DAM ENGINEERING, ITS PRACTICE AND POTENTIAL IN PAKISTAN By Amjad Agha1 ABSTRACT Most rivers in the World have seasonal flow pattern. There is more water in these rivers during rainy or snow melting season. In other parts of the year the flow in the rivers reduces and sometime becomes very small. The crop water requirement is however also important in low river flow season. Therefore the need to store water in the water surplus months to be used in the water deficient period has led to construction of dams and reservoirs. Another important use of the dams is the production of hydroelectric energy. The head of water created by the dam is used for creating water falls which run the turbines and generate electric power. The importance of creating reservoirs is becoming more critical, because the availability of water per capita is constantly decreasing due to increasing population and it is extremely important that the seasonal surplus water is stored, instead of letting it go to the sea. With global warming in the horizon, the river flows are likely to be more erratic and unpredictable, therefore, the need for storages would become even more important in the future. For all the above reasons the need of dams and storages in Pakistan is highly critical for its economy and sustainable agriculture. In this Paper, History of Dams, Modern trends in the Dam Engineering, and the experience in the modern dam engineering in Pakistan will be discussed. The Pakistani engineers are waiting to apply their knowledge & experience in the future large Dams needed in the Country. The hurdles in this respect and their remedies are also briefly discussed. 1. HISTORY OF DAMS The river basins are renowned as cradles of civilization and cultural heritage. The earliest evidence of river engineering is ruins of irrigation canals over eight thousand years old in Mesopotamia. Remains of water storage dams found in Jordan, Egypt, Yemen and other parts of Middle East date back to 3000 BC. The primary objective of serving as water storages, but also for controlling floods and allowing or improving navigation. With the advent of industrial revolution and technology for generating power from water movement, humans started to construct large dams to obtain energy. The first dams to incorporate an electric power station were built at the end of nineteenth century in Western Europe and the United States. During the middle of twentieth century there was great impetus in dam building which continued till 1980. The boom in dam construction came with start of 21st century, particularly in China. The construction of large dams by decades and worldwide regional distribution of large dams is shown in chart as follows: 6000 pdfMachine5000 trial version 4000 s m a d f o r 3000 e b m u N 2000 1000 0 Before 1900s 1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s after 1990 1900 Construction of World Dams by Decade (1900-2000) _____________________________________________________________________________________________ 1. President Associated Consulting Engineers – ACE (Pvt) Ltd. President Pakistan Geotechnical Engineering Society. 20 25,000 20,000 s m 15,000 a d f o r e b m u 10,000 N 5,000 0 China Asia North and Western Africa Eastern South Austral Asia Central Europe Europe America America Regional distribution of world large dams at the end of the 20th century In all about 800,000 dams have been built worldwide out of which about 50,000 are large (higher than 15 meter). These dams generate altogether about 19% of the world’s electricity and supplying water for 30 – 40% of the irrigated crop lands. The dams and diversion system (barrages and canals) are thus meeting 35 percent of world cereal requirements. Until recently large dams were considered a milestone on the development plans of nation and they were often viewed as a symbol of modernity and economic progress. However effects derived from their building on the environment and the society did somewhat changed this vision. As a consequence some developed countries such as France and United States have interrupted dam construction and even started some demolition. Since the primary effect of dams is modifying river flow, this can result in several changes on natural habitats. Social consequences are linked with forced human resettlement. These effects were significant, but were highly publicized and a great anti-large-dam lobby was created. The result was that funding agencies almost totally stopped providing funds for large dam construction to the developing countries. The developing countries needed the dams since they were vital for the agriculture sustainability and for cheaper electric power. Therefore the environment effect mitigation and resettlement issues have now become a part of the planning of such projects. Better ways of resettlement and land acquisition are being adopted. Out of area resettlement is avoided as far as possible, land and dwelling compensation is becoming generous. Similarly mitigation of environment effects on the infrastructure and aquatic life are given due attention. With this change of attitude the World Bank etc. are coming back to funding the large dams. Recently completed (2004) Ghazi Barotha Hydroelectric Project in Pakistan (1450 MW) is being sited as a “good illustration of the usefulness of dams and water resource st projects in the 21 century” (HRW Dec. 2005) primarily because particular attention was paid to minimize environmental and social effects. Now once again large scale dam construction is taking place. According to ICOLD information at present some 1700 large dams are under construction. The dpdfMachineistribution of water runoff ( rtrialiver and sversiontream flow) is very uneven from the point of view of continents. Asia which supports 60 percent of global population has only 36 percent of runoff, while South America with 6 percent population receives 26 percent of world runoff. Higher temperature prevailing in major parts of Asia and Africa and highly skewed rainfall, places Asia and Africa at a tremendous disadvantage due to greater evapotranspiration losses. In Asia with the high population growth, it is vital that water resource is harnessed and preserved as building of new dams and reservoirs is absolutely essential to sustain the cereal needed for its growing population. 2. MODERN TRENDS IN DAM ENGINEERING The knowledge of Geotechnical Engineering plays a very important role in the Dam Engineering. The advancement in this specialty particularly with respect to computer-aided 21 analysis tools and the quantum jump in Seismo-tectonic approach have brought important changes in the State of the Art of Dam Engineering in the modern times and the confidence level on design is substantially improved. In this context the approach to seismic-resistant design of dams have been completely modified and requires proper understanding. The availability of fast running finite element computer modules and various non-linear models for concrete and particulate materials have allowed simulation of deformation behaviour of dam body and foundation under seismic loadings. Consequently, confident decisions are now made with respect to seismic design of dam structures. Development of automated and remote performance monitoring instrumentation systems have enabled to understand the behaviour of dam in terms of pore water pressures and deformations during events of short-lived incidents of seismic shaking and passing of flash floods. The use of satellite images and GIS maps have enhanced the hydrological analysis and evaluation of reasonable and accurate assessment of design floods and risks associated with them. In Pakistan, we have had good experience in using these modern concepts while designing projects like Kalabagh Dam, Basha Dam and Ghazi Barotha Project. 3. WATER STORAGES AND DAMS IN PAKISTAN Pakistan has three big rivers i.e. Indus, Chenab and Jehlum and these and other rivers generate of 145 Million Acre feet (MAF), or 179 billion cubic meters of total flow. In 1950s per capita availability of water per year was about 5000 cubic meter, at that time Pakistan was water affluent country. However with the passage of time our population kept increasing, which is now reaching about 170 million, and the per capita annual availability of water has come down to only 1000 cubic meter. It is well known that countries with less than 1000 cubic water of per capita are water deficient countries and we have reached that level; situation will further deteriorate as the population growth is continuing. There is another serious problem of water availability in Pakistan and that is due to two distinct water flow seasons, i.e. Kharif and Rabi season. In Kharif season about 83% of the flows occur, while in Rabi season bring only 17% of annual flows. The crop water requirements are however 60% in the Kharif season and 40% in Rabi. There is thus a great disparity between the water availability and requirement in the Rabi season. For getting optimum production from the crops it is essential that water is available when it is needed. In view of shortage of water in the Rabi season, it is not possible to have the required water available at the required time. In Punjab the farmers who can afford tubewells can obtain the water at critical times through the groundwater, but in most of Sind where groundwater is saline, the situation of water availability in Rabi season is worse. The direct effect of the disparity is in our cereal production which is very poor as compared to the rest of the world. The cereal production in Pakistan is only 0.13 kg/cubic meter of irrigation water. In China it is 0.8 kg, in USA it is 1.66 kg and in India 0.39kg of cereal is produced with the same quantity of water. Obviously if water can be made available on time our cereal production can considerably improve.