Hard And Soft Engineering

Question 1

Name 5 hard engineering techniques

Answer 1

Dams 
Artificial levees 
Wing dykes 
Channel straightening 
Diversion spillways

Question 2

What is a Dam? (Definition)

Answer 2

Giant walls built across a river’s channel to impede its flow.

Question 3

Advantages of Dams

Answer 3

1. Water can be held behind the dam in a reservoir and then steadily drained at a controlled rate over time.
2. Keeps discharge downstream of the dam low even during even prolonged heavy rainfall.
3. Used to generate hydroelectric power, they can bring economic benefits to an area by attracting manufacturing factories or being exported to other countries.
4. Reservoir behind a dam can be used for drinking water or for leisure activities.

Question 4

Disadvantages of Dams

Answer 4

1. Most expensive of all hard engineering techniques and require access to lots of raw materials, steel and concrete.
2. Huge impact on local environment as area behind the dam has to be flooded which destroys habitats and forces people out of their homes.
3. Dams disrupt the processes that take place within a river too by for example preventing sediment being transported downstream. This can result in landforms being destroyed which can result in the destruction of habitats.
4. When sediment gets trapped behind a dam, it can change chemical composition of water behind the dam which can kill aquatic animals upstream.
5. If they were to fail, they cause widespread death and damage downstream as all water is released at once.

Question 5

What is the dam used for an example

3 stats for it?

Answer 5

1. Mega dam located on Yangtze River in central China.

- 2.3 Km wide, 158m and took over 15 years to build.

Question 6

What was the dam built in response to?

Answer 6

1. Seasonal flooding that takes place along Yangtze that has killed hundreds of thousands of people. A flood in 1998 killed over 3,500 people, left 13m homeless and caused billions of dollars of damage.

Question 7

Economic impacts of the dam?

Positives and negatives

Answer 7

The overall cost of the dam is estimated at roughly 180 billion yen. It will take nearly a decade for the dam to pay for itself by generating electricity.
Project funded by China development bank and profits from another dam located on the Yangtze.
Overall dam will have a positive effect on China’s economy; reduce its dependency on coal, meaning it doesn’t have to spend as much on mining or importing coal for electricity.
Less economic damage in the future, so will save money in long run as reduced risk of flooding.
The inundation of land behind the dam is costly because many factories were located near the river and had to be relocated- high cost.
The lack of annual flooding means that much of the farmland that is located on the Yangtze’s floodplain will gradually become less fertile, reducing agricultural yield.

Question 8

Hard engineering definition

Answer 8

Ones that involve the construction of artificial structures that, through a combination of engineering and a bit of brute force, prevent a river from flooding.

Question 9

Soft engineering definition

Answer 9

Projects that use natural resources and local people’s knowledge of the river to reduce risk posed by a flood. Focus more on reducing the impacts of flood than preventing one.
More holistical

Question 10

General pros and cons of hard engineering

Answer 10

Cons - v expensive to build and maintain so not available to countries without large economic resources.
- containment of large body of water- if released, could be catastrophic.
- disrupts rivers natural processes
- impacts on habitats of wildlife.
Pros - v. Effective / successful in preventing flooding.

Question 11

General pros and cons of soft engineering

Answer 11

Soft engineering is significantly cheaper ; ledcs
Lower education and technology needed so appropriate for people in isolated places by locals.
More sustainable
Less maintenance
Don’t disturb natural processes; integrate rather than disturb.

Cons
Not as effective in extreme storm events.

Question 12

Social impacts of Yangtze River dam

Answer 12

Dam has succeeded in reducing the risk of flooding, taking recurrence interval for large floods from 1 in 10 years to 1 in 100 years.
Over 1.2 million people were required to leave their homes as they were going to be inundated by the dams reservoir.
Forcibly removed if the refused.
The reservoir flooded 13 cities and hundreds of villages. Those that were displaced were relocated to cities that had been specially constructed for the dam.
Many of those relocated lived on less than 1$/day and were simply farmers. They struggled to find work as little others skills and not many agricultural jobs - exacerbated poverty.

Question 13

Environmental impacts of Yangtze River dam

Answer 13

Transported a lot of sediment now blocked behind dam. Gradual destruction of Yangtze delta and increased erosion downstream.
Potential extinction because of sediment (see earlier)
Lack of annual flooding means farmers now have to use artificial fertiliser that will drain into the river and pollute downstream section of river.
It supplies about 5% of China’s power.

Question 14

Political impacts of Yangtze River dam

Answer 14

Forced relocation of 1.2 million people raised human right concerns.
Environmental impacts created opposition of environmental groups. World bank refused to fund project.

Question 15

What are artificial levees?

Answer 15

• act as embankments, extending the channels height and its bankful discharge.
• unlike natural, it is normally bigger and made out of material like concrete that is resistant to erosion.

Question 16

Main advantage/disadvantage of Artificial levees?

Answer 16

Advantage is that is allows building on floodplains.
Dis: encouragement of the development of flooding will increase risk of flooding and if they fail than effects are way worse than if the embankments didn’t exist.

Question 17

Define wing dykes?

