Assignment Dams....docx

ASSIGNMENT

SUBMITTED BY: Zain-ul-Abedeen

REGD.NO: 196A-315005

PROGRAM: BS-Technology

SPECIALIZATION: Electrical

PROJECT: Dams

PRESTON UNIVERSITY

DAMS

Definition: A dam is a barrier that stops or restricts the flow of water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aquaculture, and navigability.

Hydropower is often used in conjunction with dams to generate electricity. A dam can also be used to collect water or for storage of water which can be evenly distributed between locations. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates are used to manage or prevent water flow into specific land regions. The earliest known dam is the Jawa dam in

Jordan, dating to 3,000 BC. The word dam can be traced back to Middle English and before that, from Middle Dutch as seen in the names of many old cities. The first known appearance of dam occurs in 1165. However, there is one village Obdam that is already mentioned in 1120. The word seems to be related to the Greek word taphos, meaning "grave" or "grave hill". So the word should be understood as "dike from dug out earth". The names of more than 40 places (with minor changes) from the Middle Dutch era (1150–1500 CE) such as Amsterdam and Rotterdam also bear testimony to the use of the word in Middle Dutch at that time. Different parts & terminologies of Dams:  Crest: Top of the Dam. These may in some cases be used for providing a roadway or walkway over the dam.  Parapet Walls: Low Protective walls on either side of the roadway or walkway on the crest.  Heel: Portion of Dam in contact with ground or river-bed at upstream side.  Toe: Portion of dam in contact with ground or river-bed at downstream side.  Spillway: It is the arrangement made (kind of passage) near the top of dam for the passage of surplus/ excessive water from the reservoir.  Abutments:

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The valley slopes on either side of the dam wall to which the left & right end of dam are fixed to. Gallery: Level or gently sloping tunnel like passage (small room like space) at transverse or longitudinal within the dam with drain on floor for seepage water. These are generally provided for having space for drilling grout holes and drainage holes. These may also be used to accommodate the instrumentation for studying the performance of dam. Sluice Way: Opening in the dam near the base, provided to clear the silt accumulation in the reservoir. Free Board: The space between the highest level of water in the reservoir and the top of the dam. Dead Storage Level: Level of permanent storage below which the water will not be withdrawn. Diversion Tunnel: Tunnel constructed to divert or change the direction of water to bypass the dam construction site. The dam is built while the river flows through the diversion tunnel.

Demonstration of different parts of dams through diagram:

Types of Dams: Dams are based on:  Functions  Structure and design Based on functions:  Storage Dams: They are constructed to store water during the rainy season when there is a large flow in the river. Many small dams impound the spring runoff for later use in dry summers. Storage dams may also provide a water supply, or improved habitat for fish and wildlife. They may store water for hydroelectric power

generation, irrigation or for a flood control project. Storage dams are the most common type of dams and in general the dam means a storage dam unless qualified otherwise.  Diversion Dams: A diversion dam is constructed for the purpose of diverting water of the river into an off-taking canal (or a conduit). They provide sufficient pressure for pushing water into ditches, canals, or other conveyance systems. Such shorter dams are used for irrigation, and for diversion from a stream to a distant storage reservoir. A diversion dam is usually of low height and has a small storage reservoir on its upstream. The diversion dam is a sort of storage weir which also diverts water and has a small storage. Sometimes, the terms weirs and diversion dams are used synonymously.

 Detension Dams: Detention dams are constructed for flood control. A detention dam retards the flow in the river on its downstream during floods by storing some flood water. Thus the effect of sudden floods is reduced to some extent. The water retained in the reservoir is later released gradually at a controlled rate according to the carrying capacity of the channel downstream of the detention

dam. Thus the area downstream of the dam is protected against flood.

 Debris Dams: A debris dam is constructed to retain debris such as sand, gravel, and drift wood flowing in the river with water. The water after passing over a debris dam is relatively clear.  Coffer Dams: It is an enclosure constructed around the construction site to exclude water so that the construction can be done in dry. A coffer dam is thus a temporary dam constructed for facilitating construction. A coffer dam is usually constructed on the upstream of the main dam to divert water into a diversion tunnel (or channel) during the construction of the dam. When the flow in the river during construction of the dam is not much, the site is usually enclosed by the coffer dam and pumped dry. Sometimes a coffer dam on the downstream of the dam is also required.

