Glossary
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© Atlantic Europe Publishing 2002 Aqueduct A canal, tunnel or pipe designed to carry water for drinking purposes. Aqueducts have been in use since ancient times. Some of the largest modern aqueducts are in California, USA, where there is a great need to supply irrigation water to farmers and drinking water for cities such as Los Angeles. The California Aqueduct, for example, is over 700km long. Most Aquifer A water-bearing rock. Typical water-bearing rocks are chalk, limestone and sandstone. If the greater part of an aquifer is trapped between two layers of watertight rocks (aquicludes), the trapped water is called artesian water. Aquifers are vital sources of drinking water in most countries of the world. However, they can be overused if the amount taken out is greater than the amount added by rainfall. When aquifers are over used then the water is 'mined' and they will have a limited useful life before they dry up. Artesian water Groundwater that comes from an aquifer trapped between two confining watertight beds. The water may seep into the aquifer where the rock is exposed in hills, but because it is confined between watertight layers, it has no means of escape. As a result, the water in the artesian aquifer is often under considerable pressure. The world's largest artesian basin lies under much of northern central Australia. Condensation Water vapour condenses into liquid water when the temperature of the air falls. Air can cool because it comes into contact with a cold surface. This is why, for example, a glass containing ice cubes soon gathers a coating of condensation. Air can also cool if it rises in the atmosphere. This is the reason clouds form. Dam An artificial wall or embankment designed to hold back water. The water held back makes a reservoir (sometimes called a 'lake' if it is large). Earth and rock dams are broad structures with gently sloping sides and a very wide base. They are used only for dams of modest height. An earth dam is usually faced with stone so that it is not eroded by running water or lake waves. Masonry and concrete are used to build the world's tallest dams, or where a dam must be strong enough to block a narrow valley. The world's biggest dam is the Three Gorges dam on the Yangtze River in China. Developing country A country that does not have the wealth to provide many of the services, such as providing clean water, we take for granted. Dilution To reduce the concentration of a liquid by adding water. Disinfectant A chemical that kills germs but is otherwise not harmful to people. Disinfectants are added to water supplies, usually in the form of chlorine. Distillation A process of heating water so that the water evaporates, leaving any pollution behind. The water vapour is cooled, so that it condenses and turns back into pure water. Drinking water Water that is safe to drink. Very strict regulations are in place in many countries to make sure that drinking water is of the highest quality and does not contain poisonous substances, pieces of soil, or disease-carrying organisms. Drinking water has to be both clarified (made to look clean) and purified (disinfected) by the time it reaches taps. This is a complicated and expensive process. Drought An unusually long period without significant rainfall. Some parts of the world, particularly between latitudes 10' and 35 °, have a more variable rainfall pattern than others, and so they can be said to be more drought-prone. These places include the Sahel region of Africa just south of the Sahara Desert, southern Africa, northeast Brazil, Australia, southern California, the southwestern United States, and India. Some places have seasons when rain never falls. They are called dry seasons, but they are not droughts. In these areas droughts occur in the rainy season when the rains do not fall as normal. Evaporation The change of water from liquid to vapour at temperatures below boiling. Flood Floods occur whenever water flows across normally dry land. Both rivers and seas can cause flooding. To either side of a river channel there is flat land which has been made by the river during previous floods. This is called a floodplain. Anything built on the floodplain-no matter how far it might be from the river-will be flooded from time to time. Floods are not just water. All floodwaters carry huge amounts of sediment with them. Groundwater The water held within water-bearing rocks, or aquifers, in the ground. Water may flow naturally to the surface and come out as a spring or bubble upward as a flowing pool, or it may be taken out of the rocks by using a well or a bore hole. Limestone, chalk, and sandstone are the main rocks that are permeable enough for groundwater to flow through them readily. Water that is trapped in aquifers is called artesian water. It is a particularly important source of water in dry areas, but is exploited in all parts of the world. Hydro-electric power station Electricity produced by forcing water to turn turbine blades which are connected to a shaft which turns an electric generator. Irrigation The supply of water to farmland so that crops can grow in areas where natural water supplies are scarce or unreliable. Water for irrigation comes either from groundwater supplies or from reservoirs and river diversions. (See also: Aqueduct.) In dry countries irrigation can use more water than all other demands (home, industry, power) put together. Latrine A pit in the ground intended to be used as a toilet. Oasis (pl oases) A reliable natural spring in a desert. Oases are fed by springs flowing from rocks. The source of the spring may be hundreds of kilometres away from the spring in a place where water is more plentiful, such as a mountain range. Many oases are very small, but some can be hundreds of square kilometres in area. Polluted water Water that is unfit for its intended purpose. Purify (purification) To clean water so that it becomes fit for its intended purpose. Reservoir A reservoir is an artificial lake created by building a dam across a river. Some reservoirs are named lakes because of their size. River flows naturally vary through the year, so that there may be more water than can be used at one time of year and too little at another. During periods off heavy rainfall rivers may also swell and burst their banks, leading to widespread destruction. Reservoirs are built to control the flow of water in a river to prevent flooding and to give a reliable flow of water through the year. Reservoirs are used for providing drinking water, for irrigation water and for hydroelectric power. Runoff Water that reaches a river as a result of rainfall or snowmelt in the river basin. It is part of the water cycle. Runoff is mostly unseen, occurring as seepage through soil and rocks. Rain only flows directly to rivers after torrential rain or very long periods of rain. That is when floods occur. Sewage works A place designed to treat wastes in public water supplies. It consists of stages of getting rid of dirt, oil, metal and so on and then a stage of disinfecting. Sewer A large pipe designed to handle water-borne wastes from toilets, baths, sinks etc. Sludge The solid material, mostly soil, that settles out of water while it is being purified. Solution Water containing dissolved chemicals. These may of may not colour the water. Spa A town developed around the supposed health-giving waters of a spring. Bath and Buxton are spa towns. Spring A place where water naturally seeps or gushes from the ground. Springs are fed by groundwater. They occur in aquifers, often where a river cuts down to the water table. Other springs happen where a permeable rock is underlaid by an impermeable rock. This sometimes gives rise to 'weeping cliffs,' as water seeps from the base of the permeable rock. Bubbling or swiftly flowing springs are not especially common. Most rivers begin with muddy patches on a hillside rather than a bubbling spring. Water company A company whose main job is to provide clean water and to deal with sewage. Water cycle The circulation of water between the seas, the air, the plants, the rocks and the rivers. The energy for this, the world's greatest cycle, comes from the Sun and gravity. The energy of the Sun allows evaporation and powers the winds that carry moist air from the oceans to the land, while gravity brings water back from the clouds and rivers to the oceans. The water cycle is the main means of transferring water in the world. Water treatment plant A place designed to treat water from, for example a river or a lake, and purify it so that it is suitable for drinking. Well A well is a vertical shaft that is drilled down into an aquifer in order to obtain water for drinking and other home uses, for industry or for farming. A small well meant to serve a single house may be about 1m across and be lined with brick. Water is drawn by a bucket or a small pump. The wells needed to supply water to a city are on altogether a different scale. These wells are often sunk many tens of meters down into a large, reliable aquifer. They are not open wells, but enclosed and with pipes about 30cm across. These wells are sealed so that the clean water coming from the well is not contaminated from the surface. The water is pumped out of the aquifer using high-power pumps. |