Dams are some of the most magnificent man made structures on Earth with some of the most well known being the Three Gorges Dam in China and the Hoover Dam in America. These structures are designed to block the flow of water in order to prevent flooding or store water to be used for drinking, crops, power generation, etc. Dams are made of numerous materials such as wood, steel, concrete, and dirt depending on the purpose. There are a few main types of dams; arch dams, gravity dams, barrage dams, and embankment dams. Furthermore these dams are used in various applications; diversionary, dry, saddle, wind, weir, and check dams all fulfill specific roles. This article will outline the popular structural dam types and their variety of uses.
Types of Dam Structures
Arch dams are among the most common types of dams. Generally, arch dams are made of concrete and don’t require the use of as much building materials as other types of dams. This has the added benefit of making them inexpensive. Arch dams form an arch between two structures and are often built in narrow areas. Typically arch dams span between two natural structures like mountains, canyons, valleys, or gorges. The arch shape curves back against the water offering very effective support even though they are thin and steep. Structural support from the shape and design of the arch keeps the water back as opposed the size and mass of the dam like in other types of dams.
There are also different types of arch dams, such as multiple arch, constant radius, and constant angle dams. Multiple arch dams are basically the same as regular arch dams, except that they have more than one arch. Constant radius and constant angle dams are single arch dams, but they vary in terms of the height and positioning of the structure. Constant radius dams are positioned at a constant radius across, but they tend to get narrower towards the bottom. Constant angle dams are positioned at a constant angle, but the bottom part of the dam is at a different radius. Video below shows footage from construction of the Deriner Arch Dam in Artvin, Turkey.
Gravity dams are basically massive structures that use sheer size and mass alone to block the flow of water due to the force of gravity. Since they are made of concrete these must have a solid sturdy foundation. Obstructions must be removed from the foundation area before construction. Gravity dams are effective because they are so solid and have a high load bearing strength. Essentially due to gravity the size of a these dams make them able to resist being pushed by the water reservoir behind. They stretch across an area and often include a concrete extension that helps them span larger distances.
Arch and gravity dams can be combined when building materials are sparse. These arch-gravity dams stay true to the gravity design but incorporate a slight arch for the added structural support. One of the most famous arch-gravity dams is the Hoover Dam in Nevada, USA. Below is a video detailing the story of Hoover Dam.
Barrage dams are series of gates built into a wall made of concrete, steel, or other materials. Raising or lowering these gates controls the flow of water to the other side. Typically barrage dams are located across existing water inlets or over rivers. An example would be building a barrage dam where a river meets an estuary allowing the use of tides for generating electricity, such barrages are also known as tidal barrages. Often the purpose of a barrage dam is to control the flow of water for irrigation or safety rather than generating electricity. Reservoirs aren’t required for barrage dams because of this and only minor water level differences are created. Some tidal barrages actually prevent the rising tides from raising water levels up river to allow for more useable land and protect settlements and harbors. The video below shows Couesnon tidal barrage in France.
Embankment dams are primarily built of materials such as dirt and rock. Often clay, asphalt, or concrete cores are incorporated for additional strength and to create a water impermeable layer. Earthen or terrain dams use compacted dirt for their core and rock-filled dams use crushed rock. Layered on the core will be dirt, rock, or a mixture of both to further enhance the mass of the dam to it’s required size. Embankment dams rely on the same gravitational pull resistance to the water reservoir so size is an issue that is dictated by the force of the reservoir. Typically these dams are found in areas where construction materials like concrete are harder to come by or difficult to bring to the construction site. Video below shows a stone embankment dam located in LaoShan, China.
Types of Dam Uses
Diversionary dams are intended to redirect the flow of a natural water source. Such diversions may be complete or partial depending on the goal of the dam. Uses of diversionary dams include creating water canals for irrigation, altering the course of water for hydroelectricity, and the creation of reservoirs. Below is a video showing a diversion dam used for hydroelectricity in Lander, WY, USA.
Dry dams are typically built without any turbines or other mechanical features. These dams have water outlets built into the structure which restricts the rate that water can flow past prevent flooding. During heavy rain, summer glacial melt, or other changes in water level the dam holds back the water letting it gradually flow out in a controlled manner. Video below displays a dry dam used to prevent flooding and optimise agricultural use of water.
Saddle or Auxillary Dams
These dams are used to control the flow of water in a reservoir created by another dam. Creating a secondary, or auxiliary, dam can create a more efficient reservoir by limiting the amount of water required to raise the water level. So called “saddles” in the terrain can also allow water to escape so a saddle dam is used to prevent this. Building these dams also limits the amount of arable land lost to the reservoir.
Weir or Overflow Dams
Weirs or overflow dams are simple dams built across small rivers or streams that allow water to flow over the top. Construction of a weir can maintain the water height behind as water conditions change seasonally. Measuring the depth of water flowing over the weir can also provide accurate measurements of flow rates since the structure is known. Similar to dry dams weirs can also prevent flooding by limiting flow rate. So called mill ponds are also created with weirs where the height difference created is used to turn a wheel for milling. Below is a video of a labyrinth weir dam.
Check dams are used to prevent sediments and pollution from being carried away by water, reduce erosion or channelling of soil, retain water in soil in low water areas, and slow the flow of water in flood areas particularly flash floods. Construction is primarily done with rocks, sandbags, and wood but many materials can be used. The intent is to simply create a small blockage in the path of flowing water that allows water to slowly seep through. Below is a video demonstrating the effectiveness of check dams at reducing sediment, erosion, and increasing water retention. At 1:15 in the video is a close up demonstrating water flow without and with check dams.
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