Based on Structure and Design:  Gravity Dams: A gravity dam is a massive sized dam fabricated from concrete or stone masonry. They are designed to hold back large volumes of water. By using concrete, the weight of the dam is actually able to resist the horizontal thrust of water pushing against it. This is why it is called a gravity dam. Gravity essentially holds the dam down to the ground, stopping water from toppling it over. Gravity dams are well suited for blocking rivers in wide valleys or narrow gorge ways. Since gravity dams must rely on their own weight to hold back water, it is necessary that they are built on a solid foundation of bedrock. Example: Grand Coulee Dam (USA),Nagarjuna Sagar Dam (India) and Itaipu Dam ( Between Brazil and Paraguay).

 Earth Dams: An earth dam is made of earth (or soil) built up by compacting successive layers of earth, using the most impervious materials to form a core and placing more permeable substances on the upstream and downstream sides. A facing of crushed stone prevents erosion by wind or rain, and an ample spillway, usually of concrete, protects against catastrophic washout should the water overtop the dam. Earth dam resists the forces exerted upon it mainly due to shear strength of the soil. Although the weight of the earth dam also helps in resisting the forces, the structural behavior of an earth dam is entirely different from that of a gravity dam. The earth dams are usually built in wide valleys having flat slopes at flanks (abutments).The foundation requirements are less stringent than those of gravity dams, and hence they can be built at the sites where the foundations are less strong. They can be built on all types of foundations. However, the height of the dam will depend upon the strength of the foundation material. Example: Rongunsky dam (Russia) and New Cornelia Dam (USA).

 Rock fill Dams: A rock fill dam is built of rock fragments and boulders of large size. An impervious membrane is placed on the rock fill on the upstream side to reduce the seepage through the dam. The membrane is usually made of cement concrete or asphaltic concrete. In early rock fill dams, steel and timber membrane were also used, but now they are obsolete. A dry rubble cushion is placed between the rock fill and the membrane for the distribution of water load and for providing a support to the membrane. Sometimes, the rock fill dams have an impervious earth core in the middle to check the seepage instead of an impervious upstream membrane. The earth core is placed against a dumped rock fill. It is necessary to provide adequate filters between the earth core and the rock fill on the upstream and downstream sides of the core so that the soil particles are not carried by water and piping does not occur. The side slopes of rock fill are usually kept equal to the angle of repose of rock, which is usually taken as 1.4:1 (or 1.3:1). Rock fill dams require foundation stronger than those for earth dams.

Example: Mica Dam (Canada) and Chicoasen Dam (Mexico).

 Arch Dams: An arch dam is curved in plan, with its convexity towards the upstream side. An arch dam transfers the water pressure and other forces mainly to the abutments by arch action. An arch dam is quite suitable for narrow canyons with strong flanks which are capable of resisting the thrust produced by the arch action. The section of an arch dam is approximately triangular like a gravity dam but the section is comparatively thinner. The arch dam may have a single curvature or double curvature in the vertical plane. Generally, the arch dams of double curvature are more economical and are used in practice. Example: Hoover Dam (USA) and Idukki Dam (India).

 Buttress Dam: Buttress dams are of three types. i. Deck type. ii. Multiple-arch type. iii. Massive-head type. A deck type buttress dam consists of a sloping deck supported by buttresses. Buttresses are triangular concrete walls which transmit the water pressure from the deck slab to the foundation. Buttresses are compression members. Buttresses are typically spaced across the dam site every 6 to 30 meter, depending upon the size and design of the dam. Buttress dams are sometimes called hollow dams because the buttresses do not form a solid wall stretching across a river valley. The deck is usually a reinforced concrete slab supported between the buttresses, which are usually equally spaced. In a multiple-arch type buttress dam the deck slab is replaced by horizontal arches supported by buttresses. The arches are usually of small span and made of concrete. In a massive-head type buttress dam, there is no deck slab. Instead of the deck, the upstream edges of the buttresses are flared to form massive heads which span the distance between the buttresses. The buttress dams require less concrete than gravity dams. But they are not necessarily cheaper than the gravity dams because of extra cost of form work, reinforcement and more skilled labor. The foundation requirements of a buttress dam are usually less stringent than those in a gravity dam. Example: Bartlett dam (USA) and The Daniel-Johnson Dam (Canada).

