Groundwater for the North of Namibia
Surface water is restricted to four perennial rivers at the Northern and Southern borders in Namibia. As part of the technical co-operation between Namibia and Germany, the Government of the Federal Republic of Germany provided financial and technical support through the project “Groundwater for the North of Namibia” executed by the Ministry of Agriculture, Water and Forestry (MAWF) and the Federal Institute for Geosciences and Natural Resources (BGR). Phase I commenced in January 2007 and was completed in the first half of 2010. Currently, Phase II is running until May 2014.
The goals of this project are to improve access to safe drinking water and to provide well founded information concerning the groundwater resources in the Cuvelai-Etosha Basin (CEB) as a basis for Integrated Water Resource Management (IWRM).” The ongoing investigations and their resulting outputs have to be converted into an applied management of the groundwater resources.
The Cuvelai-Etosha Basin is situated in the central-northern area of the country. It extends northwards into Southern Angola and represents the largest aquifer system in the northern part of Namibia, covering an area of approx. 100,000 km⊃2;. Due to the immediate proximity of this area to Angola and further favorable conditions, the CEB is developing rapidly. While the country currently has a population growth rate of 1.57 % per annum, the annual growth rate in the CEB runs to 2.8 % per annum. In fact, half of the country’s population is living in the CEB. Currently most of the population in the CEB is supplied with drinking water by a pipeline system conveying water into the basin from the Kunene River, more precise the Calueque Dam in Angola. Intermittent droughts and floods as well as population growth lead to an increasing demand and put pressure on the existing water resources.
- The technical tasks of the project are divided into three main areas of focus:
- The delineation of freshwater yielding groundwater bodies in the CEB to provide access to safe and sustainable water resources.
- The development of a national groundwater information system to enhance and support management procedures and decision processes.
The development of a decision support system for water resources information management in the CEB and combination with a numerical groundwater model for pilot-areas.
The CEB is divided into six groundwater regions based on geological units (Damara Sequence) and local occurrence (Kalahari Sequence):
- The Otavi Dolomite Aquifer (DO) is a fractured, partially confined and locally karstified fresh water aquifer within the Damara Sequence. The highly productive Otavi Dolomite Aquifers are of high economic importance and represent the only water control area around the Tsumeb Area in the CEB.
- The Oshivelo Aquifer (KOV and KOV II) contains fresh to brackish water. It is mainly porous, locally fractured, confined and becomes artesian towards the North.
- The Etosha Limestone Aquifer (KEL) is mainly fractured and often karstified.
- The Omusati Aquifer (KOM) comprises unconsolidated and semi-consolidated sediments of the Kalahari Sequence. The groundwater is mainly brackish, locally fresh water lenses occur.
- The Oshana Aquifer (KOS), a mainly porous, unconfined aquifer, is characterized by saline to hyper-saline water.
The Ohangwena Aquifer (KOH I and KOH II), a multi-layered, continuous porous aquifer system of the Eastern Ohangwena and Northern Oshikoto regions with a groundwater flow from Angola to the South. The Eastern part of the Ohangwena I Aquifer is currently tapped through small scale abstraction schemes for livestock and human consumption. The newly discovered Ohangwena II Aquifer which is being investigated in detail at the moment is underlying the brackish to saline western part of the Ohangwena I Aquifer.
The identification of freshwater aquifers followed several steps. In 2007 to 2008 a groundwater hydro-census was conducted as a baseline study. Transient Electro-Magnetic (TEM) field surveys revealed potential freshwater horizons in the Ohangwena and Omusati Region. Drilling campaigns between 2009 and 2010 verified a deep aquifer in the western part of the Ohangwena Region.
Additional observation boreholes were drilled 2011 in the Ohangwena Region to delineate the freshwater extent and to set-up a groundwater monitoring network. The geological setting of the Ohangwena I and II Aquifer was translated into a conceptual hydrogeological model. Extensive drilling campaigns, hydraulic tests, recharge calculations, water level and water quality monitoring provide information to parameterize the conceptual model and to develop a numerical groundwater model. Based on the groundwater model, water availability will be determined and climate change scenarios and water abstraction schemes can be evaluated.
Preliminary results reveal a huge potential of the Ohangwena II Aquifer (KOH II) for regional water supply. In cooperation with the bulk water supplier Namibia Water Corporation Ltd (NamWater) and the EU funded Integrated Water Resources Management Project, a pilot scheme for water supply tapping the KOH II water resource is currently being developed.
Although water quality of the KOH II Aquifer is generally good, groundwater samples revealed that treatment in some areas is still necessary. High fluoride content is the main limiting factor. Fluoride exceeds the Namibian limit of 3 mg/l with a factor of 1.5 to 3 in around 50% of the samples. Depth-specific sampling of KOH II waters showed reduced fluoride concentrations if wells are screened in the upper layers of the aquifer.
Another major activity in the second and current phase of the project is the development of the National Groundwater Information System GROWAS II. A detailed workflow analysis executed in 2010 revealed, that the current database lacks essential features for the management of groundwater relevant data. As a consequence of the imminent Namibian Water Act, licensing procedures for the application of groundwater abstraction and drilling permits need to be incorporated into the Information System. The development of enhanced features includes:
- Development of a completely new database structure and graphical user interface based on PostgreSQL.
- Development of a Geo-Database.
- Development of a hydrogeological code and database dictionary for Namibia.
- Licensing module for drilling and water abstraction permits.
- Interactive map visualization/GIS module and query features.
- Import templates for borehole completion reports, lithology logs, Screenshot of the map visualization module of GROWAS II well installation logs, water sampling forms, water analysis forms, water level measurements and pump tests forms.
- Development of export templates for reporting.
- Borehole information module.
- Lithology module.
- Water level monitoring module.
- Hydrochemistry module.
- Report function for queries and annual reporting on groundwater information situation for basin management units and political regions.
- Seamless linkage to third party software like Google Earth
The implementation of the new Water Act in Namibia goes hand in hand with the development of a nationwide integrated water resource management strategy. Decisions on water resources will in the future not only be made by centralized authorities but will also address the basin level through Basin Management Committees (BMC).
Due to the involvement of stakeholders with a wide range of responsibilities and experiences, the challenge is to make hydrogeological knowledge accessible to a broad audience. The development of a Decision Support System (DSS) for water resources management in the Cuvelai-Etosha Basin gives decision makers the necessary insight into the current status and possible scenarios of future development (e.g. addressing demographic growth and climate change). Through visualization of these scenarios, the different stakeholders can discuss and jointly decide on development strategies. This will reduce the conflict between concurrent water-users and will lead to a sustainable management of the limited water resources.
The DSS will be realized in four steps:
1. Development of an integrated water resource data warehouse, the so-called BWIS (Basin Water Information System);
2. Improvement of the national groundwater data base (GROWAS II)
3. Conceptualization and development of a numerical water quantification module on basin scale
4. Interfacing to the Water Evaluation and Assessment Tool WEAP, which allows an easy-to-use Graphical User Interface (GUI) while having all benefits of an advanced numerical model for groundwater management.