Flashcards in River Landscapes Deck (121):
When does mechanical weathering happen? (River)
This happens when rainwater enters cracks or gaps in the rock and then freezes if temperatures drop below zero. The water expands as it turns into ice and then exerts pressure on the rock causing it to break into smaller pieces
What is chemical (acid rain) weathering? (River)
All rainwater is slightly acidic. If the air is polluted by factories and vehicles, it can become more acidic. When rain falls on rocks, the acid in it can react with weak minerals, causing them to dissolve and the rock to decay.
What is biological weathering? (River)
The roots of plants, especially trees can grow into cracks in a rock and split them apart
What is mass movement?
Mass movement is the movement of rocks and soil downslope due to gravity, helped by weaker rocks, steep slopes and heavy rainfall. Mass movements can be very slow - only a few mm a year - or sudden and rapid. Types of mass movement that affect river valleys include soil creep, sliding and flows
What is sliding? (River)
Where material moves rapidly downslope in one go, for example in a landslide. In a slump, the material often rotates as it moves
What is soil creep?
It is a form of mass movement where individual particles of soil move slowly down a slope
What is Hydraulic action? (River)
This results from the sheer force of the water hitting the river bed and banks and wearing them away. This action is particularly important during high-velocity flow.
What is attrition? (River)
It is a form of erosion, when sediment particles carried in the river collide with each other, causing the edges to be knocked off. The continued collision of particles in the river causes them to become rounder and smaller downstream
What is solution? (River)
It is a form of erosion, which is when the river water is lightly acidic, so it can dissolve some rocks and minerals in contact with the he river. Limestone and chalk are most affected
What is abrasion? (River)
It is a form of erosion which is caused by material carried in the river rubbing against the bed and banks of the channel, so wearing the away. Overall abrasion causes the most erosion
Describe the transportation of a load in a river
A river picks up and carries material as it flows downstream. The four types of transportation are traction, saltation, suspension and solution
What is deposition? (River)
When a river no longer has enough energy to carry its load, deposition occurs. As the rivers discharge and velocity reduce, the heaviest material is deposited first, for example after flooding
What is traction?
It is a form of transportation, for when large boulders are rolled along the river bed
What is suspension?
It is a form of transportation for when finer sand particles are carried along in the flow, giving a brown appearance
What is saltation?
It is a form of transportation for when smaller pebbles are bounced along the river bed, picked up then dropped as the river flow changes
What is solution? (In transportation)
For when minerals, such as chalk are dissolved in the water and carried along in the flow, although they cannot be seen
Where do rivers and the valleys they flow in change in different ways?
Between their source (where they start) and their mouth (where they join the sea)
Describe a river profile
A rivers profile shows the height and distance downstream from the rivers source to its mouth. It is a curved shaped, steeper near the source and flatter near the mouth
describe the gradient in the upper, middle and lower course
Upper - steep
Middle- less steep
Lower - shallow gradient
Describe the discharge in the up, mid, low course
Up - smaller
Mid - large
Low - very large
Describe the depth in the up, mid, low course
Shallow, deeper, deep
Describe the channel shape in the up, mid, low course
Up - narrow, steep sides
Mid - flat, steep sides
Flat floor, gently sloping sides
Describe the velocity in the up, mid, low course
Up - quite fast
Mid - fast
Low - very fast
Describe the valley profile in the up, mid, low course
Up - steep sides
Mid - flat with steep sides
Low- flat with gently sloping sides
Describe the features in the up, mid, low course
Up - waterfalls, interlocking Spurs
Mid - meanders, floodplain
Low- meanders, floodplain, levées, ox-bow lakes
Describe the sediment shape and size in the up, mid, and low course
Up - angular boulders
Mid- more rounded rocks
Low - smooth, rounded pebbles
How does the uk's water and climate have an effect on river processes ?
Causes changes to landforms and landscapes
With the impact of climate What is the erosion rate?
Erosion rate will be higher with grater discharge, so rivers in wet climates will erode more material than those in dry climates, widening and deepening river valleys and increasing the amount of eroded sediment
With the impact of climate, what is the transport rate?
The transport rates will be grater where the energy of the water is greater, so rivers in wet climates will transport more material than those in dry climates
With the impact of climate what is the amount of discharge?
