Have you ever walked along a raised river bank and wondered why the banks were shaped to be gently sloped? This is one of the many strategies that prevent water from flooding areas we live in and an example of flood management that can be seen in our everyday. It can seem a simple solution, but with approximately 1.9 million people in the UK living in areas of significant risk of flooding, even the smallest interventions need to be considered. This article will talk about the different strategies of approaching how we can prevent disastrous floods (natural and coastal) from happening, from soft engineering to hard engineering. Let's dive in!
Flood management definition
So, how do we define flood management? Flood management is the technique and strategy to reduce the risk and damage from flooding. In the case of rivers, flooding occurs when the river bursts its banks and water spills into the floodplains. There are different strategies to manage floods, and the government usually chooses which strategies are used.
In the UK, there is the Flood and Water Management Act which is a law that manages flood risks for homes and businesses. It also aims to reduce the flood risk associated with extreme weather.
Flood management strategy
Flood management strategies are usually divided into hard engineering and soft engineering. It depends on the situation which is more suitable, and both have advantages and disadvantages.
Hard engineering is when major building work is needed to stop the flood, using machinery, concrete, and building materials. It works with artificial structures to disrupt, stop or reduce the impact of river processes.
Soft engineering uses methods that need the least amount of building work and prevents floods rather than managing them. It uses the natural environment surrounding the river, working with the river's natural processes. It is usually more sustainable than hard engineering methods.
Hard engineering methods
Hard engineering methods are more expensive and use many raw materials to build. The construction can significantly impact the surrounding environment, and it makes bigger alterations to the existing environment to stop flooding.
| Method | Explanation |
| Dams | Dams are large structures built across a river channel to control the water flow. Usually, water builds up behind the dam to fill a reservoir which can be drained at a controlled rate. This is useful during periods of heavy rainfall. Dams can also be used to generate energy through hydroelectric power.However, dams are expensive to construct and require raw materials. To build a dam, the area behind it has to be destroyed, meaning people have to leave their homes, and animals are forced out of their habitat. |
| Levees | Levees are raised banks of a river which is created artificially or naturally. Artificial levees are built along river banks, so when the river floods, the levee stops the water from reaching and flooding surrounding areas.Artificial levees can be expensive and ruin the river's looks. They also wear away with erosion, so there is a constant need for maintenance. Levees take up space and squeeze the river's flow, making the water flow faster and creating higher water levels. |
| Channel straightening and deepening | River channels are straightened to speed up the water flow in areas prone to flooding and stop the water from collecting in those prone areas. Also, river channels are deepened so they can carry more water. However, this can cause flooding and erosion downstream as the kinetic energy strengthens due to water running further downstream. |
| Diversion spillway | Diversion spillways are artificial channels that divert water overflow when the river discharge, which is the volume of water flowing through the river channel, rises. The channel moves the water from the areas at risk of flooding and puts the water back further down or into another river. Spillways have floodgates, so the spillway's water amount can be controlled. The disadvantage of the diversion spillway is that it can cause a risk of flooding at the confluence, which is the junction where two rivers meet and also the river that the diversion spillway is flowing into. |
Table 1
Fig. 1 - Levee along the Sacramento River in the US, an example of hard engineering
Soft engineering methods
Soft engineering methods are seen as more ecologically sensitive and try to manage the flood instead of preventing it. It also attempts to work with the surrounding environment instead of against it.
| Method | Explanation |
| Floodplain zoning | Floodplain zoning restricts the areas surrounding the river from being built so that houses and buildings don't get flooded. It also stops floodplains from being urbanised, which increases the amount of land where infiltration can occur and, therefore, lessen surface runoff.Floodplain zoning can be problematic as it can limit the development of specific areas, and if the floodplain has already developed, it is hard to force people off the floodplain. |
| Afforestation | When planting trees in the drainage basin, there is greater interception and lower river discharge. It also helps with the environmental quality of the river's surroundings. While afforestation can help to reduce flood risks, it cannot prevent flooding.Interception is when water is absorbed and collected by vegetation. Remember: don't confuse afforestation, the planting of trees in an area that had no tree coverage before, with reforestation, which is the replanting or restocking of existing woodlands and forests that were depleted due to deforestation! |
| Wetland restoration | Wetland restoration is making areas favourable for the development of wetlands. They can act like a sponge and absorb water that traps and slowly releases surface water, rain, ground- and floodwater. Wetlands can increase biodiversity by creating wildlife habitats. However, they can also reduce the amount of useful farming land.Wetland is areas of land permanently or seasonally covered in water, such as marshlands, swamps, and bogs. |
| Washlands | Washlands are areas of land that water can flood into when there is too much river discharge. They have sluice gates that allow excess water to flood marginal land so that other areas, such as towns, are safe from flooding. The problem, however, is that there needs to be space to make washlands, which is difficult to find near urbanised areas. |
Table 2
Fig. 2 - Viru bog in Estonia, an example of soft engineering methods
Remember: A flood management scheme is a site-specific plan that would reduce the risk of flooding.
