Towards groundwater security in coastal East Africa

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Groundwater resources in the coastal zone of EA are at risk. Increased demand, linked to rapid population growth in the coastal margins, has led to unsustainable and ill-planned well drilling and abstraction. Sea water intrusion into formerly freshwater aquifers frequently occurs as recharge from rainfall is insufficient to support the rate at which water is extracted. Wells supplying domestic, industrial and agricultural needs have, in many areas, become too saline for use.Climate change is expected to exacerbate this problem. Rising sea levels in the Indian Ocean region are projected to cause inundation of saltwater along the coastal zone, which is dominated by highly-permeable rock, while altered precipitation patterns and temperature change will affect the amount of water replenishing the aquifer through infiltration and recharge. Local communities across the region are already reporting changing tidal and rainfall patterns. The multiplicity of hydrological and demographic driving factors makes this a very challenging issue for management. At present the state of coastal aquifers in the EA region is not well constrained and past practices which may have exacerbated the problem have not been clearly identified. This project will bring together teams from Kenya, Tanzania and the Comoros Islands to address this knowledge gap; collaborating and working towards achieving water security in their respective areas. An integrative approach, combining the expertise of hydrogeologists, hydrologists and social scientists, will target selected sites along the coastal zone in each country. Hydrogeologic observatories will be developed where focussed research will identify the current condition of the coastal aquifers and identify future threats based on projected demographic and climate change scenarios. Water supply and monitoring needs will be identified through consultations with end-users and local authorities and optimum strategies for addressing these sought.An initial step will be to survey and bring together all existing data on well installations, abstraction, groundwater gradients and the salinity of existing wells at each pilot site. Understanding where wells are located, how deep they are, how much water is abstracted, what the flow directions are and what the salinity is, provides an overview of the state of the aquifer. Local data on hydraulic properties, such as the permeability, porosity, and storativity of the aquifer will be investigated and synthesised. Targeted electrical geophysical surveys, which provide relevant spatial information on both the aquifer structure and the saltwater distribution, will be undertaken.Similarly data is needed on the hydrological drivers in the system; to understand how much of annual rainfall infiltrates to replenish groundwater reserves (compared to the amount abstracted for human use) and how this might be impacted by changes in rainfall intensity or frequency. Land use and land use change is also important; controlling the proportion of incident rainfall which reaches the soil and subsequently groundwater. Recharge modelling will be an important tool for investigating different scenarios for climate and land use change and evaluating groundwater vulnerability. The social and political aspects of water use and development will be incorporated to assess the compatibility between the evolution of the availability of coastal freshwater resources and those of society and water politics. Researchers will engage with local community and stakeholder groups in each area and work together towards understanding the issues most affecting the communities with regards accessibility to water supply. A two-way exchange of knowledge between researchers and community members is essential in working towards feasible solutions to existing problems and ensuring preparedness for the changes in demographics and environment in the future.