Rivers Flashcards
What are drainage basins?
Areas surrounding rivers where rain falling on the land flows into that river.
What kind of systems are drainage basins and the hydrological cycle?
The hydrological cycle is a closed system and global. Drainage basin systems are open and local.
What’s a watershed?
The boundary between drainage basins. Any rain beyond this point flows into a different basin.
What are the inputs to a drainage basin system?
Precipitation - rain, hail, snow etc.
What is interception?
Where precipitation lands on vegetation or buildings before it reaches the soil. Temporary as evaporates quickly.
What is groundwater storage?
Water in the ground (soil or rocks)
What’s the water table
The top of the zone of saturation (the bit of the soil with water in it)
What are the 5 ways of storage in a drainage basin system?
Interception. Vegetation storage. Surface storage. Groundwater storage. Channel storage.
What’s throughfall
Water dropping from one leaf to another
What’s throughflow
Water moving downhill through the soil.
What’s infiltration
Water soaking into the soil
What’s percolation
Water seeping through the soil into the water table
What’s groundwater flow
Water flowing slightly below the water table through permeable rock
What’s baseflow
Groundwater flow that feeds into rivers through banks and beds
What are the 10 flows in drainage basin systems
Surface runoff. Throughfall. Stem flow. Through flow. Infiltration. Percolation. Groundwater flow. Base flow. Inter flow. Channel flow/River discharge.
What are the 4 outputs of drainage basin systems
Evaporation. Transpiration. Evapotranspiration. River discharge.
What’s the water balance like in the wet season?
There’s more precipitation so water surplus. Groundstores fill with water so higher discharge so river levels rise.
What’s the water balance like in dry seasons?
Evaporation is highest. Groundstores depleted as some water used (eg by plants) and some flows into river. There’s a deficit that’s recharged next season.
What is river discharge and what’s it measured in
Volume of water that flows past w certain point per second. Measured in cumecs which are cubic metres per second - m^3/s
What affects river discharge
Precipitation. Heat (increases evaporation) and abstraction (removal of water)
In a hydrograph, what’s peak discharge
The point where river discharge is highest
In a hydrograph, what’s lag time
The delay between peak rainfall and peak discharge
What’s a rising limb
The part of the hydrograph up to peak discharge where discharge is increasing.
What’s a falling limb
The part of a hydrograph after peak discharge where discharge is decreasing
What 8 things affect hydrographs
Drainage basin characteristics. Antecedent moisture. Rock type. Vegetation. soil type. Precipitation. Temperature. Human activity.
How does drainage basin size affect hydrographs
Large means high peak discharge. Small means shorter lag time.
How does steepness, circularness and amount of tributaries affect hydrographs
Steep is shorter lag time and peak discharge. Circular is very high peak discharge. Many tributaries means short lag time and high drainage density.
What’s anticedent moisture and how does it affect hydrographs.
Amount of water already in basin. If waterlogged then reduced lag time as more surface run off
How does rock type affect hydrographs
Impermeable rocks means increased surface runoff so reduced lag time and increased peak discharge.
How does soil type affect hydrographs
Sandy means increased infiltration. Clay means low infiltration rate so more surface run off so reduced lag time and increased peak discharge
How does precipitation affect hydrographs
Intense storms means more rain so higher peak discharge
How does temperature affect hydrographs
Hot and dry or cold means hard ground so increased surface runoff so reduced lag time and peak discharge. Warm means increased evap. So reduced peak dis.
How does human activity affect hydrographs
Concrete is impermeable so increased surface run off so higher peak d and shorter l time. Drainage systems means flow direct to river so short lag time.
Name the three main places erosion occurs and say what they are
Vertical is in the upper stages and deepens the channel. Headward makes the river longer. Lateral makes the river wider and occurs in the middle and lower stages.
Name the 5 processes of erosion.
Hydraulic action. Abrasion (corrasion). Attrition. Cavitation. Corrosion (solution).
What is hydraulic action and where is it strongest.
Pressure of water breaks rock particles from the bed and banks. Strongest in waterfalls, floods and rapids.
What is abrasion (corrasion)
Eroded rock in the water scrapes bed and banks, removing material. How most erosion happens.
