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hillside in a narrow ravine as a 

 mountain torrent much interrupted 

 by falls. In the valley course the 

 gradient is more gentle and the 

 velocity of the stream less ; the 

 river" is relatively easily deflected 

 from its course by obstructions, 

 and begins to wind or meander. 

 Its destructive work is horizontal 

 as well as vertical, the valley 

 being widened by the destruction 

 of the concave banks at the bends. 



In its plain course the river has 

 eroded downwards almost to sea 

 level, and so has a gentle gradient 

 and a low velocity. It meanders 

 widely, but its work is mainly con- 

 structive hi the formation of 

 shoals, flood plains, and deltas. 

 Many rivers have only a torrential 

 course ; hi others the plain course 

 has been drowned beneath the sea 

 by depression of the land. In 

 this case an estuary or firth is 

 formed. In all its stages a river 

 does transport work, but the 

 amount of material that can be 

 carried in suspension or rolled 

 along the bed depends on the 

 velocity. A great deal of matter is 

 also carried in solution. 



The annual flow of the Mississippi 

 carries to the sea about 400,000,000 

 tons of solid matter, and about 

 80,000,000 tons of dissolved mineral 

 salts. It is estimated that the de- 

 structive action of a river like the 

 Mississippi lowers its whole basin 

 on an average one foot in 6,000 

 years. Among the longest rivers 

 of the world are the Nile, 4,400 m. 

 long, the Mississippi-Missouri, 

 4,200 m., the Amazons, 4,000 m., 

 the Yang-tse, 3,500 m., the Ob- 

 Irtish, 3,500 m., and the Amur, 

 3,000 m. The speed of a river 

 varies with the gradient. A torren- 

 tial stream flows at 18 to 20 m. an 

 hour ; a moderate current is about 

 one m. an hour. In flood time the 

 velocity of a river is increased, very 

 often with disastrous results, since 

 the increased velocity makes the 

 river change its course suddenly. 



Navigable rivers are natural 

 highways, and since their valleys 

 are generally fertile they afford 

 routes through densely populated 

 regions. With the increased size 

 of vessels only the lower courses of 

 the largest rivers are navigable by 

 ocean-going steamers, but river 

 steamers of shallow draught ply on 

 upper reaches. The head of navi- 

 gation, which is often, but not 

 always, the head of tidal influences, 

 has determined the site of many 

 great seaports like London and 

 Glasgow. ;' 



Deltas frequently interfere with 

 navigation from the sea, as in 

 the Ganges, Mississippi, and Nile, 

 three rivers with long navigable 

 courses. The value of rivers as 



River Clyde. Troops landing on V Beach, Gallipoli, from the British collier 



lines of communication is reflected 

 in the establishment of certain 

 rivers as international waterways, 

 e.g. Congo, Danube, Elbe, etc. 

 Unnavigable rivers are often used 

 for floating timber, as hi Canada 

 and Sweden. Rivers of high gra- 

 dients, particularly if interrupted 

 by falls, provide abundant water 

 power, as in Norway, Finland, the 

 United States, and elsewhere. 

 Before the industrial revolution 

 this located many industries in 

 Britain, such as cutlery at Shef- 

 field, and woollens at Galashiels. 

 Rivers flowing through dry lands 

 are valuable for irrigation pur- 

 poses,as the Nile and the Euphrates. 

 All production in these basins has 

 always been based on irrigation. 

 Rivers are also of great importance 

 in connexion with the supply of 

 water to towns. See Amazon ; 

 Canal ; Delta ; Mississippi ; Nile ; 

 Physiography ; Reservoir; Thames; 

 Transport; Water Power; consult 

 also River Development as Illus- 

 trated by the Rivers of N. America, 

 I. C. Russell, 1909 ; The Work of 

 Rains and Rivers, T. G. Bonney, 



1912. B. N. B. Brown 



Rivera. Department of N.E. 

 Uruguay. It is bounded on the N. 

 by the Brazilian state of Rio 

 Grande do Sul and S. by the dept. 

 of Tacuarembo. The surface is un- 

 dulating pasture land, supporting 

 large herds of cattle. Gold is found, 

 and cattle and animal products are 

 exported. Its area is 3,793 sq. m. 

 Pop. 43,000. Rivera, the capital, 

 is situated in the N. of the dept. 

 Pop. 8,000. 



River Clyde. British steam col- 

 lier of 3,913 tons gross, converted 

 into a troopship, from which a 

 memorable landing was made on 

 " V " beach at Gallipoh', April 25, 

 1915. After the landing the vessel 

 was refloated by an Admiralty 

 salvage party, and then taken into 

 Mudros Harbour, June 8, 1919, 

 later to Malta, and hi Jan., 1920, 



was sold by auction in London to 

 Spanish shipowners for 11,500. 

 See Dardanelles ; Gallipoli, Land- 

 ing at. 



River Engineering. Branch of 

 civil engineering dealing with the 

 canalisation, diversion, and main- 

 tenance of rivers and with works 

 for their improvement generally. 



Canalisation includes all work 

 involved in rendering a river or 

 stream navigable,which hi its natu- 

 ral or existing state is either wholly 

 or partially unnavigable for any or 

 all of the following principal rea- 

 sons : variation of flow due to tidal 

 range and rapid fall ; alternate 

 drought and floods ; insufficient 

 volume of water ; the presence of 

 shoals, rocks, etc., or the formation 

 of a bar, sandbanks, or a delta at 

 its outlet ; tortuous course ; varia- 

 tions in depth and width due to 

 scour, silting, and the absence of 

 proper banks and the existence of 

 low level bridges. In order to de- 

 termine whether a river can be 

 made navigable, it is necessary to 

 ascertain the sources and volume 

 of water, the variation in flow, 

 whether it can be increased or ren- 

 dered more uniform, the gradient 

 or fall, especially of the section to 

 be canalised, the causes and extent 

 of obstructions and the practic- 

 ability of their removal, and of sub- 

 sequently maintaining a navigable 

 channel, and the rights and inter- 

 ests of riparian owners and others. 



Deltas are formed by the deposit 

 of sediment carried down by the 

 stream and silting up at the outlet ; 

 bars and sandbanks are due to 

 similar causes. The remedies are 

 dredging and the construction of 

 training jetties and sluicing basins 

 at the mouth, such as are employed 

 for scouring estuary harbours. 

 Rock is removed by blasting with 

 dynamite. Shoals of sand and mud 

 and deposit hi a river bed are 

 dredged until a sufficient depth and 

 width are attained. A tortuous 



