The Basic Concepts
In this chapter, I will explain the type of floods and how flooding occurs.
Let’s get started
What is flooding?
When there is an excess flow of water onto the land that is normally dry, flooding occurs. It is a type of a natural disaster.
What are the common reasons for flooding?
- Rainfall
Heavy rains are a major and important cause of flooding.
- Melting ice/snow
During winter, when there is unusually heavy precipitation and the ice/snow start melting at a later stage, flooding occurs.
- Storms
When there is a surge in storms, it can lead to natural disasters like hurricanes and other disasters which can be a factor in causing flooding.
- Broken dams
Dams can sometimes break owing to huge amounts of rainfall and ensuing increase in the level of water leading to floods.
- Drainage basins
When drainage basins are built of concrete, there is no space for the groundwater to seep through the concrete basins and hence the water accumulates leading to floods.
Did you know?
It is predicted that climate change will increase the risk of flooding in the UK and other parts of the world.
£5.2 BN
Investment in flood and coastal programme from April 2021 to April 2027
4 °C
Global warming that the construction industry is advised to plan for
55,000
Homes and Business flooded in 2007
Types of floods in the UK
The common types of floods that affect UK are:
- Flash floods – Caused by sudden heavy rainfall and often unexpected.
- Coastal floods – Coastal floods cause damage to the properties that are in the coastal areas. Since the UK is an island, it has a large coastline and therefore risk from coastal flooding is high.
- Surface water flooding – When there is no room for the excess water to drain away, surface water flooding occurs. If you’re looking for surface water drainage solutions, make sure to check this blog out – (link to our blog to be included)
- Groundwater flooding – When oversaturated and porous ground overflows with water. At this point groundwater flooding occurs.
- Sewer flooding – Occurs due to the failure of the sewage system.
Flood Risk Mapping
Let’s understand in more detail how flood risk mapping is created and why it is important.
Also, I will show you the uses of flood risk mapping.
What is Flood Risk Mapping?
Flood Risk Mapping identifies areas that are under significant risk of flooding. The mas describe the depth, extent and hazard of the flood.
A flood map is usually created by combining the topographic data and modelled information on wave heights and sea levels. This helps to determine the flood level at the coast and floods could impact the land and coastal area.
What is Flood Hazard Mapping?
Flood hazard mapping is used to identify coastal and river areas that are at risk of flooding. This map can help us in preparing for a disaster in the future and also help strengthen the existing flood systems. These maps analyse and inspect the extent of flooding in a given area based on the impact over the years.
To improve the existing flood systems, one must consider analysing specific risk areas by taking into account various factors like land-use, flood proof measures etc of the identified areas exposed to flood risk.
Climate change is an important factor to be considered when it comes to Flood Hazard Mapping. The dynamic causes must be taken into account while considering climate change for flood hazard mapping.
These maps are periodically updated to reflect the changes in the exposed areas especially due to climate change.
These maps can be used by developers, planners and insurers. Planners use these maps to plan design interventions. Developers use them to assess the risk of flooding in an area. Insurers use them to fix flood insurance premiums in flood prone areas.
With flood hazard maps, the awareness of flood is increased among people in the flood prone areas, general public and other organizations and authorities.
Using Geographic Information Systems(GIS), flood hazard maps are created and by comparing local elevations with water levels, the extent of floods can be determined.
What’s the use of a Flood Hazard Map?
To plan crisis response more efficiently.
Helps in quantification of risk – the number of properties at risk due to flooding.
Assists in building awareness campaigns that help in identifying properties at high risk due to flooding.
By integrating flood hazard maps into planning designs, sustainable development of areas can be ensured after careful consideration and impact of the flood-prone areas.
Detailed information about flood risk analysis.
Provides flood risk information for planners, developers and insurers.
Identifies potential flood risk areas and provides information to effectively manage flood risk.
Multi-purpose: These maps are used for a variety of purposes including crisis-management, flood-proof, land development planning etc.
Universally applicable: These measures can be used along with other adaptation measures.
Check your flood risk
You can use the flood risk maps on our site to check if your property is in a flood risk area.
Just enter your postcode in the box and press enter to view the flood risk map of your area.
These maps are extracted from the Environment Agency flood risk maps.
