Caterham on the Hill and Old Coulsdon flood resilience project guidance

This is an evolving guidance web page and the multi-agency project board will continually add to the list as the community engagement progresses.

  1. Property Flood Resilience Project overview
  2. Flood questions
  3. Options questions
  4. General information / any other questions

1. Property Flood Resilience Project overview

What is a flood risk management scheme?

A flood risk management scheme can take many forms, from hard engineered walls to creation of areas designed to flood, away from property. Whatever the type, the purpose is to reduce the risk of flooding to people, property and infrastructure.

Why do we need a flood risk management scheme in the Caterham on the Hill and Old Coulsdon area?

Recent flooding events occurred in Winter 13/14, 7 June 2016, December 2019 and February / March 2020 (Storm Ciara and Dennis). Flood risk modelling has identified more than 200 properties at risk of flooding in the area. This scheme aims to reduce the risk from surface water flooding. There was a significant flood event on 7 June 2016 where there was 79 reported internal and 52 external property floods within the catchment. These floods have caused damage to property, disruption to businesses and distress and upheaval to people's lives. We have therefore been working to identify and implement ways to reduce flood risk in the catchment.

What geographic area does this project cover?

This flood scheme covers flood mitigation opportunities in the Old Coulsdon to Caterham on the Hill surface water catchment. The catchment extends from north of Caterham Drive southwards to the upper reaches of the catchment south of Queen Park recreation park.

This can be viewed on the flood resilience project map (PDF).

Who is involved in the project?

No single organisation, especially if working in isolation, can address flooding. Therefore the project has a multi-agency approach involving the local authorities; Surrey County Council, London Borough of Croydon and Tandridge District Council, the Environment Agency and water companies (Thames Water). Other stakeholders, including affected individuals, local communities and special interest groups (e.g. the Caterham on the Hill and Old Coulsdon Flood Action Group) will be invited to contribute as the project progresses. We believe that better results will be achieved this way. Ultimately, this will be a community-based project, with residents central to delivering outcomes.

What will the outcome be?

The multi-agency project board is working on a programme of phased interventions in order to slow the flow through-out the catchment. One of the first phases is applying for central Government funds through a process called an Outline Business Case (OBC). Work carried out to date has identified Property Flood Resistance (PFR) as the preferred strategic option.
If funding is approved those properties that have signed up to the PFR scheme will be offered a survey to see if their property can benefit. Following this PFR measures will be installed to help reduce the risk to property. We envisage that this will take around 2 years dependant on the numbers of take-up.

2. Flood questions

How often do flood events occur in this area?

Localised flooding occurs in areas where surface water run-off overwhelms the capacity of the surface water infrastructure often following large storm events. Recent flooding occurred in December 2019 and February – March (Storm Ciara and Dennis) storm events. Significant flooding occurred in Winter 13/14 and widespread flooding occurred on 7 June 2016.

In 2018, Surrey County Council on behalf of the multi-agency project board commissioned Atkins Consulting to build an integrated catchment model. This has improved our understanding of the flooding mechanisms in the catchment. This showed that around 200 properties are at risk of flooding from surface water in a 5% (1 in 20) annual probability event.

What is surface water flooding?

Surface water flooding occurs when the volume of rainwater does not drain naturally into the ground or into a surface water drainage network. The resulting rainwater flows across the landscape or ponds in local depressions. Commonly, surface water flooding occurs after heavy downpours or thunderstorm events, particularly where the landscape is steep-sided.

Find out if you're at risk of flooding by looking at the online flood map on the Environment Agency website.

The modelling does seem to reflect the flooding experienced by residents in the area. If you think that the surface water model doesn't represent what you have experienced then contact Surrey County Council on and we will pass this onto the Environment Agency.

How accurate are the flood maps?

The flood maps are created using the best available hydrological information and data from river surveys and are processed with computer models. They represent our best estimate of what could happen in a flood, however the unexpected can always occur, for example a culvert entrance becomes blocked and flood water is diverted along another route, or the storm could persist and stay in one place longer than is usual.

3. Options questions

Do you have an idea of what the solution looks like?

Our preferred way forward to reduce surface water flooding in Caterham on the Hill and Old Coulsdon is a PFR scheme.

Why can't we store water upstream?

