River Processes And Pressures Flashcards
Define course
The distance between a rivers mouth and its source which is divided into the upper, lower and middle course
Define width
Distance from one bank the other
What happens to the width as you get further down a river and why?
It gets wider because there is a greater volume of water which allows erosion of the banks to take place more quickly
Define depth
The distance form the water surface to the river bed
What happens to depth as you move further down the river and why?
It gets deeper because there is more abrasion due to the higher load quantity, also erosion takes place more quickly due to higher volume of water
Define velocity
How fast the river is flowing
What happens to velocity as you move downstream and why?
It gets faster because the river is going downhill so it’s accelerating, the force of gravity is acting upon it
Define discharge
The amount of water moving in the channel
What happens to discharge as you move downstream and why?
It gets greater due to little tributataries joining the river
Define gradient
The steepness of the river bed
What happens to gradient as you move downstream and why?
It gets flatter because rivers start in the mountains
What happens do load quantity as you move downstream and why?
It increases because the river picks up sediment through deposition of the river banks
What happens to load particle size as you move downstream and why?
It decreases due to abrasion and attrition eroding the rocks
What percentage of rivers start in soggy moorlands?
80
How do interlocking spurs form?
In the upper course rivers are small and use their limited energy to erode vertically, they carve around areas of resistant rock creating steep valley sides called spurs and as the river winds around them the spurs on one side of the valley overlap those from the other side
What are meanders and how do they form?
Large bends in a river course which occur due to erosion on the outside bend where flow is fastest of a river and deposition in the inside where flow is slower
How do slip off slopes form?
Fragments of rock act as abrasive tools to deepen the river bed
Define suspension
Fine, light material is carried along by the river
Define solution
Minerals are dissolved in the water which is a chemical change
Define traction
Large boulders and rocks are rolled along the river bed
Define saltation
Small pebbles and stones are bounced along the river bed
How do oxbow lakes form?
Erosion of the neck of of a meander causes it to narrow as the fastest flow is here, the river takes the shortest path and breaks through the neck, deposition of the inner neck causes the isolated oxbow lake to form
How do floodplains form?
When the river contains too much water it floods the surrounding wide flat areas of land
Why are floodplains found in the lower course? (2)
Rivers able to meander, higher capacity of water
How do levees form?
When water moves away from its channel after flooding it becomes shallower and friction increases but energy decreases and it has to deposit some of the load it is carrying. Larger, heavier mounds of sediment are deposited first forming mounds of sediment on the river banks. Increased deposition on the river bed when the river is low gradually raises the river bed upwards. After many floods the sediment deposits build up to form levees
How do deltas form?
Speed of river decreases as it approaches the sea and it deposits most of its material, sediment builds to create an almost fast area of land (the delta) and because the river is flowing over an almost flat gradient its channel fills with sediment so the river splits into different streams
Define watershed
The area of high land forming edge of river basin
Define confluence
Point at which two rivers meet
Define tributary
Small stream which joins a larger river
Define main river channel
Main area through which a river flows
Define drainage basin
Area of land drained by a river
Define precipitation
Any source of moisture reaching the ground
Define interception
Water being prevented from reaching the ground by trees or grass etc
Define watertable
Current upper level of saturated rock/soil where no more rock can be absorbed
Define infiltration
Water sinking into soil/rock from ground surface
Define groundwater flow
Water flowing through the rock layer parallel to the surface
Define percolation
Water seeping deeper below the surface
Define throughflow
Water flowing through the soil layer parallel to the surface
Define transpiration
Water lost through pores in vegetation
Define surface run off
Water flowing on top of ground
Define evaporation
Water lost from ground/vegetation surface
How does geology affect the river landscape and sediment load? 3 ways
The softer the rock in that area, the more erosion and therefore the wider the river channel and the more deposited sediment. Waterfalls occur where bands of hard rock lay over soft rock, interlocking spurs occur where there is a mixture of hard and soft rock so rivers carve a path around the less resistant rock first
How do slope processes affect the river landscape and sediment load?
Large amounts of rock deposited by slumping block off the river like a natural dam therefore a lake forms behind and eventually overflows. Then the dam would erode and cause an increase in sediment load
Define peak rainfall
The hour of greatest rainfall during a storm
Define peak discharge
The time of maximum discharge in the river
Define lag time
The period of time between peak rainfall and peak discharge
Define falling limb
The period of time when the rivers discharge is falling
Define normal flow
The base flow of a river
Define rising limb
The period of rising river discharge following a period of rainfall
How does geology affect peak discharge?
