Dams are water structures built to meet the water needs of people, irrigate agricultural areas and generate electricity. There are nearly 700 dams and hydroelectric power plants in our country. Dams are very difficult and expensive to construct. Before the dams are built, geologists and topographers come. They examine the structure of the land, its environment and soil durability. The alluvial layer on the ground should be removed in order to lay deep foundations and impervious curtains should be used to prevent water leakage. After the dam construction is completed, the streams and rainwater accumulating behind the embankment form a lake. These are called dam lakes. After enough water has accumulated, special covers are made to the dam to remove the excess water and the water overflows from the top of the dam.
Dams according to their size;
International Comission on Large Dam stated the following for the definition of large dams;
– Dams with a height of more than 15 m between their crest and foundation,
– Height between 10-15 m but in addition,
. With crest length longer than 500 m,
. With a reservoir volume greater than 1000000 cubic meters
. Largest flood flow rate > 1000 m3 /sn
Dams carrying at least one of these are called big dams.
Pond (small dam): These are dams whose projects are smaller and simpler.
High dams: Dams with a height of more than 50 m.
Construction Purposes of Dams
Dams are built as a single-purpose or multi-purpose. Single purpose dams are structures built for drinking water supply, industrial water supply, irrigation, and hydroelectric energy. Dams that contain several of these are multi-purpose dams.
Classification Of Dams According To Body Types
Dams are classified according to the material used in the body filling as well as according to the body shapes. Since the Keban Dam is a concrete gravity and rock fill dam, both types will be examined.
- Filled Brackets
– Earth Fill Dams
– Rock Fill Dams
– Concrete Faced Filled Dams
- Concrete Dams
– Concrete Gravity Dams
– Buttress concrete dams
– Concrete Arch Dams
– Roller Compacted Concrete Dams (RCC)
Earth Fill Dams
Landfill dams created by compacted soils made of gravel, sand and clay are one of the most used dam types. There is a wall or core in the middle of this dam that prevents water from leaking.
Concrete Faced Dams
The front face of the dam is covered with materials such as reinforced concrete, asphalt or geomembrane to ensure the incompatibility of the dam. In this type of dams, the core is made of clay or concrete.
Buttress Concrete Dams
It is calculated according to almost the same static calculation as concrete gravity dams. Buttress dams are generally built with flat crests. It provides 30-70% savings compared to concrete gravity dams. Copper and special plastic materials are used to prevent leaks.
Concrete Arch Dams
It is designed to transfer the water pressure force and the dam’s own weight to the slopes in the valley with the arch effect. The valley must be narrow in order to construct the Kemer dam. Foundations and slopes must have high bearing capacity. The ratio of the base thickness of the arch dam to the dam height varies between 0.2 and 0.6. Arch dams are classified according to their thickness. They are classified as thin belts, medium belts and thick belts. Peak thickness (TC) and base thickness (TB) to height
These types defined by their ratio are shown below
Roller Compacted Concrete Dams (RCC)
Recently, dams have been built with various technologies. It is one of the techniques used to minimize the cost. The cement content in this concrete is less than that of normal concrete. Since this mixture is compressed with vibrating rollers, it got its name from here.
Rock Filled Dams
More than 50% of the fill consists of rock type materials. It can be used on compressed clay, concrete or asphalt to ensure impermeability. Upstream rockfill dams can be concrete or asphalt covered. Asphalt pavement can withstand large amounts of deformation. This type of dam can be used in any narrow or wide valley. Sections are in the form of a steep trapezoid. There is a core in the middle of the section to provide impermeability. These cores are made of clay or concrete.
Concrete Gravity Dams
Concrete dam types are generally preferred in places with solid foundations. It is more appropriate to choose concrete gravity dams in rock foundations of solid and medium strength. When the dam height increases, they are more costly than other dam types. Concrete gravity dams are structures that primarily meet the water load and other secondary loads with their own weight and transfer them to the foundation. This type of structures consists of solid-body, hollow blocks or buttress that are closed between them.
Solid Body Gravity Dams:
It is formed by bringing 10 to 20 m wide trapezoidal concrete blocks side by side. Block widths should not exceed 20 meters. If this width is exceeded, thermal cracks may occur.
Buttress and Hollow Concrete Bodies:
They can be more economical in wide valleys than full-bodied dam types. Their height is limited. The spaces of the struts lined side by side are plates, arches, etc. It is closed with such elements.
Calculation Principles of Concrete Gravity Dams:
Hydrostatic external pressure is the most important external force affecting gravity dams. Therefore, a triangular section that expands towards the base is used to best meet the hydrostatic pressure. Upstream surfaces are arranged upright or close to vertical. Upstream surface can be made vertical or with a maximum slope of 10%. The reason for the inclination of the upstream surface is to prevent tensile stresses when the dam is empty and to increase the slip and overturning safety when it is full.
Hydroelectric Power Plant
Hydroelectric power plants, one of the renewable energy sources, convert the power of the violently flowing water into electricity. The amount of energy is determined by the flow and fall rate of the water. Water taken in channels or pipes is transferred to turbines. Turbines with arms like propellers begin to rotate with the flow of water. Turbines are connected to generators so they can convert mechanical energy into electrical energy. Keban Dam is one of the largest hydroelectric power plants in our country.