Graham's Magazine, Vol. XLI, No. 6, December 1852

The periodical rise of rivers is either diurnal, semi-annual, or annual, and proceeds from a variety of causes. Where streams descend immediately from mountains covered with snow, the heat of the sun melting the snow produces high water every day, the increase being the greatest in the hottest days. In Peru and Chili there are small rivers which flow only during the day, because they are fed entirely by the melting of the snow upon the summit of the Andes, which takes place only when the solar influence is in action. In Hindûstan, and some parts of Africa, rivers exist, which, though they flow night and day, are, from the accession of snow-water, the greatest by day. Those rivers also which fall into the sea have their level daily varied by the tidal wave for some distance from their mouths, the extent through which the influence of the tides is felt being modified by the breadth and shape of their channels and the force of their current. The wider and more direct the bed of a stream communicating with the ocean, and the slower its motion the farther the tide will penetrate; whereas a narrow and sinuous course, and a great velocity, offer obstructions to its progress. The tide of the Atlantic is perceived four hundred miles along the course of the Amazon, and that of the German Ocean extends about seventy miles up the Thames. Important facilities are afforded to the navigation of many rivers by this circumstance, for they are only accessible to vessels of large burden at high water. The rapid of Richelieu, on the St. Lawrence, where the river contracts, and has its course obstructed by rocks, impedes the navigation between Montreal and Quebec, except at high tide, when the water rises fifteen or eighteen feet, and the rapid entirely disappears. A semi-annual or annual rise alone distinguishes the rivers of inter-tropical regions, and of countries bordering on the torrid zone. The semi-annual rise is a feature of those rivers which drain high mountain ranges, and proceeds from the two independent causes, of the melting of the snows in spring or summer, and the great seasonal rains to which such districts are subject. The rivers which have only one annual rise are influenced by the latter cause alone, or by the two acting coincidently, and producing a grand periodical flood. The Tigris rises twice in the year – first, and most remarkably, in April, in consequence of the melting of the snows in the mountains of Armenia; and secondly, in November, through an accession from the periodical rains. The Mississippi likewise is subject to two rises in the year – one about January, occasioned by the periodical rains that fall toward the lower part of its course; but the grand flood commences in March, and continues till June, proceeding from the melting of the ice in the upper part of the continent, where the Missouri and other tributary streams have their origin. A very striking spectacle is exhibited by this river in the season of inundation. It rises from forty to fifty feet in some parts of its course, and is from thirty to a hundred miles wide, all overshaded with forest, except the interior stripe consisting of its bed. The water stands among the trees from ten to fifteen feet in height, and the appearance is exactly that of a forest rising from a lake, with its waters in rapid motion. For the protection of the cultivated lands, and to prevent their conversion into permanent swamps, an embankment, called the Levee, has been raised, which extends two hundred miles on the eastern shore of the river, and three hundred on the western. In Asia, the Ganges, Indus, and Euphrates exhibit inundations upon a similarly great scale. The Euphrates slightly increases in January, but the grand flood begins soon after the middle of March. It attains its height about the 20th of May, after which it falls rapidly till June. The decrease then proceeds gradually until the middle of November, when the stream is at its lowest. The rise of the water at Anah, above the site of ancient Babylon, occasionally amounts to eighteen feet, sometimes entering that town, running with a velocity exceeding five miles an hour. The moment that the waters of the river recede, the rice and grain crops are sown in the marshes, and villages of slightly made reed cottages are reared in their neighborhood. These last, in consequence of being suffered to remain too long, are often surprised by the returning inundation, and it is no uncommon spectacle for their occupants to be seen following the floating villages in canoes, for the purpose of recovering their property. But of all inundations that of the Nile, if not the most extensive, is the most regular, and has become the most celebrated, from the knowledge of it going back to the earliest periods to which history recurs. The rise of the river commences about the time of the summer solstice, attains its maximum height at the autumnal equinox, remains stationary for some days, and then gradually diminishes till the time of the winter solstice. The ancients, unacquainted with the climate of the interior country from which it descends, and not caring in general to inquire for physical causes, possessing also a very limited knowledge of terrestrial phenomena, deemed the annual overflow of the Nile a unique event, and attributed it to the special interference of a supernatural power. Lucretius, however, who soared in many respects above the prejudices of his age concerning the natural world, assigned it to a proper cause; though he ascribes too much influence to the Etesian wind, and shows his imperfect acquaintance with the geography of the globe, by supposing the occurrence without a parallel.