Water runs over land where there is impermeable rocks as surface run off and therefore enters the river and increases its discharge
How does geology affect lag time?
Rocks can infiltrate into permeable rocks therefore more water is stored in the ground and moves towards the river more slowly which increases lag time
How does soil type affect peak discharge?
Soils with small pores like clay and those which are frozen prevent water infiltrating meaning more flows as surface run off and increases peak discharge however sandy soils with larger pores hold more water and prevent it reaching the river
How does soil type affect lag time?
Soils with bigger pores such as sandy soils allow infiltration to occur meaning water can be held for longer which increases lag time
How does the gradient of a drainage basin affect peak discharge?
The steeper the slope, the harder it is for water to infiltrate and more flows as surface runoff into the river which increases peak discharge
How does the gradient of a drainage basin affect lag time?
Gentle slopes allow for infiltration which takes water longer to reach the river as there is less gravity, increasing lag time
How does the drainage basin shape affect peak discharge?
When a drainage basin is smaller or elongated, the peak discharge will increase as there is a smaller surface area, making it easier to run into river
How will drainage basin shape affect lag time?
The larger the drainage basin shape or the more circular, the further the water has to travel which would increase lag tim
How do antecedent conditions affect peak discharge?
If there has previously been rainfall the ground will become saturated more easily and more water will be surface run off which increases peak discharge
How do antecedent conditions affect lag time?
When the ground is more saturated, it is easier for the water to flow as surface run off meaning it runs straight into the river without getting infiltrated
How does deforestation increase flooding?
Infiltration and interception is reduced which results in an increase of surface run off, erosion increases due to a higher volume of water making it more likely to exceed the rivers capacity and flood
How does land use change increase flooding?
Lack of soil infiltration and interception increases river discharge due to an excess of surface runoff, possible Change of gradient to make farming easier would impact the speed at which water reaches the river
How does urbanisation increase flooding?
The reduction of interception and increase of impermeable surfaces leads to more surface runoff, drains are designed to move water quickly away from houses to rivers
Why did rainfall cause Sheffield’s river Don to flood?
June 2007 was Sheffield’s wettest month since 1882 because 90mm rainfall fell on 15th June and almost 100mm fell on 25th June (the most Sheffield had ever received in one day), this rainfall was a 1 in 400 year event
How did Sheffield’s rivers and landscape cause flooding?
Sheffield has seven very steep hills so surface run off occurs quickly, the city lies at the foot of the Pennines where three rivers (Rivelm, Loxley, Don) meet meaning the volume of water increases, the river Don was already almost up to its banks so a backlog of water occurred so water backed up along the other two rivers and overflowed
How did Sheffield’s drainage cause floods?
The drains became blocked and overflowed due to the amount of surface run off, the city’s drain system is designed to cope with rainfall that may occur once every 30 years, the drains were the heaviest they’d been for 35 years
What were three effects of Boscastle’s 2004 floods?
100 homes and businesses damaged, tourist industry affected, 75 cars washed into the sea
What were four effects of Tewkesbury’s 2007 floods?
48,000 homes flooded, £3.2 billion cost, water polluted with sewage, many schools and businesses closed
What were three effects of Somerset Levels’ 2014 floods?
Flood waters took 12 weeks to drain away which disrupted transport, 1000 hectares of farmland left underwater, local residents of moorland and fordgate evacuated
How has the UKs population increased flood risk?
Since 1964 the population has grown by over 10 million people (18.7%) and half of this growth has occurred since 2001
How have changes to land use increased the UK’s flood risk?
More trees are being cut down than planted for the first time in 40 years, tree cover in the UK stands at about 10% which is well below the EU average of 38%
How do flood walls work?
Artificial barriers along the side of the river raise the height and increase river capacity so it floods less easily
Give 2 benefits of flood walls
Can be built in areas with high flood risk, require minimal maintenance
Give three costs of flood walls
The stronger the building material the more expensive, cause water to build up further down the river due to less friction, look unnatural/block view of river
How do embankments work?
Artificial levees which raise the height of the river channel which increases the rivers capacity so it floods less easily
Give two benefits of embankments
Cheaper than floodwalls (maximum £1 million), blend in with environment as they use natural materials
Give two costs of embankments
Subject to slumping or erosion, water can get stuck behind them if they get overtopped or burst which can cause widespread flooding
How do flood barriers work?
Gates built near the mouth of a river which are closed when a storm surge is predicted
Give three benefits of flood barriers
Effective at preventing flooding of large areas, effective predictive technology, can be moved to where needed and erected quickly
How does floodplain retention work?
