Small streams, flowing down on slopes, merge in the rivers which run into the seas or lakes. At all seeming simplicity of this scheme process becomes complicated many factors.
The Areas covered by river systems, are called as water modular (or river) pools. They are separated from each other by natural water separate ridges, or watersheds. For example, the Great continental watershed passes in the North America across Rocky mountains from the north on the south. On its one party of the river flow in the western direction to Pacific ocean, and on another - on the northeast to Arctic ocean, on the east to Atlantic ocean or on the southeast to Gulf of Mexico.
Together with inflows which join them on a way to the sea, the rivers form intricate, original drawings of a hydrographic network, well visible from air and familiar to us on cards. In separate places the configuration of these networks is so difficult that at geomorfologov (the scientists studying formation and change of a lay of land) there are serious problems with definition of their origin.
Hydrographic networks can have different configurations depending on several factors: a climate, relative hardness and friability of superficial breeds, a district bias, and also its geological history (including an earth movement and the mountain building periods). geomorfologov also interests, why some areas abound with the rivers while in the next territories (at almost equal quantity of loss of deposits) there are some streams.
There are about ten various configurations of such networks, from them the most widespread - branched out, rectangular and radial. The elementary is the branched out (treelike) network looking on a card as vetvjashcheesja a tree. It meets there where the channel of the rivers is laid as a whole homogeneous (often clay) to breed and where as a result of earth movements there were no such geological formations, as dumps (breaks of rocks), strongly influencing a drain of a surface water.
The Rectangular (trellised) network is characteristic for skarplendov - areas with the steep hilly ridges, formed by rather firm breeds and divided by wide valleys with more friable breeds leaving on a surface. Local rivulets run into the basic river flowing between hills, at right angle. As a result in districts with such relief there is an accurate rectangular hydrographic network.
the Radial network
The Third type of a hydrographic network is similar to wheel spokes as the rivers in this case spread in all directions from the center. Such network is called as radial or centrifugal. It often meets around mountains of the conic form (for example, volcanoes) or dome-shaped mountains. Domes are formed or folds of rocks, or under the pressure of a rising surface of magma (the fused breed).
Density of a network
Density of a hydrographic network of any district is defined by distance between separate waterways in this network.
Density of a river network is influenced by some factors, including a climate. In rainy areas the most part of rain water flows down on a surface and forms a dense network of water currents.
Other factor - type of spreading breed. The rivers meet there where impenetrable breeds through which it is hard to water to filter. Are bared is more often and, on the contrary, in exit places on a limestone surface (water-permeable breed) water filters into a ground through many cracks (crack) and a time in the breed, named karstic funnels or ponorami. Thus the earth surface remains dry, and water begins the way on underground cracks, channels and caves.
Development of river system
For occurrence of river system rains and the earth on which they drop out and on which flow down are necessary. All begins with the moment of hit of a rain on again formed or changed surface of the earth. It occurs, for example, as a result of formation of a new volcano after a series of strong eruptions or if slowly "т№фртыштрх=ё " a mountain ridge at collision of two plates of a firm cover of the Earth. As soon as any breed adjoins to air, its natural erosion begins. The main reason of erosion in areas of a damp climate is the rain water forming sometimes streams, its surfaces flowing down by the ground at any bias.
the Rivers which direction of a current is caused by a primary bias of a surface, are called konsekventnymi. Inflows of the basic river are called lateralno-konsekventnymi or, if they run into the river at an acute angle (as in case of the branched out hydrographic network) - insekventnymi. However the situation often becomes complicated that again formed terrestrial surface can consist of breeds of various hardness. As a result konsekventnaja the river behaves differently depending on, whether it proceeds on more friable or firmer breeds. Breeds of the first type (for example, clay) it washes away and forms wide valleys, and only narrow valleys to it it is possible to cut in firm breeds which, finally, remain in the form of mountain ridges and hills. Such narrow valleys often name gorges.
Similar landscapes are typical for Southern England with its ridges of hills from steady breeds of limestone and a chalk. Between hills wide dales with clay soil on which inflows konsekventnyh the rivers flow lie. geomorfologi name such inflows subsekventnymi waterways. The konsekventnye rivers cutting in hills of gorge and flowing in a direction of the basic bias of district, together with subsekventnymi the waterways flowing on clay dales it is perpendicular to the basic bias, often form a rectangular hydrographic network.
