Upload
estee-seetoh
View
1.160
Download
3
Embed Size (px)
DESCRIPTION
Citation preview
Rivers
SEC ONE TEXTBOOK PAGE 101
What is a river?
• A river is a natural watercourse, usually freshwater, flowing towards the sea.
• Without the hydrological cycle, rivers cannot be formed.
HYDROLOGICal CYCLE
HYDROLOGICAL
CYCLE
SURFACE RUNOFF
INFILTRATION
CONDENSATION
TRANSPIRATION AND EVAPORATION
PRECIPITATION
HYDROLOGICAL CYCLE
• Precipitation – water from clouds come to the Earth’s surface as rain, snow and hail• Transpiration – plants release water vapour into atmosphere
HYDROLOGICAL CYCLE
•Surface Run-off – rain that falls on Earth’s surface flows over land
• Condensation – water vapour rises, cools and changes into tiny water droplets
HYDROLOGICal CYCLE
• Infiltration – water that soaks into the soil subsurface
• Percolation – water moves further down into the underlying soil after infiltration
HYDROLOGICal CYCLE
•Throughflow – infiltrated water that flows sideways in the soil subsurface
• Interception – water is absorbed by trees
RIVER SYSTEM
• Source – the starting point of a river• Mouth – the ending point of a river• Drainage Basin – The area drained by a river and its tributaries
RIVER SYSTEM
•Confluence – the point at which a tributary joins the main river • Watershed – The boundary formed by the edges of the drainage basin
Waterfalls
• Sudden, steep and vertical flow of fast-flowing water falling from great heights
• Formed by river erosion
Niagara Falls on Niagara River, Canada and USA
• formed by erosion of rock of different resistance
Formation of Waterfalls
Formation of Waterfalls• River flows across rocks of different
resistance.
Formation of Waterfalls
• River erodes the less resistant rock more rapidly• This cause a change in the gradient of the river
course.
Formation of waterfalls• Over time, river plunges from a great height to
hit the riverbed below, • This forms a waterfall.
Formation of plunge pools
• Repeated pounding of the river bed leads to a depression at the base of a waterfall
• A plunge pool is formed.
Meander
• A river that follows a winding course, usually forming hoop-like bends.
• River may meander because
Lower gradient lower speed lower river energy river turns to avoid obstacles
Meander
Note: Outer Bank = Concave Bank
Note: Inner Bank = Concave Bank
River Cliff
• Constant erosion (undercutting) erodes the outer (concave) bank of the meander
• forming a river cliff.
Slip-off slope
River cliff
Slip-off slope
• Constant deposition at the outer (convex) bank deposits sediments
• forming a slip-off slope.
Slip-off slope
River cliff
Floodplain
Levees
FloodplainAreas of low-lying ground adjacent to a
river at the lower course
Formation of Floodplain and Levee
Formation of Floodplain and Levee
Floodplain and Levee• During a heavy rainfall, river water
overflows its bank. River loses speed as it encounters friction.
Floodplain and Levee• Deposition occurs as river’s energy decreases. • Coarser and heavier sediments are deposited
nearer to the river bank. • Finer and lighter sediments are deposited
further away.
Formation of Floodplain and Levee
Floodplain and Levee• Overtime, the accumulation of fine
sediments results in the formation of flat plains
• Coarser and heavier sediments are acculumated
• Results in the formation of raised banks • Known as levees.
Formation of Delta• At the river mouth, a river loses energy and starts to deposit its sediments.
Formation of Delta• As the
sediments build up, the mouth will be blocked
• The river also split into several small channels called distributaries to flow to the sea.
DistributariesDelta
Over time, the accumulated sediments that rise over the water and the distributaries form a delta.
Positive Impact of river
• Rivers provide water for domestic purposes such as drinking, bathing and washing.
• Rivers are a good source of food such as fish and prawns.
Positive Impact of river
• Rivers are important waterways for transporting people and goods.
Negative Impact of river
• River water overflows river bank cause lives to be lost and destroy property and crops.
• .
Negative Impact of river
• Consuming contaminated river water can cause people to fall ill
• Eg contract diseases such as cholera.