Dams and the UK
A dam is a man made barrier usually built across a river to hold back water and it forms a lake, or reservoir, behind it. It can be constructed from concrete or natural materials like earth and rock.
Types of Dams
The type of dam implemented depends upon the topography , the geology and hydrology of the area and also the foundation conditions and most importantly in developing countries the availability of construction materials, as developing countries would not have the funding for expensive construction project even if the results resulted in economic growth which is another advantage of multi-purpose. Yet many dams have been built in the UK and this explores the type of dam most beneficial to the UK.
Buttress dams: depend for support on a series of vertical supports called buttresses. The buttresses run along the side facing away from the water's flow also known as the dam's downstream face . The downstream face of a buttress dam usually slopes outward at about a 45-degree angle. The sloping face and the buttresses transfer the force of the water downwards to the dam's foundation. Since 1945, 14 buttress dams have been constructed in the UK [2], mainly for hydroelectric schemes in Scotland. As buttress dams depend on slopes of a 45 degree angle this dam could not be implemented in the flat areas of the UK and would only be most effective in Scotland and therefore butress dams are not the most benefical dam for the UK and would be best in more mountain/hilly countries.
Gravity dams: depend entirely on their own weight to resist the force of the stored water. Some early gravity dams have been constructed with masonry blocks and concrete and are known as masonry dams. Today gravity dams are constructed by mass concrete or roller-compacted concrete (concrete placed in layers and compacted by a roller) and are referred to as concrete gravity dams. 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 which may not be possible in all areas due to their geology.There are more than 250 gravity dams in Britain [2]. Masonry was used in many early dams, as far back as the 17th Century. However, concrete became more common from about 1900.
Arch dams: are concrete dams that curve upstream towards the flow of water. Most are built in narrow canyons with strong flanks which are capable of resisting the thrust produced by the arch action. As the water pushes against the dam, the arch transfers the water's force to the canyon wall. Arch dams require much less concrete than gravity dams of the same length. They also require a solid rock foundation to support the weight of the dam. There are only a few arch dams in the UK, including Monar Dam in Scotland. Very few dams have been built due to the specific geology needed and the lack of narrow canyons and strong supporting sides and bases make arch dams unsuitable in most places in the UK, however, parts of America would greatly benefit from arch dams due to the differing geology in the area.
Embankment dams: are constructed of either earth fill or a combination of earth and rock fill. Engineers generally choose to build embankment dams in areas where large amounts of earth or rocks are available. Embankment dams represent about 75% of all of the dams in the world [1]. Earth embankment dams are the most common type since they accommodate all the material from required excavation which saves money which could be a major factor for economically developing countries. The earth dams are usually built in wide valleys having flat slopes at flanks. Also embankment dams can be built where the foundations are less strong and therefore can be suitable in more locations compared to buttress dams. The main type of dam in Britain is the embankment dam, and there are over 3000 of them [2]. Some of them date back to the 9th Century, including Fishers Pond Dam, near Winchester, which was built by monks to provide fish. The average age of our embankment dams is over 100 years old [2]. Embankment Dams are the most useful dam for the UK due to cheap construction and the need for flat slopes which is the main UK topography.
Rubber Dams: Use a sophisticated simple and efficient design, this most recent type of dam uses huge cylindrical shells made of special synthetic rubber and inflated by either compressed air or pressurized water. These can be deflated when pressure is released and hence even the crest level can be controlled. Surplus waters would simply overflow the inflated shell. They need extreme care in design and erection and are limited to small projects.
Uses of Dams
Water Supply
Reservoir water can be used to supply water to our homes and factories. Reservoirs are designed to store the rain that falls during the wetter parts of the year, so that there is a continuous supply of water for the drier periods. The water from reservoirs must be cleaned before it is used. This is done at a water treatment works. Chemicals are added to help remove unwanted naturally occurring mineral particles and harmful bacteria. Dirt and other small particles are usually removed by filtering the water through beds of sand and gravel, or by adding chemicals that cause the particles to stick together so that they can be separated off from the water. Once the water is treated, it is transferred to storage reservoir ready for distribution. In the UK, there is a network of tens of thousands of kilometres of underground pipes that carry billions of litres of clean water every day to homes, offices, schools, factories and hospitals.
Flood Control
After severe storms, or heavy snow or rain over a number of days, the water level in rivers can rise dramatically. Sometimes, the water flows over riverbanks or walls causing flooding of farmland, property, and in the worst cases, loss of life. A reservoir can be used to control the amount of water flowing in a river after heavy rain. The water level in the reservoir is kept low during the rainier periods of the year. When heavy rain occurs, it is stopped by the dam and held back in the reservoir. When the reservoir gets too full, the floodwater can be passed downstream over a spillway.