Maintains and restores original floodplain by lowering the level of them and planting shrubs and grasses, the floodplains are then able to flood
Give four benefits of floodplain retention
Prevents flooding in areas further downstream, provides somewhere for water to go, attractive, provides space for leisure and recreation
Give three costs of floodplain retention
Floodplains lose current use, does not protect buildings, restricts economic development
How does river restoration work?
Soft engineering method involves strategies to restore the rivers original course e.g meanders, slowing down water so it will not move through river quickly which could lead to a build up of water and flood
Give a cost of river restoration
Land use may have to be changed
What were we investigating in river fieldwork?
How do river characteristics change along the wear
Give three reasons Bedburn Beck was suitable for river fieldwork?
The area is only about 45 mins from the school, safe as it wasn’t too deep, the area has a history of flooding
How did we measure width?
Two people a tape measure on either side of the river and measured from the water line
What effect does width have on flooding?
The wider a river is, the lower flood risk is because more water can be stored in the river
Give four reasons the method for measuring width was suitable
That river was narrow enough to use a tape measure, shallow enough to walk across, tape measure was easy to read, not much equipment needed
How did we measure depth?
At 11 places along the river we measured depth using a meter stick, placing it on the river floor then measuring up to water level
How does depth affect flood risk?
The deeper a river is, the lower flood risk is because the river can hold more water
Give three limitations of the method for measuring width
Required two people, one person could be stood slightly upstream, tape measure may not be pulled tightly
Give three reasons the method for measuring depth was suitable
River was shallow enough to get in, metre stick was easy to read, didn’t require much equipment
Give two limitations of the method for measuring depth
Waves could be created when we got in the river, the water level may rise when we got in
How did we measure velocity?
We measured a distance of 2m down the river with 2 ranging poles then dropped a ping pong ball at the one which was upstream and timed how long it took the reach the second. Carried this out three times to work out an average
How does velocity affect flood risk?
The higher the velocity, the higher flood risk because the river has a lot of energy but very little friction
Give four reasons the method for measuring velocity was suitable
Carried it out three times to work out an average, river was flowing slowly so the most accurate reading could be taken from the surface, only took place over a short area, didn’t require a lot of equipment
Give three limitations of the method for measuring velocity
Wind could have altered our results, required more than one person, ping pong balls got stuck on the river banks
How did we measure gradient?
We placed one ranging pole in the middle of the river then placed another 5m downstream. We then lined up the clinomètre on the first ranging pole with the same point on the second and took the reading
How does gradient affect flood risk?
The flatter the land is, the higher flood risk because the land cannot travel downwards and therefore floods the banks
Give two reasons the method for measuring gradient was suitable
Did not require much equipment, the clinomètre was easy to read
Give three limitations of the method for measuring gradient
5m may not have been measured accurately, the clinomètre may not have been lined up accurately, required two people
How did we measure stone size?
At the same intervals which we measured depth, we picked up a stone and measured its length in cm using a ruler
How does stone size affect flood risk?
Larger pieces of sediment means higher flood risk because they may block the channel and overflow due to having no where to go
Give three reasons the method for measuring stone size was suitable
Only required a ruler, only required one person, river was shallow enough to reach the bottom
Give a limitation of measuring stone size
If the stones were too heavy we would have been unable to pick them up
How did we measure stone shape?
For each piece of sediment we measured, we compared its shape to a stone chart
How does stone shape affect flood risk?
When stones are more rounded we can identify attrition has occurred which would mean the river was powerful and more likely to flood
Give two reasons the method for measuring stone shape was suitable
Did not require much equipment, river was shallow to reach the bottom
Give two limitation of measuring stone shape
If stones had been heavy we may have struggled to pick them up, if they were sharp we may have cut ourselves
How did we measure valley characteristics?
We chose a suitable place on the site where you could see valley shape, vegetation, human influence, evidence of precious floods, stream shape and drew an annotated field sketch
How does valley shape affect flood risk?
V shaped valleys allow more surface run off than u shaped therefore have higher flood risk
Give three reasons the method for measuring valley characteristics was suitable
The sketch showed a lot of characteristics, this did not require a lot of equipment, only required one person
Give two limitations of measuring valley characteristics
If you were bad at drawing it is hard to identify what is on your sketch, we did not have time to draw in detail
What are geographical information systems
Systems used to capture, store and present data related to positions on the earths surface. The result is a digital map with layers of information
What are three useful layers of information for evaluating flood risk?
Geology, land use, population density
How did we access the flood risk map?
We accessed the flood map for planning on the environment agency website then typed in a place names
Why were the flood risk maps relevant to our investigation?