 Steel Dams: A steel dam consists of a steel framework, with a steel skin plate on its upstream face. Steel dams are generally of two types. i. Direct-strutted steel dams. ii. Cantilever type steel dams. In a direct strutted steel dam, the water pressure is transmitted directly to the foundation through inclined struts. In a cantilever type steel dam, there is a bent supporting the upper part of the deck, which is formed into a cantilever truss. This arrangement introduces a tensile force in the deck girder which can be taken care of by anchoring it into the foundation at the upstream toe. Hovey suggested that tension at the upstream toe may be reduced by flattening the slopes of the lower struts in the bent. However, it would require heavier sections for struts. Another alternative to reduce tension is to frame together the entire bent rigidly so that the moment due to the weight of the water on the lower part of the deck is utilized to offset the moment induced in the cantilever. This arrangement would, however, require bracing and this will increase the cost. These are quite costly and are subjected to corrosion. These dams are almost obsolete. Steel dams are sometimes used as temporary coffer dams during the construction of the permanent dams. Steel coffer dams are supplemented with timber or earth fill on the inner side to make them water tight. The area between

the coffer dams is dewatered so that the construction may be done in dry for the permanent dam. Example: Red ridge Steel Dam (USA) and Ash fork-Bainbridge Steel Dam (USA).

 Timber Dams: Main load-carrying structural elements of timber dam are made of wood, primarily coniferous varieties such as pine and fir. Timber dams are made for small heads (2-4 m or, rarely, 4-8 m) and usually have sluices; according to the design of the apron they are divided into pile, crib, pile-crib, and buttressed dams. The openings of timber dams are restricted by abutments; where the sluice is very long it is divided into several openings by intermediate supports: piers, buttresses, and posts. The openings are covered by wooden shields, usually several in a row one above the other. Simple hoists permanent or mobile winches are used to raise and lower the shields.

Location for building Dams: One of the best places for building a dam is a narrow part of a deep river valley; the valley sides then can act as natural walls. The primary function of the dam's structure is to fill the gap in the natural reservoir line left by the stream channel. The sites are usually those where the gap becomes a minimum for the required storage capacity. The most economical arrangement is often a composite structure such as a masonry dam flanked by earth embankments. The current use of the land to be flooded should be dispensable. Significant other engineering and engineering geology considerations when building a dam include:     

Permeability of the surrounding rock or soil. Earthquake faults. Landslides and slope stability. Water Table. Peak flood flows.

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Reservoir silting. Environmental impacts on river fisheries, forests and wildlife. Impacts on human habitation. Compensation for land being flooded as well as population resettlement.  Removal of toxic materials and buildings from the proposed reservoir area. Dams in Pakistan:  Terbela Dam: First biggest dam in the list is Terbela Dam that’s situated on the Indus River and is also the largest earth filled dam in the world and is the 2nd largest by the structural volume. The dam is 148 meter high above riverbed. Development started in 1968 and completed in 1976 at cost of $1,497 million. Total capacity of the dam is 13.69 cubic kms spread over the construction area of 168,000 km2.

 Mangla Dam: Next biggest dam in Pakistan is Mangla Dam that’s built in the Jhelum River in the Mirpur District of Azad Kashmir, Pakistan. It’s also the Ninth largest dam in the world. The development was started in 1961 and completed in 1967. It was constructed at the cost of $1.473 billion and also funded by the World Bank and Asian Development Bank.

 Mirani Dam: Mirani Dam is yet another major dam in Pakistan. It is a medium-sized multi-purpose dam that’s situated on the Dasht River in Baluchistan. In terms of volume for flood protection it’s the largest dam in the world having flood stock of 588,690 cubic hectometer. Its development was began on July 8, 2002 and completed on October 2006.

 Warsak Dam: Warsak Dam is a mass concrete gravity dam and located on the Kabul River north west of the Peshawar city in Khyber Pakhtunkhwa. It was completed in 2 phases. 1st phase was completed in 1960 and the 2nd phase was finished in 1980-81. Total capacity of the Warsak Dam Hydropower Project us 243 MW.

 Sabakzai Dam: Sabakzai Dam is an embankment dam at Zohb River in Baluchistan. The building of the dam started in 2004 and the irrigation works for the dam are still being built. Based on ICOLD, Sabakzai Dam is the seventh largest in the world with a flood stock of 23,638 cubic hectometer.

Pros of Dams: Dams provide a range of economic, environmental, and social benefits, including recreation, flood control, water supply, hydroelectric power, waste management, river navigation, and wildlife habitat.