The amount of discharge is affected by climate. Wetter climates mean greater discharge. Hotter temperatures mean greater evaporation so less discharge. The greeter the discharge, the height the velocity of the river
With the impact of climate what is the weathering.,
The weathering of rocks will be greater in some climates: for example, freeze-thaw weathering increase where temperatures range from just below freezing
How can increasing frequency of storms increase the risk of flood?
More periods of heavy, intense rainfall meaning more water flowing into rivers, which then overflow
How can increasing periods of hot dray weather increase the risk of flood?
It bakes the upper soli is when it does rain the water runs off the surface, it can't soak in, reaching rivers and rapidly increasing discharge
How can soil becoming impermeable during cold conditions increase the risk of flood?
Snowmelt cannot infiltrate and flows rapidly into rivers increasing flood risk
how are interlocking Spurs, waterfalls, gorges and river cliffs formed?
By erosion processes and the influence of geology in the upper course of the river
What are interlocking Spurs?
Near the rivers source, rivers are small and do not have a lot of power. They tend to flow around valley slide slopes, called Spurs, rather than being able to erode them. The Spurs are left interlocking, with those from one side of the valley overlapping with the Spurs on the other side
How are waterfalls formed?
A waterfall is formed along a river when a band of hard, more resistant rock lies over a band of soft, less resistant rock. The river erodes the less resistant rock at a faster rate, gradually undercutting the more resistant rock. The continued erosion of the soft rock by abrasion and hydraulic action causes an overhang of the hard rock. Eventually the hard rock cannot support its own weight and collapses under the force of gravity. The force of the falling water and abrasion by large angular boulders leads to erosion of the river bed and formation of a plunge pool
How are gorges formed?
After a waterfall is formed, as the soft rock continues to be eroded and the hard rock collapses, a steep-sided gorge is formed as the waterfall retreats upstream. Gorges form in hard rocks, where vertical erosion by rivers is dominant.
What is the weathering process?
Weathering is the wearing away in situ of the river valley side. There are three weathering processes common to the river valleys
How is a plunge pool formed?
Hydraulic action and abrasion
What is a floodplain?
A flood plain in the flag area of land either side of a river in its lower course. It is formed by erosion and deposition. Lateral erosion on the outside bends of meanders means they migrate across the valley floor and can erode the valley sides, so the valley floor becomes wide and flag. During floods, the flood waters spread out across the valley floor. As they slow down, with less energy for transport, the river deposits fine sediments called alluvium.
How is a flood plain shaped?
In the lower course, the river is nearing the sea and carries a huge amount of sediment (alluvium)
When the river floods,excess water spills over the. Surrounding areas urging flooding, the velocity of the river is reduced, it loses energy, and deposits sediment , forming the floodplain
The floodplain is shaped by the lateral erosion of meanders as they gradually migrate downstream and by deposition of material of the inner bends
What are levees?
Levees are natural embankments of sediment formed along the banks of rivers that carry a large load and occasionally flood. In times of flood, water and sediment come out of the channel as the river overflows its banks. As it overflows, the river immediately loses velocity and energy and deposits the larger and heavier sediment first, on its banks, repeated flooding causes these banks to get higher, forming levees.
Go and look at the diagram
On page 19
How are the landforms meanders and ox-bow lakes created?
But the interaction of deposition and erosion process in the middle and lower courses of a river
What are meanders?
Meanders are bends found in a rivers course, commonly found on a rivers flood plain. The flow of the water swings from side to side, directing the line of maximum velocity and the force of the water towards the outside of the bend. This results in lateral erosion by undercutting and an outer, steep bank is formed. This is called a river cliff. On the inside of the bend the velocity and force of the water is less, leading to deposition and the formation of gently sloping bank known as a slip-off slope. The material deposited is called a point bar and is characteristically curved in shape. Due to erosion and deposition, the cross section of a meander is asymmetrical-steep on the outside of the bend, gentle on the side.
What is a river cliff?
In the outer bend of a meander, where the current is faster, there is greater erosion. This wears away the bank creating a river cliff
What is a point bar?
On the inner bend of a meanders, where the current is slower, there is greater deposition, creating a point bar
What are the steps to ox-bow being formed?
