Geography Theme 2 - Rivers Flashcards
Erosion by Hydraulic Action
water forced into gaps and sediment breaks away
Erosion by Abrasion
Particles in water rubs against the side of the river bed
Erosion by Attrition
Rocks hit each other and break away
Erosion by Solution
river is acidic and corrodes side
Transportation by Saltation
pebbles bouce along the river bed
Transportation by Traction
moving of large boulders along river bed
Transportation by suspension
small sediment carried at surface of river
Transportation by solution
so small they are dissolved in the river
The long river profile
Starts at the source to the moth
- Increases in size of channel, velocity and amount of load widens and deepens as you go down
- Most efficient lower course
- Decrease in gradient as you go down towards the mouth
- Large materials - source
- Upper course - waterfalls and , v-shaped valley (vertical erosion)
- Middle course - meander create flood plain, oxbow lake
- Lower course - delta
River Landforms - Waterfalls
Waterfalls eg Niagra
- hard rock overlays soft rock
- upper course and vertical erosion
- hydraulic action erode the soft rock
- creates plunge pool
- leads to overhang
- waterfall retreats upstream leaving a gorge
River Landforms - Meanders
eg River Severn
- middle course
- deposition and lateral erosion
- fastest flowing on outside so more erosion = river cliff formed
- slower on inside, less energy and more deposition = slip off slope formed
- helicoidal flow = corkscrew like flow
- oxbow lake = over time when the meander gets cut off
River Landforms - Deltas
eg the Ganges Delta
- lower course at the Mouth and deposition
- when river meets the sea loses energy
- deposits the sediment it is carrying
- extremely fertile soil due to the load being carried
- vulnerable to flooding
Delta - definition
fan shaped landform created at the mouth of a river when its load is deposited into many channels as it slows down
Floodplain - definition
the wide, flat areas of land either side of a river that are liable to flood.
Levees - definition
an embankment built up either side of a river after flooding
River Processes and landforms
Energy in the river is controlled by velocity of the water.
-the more energy = more erosion and transportation
Velocity increases with channel efficiency and gradient
Channel efficiency is controlled by the
- amount of friction which is controlled by the channel shape and smoothness
River estuary
the wider lower course of a river where it flows into the sea
- mixture of fresh and sea (salt) water
River Management Techniques in an MEDC
eg Mississippi, USA
eg Mississippi River (USA)
- levees - concrete wall over 3000km long : better protection river side and allow the river greater discharge increasing channel capacity
- burst control banks
- wing dykes - traps large sediment makes channel smaller
- control dams and reservoirs - store flood waters until needed and then controlled by the dam
- change shape of valley
- matress of concrete slabs
Drainage Basin
AREA DRAINGED BY RIVER AND ITS TRIBUTARIES
Factors encouraging flooding
- High rainfall
- Saturated ground (from previous rainfall)
- impermeable rocks and soil
- steep slopes
- frozen ground
- Deforestation reduces interception
- Urbanisation creates impermeable surfaces
River Management Strategies - Hard Engineering - 4 points
- Levees - concrete wall along banks of a river or canal. They allow the river to greater discharge increasing channel capacity
- Flood spillways - alternative channels build to carry water at time of flood. The water will re-enter the river further down the river channel
- Reservoir - designed to store flood waters thus moving water out of the river.
- Dams help to control the water flow
Hard Engineering of Rivers - negative effects
-ve
Changes the natural flow of the river
cost lots
disrupt natural flooding cycles and river ecosystems
Erosion - definition
the wearing away and removal of rocks and surfaces
Deposition - definition
when transported material is laid down
Transportation - definition
when matter is carried along/moved eg by a river
Watershed - definition
a boundary between two drainage basins
confluence- definition
meeting point of two rivers
discharge - definition
how much water in the river
annnual hydrograph - definition
discharge of flood
flood hydrograph- definition
shows how river responds to flood