Sometimes, floodgates are used on top of spillways, and they can be fully or partly opened to control the amount of water let out into the river downstream.
Irrigation
Plants will grow naturally on fertile soil that is watered by rain. However, in regions of the world where the climate is very dry for some seasons, the soil becomes so dry that it restricts the growth of vegetation. This problem can be overcome by irrigation, a man-made system for watering the land. Irrigation water can be stored in reservoirs during the rainy season, then in the drier seasons it can be released from the reservoir and distributed over the land through a system of canals. Usually, the water flows under the influence of gravity to the areas requiring it, or the water can be pumped out of the canals onto the land. Even though the UK does not have specific rainy and dry seasons irrigated land is still very important to help farmland production.
Navigation
The construction of a dam across a river forms a reservoir that raises the water level upstream, stores the water, and slows down its rate of flow. This improves the navigation conditions upstream of the dam for ships and boats. Dangerous areas of rocks and sandbanks, previously in shallow water, become well covered, and rapids in the river disappear. Also, water from the reservoir can be released into the river downstream during the drier seasons of the year to make sure that it is deep enough for navigation all the year round. A dam forms a barrier to any shipping, so navigation locks (similar to the canal locks in Britain) can be constructed to one side of the dam, or special lifts can be built into the dam for raising and lowering vessels.
Disadvantages
The construction of the dam itself brings the first problem with the initial costing of constructing and maintaining the dam; dams are extremely expensive and thus not all countries will be able to afford dams in all situations they wish to implement them in and thus countries may need to decide upon another scheme. However, once built the effectiveness of a dam can potentially be decreased. If dirt builds up at the bottom of the dam then the dam itself will be less effective and thus other schemes may be better suited.
Dams must be used in suitable areas as otherwise it can cause wide scale problems for its ecosystem; in Cambodia proposed dams will stop the migration path of migratory fish and it is predicted to cause severe socio-economic problems for people whose livelihoods are dependent upon the Tonle Sap Lake and its fish within. The natural flow of the water through the environment can also be affected which can cause flooding in the river valley and force people to leave their homes and can leave agricultural land unusable which will also affect the socio-economics for its local people.
[1] http://ussdams.com/ussdeducation/BookforY.pdf
[2] http://britishdams.org/about_dams/gravity.htm
Types of Dams
The type of dam implemented depends upon the topography , the geology and hydrology of the area and also the foundation conditions and most importantly in developing countries the availability of construction materials, as developing countries would not have the funding for expensive construction project even if the results resulted in economic growth which is another advantage of multi-purpose. Yet many dams have been built in the UK and this explores the type of dam most beneficial to the UK.
Buttress dams: depend for support on a series of vertical supports called buttresses. The buttresses run along the side facing away from the water's flow also known as the dam's downstream face . The downstream face of a buttress dam usually slopes outward at about a 45-degree angle. The sloping face and the buttresses transfer the force of the water downwards to the dam's foundation. Since 1945, 14 buttress dams have been constructed in the UK [2], mainly for hydroelectric schemes in Scotland. As buttress dams depend on slopes of a 45 degree angle this dam could not be implemented in the flat areas of the UK and would only be most effective in Scotland and therefore butress dams are not the most benefical dam for the UK and would be best in more mountain/hilly countries.
Gravity dams: depend entirely on their own weight to resist the force of the stored water. Some early gravity dams have been constructed with masonry blocks and concrete and are known as masonry dams. Today gravity dams are constructed by mass concrete or roller-compacted concrete (concrete placed in layers and compacted by a roller) and are referred to as concrete gravity dams. 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 which may not be possible in all areas due to their geology.There are more than 250 gravity dams in Britain [2]. Masonry was used in many early dams, as far back as the 17th Century. However, concrete became more common from about 1900.
Arch dams: are concrete dams that curve upstream towards the flow of water. Most are built in narrow canyons with strong flanks which are capable of resisting the thrust produced by the arch action. As the water pushes against the dam, the arch transfers the water's force to the canyon wall. Arch dams require much less concrete than gravity dams of the same length. They also require a solid rock foundation to support the weight of the dam. There are only a few arch dams in the UK, including Monar Dam in Scotland. Very few dams have been built due to the specific geology needed and the lack of narrow canyons and strong supporting sides and bases make arch dams unsuitable in most places in the UK, however, parts of America would greatly benefit from arch dams due to the differing geology in the area.
