River Environments Flashcards
(124 cards)
1
Q
What are the features of a drainage basin?
A
Source, watershed, channel network, mouth.
2
Q
Define source.
A
The upland area where the river starts.
3
Q
Define tributary.
A
A much smaller river, which joins onto a larger river.
4
Q
Define confluence.
A
The point at which two rivers join.
5
Q
Define mouth.
A
Where the river flows into the sea.
6
Q
Define drainage basin.
A
The area which is drained by a river and its tributaries.
7
Q
Define watershed.
A
The boundary between each drainage basin.
8
Q
What are the characteristics of the hydrological cycle?
A
- There is a finite (fixed) amount of water.
- There is never more or less in the global system.
- It is a closed system.
- The water is infinitely recycled.
9
Q
What are the stores in a hydrological cycle?
A
The atmosphere, snow and ice, interception storage, surface storage, soil moisture, groundwater in rocks, seas and oceans.
10
Q
What are the transfers (flows/main water movements) in the hydrological cycle?
A
Evaporation (from land and sea). Precipitation (from condensed water in the atmosphere). Wind (causing a net movement of water inland by blowing clouds inland). Overland flow. Infiltration. Percolation Through flow. Groundwater flow.
11
Q
Define hydrological cycle
A
A global circulation of water which is also a closed system.
when precipitation does not infiltrate the soil and flows on the surface of the land to the sea/lake
12
Q
Define precipitation
A
The transfer of water in any form from the atmosphere to the land or sea surface.
13
Q
Define condensation.
A
The change in the atmosphere when water vapour cools and becomes a liquid: the water takes the form of water droplets that appear in the atmosphere as clouds.
14
Q
Define transpiration.
A
Plants take up liquid water from the soil and ‘breath’ I into the atmosphere as water vapour.
15
Q
Define evaporation.
A
The hydrological cycle starts with evaporation due to the heat and solar energy emitted by the Sun. Water is converted from a liquid to a gas (water vapour). This takes place on the surface of the sea and from water surfaces (ponds and lakes) on land. Evaporation is particularly important in the transfer of water from the sea store into the atmosphere.
16
Q
Define evapotranspiration.
A
The loss of moisture from the ground by direct evaporation from water bodies and the soil, plus transpiration from plants (water evaporated directly from the leaf and water released in transpiration).
17
Q
Define through flow.
A
This takes place between the ground surface and the top of the groundwater store. As a exult of gravity, water moves slowly through the soil until it reaches a stream or river (horizontal movement).
18
Q
Define groundwater flow.
A
This happens in the rocks of the aquifer and is the underground transfer of water to rivers, lakes and the sea.
19
Q
Define channel.
A
The flow of water through a river.
20
Q
Define system.
A
A series of inputs, processes and outputs. Systems can be open or closed.
21
Q
Define open system.
A
A set of interrelated objects in which there are both inputs and outputs.
22
Q
Define closed system.
A
A set of interrelated objects in which there are no inputs or outputs.
23
Q
Define surface runoff.
A
When precipitation doesn’t infiltrate the soil and flows on the surface of the land to the sea/lake.
24
Q
Define infiltration.
A
Water seeping into the soul after falling on the surface (vertical movement).
25
Define percolation.
Water which has infiltrated the soil and is flowing between cracks in the bedrock (vertical movement).
26
What would happen to the movement of the water if the rock was saturated?
There will be an increased amount of water moving through the soil as through flow if the rock is saturated (‘full’ to capacity with water).
27
What would happen to the movement of the water if the soil was saturated?
When the soil is saturated, no infiltration takes place and water will flow on the surface towards the river. This is known as surface runoff or overland flow.
28
Define river regime.
The difference in the discharge of the river throughout the year (as river discharge can vary).
It closely reflects the local climatic conditions, particularly rainfall.
29
Define river discharge.
The volume of water carried by a river at any one time (measured in cumecs - m3/s of water passing a particular point along the river’s course).
Depends on precipitation, evapotranspiration and storage factors.
30
What is a hydrograph?
A graph showing the discharge of water over a given period of time.
