- Created by: Lucy.B
- Created on: 17-05-15 10:31
Source: start of the river
Meander: is a bedn in the river
Floodplain: is an area that is flat and vulnerable to flooding ofthen in the lower section of the river.
Confluence: is the meeting point (or junction) of where two river's meet.
Tributary: is the smaller river that eventually joins the main river.
Drainage basin: is the whole area around where eventuallt water is drained into the river. Sometimes referred to as the 'Catchement area'.
Watershed: is the boundary line between two drainage basins.
Mouth: when the river joins the end and flows out to sea.
Case Study : The River Severn
Upper Course: gradient is very steep, bedload size is big, very shallow, channel shape ( ), high velocity (speed), valley shape ( ), waterfall gauge.
Middle Course: gradient is less steep, bedload size is less big, getting deeper, channel shape ( ), less velocity (speed), valley shape ( ), meander ox boe lake.
Lower Course: flat, small bedload size (fine particles), very deep, channel shape ( ), little velocity (speed), valley shape ( ), flood plain.
Characteristics of how a river changes
Upstream (source) Downstream (mouth)
Gradient: steep flat
Bed load size: big small
Channel depth: shallow deep
Channel width: narrow wide
Human activity: less more
EXAM STYLE QUESTION
Describe how the shape and characteristics of river channels change form source to mouth. (6 marks)
Near the source of the river (upper course), the river channel will be narrow and shallow, having a big bed load size. Here the gardient is very steep which can result in the river having a high velocity. The middle course of the river the sides are often still quiet steep, the bed load size is not as big and the depth of the river increases. the gradient becomes less steep, resulting in the velocity of the river being less fast. Near the mouth of the river (lower course), the river is wider, floodplain is flat with very gentle sides, the depth of the river increases dramatically. The gradient is gentle, flat causing the velocity of the river to be slow.
Rivers at work
1. Erosion: means the wearing away of the landscape.
- Abrasion: where the sand and pebbles erode the river bank and beds.
-Attrition: where rocks ans stones wear away as they collide into each other.
-Solution: where rocks are dissolved.
-Hydraulic action: where fast flowing water erodes the river banks.
2. Transportaion: is the movement of sediment by a river.
-Suspension: very small bits of soil and rock are carriedn in the river.
-Traction: large rocks dragged and rolled along the river bed.
-Saltation: smaller stones and pebbles bounce along the river bed.
3. Deposition: is where sediment from a river is dropped as the energy from the river is not suffiecient to carry the sediment any further.
Causes of flooding 2
Causes of flooding:
-Heavy rainfall: increase in precipitation in a short period of time causes a river to over flow.
-Impermeable rock: when it does rain all the water has no where to be absored therfore it will build up resulting into flooding.
-Hard baked soil: this acts like an impermeable rock, causing a major decrease in infiltration but increase in chances of flooding.
-Steep slopes: as the slopes are very steep the water running down it has no time to infiltrate, as there is an increase in surfae run off, the watr will built up at the bottom that could result into flooding.
-Deforestation: there are not trees/plants to intercept (decrease) causing an increase in overland flow.
-Building on floodplains (urbanisation): due to the impermeable rock, water is unable to infiltrate, this increases surface fun off; the water will flow done to the river causing the levels of the river to increase which will result into flooding.
Flood hydrographs: they show the relationship between rainfall (precipitation) and how much water is in a river (discharge)
Peak discharge: the highest level of the river
Lag time: the difference between peak discharge ad peak rainfall
Peak rainfall: highest level of rainfall
Case Study : Boscastle, 2004
Boscastle is situatesd in the North Cornwall Coast, South West of England.
Causes of Boscastle flood:
-6 hours of heavy rainfall, 6 inches of rain
-Buildings on a flood plain (urbanisation)
-Boscastle is near a confluence
-Steep-sided hills, increase in surface run off
EXAM STYLE QUESTION 2
For a named location, explain how human actions have increased flood risk. (6 marks)
Two human actions in Boscastle have increased the threat of flooding. Clearing vegetation has increased the rate of surface run off as less rainfall is being absorbed by the plants and trees as they have been cut down, this results to a shorter lag time. There would further be a decrease in interception as thos plants and trees that have been cut down are not able to interceot and absorb the rainfall. Building on a floodplain has also decreased the amount of rainfall beign infiltrated into the ground. This is beacause the water from the rainfall is unable to be infiltrated within the impermeable rock. This causes river levels to increase resulting in flooding, as it has resulted into a shorter lag time.
