While there is considerable opposition to dams and reservoirs in the Western world, reservoirs built to store water during the rainy season so it can be used during the dry season can save lives and secure values when the rains fail.
East Africa is in the grips of a devastating drought, an unfortunate and all-too-common tragedy. Crops are failing, and both livestock and people are dying from lack of access to food and drinking water. While there is considerable opposition to dams and reservoirs in the Western world, reservoirs built to store water during the rainy season so it can be used during the dry season can save lives and secure values when the rains fail.
How reservoirs work
Water reservoirs allow us to even out the differences in water availability between dry and wet seasons. Too much water in the wet season can cause floods, or too little in the dry season can cause droughts, both of which pose obvious problems for the people who are affected. The tropical region of East Africa may even receive enough rain during the dry season, but the problem is the duration and distribution. High-intensity rain may last for only a short period, generating floods. The water is also lost without people being able to use it.
A region may have enough water as seen from an annual perspective, but may nevertheless experience periodic water shortages and restrictions in use, as the natural supply may be unevenly distributed over the year. The larger the difference between periods of limited water and periods of too much water, the more storage is needed. Water reservoirs smooth out these differences in water availability. A country’s water security can be described by the capacity it has to store excess water, compared to natural variations of runoff throughout the year.
Norway has developed storage capacity to ensure hydropower production throughout the winter, when the natural runoff of water is low. In other areas of the world, dams and reservoirs can provide water for irrigation or drinking water, particularly where the rainy season lasts from 3-4 months and provides an abundance of water, followed by an 8-9 month-long dry period. At an international level, flood control is also one of the main reasons to build reservoirs, often in combination with one or more of the other aforementioned goals.
Drought and the development of reservoirs in East Africa
The eastern parts of Kenya and parts of Somalia are especially affected by the current severe drought. The infrastructure in this region is quite limited and poorly developed in terms of water storage. Nor is there any connection via channels or other delivery systems to areas with more abundant water resources. This kind of infrastructure would have reduced the region’s vulnerability to drought.
When parts of Ethiopia were affected by drought in 2015/2016, it was similar to the 1980s, when Bob Geldof organized the “Live Aid” concert with his musician friends, bringing an outpouring of support and focusing the whole world’s attention on the problem. Studies from NTNU in Norway, supported by an analysis from Ethiopia, suggest that a reasonable development of reservoirs and diversion channels for irrigation in the drought-prone parts of Ethiopia can save lives and value the next time drought strikes this area. When the Ethiopian drought finally ended in the spring of 2016, the same area was tragically hit by heavy rains and floods. People died in the flooding and landslides. Water reservoirs would have most likely reduced this problem.
The World Bank confirms that a steady and secure supply of water can support economic growth in Ethiopia. Ethiopia is currently building many reservoirs to improve its food and energy security. The country has great ambitions to become East Africa’s powerhouse. However, the larger reservoirs are on the Blue Nile, which flows towards Sudan and Egypt, and south on Omo Ghibe River system, which drains into Lake Turkana in Kenya. Neither of these areas experienced the 2015/2016 drought.
Egypt controls the water
The relationship between the availability of water storage capacity and the problems posed by drought has been comprehensively documented. One commonly cited case that illustrates this relationship is the Aswan Dam and Lake Nasser reservoir, which help protect Egypt from drought and food shortages. Researchers have documented how Egypt managed droughts in 1973, 1974, 1983 and 1984 because of the country’s ability to store water. Ethiopia suffered great human and material losses during these same years. It is hard to imagine that the authorities in Egypt would be able to supply a population of more than 80 million people with food without Lake Nasser. In addition, Egypt has benefited greatly from the ability to generate power while reducing flood risk along the Nile River.
The California drought
What about the 2012-2015 California drought? Many of California’s rivers are strongly regulated and the state should be better prepared than Ethiopia, for example. Reservoirs made it possible to store and allocate the little water that came as rain or snow in the best possible way, reducing damage to agriculture, private households and ecosystems. The end of the drought was followed by heavy rainfall, filling most of the state’s reservoirs to average levels or higher. At the same time, a damaged spillway at Lake Oroville caused the state to urge nearly 200 000 people to evacuate because of fears that there would be an uncontrolled release of water.
Heavy rainfall and snowmelt caused damage to the spillway and created a dramatic situation in California. At the same time, if the Lake Oroville reservoir had not been in place, downstream areas might have suffered great damage, because the reservoir gave the state the ability to capture and regulate the large natural flood.
Reservoirs reduce damage during floods
The United Nations considers floods to be the natural disaster with the greatest potential for damage.
The construction of the Three Gorges Dam and reservoir in China entailed the relocation of roughly 1 million people and has been very controversial internationally. Chinese scientists and authorities describe the main purpose of this project as reducing the flood risk from the Yangtze River. The reservoir will protect downstream areas, where roughly 300 000 lives have been lost over the past century from floods. The project will also provide huge hydropower production and is vital to allowing transport on the river. Ships now sail into the metropolis of Chongquing, 1600 km from the sea. The cost of construction of the project has been substantial, but Chinese authorities argue that the total value of flood control, power generation and transport will be repaid after only three years.
The World Bank has collected data on the effects of constructing protective infrastructure in the US. The calculations showed that the US government has invested roughly USD $200 billion since 1920, which in turn has provided USD $700 billion in benefits. In addition, many of these same water reservoirs have ensured access to water during dry periods and have supported large-scale development of irrigation systems.
Floods in Norway
In 1995, there were large floods of two of Norway’s largest river systems, the Gudbrandsdalslågen and Glomma Rivers. Analyses by NTNU and the Norwegian Water Resources and Energy Directorate (NVE) showed that reservoirs are the only flood mitigation measures that substantially reduce large floods. Reservoirs in the upper parts of the river basins reduced flood levels at Lillestrøm, in the lower part of the basin, by almost 2 metres.
Similarly, the regulation of Nesjøen, Sylsjø along with the construction of other smaller reservoirs in Selbu and Tydal in mid-Norway has protected both Trondheim and Selbu from flooding. In the absence of this water regulation, a major flood that occurred in 1973 would have raised Selbusjøen by as much as 2 metres, which would have caused major damage. This regulation has also protected Trondheim, one of Norway’s largest cities. Analyses show that dramatic floods in 1807, 1822, 1889 and 1934 could have been reduced by almost 3 metres if these events had happened after water regulation was in place.
Recently, we have also seen potentially damaging floods in western Norway, which have been much less dramatic due to regulation.
The final report of the World Commission on Dams concludes that “… a simple accounting for the direct benefits provided by large dams – the provision of irrigation water, electricity, municipal and industrial water supply, and flood control – often fails to capture the full set of social benefits associated with these services. It also misses a set of benefits and indirect economic (or multiplier) benefits of dams”.
Water reservoirs reduce damage and create values
In many areas, climate change will make dry areas drier and wet areas wetter, increasing the need for reservoirs. There are numerous examples of dams and reservoirs with major environmental and social consequences, but it is important to be aware and highlight the fact that water reservoirs also save lives and create value. The Intergovernmental Panel on Climate Change (IPCC) emphasizes the very important present and future role that reservoirs do and will play in ensuring access to water and protecting people and property from floods.
This viewpoint was first published in Norwegian by Dagens Næringsliv.