31
What are the factors affecting river regimes?
- Amount and intensity of rain.
- Temperature.
- Slope of the surface (gradient).
- Rock type.
- Vegetation and land use.
- Human intervention.
32
How does precipitation affect river regimes?
Heavy rain will not sink into the ground but enter the river due to increased overland flow.
33
How does temperature affect river regimes?
Affects the form of precipitation (eg. Below freezing, there would be snow which could take weeks to melt and enter the river, and if the ground remains frozen, melting snow on the surface can reach the river quickly).
34
How does the gradient of the surface affect river regimes?
A steep surface will cause rapid surface runoff, so water will reach the river more quickly, however, water may infiltrate into the soil if the land is flat or gently sloping, delaying it from entering the river.
35
How does rock type affect river regimes?
Impermeable rocks don’t allow percolation, so surface runoff is increased, but permeable rocks allow percolation to occur, so the delivery of water to the river is delayed.
36
How does vegetation and land use affect river regimes?
Trees and other plants intercept and delay the rain from reaching the ground, whereas loose soil and rocks speed up the runoff and reduce lag time (same with tarmac and concrete in urban areas).
37
How does human intervention affect river regimes?
Dams hold back discharge and reduce the risk of flooding while reservoirs control the flow of water by opening and closing sluice gates for abstraction of water from rivers for a range of human needs.
38
What is a storm hydrograph?
These record the changing discharge of a river after a rainstorm.
They record the discharge of a river as being made up of two flows:
- Base flow (the ‘normal’ discharge of the river).
- Storm flow (the additional discharge of the river as a result of the rainstorm).
39
What is the lag time?
The delay between peak rainfall and peak discharge.
The shorter the lag time, the the quicker the water reaches the river channel. A short lag time causes the river discharge to rise quickly, forming a steep gradient on a storm hydrograph. The steeper the rise in discharge, the greater the chances of flooding. It is possible to mark on the storm hydrograph the level of discharge above which the river will flood. Once the storm and its peak discharge have passed, the amount of water in the river starts to decrease.
40
What are the main processes in a river and its drainage basin?
- Weathering (physical, chemical and biological)
| - Erosion (corrosion, solution, hydraulic action, attrition)
41
What is weathering?
The breakdown and decay of material and bedrock in one place. The weathered material doesn’t move (in situ) unless by gravity.
42
What is physical weathering?
Breaking of rocks into smaller and smaller pieces by force (and changes in temperature)
Eg. Freeze to thaw weathering (thawing in rock cracks)- liquid turned into solid ice when rainfall in rock cracks freezes. Forces are exerted as solid ice expands.
43
What is chemical weathering?
Rocks decaying and disintegrating by the changing chemical composition of rock through chemical reactions.
Eg. Limestone + water —> carbonation
44
What is biological weathering?
Material broken down by the action of living things (bio).
Eg. Trees growing into the cracks of the rocks and gradually splitting the rock apart.
Rabbits digging holes weakens the rock.
45
What are the two main mass movement events?
- Slumping (fast)
- Soil creep (slow)
Weathered or loose material is called ‘scree’ or ‘regolith’.
Movement of loose material by gravity can be catastrophic.
46
What is erosion?
The breakdown and transportation of material from one place to another, where it is deposited (always involves an agent of erosion: river/sea/water, wind, ice (glaciers).
47
What are the four main types of erosion that occur in a river and its drainage basin?
```
Corrosion (abrasion).
Attrition.
Solution.
Hydraulic action/power.
(Mnemonic = CASH)
```
48
What is corrasion/abrasion?
‘Sand paper’ action of load (material that has been washed or has fallen into the river) between the sides and floor of the channel.
49
What is attrition?
The load becoming smaller as it collided with each other.
| Doesn’t cause erosion of river channel or valleys
50
What is solution?
Water dissolving materials in rocks into a solute and carrying it away.
51
What is hydraulic action/power?
Power of the water forcing air into cracks in the rocks and forcing them apart as air expands under pressure. (Occurs mainly on the river channel and sides)
52
How is eroded material transported?
