Types of dams
Contenido
Los diferentes tipos de presas responden a las diversas posibilidades de cumplir la doble exigencia de resistir el empuje del agua y evacuarla cuando sea preciso. En cada caso, las características del terreno y los usos que se le quiera dar al agua, condicionan la elección del tipo de presa más adecuado.
Existen numerosas clasificaciones, dependiendo de si son fijas o móviles (hinchables, por ejemplo), su forma o manera de transmitir las cargas a las que se ve sometida y los materiales empleados en la construcción. Las presas hinchables, basculantes y pivotantes suelen ser de mucha menor entidad.
According to its structure
The gravity dam is one in which its own weight is responsible for resisting the push of the water. The thrust of the reservoir is transmitted to the ground, so it must be stable enough to support the weight of the dam and the reservoir. They constitute the dams with the greatest durability and require the least maintenance.
Within gravity dams there are:
Its structure is reminiscent of an isosceles triangle since its base is wide and narrows as you ascend towards the top, although in many cases the side facing the reservoir is almost vertical. The reason there is a noticeable difference in wall thickness as the height of the dam increases is because the pressure at the bottom of the reservoir is greater than at the surface. In this way, the wall will have to withstand more pressure on the bed of the channel than on the surface. The inclination on the upstream face causes the weight of the water on the dam to increase its stability.
The arch dam is one in which its own shape is responsible for resisting the pressure of the water. Because the pressure is transferred in a very concentrated way to the slopes of the cliff, it is required that it be made of very hard and resistant rock. They are the most innovative dams in terms of design and the least amount of concrete is needed for their construction. The first known arch dam is located in Vallon de Baume, made by the Romans near Glanum (France).[32][33].
The vault dam, double arch, or double curvature arch is one that has curvature in the vertical plane and in the horizontal plane, it is also called vault. To achieve their complex shapes, they are built with concrete and require great skill and experience from their builders, who must resort to unusual construction systems.
When the slopes are too far apart, or when the local material is so compact that it is almost impossible to extract it, the buttress design allows creating a dike with great material savings.
One of the most notable examples of this type is the Daniel-Johnson Dam in Quebec, Canada, completed in 1968 as part of the Manic-Outardes project. Measuring 214 m high and 1,312 m wide, the dam, designed by André Coyne, is supported by two central buttresses 160 m apart at its base. The 13 lateral arches form inclined half cylinders 76 m apart. Beyond aesthetic considerations, the construction company chose to build a buttressed dam for economic reasons. According to design studies, the construction of the structure required just over 2.2 million m³ of concrete, five times less than a heavy dam.
The gravity arch dam is one that combines characteristics of arch dams and gravity dams and is considered a compromise solution between the two types. It is curved to direct most of the effort against the walls of a canyon or valley, which support the arch of the dam. In addition, the retaining wall is thicker at the base and the weight of the dam allows it to withstand part of the pressure of the water. This type of dam requires a smaller volume of fill than a gravity dam.
The dam-bridge combines two characteristics, on the one hand there is the dam and on top of it an elevated bridge. This type of dam-bridge was proposed in the context of a megalomaniac project to link Europe and Africa through the Strait of Gibraltar.
According to your materials
Concrete dams are the most used in developed countries since with this material more stable and durable constructions can be made; because its calculation is completely reliable compared to those produced in other materials. Normally, all gravity, arch and buttress type dams are made of this material. Some small and the oldest dams are made of brick, ashlar and masonry. In Spain, 67% of dams are gravity dams and are made with concrete either with or without steel reinforcement.
The Three Gorges Dam located on the Yangtze River in China is the largest hydroelectric and flood control plant in the world. It was completed in 2009. A dozen cities and thousands of towns were engulfed by the waters, forcing the displacement of more than one and a half million people.
They can be made of conventional massive concrete or compacted with a roller.
Loose material dams are the most used in underdeveloped countries since they are less expensive and represent 77% of what we can find on the entire planet. They are those that consist of a fill of earth, which provides the necessary resistance to counteract the push of the waters. The materials most used in its construction are stones, gravel, sand, silt and clay, although among all of these the ones that stand out the most are stones and gravel. In Spain they only account for 13% of the total.
This type of dam has very permeable components, so it is necessary to add a waterproofing element. Furthermore, these structures always resist by gravity, since the weak cohesion of their materials does not allow them to transmit the forces of water to the ground. This element can be clay (in which case it is always located in the heart of the fill) or a concrete screen, which can also be built in the center of the fill or upstream. These dams have the disadvantage that if they are overwhelmed by the waters in a flood, they run the risk of collapsing and ruining. In Spain, the accident at the Tous dam, popularly known as the Pantanada de Tous, is well remembered.
They are made of breakwater, clay core, with asphalt screen, with concrete or homogeneous screen.
This type of dam is sometimes classified as loose material dam; but its form of execution and its structural work are different. The water retention element is a curtain formed with rock fragments of various sizes, which support a concrete face on the side of the reservoir which is the impermeable element. The screen or face is supported in contact with the foundation by a transition element called a plinth, which supports the concrete slabs. This type of structure was widely used between 1940 and 1950 in curtains of intermediate heights and fell into disuse until the end of the century, when it was taken up by designers and builders with better construction methods and more efficient construction equipment.
They are those built by manually or machine placing the elements that compose them, called ashlars or masonry.
According to your application
Filter dams or retention dams are those that have the function of retaining solids, from fine material to large rocks, transported by torrents in mountainous areas, while still allowing the passage of water.
Flood control dams are those whose purpose is to laminate the flow of torrential floods, so that no damage is caused to the land located downstream of the dam in cases of strong storms.
Diversion dams are those whose main objective is to raise the level of the water to make its diversion feasible, controlling the sedimentation of the channel so that the diversion inlets are not obstructed. These types of dams are, in general, of low height since water storage is a secondary objective.
Storage dams are those whose main objective is to retain water for regulated use in irrigation, electricity generation, supply to populations, recreation or navigation, forming large vessels or artificial lagoons. The highest percentage of dams in the world, those with the greatest reservoir capacity and highest curtain height correspond to this objective.
Tailings dams (Mexico) are structures for retaining loose solids and waste liquids, a product of mining exploitation, which are stored in vessels for decantation. They are usually smaller than dams that retain water, but in some cases they correspond to structures that contain enormous volumes of these materials. Like hydraulic dams, they have a curtain (normally made of the same type of material), a spillway, and instead of having an intake or intake work, they have a system to extract liquids.