A dam is a bank or construction of stone, earth, or wood etc across a stream or river for the purpose of keeping back the current to give it increased head, for holding back supplies of water, for floodinglands, for rendering the stream above the dam navigable by increased depth, and for generating electricity. Its material and construction will depend on its situation and the amount of pressure it has to bear. For streams which are broad and deep strong materials are required, usually stone masonry bound in hydraulic cement and a strong framework of metal or timber. The common forms of a dam are either a straight line crossing the stream transversely, or one or two straight lines traversing it diagonally, or an arc with its convex side towards the current. Research Dam
Lakes are accumulations of water in hollows on the earth's surface. When they are drained by rivers their waters are fresh, but when they have no outlet they are salty, e.g. the Dead Sea, Sea of Aral, etc.
Lakes may owe their origin to:
Barriers across a river valley hold back the water, which forms a lake. Such barriers may be of various types. (a) Sometimes artificial barriers of concrete and masonry are built across a valley so as to make a lake which can act as a reservoir for the water-supply of a large city, e.g. LakeVyrnwy for Liverpool. (b) A glacier may deposit a mass of morainic material across a valley. In this way the lakes of the Lake District and many of the Scottish lakes were formed. (c) A landslip may occur. A lake was formed thus in the Upper GangesValley in 1892. Two years later the landslip dam gave way, and disastrous floods occurred downstream. (d) Oxbow lakes are formed from the meanders of rivers. The deposition of silt at the two ends of the 'oxbow' closes the channel between the main river and its old loop. Many oxbow lakes border the River Murray in Australia, and the lower Mississippi. (e) Sometimes a lavastream may flow across a valley and cause the formation of a lake, e.g. LakeTaupo in New Zealand. (f) Sometimes large estuaries are partially filled with silt. In the portions not so filled are large shallow lagoons. Such lagoons are found in deltaic areas. The NorfolkBroads are portions of an old river estuary. (g) When a silt-laden stream enters a lake its speed is checked and a barrier or delta is built across the lake splitting it into two portions. This has happened in the Lake District, where Keswick stands in the alluvial flats between Lakes Bassenthwaite and Derwentwater, and in Switzerland, where Interlaken is situated in the flats between Lakes Thun and Brienz. (h) The action of the sea often causes an accumulation of sand and pebbles which cuts off a lagoon of sea water. The Fleet in Dorset is such a lagoon, cut off from the sea by Chesil Bank, a long pebble beach which joins Portland Island to the mainland.
The nehrungs of East Prussia are sand-spits which enclose the shallow salt-water lagoons or halls, such as Kurische Haff. Earth movements cause lakeformation when subsidence occurs. This is most easily seen in rift valleys. Examples of riftvalley lakes are the Dead Sea, Lakes Nyasa and Tanganyika in Africa, and LakeTorrens in Australia. These are all long, narrow, and very deep lakes.
In Cheshire, the removal of underground beds of salt has caused subsidence resulting in the 'meres' of the Weaver Valley. The 'folding' of the earth across the line of a river valley may partially block a river and help to form a lake. The study of a good physical map will reveal the connection between mountain building and the formation of LakeGeneva and LakeConstance in Switzerland. Where there are large areas of depressed lowland wide and shallow lakes are formed in the lowest part of the depression, for example the Sea of Aral in Asiatic Russia, LakeBalaton in Hungary, and LakeEyre in Australia. Ice sheets and valley glaciers may scoop out hollows to form 'rock basins'. Mountain tarns and corrie lakes in North Wales and Scotland have been formed in this way. Water also accumulates in the hollows of unevenly- distributed glacial drift. Such are the lakes of East Prussia, and also those of the Cheshire-Shropshire borders near Ellesmere. Subsidence of the land surface and consequent lakeformation may be directly related to volcanic action. Lough Neagh in Northern Ireland is a shallow lake formed by subsidence of this type. Lakes are often formed by the accumulation of water in the craters of extinct volcanoes, for example the Laachersee in the Eifel region of Germany. Research Lakes
The Balwen Welsh Mountain is a breed of Welsh mountain sheep. The Balwen has a base colour of black/ brown or dark grey, with a white blaze on the face, four white feet and a half white tail. The name Balwen is derived from the Welsh phraseBal meaning white blaze. It is thought farmers over the years used the Balwen as landmarks on the hills as a means of recognizing ones flock. By whatever means, the Balwen has been preserved by the continued belief of committed enthusiasts that the Welsh Mountain is a 'sheep for all seasons'. For many years the Balwen was confined to an area of central Wales on the borders of the old counties of Cardigan, Brecon and Carmarthen. The catchment area of the river Tywi, north of Rhandirmwyn (now the Llyn Brianne Dam) was the breeding grounds for the Balwen sheep, and the ancestry of all Balwens can be traced back to the Tywi valley. The
Balwen Welsh Mountain Sheep is a small very hardy breed. They are easy to manage having very few health problems associated with many of the larger breeds. They have excellent feet requiring little attention and can get by with only the minimum of feeding at peak times of the year. The Balwen is an excellent mother, having very few lambing problems with plenty of milk capable of rearing twin lambs under the right circumstances. Research Balwen Welsh Mountain More information about Balwen Welsh Mountain
The beaver (Castor) is the only genus of the family Castoridae. The family contains a single genus, Castor, with two species: Castor canadensis, found in the New World, and Castor fibre, found in the Old World. Both species are semi-aquatic rodents noted for the building of dams. The two species differ chiefly in the shape of the nasal bones and are so much alike that some authorities consider them to be varieties of the same species. They are large rodents; the average adult beaver weighs about 16 kg, but specimens as heavy as 40 kg have been found, and some extinct beavers were almost bear- like in size. The beaver is usually about 76 centimetres long and stands less than 30 centimetres high, with a broad, flat, scaly tail about 25 centimetres long.