- Traction: large boulders and rocks are rolled along the river bed.
- Saltation: small pebbles and stones are bounced along the river bed.
- Suspension: lighter materials are carried along by river flow.
- Solution: materials dissolved in the water are carried along.
When energy levels are HIGH, large rocks and boulders can be transported (this is usually near a river’s source where the course is steep and the valley narrow).
When energy levels are LOW, only small particles (if any) can be transported (this is usually at the mouth of the river where velocity drops when the river enters a lake or sea).
53
What are the factors affecting the responsiveness of a river (storm hydrograph shape)?
- Relief (shape of the land). PF
- Rock type. PF
- Soil type. PF
- Vegetation. PF and HF
- Nature of precipitation. PF
- River use. HF
- Drainage density. PF
- Land use. HF
- Season/time of year. PF
54
How does relief affect the responsiveness of a river?
The steeper the slopes, the lower the rate of infiltration and the faster the rate of runoff when the soil is saturated or when rainfall intensity is high.
55
How does rock type affect the responsiveness of a river?
Runoff will occur quickly where impermeable rocks are exposed at the surface or quickly when they underlay soils (limited amount of infiltration). Soils with large amounts of clay do absorb moisture but only very slowly - therefore their permeability is low.
56
How does soil type affect the responsiveness of a river?
The deeper the soil, the more water can be absorbed. Soils which have larger particle sizes (eg. Those derived from the weathering of sandstones) have larger infiltration capacities.
57
How does vegetation affect the responsiveness of a river?
The more vegetated an area is, the more interception by trees and plants will occur, decreasing overland flow. This is further decreased by afforestation. However, if deforestation has taken place to be used as building materials or fuel, or to clear space for farmland or settlements, there will be increased overland flow due to less obstruction, and water will reach the river channel faster.
58
How does the nature of precipitation affect the responsiveness of a river?
Rainfall intensity- the greater the rate of rainfall per unit of time (millimetres per hour), the more likely that overland flow will take place.
Snowfall- this will result in less runoff initially but a sharp rise in temperature may result in a quick thaw and flooding (especially where the ground underneath the snow is frozen and thus the melted snow will reach the river rapidly via overland flow).
59
How does river use affect the responsiveness of a river?
Building dams and creating reservoirs in flooded valleys acts to slow down the rate of discharge at peak times as water is ‘held back’ to protect the low lying land downstream. The water is extracted for industry, domestic use and irrigation.
60
How does drainage density affect the responsiveness of a river?
This is the length of a river course per area of land. The larger the amount of streams and rivers per area, the shorter distance the water has to flow and the faster the rate of response.
61
How does land use affect the responsiveness of a river?
Urbanisation- impermeable road surfaces, sloping roofs, guttering and underground drainage systems transfer water very quickly to rivers.
62
How does season/time of year affect the responsiveness of a river?
In summer, similar amounts of rainfall as the winter may not lead to flooding as more of the water will be evaporated back into the atmosphere from leaf surfaces, tarmac or from the river itself due to increased temperatures.
63
Why are storm hydrographs useful?
- As many people are living in drainage basins (due to the high soil fertility and ability to grow food that they offer) and much money is being invested in them to provide transport, residence and to locate businesses, it is important to be able to predict a river’s behaviour, especially after heavy rainfall, and follow the correct course of action. Hydrographs from previous years allow us to do so.
- It is important to know how much a river’s channel can hold so that the correct adjustments can be made to prevent flooding/prepare for a flood.
- It is also important to know how quickly any rain falling in a drainage basin will reach the drainage network.
64
What are interlocking spurs?
A series of ridges projecting out on alternate sides of a valley, and around which a river winds.
65
How are interlocking spurs formed?
Formed where the river swings from side to side, winding and bending to avoid areas of more resistant rock whilst eroding the land and cutting down into the river bed (vertical erosion).
66
What are rapids?
Fast-flowing and turbulent water in shallower parts of a river with rocks exposed, protruding from the surface.
67
How are rapids formed?
