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Flood survey guide: how to get the most out of a property flood assessment

Chris Hall
19/02/2020
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We’ve teamed up with our friends at Cluttons to help commercial property owners know how to set up a flood survey (also known as a flood risk analysis) so they can prepare for flooding better. For more information on their approach to flood risk analysis visit https://www.cluttons.com/.

This is part of a FloodFlash series about better preparing your business for flooding. Check out others in the series to understand:

The types of flood survey you can undertake for your property

There are lots of different surveys on offer so it can be tricky choosing amongst them, or knowing what you’re going to get. Here is a list of the types of surveys or assessments that can contribute to your understanding of a property’s flood risk.

Building survey – This survey is concerned with understanding the form and condition of any buildings on site relevant to the proposed flood defence design and may include intrusive investigations to open up and expose parts of the structure to do so.

Drainage survey – a CCTV drainage survey is a process for examining the foul and surface water drainage systems remotely with a camera system that records video footage and captures other useful data. The survey should map the drainage network, confirm flow directions, invert levels, pipe diameters, materials, condition and blockages. If blockages in the system are suspected, it is sensible to instruct the engineer to bring equipment to clear them when encountered during the survey, so as to avoid abortive costs and the need to revisit the site.

Flood risk – this survey is called a ‘Flood Risk Assessment (FRA)’ – its main purpose is to assess the risk of flooding from all mechanisms and should include the effects of climate change. It should also provide advice on managing the flood risk. It is a specialist report in its own right and is required for planning application purposes. It may use some of the data obtained from the other surveys mentioned and uses Environment Agency historic flood data and modelling.

Geotechnical investigations: A specialist report prepared following intrusive site investigations, including sub-surface explorations, soil sampling and laboratory analysis, in order to assess soil conditions relevant to the proposed development.

Measured survey – A survey undertaken to provide scale plans, elevations and sections of existing structures on site relevant to the design and includes spot levels AOD (see Ordnance Datum below).

Ordnance Datum (OD) – The term ‘Ordnance Datum’ refers to the height above mean sea-level, measured between 1915 and 1921, from a reference point at Newlyn, Cornwall (Ordnance Datum Newlyn). Above Ordnance Datum (AOD) refers to the height above Ordnance Datum and is used for deriving altitudes on maps. It is the basis of the national height mapping system in Britain. Prior to 1921 OD was taken from the level of the Victoria Dock, Liverpool (ODL).

Topographical survey – a scale survey of the subject area, with spot levels provided ‘Above Ordnance Datum (AOD)’*. The survey shows all natural and manmade features and is the base plan for the design drawings.

Utility survey – a survey to trace and map underground utilities and buried services. Take this out to provide information about the location, depth and type of services present. This is key information for health and safety purposes when cutting into or driving over land with heavy machinery. It is also essential for designing flood defences. That’s because there are often service penetrations that require sealing to prevent flood water ingress.

Five steps to a full flood survey

Looking to carry out a comprehensive flood survey for your commercial properties? It’s worth making sure that you cover off the following steps:

  1. Appoint an independent flood resilience professional to ensure you receive the best advice. There are many out there for different sized projects so it can be good to shop around.
  2. Undertake a Flood Risk Assessment to assess the risk of flooding. That equips you to design or commission appropriate flood resistance and resilience measures.
  3. Carry out topographical, utility, drainage, building and measured surveys to obtain site information. This can include scale drawings with spot levels ‘Above Ordnance Datum (AOD)’.
  4. Undertake geotechnical investigations to assess soil properties and sub-surface conditions, such as permeability, strength and groundwater flows. 
  5. Analyse the information received and develop a site-specific design proposal and associated cost plan, programme and project risk analysis.

The measures you can install after a survey

Flood resilience measures can take many forms. Flood gates are often the most visible but there are other ways of protecting a property:

Flood resilience: A collective term used to refer to resistance and recoverable measures.

Flood defences (also known as flood resistance): Reducing the likelihood of water entering a building.

Flood recoverability (also, confusingly, known as flood resilience): Reducing the damage caused in a building if water does get in.

Flood Risk Assessment (FRA): A specialist report providing advice on the risk of flooding from all potential mechanisms and often required as part of the planning application for the proposed development.

Flood insurance: this is where FloodFlash comes in. Having insurance means that if your flood defences or recoverability measures don’t protect you from every cost, you have money available to make the business or property operational again.

For more information on what to expect next, check out our blog on How flood resilience can help your property.

About Cluttons

Cluttons offers exceptional depth of property knowledge from a diverse group of experts, with a focus on delivering commercial results for its clients. 

Employing over 240 staff through a network of offices in the UK and internationally, Cluttons providing a wide range of commercial and residential property services, including asset management, valuation, corporate services, telecoms and consultancy.  It uses its proprietary portal technology and deep knowledge in sectors such as telecoms, charities and education to provide clients with unique insights and innovative solutions to help them maximise returns on their assets.