   “The Nile now calls us, pride of Egypt’s plains:  Sole stream on earth its boundaries that o’erflows  Punctual, and scatters plenty. When the year  Now glows with perfect summer, leaps its tide  Proud o’er the champaign; for the north wind, now  Th’ Etesian breeze, against its mouth direct  Blows with perpetual winnow; every surge  Hence loiters slow, the total current swells,  And wave o’er wave its loftiest bank surmounts.  For that the fixed monsoon that now prevails  Flows from the cold stars of the northern pole  None e’er can doubt; while rolls the Nile adverse  Full from the south, from realms of torrid heat,  Haunts of the Ethiop tribes; yet far beyond  First bubbling, distant, o’er the burning line.    Then ocean, haply, by th’ undevious breeze  Blown up the channel, heaves with every wave  Heaps of high sand, and dams its wonted course;  Whence, narrower, too, its exit to the main,  And with less force the tardy stream descends.    Or, towards its fountain, ampler rains, perchance,  Fall, as th’ Etesian fans, now wide unfurled,  Ply the big clouds perpetual from the north  Full o’er the red equator; where condensed,  Ponderous and low, against the hills they strike,  And shed their treasures o’er the rising flood.  Or, from the Ethiop mountains, the bright sun  Now full matured with deep-dissolving ray  May melt th’ agglomerate snows, and down the plains  Drive them, augmenting hence th’ incipient stream.”

The annual overflow of the Nile is now well known to proceed from the heavy periodical rains within the tropics. They fall in copious torrents upon the great plateau of Abyssinia, which rises, like a fortress, 6000 feet above the burning plains with which it is surrounded on every side, attracting the clouds, cold fogs, and tremendous showers, enveloping An Rober, the capital, while, whenever the curtain of mist is withdrawn, the strange contrast is presented of the sulphureous plains, visible below, where the heat is 90°, and the drought excessive. A peculiar character has been given to this district by the violence of the periodical rains. Bruce speaks of the mountains of this table-land, not remarkable for their height, but for their number and uncommon forms. “Some of them are flat, thin, and square, in shape of a hearth-stone or slab, that scarce would seem to have base sufficient to resist the winds. Some are like pyramids, others like obelisks or prisms, and some, the most extraordinary of all, pyramids pitched upon their points, with their base uppermost.” Mr. Salt confirms this delineation in the main. The peculiar shapes referred to have been formed by the action of the torrents discharged from the clouds, which have, for ages, been skeletonizing the country, dismantling the granite with its kindred masses of the softer deposits, gradually wearing away also these harder rocks, and carrying along the soil of Ethiopia, strewing it upon the valley of the Nile, to the shores of the Mediterranean. When Bruce was ascending Taranta, a sudden noise was heard on the heights louder than the loudest thunder, and, almost directly afterward, a river, the channel of which had been dry, came down in a stream several feet in depth, and as broad as the whole bed. Hence the steeple and obelisk form of the rocks, with their naked aspect – which has, not unaptly, been compared to bones stripped of their flesh.