Impacts on the Boscastle flood
-Lose of jobs
-Damage of possessions
-Lose of stock, pets, business'
-Re-building of houses
-Decrease in tourism
-Damage of cars
-Insurance premiums went up
-Escape was hard
-People lifted to safety
-Flooded houses, ruined furniture
Responding to the 2004 flood (Boscastle)
In order to prevent flooding in Boscastle again, authorities have:
-Deepened the river channel to allow more water to be stored
-Widened the river to allow more storage of water
-Demolished the old bridge (thick) and built a new thinner one using better materials
-Put in a new drainage system
-Raised car park levels
They spent £4.5million on a new scheme to prevent flooding in the future.
Flood management: Hard engineering
Hardengineering: designed to prevent flooding by expensive construction projects e.g. dams, flood walls, channel diversion, increasing channel size Type Benefits Problems
Build flood plains (leeves) Preventing flooding in Expensive, can increase flood built up areas. problems furthur downstream.
Increase the size of the It allows the river to hold Expensive to construct, affects river channel more water, reduces flood wildlife by the river banks. risks.
Divert the river away Reduce the risk of flooding in Very expensive, can cost £14 from the ciry centre the town centre. million per 1km stretch.
Building dam Prevent flooding, produce hydro- Very expensive, flood area electric power, control between the dam, takes river when flow is low. time to build/make.
Soft engineering: deisgned to reduce the impacts from flooding. Tries to work with nature rateh the against and realises the importance of natural ecosystems as a way of reducing flooding e.g. afforestation. flood warnings, floodplain zoning.
Type Benefits Problems
Flood abatement Prevents flooding in a Takes a long time to plant trees.(afforestation) natural way & is relatively This will not have immediate impact. cheap.
Floodplain zoning It is cheap as it does not Doesn't protect the existing buildings (area designed to require any building of flood already found in these zones. flood) plain.
Flood warnings Helps to save lifes rather than Doesn't people's property. to stop flooding.
EXAM STYLE QUESTION 3
With reference to a named example, describe the measures that can be taken to prevent the impacts of flooding. (6 marks)
In Boscastle in 2004, there was a devastating flood that caused alot of damage to the village. £4.5 million was spent to prevent future flooding events. Firstlt, authorities have deepened and widened the river channel to allow more water to be stored. So, they have they have re-shaped the river in the way so for it to stop over flowing resulting in flooding. They have further demolished the old bridge into building a new one that is thinner built using better materials. This will allow more water to flow down the river. Raising the car park level will decrease the chance of flodding as the water wont flood the cars as easily. These are all examples of hard engineering as it prevents flooding but also harms the environment.
Case Study : Mississippi, USA
The Mississippi river burst its banks in 1993, it is over 3000 km long. It is one of the heaviest hard engineering river. Authorities have changed the map of the valleys, built controlled dams along the river, alot. This caused the river to shorten by 250km. Leeves were made, straightend the river channel, wing dytes narrowed and deepened the river.
- Economy has grown as there is no more floding
- created jobs
- controled dams generate electricity
- Straightining the river made shipping easier.
- Very expensive, $7million
- 100 years of builing it to where it is now
- Has affecetd the environment, destroyed animals habitats
- River will possibly flood
- Warm air and cold air collided, caused extreme amount of rainfall which resulted in the leeves to burst.
Case Study : River Rhine, Germany
It is a soft engineering scheme, allowed flood plain zoning (ecological flooding) - a way of flooding in the natural environment. 24 zones were designed to be flooded.
- Ecological flooding
- Creates new wet land, plants, habitats
- Doesn' harm the environment
- Generated hydroelectric power down stream in France
- Creates a conflict between France and Germany
- Millions of pounds of damage
- Flooded houses
- The architecture flood walls is what caused the major flood, as the water built up behind the walls and was relished all at once.
EXAM STYLE QUESTION 4
With referrence to named examples, describe the measures that can be taken to prevent the imapcts of flooding (8 marks)
Flooding of rivers can be managed in two ways; hard engineering or soft engineering. An example of a hard engineering project is the Mississippi river schem. In this scheme American architects re-created the shape of the river, making it straight. This was a benefit to shipping as it made it asier to trade ot transport goods. They further built dams along the river, this prevented flooding as the dams controlled how much water was flowing down the other side. However, this shortened the river by 250km. Lastly, they built wing dytes that narrowed and deepened the river, allowing more water to be stored.
An example of a soft engineering scheme, is the River Rhine scheme in Germany. They prevented flooding by ecological flooding. This allowed new wet land to be formed which aevolved new planst and animals. They allowed 24 zones to be flooded which helped prevent flooding in built up areas i.e cities.