There are a number of reasons why sustainable answers to flood control, or soft engineering, are preferred better than hard engineering, in other words, non-sustainable methods.
Firstly these terms need to be stated. Sustainability is when improving it for the present, but also to create a better environment for the future generations as well carries out development. Soft engineering is when people try to work with the environment by using ecological materials. This is so there is minimal impact on the environment. These methods try to create a balance by using more natural resources. Hard engineering is the opposite, as it uses resources like concrete, and it does not provide a sustainable environment for the future.
A case study of where hard engineering has been used is the River Mississippi. This river has had extensive hard engineering done on it. For example, channelisation took place by straightening all the meanders and thus making it over 250km shorter. Also many dams were placed along the river in order to hold back the water and therefore provided flood control. Even though this channelisation worked upstream, the water continued to flood downstream, causing just as many problems and damage. This is why hard engineering is seen as unsustainable.
When channelisation was put into place, habitats and ecosystems were destroyed to make way. Also this sort of solution is never permanent and thus it always needs to be maintained. This will be very expensive and at the end of it migration will still take place, not solving the problem. Recently, rainfall has increased due to climate changes and therefore the rivers are more likely to flood, as there is a higher amount of water. Lastly due to and overall global rise in population, more people are being forced to live on floodplain land, as there is no space. This puts a lot of pressure onto the land. This is dangerous as there are now great risks of flooding.
All of these methods seemed to be working, but then in 1993 the river flooded causing terrible consequences. Many properties and people were lost. This showed that although in the short term, the engineering helped, in the end, it made it increasingly worst. This is no longer and good option.
On the other hand, soft engineering is a much better choice. Examples of this are rehabilitation, restoration and source control. There are many ways in which rivers can be managed by working with nature. One way would be to restore rivers by bulldozing them back into their original shapes. As a result of this, new habitats and wetlands can be created. These wetlands can then act as sponges to absorb the water and slow down the rate of infiltration, reducing the risk of flood. Another way of slowing infiltration is aforestation as this increases evapotranspiration. Also, people could be told not to build on floodplain land.
A case study of this is Darlington. There are two rivers that were focused on called the River Cole and the River Skerne. On these rivers, they only used soft engineering techniques as to reduce flooding risks and make it more sustainable for the future. This included narrowing, re-profiling, increasing floodplain storage and in-stream features being put in. All of this stopped the river becoming polluted and also it has created a more attractive environment for people to admire.
Soft engineering is much more sustainable as it is cheaper using nature materials and it does not try to halt the natural processes of the river. Instead it works with them to create a balance of management.