Showed the difference between flood risk in rural and urban areas (whether it was high, medium, low or very low). They were annotated with qualitative data about vegetation cover, geology and land use which allowed us to see how drainage basin characteristics affected flood risk
Why was the flood risk map reliable?
It is a national organisation which is funded by the government which we would assume to be accurate
What is a limitation of the flood risk map?
It is slightly pixelated
How did we access the geology map?
We accessed the geology of Britain viewer by the British geological survey
How does geology affect flood risk?
If rocks are permeable water infiltrates into them and prevents it reaching the river therefore decreasing flood risk
Why was the geology map suitable?
This is a national organisation of geologists therefore the data should be accurate and reliable as it will have been repeated
What are two limitations of the geology map?
It is quite difficult to pick out every rock type along the wear and quite a difficult map to interpret if you have never encountered geology before
What did we do with the OS map?
We looked at the large OS map of the NE to evaluate changes in the river channel we were studying and looked at land use
What are two reasons the OS maps were suitable?
The area we were studying was laid out in front of us and could easily be interpreted, we did not have to access the internet
What is a limitation of the OS map?
We could not identify changes in all river characteristics for example velocity or sediment
Which rivers lie to the north and south of the wear?
Tyne to the north, tees to the south
How many people live within the wear catchment area?
620,000
Which area of the Wear catchment is most at risk of flooding?
East
How much critical infrastructure is at risk in the Wear catchment area?
42
How many healthcare facilities are at risk in the Wear catchment?
3
How many gas and electricity assets are at risk in the Wear catchment?
25
Which settlement has the most properties at risk of flooding in the Wear catchment?
West Auckland
Name three settlements in the Wear catchment with more than 100 properties at risk of flooding?
Hougton-le-spring, chester-le-street, Durham
How do you present width and depth data?
Cross sectional areas
What was good about the cross sectional areas?
This combined two characteristics into one graph which meant we could identify their relationship
What was a limitation of the cross sectional areas?
The boxes were very small but equivalent to 2 or 5cm which made it difficult to plot accurately
How did we present gradient?
Line graph
Why was using a line graph suitable for gradient?
The sites were placed next to each other which made the changes over its course easier to notice
What were the limitations of the line graph for gradient?
Could have combined it with width and depth to show the relationship
How did we present sediment size?
Proportional symbols
Why were proportional symbols for sediment size suitable?
We could identify three difference in sizes easily
How did we present sediment shape?
Compound bar chart
Why was the compound bar chart for stone shape suitable?
A lot of data was presented on one graph
What is a limitation of the compound bar chart?
A radar chart would be easier to interpret has it combines all the data on one spider diagram
What two factors need to be considered when choosing fieldwork locations?
Locations need to be accessible for safety reasons, locations need to be close to school to allow time for data collection
Define solution
Acid in seawater dissolves calcium carbonate in chalk
Define saltation
Small pebbles and stones are bounced along the river bed
Define suspension
Fine light material is carried along in the water
Define traction
Large boulders and rocks are rolled along the river bed
Define deposition
Sediment, soil and rocks are added to a landform or land mass
What did the flood risk map show us? 3 things
Geology is very similar throughout the drainage basin -milestone grit- so doesn’t explain variations in flood risk, flood risk increases as the river reaches Durham (urban area with impermeable surfaces such as tarmac and a dense population), flood risk was low at all study sites due to interception from coniferous forest and a low population density
Why might our river fieldwork conclusions be unreliable? 2 reasons
We had to visit sites which were close together therefore had similar drainage basin characteristics because the channel at Durham was too deep and unsafe, all our data was collected in June when flooding is less likely so they were not representative of flood risk all year round
What did the geology map show us?
Geology of the river Wear near Durham is mainly sedimentary like milestone grit which is a permeable rock that reduces risk of flooding
How do waterfalls form?
Band of more resistant rock lies over less resistant rock, less resistant rock is eroded more quickly leaving a step (waterfall), more resistant rock is undercut forming an overhang, overhand can no longer be supported so blocks of rock fall into a plunge pool, powerful fall of water erodes the plunge pool using fallen rocks (abrasion)
What two types of erosion are dominant in the formation of a waterfall plunge pool?
Hydraulic action from force of waterfall hitting bed of plunge pool, abrasion
How do erosion and deposition form floodplains?
As a river meanders in its lower course lateral erosion erodes away the valley sides making it flatter, meanders migrate downstream and at the same time deposition occurs as every time the river floods fine particles of silt are deposited onto valley sides forming the floodplain over thousands of years
Identify 2 upper course features
Interlocking spurs, waterfalls
Identify 5 lower course features
levees, deltas, meanders, floodplains, oxbow lakes
Identify 4 effects of climate on river landscapes and sediment load
Rivers in wet climates erode more material as they have a greater discharge, freeze haw is most likely to occur when temperatures move from just above to just below 0, rivers in hot climates transport less material as more evaporation occurs and they have less discharge
How to calculate discharge?