Embankment dams: are constructed of either earth fill or a combination of earth and rock fill. Engineers generally choose to build embankment dams in areas where large amounts of earth or rocks are available. Embankment dams represent about 75% of all of the dams in the world [1]. Earth embankment dams are the most common type since they accommodate all the material from required excavation which saves money which could be a major factor for economically developing countries. The earth dams are usually built in wide valleys having flat slopes at flanks. Also embankment dams can be built where the foundations are less strong and therefore can be suitable in more locations compared to buttress dams. The main type of dam in Britain is the embankment dam, and there are over 3000 of them [2]. Some of them date back to the 9th Century, including Fishers Pond Dam, near Winchester, which was built by monks to provide fish. The average age of our embankment dams is over 100 years old [2]. Embankment Dams are the most useful dam for the UK due to cheap construction and the need for flat slopes which is the main UK topography.
Rubber Dams: Use a sophisticated simple and efficient design, this most recent type of dam uses huge cylindrical shells made of special synthetic rubber and inflated by either compressed air or pressurized water. These can be deflated when pressure is released and hence even the crest level can be controlled. Surplus waters would simply overflow the inflated shell. They need extreme care in design and erection and are limited to small projects.
Uses of Dams
Water Supply
Reservoir water can be used to supply water to our homes and factories. Reservoirs are designed to store the rain that falls during the wetter parts of the year, so that there is a continuous supply of water for the drier periods. The water from reservoirs must be cleaned before it is used. This is done at a water treatment works. Chemicals are added to help remove unwanted naturally occurring mineral particles and harmful bacteria. Dirt and other small particles are usually removed by filtering the water through beds of sand and gravel, or by adding chemicals that cause the particles to stick together so that they can be separated off from the water. Once the water is treated, it is transferred to storage reservoir ready for distribution. In the UK, there is a network of tens of thousands of kilometres of underground pipes that carry billions of litres of clean water every day to homes, offices, schools, factories and hospitals.
Flood Control
After severe storms, or heavy snow or rain over a number of days, the water level in rivers can rise dramatically. Sometimes, the water flows over riverbanks or walls causing flooding of farmland, property, and in the worst cases, loss of life. A reservoir can be used to control the amount of water flowing in a river after heavy rain. The water level in the reservoir is kept low during the rainier periods of the year. When heavy rain occurs, it is stopped by the dam and held back in the reservoir. When the reservoir gets too full, the floodwater can be passed downstream over a spillway.
Sometimes, floodgates are used on top of spillways, and they can be fully or partly opened to control the amount of water let out into the river downstream.
Irrigation
Plants will grow naturally on fertile soil that is watered by rain. However, in regions of the world where the climate is very dry for some seasons, the soil becomes so dry that it restricts the growth of vegetation. This problem can be overcome by irrigation, a man-made system for watering the land. Irrigation water can be stored in reservoirs during the rainy season, then in the drier seasons it can be released from the reservoir and distributed over the land through a system of canals. Usually, the water flows under the influence of gravity to the areas requiring it, or the water can be pumped out of the canals onto the land. Even though the UK does not have specific rainy and dry seasons irrigated land is still very important to help farmland production.
Navigation
The construction of a dam across a river forms a reservoir that raises the water level upstream, stores the water, and slows down its rate of flow. This improves the navigation conditions upstream of the dam for ships and boats. Dangerous areas of rocks and sandbanks, previously in shallow water, become well covered, and rapids in the river disappear. Also, water from the reservoir can be released into the river downstream during the drier seasons of the year to make sure that it is deep enough for navigation all the year round. A dam forms a barrier to any shipping, so navigation locks (similar to the canal locks in Britain) can be constructed to one side of the dam, or special lifts can be built into the dam for raising and lowering vessels.
Disadvantages
The construction of the dam itself brings the first problem with the initial costing of constructing and maintaining the dam; dams are extremely expensive and thus not all countries will be able to afford dams in all situations they wish to implement them in and thus countries may need to decide upon another scheme. However, once built the effectiveness of a dam can potentially be decreased. If dirt builds up at the bottom of the dam then the dam itself will be less effective and thus other schemes may be better suited.
Dams must be used in suitable areas as otherwise it can cause wide scale problems for its ecosystem; in Cambodia proposed dams will stop the migration path of migratory fish and it is predicted to cause severe socio-economic problems for people whose livelihoods are dependent upon the Tonle Sap Lake and its fish within. The natural flow of the water through the environment can also be affected which can cause flooding in the river valley and force people to leave their homes and can leave agricultural land unusable which will also affect the socio-economics for its local people.
[1] http://ussdams.com/ussdeducation/BookforY.pdf
[2] http://britishdams.org/about_dams/gravity.htm