Irrigation dams

Date: 2015-10-07; view: 1073.

Irrigation dams

Unit 6

a feeder canal- магистральный оросительный канал

a main drainage channel - осушительный канал

а receiving basin - водоприемник

an outlet- выход, выпуск

drainage network- дренажная сеть

to surge-вздыматься

surplus-излишний

Irrigation dams are designed to store water. The next step in irrigation is to construct a system of canals and channels feeding the land from a natural or man-made source: a river, or a reservoir. When the feeder canals reach the area to be irrigated, they branch out into many smaller channels, which are spread out systematically, and share out the water over the dry land. As the irrigation network gives up more and more of its water, the channels get smaller and smaller.

To drain land of an excess of water, aim is just the opposite of irrigation. Man digs many small channels, or drains, which collect the excess water from particular areas of the marsh - and carry it to the main drainage channel, just as the tributaries of a river flow into the main river. As the drainage network collects more and more water, the main collecting drain gets larger.

There are important differences between the two kinds of network, for irrigation is adjusted to needs, whereas drainage, depending mainly on rainfall, is not subject to man's will. The bed of an irrigation channel is kept as high as possible so that water can flow onto the land the bed of a drainage channel is kept as low as possible so that excess water flows off the land.

The main drainage canal, carrying all the water it has collected from its tributary channels, empties into a receiving basin, which may be a river, lake, or sea. If the water in this basin is subject to floods or high tides, the engineer must build a check structure at or near the outlet to prevent the floodwater from surging back into the drainage channels. The structure contains gates -or sluices that may be closed to prevent back-flow, or opened to allow the drainage canal to empty into the receiving basin.