The body is plump, the back arched, the neck thick, the hind feet webbed, and all the digits clawed. The fur is usually reddish- brown above and lighter or greyish below. The eyes are small and the nostrils closable. The skull is massive, with marked ridges for fixing the muscles that work the jaws. The two front teeth on either jaw are like those of other rodents, wearing away more rapidly behind so as to leave a sharp, enamelled chisel edge. With these the beaver can cut down large trees. It usually selects trees five to 20 centimetres in diameter, but it can fell trees with diameters as large as 76 cm.
Beavers have a pair of anal scent glands, called castors, that secrete a musk-like substance called castoreum, probably for marking territories. The animals tend to be monogamous and have a life span of 20 years or more. The female has one litter a year, usually of two to four young.
Beavers are social animals and in areas where food is abundant and the locality secluded, the number of families in a beaver community can be rather large. The so-called beaver lodge is a unique structure. Three distinct kinds exist, their differences depending on whether they are built on islands, on the banks of ponds, or on the shores of lakes. The island lodge consists of a central chamber, with its floor a little above the level of the water, and with two entrances. One of these, the 'wood entrance', is a straight incline rising from the water, opening into the floor of the hut. The other approach, the 'beaver entrance', is more abrupt in its descent to the water.
The lodge itself is an oven-shaped house of sticks, grass, and moss, woven together and plastered with mud. The room inside is carpeted with bark, grass, and wood chips, sometimes with special store rooms adjoining. The pond lodge is built either a short way back from the edge of the bank, or partly hanging over it, with the front wall built up from the bottom of the pond. The lakelodge is built on the shelving shores of lakes. Dams are used by beavers to widen the area and increase the depth of water around their homes and are constructed either of sticks and poles or more firmly and solidly of mud, brushwood, and stones. As time goes by the beaver repairs and adds to the dam. Floating material lodges there, and vegetation growing on the top adds its roots to the strength of the dam. Frequently the beaver builds a smaller dam downstream in order to back up some water against the original dam and thus decrease the pressure of water on it from the other side. The dams are about 1.5 metres high, usually more than three metres wide at the base, and narrow at the top. A beaver dam more than 300 metres long was found in Rocky Mountain National Park, Colorado.
Beaver ponds eventually fill with sediment, and the animals move to a new location. The abandoned area becomes good meadowland. Beaver dams also help control runoff. Although the beaver is a powerful swimmer, it has difficulty dragging over the ground the logs and branches it needs for building and for food. Colonies of beavers therefore often dig canals from the pond to a grove of trees. Such canals are up to one metre wide and deep and often a few hundred metres long. The timber is then readily floated down the canal toward the pond.
Beavers have long been exploited for their fur, and for many years during the 18th and 19th centuries hundreds of thousands of beaver skins were exported to Europe from North America annually. The animals were also sometimes destroyed because of the damage they did to forests and the flooding occasionally caused by dams. Ceaseless slaughter led to near extinction of beavers in both Europe and North America. The beaver is almost extinct in Europe, but is becoming re-established in Canada and in protected areas of the USA. Research Beaver
The Battle of Mechanicsville, Virginia was a battle of the American Civil War that occurred on June the 26th, 1862, during McClellan's attempted approach to Richmond. Robert E Lee crossed the Chickahominy with 35,000 Confederates, intending to join Jackson's 25,000 troops and demolish Porter's command of 20,000 of McClellan's troops and cut off the latter's communications with his base. Jackson was for once late in arriving, and Richmond was for a time in considerable danger. A P Hill's division advanced first and encountered at Mechanicsville a small-force of Confederates, who were dispersed. Just beyond the town McCall. was drawn up with a strong force on Beaver Dam Creek. The Confederates attempted to turn McCall's flanks, but were repulsed with great loss each time. Research Battle of Mechanicsville
The bouncing bomb was a rotating bomb used by the British in the Second World War to attack the Ruhrdams. The bouncing bomb was designed by Dr Barnes Wallis and derived its name from the way it 'bounced' along the surface of the water in front of the dam, rather like a stone skimmed across the surface of a pond.