In the tropical countries of South America, the seasonal rains are, perhaps, more intensely copious than in any other part of the torrid zone, and the floods of its rivers are of corresponding magnitude. At the mission of San Antonio de Javita, on the Orinoco, during the wet season, the sun and stars are seldom visible, and Humboldt was told by the padre, that it sometimes rained for four or five months without intermission. The traveler collected there, in five hours, 21 lines of water in height on the first of May, and 14 lines on the 3d, in three hours; whereas at Paris there fall only 28 or 30 lines in as many weeks. Humboldt traces the transition from the one great season of drought to that of rain, which divides the year, in an interesting manner, with the atmospheric phenomena which accompany the change. About the middle of February in the valleys of Araqua, he observed clouds forming in the evening, and in the beginning of March the accumulation of vesicular vapors became visible. “Nothing,” he remarks, in beautifully graphic style, “can equal the purity of the atmosphere from December to February. The sky is then constantly without clouds, and should one appear, it is a phenomenon that occupies all the attention of the inhabitants. The breeze from the east and north-east blows with violence. As it always carries with it air of the same temperature, the vapors cannot become visible by refrigeration. Toward the end of February and the beginning of March, the blue of the sky is less intense; the hygrometer gradually indicates greater humidity; the stars are sometimes veiled by a thin stratum of vapors; their light ceases to be tranquil and planetary; and they are seen to sparkle from time to time at the height of 20° above the horizon. At this period the breeze diminishes in strength, and becomes less regular, being more frequently interrupted by dead calms. Clouds accumulate toward the south-east, appearing like distant mountains with distinct outlines. From time to time they are seen to separate from the horizon, and traverse the celestial vault with a rapidity which has no correspondence with the feebleness of the wind that prevails in the lower strata of the air. At the end of March the southern region of the atmosphere is illuminated by small electric explosions, like phosphorescent gleams, confined to a single group of vapors. From this period the breeze shifts at intervals, and for several hours, to the west and south-west, affording a sure indication of the approach of the rainy season, which, on the Orinoco, commences about the end of April. The sky begins to be overcast, its azure color disappears, and a gray tint is uniformly diffused over it. At the same time the heat of the atmosphere gradually increases, and, instead of scattered clouds, the whole vault of the heavens is overspread with condensed vapors. The howling monkeys begin to utter their plaintive cries long before sunrise. The atmospheric electricity, which, during the period of the greatest drought, from December to March, had been almost constantly in the day-time from 1·7 to 2 lines to Volta’s electrometer, becomes extremely variable after March. During whole days it appears null, and again for some hours the pith-balls of the electrometer diverge from three to four lines. The atmosphere, which in the torrid as in the temperate zone is generally in a state of positive electricity, passes alternately, in the course of eight or ten minutes, to a negative state. The rainy season is that of thunder-storms. The storm rises in the plains two hours after the sun passes through the meridian, and therefore shortly after the period of the maximum of the diurnal heat in the tropics. In the inland districts it is exceedingly rare to hear thunder at night or in the morning – nocturnal thunder-storms being peculiar to certain valleys of rivers which have a particular climate.” The substance of the explanation of the preceding phenomena, by the philosophic writer of the statement, may be briefly given:

The season of rains and thunder in the northern equinoctial zone coincides with the passage of the sun through the zenith of the place, the cessation of the breezes or north-east winds, and the frequency of calms and furious currents of the atmosphere from the south-east and south-west, accompanied with a cloudy sky. While the breeze from the north-east blows, it prevents the atmosphere from being saturated with moisture. The hot and loaded air of the torrid zone rises, and flows off again toward the poles, while inferior currents from these last, bringing drier and colder strata, take the place of the ascending columns. In this manner, the humidity – being prevented from accumulating – passes off toward the temperate and colder regions, so that the sky is always clear. When the sun, entering the northern signs, rises toward the zenith, the breeze from the north-east softens, and at length ceases; this being the season at which the difference of temperature between the tropics and the contiguous zone is least. The column of air resting on the equinoctial zone becomes replete with vapors, because it is no longer renewed by the current from the pole: clouds form in this atmosphere, saturated and cooled by the effects of radiation and the dilatation of the ascending air, which increases its capacity for heat in proportion as it is rarefied. Electricity accumulates in the higher regions, in consequence of the formation of the vesicular vapors, the precipitation of which is constant during the day, but generally ceases at night. The showers are more violent and accompanied with electrical explosions, shortly after the maximum of the diurnal heat. These phenomena continue until the sun enters the southern signs, when the polar current is reëstablished, because the difference between the heat at the equinoctial and temperate regions is daily increasing. The air of the tropics being thus renewed, the rains cease, the vapors are dissolved, and the sky resumes its azure tint.

The Orinoco, when in flood, inundates a vast extent of country, six hundred miles in length, and from sixty to ninety in width. Its waters cover the savannas along its banks to the depth of twelve or fourteen feet, giving to them a lake-like appearance, in the midst of which farm-houses and villages are seen rising on islands but little elevated above the surface. The wild cattle perish in great numbers, and fall an easy prey to the carrion-vultures and alligators. In one part of the river Humboldt found marks of recent inundation at 45 feet above the ordinary level; but above the greatest height to which its waters are now elevated, he traced its ancient action at 106 or even 138 feet. “Is this river, then,” inquires he, “the Orinoco, which appears to us so imposing and majestic, merely the feeble remnant of those immense currents of fresh water which, swelled by Alpine snows or by more abundant rains, every where shaded by dense forests, and destitute of those beaches that favor evaporation, formerly traversed the regions to the east of the Andes, like arms of inland seas? What must then have been the state of those low countries of Guiana, which now experience the effects of annual inundations! What a prodigious number of crocodiles, lamartines, and boas must have inhabited these vast regions, alternately converted into pools of stagnant water and arid plains! The more peaceful world in which we live has succeeded to a tumultuous world. Bones of mastadons and real American elephants are found dispersed over the platforms of the Andes. The megatherium inhabited the plains of Uruguay. By digging the earth more deeply in high valleys, which at the present day are unable to nourish palms or tree-ferns, we discover strata of coal, containing gigantic remains of monocotyledonous plants. There was therefore a remote period when the tribes of vegetables were differently distributed, when the animals were larger, the rivers wider and deeper. There stop the monuments of nature which we can consult.”