What is attrition
Particles of eroded rock smash together and become smaller and more rounder.
What’s cavitation
Air bubbles in turbulent water implode, causing shock waves that break rock off bed and banks.
What’s corrosion (solution)
Dissolving of rock by chemical processes. CO2 dissolves in water to form a weak acid which breaks down rocks.
What are the 4 main modes of transportation
Solution. Suspension. Saltation. Traction.
What’s solution (transportation)
Dissolved particles being carried along in the water
What’s suspension
Fine material picked up and carried. How most transported.
What’s saltation
Larger particles bounced along river bed
What’s traction
Very large particles eg boulders pushed along the bed
When does deposition occur?
When river loses energy, causing it to drop its load
What causes rivers to have less energy?
Reduced rainfall. Increased evap or abstraction cause lower discharge. Friction. Narrow section. All reduce speed of river. Meeting sea as sea absorbs some of the energy
What is a rivers capacity?
The total load a river can transport at a given point
What is a rivers competence
The maximum particle size a river can transport at a given point
What are long profiles
They show how the gradient of a river changes. The base level is sea level.
What happens in the upper part of a long profile
Steep gradient, high above sea level so lots of potential energy
What’s the long profile like in the middle of the river
Potential energy converted to kinetic energy, gains velocity
What’s the long profile like in the lower section of the river
Little potential energy, lots of kinetic energy so fast flowing.
How do you calculate efficiency
Hydraulic radius: cross sectional area / wetted perimeter length
What does a large hydraulic radius mean
A smaller promotion of water Is touching the wetted perimiter so friction is reduced, energy loss low so velocity increased. Efficient river!
How does channel roughness impact on efficiency and where is it greatest
More friction so less velocity. Greatest in upper stages of the river. Increases turbulence so more erosion occurs.
What’s erosion like in the upper stage of a river
Mainly vertical and by abrasion. Channel is rough and bedload dragged along it, causing intense vertical erosion.
What’s transportation like in the upper stage of a river
Mostly large particles eg boulders carried by traction or saltation
What’s deposition like in the upper stages of a river
Not much. Mainly largest particles eg boulders when energy levels drop.
What’s erosion like in the middle stage of a river
Mainly lateral and by abrasion. Attrition occurs which means particle size decreases over the rivers course.
What’s transportation like in the middle stage of the river
Most particles carried in suspension. Some larger ones by saltation
What’s deposition like in the middle stage
Sand and gravel deposited across the floodplain, especially during floods
What’s erosion like in the lower stage of a river
Less erosion as low turbulence and small particles. Lateral occurs if meanders are being firmed.
What’s transportation like in the lower stage of a river
Smaller particles eg silt and clay are in suspension, or substances carried in solution
What’s deposition like in the lower stage of a river
Small particles like sand silt and clay deposited on floodplain during floods and in river mouth as sea absorbs energy.
What’s the cross profile like in upper stage valleys
Steep V shape. Vertical erosion creates narrow valley floors and steep sides.
What’s the cross profile like in middle stage valleys
Wider due to lateral erosion. Deposition makes flood plain on valley floor. Still quite steep sided but more gently so. More like elongated U shape
What’s a cross profile like in lower stage valleys
Wide and gently sloping. Much wider flood plain due to deposition.
How are waterfalls made
Fluvial erosion. Band of hard rock meets band of soft rock. Soft is eroded more, causing a ‘step’. Water over us is faster as less friction. Soft rock erodes more and hard rock undercuts. Plunge pool carved out by abrasion. Undercutting causes rock collapse so waterfall retreats, leaving a steep sided gorge.
What are potholes and how are they former
Circular hollows in the river bed formed by abrasion.
What are rapids and how are they formed
Steep sections of river with turbulent flow where there are several sections of hard rock.
What are pools and what are riffles and where do they occur
Pools are areas of deep water and occur on the bends of meanders. Riffles are areas of shallow water and they occur on the straight part of meanders. Before the river meanders pools and riffles are equally spaced alternately along the river channel.