Narrow Neal of meander is gradually being eroded
Water now takes the quicker route
Deposition takes place, sealing off the old meander
Meander neck has been cut through completely
Ox-bow lake left behind meander completely cut off
How can urbanisation affect rivers and change river landscapes?
Urbanisation has caused towns to grow, meaning they are fewer permeable surfaces. Water flows into the river, increasing discharge
Increasing demand for housing has led to new houses being built on floodplain so. This changes the natural landscape
River may be channelised or made to flow underground to make room for urban developments. If this happens, erosion and deposition cannot take place
How does agriculture affect rivers and change river landscapes?
Field drains can improve farmland, but quickly move water into streams and rivers, and can destroy natural wetland landscapes
Forests can be felled yo make way for farmland. Trees intercept rainfall, helping to reduce surface run-off. Removing trees means water reaches rivers more quickly
Abstracting water for irrigation reduces the flow and velocity of a river so deposition occurs rather than erosion
Ploughing fields up and down a slope can increase the amount of sediment in rivers and increase deposition
How can the industry affect rivers and change river landscapes?
Industry is a big user of water, so can reduce the amount of water in rivers, leading to less erosion
Industrial processes can pollute if chemicals or waste are spiller or dumped into them. This can destroy plants and animals and change the natural landscape
How is river flooding caused?
By a combination of physical and human factors, and has a range of physical and human effects
How does the rainfall intensity affect flooding?
A lot of rainfall over a short period of time prevents soil infiltration,
How does geology affect flooding?
Rocks like granite are impermeable, so water is unable to percolate from thin soil above
How does snowmelt affect flooding?
At spring time warmer temperatures will melt snow creating more water
How do drainage basins affect flooding?
Steep-sided valleys or a lot of rebut arises means the water enters the river system quicker
What happens after rainfall intensity,geology, snowmelt or drainage basins has affected flooding?
Excess water will flow towards the river as surface run-off (overland flow) or groundwater
Then water will reach the river channel more quickly and force the level or river to rise above the bank level of river to rise above the bank level. Flooding can then occur
What are the physical effects of floods?
Physical effects include landslides, soil erosion, loss of natural habitats, contamination of water supplies
What are the human effects of floods?
Human effects include death, disease, damage to property, insurance claims, loss of livelihoods,moss of crops and farm animals, disruption to transport
What is hard and soft engineering used for?
To help protect river landscapes from flooding
What does hard engineering involve?
It involves building structures as a defence against flooding
What are dams and reservoirs? Name advantages and disadvantages
They are barriers constructed to hold back water in artificial lakes
Advantages: you can store large volumes of water until needed, and they are long lasting; can be used to generate hydro-electric power (HEP)
Disadvantages: expensive to build, sediment can build up in reservoirs
Landscape impact - the natural river valley landscape is flooded
It is hard engineering
What is channelisation? Name advantages and disadvantages
Channelisation is deepening or widening the river channel
Advantage: it allows water to flow more quickly from areas of flood risk
Disadvantages: visually unattractive, and more water is taken downstream, increasing the flood risk to other settlements
Landscape impact - replaces the natural meanders and floodplain with an artificial channel
It is hard engineering
What is soft engineering?
It uses natural processes to reduce the impacts of river flooding
What are washlands? Name advantages and disadvantages
Washlands are areas next to rivers that are deliberately flooded to avoid flooding residential or important agricultural areas
Advantages: creates an area for floodwater to go
All natural river processes such as deposition
Disadvantage: might limit the use of land
Landscape impact - preserves the natural floodplain landscapes in the mid and lower river courses
It's soft engineering
How was the river Dee formed?
The source of the river Dee is in Ddualt, an upland area in snowdonia, north wales,
Here annual precipitation is high
The Dee flows south-easterly, eroding this heavily glaciated upland landscapes formed of igneous and metamorphic rocks
Near Chester the river meanders across a wide floodplain, eroding softer sedimentary rocks and depositing sediments
A section is artificially straightened, giving a man-made landscape
Further position occurs to form the Wirral estuarine landscape
What human factors caused changes to the river Dee?
1732-1736, channelisation of 8km improved navigation, increasing discharge and velocity and creating an artificial landscape
Under the river Dee regulation scheme a series of reservoirs was built eg Llyn Celyn
Early embankments were built along the middle course to protect agricultural land and properties, preventing further development of the floodplain landscape
To what physical factors caused change to the river Dee?