The cylindrical bomb was slung beneath a Lancaster bomber and rotated prior to dropping from a carefully calculated height. It then rolled or 'bounced' along the surface of the water as far as the dam and then sank when it came into contact with the dam wall. A depth-sensitive fuse detonated the bomb at the point calculated to make the most effective breach, the water in the reservoir acting as a tamping device to direct the full force of the explosion at the dam. Research Bouncing bomb
Operation Chastise was a bombing raid carried out by nineteen Lancasters of No 617 Squadron, RAF on the night of the 16th/17th of May 1943 during the Second World War against the Mohne, Eder and Sorpe dams in the Ruhrvalley. The raid used the new bouncing bombs invented by Barnes Wallis. The raid was led by Guy Gibson who was later awarded the Victoria Cross, thirty-two other members of the Squadron was also decorated. The raid was designed to flood the Ruhrvalley, where most of Germany's war industry was located, thus severely hampering her efforts to manufacture weapons. The raid was immortalised in the film 'The Dam Busters'. Research Operation Chastise
Acrylamide is an odourless, free-flowing white crystalline used as a chemical intermediate in the production and synthesis of polyacrylamides. These high-molecular weight polymers can be modified to develop non-ionic, anionic, or cationic properties for specific uses. The principle end use of
acrylamide is in water-soluble polymers used as additives for water treatment, enhanced oil recovery, flocculants, papermaking aids, thickeners, soil conditioning agents, sewage and waste treatment, ore processing, and permanent press fabrics.
Acrylamide is also used in the synthesis of dyes, in copolymers for contact lenses, and the construction of damfoundations, tunnels, and sewers. The largest use for polyacrylamide is in treating municipal drinking water and wastewater. The polymer is also used to remove suspended solids from industrial wastewater before discharge, reuse, or disposal.
Acrylamides also find use in oil-drilling processes to control fluid losses. In the pulp and paper industry, polyacrylamides are used as binders and retention aids for fibres and to retain pigments on paper fibres.
Acrylamide is a soil stabiliser and also finds use in foundry operations to facilitate free sand flow into moulds. Home appliances, building materials, and automotive parts are coated with acrylamide resins and thermosetting acrylics. Acrylamides are formulated in cosmetics and soap preparations as thickeners and in dental fixtures, hair grooming preparations, and pre-shave lotions. Minor uses of acrylamide are as latex thickeners, emulsion stabilisers for printing inks, gelling agents for explosives, binders in adhesives and adhesive tape, in the production of diazo compounds, and for gel chromatography and electrophoresis.
Acrylamide occurs in crystalline form and in aqueous solution. It is soluble in water, methanol, ethanol, dimethyl ether, and acetone; it is insoluble in benzene and heptane. The monomer readily polymerises at the melting point or under ultraviolet light. Solid acrylamide is stable at room temperature, but may polymerise violently when melted or in contact with oxidising agents such as chlorine dioxide and bromine. When heated to decomposition, acrylamide emits a poisonous gas, acrid fumes, and NOx. If heating to high temperatures, acrylamide can explode. Acrylamide is also known as
acrylamide monomer, acrylic amide, propenamide, and 2-propenamide. Research Acrylamide
An air dam is a spoiler mounted at the front of a motor vehicle to reduce air flow to the underside of the vehicle and thereby improve stability. Research Air Dam
A caisson is a water-tight box, usually of sheet iron, and constructed so that it may be floated or sunk at will. Caissons are used for two distinct purposes. 1) for closing the entrance to docks, the caissons being of two general types, floating and sliding. Floating caissons include those which, when the height of the water inside and outside of the dock is the same, are raised by their natural buoyancy from the bottom, and may be floated out of their position against the sill into a recess provided for the purpose, leaving the entrance open. Sliding caissons fulfil the same purpose, but instead of floating are drawn back on a plane sliding surface or on rollers which bear some portion of their weight. 2) As foundations to a dam, quay wall or bridge, the caissons being so constructed as to be capable of being floated into the required position, and there sunk. Research Caisson
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