Rivers Flashcards
What are the 4 processes of erosion?
- abrasion
- hydraulic action
- attrition
- solution
What are the 2 processes of transportation?
- saltation
- traction
What is abrasion?
-small boulders scratch and scrape their way down the bank, wearing the bank and bed
What is hydraulic action?
- water is forced into cracks by the fast flowing river
- repeated causes weakened rocks, banks
What is attrition?
-stones transported down the river collide with each other and the banks and causes the stones to be small and round
What is solution?
-dissolving of rocks e.g chalk and limestone
What is saltation?
-small pebbles and stones bounce along the river bed
What is traction?
-large boulders and rocks are rolled along the river bed=bedload
Describe the upper course of a river
- wet and boggy valley
- narrow and shallow river
- steep v-shaped valley
- more vertical some lateral
- waterfalls
- small streams
Describe the middle course of the River Tees
- there are gorges as the waterfall moves upstream
- river meanders-changing shape
- the town Yarm=in a meander (18km from sea)
- less rainfall
- 95%of land is farmland
- river is at it’s most powerful + broadens out
Describe the lower course of a river
- flat and floodplain
- no power for erosion
- small bedload and fine silt
- large cities and factories built on the marshy land
Describe the middle course of a river.
- large sized bedload, smoother rocks
- lateral erosion=wide river
- area of warmer temps and less rain
- towns built
- arable and pastoral farming
Describe the upper course of the river Tees.
- the source starts where Cumbria borders county Durham and is a big soggy mass
- cuts a v-shaped valley and carries lots of sediment
- at 5km, the angular rocks are mainly smooth
- high force waterfall, made of rhinestone
- the flow rate = 20km per second
Describe the lower course of the river Tees.
- carries a small amount of material
- next to a factory, used for ships to off load goods
- 15 degrees at the end
- man made
- Stockton on Tees= the main town
How do waterfalls occur?
-when a band of hard rock overlies softer rock
What does splash back cause?
- hydraulic action which weakens the rock behind the fall of water.
- the undercutting leads to an overhang
What develops at the bottom of the waterfall?
-An indentation which turns into a plunge pool
What happens when the overhang breaks off?
-rocks swirl in the plunge pool creating abrasion
What is created as the undercutting continues?
- the waterfall retreats upstream creating a gorge
- the gorge retreats and grows longer
What is an interlocking spur?
-projections of high land entering the valley from alternate sides
How are interlocking spurs made?
- the winding path of the river is due to obstacles being in the way
- the river takes the easiest route over the land resulting in projections of high land
Why do rivers meander and how are meanders created?
- due to obstacles in the way
- fastest flowing on outside bend which cause lateral erosion making the river wider
- outer bends are eroded by abrasion and hydraulic action
What is the fastest flowing part of a river called and why is it the fastest?
- the thalweg
- there is less friction because it is the deepest part
How are ox-bow lakes created?
- the meanders become very narrow and at times of high discharge, the river takes the shortest route and does not meander
- the deposition of alluvium seals off the meander forming a straight river channel
- The cut off meander is called an ox-bow lake
What is the name for a dried up meander?
-meander scar
How are levees made?
- at times of high discharge, the river will overflow it’s banks
- the increase in friction =drop in river’s velocity, resulting in the river’s load being deposited (coarsest and sediment deposited first)
- as this process repeats, the deposition builds up creating natural levees
How are floodplains created?
- the deposition at the slip-off slopes provides sediment to build up on the valley floor
- the river carries large amounts of suspended load and when it floods, it is deposited onto the flood plain as alluvium
- this process builds up the flood plain
List some human factors that affect flood risk. (7)
- new infrastructure increases impermeable surfaces
- more houses are being built on flood plains
- when new houses are built, roads must also which increases impermeable surfaces
- deforestation reduces interception and the roots no longer take water from the soil
- felling results in the soil getting saturated, run-off occurs and river discharge increases
- farming, loss of hedges =less interception
- ploughing fields= more channels for the water to run down ending up in river
List some physical factors that affect flood risk.