Floodplain. Landscapes between Holt and Wothernbury with meanders, alluvium and river terrance deposits formed by active erosion and deposition, causing the river to change course over time.
If sea levels rise by 1m by the year 2100, coastal landscapes will replace salt and freshwater marsh landscapes.
In the Dee estuary, rises in sea level will destroy the estuary landscape.
In periods of drought, river flows are low, by contrast, heavy rainfall and high surface runoff cause high river flows where most erosion and transportation occur
How can duration of rainfall affect flooding?
Long periods of rainfall cause the soil to become saturated and prevent further infiltration of rainwater, leading to increased surface run off
How do rocks affect flooding?
Different rock types in the catchment can affect flooding. Permeable rocks such as chalk allow water to soak in, so reducing surface runoff. Impermeable rocks such as clay do not allow water to pass through them, so rainwater will run off the surface and straight into the river channel
How does relief (the height and shape of the land) affect flooding?
Water reaches the river channel much faster where slopes are steeper
How does deforestation (human factor) cause flooding?
Vegetation collects, stores and uses water from rainfall: this is called interception. Plant roots also encourage water to pass into soil and rock, so vegetation reduces runoff: if it is removed, more water can reach the river channel more quickly
How does urbanisation (human factor) cause flooding?
In towns and cities, rainwater will not infiltrate the hard, impermeable surfaces of concrete and Tarmac. This causes the water to run off immediately into drains and river channels.
How does climate change (human cause) flooding?
Warmer air can hold more water, which leaves to more rain and more intense storms, so there is more water
What is a hydrograph?
A graph that shows how a river responds to a storm event.
What is the discharge of a river measured in?
Cubic metres per second
In a hydrograph what does the rising limb represent?
It represents the rapid rise in water after a period of heavy rainfall
In a hydrograph what is the lag time?
The difference between the time of the heaviest rainfall and the point at which the river contains the largest amount of water
On a hydrograph what does the falling limb show?
Shows the reduction in the amount of rainfall reaching the channel
What are embankments?name advantages and disadvantages
They are high banks built on or near river banks.
They stop water from spreading into areas where it could cause problems such as housing, and they can be earth and grass banks, which blend in with th environment.
However flood water may go over the top and then get trapped behind them and they can burst under pressure possibly causing even more damage
This is hard engineering
What is flood relief channels? Name advantages and disadvantages
They are extra channels that can be built next to rivers or leading from the.
The relief channels can accommodate high flows so that a river will not overflow its banks.
However they can be unsightly and may not be needed very often and costs can be high
This is hard engineering
What is flood-plain zoning? Name some advantages and disadvantages
It's when the government allocate are ads of land to different uses, according to their level of flood risk.
Flood risk management aims to prevent building homes and businesses in high risk zones. Here, such as open space for leisure and recreation are allowed because flooding would be less costly.
However these may not be the best places for the different activities in terms of pubic accessibility and flood plains are attractive places to build
This is soft engineering
What is weathering? (River)
Weathering is the breakdown and decay of rock by natural processes usually acting on the river valley sides
What is a drainage basin?
A drainage basin is the area of land usually drained by a river and its tributaries. When it rains, much of the water usually finds its way into rivers eventually, either by moving across the surface or by goi g underground and moving through the soil or rock beneath
What is a watershed in a river?
The boundary of a drainage basin separates one drainage basin from another and is usually high land, such as hills and ridges
What is the tributary in a river?
A stream or small river that joins a larger stream or river
What is the source of the river?
The starting point of a stream or river, often a spring or lake
What is the confluence in a river?
A point where two streams or rivers meet
What is the mouth of the river?
The point where a river leaves its drainage basin and flows into the sea
What is flows?
It's a form of mass movement where masses of soil or rock, usually mixed with water, flow like liquid downhill
After mass movement the material moves down valley sides and collects at the bottom, where a river may erode it. What does this make the slope?
Steeper, causing more mass movement
What does river erosion involve?
River erosion involves the action of water wearing away the rocks and soils on the valley bottom and sides. Rivers have most energy for eroding and transporting sediment when there is a large amount of water and a steep gradient.
How are ox-bow lakes formed?
