Adapting to future challenges4 January 2012
Bernhard Wehrli explains how scientific research currently focusing on large dams in Africa’s Zambezi River basin will help contribute towards the sustainable design and management of hydraulic structures in the future
Of all continents, Africa has the smallest reservoir storage capacity, the lowest proportion of irrigated agriculture, and the lowest degree of electrification. Dams offer solutions to these problems and could thereby contribute to socio-economic progress. However, the urgent need for expanding water storage capacity in Africa conflicts with the negative social and ecological impacts of large dams that have been identified in the past. In exploiting the hydroelectric potential and the irrigation capacity of African rivers, major challenges will be to improve the operation of existing dams and to avoid past mistakes when designing new ones.
Meeting these challenges requires scientific progress in order to design and manage complex hydraulic structures in sustainable ways; and it will also require improved institutional settings for transboundary water management.
The acronym ADAPT stands for an interdisciplinary research project on integrated water resource management in the Zambezi River basin, which will offer scientific insight to adapt the planning and operation of large dams to social needs and environmental constraints. The overarching goals of the ADAPT project are to:
• Strengthen the interdisciplinary science of integrated water resource management (IWRM) by creating new models for the real-time control and multi-objective optimisation of large hydraulic structures.
• To develop the data resources and conceptual frameworks to drive these models. The models will be useful not only for optimising the operation of existing structures but also for designing new ones.
Specific milestones of the project are detailed below.
1) New technologies with spatially distributed hydrologic and hydraulic models are being developed based on new approaches for real-time incorporation of remote-sensing data. Such models give managers and stakeholders spatially and temporally explicit information on flow rates and water storage in the entire Zambezi River basin. More detailed versions are now already available for the Kafue River basin and allow predicting the extension of flooded areas in the Kafue Flats, a large wetland downstream of Itezhi-Tezhi dam. Such predictions are essential for optimising dam operation in this ecologically sensitive environment.
2) Balancing water supply and demand requires a conceptual framework and models for determining spatially explicit water demand based on demographic and socioeconomic data and trends. This large scale analysis was performed over the entire Zambezi River basin and not only included scenarios for the development of hydropower and irrigation but also for climate change. Based on the scenarios, future gaps between water supply and demand were identified for the riparian countries. This information supports the discussion of trade-offs and decision making for the future development of water resources.
3) In order to assess water quality effects of large dams, detailed sampling and analysis campaigns were conducted over the past four years in the Kafue and Itezhi-Tezhi reservoirs and in downstream river reaches. The studies of the transport and transformation of carbon, nutrients and particles revealed that lakes Kariba and Itezhi-Tezhi act as effective sinks for nutrients and sediments. As much as 70% of nitrogen and 90% of phosphorus are trapped in Lake Kariba and this nutrient supply is missing in downstream ecosystems. In addition the riparian zone of Lake Kariba dam acts as an important source for the bubble-emission of methane, an important greenhouse gas. The study also revealed that the dam’s water intake is well-designed for minimising the release of greenhouse gases downstream of the turbines.
4) Mitigating the downstream effects of dams on large wetlands is only possible if the consequences of different operation rules on biodiversity hotspots can be predicted. Ongoing research into the changes in terrestrial vegetation in the Kafue flats after dam closure document the invasion of shrubs and the expansion of lagoons, both at the expense of grassland which is the feeding ground of the Lechwe (an endemic antelope species). Analysis and modelling of these landscape-scale changes as a response to the hydrologic regime will help quantify optimal managed floods for the ecosystem.
5) Knowledge integration in IWRM requires innovative optimisation techniques. The ADAPT project contributes to the development of methods for identifying optimal water allocation schemes. Disaggregated cost and benefits of water resource uses are determined and used in optimisation models which include the particular geographic areas, economic sectors, social groups, and upstream or downstream countries. The first analysis has identified areas where the expansion of irrigation is not conflicting with hydropower production.
The Zambezi River basin was chosen as the focus of this study because it offers a particularly interesting system within which to address these challenges. With its large seasonality and low specific runoff (70mm/yr-1 or 6% of the annual precipitation), the Zambezi is highly susceptible to natural and anthropogenic perturbations, including floods, droughts and water pollution. These threats are likely to increase due to substantial forecasted changes in water demand and water supply.
The basin harbours extensive floodplains of high ecological and tourism value, and also several large hydropower schemes that span national boundaries. Several of the riparian countries plan to invest in new hydropower schemes, while realising the need to develop their water resources sustainably. In order to achieve this goal, stakeholders need data-driven, analytical tools to evaluate water supply and water demand from both socioeconomic and ecological perspectives.
The ADAPT project started in August 2006 with a pilot phase for establishing a close collaboration between Swiss research groups and partners in Zambia, Mozambique and Zimbabwe. The synthesis phase will end in 2012.
The project team is based in the domain of the Swiss Federal Institute of Technology (ETH) in Zurich and Lausanne and includes the groups of Wolfgang Kinzelbach and Anton Schleiss (hydrology and hydraulic engineering), Thomas Bernauer (political science) and Rolf Kappel (economy). The natural science groups are analysing biogeochemical cycles (Bernhard Wehrli and Alfred Wüest) and ecological impacts (Peter Edwards). This combined competence in engineering, natural and social sciences allows for a comprehensive analysis and model development.
Important African project partners include the Zambezi River Authority which runs Kariba dam, the national electricity company of Zambia (ZESCO) and the Integrated Water Resource Management Centre at the University of Lusaka which is run by Imasiku Nyambe. The project also successfully teamed up PhD students from Switzerland with master students at the University of Zambia in Lusaka.
The research project is funded by the Competence Centre for Environment and Sustainability at the ETH with additional support from the Swiss National Science Foundation and the participating universities. After the synthesis phase, a continuation is foreseen in order to validate the methodologies developed for the Zambezi system in other large river basins. Other urgent topics, such as water use for agriculture or greenhouse emissions from large dams, will also be addressed in more depth.
The experience of this interdisciplinary and transcultural work has been very positive. Specifically, the collaboration of teams of African and European students proved to be essential for conducting field work under complex conditions and to transfer methodological know-how to African stakeholders. The research teams also benefited from essential support by the dam operators.
Translating the different research results into useful tools for decision makers is, however, a major remaining challenge for the final phase of the project. In addition to scientific publications, the research experience will also be made available on the project website http://www.cces.ethz.ch/projects/nature/adapt
Bernhard Wehrli, Professor of Aquatic Chemistry, Swiss Federal Institute of Technology (ETH) and Swiss Federal Institute of Aquatic Science and Technology (Eawag), Seestrasse 79, CH-6047 Kastanienbaum, Switzerland. Email: email@example.com