- heavy rain and sudden bursts=surface runoff, discharge increases and flash floods occur
- snow melt=release of stored water results in surface runoff
- steep slopes=surface runoff occurs before rain v=can infiltrate soils
What is the difference between deforestation and felling?
- felling=cutting down a few trees
- deforestation=large scale removal of trees
What is the rising limb on a hydrograph?
- period of rising river discharge following periods of rainfall
- the upward line of the hill
What is (basin)lag time on a hydrograph?
- time difference between the peak of the rainstorm and the peak flow of the river
- arrow line from the bar graph to the top of the hill
What is the recession limb on a hydrograph?
- period of time when discharge is falling after reaching peak
- the downwards part of the hill
What is the through flow on a hydrograph?
- the horizontal flow of water within the soil layer
- dot line in between hill
What is storm flow on a hydrograph?
-the water that arrives in the river during surface run off
What is the baseflow on a hydrograph?
-normal discharge of the river
Where is Morpeth?
- situated in a loop of the river Wansbeck
- Northeast UK
- 15 miles from Newcastle upon Tyne
- 12 miles from North sea
When was the Morpeth flood?
-6th and 7th of September, 2008
What were the causes of the Morpeth flood?
- prolonged rainfall, 235% that could be expected for a month
- river Wansbeck=narrow and steep sided=lots of surface run off
- soil already saturated because of wet summer
- increased urbanisation since 1960
- trash screens at the culverts of tributary were blocked
What was the peak water level in Morpeth?
-3.99m
What were the social impacts of the Morpeth flood?
- 400 residents evacuated due to mud in houses
- 913 residential properties affected
- shelter provided in King Edward high school
- 198 properties in middle greens area did not receive a flood warning
What were the economic impacts of the Morpeth flood?
- 89 commercial properties affected, stock destroyed
- overall damage =£40 million
- Morpeth flood disaster raised over £20,000
What is the flow rate of the river Tees?
-20km per second
What temp is the river Tees towards the end?
-15 degrees
When does angular material turn smooth in the river Tees?
-5km
What % of rainfall happened before the Morpeth flood?
-235% of the rainfall expected for a month
How many properties in middle greens area did not receive a flood warning?
-198
How many residential properties were affected in Morpeth?
-913
How many residents evacuated due to mud in their home?
-400
How many commercial properties were affected?
-89
How much money was the overall damage of the flood?
-£40 million
How much did the Morpeth flood disaster fund raise?
-£20,000
What are the pros and cons of building dams and reservoirs?
- expensive, ecosystems disrupted, can cause landslides
- highly effective, creates jobs, reduces green house gases
What is suspension?
-fine, light material e.g alluvium is held up and carried within the river flow=suspended load
What is a flood relief channel?
-artificially made channel that is designed as a backup channel for floods
What is a pro and con of flood relief channels?
- habitats destroyed
- reduces flooding
How do planting tees help reduce the impacts of flooding?
-more interception
Pros and cons of planting trees?
- creates new habitats and cheap
- loss of potential grazing land
Pros and cons of flood warnings and preparation?
- only effective if people listen
- cheap, people can evacuate and take valuables with them
How much did insurance costs increase to after the Morpeth flood?
-£900 per year to £2,500 per year
How much water was Morpeth high street under at the peak of the flood?
-60cm of water
What were the responses to the Morpeth flood?
- By 2010, £2.25 million was spent on essential work and repairs
- replaced waterproof seals on flood walls
- repaired damaged culverts + removed debris and silt
- environment agency created a new evacuation route
- in August 2015, a multi million pound flood defence, including a dam and storage area on the Mitford estate
- a new flood defence wall-1.8 m tall and 3 flood gates constructed in High Stanners
How much money was spent on repairs by 2010?
-£2.25 milliom
When and where was the multi million pound flood defence built?
- August 2015
- Mitford estate
How tall was the new flood defence wall in Morpeth?
-1.8m
What area was the new flood defence wall in Morpeth?
-High Stanners
How does using alternative energy production and planting trees reduce the rate of global warming?
- trees take in CO2
- renewable energy does not produce greenhouse gases
- increasing CO2 in atmosphere increases the greenhouse effect, causing the planet to become warmer