Large angular rocks forming the bedrock create turbulent waters eg. Rapids are formed at Low Force waterfall (upper course of river Tees) by smaller outcrops of whin sill (more resistant rock).
68
What are potholes?
A deep hollow in the bed of a river.
69
How are potholes formed?
Found in the upper course of a river where it has enough energy to erode vertically and have a turbulent flow. The load carried is large in this part of the river, and when flowing water encounters this bedload, it is forced over it and back downwards behind the bedload as ‘eddy currents’. These erode the river bed vertically and create small depressions and hollows in it. As these deepen, pebbles can become trapped in them, deepening the potholes through abrasion.
70
What are meanders?
A winding curve or bend in the course of a river.
71
How are meanders formed?
- A natural bend in the river is formed due to different rock resistance, causing a faster flow of water on the outside bend and a slower flow of water on the inside bend.
- The outside bend therefore undergoes more erosion (hydraulic power and corrasion), forming a river cliff.
- The water with less energy on the inside bend deposits more materials, forming a slip-off slope.
- These processes continue, gradually exaggerating the bend until it becomes a meander.
- The neck of the meander may then be broken over time, and, with continued deposition, a completely sealed-off oxbow lake may form.
72
What is a levee?
Raised river banks formed by layers of silt deposited by the flooding of the river.
73
How are levees formed?
a) Before the flood: water levels are normal.
b) During the flood: water levels rise and overflow. The river loses its energy as it flows over the flood plain, therefore depositing large material first: thickest and coarsest sediments are deposited at the channel edges, whilst thin and fine sediments (alluvium) are deposited over the outer floodplain.
c) After many floods: natural levees are built.
74
How are waterfalls formed?
Waterfalls often form in the upper stages of a river where it flows over different bands of rock. It erodes soft rock more quickly than hard rock and this may lead to the creation of a waterfall.
Formation of a waterfall:
- The soft rock erodes more quickly, undercutting the hard rock.
- The hard rock is left overhanging and because it isn’t supported, it eventually collapses.
- The fallen rocks crash into the plunge pool. They swirl around, causing more erosion.
- Over time, this process is repeated and the waterfall moves upstream.
- A steep-sided gorge is formed as the waterfall retreats.
75
What happens to the gorge as the waterfall retreats?
The gorge lengthens due to erosion of the soft rock (limestone in ‘High Force’), leaving an overhang of hard rock (whinstone in ‘High Force’). This then cracks and collapses due to the gravitational forces exerted upon it. This continues to happen, making the gorge longer and longer as the waterfall retreats.
76
How are oxbow lakes formed?
- Corrasion and hydraulic power erode the outer bends of a meander and deposition builds up.
- Eventually, usually in times of flood, the neck of the meander is broken through, leaving a loop of stagnant water.
- Deposition continues to build up (as the river is slower on the side of the bank on which there is the meander), forming a bar of land along the river channel.
- Gradually, the bar of deposition thickens with vegetation, becoming land.
77
What are valleys?
A valley is an extended depression in the Earth's surface that is usually bounded by hills or mountains and is normally occupied by a river or stream.
78
How are ‘v-shaped’ valleys formed?
- Rivers begin high up in the mountains so they flow quickly downhill eroding the landscape vertically.
- The river cuts a deep notch down into the landscape using hydraulic action and corrasion.
- As the river erodes downwards the sides of the valley are exposed to freeze-thaw weathering which loosens the rocks (some of which will fall into the river) and steepens the valley sides.
- The rocks which have fallen into the river help the process of corrasion and this leads to further erosion.
- The river transports the rocks downstream and the channel becomes wider and deeper creating a V-shaped valley between interlocking spurs.
79
What are floodplains?
A floodplain is the area around a river that is covered in times of flood. A floodplain is a very fertile area due to the rich alluvium deposited by floodwaters. This makes floodplains a good place for agriculture.
80
How are flood plains formed?
A flood plain is formed is when a river system undergoes a decrease in velocity and thus carrying capacity. This can either be a change in gradient, a widening of the overall channel width and in an extreme case a loss of the water through infiltration or evaporation.