In subsekventnye waterways often run other rather long inflows which are flowing down on more gentle slopes, formed by crests of firm breed, and named secondary konsekventnymi waterways (flowing in parallel falling of layers). Inflows flow in an opposite direction on an abrupt steep slope more shortly and also join in subsekventnye waterways. Them name obsekventnymi or anaklinalnymi waterways.
Folds of rocks
The New terrestrial surface is formed under the influence of the enormous lateral pressure caused by movement of plates of an external cover of the Earth. Thus flat layers of rock form folds like the crumpled cloth, and there is a number sinklinalej (the bent folds) and anticlines (the curved folds). Sinklinali anticlines - from treshchinovatyh, shattered and uploshchennyh breeds consist of the condensed breeds, and. As a result the last are more subject to river erosion.
Often as a result of washout of anticlines valleys while resistant erosion sinklinali turn to mountains are formed. Such phenomenon when real mountains and valleys "юсЁр=э№х in relation to geological structures, is called "юсЁрЁхээ№щ Ёхыіх¶". Development of a hydrographic network on the turned relief begins in the regular way: the basic konsekventnaja the river flows on the natural hollow formed sinklinalju. But treshchinovatye breeds of the next anticline soon collapse subsekventnymi waterways, and obsekventnye streams start to flow down on abrupt internal slopes.
The Rivers wash away valleys not only in a direction from an upper course to a mouth, but sometimes and from lower reaches upstream. This phenomenon named moving back erosion, often grows out of spring undermining of slopes or dredging of a stony ground round a source (source) of the river.
River Interception is a form of natural capture of a drain of other river which takes place when powerful subsekventnyj the waterway lays a way in the opposite direction in the bared friable breeds. This process removes a watershed between subsekventnoj the river and adjacent river system. Finally subsekventnyj the waterway can make the way through a watershed and intercept a drain of the next river, thus, grasping its top inflows, or an upper course then its waters go to a channel subsekventnogo a waterway. The decapitated river turns to the dying stream flowing on a valley which it never could lay itself.
The Type of drainage system in case of river interception can be defined on the inflows running into the basic river around a return loop - an abrupt bend. geomorfologi name such hydrographic networks borodoobraznymi.
River Interception - only one of variants of tap of its waters. It can be caused and natural obstacles which have appeared as a result of landslips. And the person can direct the rivers to other party for an irrigation of the droughty earths.
But the main cause of infringement of process of a drain of water throughout all geological history were gljatsialnye processes - formation of a terrestrial surface by huge files of ice. So, waters of a riverhead of Missouri in the North America once aspired on the north to Hudson bay. But during last glacial age approaching ice boards have forced this river to turn the channel towards the river Mississipi and further on the south to the Mexican gulf.
the Imposed drain
Some river systems managed to remain invariable throughout a geological history. Hydrographic networks which were generated in conditions for a long time the disappeared ancient reliefs, but have thus kept the primary configuration, are called as the imposed drain. This phenomenon takes place when almost flat files of a land located near to a sea level, start to rise slowly, or, on the contrary, - at sea level fall. As a result of such changes the bias rusel the rivers increases, water stream becomes gradually more powerful, and there are river valleys washed up in breed. This process is called as a rejuvenation.
The Rivers often continue to flow on the channel, running all is deeper in spreading breed. The former river bends turn to the deep valleys named vrezannymi meanders. The remained sites of a former valley which are now it is high over a new channel of the river, are called "=хЁЁрёрьш юьюыюцхэш ". Some (as, for example, the Grand Canyon in the USA) were formed of the most beautiful river valleys as a result of a rejuvenation caused by an earth movement.
The Rivers, continuing to wash away the valleys while as a result skladchatosti and raisings slowly arise mountain ridges, are called antetsedentnymi as waterways. It occurs because age of the rivers of more prescription of earth movements. So, antetsedentnye the rivers flow through the powerful mountain chain of the Himalayas generated as a result of collision of two plates for last 50 million of years. Here the rivers had to struggle with growing mountains, but, thanks to the more abrupt biases and the increased inflow of water (especially in the spring - in snow thawing in mountains), the rivers have got necessary power for breed washing out. In some places they cut tesniny depth to 1500 m.