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Read the following text and fill in the gaps with the words from the boxes below.
| prevent organize level provide construction dams collect |
A dam is a barrier that impounds (= takes water away) water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees (also known as dikes) are used to manage or (1) __________ water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are often used in conjunction with dams to (2) __________ clean electricity for millions of consumers. It can also be used to (3) __________ water or for storage of water which can be evenly distributed between locations.
Early dam building took place in Mesopotamia and the Middle East. Dams were used to control the water (4) __________ . Mesopotamia's weather affected the Tigris and Euphrates rivers and could be quite unpredictable.
One of the earliest (5) __________ is situated in Jawa, Jordan, 100km north-east of the capital Amman. This gravity dam featured a 9m high and 1m wide stone wall, supported by a 50m wide earth rampart (= a high wide wall of stone with a path on top, built around a castle, town, etc.). The structure is dated to 3000 BC. The Ancient Egyptian Sadd Al-Kafara at Wadi Al-Garawi, located about 25 kilometers south of Cairo, was 102m long at its base and 87m wide. The structure was built around 2800 or 2600 BC as a dam for flood control, but was destroyed by heavy rain during construction or shortly afterwards.
Roman dam construction was characterized by the Romans' ability to plan and (6) __________ engineering construction on a grand scale. Roman planners introduced a new concept of large reservoir dams which could secure a permanent water supply for urban settlements (= towns) also over the dry season. They were pioneers in the process of (7) __________ of much larger dam structures than previously built, such as the Lake Homs Dam, possibly the largest water barrier to date, and the Harbaqa Dam, both in Roman Syria. The highest Roman dam was the Subiaco Dam near Rome; its record height of 50m remained unsurpassed until its accidental destruction in 1305.
| river regulate bridges through cities prevent engineers |
Roman (8) __________ made routine use of ancient standard designs like embankment dams and masonry gravity dams. Apart from that, they displayed a high degree of inventiveness, introducing most of the other basic dam designs which had been unknown until then. These include arch-gravity dams, arch dams, buttress dams and multiple arch buttress dams, all of which were known and employed by the 2nd century AD. Roman workforces also were the first to built dam (9) __________ , such as the Bridge of Valerian in Iran.
The word ‘dam’ can be traced back to Middle English, and before that, from Middle Dutch, as seen in the names of many old (10) __________ . For example, in the Netherlands, a low-lying country, dams were often applied to block rivers in order to (11) __________ the water level and to (12) __________ the sea from entering the marsh lands. Such dams often marked the beginning of a town or city because it was easy to cross the river at such a place. This often gave rise to the name of a city or a town. For instance the Dutch capital Amsterdam (old name Amstelredam) started with a dam (13) __________ the river Amstel in the late 12th century, and Rotterdam started with a dam through the (14) __________ Rotte, a minor tributary of the Nieuwe Maas. The central square of Amsterdam, covering the original place of the 800 year old dam, still carries the name Dam Square or simply the Dam.
Types of dams
| power tallest building function classified city walls |
Dams can be formed by human agency, natural causes, or even by the intervention of wildlife such as beavers. Man-made dams are typically (15) __________ according to their size (height), intended purpose or structure.
1) International standards define large dams as higher than 15–20 meters and major dams as over 150–250 meters in height. The (16) __________ dam in the world is the 300-meter-high Nurek Dam in Tajikistan.
2) Purposes include providing water for irrigation to a town or (17) __________ water supply; improving navigation; creating a reservoir of water to supply industrial uses; generating hydroelectric (18) __________ ; creating recreation areas or habitat for fish and wildlife; retaining wet season flow to minimize downstream flood risk. Some dams can also serve as pedestrian (= a person who is walking in the street) bridges or bridges for vehicles across the river as well. Few dams serve all of these purposes but some multi-purpose dams serve more than one.
A saddle dam is an auxiliary dam constructed to confine the reservoir created by a primary dam either to permit a higher water elevation and storage or to limit the extent of a reservoir for increased efficiency. An auxiliary dam is constructed in a low spot or saddle through which the reservoir would otherwise escape.
An overflow dam is designed to be over topped.
A check dam is a small dam designed to reduce flow velocity and control soil erosion.
A wing dam is a structure that only partly restricts a waterway, creating a faster channel that resists the accumulation of sediment.
A dry dam is a dam designed to control flooding. It normally holds back no water and allows the channel to flow freely, except during periods of intense flow that would otherwise cause flooding downstream.
A diversionary dam is a structure designed to divert all or a portion of the flow of a river from its natural course.
3) Based on structure and material used, dams are classified as timber dams, arch-gravity dams, embankment dams or masonry dams, with several subtypes.
One of the best places for (19) __________ a dam is a narrow part of a deep river valley; the valley sides can then act as natural (20)__________ . The primary (21) __________ of the dam's structure is to fill the gap in the natural reservoir line left by the stream channel. The sites are usually those where the gap becomes a minimum for the required storage capacity. The most economical arrangement is often a composite structure such as a masonry dam flanked by earth embankments. The current use of the land to be flooded should be dispensable.
