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					GEOMORPHOLOGY
    RIVERS




                1
The way in which water moves from the
ocean to the land and back to the ocean is
                known as




      The Water Cycle
                                         2
   The Water Cycle
     The water cycle consists
     of five distinct stages

           • Storage
• Evaporation and Transpiration
       • Condensation
        • Precipitation
  • Runoff – direct or indirect

                                  3
                  STORAGE
• The water on the earth spends most of its time
    in the ocean
•   Water is also found in the atmosphere either
    as water vapour or water droplets (clouds)
•   Water is also found in rivers, lakes and dams
    as surface water
•   Water may also be found as ice in ice caps and
    glaciers
•   Water may also be found underground and is
    called ground water
•   Water is found stored in plants

                                                   4
Evaporation and Transpiration

• Water evaporates from the earth’s surface or
    from the oceans
•   Evaporation occurs when energy from the sun
    causes water to heat up and evaporate from
    the earth’s surface. The water rises into the
    atmosphere as water vapour
•   Transpiration is the evaporation of water
    particles from plant surfaces, especially from
    the surface openings (stomata) on leaves

                                                 5
         Condensation

• Condensation in Meteorology is the
 process whereby water vapour is cooled
  until a critical temperature is reached
    (the Dew Point Temperature)
and the vapour changes back into water
         droplets to form clouds



                                            6
            Precipitation

• Precipitation occurs when water vapour
  in the atmosphere condenses into clouds
  and falls back to the earth
• It can take a variety of forms, including
  rain, snow, hail and sleet.




                                              7
                       Runoff
• Water that flows down streams and rivers is called
    runoff.
•   Water reaches rivers and the sea in the form of either
    surface runoff (direct) or undergroundwater
    runoff (indirect)
•   Surface runoff occurs during and shortly after intense
    rainstorms or periods of rapid melting of snow and ice.
•   Groundwater flow runs through rocks and soil.
    Surface water infiltrates into the soil and forms the
    water table, the level at which all of the spaces in the
    rocks are filled with water
•   Eventually the water either runs into the seas or re-
    evaporates into the atmosphere
•   Almost all the water on the earth has passed through the
    water cycle countless times                           8
The Water Cycle




                  9
The Longitudinal Profile




                           10
              The Upper Course

• is the highest section
  which is found in the
  mountains or hills
• Here the river erodes a v-
  shaped valley, the path is
  fairly straight and it flows
  downhill steeply
• The landforms that are
  common in this course of
  the river are waterfalls
  and gorges

                                 11
The Upper Course




                   12
            The Middle Course
• the gradient that the
  river flows down is
  less steep, the river
  begins to meander
  and the valley sides
  are also less steep.
• Common landforms
  here are a wider river
  valley – slightly U
  shape, meanders


                                13
The Middle Course




                    14
             The Lower Course
• has the gentlest slopes -
  both in long profile and
  across the valley floor
• This almost flat land is
  known as the flood
  plain.
• The river may have very
  large meanders and ox-
  bow lakes. T
• The mouth of a river is
  when it reaches open
  water - either a lake or
  the sea.
• Under certain conditions
  a delta can be found
  here                          15
               Types of Flow

   Laminar Flow - at low velocities the fluid
    particles follow the streamlines

   Turbulent Flow - at higher velocities the
    flow breaks up into a fluctuating velocity
    pattern or eddies


                                                 16
                    Types of Rivers

        Perennial Rivers – flow all year round
           Permanent Rivers
           Exotic Rivers


        Non Perennial Rivers – flow in rainy season
           Periodic Rivers
           Episodic Rivers


