The Hydrological Changes associated with Multi-purpose Dams and Reservoirs

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1 The Hydrological Changes associated with Multi-purpose Dams and Reservoirs Large dams and reservoirs have many impacts on the hydrological conditions of the catchment area. The most obvious impact is on discharge. Dams act to hold back the flow of water and in doing so create a reservoir of deep water stored upstream. At the same time, discharge downstream becomes regulated. This at best, can prevent large scale floods and protect lives but at worst, can deprive natural wetlands of vital flows and increase rates of channel erosion due to the extreme variations in discharge. This increase in erosion can cause channel depth to fall resulting in a lowering of the watertable. Suitable sites for dam projects require steep sided ravine valleys, with considerable depth to store large quantities of water. The water quality of these reservoirs can unfortunately deteriate. Upstream towns and and industry as well as agricultural areas feed a constant supply of sewage, industrial effluence and agricultural run-oof into the resevoir. The reservoir also slows down discharge upstream and so these pollutants are not really broken down by the flow of the river. In affect, this can lead to more stagnant waters transporting soild wastes and storing them in the reservoir. The natural flow of water is stopped by the dam and so sediment being transported by the river quickly builds up within the reservoir. This reduces its storage capacity over time and requires long term maintenance. In large reservoirs and where the valley sides are made up of unconsolidated materials, mass movements such as landslides and slumping make occur. This problem is already developing along the sides of the 3-Gorges Reservoir, in China. The problems of water quality and sedimentation are developed in the video below: This disruption to sediment flow aslo reduces the amount of sediment being transported downstream. This changes the flow patterns of rivers downstream. This can have negative impacts on farmers who require a rich supply of fertile alluvium. In addition, this interception of sediment reduces the supply to the marine environment, speeding up rates of erosion in delta areas and starving the marine environment of crucial nutrients. When dams are built as part of multi-purpose schemes to produce hydroelectricity it is common for output from the dam to vary over time. Hydroelectricity stations need to be maintained and serviced, therefore river outout and electricity generation is rarely at a maximum. These variations in output have a big impact on downstream hydrology. Increases in flow increase rates of channel erosion. Erosion deepens the river channel and widens the bank, also removing riparian vegetation, which further increase rates of channel erosion. As a result of increased erosion, the water table of the local catchment down stream can fall, making it harder and harder for local farmers to access water. This in turn creates a lowering of downstream aquifers. Large dams also create a problem of cooling the water downstream. Large deep reservoirs store colder water and when released downstream the natural temperature and ecology of the river changes. The Costs and Benefits of Multi-purpose Dams The above example of the 3-Gorges dam has become a classic Geography

2 case study for developing the costas and benefits of dams. So it would be wrong not to develop it as an example here. However, in discussing the relevance of large scale multi-purpose dam projects its is important to see them in place context and for this reason we will refer to a number of countries to discuss the importance of dams for their needs. For China, the 3- Gorges has far greater significance than just a large dam that produces electricity it represents China's recent emergence as a global superpower. It represents one of the world's most spectacular engineering feats and was also one of biggest landmark achievements of the 21st Century. Politically this project presents China as a powerful force in the world and it attempts to show the world that China can in someway control mother nature. The shear scale of the 3-Gorges is mind boggling. It's the world's biggest dam and the largest hydroelectric power station. It has flooder over 62,000 acres of farmland, 13 major cities, 140 large, and hundreds of small villages along the river's banks and force the relocation of just shy of 1.5 million people and is expected to grow to 4 million by Made of concrete and steel, the dam is 2,335 m (7,661 ft) long and the top of the dam is 185 metres (607 ft) above sea level. The project used 27.2 million cubic metres of concrete (mainly for the dam wall), 463,000 tonnesof steel and moved about million cubic metres of earth. The concrete dam wall is 181 metres (594 ft) high above the rock basis. When the water level is at its maximum it will reach 75 metres (574 ft) above sea level, which is 110 metres (361 ft) higher than the river level downstream, the dam reservoir is on average about 660 kilometres (410 mi) in length and 1.12 kilometres (3,700 ft) in width. It contains 39.3 km3 of water and has a total surface area of 1,045 square kilometres (403 sq mi). On completion, the reservoir flooded a total area of 632 square kilometres (244 sq mi) of land. It is estimated to cost $22.5 billion. So how can such a scale of production be justified? Well, there is a lot to be said in criticism of the 3-Gorges Dam. There are a great deal of environmental and social issues, not to mention the potential risks of dam failure. However, it is important to establish some weight of importance in looking at the costbenefit analysis. I don't think this has really been well addressed in the media or for that matter in text books. So for that reason I would like to be provocative and write a short defense of the 3-Gorges Dam.You can look in more detail at the costs on Jeffrey Hay's site below. If we consider first then the economics of the 3-Gorges, then China can actually afford it. Through its policy of opening up to the world market and joining the WTO, China has become the 'factory of the world'. In doing so it has created huge revenues, with its balance of payments in trade posting annual positive returns in the hundreds of billions over the last decade. Having said this, China's economy remains immature. Too oversimplify it produces vast amounts of goods that are of low value and it achieves this through low wages and cheap raw materials. In order to mature as an economy and maintain economic growth in the future it needs to increase its value of production and its domestic market. It can do this by shifting to higher value goods and by increasing the purchase power of its population. However, to achieve the latter it must create employment. In the context of having money to burn and the need for job creation, large scale infrastructural

