2.2 Rivers Flashcards
Tributary?
A stream which joins a larger river
Drainage basin
The area of land drained by a river system (a river and its tributaries).
Watershed
A ridge or other line of separation between two river systems.
Confluence
The point at which two rivers meet
Interception
The precipitation that is collected and stored by vegetation
Infiltration
The movement of water into the soil. The rate at which water enters the soil (the infiltration rate) depends on the intensity of rainfall, the permeability of the soil, and the extent to which it is already saturated with water
Throughflow
The downslope movement of water in the subsoil
Evaporation
The process in which liquid turns into a vapour
Overland flow
Overland movement of water after rainfall. It is the fastest way in which water reaches a river. The amount of overland runoff increases with heavy and prolonged rainfall, steep gradients, lack of veg, and saturated or frozen soil
what is CASH
Corrasion, attrition, solution, hydraulic action
what is corrasion
The wearing away of the bed and bank by the load carried by a river
Attrition?
The wearing away of the load carried by a river. It creates smaller, rounder particles
Hydraulic action
The forces of air and water on the sides of rivers in cracks
Groundwater flow
The movement of water from land to river through rock. It is the slowest form of such water movement, and accounts for the constant flow of water in rivers during times of low rainfall
Suspension
Small particles are held up by turbulent flow in the river
Saltation
Heavier particles are bounced or bumped along the bed of the river.
Solution?
The removal of chemical ions, especially calcium, which cause rocks to dissolve.
The chemical load is carried dissolved in the water.
Traction?
The heaviest material is dragged or rolled along the bed of the river.
Drainage basin cycle
What is the hydrological cycle
The movement of water between air, land and sea. It varies in scale from the global hydrological mode to a small-scale drainage basin hydrological model.
What factors affect erosion
Greater velocity and discharge
increased gradient increases rate of erosion
solution can be increased when water is more acidic
Transport
Suspension Saltation Solution Traction Flotation
How does deposition occur
Decline in energy or velocity - river becoming more shallow. For example
When a flood spills onto a floodplain; the river gets trapped behind a dam or enters a lake or the sea; vegetation. slows down the river; or gradient becomes gentler
How does the shape of a river generally change
From being steep and V-shaped in its upper course, to bring much flatter and wider in its lower course.
Why do river generally change shape.
Tributary streams, changes in climate and vegetation, human impacts and river processes- erosion, transport, deposition
How are waterfalls, gorges and potholes created?
Rivers erode softer rock and undercut harder rock.
This causes harder rock to collapse and turn into a waterfall.
If water retreats it may form a gorge of recession
Landforms caused by erosion and deposition?
Meanders and oxbow lakes.
What causes the landforms caused by erosion and deposition
Erosion occurs on the outer bank of a meander whereas deposition occurs on the inner bank. This produces a river cliff in the outer bank and a slip-off slope (river beach) on the inner bank, the meanders may become so exaggerated that successive meanders touch. In time of flood, the river may break through the meander to form an oxbow lake or meander cut off
What landforms are created by deposition
Levees and floodplains
How is a levee formed
They occur in the lower course of the river.
The finer clays and silts are carried further away from river. This coarser sand and gravel may build up a small bar by the edge of the river.
How is a delta formed
When a river entered a lake or the sea where there is very little current, river slows down and deposits it’s load, forming a delta
briefly explain how waterfalls and gorges are formed (4)
Waterfalls frequently occur on horizontal bedded rocks. The soft rock is undercut by hydraulic action and abrasion, to form a plunge pool. The softer rock is eroded by fragments of the harder rock that break off. The weight of the water and the lack of support cause the waterfall to collapse and retreat. Over thousands of years the waterfall may retreat enough to form a gorge of recession
draw an annotated diagram to show the formation of an oxbow lake
How are settlements built to prevent loss of possessions and lives
building settlements on raised ground
Hazards of rivers
Erosion of their river banks thereby making some people vulnerable to losing their home and fields
loss of lives + possessions
What physicality’s cause a flood (Climatological)
Rain
Ice melting
Snow melting
What physicalitys cause a flood (part climatological)
Estuarine interactions between steam flow and tide
Coastal storm surges
What physicalitys cause of a flood (other)
Earthquakes
Landslides
Dam failure
Human causes for a flood
Urban growth Floodplain developments Obstruction of dams change in vegetation cover Human-induced climate change River engineering work
What opportunities do rivers present
A source of drinking water Fertile silt for farming a line of communication a source of power fishing
What do dams do to rivers
reduce speed of water flow control amount of water in a river cause deposition behind the dam change ecosystems can cause earthquakes
What do dams provide us
reliable water throughout the year navigation hydro-electric power water for irrigation safety from flooding
how can you reduce impacts of river flooding
raising river bank
building dams
using sandbags to prevent water getting into house
having insure me to cover valuables
diverting the steam
land use planning (building only on land free from flooding)
CASE STUDY FOR RIVER: NILE DELTA
oldest intensively cultivated areas in the word. Heavily populated and has population density of 16k people per km2.
only 2.5% of egypt is usable for agriculture.
95% of produce comes from Nile valley and delta
Long been a source of freshwater and fertile silt, excellent for import and export. Flat land makes it building easy.
PROBLEMS
Delta covers 25k km2 and home to 66% of growing population.
Provides 60% of food supply.
increase of just 1m would flood 20% population. Excessive irrigation led to pesticides and salt in water delta.