81
What are the main uses of water (include examples)?
- Domestic use (cooking, cleaning, drinking etc).
- Industrial use (generation of electricity, production of goods eg. Steel).
- Agricultural use (irrigating crops, drinking water for livestock).
(- Leisure use (watering golf courses, sailing and swimming)).
82
What are the physical factors affecting the supply of water?
- Precipitation.
- Climate and climate change.
- Availability of freshwater source, and proximity of source eg. Rivers, glaciers, lakes, groundwater aquifers.
- Heat —> high evaporation rates —> reduced water supply.
- Humidity.
- Droughts.
83
What are the human factors affecting the supply of water?
- Dams.
- Reservoirs.
- Anthropological climate change.
- Water abstraction- for irrigation of crops, industrial usage, domestic use.
- Technological advances eg. Wells or Archimedes’ screw.
84
What are the factors affecting the demand of water?
- Population increase.
- Technological development increases consumption.
- Size of city/area/population.
- Industrial development.
- Increased agricultural needs- commercial farming.
- Recreational use + tourism eg. Golf courses and swimming pools.
- Availability + supply.
85
What is the water demand in developing countries?
In developing countries:
- The vast majority (91%) of water is used in agriculture, and very little in comparison is used in industry and domestic use, indicating a lack of development.
- The domestic use of water is very low at only 4%.
- The high demand for water in agriculture, particularly irrigation, suggests a growing population, which in turn implies a lack of contraception and education in this matter.
86
What is the water demand in developed countries?
In developed countries:
- Much more water is used in domestic circumstances (14%), however most water consumption lies in industry (47%), closely followed by agriculture which takes up 39% of water consumption. This suggests that that the standard of living is much higher in developed countries, and that they are much more technologically advanced and educated.
- More water is used for hygiene and even leisure purposes, suggesting that more houses have piped water and even some have a swimming pool, for example.
- The need for much water in industry shows high industrial and technological development in developing countries, leading them into a virtuous cycle of development.
- The high demand for water in agriculture shows a rise in population in developed countries, as water dedicated to food and agriculture is relatively high, but shows a better control of population than in developing countries as some still remains for less important purposes such as leisure and domestic use.
87
What is the water supply in developing countries compared to developed countries?
Countries on and near the equator tend to be water deficient.
Countries in the tropics show water neutrality or even surplus in some cases (such as Columbia).
Developing countries in the North of Africa, for example, are water deficient, whereas MEDCs are more usually water neutral, showing a link between economic and technological development and supply of water.
88
How is water moved from areas of surplus to areas of deficit?
- Reservoirs
- Pipelines
- Wells
- Aquifers
- Desalination
- Bottles and trucks
89
Define hard engineering.
Protecting the river with manmade structures. This is:
- High tech
- Short-term
- Unnatural/manmade
- Difficult to maintain
- Expensive
90
Define soft engineering.
Protecting the river whilst working with nature/natural solutions. This is:
- Low tech
- Long-term
- Fits in with environment
- Sustainable and eco-friendly
- Easy to maintain
- Cheaper option
91
What is safe water?
Water that is fit for human consumption (ie. not contaminated by pollutants and free from disease).
92
What is the difference between MEDCs and LEDCs in terms of water safety?
There is a clear division between the more developed countries and the less developed countries, as well as the Northern and Southern hemispheres (with the exception of Australia), showing a definitive link between development and safe water access.
93
What are the domestic, agricultural and industrial causes for water pollution?
Domestic:
Untreated sewage from homes, washing, bathing.
Agricultural:
Eutrophication, silage flows into river, fertilisers and pesticides enter groundwater.
Industrial:
Spillages (eg. Oil), warm water from cooling machinery and from power stations.
94
How is the supply of clean water managed?
There are three key stages:
- Collection
- Treatment
- Delivery
95
What is collection?
Extracting water from its sources, the main sources being rivers, reservoirs and lakes.
96
What is treatment?