3 projects like 3-Gorges dam fit the bill. 3-Gorges created jobs and took over 12 years to build. Another benefit of 3-Gorges was to help China open up the interior of its country to development. China at present has an immense East weat divide annd so the reservoir offfer an important industrial routeway. The reservoir will be deep enough to tansport tonne freighters. This offers the cities of the regions along the 660 km length an important trading route. China is also under large internatonal pressure to take its new global role more seriously. As part of this it needs to be seen to to be takling the problem of climate change more. The Dam will reduce at full power, coal consumption by 31 million tonnes per year, avoiding 100 million tonnes of greenhouse gas emissions. At the same time it will provides the world s largest capacity hydroelectric power station with twenty-nine 700 MW turbines and a total capacity of 20,300 MW. Eventually, it will have 32 generators: 30 main generators, each with a capacity of 700 MW, and two plant power generators, each with capacity of 50 MW, making a total capacity of 22,500 MW. The expected annual electricity generation will be over 100 TWh, 10% of China's current energy requirements. Finally, one other major benefit of the dam is its flood control. In short, the dam has been estimated to protect 10 million people from the risk of catastrophic floods. In many ways I find myself thinking at this point, end of. If the dam, is able to protect so many people from major floods and considering the Yangtze's long history of major floods and the continued criticism that its government has downplayed the number of fatalities, yet still released the figures suggesting thousands have died in single floods events, then the dam surely justifies itself. I really do see flood defense as being a particularly important benefit. We often hear in regard to criticisms of the dam, about lost cultural heritage and displaced people. I don't wish to suggest that these factors are not important but the 10 million people protected from flooding often gets neglected. There is a really good link to a summary of the costs and benefits below, but the important role that you have in writing about these factors is to assess their relative importance against eachother. For me the 10 million people and 10% (greenhouse free) energy are both really difficult to top. For a full summary of the costs and benefits of the 3-Gorges Dam by Jeffrey Hays can be read on the following webpage Other Multi-Purpose Dam Projects In reality, similar to the case that I have just made for 3-Gorges, a full costbenefit assessment seems to be rarely carried our for multi-purpose dams. This is because dams tend be part of larger political-economic strategy. For example, In India there are are over 4300 large dams but only 27,000 MW of electricity is harnessed out of 150,000 MW potential. It is estimated that between 30 and 40 million people have displaced. The political driver fo these dam is energy. With energy demand growing at 5.2% annually, the government aims to triple the country s power generation in the next two

