Dams are large man-made structures built to store water in the upstream reservoir which is formed with their construction. Most of the dams are constructed as single-purpose structures, and among these, nearly half of them, are aimed at irrigation purposes, followed by hydropower and water supply. Other uses include flood control, recreation, navigation, and fish farming. The water of multipurpose reservoirs is shared between different users based on their rights and priority. Usually, human consumption has higher priority followed by irrigation and then hydropower.
Hydropower is accountable for approximately 16% of world electrical energy production and it is the largest renewable energy source. Like it or not, hydropower is a key element in the renewable energy mix, thus an inevitable resource to be considered when equating the reduction of carbon emissions from electricity production. For energy generation, hydropower needs flowing water and a difference between the upstream and downstream water levels (head). Dams, forming a reservoir, are used to maximize energy generation by increasing the available head and store water for dual management of hydrological variability and energy demand.
Water storage, independently of the purpose, brings economic and social benefits. However, the creation of reservoirs modifies existing natural ecosystems interrupting the connectivity of the valleys and affects local populations by disrupting local socioeconomic activities. The negative effects of dams and reservoirs are manifold; on one side, dams are acting on water quality and hydrology of the downstream part of the river, but also as a source of higher evaporation and additional greenhouse gas emissions on the upstream reservoir. Dams trap and interrupt the cycle of sediments, nutrients, aquatic species and seeds. The formation of the reservoirs causes land flooding and possible loss of agricultural areas or habitat space for different species, cutting connectivity paths in terms of regionals ecology and socio-economy. The design, the construction and the operation and maintenance of reservoirs must therefore be made in a sustainable way considering all possible negative effects mainly its interferences with food production activities and ecosystems.
Since the 90s hydropower stakeholders try to reduce and mitigate the negative effect of the dams and reservoirs. The most comprehensive guidelines have been developed by the World Commission on Dams (2000) and the International Hydropower Association (IHA) in the Hydropower Sustainability Assessment Protocol (2010). Both documents pointed out the negative influences of the dam and hydropower construction with their environmental, social and economic impacts. The Hydropower Sustainability Assessment Protocol evaluates dams in different project stages and based on up to 24 different criteria by defined scoring system. The evaluation gives possibility to detect the negative impacts and define mitigation measures for their improvement.
In the next thirty years, an increase in needs of water, energy and food in a range of 50 to 100% is expected. Water will play a dominant role in food and energy production, so more and higher impacts on water availability as well as on ecosystems and socioeconomic systems connected with water are expected. Climate disruption with the enhancement of hydrological extremes and variability will additionally sharpen the situation. Therefore the importance of water storage and water conservation will increase. Dams and reservoirs will play a larger role in the future and continuing of the operation of existing dams and the construction of new dams will be inevitable.
Limited water resources and cooperation between different users is and will be the most important task in the future. It will be necessary to share the available water resources between different users, define the priorities and when possible recirculate the water and energy. Therefore it is essential to analyses the hydro-systems, existing and future ones, within the framework provided by the Water-Energy-Food-Ecosystem (WEFE) Nexus. By implementing a sort of checks and balances methodologies for the analysis of hydro-systems, the WEFE Nexus approach should result in improved water, energy, food and ecosystem security by management and governance across sectors and scales, building synergy and promoting sustainability and transformation to green and circulated economy.
IHE Delft is working on several projects that follow these ideas. The project S-Multistor investigates and demonstrates improved approaches to sustainable multipurpose water storage. The project creates a common research and innovation platform where researchers from IHE Delft and southern partner institutions engage with leading international initiatives in a structured program of collaboration. Activities are focused in the Irrawaddy Basin of Myanmar, Zambezi Basin of Southern Africa, and Magdalena Basin of Colombia. Targeted development outcomes include improved catchment management for water, food, and energy security that is socially and environmentally sustainable and contributes directly to Agenda 2030.
Also, implementation of the hydropower in the existing hydraulic structures that are not used for hydropower production is one of IHE focusing points. Studies with implementation of hydropower in existing weir structures, extracting energy from water supply or sewage water systems in the towns and installation of the hydropower plants in the irrigation dams and along irrigation channels are one of the possible solutions. The topic, so cold “hidden treasure”, has been discussed on World Water week in Stockholm 2018.
Small hydropower, mostly defined as less than 10 MW capacity, are mostly run-of river systems without reservoirs and are an important energy source with benefits for climate mitigation. Without dam and reservoir they have, in principle, less influence and impact on the ecosystems and on the water and food production activities, but are not by definition free of impacts. Possible impact issues must be seriously considered and processed during the design, but also during the operation and maintenance works. Hydropower projects labeled as small should not be systematically categorized as environmental friendly and should follow also similar comprehensive procedure as for the so-called big hydropower.
Dams and reservoirs are and will be needed for better water conservation and more efficient water use. Place, size and operation of the dam must involve all possible stakeholders. Socio-economic and environmental aspects of upstream-downstream linkages have to be considered in detail on a river basin scale instead of on the individual project basis. A Water-Energy-Food-Ecosystem Nexus approach for the analysis of hydropower projects will probably provide sub-optimal production conditions for these, however will provide joint-optimal conditions to guarantee simultaneously water supply and food production security that is socially and environmentally sustainable.
About the authors
joined IHE Delft in September 2009 as an Associate Professor in Hydraulic Engineering and River Basin Development. He is responsible for the course of Storage and Hydropower within the core of Hydraulic Engineering and River Basin Development. Dr. Marence main research and training interests lie on dam and reservoir development and design of hydropower schemes and structures.
is Professor of Hydraulic Engineering and River Basin at IHE Delft. He served in many instances as consultant in hydraulic engineering and he was head of the hydraulics department in an engineering company, having participated and directed applied projects on dams, hydropower, water supply, river engineering, drainage, mining sites, emergency planning and safety of hydraulic infrastructures. He has served in several faculty commissions, in Lisbon and Lausanne, and recently he was involved in a Massive Open Online Course on Fluvial Hydraulics.