As a meander bends and develops, it's neck becomes narrower. Eventually the river may erode right through the neck, especially during a flood. Water then flows through the new, straight channel and the old bend is abandoned by the river. Deposition at the neck seals off the bend, which gradually begins to dry up, leaving behind a horseshoe-shoes lake.
What does a rivers long profile show?
It shows the height and distance downstream from the rivers source to its mouth. It is a curved shape, steeper near the source and flatter near the mouth.
Describe the upper course of the river Dee
The source of the river Dee is 460m above sea level on the slopes of Ddualt in snowdonia national park, north wales. Their annual average rainfall there exceeds 3000mm and runoff is high from the steep upland slopes. The geology is mainly hard igneous which are resistant to erosion. Near the source, the channel is narrow, shallow and full of angular stones, so friction with the bed and banks slows the river down. In the upper course the river erodes vertically, cutting down into the landscape and forming a v-shaped valley with steep slopes, where sliding and slumping takes place.
Describe the middle course of the river Dee
As the river Dee leaves its upland area and flows downstream, the valley becomes wider and flatter, creating areas of flood plain, and it's gradient decreases. The river now erodes sideways through lateral erosion as well as downwards, and there is some deposition, for example on the inside bends of meanders. Sooner or later the sediments will be eroded by the river again, so they become smaller and more rounded, and transported further downstream. As more tributaries join the river Dee its discharge increases.
Describe the lower course of the river Dee
The lower Dee valley, the climate changes, with average annual rainfall less than 750mm. The river flows through softer rocks, such as sandstone, towards Chester. Lateral erosion creates a wide valley with a flat bottom. The river channel widens. Because it's deep and smooth, there is less friction with the river bed and banks, so the rivers velocity is greatest. More tributaries increase the Dee's discharge. Here lateral erosion and transportation continue and the muddy river water shows its sediment load is high. This encourages deposition, for example at the river mouth where the flow is checked by the sea. After 110 km the river Dee reaches its mouth in the Irish Sea between Wales and Wirral peninsula. This part of the river near Chester is called the estuary because it's affected by rides
As the river Dee flows downstream what happens to the characteristic of the river?
Width - increases
Depth - increases
Velocity - increases
Discharge - increases
Gradient - decreases
Channel roughness - becaomes smoother, so less friction
Sediment shape and size - becomes smaller and rounder
What are contour lines?
Contour line joining places of equal height above sea level. They also tell us how much the land slopes. Contours that are close together on the map show where the land slopes steeply. Contours further apart on the map show gentler slopes.mareas with few contours, or none at all, are flat: there is little or no gradient
What are the steps to drawing a cross section of contour lines?
Choose where you are going to make your cross section. Place a strip of paper across the contour lines on the map.
Mark on the strip of paper each place where a contour line crosses it. Label the heights of the contours in you paper.
Make the horizontal axis the same length as your strip of paper.
The vertical axis is the height of the land from the lowest point to the highest point in a cross section
Use the information on your strip of paper to plot the heights on the graph paper
Joint the dots and label some of the landscape features
Describe the river Dee
94% of catchment in rural, including forestry, sheep farming and pasture in upper valley, dairy and arable farming in lower valley.
The river is a water source for 3 million people in Wales and north-west England
The river supports large areas of habitats including plant and wildlife
The river Dee and its estuary are famous for commercial and recreational fishing
Parts of the catchment are popular for recreation and tourists.
Key communication routes run along side the river Dee, including the Chester to Holyhead railway line, the A55 and A483 primary roads.
What is the environment agency responsible for in terms of the river Dee?
Responsible for managing the flood risk in England, as well as protecting the environment and water quality. It has produced a river Dee catchment flood management plan. By 2100, the plan predicts an increased risk of flooding caused by:
Increasing population - more people will be in areas of risk.
Urban development and changes in land use, causing more runoff.
Climate change, including 20% increase in river flows, and 1m sea level rise.
Together these factors will increase the number of properties in the catchment at risk from a 1% flood event from 4200 to 6400, with most impact on Chester.
What's the average annual cost of damage from flooding?
Between £500 million and £1 billion
How can intense rainfall lead to river flooding?
During periods of heavy rai fall, the soil and rocks can quickly become saturated. As infiltration is reduced, water flows over the surface and into the river at a faster rate.
How can snow melt cause flooding?