Purifying water so that it can be safely consumed by humans. Water needs treating as most water sources are contaminated by one way or another: rivers are often highly polluted, reservoir water can be polluted by acid rain and pollutants from surrounding hillsides that have seeped into the reservoir, and groundwater, once thought to be pure, can be highly contaminated by chemicals in the rocks. Substances that are removed during the treatment of water include suspended solids (silt and soil), bacteria, algae, viruses, fungi, minerals (iron, manganese and sulphur), and synthetic chemical pollutants (fertilisers).
97
What are the processes involved in purifying water?
- Chlorination (to control any biological growth e.g. algae)
- Aeration (to remove any dissolved iron and manganese)
- Sedimentation (to remove any suspended solids)
- Filtration (to remove very fine sediments)
- Disinfection (to kill bacteria)
98
What is delivery?
Transporting water to the places that need them, usually by means of pipes and bottles.
99
Why are rivers managed?
- To prevent or reduce flooding*
- To provide a water supply*
- To improve water quality and the environment
- To increase the river use for leisure and recreation
* Main reasons for management of river Tees
100
How are rivers managed?
- Construction (hard engineering)- building structures that hold back floodwater.
- Mitigation (soft engineering)- flood control schemes that minimise the chance of flooding using soft-engineered structures.
- Prediction (soft engineering)- predicting the occurrence of a flood (though they can vary, so results may not be very reliable).
101
What are dams?
Hard engineering.
| Trapping water to form a reservoir from which water can be released in a more controlled way.
102
What are the advantages of dams?
- Provide water for irrigation, human consumption, industrial use.
- Prevents floods.
- Used for the generation of electricity (hydropower), reducing consumption of fossil fuels and replacing them with a renewable energy source.
- Reservoirs can attract tourists.
- Multiple purpose.
- Taking on a utilitarian approach, the wide variety of benefits outweigh the disadvantages.
103
What are the disadvantages of dams?
- Sediment can easily build up at dams, reducing their effectiveness (‘silting up’).
- Flooding of the valley as well as the general construction of the dam can destroy ecosystems and make people move away from their homes.
- Interferes with natural wildlife migration patterns (e.g. salmon).
- Very expensive to build and maintain.
- Can disrupt certain livelihoods (e.g. fishing).
104
What are levees (embankments)?
Artificial levees: hard engineering
Natural levees: soft engineering
Raising the banks of rivers so that they can hold more water.
105
What are the advantages of levees?
- Prevent flooding.
- Slow natural changes in the water course.
- Although quite expensive, not as expensive as other methods of flood prevention (notable elevating or relocating the structure).
- One-off cost.
- Occupants are not forced to leave their homes during the construction of levees, and are reassured by the protection offered that they will probably not need to move due to flooding.
- Natural levees are completely natural and environmentally friendly.
- Two types (artificial and natural) allow for two options to decide from depending on what would be most effective for that particular river.
- Artificial levees allow the floodplain to be built on.
- Can be attractive to tourists.
- Artificial levees made from materials which effectively reduce bank erosion e.g. concrete.
- Earth and natural embankments provide habitats for plants and animals.
106
What are the disadvantages of levees?
- Increase water speed (can in turn increase erosion rates and reduce the amount of beneficial in-stream vegetation).
- Can increase the duration of floods as water is prevented from returning into the river.
- Levees can fail by overtopping (wage rising over the top of the levee), underflow (water permeating the sand deposits underneath the levee causing water levels to rise on the other side), slumping (the weight of the water pushing over the sides of the levee) or erosion.
- Reduces access to river.
- Artificial levees can encourage the development of the floodplain, increasing the chance of flooding.
- Concrete embankments can decrease the charm and aesthetic of the area whilst spoiling the view.
108
What are the advantages of dredging?
- More water can be held in the river channel.
- Reduces risk of flooding.
- Improves the river as a shipping route.
- Silt and sediment collected from the river to deepen it can be used as a fertiliser.
109
What are the disadvantages of dredging?
- Needs to be repeated frequently, making it very time-consuming and costing a lot of money in the long-term.
- Causes loss of habitats and disruption of ecosystems.
- In some cases, can decrease the flood risk further downstream of the river.