4 decade. This includes the Narmada Valley Development Project in Western India. This project is a chain of 3200 dams, including 30 large dams, which completely dams the Narmada River and its tributaries across three states. In addition, India is in the planning phase of an MW dam on the Upper Siang in North East India. There appears to be a distinct laissez-faire approach to the planning, construction and evaluation of large scale dams. Arundhatii Roy commented on on the subject, "...the Government has not commissioned a post project evaluation of a single one of its 3,600 dams to gauge whether or not it has achieved what it set out to achieve, whether or not the (always phenomenal) costs were justified, or even what the costs actually were... Isn't this astounding? How can you measure progress if you don't know what it costs and who has paid for it?". It seems quite clear from Roy's perspective that India are following a development strategy that prioritises almost blindly, the economic-energy needs of the country over any social and environmental concerns of dam construction; externalites as economists like to call them. Lets remember, million people displaced from 4300 dams simply dwarfs the 1.4 million displaced from 3-Gorges. There is a clear divide at the global scale, in regard to large-scale dam construction. Worldwide, developed countries seem to have mostly stopped building dams, whilst developing countries seem to be persuing megaprojects. In the past, this has been encouraged by the World Bank as a genuine development strategy but in the last decade or so it has been heavily criticised. Dam construction appears to have served to further indebt developing countries for little gain. At the same developed countries and their corporation have profiteered; all of this alongside the massive social and environmental consequences of dam construction. To investigate this controversy in 1998, the World Bank and World Conservation Commission chartered an expert panel, the World Commission on Dams to review the global controversy over large dams and make recommendations. They concluded, "dams have made an important and significant contribution to human development, and benefits derived from them have been considerable... in too many cases an unacceptable and often unnecessary price has been paid to secure those benefits, especially in social and environmental terms, by people displaced, by communities downstream, by taxpayers and by the natural environment." This is perfectly illustrated in the case of the Akosombo dam in Ghana. The construction of the Akosombo dam resulted in the flooding of part of the Volta River Basin and its upstream fields, and in the creation of Lake Volta which covers 3.6% of Ghana's total land area. The Akosombo dam and Lake Volta was built between the years of 1961 and 1966, and necessitated the relocation of about 80,000 people, that represented 1% of the population. People of 700 villages were relocated into 52 resettlement villages two years prior to the lake's completion; the resettlement program was under the direction of the VRA.Two percent of the resettlement population were riparian fishers and most were subsistence farmers. The project was hailed as largest single development investment in Ghana. The dam provides electricity to Ghana and its neighboring West African countries, including Togo and Benin. Initially 20% of Akosombo Dam's electric output (serving 70% of national

5 demand) was provided to Ghanaians in the form of electricity, the remaining 80% was generated for the American-owned Volta Aluminium Company (VALCO). The Ghana Government was compelled, by contract, to pay for over 50% of the cost of Akosombo s construction, but the country was allowed only 20% of the power generated. Some commentators are concerned that this is an example of neo-colonilaism. The dam's development was undertaken by the Ghanaian government and funded 25% by the World Bank and bilaterally by the US and the UK. It is no understatement to say that Ghana has benefitted from the construction of the Akosombo Dam. Since the dam was commissioned the country has seen the supply of electricity to many towns and villages through the national grid and the percentage of electricity now going to Ghana is increasing over time. In addition, electricity was supplied to neighbouring Togo and Benin, which brought in foreign currency. The dam was seen as a vital component for the industrialisation of Ghan. However, much of the negotiated industrialisation failed to arise, including the promised use of Ghana Bauxite by VALCO. It is therefore difficult to ignore the neo-colonialism comment. The UK, US and the World Bank negotiated terms that at best can be described as inbalanced but at worst exploitive.through their part funding of the project, the US secured 80% of the electricity for VALCO and the UK secured the engineering contract, which in effect, returned their loan directly back into the UK economy. There is a very good article on Akosombo here In evaluating the costs and benefits of the multi-purpose dams we should look no further than the recommendations of the Worl Commission. They suggest that Dams require: demonstrable acceptance of affected people, based on free, prior, and informed consent project planning should include a comprehensive assessment of needs and development options that top priority should be maximizing efficiency of existing water and energy systems stronger mechanisms for compensation and ecological restoration