The use of bank-side reservoirs also allows water abstraction to be stopped for some time, for instance when the river is unacceptably polluted or when flow conditions are very low due to drought.
The water stored in such reservoirs may stay there for several months, during which time normal biological processes may substantially reduce many contaminants and reduce turbidity. Both the floor of the reservoir and the bund must have an impermeable lining or core: initially these were often made of puddled clay, but this has generally been superseded by the modern use of rolled clay. Such reservoirs are usually formed partly by excavation and partly by building a complete encircling bund or embankment, which may exceed 6 km (4 miles) in circumference. Where water is pumped or siphoned from a river of variable quality or size, bank-side reservoirs may be built to store the water. Aerial view of Plover Cove coastal reservoir Bank-side The Queen Mother Reservoir in Berkshire, England is an example of a bank-side reservoir its water is pumped from the River Thames. Saemanguem in South Korea, Marina Barrage in Singapore, Qingcaosha in China, and Plover Cove in Hong Kong are a few such coastal reservoirs. Many coastal reservoirs were constructed in Asia and Europe. As the land-based reservoir construction is fraught with substantial land submergence, coastal reservoirs are preferred economically and technically since they do not use scarce land area. Coastal Ĭoastal reservoirs are fresh water storage reservoirs located on the sea coast near a river mouth to store the flood water of a river. Where the topography is poorly suited to forming a single large reservoir, a number of smaller reservoirs may be constructed in a chain, as in the River Taff valley where the Llwyn-on, Cantref and Beacons Reservoirs form a chain up the valley. In such cases additional side dams are required to contain the reservoir. Sometimes in such reservoirs, the new top water level exceeds the watershed height on one or more of the feeder streams such as at Llyn Clywedog in Mid Wales. In hilly regions, reservoirs are often constructed by enlarging existing lakes. Ĭonstruction of a dammed reservoir will usually require the river to be diverted during part of the build, often through a temporary tunnel or by-pass channel. Examples include the temples of Abu Simbel (which were moved before the construction of the Aswan Dam to create Lake Nasser from the Nile in Egypt), the relocation of the village of Capel Celyn during the construction of Llyn Celyn, and the relocation of Borgo San Pietro of Petrella Salto during the construction of Lake Salto. In many reservoir construction projects, people have to be moved and re-housed, historical artifacts moved or rare environments relocated. The valley sides act as natural walls, with the dam located at the narrowest practical point to provide strength and the lowest cost of construction.
These reservoirs can either be on-stream reservoirs, which are located on the original streambed of the downstream river and are filled by creeks, rivers or rainwater that runs off the surrounding forested catchments, or off-stream reservoirs, which receive diverted water from a nearby stream or aqueduct or pipeline water from other on-stream reservoirs.ĭams are typically located at a narrow part of a downstream of a natural basin.
It was formed after the impounding of the Holston River Valley by the Tennessee Valley Authority in 1941 as a part of the New Deal's efforts to bring electricity to the Tennessee Valley.ĭammed reservoirs are artificial lakes created and controlled by a dam constructed across a valley and rely on the natural topography to provide most of the basin of the reservoir. The East Branch Reservoir, part of the New York City water supply system, is formed by impounding the eastern tributary of the Croton River. The dam spans the Vyrnwy Valley and was the first large stone dam built in the United Kingdom.
Further information: Porosity Storage Reservoir Dammed valleys Lake Vyrnwy Reservoir.
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