- Not very useful and effective in extreme flood conditions.
110
What is straightening?
Hard engineering.
| Speeds up water so that high volumes of water can pass through an area quickly, reducing the likeliness of a flood.
111
What are the advantages of straightening?
- Speeding up the water flow prevents it from pooling, reducing the risk of a flood.
- Faster and easier to navigate by boat.
- Quite effective at reducing flood risk.
- Lasts long.
112
What are the disadvantages of straightening?
- Increases erosion rates downstream as the river has more kinetic energy.
- Increases likeliness of flooding downstream as water flows there faster.
- Changes river ecosystems.
- Spoils the natural, convoluted aesthetic of the river.
113
What are diversion channels?
Hard engineering.
Artificial channels that a river can flow into if its discharge rises, allowing the movement of water from an area at risk of flooding to an area of the river further downstream.
114
What are the advantages of diversion channels?
- Remove excess water from the river channel to reduce flooding in the high-risk area.
- Effective at reducing flood risk in that particular area.
- Makes people living close to the main river safer as the flood water is diverted into the diversion channel.
- Diversion channel can be used for recreational activities e.g. water sports.
115
What are the disadvantages of diversion channels?
- Increases the risk of flooding in the area which the excess water has been redirected to, as well as in the diversion channel itself.
- The paths that the diversion channels take can transport water around areas which are not accustomed and well adapted to high water levels and flooding, making them liable to failing and potentially causing widespread damage to the area.
- Expensive (both to build and to purchase the large amount of land needed to build the diversion channel on).
116
What is afforestation?
Soft engineering.
| Re-planting trees in the river’s catchment area.
117
What are the advantages of afforestation?
- Absorption of water from the soil by the roots of the plants reduces the risk of flooding.
- Provides habitats for various animals.
- Cheap.
- Plants intercept water, reducing the amount of water percolating the rock, infiltrating the soil and running off the surface of the ground to reach rivers (less water reaching and entering the river).
- Reduces carbon emissions into the atmosphere.
- Trees and plants can multiply and increase the area protected by rainfall, increasing the effectiveness of this methods.
- Increases aesthetic of area.
- Very sustainable.
118
What are the disadvantages of afforestation?
- Not very effective.
- Takes a long time (as the trees have to grow).
- Doesn't prevent flooding, only the amount of rainwater reaching the river.
- Conifers are usually planted, increasing the acidity of the soil.
- Increases fire risks.
119
What is zonation?
Soft engineering.
| Allowing only certain land uses in area of high flood risk to reduce the impact and liability of flooding.
120
What are the advantages of zonation?
- The impact of flooding is reduced, as no houses or infrastructure is damaged, saving lives and possessions and reducing insurance claims.
- The risk of flooding itself is reduced as no impermeable surfaces (eg. Roads) are built, reducing surface runoff.
- Very cheap.
- Sustainable (damage is limited and allows environment to flourish instead).
121
What are the disadvantages of zonation?
- Doesn’t prevent flooding.
- It does nothing in areas that have already been built on.
- The expansion of an urban area is limited if there aren’t any other suitable building sites.
- Can be hard to enforce planning regulations and controls in LICs and areas with dense populations and a shortage in housing.
122
What are flood warnings?
Soft engineering.
Warnings issued by the environment agency by radio, television, newspapers and the internet so that locals and inhabitants potentially affected by the flood can prepare.
123
What are the advantages of flood warnings?
- Prepares people for the flood and potential issues associated with it.
- Reduces the impact of flooding.
- Can potentially save lives.
- Many possessions can be saved, leading to fewer insurance claims.
- Cheap.
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What are the disadvantages of flood warnings?
- Doesn't prevent flooding.
- Living in places that get a high number of warnings could make it difficult to obtain insurance, as well as making it harder to sell the property in that area.
- Some people may not be able to access the flood warnings.
- Too slow and ineffective if a flash flood occurs (as these may happen to quickly).
- Sirens can break or be vandalised, so they are tested annually.
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What is dredging?
Hard engineering.
| Making rivers deeper so that they can hold more water.l