Natural flood management
Natural flood management reduces the risks of flooding and coastal erosion by protecting, restoring, and emulating the natural functions of catchments, floodplains, rivers, and coasts.
Catchments are areas of land which collect water when it rains.
Floodplains are the flat lands alongside the river, formed from river sediments, and flood when the river is too full.
The river landscape has changed a lot from its original natural forms. There are fewer wetlands and more hard surfaces from which water runs off, so the river channels move water quicker. With less space for the water to flow and more water collecting faster, the rivers are less able to cope with the increasing water, and it is more likely to flood.
Natural flood management uses strategies such as increasing temporary storage that can fill up when there is too much water in the river and empty slowly by reconnecting rivers to floodplains and creating storage ponds. It also tries to slow water flow by restoring meandering rivers, increasing the resistance to the surface and in-channel water flow by planting trees and vegetation. Expanding the areas where water can infiltrate by improving soil and reducing compacted soil helps manage floods.
Read more in "River processes" and "River landforms" to learn about the natural formations of the river.
Coastal flood management
Coastal flood management differs from river flood management as it focuses on a more specific area of the coast with flooding and erosion from the sea. However, using hard and soft engineering strategies is also prevalent in coastal flood management. Let's look at hard and soft engineering examples of coastal flood management.
Hard engineering examples
Hard engineering uses structures to stop the sea from flooding into the coastal areas and eroding the coast.
| Example | Explanation |
| Groynes | Groynes are low-lying wooden or concrete structures built from the shore to the sea. They absorb the waves' energy, trap sediment and stop sediment transfer away from the beach through longshore drift. Groynes stop shore erosion and try to dissipate strong waves. There are impermeable and permeable versions. The former is solid and stops sediment transfer; the latter lets some sediment through, and some longshore drift takes place.Longshore drift is when prevailing winds blow the waves across the shore carrying sediments along the beach. |
| Sea walls | Sea walls are barriers made of solid concrete that prevent high tides and storm surges from reaching inland and causing flooding. They are designed with sloped, stepped or vertical profiles, which can last, with proper maintenance, for around 30 to 50 years. There are many sea walls across the UK to lower the flood risks. |
| Breakwaters | Breakwaters are offshore concrete, stone, or rocky walls that absorb the waves' power further out from the shore so that the waves that reach the beach have lost power and momentum. This will decrease beach erosion. It can also be used to make the water calmer for ships. |
Table 3
Fig. 3 - Groynes in Shoeburyness, UK
Soft engineering examples
Soft engineering works with the coast as it is through restoring and regenerating the environment that exists.
| Example | Explanation |
| Beach nourishment | Beach nourishment is sediment replenishment after beach erosion has removed them. Combined with hard-engineered defences, beach nourishment can help a beach look more natural and protect the local areas from flooding. However, the sea will keep eroding the sediments, so the process has to be repeated regularly, driving up the costs. |
| Dune regeneration | Dune regeneration uses sand dunes as natural barriers to protect coastal towns from high tides and flooding. Sand dunes form when the dune plants trap the sand carried by wind and are situated above the high tide level. The dunes act as natural coastal protection against storm surges and high tides. It is also a rich habitat for flora and fauna. |
| Cliff stabilisation | Cliff stabilisation is a technique to stop cliff erosion in coastal areas. Stabilising the cliff can limit erosion, potential landslides and falling rocks. One method is by reducing the slope and revegetating the cliff top. Planting vegetation can strengthen the cliff structure and prevent cliff material from slumping, which creates landslides. Another method is draining excess water from the cliff. This stops the water flow through weaker cliff areas, preventing rocks and sediments from sliding to the cliff's base. |
Table 4
Flood Management - Key takeaways
- Flood management is the technique and strategy to reduce the risk and damage from flooding.
- There are two categories of flood management strategies, hard engineering and soft engineering. Hard engineering tends to be more expensive and uses more raw materials to build structures that alter the existing environment. Soft engineering works with the natural environment to prevent flooding.
- Natural flood management reduces flooding by protecting, restoring, and copying the natural forms of rivers, coasts, floodplains, and catchments.
- Coastal flood management also has strategies of soft and hard engineering. Hard engineering examples such as groynes, sea walls, and breakwaters. Soft engineering examples include beach nourishment, dune regeneration, and cliff stabilisation.
References
- Fig. 2: Viru bog in Estonia (https://en.wikipedia.org/wiki/File:Sunrise_at_viru_bog.jpg) by Abrget47j (https://commons.wikimedia.org/wiki/User:Abrget47j) Licensed by CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en)
- Fig. 3: Groynes in Shoeburyness, UK (https://commons.wikimedia.org/wiki/File:Groynes_-_geograph.org.uk_-_2027601.jpg) by william (https://www.geograph.org.uk/profile/13806) Licensed by CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0/deed.en)
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