They are categorized into
- Flood Risk Rivers and Sea – Planning
- Flood Risk Surface Water
- Flood Risk Reservoirs
- Historic Flood Map
In addition to this, these maps also provide
- Areas Benefiting from flood defences
- Flood warning areas
Now let’s have a look in more detail at each of these maps.
Where can I find more detailed flood information?
You can also request details on the groundwater flooding risk at your location and the surface water flooding map from the local council. You can also email the Highways department or the local planning office.
Product 4 information can be sought by sending an email to enquiries@environment-agency.gov.uk which can then be used to study the property levels against the river levels.
You cannot conclude if your house is at risk of flooding using maps alone. It is possible that your property is exposed to flood risk even if it lies on the flood risk area border.
The correct approach would be comparing the flood level with the property level and factoring in climate change allowances.
Map 1 – Flood Risk Rivers and Sea – Planning
In order to support the flood risk evaluation which is a part of the planning process, the Environment Agency produced this map which shows the flood risk from rivers and sea.
The flood risk is divided into the following components
- Flood Zone 1
- Flood Zone 2
- Flood Zone 3
Flood Zone 1 refers to a low risk area. Flood Zone 2 refers to a medium risk area while the Flood Zone 3 refers to a high risk area.
If you would like to get a quote for detailed flood assessment for free, just contact us.
Map 2 – Flood Risk Surface Water
The information provided by the Flood Risk Surface Water map does not include drainage systems and hence it cannot be used to assess flood risk for individual properties. But it can still be used to specify potential flood risk areas in the neighborhood.
This map gives us three important information
- The extent of flooding
- The depth
- The level of hazard
The extent of flooding – The extent of area at potential risk from surface water flooding. If the flooding likelihood is less than 0.1%, the level of risk is very low. When the flooding likelihood is 0.1%, the level of risk is low. When the flooding risk is 1% and 3.3%, the level of risk is medium and high respectively.
Map 3 – Flood Risk Reservoirs
The Flood Risk Reservoirs map is used for crisis situations only.
Map 4 – Historic Flood Map
The land areas that have been previously flooded are recorded in the Historic Flood Map. Internally flooded properties are not captured in this map.
Map 5 – Areas Benefiting from flood defences
The areas benefiting from flood defences are defined in two ways – a 1 in 100 chance of flooding from rivers each year (1%), a 1 in 200 chance of flooding from the sea each year (0.5%).
Map 6 – Flood warning areas
The Environment Agency provides flood warning services to certain areas as indicated in this map. If your property is anticipated to be in the flood prone areas (river or sea).
Did you know?
In Dorset, properties at flood risk accounts for 5% while the number of properties at medium or high flood risk is 12,589.
In Bristol, properties at flood risk accounts for 7% while the number of properties at medium or high flood risk is 15,861.
In Oxford, properties at flood risk accounts for 6% while the number of properties at medium or high flood risk is 4,996.
In Greater London, properties at flood risk accounts for 14% while the number of properties at medium or high flood risk is 58,1994
In Kent, properties at flood risk accounts for 9% while the number of properties at medium or high flood risk is 76,333.
In York, properties at flood risk accounts for 7% while the number of properties at medium or high flood risk is 7,678.
Wondering how flood risk could impact your area and what the potential risk in your area is?
Flood Risk Map Evaluation
Here, I will show you the basis for flood evaluation and how our maps can be used.
This is a basic evaluation, we have created detailed guidance for flood risk evaluation within our blogs.
Evaluation Flood Risk?
There are three components to flood risk assessments.
Component 1: The magnitude and probability of flooding
This includes assessing the magnitude of different flood conditions that cause damage and all other factors such as water quality, moving water velocity, inundation etc. For instance flood zone 2, flood zone 3. The higher the number the more flood magnitude and probability.
Component 2: The exposure of assets and vulnerability
Economic value of assets and the correlation between flood hazards and potential damage to the assets are assessed. For instance water compatible assets (pumping station, rowing clubs), more vulnerable (dwellings etc).
Component 3: Performance of flood protection measures
There are a number of measures that could be taken for flood protection and protection from damage like moving developments away from the flood zone, building flood walls, building flood defence systems, invest in long term nature based solutions, etc.
