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. Rio Cobre Dam and its main irrigation canal, in Jamaica. 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.
Model of the Three Gorges Dam with ship lift and ship lock. A ship lift and a navigation lock are being provided in the Three Gorges Dam which is currently being constructed across the Yangtze River in China. The ship lock will have two channels each 1.
There will be five steps in each channel to raise and lower vessels over a maximum height of metres. Uses for Reservoirs For centuries, the world's water resources have been developed to benefit mankind. These are some common uses for reservoirs: Water supply Hydroelectric power Flood control Irrigation Navigation They are also used to regulate the flow of water in rivers.
Water Supply Reservoir water can be used to supply water to our homes and factories. Lairg Dam in Scotland and its power station. Paritally opened floodgates on Tarbela Dam is Pakistan. Today, there are large dams. The total number of dams in Europe is now growing very slowly, as suitable sites becomer fewer and environmental concerns become greater.
Although there are only a few reservoirs in this area, they are very large. The six largest reservoirs are located in the Volga river system in Russia.
The Kuybyshevskoye km 2 and Rybinskoye km 2 are the two largest reservoirs. Of the 13 European reservoirs with an area exceeding km 2 , only the Dutch reservoir Ijsselmeer lies outside Russia and the Ukraine. The member state with the largest number of reservoirs is Spain approx.
Other countries with a large number of reservoirs are Italy approx. Reservoir construction leads to a number of environmental issues, both during building and following completion. Upon the closing of the dam the water level in the reservoir rises. As a result, major changes often take place in the area inundated with the water. For example, farmland can be lost, settlements flooded and the groundwater table elevated. Once the reservoir has been established, two types of environmental problems occur, those that:.
Since dams interrupt the natural continuity of a river and reservoirs change the hydrological cycle , the ecological consequences can be manifold. For example, access to spawning sites for migratory fish is prevented.
This is a particular problem for fish such as salmon, trout, eel and sturgeon. However, even small dams cause problems, as they constitute impassable barriers for most species of fish. Hence, small dams less that m in height , which are 10 to times more common than large ones, have had major adverse effect on fish populations.
In addition, reservoirs trap suspended matter mainly sand flowing into them. This reduces the suspended matter load to downstream reaches and ultimately to the sea, where the lack of sand leads to coastal erosion. Software updated on 09 November from version Code for developers. Systems Status. Legal notice. Creative commons license. CMS login. Toggle navigation Skip to content. The water level in the reservoir is usually highest at the end of the rainy season, and lowest at the end of the dry season or the irrigation season.
Pumps installed at reservoirs and lakes must be able to handle these fluctuations, which are not only vertical, but even more pronounced horizontally, because the water recedes back to the lowest parts of the reservoir. A dead branch of a river can also be made to function as a reservoir.
The branch is filled with water during the wet season and closed off during the dry season so that the stored water may be used. Due to the low water level, pumps are normally needed to irrigate fields from such a reservoir. Especially for large reservoirs costs are high. It must be designed by engineers and heavy machinery is necessary. If it is constructed for a hydropower water source costs are even higher because much more technical equipment as well as operation and maintenance is needed.
Because reservoirs are man-made water-bodies, they are more amenable to artificial operation and regulation than lakes. As previously noted, operational possibilities unique to reservoirs include the ability to discharge known volumes of water at predetermined times, and selective discharge of water from different water layers within the reservoir.
This must be planned carefully as it directly impacts the environment as described above. Dams, especially the very large ones, must be checked regularly to ensure their stability and security. Furthermore, many man-made water reservoirs are affected by high sedimentation rates. The accumulation of sediments in the reservoir reduces the main reservoir asset i. Moreover sediments can negatively affect pumping and hydropower equipment. There are several approaches to minimise or deal with sedimentation.
When a reservoir serves different functions it is nearly impossible to operate each function at its maximum level. Faecal pollution and other contamination of reservoirs has to be prevented by wastewater treatment and buffer zones in case of non-point sources of pollution see also the factsheets on lakes or water source and well protection.
If the reservoir is also used as a source of drinking water, please also check water purification as a measure to protect human health. Water from a reservoir as a surface water source is applicable for use for irrigation in agriculture, households or processing in industries.
Depending on the size of the reservoir, impacts ecological, riparian must be considered to avoid contamination, damage of the environment or user conflicts. This study shows what can happen if the natural processes are not considered properly. The described Australian reservoirs became fully silted very quickly, with each one being used for less than 25 years. The experience gained from these failures may be of use today for practicing engineers to prevent similar mistakes.
This training material gives an introduction to crop water needs and discusses the influence of climate, crop type and growth stage. Further, it introduces the special requirements of growing rice. Finally, it looks at the irrigation water needs within a parcel of land at the plant level. In this lecture, impacts of reservoir dams such as decreasing flow volumes in tail waters or barrier for animals are reviewed with some examples in Japanese and Asian rivers, particularly those on benthic animals and their habitat conditions in tail waters.
This online publication focuses on the differences and similarities of lakes and reservoirs considering their characteristics, use and conservation. The publication explains the water cycle as the basis to understand how water moves in nature, shows that although lakes and reservoirs appear to be very similar in fact they can also be very different from each other and also talks about how to take care of them.
This tool addresses the needs of practitioners and allows them to easily access relevant guidance materials. In this report, a managed flood is a controlled release of water from a reservoir to inundate a specific area of floodplain.
This document focuses on developing countries but most issues are relevant world-wide.
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