113 



RIVER IMPROVEMENTS. 



K1VKRS. 



possible resistance to th* current they are obliged t encounter beyond 

 the limits of the tidal action. 



Much information on the subjects alluded to in I his article is to be 

 found (in addition to the works already named) in Rot ison's i/tc/ianicat 

 . in Ellet'a Mututippi and Ohio Rirers ; in the Raccotta (let 

 A Mturi Jtaliani eki traltono del noto del ari/ue ; Weibeking's Thtoritinctit 

 fraetudie Wauerbaulnaut : De Prony's \ourtlli Architecture JJytlmtt- 

 litjiu ; D'Aubisson s llydraulupit ; General Baird Smith's Rtportt, and 

 hu works on Irrigation. Ac ., Ac. 



RIVEK IMPROVEMENTS. [RIVER EXUIXEERIX.;.] 



RIVERS are the flowing waters which bring to the sea, and some- 

 times to a lake, the water* which are collected within a certain portion 

 of the earth's surface. The country which is thus drained by a river 

 is called its loan, as the river runs in the lowest part of it, and the 

 country rises on all sides with greater or leas steepness, in the fashion 

 of the sides of a basin. The margin of such a basin generally lies 

 contiguous to the basin of another river, and thus constitutes the 

 boundary-line of the two basins. From these margins the waters 

 descend on both sides towards their respective basins, which are 

 separated by them, and hence the whole line of these margins is called 

 a wattnked, properly the water-parting. [WATERSHED.] 



The basins of rivers vary greatly in size. A brook is the name com- 

 monly given to rivers of the smallest description. When such a river 

 rises near the sea or near a large river, into one of which it flows after 

 a short course, it consequently drains a very small surface. If tin- 

 waters should be increased by those of another brook, the name of 

 brook is changed for that of riralet. The basin of a rivulet U therefore 

 more complicated than that of a brook. One or more brooks descend 

 from the margin of the basin, and by uniting their waters with those 

 of the rivulet, increase its volume. When several rirulets unite and 

 so produce a considerable volume of running water, this watercourse 

 takes the name of rinr. But all such rivers do not reach the sea, or 

 even a lake; most of them join other rivers, ami thus a large river is 

 produced. This last-mentioned large river is called the i>rinri/Hil rirrr, 

 and those which increase its waters are called, with respect t.. it, 

 affarnU or trilmtana, and sometimes fatten or brmetei. In Syria 

 .UK I Arabia and north-eastern Africa, the riter-broott, or small streams 

 which flow only in the winter or the rainy season, are called mdiet, 

 a term frequently met with in the works of travellers in those 

 countries. 



The first waters of a river are generally derived from a spring, which 

 breaks out at the foot of a declivity, or on the side of some hill or 

 mountain ; and sometimes from a swamp or a lake. This U called the 

 room of a river. From this source the river descends through the 

 lowest part of its basin until it terminates its course in the sea, a lake, 

 or another river, and this termination is called the mtmtk of the river. 

 The cavity in which the running water flows is called the bed of the 

 river, and the solid land which bounds this bed is called its Ijantt. 

 The ktad-timm* of a great river are those, proceeding from their 

 sources, which by their union or confluence produce the first principal 

 stream, with which another principal stream may be afterwards 

 emJUemt, or which may receive tributaries. 



Most large rivers have their origin in very elevated mountains, or un 

 high table-lands, in descending from which a great difference with 

 respect to the rapidity of theirfcourse, and the nature of the country 

 through which they flow, is observed. Accordingly geographers divide 

 the whole of the course of such rivers into three divisions, the upper, 

 middle, and lower course. 



The *ppir course of such a river lies within a mountain region, and 

 its source is consequently at a great elevation above the sea. The 

 waters ran with greater or less velocity, according to the greater or 

 less-extent of the mountain-region, and the greater or less rapidity 

 wi'li which the whole region declines towards the country to which 

 the whole course of the river is directed. When the elevation of the 

 mountain-region rlnrresses with great rapidity, the current of the river 

 is extremely rapid, and presents a quick succession of cataracts and 

 rapids. The force of the current is so great that pieces of rock of con- 

 siderable size, which are frequently detached from the overhanging 

 missss, cannot resint it, and are carried down by the current, until 

 they reach a point where the rapidity of the descent begins to diminish. 

 The mountains which constitute the banks of the river often rise 

 several thousand feet above it, and their bases are united by slopes 

 forming an angle, over which the water runs on bare rocks, without 

 the least covering of earth. Thus the river does not flow in a valley, 

 but in a cleft or ravine, which cuts deep into the mountain innnKHi 

 Sometimes there is space enough for a path between the river and the 

 ' unn, but in many places this space U only obtained by artificial 

 as by cutting away a projecting portion of the rock, or by 

 a tunnel through it. Where either of these means cannot be 

 rl, the path is continued over the bed of the river by a wooden 

 _ i of greater or less extent, until a place is reached which offers 

 sufficient space for a path on the sides of the rocks. The course of 

 the river is generally in a straight line, but sometimes it makes short 

 and abrupt bends which form acute angles. In the last-mentioned 

 case it is, almost without exception, observed that the mountain* 

 which inclose the river have on one side a projection, and on the other 

 a recession, which correspond so exactly that if it were possible to unite 

 the two mountains, the projecting would exactly fit into the receding 



ARTS A-1D SCI. 1.1 V. VuL. VII. 



