Mapping groundwater availability and adequacy in the Lower Zambezi River basin

Groundwater plays an important role as a source of water for various socio-economic uses and environmental requirements in the lower Zambezi basin in Mozambique. Hence it is important to know its availability and adequacy in space to inform decision making for sustainable water management practices. For a derivation of a Groundwater Availability map and a Groundwater Adequacy map we adapted the DRASTIC methodology in a GIS environment to determine how different parameters, such as precipitation, topography, soil drainage, land use and vegetation cover, aquifer characteristics and groundwater quality affect (i) groundwater recharge on a long-term sustainable basis, (ii) the short-term abstraction potential and (iii) the long-term adequacy of groundwater utilization for domestic use. Results showed that groundwater availability in the Zambezi basin varies mostly from medium to low, with highest potential along the perennial rivers and in the delta where it plays a crucial role in environmental preservation. The southern margin of the Zambezi River shows low groundwater availability and also presents low adequacy for domestic use due to poor groundwater quality. The results from this study will be used in determining the most promising future development pathways and select the most attractive strategic development plans of the Mozambican government for the Lower Zambezi basin

Modeling for transboundary water resources planning and allocation: the case of Southern Africa

International water resources agreements for transboundary rivers in southern Africa are generally founded in system analysis models for water planning and allocation. The Water Resources Yield Model (WRYM) developed in South Africa has so far been the only model applied in official joint water resources studies aimed to form water-sharing agreements. The continuous discussion around the model performance and growing distress over it being South African, where it was originally developed, while South Africa is one of the interested parties in the process, results in an increased controversy over the system analysis results that are often only meant to guide in selecting the options for water resources management in a given set of scenarios. The objective of this study was therefore to assess the model performance of two other models; WAFLEX and WEAP21 in the Umbeluzi River Basin system where the WRYM was previously applied as part of a Joint River Basin Study. A set of basin development scenarios was equally tested in the three models and the results compared. The results show that the three models all are possible tools for system analysis of river basins in southern Africa, although the structure and complexity of the models are different. The obtained level of satisfaction for specific water users could, however, vary depending on which model was used, which causes uncertainties. The reason for the diverse results is the structurally different ways of describing allocation and prioritization of water in the three models. However, the large degrees of freedom in all system models cause even larger uncertainty in the results since the model developer can, intentionally or unintentionally, direct the results to favor certain water user. The conclusion of this study is therefore that the choice of model does not per se affect the decision of best water allocation and infrastructure layout of a shared river basin. The chosen allocation and prioritization principles for the specific river basin and the model developer's experience and integrity are more important factors to find the optimal and equitable allocation

Improving the groundwater-well siting approach in consolidated rock in Nampula Province, Mozambique

Vertical electrical sounding was used for assessing the suitability of the drill sites in crystalline areas within a water supply project in Nampula Province in Mozambique. Many boreholes have insufficient yield (420 ohm-m) with low porosity and high permeability. In addition to this, there is unfractured nonpermeable intact rock with resistivity of thousands of ohm-m. The unsuccessful boreholes were drilled over a highly resistive zone corresponding to fresh crystalline rock and a narrow altered layer with lower resistivity. Successful boreholes were drilled in places where the upper layers with lower resistivity correspond to a well-developed altered layer or a well-fractured basement. There are a few exceptions with boreholes drilled in seemingly favourable locations but they were nevertheless unsuccessful boreholes for unknown reasons. Furthermore, there were boreholes drilled into very resistive zones that produced successful water wells, which may be due to narrow permeable fracture zones that are not resolved by ERT. Community involvement is proposed, in choosing between alternative borehole locations based on information acquired with a scientifically based approach, including conceptual geological models and ERT. This approach could probably lower the borehole failure rate

Modelling trade-offs between livelihoods and wetland ecosystem services: the case of Ga-Mampa wetland,South Africa

International audienceThis paper presents an integrated dynamic simulation model that represents the functioning of a small South African wetland. The model was developed using the STELLA platform and comprises six interactive sectors namely: hydrology, crop production, crop economics, use of natural wetland resources, land use decision and community well-being. These sectors are inter- linked and changes in one sector impact on other sectors through feedback loops between sectors. Key parameters in the model are demand for food, demand for income, and biophysical drivers (soils, rainfall, groundwater and surface flows). Taking into account these factors, the local community makes choices about uses of different categories of land and water resources available to them (irrigation scheme and wetland). These activities impact on the wetland functioning, which in turn influences economic returns of wetland related activities and ultimately livelihoods. The model is used to simulate several land management options under various localised scenarios of global changes