In some places a lot of snow falls during the winter months. When temperatures rise above zero in the spring, all the snow that has built up melts, releasing large volumes of meltwater.
Describe the boscastle flood of 2004
On 16 August 2004, a months worth of rain fell in one day, leaving the small village of boscastle in ruins. Around 100 homes and businesses were destroyed and 75 cars were washed into the sea. The tourist industry was significantly affected, with the Wellington hotels lower floor unrecognisable and many local businesses destroyed. The des astatine caused by the floods left many local residents struggling to deal with what they had to experience that day.
Describe the flood in the UK 2012
In 2012, it rained persistently from April to November. Between 21 and 24 November, a series of low-pressure systems crossed the UK, bringing strong winds and intense rain that fell on saturated ground, causing immediate surface runoff and flooding. North Wales, Cumbria and South west England were badly hit. 2012 was England's wettest and Wales third wettest year on record, causing flooding in many parts of the UK that killed 9 people, flooded 800 homes and ruined £600 million worth of crops
Describe the Tewkesbury flood of 2007
During July 2007, heavy rainfall caused the river Severn and Avon to flood, leaving 48000 homes affected and estimated repair cots for each home between £20000 and £30000. For the local councils economy the floods cost £140000 and for the British economy and estimated £3.2 billion. The floods left many local schools and businesses closed
Describe the Somerset flood of 2014
During January and February 2014 in Somerset, persistent heavy rainfall resulted in disruption to transport (road and railway) because the flood waters took around 12 weeks to reduce. A total of 1000 hectares of farmland were left under water and six farms, including their animals, had to be evacuated. In the villages of moorland and fordgate homes were destroyed and local residents were evacuated because of fear for their safety
What are the main reasons the flood risk is likely to increase in future?
The main reasons are changes to land use and an increasing population and changes to weather patterns, particularly linked to climate change.
What is river restoration? Name advantages and disadvantages
River restoration is restoring the rivers original course.
Restoring rivers to a more natural course by taking away embankments aims to slow them down (eg restoring meanders). And natural rivers are more attractive and create natural habitats for wildlife.
However some flood banks are often still needed, and like floodplain retention, changes in land use may bring some disadvantages.
How does the environment agency manage the risk of flooding in England?
They reduce the chances of a flood happening by managing rivers and land use, controlling development in flood plains and building flood defences.
And reduces the impact of flooding by helping people prepare for flooding and giving flood warnings
Where does the environment agency have to work out before they put in flood defences?
They work out where flood defences would be most effective in preventing floods, and where they would not cause environmental damage. In the past people controlled floods by hard engineering methods, often building defences out of concrete. However these methods are expensive and do not reduce the risk of flooding in other parts of the catchment, and some may even increase it.
Why may soft engineering techniques be the answer long term?
Soft engineering uses a more natural approach to managing floodwater. This approach aims to create space for flood water in the landscape, which also reduces the risk of flooding in other areas. Soft defences are usually cheaper, need little maintenance and often provides habitats for wildlife
What does changes in land such as deforestation and urbanisation increase in rivers?
It increases the amount and speed of surface runoff and river discharge. By contrast, improving land use aims to help rainwater infiltrate into the soil and slow runoff.
How does afforestation help reduce the flood risk of rivers?
Because woodland intercepts rainfall, and tree roots encourage infiltration of water
How can managing farmland reduce runoff in rivers?
Managing farmland can reduce runoff, for example by avoiding overgrazing by animals, and ploughing across slopes rather than downhill
How can managing drain ab in urban areas help reduce flash floods?
Managing drainage in urban areas more sustainably helps reduce flash flooding, for example by increasing green areas and building ponds to store runoff
The environment agency and the local government and agencies work together to educate people about the hazards of living in flood risk areas, what do they use and what advice do they give?
They use tv, the Internet, leaflets, helplines and training exercises to make people aware of they they should do before, during and after a flood, advice for homeowners include: lay tiles on the ground floor and use rugs instead of fitted carpets, raise the height of the electrical sockets to 1.5m above ground floor level, fit stainless steel or plastic kitchens instead of chipboard ones, position any main parts of a heating of ventilation system such as a boiler upstairs, fit removable barriers and non-return valves to al, drains and water inlet pipes, replace wooden window frames and door with synthetic ones