 Recreation: Dams provide prime recreational facilities throughout the United States. Boating, skiing, camping, picnic areas and boat launch facilities are all supported by dams.  Flood Control: In addition to helping farmers, dams help prevent the loss of life and property caused by flooding. Flood control dams impound floodwaters and then either release them under control to the river below the dam or store or divert the water for other uses. For centuries, people have built dams to help control devastating floods.  Water Storage: Dams create reservoirs throughout the United States that supply water for many uses, including industrial, municipal, and agricultural.  Irrigation: Ten percent of American cropland is irrigated using water stored behind dams. Thousands of jobs are tied to producing crops grown with irrigated water.  Mine Tailings: There are more than 1,300 mine tailings impoundments in the United States that allow the mining and processing of coal and other vital minerals while protecting the environment.  Electrical Generation: The United States is one of the largest producers of hydropower in the world, second only to Canada. Dams produce over 103,800 megawatts of renewable electricity and meet 8 to 12 percent of the Nation's power needs. Hydropower is considered clean because it does not contribute to global warming, air pollution, acid rain, or ozone depletion.

 Debris Control: In some instances, dams provide enhanced environmental protection, such as the retention of hazardous materials and detrimental sedimentation.  Navigation: Dams and locks provide for a stable system of inland river transportation throughout the heartland of the Nation. Cones of Dams:  Risk of sediment buildup: When water rushes through a dam and its internal turbines, it can create a great spot for sediment layers to be trapped and congregate, which then can pollute the water and disrupt the ecology of the water environment.  Damaging to Environment: Rushing floodwaters replenish the nutrients in the soil in water, which is beneficial to all plant and animal life in rivers and other waterways. When water is diverted due to a dam, it can greatly disrupt the delicate natural ecosystem. Some flora and fauna are able to adapt to the changing conditions, but many will not, and could be destroyed in the new environment. After the Aswan High Dam in Egypt was built, scientists noticed a marked decline in fish production around the area, as the amount of nutrients and food was now less than before the dam. Fish ladders have been build at some dams to help fish migrate, but some are not able to use the ladder properly, especially if they are used to fast-moving water.  Erosion of surrounding soil: After the construction of many dams, erosion of the surrounding land has been noticed. The large reservoir at China’s Three Gorges Dam has eroded nearby shoreline, which has led to

landslides along the side of the reservoir. The Nile Delta has experienced erosion due to the reduction of sediment after the construction of the Aswan High Dam. Much of the sediment has fallen into the reservoir, which means there is less land around to farm and work on.  High cost and risk for Disaster: The cost of building a dam often reaches astronomical levels. The engineering and technical aspects, along with the actual construction, are a time intensive and laborious process that has to be done with absolute precision. China’s Three Gorges Dam was built in an area with seismic activity, and small cracks have already been found in the infrastructure. A dam collapse or break would be an absolute catastrophe, especially from one the size of the Three Gorges Dam. After Hurricane Harvey hit Texas, dams in the Houston area were pushed to their limit by massive floodwaters. According to the Texas Observer, worries are that water could overflow from some of the dam’s spillways, and not be controlled. If a dam were to be removed, rivers and other waterways would most likely try to reclaim its old channel, which means that expensive river training structures, like bank protection and bend way weirs, would have to be deployed in order to keep the river on a certain path. This is often hard to do and relies on the accuracy of hydraulic modeling studies and other advanced analytics. It can be hard to imagine what civilization would be like without the presence of dams to control waterways and build reservoirs of water. Even though dams are a major part of modern infrastructure, their positives and negatives on society and the environment are still being studied.

How important it is for Pakistan to build Dams? This week Water and Power Development Authority (WAPDA) in Pakistan announced that water capacity of the Tarbela Dam, one of Pakistan’s most important dams, has fallen by 30%. WAPDA warned the Senate in Islamabad on Wednesday that while water consumption is increasing in Pakistan, the country’s ability to store water is decreasing, urging leaders to build more dams in Pakistan. Activists and concerned citizens in Pakistan have taken to social media to ask if it’s time for Pakistan to build dams. Why is it important for Pakistan to build Dams? More than 80 percent of water in Pakistan is considered unsafe. Meanwhile, in 2017, the Pakistan Council of Research in Water Resources (PCRWR) announced that Pakistan would run out of water by 2025. According to water aid, Pakistan is one of the 36 most water-stressed countries in the world. Pakistan is also in the top 10 of countries with the most people living without clean drinking water. Currently, 16 million people in Pakistan have no other option than collecting unsafe water for drinking and cleaning, leading to massive amounts of waterborne disease. Available water per capita has dropped from 5,600 to 903 cubic meters, as of 2016. At the current levels of consumption, this number is expected to drop to 500 cubic meters per person in the coming years. With 60% of Pakistan’s population directly involved in the agricultural sphere, up to 95% of Pakistan’s water is used in agriculture. However, it it estimated that 50% of the water directed towards agricultural purposes is lost, due to defects in irrigation systems, including misuse, defective canals, and leaking pipes. While water supply and storage are

