Rivers Flashcards
How waterfalls and gorges are formed
-river flows over a layer of hard rock with softer rock more easily eroded rock underneath
-over time the softer rock is worn rapidly by processes like hydraulic action and abrasion creating a plunge pool at the foot
-the ledge which overhangs the plunge pool eventually collapses under its own weight
-the material is then eroded (by abrasion or hydraulic action) and transported downstream
-the waterfall retreats upstream leaving behind a steep sided gorge, every time the overhanging cap rocks breaks off the gorge retreats further and grows longer
-there is turbulent fast flowing water in the gorge
Features that are found in each section of the river
Upper course :
-waterfalls
-interlocking spurs
Middle course:
-Meanders
Lower course:
-floodplain
-levees
What does middle course of the river look like and features
-wider river
-starts to meander
-flooding more likely
What does upper course of the river look like
-soft wet marshy
-thin channel
-hill steep
-V shaped valley
-water erodes vertically
-waterfalls likely
-little human activity/ settlements
What does lower course of valley look like
-widest and deepest
-sediment is deposited
-estuaries
-docks have been built
-flooding more prone
-erosion, transportation and deposition most dominant here
Label the drainage basin
Characteristics of river tees upper course
-source of river is 893m above sea level near Cross cell in the Pennnine hills
-area revieves over 2000 millimetres of precipitation
-boggy land
-large sediment
-V shaped valley
-reservoirs are common
-sediment eroded most here
-high force watefall
-dolarite is the hard rock
-limestone is the soft rock
Characteristics of river tees middle cours
-river energy is lost here
-can’t carry harder heavier sediments so it is deposited
-meanders more likely
-90% of valley is used for farmland
-10km wide floodplain
-river meanders around a town called Yarm
Characteristics of river tees lower course
-deposit fined material
-90% of port material comes from ships that flow through the river
-artificial river straightening
-wide and deep river so allow large shops
-estuaries reclaimed mud flat to make them land
What is an estuary
-estuaries were formed when sea levels rose after the last ice age filling glacial troughs
-estuaries are the widest part of the river as lateral erosion occurs when tides are high and as the discharge and velocity it’s increases (this is in the lowest course)
-this energy is used to widen the river mouth and estuary through processes like hydraulic action
-due to the volume of water and the velocity of water the river is able to carry large amounts of sediment
-as saltwater and freshwater mix velocity decreases meaning that mud, sand and gravel carried by river from ocean floor carried by tides are deposited at the mouth as water loses energy
-tidal mud flats build along the shoreline as these sediments accumulate
-tidal mud flats are very fertile and are colonised by plants with freshwater marshes this provides an important habitat for wildlife
-they can also be used to create sheltered ports or land for heavy industry
Explain how a meander may be formed by both erosion and deposition (with diagram)
-a meander is a winding curve or river band
-water flows fastest on the outer bend of the river where the channel is deeper and there is less friction, this is called the thalweg
-lateral erosion such as hydraulic action and abrasion results in undercutting the river bank and the formation of a steep sided river cliff
-on the inside of bend where river flow is slower and water is shallower, material is deposited on a slip off slope as there is no more friction and energy
-as a result of erosion and deposition meanders gradually change shape and move across the floodplain and migrate downstream
Explain the formation of an oxbow lake
-a meander is a winding curve or bend in the river
-water flows fastest on the outer bend of the river where the channel is deeper and there is less friction
-lateral erosion results in undercutting of the river bank and formation of a steep sided valley cliff
-on the inside bend where the river is slower material is deposited on a slip off slope as there is more friction
-development of meanders is due to deposition and erosion
-over time the meander changes
-during high flow flood conditions the meander neck is broken through as it becomes very narrow
-the river now adopts the shorter easier route, bypassing the old meander
-deposition occurs at the edges of the new straight section effectively cutting off the old meander as velocity slows down
-the old meander now forms an ox bow lake separated from the main river
-over time the lake can fill will silt which can form marshland or the lake may dry leaving behind a meander scar
Human factors that affect flood risk
Land use in urban areas =
surfaces such as concrete and tarmac are common and they’d are impermeable, therefore less rain can infiltrate into the soil, this means that there will be more surface runoff which is the fastest flow and drainage systems taking water to river quickly, making it more likely to flood
There is also less vegetation and so less water can be intercepted and évapotranspiration can occur off the plants, therefore there will be a steeper rising limb and a greater chance of flooding .