There is limited space for traditional large flood storage area at the top of the catchment due to the built environment. Queens Park recreational park has been identified as a location of potential flood storage and was short-listed in the Outline Business Case. Currently the use of the park is being reviewed by Tandridge District Council.

How much will the scheme cost?

The estimated cost at this stage is £1.8 million. This cost is based on uptake of the scheme by all 205 eligible properties. The scheme cost will be lower if there is reduced homeowner uptake.

What timescales are you looking at for completion of the project?

This project needs community participation and we cannot move on until we have buy-in from you as residents. We are therefore looking for an indication of positive homeowner uptake. As property resilience projects are simpler than large civil engineering works, we will then be able to start putting these measures in place quickly, aiming for installation to be complete by Spring 2022.

Will you protect key assets?

This scheme focuses on protecting property. Through wider measures we are aiming to reduce flood risk to local infrastructure.

Will all properties be protected by this scheme?

No. There are some properties whose level of risk will remain about the same. No properties will be at increased risk of flooding.

Which and how many properties will receive increased protection?

In our initial screening exercise, 205 residential properties in Caterham on the Hill and Old Coulsdon have been identified as eligible for property level flood resilience. The majority of these properties are located in Caterham on the Hill. These are the properties currently modelled to be at risk of flooding (river and / or surface water) in the 5% (1 in 20) annual probability event and / or those with reported to have flooded in June 2016. We have also included attached properties (semi-detached or terraced) where necessary, although these may not have been identified as having flooded. At this stage, we have not however ruled anyone in or out and would like to listen to your individual circumstance.

I live in a semi-detached / terraced house. What happens if my neighbour is not interested?

We cannot force people to be part of the scheme. All parties would be offered it. In semi-detached and terraced houses PFR will need to be fitted to the whole building. This is to ensure that the whole building is protected.

My property won't receive protection – why not?

We cannot protect everyone. We have used national guidance to determine which properties are eligible.
I've already spent money installing measures to protect my property. Am I eligible? Can I get my money back?
We cannot give money back for work which has previously been undertaken. You are however still eligible (if you meet the criteria) for a survey under this scheme. This survey may identify future measures which would help protect your property.

Who will meet the cost of maintenance of the new measures?

Maintenance will be the homeowner's responsibility. This scheme will not cover the costs of future maintenance. We will organise further meetings attended by the installation contractors. This will provide you with the opportunity to look at products, and discuss information relating to warranty, lifespan, maintenance requirements and any other concerns you may have.

4. General information / any other questions

What do you mean by likelihood of flooding? What is a 1% annual probability storm?

The probability or likelihood of flooding is described as the chance that a location will flood in any one year. The likelihood is expressed as a percentage (e.g. 1%), or as a chance (e.g. 1 in 100 chance in any given year). It is important to remember that the risk of a flood occurring is there at all times - this year, next year and future years. Some people find it helpful to think of a betting analogy.

Why is this the first I'm hearing of this? How long has this been in the pipeline?

Surrey County Council, London Borough of Croydon, Tandridge District Council, Thames Water and the Environment Agency have been working on this programme since the floods in 2016. We have also been working with the Caterham on the Hill and Old Coulsdon flood action group for the last few years, who are open to and supportive of the project. Recently we have reached an important milestone in the project and so are taking this opportunity to engage with a wider audience.

What can people do to help both themselves and others?

Everybody has some responsibility, including residents. Some actions may be simple (e.g. avoiding the clogging of drainage areas), others more complex. Where appropriate, we will be actively engaging with local people to raise awareness, inform them about flood risk and help to reduce it.

Have you considered Sustainable Drainage Systems (SuDS)?

The risk of surface water flooding could be further reduced through the installation of Sustainable Drainage Systems (SuDS). This option could consist of a range of measures including water butts, green roofs and permeable paving. The benefit of this option would depend on the type and location of systems installed. Surrey County Council, Tandridge District Council and Thames Water will investigate this option further in the long term. Furthermore, Tandridge District Council, in drawing up its emerging Local Plan, has proposed new planning policy which will ensure that all new residential development incorporate SuDS; the emerging Local Plan is currently undergoing its examination by the Planning Inspectorate. Over time this will help reduce surface water flows in the catchment.

Files available to download