17
                 Permanent Rivers

        Flow all year round




18
                     Exotic Rivers

        Flow all year round
        Reflect the characteristics of source
        Not of the region they are flowing through
        Nile River flows all year yet it runs through a
         desert region – source is the Ethiopian
         Highlands
        Orange River also flows through driest
         areas of South Africa – source is the
19       Drakensberg
                   Episodic Rivers
        Flow only after an episode of rain
        After a thunderstorm a river may only flow
         for a few hours
        A river may flow for a few days or weeks after
         an extended episode of rain
        For much of the year, the Fish River is barely a
         stream, and in parts it dries up completely.
         When the short wet season arrives, however,
         torrential rains run off the rock-hard soils. In a
         few hours the river swells into a raging
         torrent
20
                  Periodic Rivers

        Only flow after a period of rain
        Is a seasonal flow – winter, summer
        Rivers may flow for 3 to 6 months




21
The Flood Plain




                  22
            The Flood Plain
 The Flood Plain is a flat region of a valley
  floor located on either side of a river
  channel
 A floodplain is built of sediments
  deposited by the river that flows through it
  and is covered by water during floods when
  the river overflows its banks.
 Floodplains tend to develop on the lower
  and less steep sections of rivers.

                                            23
    Meandering and Braided Streams

 River channels in floodplains form two
  kinds of patterns: meandering and braided
 Meandering rivers consist of a single main
  channel that bends and loops
 Braided rivers have numerous distinct
  channels that repeatedly divide and then
  merge again downstream

                                           24
                     Oxbow Lakes
   In meandering rivers, sediment is eroded on the outside of
    bends (undercut banks) and deposited on the inside of bends
    (slip off slope)
   Over time, this causes meander loops to migrate downstream
   If the movement of one meander loop overruns the next one
    downstream, then a meander cut-off is formed
   This causes the course of the channel to be shortened as the two
    meander loops join
   The abandoned meander loop is gradually isolated as sediment
    is deposited at each end by the water flow in the main channel.
    This process eventually leads to the creation of an ox-bow lake

                                                               25
     The Amazon River




26
     The Orange River




27
     The Niagra Falls




28
     The Victoria Falls




29
     The Fish River




30
                   Deltas

 Delta (geologic formation), deposit of soil or silt
  formed wherever a swift stream or river
  empties into a lake, ocean, or slower river, so
  called because its triangular shape resembles
  the Greek letter (delta)
 The triangular shape and the great width at the
  base are due to blocking of the river mouth by
  silt, with resulting continual formation of
  distributaries at angles to the original course.
  Deltas are usually characterized by highly
  fertile soil

                                                    31
  Requirements for the
  formation of a Delta
 Constant supply of silt and sand
 Shallow lake or sea
 Little or no tidal action, wave action or
  current action




                                              32
Types of Deltas

    Arcuate delta – Nile river
    Cuspate delta – Elbe River
    Bird’s Foot delta - Mississippi
    Estuarine delta -




                                       33
Types of Deltas




                  34
Dendritic Pattern




                    35
Centripetal Pattern




                      36
Drainage Patterns




                    37
38
Radial Pattern




                 39
Trellis Pattern




                  40
Deranged Pattern




                   41
Rectangular Pattern




                      42
Stream Order
  Hierarchical ordering
   system based upon the
   degree of branching
  (A second-order stream
   is formed by the joinig of
   two first order-streams;
   the junction of two
   second-order streams
   forms a third order
   stream

                                43
44
45
   The peak rainfall is the time of highest
    rainfall. The peak discharge (the time
    when the river reaches its highest flow)
    is later because it takes time for the
    water to find its way to the river (lag
    time) .
   The normal (base) flow of the river
    starts to rise (rising limb) when run-
    off, ground and soil water reaches the
    river.
   Rock type, vegetation, slope and
    situation (ie is this an urban river?)
    affect the steepness of this limb. The
    falling limb shows that water is still
    reaching the river but in decreasing
    amounts.
   The run-off/discharge of the river is
    measured in cumecs - this stands for
    cubic metres per second. Precipitation
    is measured in mm - this stands for
    millimetres.

                                               46

				
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posted:10/9/2012
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