Surface water

Surface water

Land surface water is the water that runs (watercourse) or collects on land surface (water bodies). There are sea, lake, river, swamp and other types of water. Surface water is confined in surface water bodies on a permanent or temporary basis. There are the following types of surface water bodies: seas, lakes, rivers, swamps, and other water courses and bodies. Surface water is contrasted with ground water.

A river is a natural water flow (watercourse) running through a channel cut down by it, i.e. perennial natural channel, and fed by surface runoff and groundwater runoff from its catchment area. A river is an object of study within one of the branches of land hydrology, viz. river hydrology (potamology).

Each river has its source (head) and place of inflow into the sea, lake, or confluence with another river (mouth).

Rivers directly falling into oceans, seas, or disappearing in deserts and losing themselves in swamps are called main streams; ones inflowing into main streams are called tributary streams (or inflows).

A main stream with all its inflows makes up a river system characterized by drainage density.

The land surface from which a river system collects water is called a watershed or catchment area. A catchment area, together with the upper layers of the earth’s crust, covering a river system and separated from other river systems by watershed divides is called a river basin.

Rivers usually flow through elongate depressed land forms, valleys, the lowest part of which is called a channel and the valley part flooded by high river water is called a floodplain or floodplain terrace.

Rivers have deeper sections (reaches) and shallow-water sections (ripples). The line of the deepest water (thalweg) forms a waterway; the line of fastest flow is referred to as a midstream.

The boundary of a river stream is called a bank. Depending on their location along the stream with respect to the channel centerline, they divide stream banks into right bank and left bank.

A difference in the river head and mouth elevation is referred to as river gradient; ratio of the gradient of a river (or its reaches) to its (or their) length is called a river (section) slope and is expressed as a percentage (%) or per mille (‰).

Depending on relief of the terrain where rivers run, those are divided into mountain and lowland ones. On many rivers, mountain reaches alternate with lowland reaches. Mountain rivers are marked, as a rule, by steep slopes, rapid streams; they run through narrow valleys; erosion processes prevail thereon. Lowland rivers are characterized by meanders that are formed in the course of river bed evolution. On lowland rivers, riverbed erosion reaches alternate with accumulations of sediment loads causing formation of braid bars and ripples, and deltas are formed in river mouths. In some cases, arms branched off a river merge with other rivers.

Rivers are very irregularly distributed over the Earth's surface. One can be mark major watershed divides, boundaries of the drain region of the waters flowing to different oceans, on every continent. The main Earth’s divide breaks down the surfaces of continents into two major basins: Atlantic-Arctic (flow from the area of which comes to the Atlantic-Arctic Oceans) and Pacific ones (flow from the area of which comes to the Pacific and Indian Oceans). The drainage from the first watershed is much greater than that from the second one.

The river (drainage) network density and thread of stream depend on a set of current environmental conditions and often, to some extent, keep the traits of former geological epochs. A river network has the highest density in the equatorial belt where the world’s greatest rivers, Amazon and Congo, run; in tropical and temperate belts, especially in mountain zones (Alps, the Caucasus, Rocky Mountains, etc.), also river networks have high density. In desert zones, here and there running rivers are widespread, which rarely, at snow melting or heavy showers, turn into large streams (flat-land Kazakhstan rivers, Saharan wadis, Australian creeks, etc.).

A river system is a group of rivers discharging their waters through one common channel into a sea, lake, or some other water body.

It consists of a principal river (main stem of the system) and first, second, and following (higher) order tributaries. First-order tributaries are those directly inflowing into the main stem; second-order those are tributaries of the first-order tributaries, etc. Sometimes, the river order name comes back to front from small rivers to the main stem.

A river system is nominated according to the name of the main stem which is usually the longest and most abundant river of the system.

Water body basin (also drainage basin, catchment area, watershed) is a territory on the land surface from which all surface and ground waters flow in this water body, including as well its various inflows. Most often this refers to river basins.

Every water body basin includes surface and subsurface drainage basins. Surface drainage basin is a land surface area from which water comes to a given river system or a certain river.

Subsurface drainage basin forms strata of loose deposits from which water flows into a river network. In general, surface and subsurface drainage basins do not coincide. However since it is quite difficult to identify the boundaries of a subsurface drainage basin, only the relevant surface drainage basin is regarded as the size of their river basin.

Errors arising in the result of a conventional matching of the sizes of a basin and its subsurface drainage basin may turn out to be significant only for small rivers and lakes as well as for large rivers running under geological conditions that provide good water exchange between adjacent basins (e.g. karst). The boundary between the basins of separate water bodies lies along the watershed divide.

There are drain/open (with a connection to world’s oceans) and closed/inland (endorheic) drainage basins. Closed drainage basins are represented by inland flow areas that have no connection with the world ocean through river basins. Basins may have widely differing shapes and sizes which depend on geographical position, landscape, and geologic structure of the local area. Tributaries have their small basins the aggregate area of which comes to the area of the main steam basin.

Source: Wikipedia