Do you need a flood risk assessment?
You need a flood risk assessment if one of the following applies:
- When your development falls in one of the flood zones, you may need a flood risk evaluation.
- If your development is for greater than 1 ha in flood zone 1.
- Change of use and minor development in flood zone 2, flood zone 3. See more information in the flood risk assessment guidance.
- If your development in flood zone 1 is less than 1 ha which includes a change of use in the type of development to a more vulnerable class, which may be prone to flood risk other than those caused by rivers and sea.
- If the Environment Agency has designated the area in flood zone 1 to have critical drainage problems.
To find out the flood zone you are in, you can use our maps or the Environment Agency maps.
The flood risk evaluations are approved by the Environment Agency based on the recommendations from the National Planning Guidance. For house extensions the flood risk assessments are approved by the local council.
How to get flooding history for a property?
- Produce a site location map.
- Write to enquiries@environment-agency.gov.uk to request flooding history and provide your contact details. This costs about £25.
- You will receive the flooding history report after 20 working days.
What does a flood risk assessment include?
A flood risk assessment includes the following
- Location and address of the site
- Proposal description
- Sequential and exception test application
- Flood risk management
- Local strategic flood risk assessment review
- Site geology, hydrology and hydrogeology evaluation
- Flood hazard assessments evaluation
- If the flood levels are not available the flood risk assessment should include river modelling to determine them
- Off-site assessment of flood risk impact. Do you need a flood risk activity permit?
- Residual risk determination. In some cases you will need a drainage strategy
For more information, check out our blog on Flood Risk Assessments
Risk Management Authorities
Flood risk and development is highly regulated and has many stakeholders.
We have named a few!
There are a few Risk Management Authorities(RMAs) that deliver national policies. Let us see them below.
Environment Agency
The overview of all sources of coastal erosion and flooding is taken care of by the Environment Agency.
Lead Local Flood Authorities(LLFAs)
They are the unitary authorities and county councils. Local flood risks are managed by them.
District and Borough Councils
Flood risk management efforts outside IDB areas, on minor watercourses can be carried out by District and Borough Councils.
Coastal Protection Authorities
Coastal erosion risk management initiatives are led by Coastal Protection Authorities in their area.
Water and Sewerage Companies
Long term Flood risks to sewerage facilities and water supply and flood risks from their infrastructure failure are managed by Water and Sewerage Companies.
Internal Drainage Boards
Water capacities in low-lying areas are managed by Internal Drainage Boards which are independent public bodies.
Highways Authorities
The responsibility of managing and providing the roadside ditches and highway drainage under the Highways Act 1980 is led by the Highways Authorities.
Managing Flooding
You can protect you development from flooding.
This are our pointers on how best to do it.
How can you manage flooding?
Flood Management in UK consists of three components:
- Prevention of flood risk
- Protection of flood risk
- Preparedness to flood risk. You can check this guide for Oxford
The elements and efforts used to minimise the flow of water before it connects to rivers is a natural flood management technique.
What can you do to avoid or prevent flood risk?
A sustainable and cost-efficient approach would be to concentrate on green infrastructure that is capable of getting rid of water at the source.
Using an integrated sustainable development system provides dual benefits. It greatly enhances the quality of the development and reduces costs.
The rain water that collects on the buildings can be used for a variety of purposes like gardening, irrigation etc. Reusing this water can be quite beneficial to water conservation efforts and flood risk.
It is important to keep in mind climate change and its impacts for the future. Hence, contributing to zero carbon efforts will help reduce not only climate change but also flood risk and future impacts.
There are many actions you could implement towards reducing carbon footprint from as simple as driving less, planting more trees, focusing on clean energy etc.
By placing retrofit sustainable drainage systems in community centers.
Trees can be planted across the streets which will reduce the speed of water and in turn contribute to mitigating flood volumes.
Green roofs can be installed on top of your shed to reduce run-off and eventually flooding.
Constructing rainwater gardens is a great way to utilize rainwater efficiently and to mitigate floods.
Based on the water depth, water resistant and resilient intervention can be used.
Also, local MP of your area can be contacted for an update on the flood defence initiatives that are in progress in your area put forth by the Environment Agency.
Hope you found this piece informative!