How are meanders formed
More efficient in pools so erodes more. River becomes uneven and maximum flow concentrated on one side of river. Turbulence increases in Poole causing helicoidal flow which deepens pools. Causes material to be deposited on inside of next bend as less energy
How do oxbow lakes form
A loop of a meander is broken through, often in a flood, and deposition dams off the loop.
Draw a birds eye view of meander formation
Check with notes
Draw a cross section of a meander
Check with book
What is braiding and how does it form
Fluvial deposition. It’s where one river splits into several streams and then rejoins together. It occurs when a river deposits it’s bedload in the channel. It has to divide then to flow past these deposits.
What’s a levee and how does it form
Natural raised embankment. Formed when a river floods as it deposited heaviest material closest to channel. This builds up over time.
What are river deltas
When a river reaches the sea the sea absorbs the energy so river deposits it’s load. This builds up until above sea level so river has to braid to reach the sea
What’s rejuvenation
Where a rivers base level is lowered, causes by ground rising or drop in sea level. Gives greater potential energy so vertical erosion increases.
What’s a knick point
Because of rejuvenation, the long profile of a river extends and a knick point marks the change between original long profile and new one. Often a waterfall forms here too.
What’s a river terrace
Former flood plain that has been left above the level of present day flooding following increased vertical erosion.
What’s an incised meander and how does it form
Forms when a river continues to meander as vertical erosion increases. It’s a deep winding valley with steep sides.
What’s the technical definition of a flood
Where river discharge is so high that it spills onto the floodplain
What are the 6 physical factors that can cause flooding
Sparse vegetation. Deciduous trees. Impermeable ground. Circular drainage basins. High drainage density. Steep slopes.
How does sparse vegetation affect flooding
Little rainfall is intercepted so more reaches the river as isnt being used by plants so river discharge is high
How do deciduous trees affect flooding
They have no leaves in winter so don’t intercept rain
How does impermeable ground affect flooding
Eg clay. Doesn’t allow infiltration so more surface run off which increases discharge.
How do circular drainage basins affect flooding
Water all arrives in a short space of time so high discharge
How do steep slopes affect flooding
Water reached channel faster so high discharge
What are the 4 human factors that increase risk of flooding
Urbanisation. Deforestation. Agriculture. Climate change.
How does urbanisation affect flooding
Lots of impermeable Tarmac etc do surface run off is high. Also drains take runoff directly to river at high speed
How does deforestation affect flooding
Reduces intercepton and evapotranspiration so more water reaches channel
How does agriculture increase the risk of flooding
Overgrazing means less vegetation so more water reaches the channel
How does climate change affect flooding
May cause increased storms and rainfall so more discharge
What are 3 social impacts of flooding
People/animals drown. Contaminated water causes disease. People made homeless.
What are 3 economic impacts of flooding
Businesses have to close due to damage so unemployment. Costly repairs. Crops destroyed so rise I’m food price.
What are 4 environmental impacts of flooding
Contamination if rivers. Riverbanks eroded. Sediment deposited on floodplain so more fertile soil. Wetland habitats created.
What is a flood frequency and how is it calculated
Predicting how often floods of certain magnitudes will occur. Flood return interval.
Where and when are your 2 flooding case studies
South Asia, July and August 2007. Carlisle, Cumbria, January 2005. River Eden.
What were the 4 physical factors that caused the south Asian floods
Monsoon climate. Low lying, Bangladesh 90% less than 10m above sea level. Heavy rainfall, Assam had 900mm in July. Peak discharges of Ganges and brahmaputra coincided.
What were 2 human factors that caused the south Asian floods
Deforestation in Nepal so less interception and evapotranspiration. Urban growth due to migration so more impermeable surfaces so more surface runoff.
What where 3 social impacts of the south Asian floods
2000 deaths. 100,000 caught water Bourne diseases. 25 million made homeless.
What were 2 economic impacts of the south Asian floods
Estimated cost of $1 billion. Loss of livestock - 80% bangladeshis work in agriculture
Give 2 environmental impacts of the south Asian floods please
River deposited fertile silt on flood plain. Sewage polluted river.
What were three physical factors that led to the Cumbrian flood
200mm rain in 36 hours. Saturated ground so surface runoff increased. High peak discharge - over 1500 cumecs.
