Extended Diploma Mechanical and Electrical Services Construction Dams and Reservoirs

Extended Diploma – Building Services Aims : - to investigate the use and construction of dams and reservoirs in this country. Objectives : - to describe the different forms of Dams and Reservoirs and understand their construction process. To investigate the environmental and management issues associated with dams and reservoirs

Extended Diploma – Building Services Fresh Water is a very precious resource. Of all the water available on Earth only 3% is fresh water. The remaining 97% is either Seawater or Ice. Of the 3% of Freshwater only 0.1% is contained within Dams and Rivers. The remaining fresh water is contained within the ground. As the population increases, current figures estimate a world population of 6,817,500,000 (6.8billion) as of It is estimated that this figure will grow to 9 billion by We will come under severe pressure to manage our water resources, as the population increases. (Code for sustainable homes) From a Civil Engineering point of view, storing and using water for domestic and industrial use, involves the construction of Dams and reservoirs.

Extended Diploma – Building Services A dam can be defined as ‘a barrier constructed across a waterway to control the flow or raise the level of the water. (The Free Dictionary.com) A reservoir is defined as ‘a natural or artificial pond or lake, used for the storage and regulation of water’. (The Free Dictionary.com) From these definitions we can determine that we construct dams to create a reservoir of water that we can then regulate or manage. We can categorise the use of reservoirs in two ways Primary and Secondary. The Primary use of a reservoir can be classed as Holding water for domestic, agricultural and industrial uses. These can include drinking water, energy supplies in the form of generating electricity. They can supply water for a canal or an irrigation system. They can also hold water, that may otherwise flood a local community, the water is then released slowly and safely, and is known as attenuation. The Secondary uses are holding and farming Fish, leisure activities such as sailing, canoeing, wind surfing etc.

Extended Diploma – Building Services In Civil Engineering terms, we refer to any structure that has the ability to divert, restrict, stop or manage the natural flow of water as a Hydraulic Structure. Therefore a Dam is also described as a Hydraulic Structure. In creating a reservoir there are also other elements that need to be considered. Firstly there has to be a source of natural running water, rivers or mountain streams etc. required for feeding the reservoir. Secondly a large hollow expanse is required, allowing us to collect the water. The hollows can be naturally forming or man made, (Known as cisterns) but it is essential to look at the topography of a potential site. Other important elements would be the accessibility to the hydraulic structure, getting materials to and from the site. The volume of water that can be retained by the structure. Is the reservoir sited at a level that avoids the pumping of water, I.E. is it at a higher level.

Extended Diploma – Building Services We can then look at the ways Dams are constructed and then classify them into five main types. Earth or Embankment Dams Gravity Dams Arch Dams Buttress Dams MultiArch Dams However the Geology and Topography will determine the type of dam to be constructed.

Extended Diploma – Building Services Earth or Embankment Dams Constructed from loose rock, Soil, and an Impermeable material situated within the core of the Dam. The Actual slope of the Dam structure is constructed to resemble the natural slopes of its environment, helping to lessen its impact on the environment. The waterproof layer can be constructed from concrete, flat stones or any impermeable material such as clay as the core. As opposed to Concrete Dams, (Concrete being a dense material) Earth Dams require a lot more material in their construction. Regular checks need to be carried out to check the reliability and safety of the dam, as regular seepage will occur.

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The Brenig Reservoir situated in the Denbigh moors, was constructed in the 1970’s. ( ). This Dam is of Earth type construction, and has a capacity of 60 million m³. This dam, Brenig, is used as a top up reservoir, backing up the reservoirs of Llyn Tegid and Celyn at Bala, helping to maintain water levels in the River Dee system. Water from the River Dee is extracted at Chester for local industry, and is used to supply water for the canal system.

Extended Diploma – Building Services Gravity Dams As the name would suggest, gravity dams use the force of gravity to resist the weight of water and the mass of material used to construct the dam. This means the weight of the water must not be able to tip over or push the dam downstream in any way. Due to the amount of concrete required to construct this type of Dam, it becomes an expensive structure to complete.

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Arch Dams. In areas with steep sided cliffs, an Arch Dam could be an alternative form of Dam Construction. The Dam is constructed with a concave profile jutting out into the water. This design makes the Dam very strong in compression, helping to transmit the forces into the rock wall on either side of the Dam. This type of construction is only really suited to specific locations, such as narrow river canyons. They do not need the same mass of material as a Gravity Dam.

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The Alwen Reservoir was constructed between The original purpose of this reservoir was to supply water to the people at Birkenhead. It is now used as the Brenig reservoir, to back up the River Dee catchment area.

Extended Diploma – Building Services Buttress Dams Consists of a concrete wall supported by a number of buttresses. As with a gravity dam, most of the material is concrete, however the buttressing effect will help to reduce the amount of material required for construction. The two most popular forms of Buttress Dams are Flat Slab and multiple arch.

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Llyn Stwlan Dam built in the 1960’s as part of the Tanygrisau hydro electric scheme. Water from this dam is released to drive 4 water turbines situated along side the bottom lake. The amount of electricity produced is governed by the amount of water contained within Llyn Stwlan. The topography of this part of the world again dictated this method of construction.

Extended Diploma – Building Services Multiple Arch Dams. This comes under the same heading as a Buttress dam. However in this instance the dam is made from a series of arches all pointing out into the lake. Another important consideration for choosing a Buttress or Multiple Arch Dam is the ground conditions. The reduced weight of one of these Dams may well suit the terrain, rather than the weight of a gravity Dam.

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In Civil Engineering terms, managing water supply is one of our main areas of work. By understanding the Hydrological cycle, this allows us to manage our water, and supply homes, businesses and leisure facilities throughout the country. Water is stored, cleaned and then delivered through a series of pipes.

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Conclusion. Dams are a structure constructed to create a reservoir. A reservoir has primary and secondary functions. Five different types of Dam construction. Each type is dependant on Ground Conditions, local Geology and Topography. The Costs of Constructing a Dam are Huge!