Read the text again and answer the following questions.
1. What is the main purpose of a dam?
2. What measurements did the earliest dam have?
3. How far from the capital of Egypt was the first ancient dam constructed?
4. Why are the Romans considered to be the pioneers in the process of dam-construction?
5. What is the connection between the word ‘dam’ and the name of some cities in Europe?
6. What is the main principle of classification of dams?
7. Where do people usually construct dams?
CANALs
Read the following text. Try to understand it. Use your dictionary if necessary. Make up 8 – 10 questions to the text. Let your classmates answer your questions. Check the answers.
Canals are human-made channels for water. There are two types of canals:
- Aqueduct canals that are used for the delivery of fresh water, for human consumption, agriculture;
- Waterway canals that are navigable transportation canals used for carrying ships and boats loaded with goods and people, often connected to existing lakes, rivers, or oceans. Included here are inter-ocean canals such as the Suez Canal and the Panama Canal.
The word "canal" is also used for a city-canal in cities such as Venice, Amsterdam or Bangkok.
Smaller transportation canals can carry narrow-boats, while ship canals allow seagoing ships to travel to an inland port (e.g.: Manchester Ship Canal), or from one sea or ocean to another (e.g.: Caledonian Canal, Panama Canal).
At their simplest, canals consist of a trench (= a long narrow hole that is dug in the ground for water to flow along) filled with water. Depending on the stratum the canal passes through, it may be necessary to line the cut with some form of watertight material such as clay or concrete.
Canals need to be leveled. Different methods of solving this problem exist nowadays.
The oldest known canals were irrigation canals, built in Mesopotamia circa 4000 BC, in what is now modern day Iraq and Syria.
In ancient China, large canals for river transport were established as far back as the Warring States (481-221 BC), the longest one of that period being the Hong Gou (Canal of the Wild Geese), which according to the ancient historian Sima Qian connected the old states of Song, Zhang, Chen, Cai, Cao, and Wei. By far the longest canal was the Grand Canal of China, still the longest canal in the world today. It is 1,794 kilometres (1,115 mi) long and was built to carry the Emperor Yang Guang between Beijing and Hangzhou. The project began in 605 and was completed in 609.
In the Middle Ages, water transport was cheaper and faster than transport overland. This was because roads were unpaved and in poor condition; so greater amounts could be transported by ship. The first artificial canal in Christian Europe was the Fossa Carolina built at the end of the 8th century. More lasting and of more economic impact were canals like the Naviglio Grande built between 1127 and 1257.
Canal building progressed steadily in Germany in the 17th and 18th centuries with three great rivers, the Elbe, Oder and Weser being linked by canals. In post-Roman Britain, the first canal built appears to have been the Exeter Canal, which opened in 1563. The oldest canal built for industrial purposes in North America is Mother Brook in Dedham, MA. It was constructed in 1639 to provide water power for mills. In Russia, the Volga-Baltic Waterway, a nationwide canal system connecting the Baltic and Caspian seas via the Neva and Volga rivers, was opened in 1718.
Modern uses
Large scale ship canals such as the Panama Canal and Suez Canal continue to operate for cargo transportation; as do European barge canals. Due to globalization, they are becoming increasingly important, resulting in expansion projects such as the Panama Canal expansion project.
A movement that began in Britain and France to use the early industrial canals for pleasure boats, such as hotel barges, has began very popular. In some cases abandoned canals such as the Kennet and Avon Canal have been restored and are now used by pleasure boaters. In Britain canal-side housing has also become popular in recent years.
The Seine-Nord Europe Canal is being developed into a major transportation waterway, linking France with Belgium, Germany and the Netherlands.
Canals have found another use in the 21st century, as ducts for fibre optic telecommunications networks.
Canals are still used to provide water for agriculture. An extensive canal system exists within the Imperial Valley in the Southern California desert to provide irrigation to agriculture within the area.
Cities on water
Canals are so deeply identified with Venice that many canal cities have been nicknamed "the Venice of ..." The city is built on marshy islands, with wooden piles supporting the buildings, so that the land is man-made rather than the waterways. The islands have a long history of settlement; by the 12th century, Venice was a powerful city state.
Amsterdam was built in a similar way, with buildings on wooden piles. It became a city around 1300.
Other cities with extensive canal networks include: Delft, Haarlem and Leiden in the Netherlands, Brugge in Flanders, Birmingham in England, Saint Petersburg in Russia, Hamburg in Germany, Fort Lauderdale, Florida, and Cape Coral, Florida in the United States.
Inland canals have often had boats specifically built for them. An example of this is the British narrow-boat, which is up to 72 feet (21.95 m) long and 7 feet (2.13 m) wide and was primarily built for British Midland canals. Some canals has a limitation to boats of under 10 tons. Most canals have a limit on height because of bridges or tunnels.
Part III
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