The bifurcation of flowing waters is sufficiently illustrative of the physics of the earth to justify a few words: – Europe presents two instances of bifurcation – one in Italy, between the Arno and the Chiana; the other in Germany, between the Haase and the Else, in Westphalia. Asia also possesses, on the peninsula lying beyond India, two grand examples. What we know about them is principally founded upon the information gathered by Dr. Buchanan Hamilton, during his stay in Ava, the capital of the Birman empire. But it is to be observed, that the communications of these Indian rivers, at least as regards those in the country of the Jun-Shan, appear doubtful. British travelers have succeeded in penetrating, from Maulmain, at the mouth of the river Saluan, into the interior of the country of the Shan, which has been so long shut up; but Lieutenant M’Leod, who reached the river of Kambodja, says nothing to confirm the information Dr. Buchanan gives us. The most important of all known divisions in the form of a fork, however, is the bifurcation of the Orinoco, which communicates through the Cassiquiare with the Rio Negro, and through this river with the Amazon. It has already been remarked, that the observations of A. von Humboldt have put this bifurcation beyond a doubt; but the subject deserves a recurrence to it, as presenting to our attention a singular physical feature, and illustrating the energy of the great traveler of modern times.

He and Bonpland left Carracas in the year 1800, crossed the valleys of Aragua, and the Llanos of Calabozo – excellent pastures, which separate the cultivated part of Venezula from the region of the forests and missions – and embarked at San Fernando, on the Rio Apure, to follow its course downward to its discharge into the principal branch of Orinoco. They then ascended the Orinoco, passing its two great cataracts of Apures and Maypures, and reached the village of San Fernando de Atabapo, situated at the junction of the Guaviare and Atabapo, and near lat. 4° N. Here they left the river, and sailed up the Atabapo to the mouth of the Rio Temi, which latter they followed as far as its confluence with the Tuamini, and arrived at the village of San Antonio de Javita, formerly mentioned as remarkable for its amount of rain. From this point the Indians carried their boat across the isthmus which separates the Tuamini from the Rio Pimichin, the travelers following on foot, passing through dense forests, often in danger from the number of snakes that infested the marshes. Embarking on the Pimichin, they came in four hours and a half into the Rio Negro. “The morning,” says Humboldt, “was cool and beautiful. We had been confined thirty-six days in a narrow canoe, so unsteady that it would have been upset by any one rising imprudently from his seat, without warning the rowers to preserve its balance by leaning to the opposite side. We had suffered severely from the stings of insects, but had withstood the insalubrity of the climate; we had passed without accident the numerous falls and bars that impede the navigation of the rivers, and often render it more dangerous than long voyages by sea. After all we had endured, I may be allowed to mention the satisfaction which we felt in having reached the tributaries of the Amazon.” The Rio Negro, which flows into that river, was navigated downward as far as San Carlos, then supposed to lie under the equator, but actually about 2° N. From thence the travelers retraced the river, passed from it into the Cassiquiare, and again entered the main channel of the Orinoco, three leagues below the mission of Esmeralda; thus demonstrating a junction between the two great floods of the Amazon and Orinoco, which had been, in the year 1798, declared by Bauche to be a geographical monstrosity. The bifurcation of the Orinoco takes place in the following manner: – The river, issuing from among the mountains, reaches the opening of a valley or depression which terminates at the Rio Negro. Here it divides into two branches, the smaller, or the Cassiquiare, turning off to the south, while the main stream continues its original direction – west-north-west. A reference to Humboldt’s map, of which we give a translated copy, will render further explanation unnecessary.

