REPORT 2014:2 FINAL REPORT Increase of Water Supply Safety by Managed Aquifer Recharge along the North-South Carrier – A pre-feasibility study ANDREAS LINDHE, LARS ROSÉN, PER-OLOF JOHANSSON, TOMMY NORBERG Department of Civil and Environmental Engineering Division of GeoEngineering Research Group of Engineering Geology CHALMERS UNIVERSITY OF TECHNOLOGY Göteborg, Sweden 2014 FINAL REPORT, Increase of Water Supply Safety by Managed Aquifer Recharge along the North-South Carrier – A pre-feasibility study © ANDREAS LINDHE, LARS ROSÉN, PER-OLOF JOHANSSON, TOMMY NORBEG, 2014 ISSN 1652-9162 Report/ Department of Civil and Environmental Engineering, Chalmers University of Technology No. 2014:2 Department of Civil and Environmental Engineering Division of GeoEngineering Research Group of Engineering Geology Chalmers University of Technology SE-412 96 Göteborg Sweden Telephone: + 46 (0)31-772 1000 Chalmers Reproservice Göteborg, Sweden 2014 FINAL REPORT, Increase of Water Supply Safety by Managed Aquifer Recharge along the North-South Carrier – A pre-feasibility study ANDREAS LINDHE, LARS ROSÉN, PER-OLOF JOHANSSON, TOMMY NORBERG Department of Civil and Environmental Engineering Division of GeoEngineering Research Group of Engineering Geology Chalmers University of Technology PREFACE The present pre-feasibility study on artificial groundwater recharge in Botswana was carried out within the Swedish International Development Cooperation Agency’s (Sida) policy framework Partner Driven Cooperation (PDC) with Botswana Department of Water Affairs (DWA) and Chalmers University of Technology, Department of Civil and Environmental Engineering as the two main partners. A planning grant was received from Sida and an application for a PDC Cooperation Grant was developed jointly by Chalmers and DWA. In October 2012 Sida made the decision to finance the pre-feasibility study and the project was started in November 2012 and ended in March 2014. The project involves the development of a water supply safety model that is capable of modelling future water supply scenarios, taking into account the dynamic variations over time of water availability and demand in the supply system along the so called North-South Carrier (NSC) distribution system in eastern Botswana. Possible future scenarios of Managed Aquifer Recharge (MAR) are defined, where identified groundwater aquifers and already existing wellfields are used for injection of treated surface water to improve the supply safety of the system. The project assesses the need for increased water supply safety, if large-scale MAR can provide the desired increase in water supply safety, and if MAR is economically viable. It is our sincere belief that the development of the water supply safety model, the results achieved in this project, and future developments and applications of the model by the DWA will provide important support to decisions at DWA on more efficient and sustainable use of water resources in Botswana. Lars Rosén, Andreas Lindhe, Per-Olof Johansson, Tommy Norberg CHALMERS, Civil and Environmental Engineering, Report 2014:2 3 4 CHALMERS, Civil and Environmental Engineering, Report 2014:2 Executive summary Background Water scarcity is a major challenge for sustainable development in Botswana and calls for integrated water resources management, including measures to avoid water losses, efficient use of water, introduction of water saving technologies, as well as of water re-use and recycling. Furthermore, expected climate change implies risks for rainfall seasons being shorter and less reliable in the future. The arid and semi-arid climate of Botswana provides a situation with low rainfall and high rates of potential evapotranspiration. Combined with the country’s generally very flat topography, this results in low rates of surface runoff and low rates of recharge to groundwater. There are no perennial streams originating in Botswana. Most of Botswana’s population lives in the eastern grassland region of the country, along the border with South Africa and Zimbabwe. The hydrological conditions and a continuously increasing water demand in this area results in a water stressed situation. Managed Aquifer Recharge (MAR), sometimes denoted Artificial groundwater Recharge (AR), is a well-established technique to increase available water quantities for water supply and to improve water quality. Water scarcity accentuated by urban growth, especially in semi-arid and arid regions, has resulted in a growing interest in MAR as a basis for water supply by collection of surface water runoff for infiltration to avoid evaporation losses. Scope and objectives The overall aim of this project is to investigate the potential for using large scale MAR to improve future water supply safety in Botswana. This pre-feasibility study focuses on the area along the North-South Carrier (NSC), which is a bulk water supply system running from north to south in eastern Botswana, connecting a number of surface water dams, groundwater aquifers and water treatment facilities. The NSC supplies drinking water to a large portion of the Botswana population. According to previous studies, there exist a number of opportunities for conjunctive surface water and groundwater use along the NSC. In order to meet the overall aim of the project, the specific objectives of the study are to: Define the need for increased water supply safety. Assess if large-scale MAR can provide the desired increase in water supply safety. Assess the economic viability of MAR for provision of the desired water supply safety. The study of the potential for MAR along NSC is divided into the following major parts: Evaluation of the NSC water supply system and identification of components to be included in the water supply safety study. CHALMERS, Civil and Environmental Engineering, Report 2014:2 5 Development of a risk-based water supply safety model, taking into account the water demands and availability over a specified future time horizon. Definition of modelling scenarios, including MAR scenarios and Non-MAR scenarios. Modelling of the potential effects on water supply safety in the NSC from implementing MAR. Evaluation of the cost-effectiveness of MAR. The current study supplements previous studies performed in the area by studying in detail the effects on water supply safety from MAR with respect to the temporal variability of water availability and predicted future demand. Project realization The project was carried out in collaboration between Chalmers University of Technology, Department of Civil and Environmental Engineering, in Sweden and the Department of Water Affairs of Botswana. The Swedish part of the project was financed within the Swedish International Development Cooperation Agency (Sida) policy framework programme Partner Driven Cooperation (PDC). The Botswana part of the project was financed by The Ministry of Minerals, Energy and Water Resources. Capacity building was an important component of the project including seminars, workshops and on-the-job training on concepts, methods and conceptual design of MAR facilities as well as on water supply safety modelling. The project was implemented during the period of November 2012 – March 2014. The Swedish partners visited Botswana 5 times during this period. The study area In eastern and southern Botswana, with its relatively high density of population and substantial water demand, a number of surface water dams have been constructed to collect and store rain water. The largest dams are the Shashe, Dikgatlhong, Letsibogo, and Gaborone Dams. The storages of the dams are very variable due to the highly seasonal, occasional and variable riverflows. In addition, the need to store water for drought periods and the flat topography in most areas result in large losses of water to evaporation from these dams. Surface water dams in eastern Botswana have been connected through a pipeline transfer system denoted the North-South Carrier (NSC), providing possibilities to transfer water to urban centres and thus improving the reliability of the water supply in this part of the country. In addition to the surface water dams a number of groundwater wellfields are connected or are planned to be connected to demand centres supplied with water from the NSC, e.g. Palla Road, Chepete, Masama, Makhujwane, Malotwane, and Palapye Wellfields. The demand centres, surface water dams and aquifers included in this study are shown in Figure A. 6 CHALMERS, Civil and Environmental Engineering, Report 2014:2 Figure A. Map showing the demand centres, wellfields and surface water dams included in this study. Due to the highly variable storage in surface water dams, the groundwater aquifers have a potential to support the NSC demand centres during drought periods. Because of the very limited natural recharge to these aquifers their long-term sustainable capacity could be improved if artificially recharged with surface water. Artificial CHALMERS, Civil and Environmental Engineering, Report 2014:2 7 recharge with collected surface water from dams may also reduce the total loss of water to evaporation. The NSC water supply system This pre-feasibility study