About the project

In 2015 and 2019, Ambiental were approached to provide an updated Flood Risk and Surface Water Mitigation Scheme for The National Archives in London. The assessment was focused to supporting their business continuity plan to identify possible areas of risk that then could of required intervention.

The National Archives are the official archive and publisher for the UK Government for England and Wales. This includes a huge variety of records, such as Shakespeare’s tax records to Downing Street Tweets. It is considered to be of National Importance – “priceless” some may say.

The site itself comprises of two buildings. The archives are spread throughout both with the total footprint taking up approximately 1.67ha of the full 4.8ha site. There are approximately 500 staff on site and roughly 90,000 visitors per year.

The buildings are home to over 1,000 years’ worth of national documents. These records document history, cultural importance and as such they need to regularly update their flood mitigation schemes in order to protect their vital contents.

A little more about the project

Ambiental were tasked to create a bespoke Flood Risk Assessment (FRA) to assess the potential flood risk posed to the site from multiple sources of flooding.

Ambiental were further appointed to produce an independent 2D pluvial model for a number of potential flood levels, including extreme events, were used to allow detailed analysis of the potential surface water flood risk posed to the National Archive site.

As shown on the map above, the National Archives is located roughly 100m from the River Thames to the North and North East of the site.

The National Archives Flood Zone Map (Taken from: Flood Map For Planning)

The Risk and Need For The Assessment

The proximity to the River Thames means the National Archives are classified by the Environmental Agency as being within Flood Zone 3 (high risk of flooding).

Like many areas of London, this means it has a high risk of flooding. Given the location of The National Archives the dominant source of flooding at this point was from tidal sources (>0.5%). This area of Central London benefits greatly from the presence of defences - The Thames Barrier and linear defences. Our team reviewed the risk of these defences failing and the impact it could have onto the The National Archives. Our experts further reviewed the flood risk from a pluvial source using our independent surface water flood modeller – FlowRoute-i™ which includes the UKCP09 climate change allowances.

The Solution

Ambiental’s approach was tailored completely to the National Archives requirements and we worked in close communication with their representatives.

The work involved:

• A full site survey and walkover
• Identifying the main source of flood risk to each area of the site using a combination of Ambiental’s in-house software, FlowRoute-i™ and third party data sources (e.g. Environment Agency data)
• A detailed analysis of flood depths on site using remotely sensed LiDAR topographic data through FlowRoute-i™
• A 2D pluvial model for a number of return periods, including extreme events, taking into account the latest climate change data

This data was then amalgamated into a Flood Risk Assessment and Surface Water Model to accurately determine the flood risk throughout the whole site.

The Outcome

The National Archives now have a document that identifies the multiple sources of flood risk to their assets. The assessment identifies an evacuation plan for their staff and other occupants of the building.

It has also provided an independent review of the Surface Water risk to the site accounting for the climate change allowances relevant at the time of the assessment. Finally, the assessment has provided recommendations of how to better mitigate the risk of flooding to The National Archives where a risk area was identified as part of the assessment.