CROSS SECTIONAL AREA X VELOCITY
What is soil creep?
Slope process: particles of soil slowly move down valley sides under the influence of gravity
What is slumping?
Slope process: valley sides eroded by river making it steeper and increasing downward movement of material, can be triggered by heavy rainfall
What is the difference between rivers flowing over resistant rock and rivers flowing over soft rock?
Rivers flowing over resistant rock tend to have steep sides, rivers flowing over soft rock have gentle slopes
How does climate change increase flood risk? 3 ways
Increased frequency of storms means more water flows into the river and increases antecedent conditions, increased periods of hot dry weather bakes the soil so when it rains the water runs as surface runoff as it can’t soak in, increased periods of extreme cold weather freeze the soil so water cannot soak in
Identify 2 changes in land use which can increase flood risk
Deforestation, replacing soil with impermeable surfaces such as paving over gardens to create parking spaces
Identify 7 threats to people of flood risk
Damage to homes, damage to farmland/crops causing problems with food supply, damage to roads/bridges/railways causing problems with transport, damage to businesses through destruction of goods and property and transport and communication delays, damage to freshwater, damage to electricity supplies
Identify 5 threats to the environment of flood risk
Death/injury of animals. damage to habitats, reduction in animal food supply, pollution damages land if sewage and chemicals are in floodwater, damage/destruction of plants, stress to animals that need to be rescued from flooded areas
Give a cost of flood barriers
Don’t provide long lasting protection
Give a benefit of river restoration
Can reduce flooding downstream
Identify 4 soft engineering methods of managing flood risk
Plant trees (afforestation) to increase infiltration, washlands, floodplain retention, river restoration
Give a cost of washlands
Restricts economic development
What are washlands?
Washland or washes are areas of land adjacent to rivers which are deliberately flooded at times when the rivers are high, to avoid flooding in residential or important agricultural areas.
What did we compare our river fieldwork results to?
Bradshaw model
How can you identify a site on a map which is not suitable for river fieldwork?
If it is on a different tributary to the rest of the stream its discharge and characteristics will not be comparable to the rest of the sites
Disadvantage of a scatter graph
Can only show the relationship between two variables
Disadvantage of a chloropleth map
Hide variations within areas
3 disadvantages of a pie chart
Lots of small segments make the chart difficult to interpret, do not show exact values, fail to show patterns and change over time
Disadvantage of a triangular graph
Data must be in percentages
Disadvantage of a bar chart
Do not show relationships between categories
What is a dispersion graph?
Dispersion graphs are used to display the mainpattern in the distribution of data. The graph shows each value plotted as an individual point against a vertical scale. It shows the range of data and thedistribution of each piece of data within that range.
Advantage of pie chart
Segments are proportional to the total quantity it represents which makes it easy to interpret
2 disadvantages of dispersion graph
Time consuming and difficult to construct, works best with lots of data
2 advantages of dispersion graph
Shows the spread of data from the mean, anomalies can be drawn
2 disadvantages of radial graph
Difficult to pick out anomalies, difficult to make a suitable scale
2 advantages of radial graphs
Lots of data can be put on one graph, individual variables can be compared
Give 4 points about the upper course of the river Severn
Very soggy (starts in soggy moorland), 700m above sea level, v shaped valleys, 30cm wide
Give 8 points about middle course of the river Severn
Fast flowing, high carrying capacity, load carried by river erodes river bed, waterfalls form by erosion of underlying soft rock, water falls cut back overtime to form gauges, meanders found here which erode to form oxbow lakes, 1000l per second velocity, river at peak flow in winter
Give 7 points about the lower course of the river Severn
River floods here due to excess run off in built up areas, 60,000 L per second velocity, ends in a large estuary, 350km long, mouth is 13km wide, tidal range of 15m, huge expanses of mud flats
How did depth increase between site 1 and 2?
From 7cm to 50cm
How did width increase between site 1 and 2?
From 150cm to 370cm
9 impacts of Sheffield’s floods
1200 homes flooded, 1000 businesses affected, roads destroyed, rail links flooded, two people drowned, 13000 without power for 2 days, Hillsborough Football Stadium flooded and cost several million pounds to repair, Meadowhall Shopping Centre closed for a week despite having defences to protect it against a 1 in 100 year flood