Answer 17

Wing dykes are slats that are placed in rivers channel at 90 degrees to the banks.

• generally, placed in pairs on either side of the channel with a gap between them that allows boats to pass through them.
• behind dykes sediment builds up and channel is narrowed, forcing water to flow faster. Reduce the risk of flooding by getting water away from an area at risk of flooding as quickly as possible, preventing build up of water.

Question 18

Advantages/disadvantages of winged dykes

Answer 18

Look at previous page.
Disadvantages
Reduce risk of flooding in one area to increase it downstream so only useful in sparsely populated areas.

Question 19

Channel straightening

Answer 19

Block meanders and construct alternate, straighter routes across meanders, river flows faster.
Similar to wing dykes, moves water through the river faster preventing it from pooling, reduce risk of flooding

Question 20

Advantages/ disadvantages of channel straightening

Answer 20

Advantages - reduce flooding (previous page)
Disadvantages
Flooding becomes more likely downstream, and erosion is stronger because the river has a lot more kinetic energy.

Question 21

Diversion spillways

Answer 21

Artificial channels that a river can flow into when it’s discharge rises.
-these channels move water around an area at risk of flooding and send it either back into the river or into another river.
Spillways have floodgates on them, used to control the volume of water in spillway

Question 22

Advantages/disadvantages of spillways

Answer 22

Disadvantages - increasing discharge so increase risk of flooding at the river the spillway is taken to.
The path that spillways take can take some water around areas not usually used to flooding. If the spillway was to fail for some reason, could cause widespread damage.

Question 23

Soft engineering techniques

Answer 23

Broadcasting and forecasts 
Floodplain zoning 
Wetland and riverbank conservation schemes. 
Wetland restoration 
River restoration 
Afforestation

Question 24

Floodplain zoning

Answer 24

Involves placing restrictions on land usage around river areas
Floodplain itself limited to public outdoor facilities- park and pitches.

Question 25

Floodplain advantages and disadvantages

Answer 25

Reduces the impact and the risk of flooding.
Risk because ensures land on river plain isn’t urbanised, so infiltration occur, and surface run off less, so less flooding.
Impact because there would not be a lot of things to damage.
Disadvantage; limit development to certain areas.

Question 26

Afforestation

Answer 26

Planting of more trees in a drainage basin so that there is increased interception, storage and evapotranspiration thus reducing surface run off, reducing rivers discharge and so makes it less likely to flood.

Question 27

Advantages and disadvantages

Answer 27

New habitats for animals and improves water quality as trees filter out pollutants of rainwater.
Requires a lot of space to be effective
A lot of time to be effective as trees need to grow.
Can be unpopular among farmers on floodplain as trees removing nutrients from soil.

Question 28

Wetland and riverbank conservation schemes

Answer 28

Protecting existing river channels and their valleys.
Habitats and species diversity can be maintained
Arable land returned to its former natural medowland.

Question 29

Wetland restoration

Answer 29

Allowing the conditions so that wetlands can develop ( marshes and swamps)
Store large volumes of water, helps to reduce discharge in a river.
Don’t Reduce flooding where they are but downstream.

Question 30

Advantages of wetland restoration

Answer 30

Biodiversity and habitats for animals

But area of land available to farming is reduced which makes them unpopular for farmers.

Question 31

River restoration

Answer 31

Involves restoring a river that has undergone hard engineering back to its original course- remove winged dykes. Artificial levees and straightening of the river channel.

Question 32

Advantages and disadvantages of river restoration

Answer 32

Allows natural river processes and reverts any ecological and environmental damage introduced by hard engineering methods.
No maintenance costs

Question 33

Where is river Cole and what is it?

Answer 33

It is a tributary off the river Thames in south of England.

Question 34

Why does a restoration project need to take place in Coles?

Answer 34

Because it has undergone years of heavy modifying in order to improve its efficiency for milling.
Channel has been straightened for milling and also dregded to reduce risk of flooding.
( make quicker to speed the Mills up.)

Question 35

When was the restoration project set up?

Answer 35

1995, to get it back to its original course.

Question 36

Aims of the restoration project

Answer 36

To increase water quality and reintroduce wildlife and reduce risk of flooding by introducing wetlands.

Question 37

Who was the project funded by?

Answer 37

The EU, environmental agency, river restoration centre and the national trust.

Question 38

How did they restore the river channel?

Answer 38

Restore original course looked at old maps of the river Cole to work out its natural route.
To recreate the course, new channel created flowed 1.2 m above the old one as it used to be higher before it was dredged.
In addition the new one given meanders and given space to meander naturally. Old channel blocked off so river could flow through new channel.

Question 39

Success of restoration project?

Answer 39

It has recreated wetlands, help reduce risk of flooding and also allowed river to flood naturally which will improve the fertility of surrounding land and prevent flooding downstream.
New wildlife and plants started to inhabit the area and environment is more pleasant.

Question 40

Backlash at river restoration project?

Answer 40

Floodplain surrounding the river is used for agriculture and many farmers unhappy about marshland being developed. Not happy with the land they would lose as a result of meandering and taking up more land.
Finally letting it naturally flood because although it deposits fertile alluvium, it will ruin any crop at present