Post on 18-Jan-2018
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RIVERS DRAINAGE BASINS Important Definitions / Notes
Tributary: a stream or river that joins a larger river. Confluence:
the point at which two rivers meet. Precipitation: any water that
falls from the atmosphere viz. rain snow, sleet or hail. Headwaters
/ Source: the furthest point along the course of a river from its
estuary, mouth or confluence with another river i.e. where the
river starts. Confluence and tributary of Sligachan River, Isle of
Skye.
Pollution at the mouth of the Millers River where it enters the
Connecticut River. Millers River is the tributary and its mouth is
also a confluence. Important Definitions / Notes
Headwaters may be in a marsh or formed from glacial melt waters, in
a lake or spring. Mouth: the part of the river that flows into a
lake, reservoir, sea, oceanor estuary. Groundwater: water stored
underground in permeable rock such chalk or sandstone. The source
of Nile from the underwater spring at the neck of Lake Victoria,
Jinja. The source of the Irrawaddy River Lake Laka The source of
the Rhume River in Germany is a karst spring Source of the River
Ethiope, Nigeria deepest inland waterway in Africa is a spring at
the base of a silk cotton tree El Nevado Mismi:This ice mountain is
on the continental divide, one side drains through the Amazon River
to the Atlantic Ocean, and the other to the Pacific Ocean. The
source of the River Severn the longest river in England -is a deep,
blanket-peat bog in Wales. Mouth of Cass River in Lake Tekapo
Mouth of Hoh River Features of a Drainage Basin What is a drainage
basin?
1st Definition 2nd definition An extant or area of landwithin which
surface and groundwater from rain, melting snow or ice is
transferred to a single point at lower elevation, usually the exit
of the basin, where the waters join another water body, such as a
river, lake, reservoir, estuary, wetland, sea or ocean. The area of
land drained by a river system i.e. a river and its tributaries. It
includes water found in the water table as well as surface runoff.
What is a drainage basin?
Drainage basins drain into other drainage basins in a hierarchical
pattern, with smallersub-drainage basins or sub-catchments
combining into larger drainage basins. The drainage basin acts as a
funnel, collecting all the water within the area covered by the
basin and channeling it to a single point such as the ocean, a lake
or a larger stream. Tributariesand the main stem river serve to
drain the surrounding drainage basin of its surface water
andgroundwaterby leading the water out into an ocean, sea, lake,
estuary, reservoir or another river. Each drainage basin /sub-basin
is separated topographically by a perimeter called a drainage
divide. An example of a drainage basin.
All water collected within the area enclosed by the dashed line is
channeled to a single point. The dashed line is the main water
divide or drainage divide. Main and sub-basins What is a drainage
basin?
In a drainage basin the tributary stream (A) of a brook (B) that
joins a small river (C) is the tributary of a larger river (A is
tributary of B, which is larger than A. B is a tributary of C,
which is larger than B and A) For water to flow from A to B, the
drainage basin of A has to be at a higher elevation than B. For the
same reason, B is at a higher elevation than C. A, B and C are thus
a part of a series of successively smaller area but higher
elevation drainage basins. Similarly, theMissouriRiver is part of
its own drainage basin and that of theMississippi River. What is a
drainage basin?
Other terms that are used to describe drainage basins are:
catchment catchment area catchment basin, drainage area, river
basin water basin. In North America, the termwatershedis commonly
used to mean a drainage basin, though in other English-speaking
countries, it is used only in its original sense i.e. to mean
drainage divide What is a drainage basin?
Drainage basins are the main unit used in the study of rivers and
the movement of water within the hydrological cycle. This is
because the majority of water thatdischargesfrom the basin outlet
originated asprecipitationfalling on the basin. Drainage basins are
separatedfrom each other by watersheds or drainage divides. These
are the boundaries between drainage basins: all theprecipitationon
opposite sides of a drainage divide will flow into different
drainage basins. What is a drainage basin?
Endorheic Basins: these are closed drainage basins. Areas of inland
drainage that allow no outflow to external bodies of water like
oceans or seas. Water only leaves by evaporation or seepage. Water
will converge to a single point within the basin called a sink. A
sink may be a permanent lake, seasonal lake, swamp or an area where
water is lost underground. The bottom of such a basin is usually
occupied by a salt lake or salt pan. Endorheic basin showing
waterflow input intoreg Lake, western Mongolia. The Caspian Sea is
the worlds largest lake
The Caspian Sea is the worlds largest lake. A large part of Eastern
Europe, drained by the Volga River, is part if its drainage basin.
Okovango Delta, Botswana
Okovango Delta, Botswana.Dead Sea and Sea of Galilee, Jordan Israel
Border. Watershed An area or ridge of land that separates waters
flowing to different rivers, basins, or seas. A watershed is an
imaginary line separating adjacent basins. Streams on either side
of a watershed will flow in opposite directions. In hilly areas,
the divide lies along ridges and may be in the form of a single
line of hills or mountains known as a dividing range. In flat
areas, the location of the divide is harder to discern. Watershed
Continental Divide: where waters on each side flow to different
oceans e.g. the Congo- Nile Divide. Major Drainage Divide: waters
on both sides do not meet but flow into the same ocean e.g. the
Yellow and Yangtze River Divide Minor Drainage Divide: waters part
but eventually rejoin e.g. the Mississippi and Missouri River
Divide. Diagram of a drainage basin showing the watersheds or
divides.
The position of a watershed is usually shown on maps/diagrams as a
dotted/dashed line. In reality, the watershed will take the form of
a ridge. Thus precipitation falling on such a ridge will flow
(above or below ground) in opposite directions. Global Hydrological
Cycle
This is the name given to the continuous movement of water between
the atmosphere, lithosphere and biosphere. The total mass/volume of
water remains constant over time. The partitioning of water into
the major reservoirs of ice, fresh water, saline water and
atmospheric water is variable and dependent on a wide range of
climatic variables. Thus, it is a closed system, with no inputs
andoutputs or losses. Instead there are transfers between stores.
Global Hydrological Cycle
Water moves from one reservoir to another e.g. river to ocean or
ocean to atmosphere, by the physical processes of: Evaporation
Condensation Precipitation Infiltration Runoff Sub-surface flow
Basin Hydrological Cycle
In both hydrology and fluvial geomorphology, the drainage basin is
the main unit of focus for study. Thus, when studying rivers,
frequent mention is made of the basins hydrological cycle. When
doing this, the drainage basin is said to be the unit of study as
opposed to the global system. A drainage basin is a local open
system, with inputs, outputs and processes/transfers. Basin
Hydrological Cycle
At the local scale the cycle has a single major input precipitation
(PPT). There are two major losses or outputs evapotranspiration
(EVT) and runoff. Water is stored at a number of places within the
system vegetation, surface, soil moisture, groundwater and water
channels. The basin hydrological cycle is also an open
system!
Inputs Outputs Precipitation (including rain and snow) Solar energy
for evaporation and transpiration. Evapotranspiration from
vegetation Run-off into the sea Percolation of water to underlying
rock strata into underground stores The basin hydrological cycle is
also an open system!
Stores Transfers/Flows Surface storage such as puddles, rivers and
lakes Glaciers Soil storage and ground water storage Water stored
on vegetation (interception) following precipitation. Percolation
Overland flow Infiltration Stemflow Throughflow Human modification
of the system
Large-scale changes of channel flow Irrigation Drainage Abstraction
of groundwater and surface water for domestic and industrial
use