The preceding notices refer to what have been appropriately styled the “might rivers,” and the “great rivers,” none of which are to be found in Europe. Its noblest running waters belong to a third grade. “These,” says Inglis, “I would designate the large rivers; for great and large are not entirely synonymous; and, to most minds, the term great river and large river, will present a distinct image. The lower we descend in the scale, the more numerous do we find the species. The continent of Europe abounds with examples of the third class – such as the Rhine, the Danube, the Rhone, the Elbe, the Tagus, the Ebro, and the Guadalquivir. The fourth class is still more numerous; and of this class, which I would call considerable rivers, we may find examples at home. Father Thames takes the lead; and the Severn, and perhaps the Trent, the Clyde, the Tweed, the Tyne, and the Tay, may be entitled to the same distinction. On the continent, it would be easy to name a hundred such; let me content myself with naming the Loire, the Meuse, the Soane, the Garonne, the Adige, and the Maine. Fifthly, come the small rivers. Multitudinous they are; but as examples, I may name the Wye, the Dart, the Derwent, the Dee, the Aire, the Spey, the Ex, and a thousand such; while on the continent, of the same class, may be mentioned the Gare, the Seine, the Reass, or the Sombre. The word river can no longer be employed, for now come the family of streams – nameless, except to those who live upon their banks: the rivulets follow; and, lastly, we close the enumeration with rills.” The small rivers, with the streams subordinate to them, are especially rife in countries where there is the vicinage of the sea, and high elevations on the land. This renders them so abundant in such districts as the Greek peninsula. There, Alpine tracts of territory collect from the atmosphere the vapors of the contiguous sea, arrest the castellated glories of cloudland, and awaken in the valleys and plains the refreshing music “of the voice of many waters.” The commerce of kingdoms distinguishes not the rivers of this classic soil, but they are familiar with the charms of nature, add effect to the sublime and wild in its scenery, and clothe with heightened grace the soft and pastoral. Following the course of the Angitas up to its source, we come to one of the most picturesque sites in Macedonia, supposed to be the nymphæum or grotto of Onocaris. Blocks of marble, rudely piled, as if tossed together by an earthquake, obstruct its entrance, which can only be passed in a crawling posture; but these difficulties being overcome, a cave like a temple appears, from the farther end of which runs the limpid stream, flowing silently over a sand bed, but rippling when it escapes from the grotto. In a recess, there are some remains of ancient masonry below an aperture, through which a mysterious light finds its way.

    “Pure element of waters! wheresoe’er   Thou dost forsake thy subterranean haunts,   Green herbs, bright flowers, and berry-bearing plants,   Rise into life, and in thy train appear.”

Upon the large circular valley-plain of Bœotia, the heights of Parnassus on the west, Helicon on the south, and Cithæron on the east, send down streams, covering the undulating surface of this Classic Land with a life-sustaining vegetation.

The same physical causes – high lands and the contiguous sea – operate, in Judea as in Greece, to render it a well-watered country – a “land of brooks,” according to its Scripture designation. There are no considerable rivers, owing to the scanty extent of its hydrographical basins; but the melting of the snow on the high mountains of Syria, and the periodical sound of an “abundance of rain,” contribute to furnish an ample irrigation. Its principal stream – the Jordan – though only one of the fifth class, and not remarkable for picturesque beauty except in the upper part of its course, has a sacred and historic interest, which will always strongly attract attention to it, while it exhibits a singular physical peculiarity. This is the depression of the valley, in which it flows, below the level of the Mediterranean, through the whole distance between the Sea of Tiberias and the Dead Sea; and the great inclination of its descent from the one to the other, amounting at a mean to very nearly eighteen feet per mile. Hence the force of its current, notwithstanding a comparatively small volume of water, and the few windings that mark its channel. Speaking of its appearance near the site of Jericho, Dr. Robinson states: “There was a still though very rapid current. We estimated the breadth of the stream to be from eighty to one hundred feet. The guides supposed it now to be ten or twelve feet deep. The current was so strong, that even Komeh, a stout swimmer of the Nile, was carried down several yards in crossing.” Upon the authority of some phrases in the English version of the Scriptures, which, perhaps, do not express the sense of the original Hebrew, it has been generally supposed that the Jordan periodically inundated the country in its neighborhood, at, and for some time after, the Israelitish conquest of it. If this were so, either the river must have worn for itself a deeper bed, or the quantity of rain in Palestine must have largely diminished, for there is now no overflow of its banks. At present, the “swellings of Jordan” – one of the phrases alluded to – amount only to a slight annual rise. Copious rains descend upon the mountains round its sources, and the melting of the snows of Lebanon supply numerous temporary torrents; but these contributions are received into the capacious basins of the lakes Merom and Tiberias, and are there spread over an extensive surface, so as to prevent the level of the river from rising into inundation.