Explain how river levees are formed
-levees are long narrow ridges or raised embankments alongside the river composed of gravel stones and alluvium, steeper on channel side than land side
-levees occur in the lower course of a river when there is an increase in the volume of water flowing downstream and flooding occurs
-sediment that has been eroded further upstream is transported downstream
-when the river floods the sediments spreads out across the floodplain
-friction with the land reduces the velocity and causes deposition
-when a flood occurs the river loses energy and the largest material is deposited first on the sides of the river banks and smaller material further away
-after many floods the sediment builds up to increase the high of the river banks so the levees become higher than the surrounding floodplain
-in a severe flood event levees may burst and cause serious damage to surrounding land
Physical factors that affect flood risk
Geology= rocks are either impermeable (granite)or permeable, permeable rocks such as sandstone allows water to percolate into it, this means that water as ground water flow to the river is slower, therefore the flood risk can be reduced
Precipitation = heavy rainfall results in rapid saturation of the upper soil layers and the excess water therefore reaches streams quickly as surface runoff
Relief = a steep slope will mean faster surface runoff and a shorter lag time so allowing more time for infiltration to occur
What is the lag time
The period of time between peak rainfall and peak discharge
Formation of interlocking spurs
-small streams and river tumble down mountainsides and are forced to flow around land that juts out into the river valley there, this land is called interlocking spurs
-vertical erosion occurs which depends the valley by hydraulic action and abrasion but does not erode sideways into the spurs
-low energy means that water isn’t strong enough to erode resistant rocks in the spurs so it follows the path of least resistance
-so the river is forced to flow around the,
-this erosion and movement of weathered material creates the class V shaped valley
Formation of a floodplain
-they are located in the middle and lower cours of the river and is often a wide flat area caused by meanders shifting along the valley
-erosion removes any interlocking spurs creating a wide flat area on either side of the river
-during a flood material being carried by the river is deposited
-over time the height of the floodplain increases as the material is deposited on either side of the river
Hard engineering river management strategies
-Dams and reservoirs
-river straightening and dredging
-embankments and artificial levees
-flood relief channel
What are dams and reservoirs and advantages and disadvantages
Dams = water is held back and released in a controlled way
Reservoir = water is usually stored in a reservoir behind a dam
A= highly effective (water can be released in a controlled way), can be used to produce hydroelectric power by passing the water through the turbine within the dam, reservoirs can attract tourism as attractive
D= very expensive, dans trap sediment which means the rest our can hold less water, habitats are flooded often leading decomposing vegetation which releases methane( greenhouse gas) , fish are disrupted from migrating as sediment is trapped behind dam they are prevented from spawning
What is river straightening and dredging and advantages and disadvantages of it
River straightening is when a meander is engineered to be wider, straighter and deeper, so more water can flow easier and carry more water
Dredging the removing silt and debris from the bottom of bodies of water
A= speeds up the water so high volumes of water can pass through area quicker, reduce flood risk in urban areas so increased homeowner reassurance so insurance costs go down
D= greater risk of flooding downstream as water is carried faster, needs to be done frequently and is expensive , changes in habitats can endanger animals
What are embankments and artificial levees and advantages and disadvantages
Embankments = artificially raised river bank so more water is contained in the channel
Artificial levees are built along river banks so that if floods occur water will not be able to breach wall and cause damage
A= flood water can be contained in one area, earthen embankments provide habitats for river bank animals such as voles and otters, walking routes (riverside footpaths)
D= looks unnatural and deprive people of access to the river for fishing and boating, Hugh maintenance costs as they need to be constantly monitored as could be eroded, can speed up the water in the river which will just move potential flooding downstream
What is a flood relief channel and advantages and disadvantages
It is an artificially made channel that is designed as a backup channel for a river that frequently floods, worlds like a bypass
A= removes excess water from river channel, insurance cost of homes are lower in area so value of home increases as more secure environment, calm water provides area for model boating or canoeing
D= expensive to build, people living south of a relief channel have to be moved causing disruption, schemes also take a long time to build (Exeter’s relief channel took 12 years to build), expensive and have to undergo maintenance and repairs
What is flood plain zoning
Planning the land usage around a river to minimise the damage to more valuable property and land
A= less damage is caused leading to fewer insurance claims, reduced flood risk
D= not always possible to change existing land uses so unrealistic, limits development in certain areas as the land may have been used for new businesses or for affordable residential housing
What is river restoration and advantages and disadvantages
When an artificially changed river is returned to original course, reinstates natural process and features
A= little or no maintenance is required so low cost solution, allows river to take natural course and reverts any ecological damage so restored biodiversity
D= flood risk can increase if nothing is done along the river, issues arise when river restoration takes place in areas that are still being used by people
What is river warning and preparation and advantages and disadvantages
During periods of heavy or prolonged rainfall, flood warning are sent out to public, particularly those who live in flood prone areas.
A= allows people to reduce damage to property and lives, enable people to move vulnerable and valuable items so fewer insurance claims, people have time to protect their properties
D= flash floods happen to quickly for warning, some predictions may be wrong which causes unnecessary panic, warnings of wrong intensity could leave people unprepared for real severity of flooding
What is afforestation
Planting tress to intercept rainwater and reduce surface run off, rainfall is caught in leaves and absorbed in roots
A= creates new habitats for animals and leisure areas for the public so tourism, tress act as natural water filters so rainwater is safer to drink
D= can be expensive as large areas of land will need to be planted to make scheme worthwhile, unless the trees are evergreens they will lose their leaves in winter months and won’t be as effects, this is usually when rainfall is at its highest
How does boscastles geography contribute to flood risk
-channel is very narrow which means river has reduced carrying capacity
-tress have been cut down so reduced interception and absorption through roots, increased surface runoff
-settlements have been built upstream which means more impermeable surfaces reducing infiltration and percolation
-water table is very high which means ground was already holding lots of water from previous rainfall
Effects of boscastle flooding
-Loss of tourist trade as they were warned away due to safety risks 90% of boscastles economy is from tourism, damage of 50 million pound, village did not open to residents or visitors until 8 months after flood, 115 cars washed away, damage to 58 buildings
Responses to boscastles flooding
-seven helicopters rescued 50 people, 10 million was spent on upgrading floods defences, raised the car park (reduced congestion) and used permeable surface, removed low bridges and rallies with wider bridges so more water could flow underneath, now has a wider deeper river (restricted natural habitat) , land owners were encouraged to plant new trees, no fatalities the emergency response team was quick and 100 people were evacuated
Disadvantages of boscastles new flood protection
-4.5 million tax payer money was spent on management by the environmental agency to protect 900 people
-Years of construction has reduced local business earning as tourists stayed away
-Construction work created short term noise pollution and altered river habitats
