Groundwater in SADC
Groundwater, defined as the water from rain or other precipitation that soaks into the ground and moves downward to fill cracks and other openings in soils and rocks, is an essential resource of great social, environmental and economic importance. In the SADC region groundwater is the source of water for an estimated 70 percent of the population. The status of groundwater development in each individual country in the SADC largely reflects the importance of the resource in that country. Member States such as Namibia, Botswana and South Africa, are largely dependent on groundwater and are actively integrating the use of groundwater in their water resources management policies. Other SADC Member States that rely mostly on surface water have little understanding of their groundwater resources. The vulnerability of groundwater supply systems to drought often results from the poor design and insufficient depth of wells, along with inappropriate pumping devices. The lack of water level monitoring and prediction is an aggravating factor.
In the SADC region, 37% of the populations rely upon formal or improved groundwater supplies and 23% on reticulated supplies from surface water sources. The remaining 40% rely upon unimproved sources, which may be either groundwater or surface water, and which are generally unsafe and often prone to drought. About one-third of the people in the region live in drought prone areas. In the driest part of the region, groundwater is the primary source of drinking water for the human population and livestock, irrigation for agriculture, industrial uses and town supply. It is also essential for wildlife and other biota and hence is fundamental to the tourism industry in these dryland areas.
Activities in the domestic, agriculture, mining, industry and urban sectors can also degrade the groundwater resources. The widespread use of on-site sanitation in rural and urban parts of the region can cause contamination of shallow aquifers in fractured or karstbedrock with pathogens and nitrates, and groundwater have been over-drawn in some urban and peri-urban areas. For example, waste disposal practices and uncontrolled drilling of boreholes in Lusaka greatly contribute to a simultaneous drop in water levels and an increase in contamination of the unconfined aquifer underlying the city.
The increase in commercial agriculture, particularly horticulture, in some parts of the region has led to the contamination of some aquifers with fertilizer derived nutrients. For example, nitrates from fertilizers have now contaminated the shallow alluvial aquifers in the middle reaches of the Kafue Valley in Zambia. Nitrates have also entered shallow groundwater systems in the Kutama and Sinthumule districts of Venda, South Africa because of modernagricultural practices under dryland cropping, and excessive drawdown for irrigation has affected aquifers in districts such as the Lomagundi Dolomite aquifer of Zimbabwe.
Mining activities have led to the contamination of aquifers with bacteria and other contaminants as well as the extensive loss of water, and even destruction, of some aquifers to the detriment of other users. Pollution from mineral processing has led to the contamination of aquifers with arsenic in Zimbabwe and heavy metals and sulphates in shallow groundwater systems in Botswana.
Groundwater and drought
The provision of adequate supplies of safe drinking water is a priority throughout most of Southern Africa. In most rural areas, it is groundwater - water stored below the ground surface in aquifers - that provides the only affordable means of meeting dispersed domestic demand from rural communities. One of the key advantages of groundwater is its reliability: after surface rivers and streams have dried up, groundwater can still be accessed through wells, springs and boreholes.
However, this buffering capacity to drought is not without limits. Under certain conditions - for example rising dry season demand and reduced recharge to aquifers from rainfall - some groundwater sources may fail, and a groundwater drought may occur.
The response of groundwater to drought
Because aquifers take some time to react to changes in rainfall, groundwater sources can bridge surface water deficits. The disadvantage is that groundwater also recovers more slowly after drought than surface water. Problems may take months or years to emerge; some sources may fail after the rains return, and the drought is perceived to be over.
Groundwater-Dependent Ecosystems in SADC
A number of the regions ecosystems are dependent on groundwater. Five wetland systems are recognized in the SADC Region: palustrine, riverine, lacustrine, estuarine and marine systems. Each of these systems occurs throughout the region, representing specific and usually highly localized ecosystem (including human dependence on the services provided by the wetlands). These services include habitat for fish and other food stocks, provision of fibre and natural medicines, crops for cattle grazing, and (in some cases such as the Okavango Delta and Kruger National Park) support for wildlife on which tourism industries depend.
It is clear that the impact of groundwater drought is likely to be greatest in natural wetland ecosystems such as those that occur in the Okavango Delta (Botswana), Zambezi, Kafue and Luangua flood plains (Angola and Zambia), Lake Malawi and Lake Chilwa (Malawi and Mozambique), the Oshana system (Namibia), the sand river systems (eastern Botswana, southern Zimbabwe and northern South Africa) and the dambo/mbuga/vlei valley systems (Zimbabwe, Zambia and Tanzania) amongst others. While all these ecosystems have received scientific study, these investigations have been mostly undertaken from a botanical/wildlife/natural environment perspective. The nature of the groundwater-ecosystem interaction has not been reliably established, and in many cases has not been even considered in the study of the wetland system. The extent to which these wetlands and other ecosystems are dependent on groundwater is not known and constitutes a fundamental knowledge gap for managers. However, there is qualitative evidence that the existence of many of them (and thus the existence of all flora, fauna and human activity that are part of them) may be threatened by changes in groundwater levels, groundwater discharges and/or groundwater quality.