part. This peculiarity in the formation of the ravines of mountain 

 streams was observed by the Spaniards in the Andes of South America, 

 who called them qntbradas, or broken ; by this term tacitly assuming 

 that the phenomenon had been caused by a violent disruption of the 

 mountains. This description of mountain-streams and their ravines 

 applies particularly to those of the western Alps along their southern 

 declivity, to those rivers which constitute the upper branches of the 

 rivers Doria and Sesia, to the valleys of Anzasea and Vedro on the 

 southern side of the great road of the Simplon, and to the still larger 

 valley of Aosta, through which the road leads from Switzerland to 

 Italy over the mountain-pass of the St. Bernard. The military road 

 of the Romans was made through the Val d" Aosta ; but in these parts 

 it was only practicable for beasts of burden. Such deep ravines not 

 only occur between the gigantic elevations of a high range, but like- 

 wise in the elevated table-lands. According to Dr. Beke, the rivers of 

 Abyssinia, nearly all affluents of the Nile, or of its great tributaries, in 

 the early part of their course, flow over the level surface of the table- 

 land, being little more than muddy brooks, nearly without water in 

 the dry season, but overflowing their banks so as almost entirely to 

 inundate the plain country during the rains. They escape from the 

 plateau by precipitous falls of 80 or 100 feet or more, into fissures in 

 the rocky surface, at first only a few yards in breadth, but gradually 

 opening to the extent of several miles, down which the stream hurries 

 in a succession of falls and rapids, so as to descend several thousand 

 li-L-t in the course of a few miles. In these deep-cut valleys, the rivi-rs 

 thus soon reach a depression of 3000 or 4000 feet below the & 

 level of the table-land. The larger valleys are of considerable width ; 

 that of the Abai, or Nile of Bruce, the upper course of the Bahr-el- 

 Azrek, or Blue Kivcr [NILE, in UEOG. Div.j, for example, is at least 

 twenty-five miles between the extreme points where it breaks away 

 from the table-land on either side. " And as the country is wild and 

 irregular," remarks Dr. Beke, " it U easy for a traveller, who has not 

 taken a comprehensive view of the entire region, and who finds himself 

 shut up in such a valley with a mass of broken country NiiiToiiiuliiu; 

 him, to believe that in ascending from the river he is crossing a 

 mountain chain ; whereas, in reality, he has merely reached the con- 

 tiimation of the table-land which he had left on the opposite side of 

 the river." The great rivers of India present corresponding pheno- 

 mena to those of the East African table-land, but on a more immense 

 scale. [PLAISS.] Huuiboldt observes that the plain of Quito, \\hirh 

 is nearly 10,000 feet above the sea, is intersected by ravines, which 

 in some places sink so deep that their bottoms are hardly more than 

 2000 feet above the sea- level; and he adds that some of them 

 narrow as not to contain the smallest cultivable space. Similar ravines 

 intersect the table-lands of Guatemala and Anahiiac, where they are 

 called eanadtu, a term, however, which does not imply the existence 

 of rivers in them or relate to that circumstance, but merely to the 

 abrupt descent of land. 



Wh.-n the mountain-region through which the upper course of a 

 river lies descends with less rapidity, and consequently occupies a 

 much greater extent of country, the mountain-streams, as well as their 

 Lnnks, present very different features. Both the streams and the 

 lianks show that the descent of the whole mass is not by a regular 

 slope, but is formed by an alternation of plains and declivities ; in 

 ascending such a mountain-stream, it is found that in certain places 

 the rocky misses approach so near to the banks, as to leave hardly 

 room enough for the river, and in these narrows the current i 

 extremely swift, and generally a continual rapid, interrupted by falls 

 of moderate height. These narrows however rarely extend more than 

 i few miles. Above them the mountains recede to some distance from 

 >oth sides of the river ; and thus a basin is formed, in the middle of 

 which the river flows with a comparatively slow current, nut over ban: 

 ocks, but over a gravelly ln.il, and between low banks of earth. The 

 Kittom of the basin is level, or descends with a gentle slojw, and may 

 v cultivated or used as pasture-ground. In some of the riv.-rs \\ hi.-ii 

 descend from the central and eastern Alps, this alternation of narrow 

 *! and basins occurs several times. Thus the Hm.-.-i. along which 

 .he great road runs which leads over the mountain-pass of St. Gothard, 

 rushes with incredible velocity through the ravine of the Hospendal, 

 and falls 1800 feet before it reaches the basin of the valley of Ursern, 

 which is nearly eight miles long and more than half a mile wid. 

 n which it runs with a gentle course. At the northern extremity of 

 .he valley of Ursern the river enters the second narrow at the 

 Jrm-rloch. This narrow, which extends about three miles to Gcshim-n, 

 s extremely contracted, and within these limit* the river descends 

 1074 feet, forming a succession of small cataract*. Below this is tin- 

 wain of the Krachenthal, which i not so widu as that of Ursern, and 

 about six miles long. The course of the river within this basin in 

 rapid, but there arc no cataracts. From this valley the river escapes 

 iy the third narrow, which is about four miles long, and also very 

 contracted ; it terminates at the village of Am-Stiig, where the Reims 

 enters the valley of Uri, in which it flows until it mingles its waters 

 with those of the lake of Uri (Urner-see), as the southern part of the 

 Vierwaldstadter-see is named. The same conformation is observed in 

 the southern declivity of the Alps, where the river Ticino descends 

 rom the mountain-pass of St. Gothard. This river runs in a ravine 

 rom the Hospendal to Airolo, in which it descends about 2880 feet. 

 (t then enters the upper valley of Leveutina, which is about seven 



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