shrinking, Pakistan’s population is rapidly growing, placing greater stress on the already taxed water system. Experts believe Pakistan’s existing water policy and systems will be unable to sustain the current levels of growth. Since so many of Pakistan’s citizens rely on agriculture for gainful activity, water scarcity in Pakistan would spell economic disaster and famine. A water crisis could even become an issue of national security, since trans boundary water resources have historically been a significant source of tension with nuclear rival India. The Hisaar Foundation, in partnership with the Asia Foundation, has made a series of five recommendation for improving water safety and security in Pakistan. According to the Asia Foundation, those five priorities are: “improving access to water for the poor and landless; financing the urban and rural water value chain; safeguarding the Indus Basin and its infrastructure; improving water institutions and their management and governance; and building a base for science, technology, and social aspects of water.” The Asia Foundation also recommends providing financial incentives for smarter water usage in agricultural production. They recommend the government should use a series of tariffs, taxes, and price incentives to encourage farmers to produce crops which require less water. Pakistan’s most highly produced crops are wheat, rice, cotton, and sugarcane. Although these are agricultural staples, they are also the most water intensive crops on the planet. These crops are hardly drought resistance, so if Pakistan did experience water scarcity, it would could an economic and humanitarian disaster. The Asia Foundation has also made economic arguments for greater water security and conservation to encourage authorities in Pakistan to build dams. Since agriculture makes up for about 20% of Pakistan’s GDP, while consuming the vast majority of Pakistan’s water resources, better management of water could have a huge impact on GDP. The

Asia Foundation estimates that better water management and policy could increase Pakistan’s agricultural GDP from the current $50 billion to $200 billion, annually. In addition to water scarcity, as well as waterborne disease, Pakistan has also experienced an energy crisis. Despite the powerful Indus River system, Pakistan has barely scratched the surface of hydro energy. It has been estimated that the Indus River system could produce 59,000 megawatts of energy a year. The water situation may also be impacting the education system, which would eventually have a negative outcome on development and the economy. One in three schools in unable to provide students with clean drinking water, which prevents students from concentrating and also spreads water-borne diseases that prevent children from being able to attend school. Water-borne diseases, in and of themselves, are delivering a blow to Pakistan’s economy. It has been estimated that water-borne diseases cost Pakistan $1.3 billion each year. 80% of disease in Pakistan is caused by unsafe water, accounting for 40% of deaths. Water-borne diseases include typhoid, tuberculosis, hepatitis, and intestinal parasites. Pakistan to build Dams? Attempts to build dams in Pakistan have been riddled with land conflict, political disagreements, and international disputes with India. Since it has become clear that water stress is a major issue in Pakistan, efforts have been made for Pakistan to build dams. In recent months, WAPDA has been attempting to build the Diamer-Bhasha Dam. The dam lies between the two provinces Khyber-Pakhtunkhwa (KPK) and Gilgit-Baltistan (GB) which has led to conflict and land disputes. Those who claim to hold ownership over the contested land have even

become violent. Each time dam construction commences locals’ fire on workers. So far, 12 have been killed at the construction site. China had originally planned on building the Diamer-Bhasha Dam as part of the China-Pakistan Economic Corridor. However, Pakistan rejected the deal last November. Islamabad claimed China’s conditions for the deal were “too strict.” Pakistan announced they would instead be carrying out the planned dam project. Pakistan’s Supreme Court agreed to hear cases on the water shortage in Pakistan, beginning June 7. The hearings will particularly focus on the proposed Kalabagh Dam on the Indus River. The dam could increase Pakistan’s dismal water storage capacity while providing 3,600 megawatts of electricity. In the past, Pakistan’s political parties have been unable to reach an agreement on the dam, a hurdle activists hope the Supreme Court will be able to overcome.