What you will Learn1. Describe the hydrological cycle.2. Describe the river system.
The hydrological cycle Continuous movement of water is called the hydrological cycle.
Rivers play an important role in thehydrologic cycle. Study the figurebelow. Rainfall Condensation Transpiration Runoff Evaporation Groundwater What are the different processes in the hydrologic cycle? What role does the
EvaporationThe sun’s heatcauses water toevaporate. Waterchanges into watervapour.
TranspirationPlants give outwater vapourthrough theirleaves.
CondensationWarm air cools as itrises. Water vapourchanges into waterdroplets. Small waterdroplets combine toform bigger waterdroplets. Million of
RainfallWater falls as rainor snow if the air iscold enough
RunoffWater that is left onground surfaceflows over the landas surface runoff.Water flows fromhighlands to
GroundwaterWater that seepsinto the ground maybe absorbed byplants or flow intorivers, lakes or seas.
Importance of river inthe hydrological cycle Rivers are an important part of the hydrological cycle as they contain water that is found on the Earth’s
River systemRiver is a body ofwater flowing in achannel.Aided by gravity,rivers always fallsfrom a higher point to
River source Tributaries River mouthUpper course Middle course Lower course
Characteristics Along a River — Channel and River Valley Upper Middle Lower Course Course CourseChannel Narrow, Wider, Widest, shallow deeper deepestGradient Steep Less steep Almost flatVolume of water Low Higher Highest
Drainage Basin & Watershed Read the definitionof a watershed and adrainage basin in yourtextbook.
Now study the picture belowcarefully. Where would youfind, in the picture, the:• ‘drainage basin’?• ‘watershed’?
Drainage Basin Drainage basin isthe land area drainedby the main river andits tributaries.
Watershed The edgeof thedrainagebasin ischaracterizedby thehighest pointof land