Give 2 human factors that caused the Cumbrian floods m’lady
Urbanised area so little infiltration and high surface runoff. Drains overflowed - 25% flooding problems associated with this
What were 3 social impacts of the Cumbrian floods
3 people died. 3000 homeless for up to a year. Increase in stress related illness.
What were 3 economic impacts of the Cumbrian floods
Cost £100 million. 350 businesses closed. United biscuits!!! Got £5 million damage and are largest employer here.
Give 2 environmental impacts of the Cumbrian floods
Increased bank erosion. Rivers polluted with sewage and waste.
What are disadvantages of hard engineering
Disrupts natural processes. Expensive to build and maintain.
What are dams
Huge wall across river. A reservoir (artificial lake) behind it. Releases water steadily.
Advantages of dams
Can use reservoir for recreation eg sailing. Steady water release allows irrigation of land below.
What are disadvantages of dams
Cause increased erosion downstream. Expensive. Disrupts wildlife, eg salmon can’t migrate upstream to breed
What’s channel straightening
Removal of meanders by building an artificial cut through
What’s am advantage of channel straightening
Easier to navigate river as shorter and straighter
What’s a disadvantage if channel straightening
Flooding may happen downstream instead as river flows faster. Disturbs wildlife habitats
What are levees
embankments along rivers so can hold more water and not overflow
What’s an advantage of levees
Can build on flood plains
What’s a disadvantage of levees
Expensive. If breached can be severe flooding.
Wtf is a diversion spillway
Channels that take water elsewhere if river level is too high. Gates so flow is controlled
What’s a disadvantage of diversion spillways
If they flood areas not used to flooding will be flooded
What are advantages of soft engineering
Cheap and work with natural processes
What’s land use management
Planning restrictions on floodplain to parks etc so more water can infiltrate
What’s an advantage of land use management jimbo
Impact of any flooding reduced. More recreation.
What’s a disadvantage of land use management
Restricts development. Can’t be used if already urbanised
What’s wetland riverbank conservation
Reestabliahimg and conserving wetlands, which store water naturally
What’s an advantage of wetland riverbank conservation
Little maintainence. Habitat for wildlife.
What’s a disadvantage of wetland riverbank conservation sir
Local flood risk may increase (failed flood management, surely?)
What’s alteration of urban surfaces
Porous pavements so water can infiltrate
What’s an advantage of alteration of urban surfaces
Any pollutants are filtered by soil before reaching river
What’s a disadvantage of alteration of urban surfaces
Expensive and may have to remove existing surfaces
What’s a bad thing about flood warnings
Some people might not access information. If inaccurate previously idiots might ignore it
Where’s you’re case study for hard engineering
Yangtze River in china
What are two facts about the flooding in china
5 major floods in 100 years. 6000km long river.
Hi Emmie please tell me about the three gorges dam in china
Largest dam on Yangtze River! How exciting! 100m high which is taller than my cousin Andy. Largest hydroelectric power source in world - 26 turbines on the dam
Tell mr examiner about the levees on the three gorges dam
3600km long along middle and lower sections of river
What are three positives about the three gorges dam buddy
Reduced major floods from 1/10y to 1/100y. Turbines produce lots of energy for people to watch weird Chinese game shows on TV. River shipping increased as safer to navigate captain!
What are 4 negatives of the three gorges dam
2 million people had to relocate so they didn’t get all wet. The reservoir flooded farmland. Dam (guurl) could destroy habitats downstream. Increases flooding on tributaries leading into it
What’s your soft engineering case study
Abingdon on the floodplains of Thames and Ock
How does Abingdon use land use management
Low value land allowed to flood. Planning restrictions as houses must have improved drainage systems.
How does Abingdon use flood warnings
24 hour flood helpline. Voluntary flood wardens.
Where does Abingdon use gravel soakaways
Built on the A34 road
What three things does Abingdon use to reduce the impact of flooding
Land use management. Warnings. Gravel soakaways.
Tell me a fact about Abingdon pwease
1500 properties have 1% chance of flooding each year (sounds pretty awful to me, why even manage that?)
