30 Aug London’s Hydrogeology: Understanding the Risk, Managing the Resource
Our capital sits on a huge groundwater resource that provides opportunities for extraction of both water and ground source heat energy. However groundwater levels can also represent risks to commercial property and transport as rising levels interfere with critical infrastructure.
It is essential to understanding how to harness the value from groundwater as a resource, but at the same time understand how it could negatively impact property in the face of climate change.
The Chalk constitutes the Principal aquifer in central London and is considered by the Environment Agency to transmit significant flow to support large-scale exploitation.
Abstractions from the Chalk aquifer beneath London have decreased since their peak in the 1960s and groundwater levels in the Chalk aquifer have recovered. In some parts of London the rate of rise was so great that the Environment Agency with other stakeholders launched the GARDIT strategy in the late 1990s to control levels by increased abstraction.
Our work in modelling and understanding the hydrogeology and geology below the capital for our clients is extensive and wide ranging:
Government Buildings – Ground Source Heat Energy
We have recently concluded a major study on key government buildings, in conjunction with our ground source energy partner, to review the hydrogeology below the buildings, as part of an overhaul of their ground source heating and cooling. The buildings are of such a scale that the abstraction is significant.
The government is developing a 25 year sustainability strategy for the site and we were commissioned to review the potential to increase the use of water sourced cooling (and if appropriate) heating across the Estate.
This includes assessment of options for using borehole cooling to reduce the carbon footprint and provide a resilient engineering infrastructure. They are also reviewing the potential for expanding the use of the existing borehole system as well as the installation of new boreholes.
Residential Basement Conversions
London is growing at an unprecedented rate and therefore the demand on the aquifer from residential and commercial activity will place it under greater strain.
Getting the balance right is key. Falling groundwater levels and de-saturation of the Chalk can impact local abstractors’ ability to abstract groundwater and may locally impact the environment where streams rely on baseflow (as in the south London streams rising from the North Downs).
We have undertaken many consulting projects to examine the proximity of groundwater on residential basement conversions – whether to account for dewatering needs, or the threat of inundation from hidden rivers, such as those that plague boroughs like Camden, Hammersmith & Fulham and Kensington & Chelsea.
Basements can impede local groundwater flow and quality, as well as ground movements. They can also have knock on effects to neighbouring properties. London Borough planning teams are increasingly requiring Basement Impact Assessments, which we are actively providing on behalf of our clients.
Electricity Cabling Tunnels, Croydon: Groundwater Proximity Modelling
We also supported the development of a tunnel in Croydon which was constructed close to a number of sensitive public water supply wells. The tunnel was to carry high voltage electricity cables between two electrical substations. It was to be mostly excavated in Chalk, with some excavation occurring in the Thanet Sands.
We drilled purpose monitoring wells and equipped these with sensors to monitor groundwater level, electrical conductivity and turbidity. We also collected data which transmitted to us via a telemetry system on a daily basis.
This allowed almost real time monitoring of rapid events such as changes in turbidity following rainfall. Wells with pumps allowed high quality groundwater samples to be extracted for analysis.
The data provided early indications if the tunnelling could cause problems. At the same time, our risk assessment of the shaft and tunnel construction focused on minimising impacts on groundwater quality or quantity.
The end result was a tunnel built with no significant impacts on the sensitive public supply boreholes.
Proven Expertise for the Capital
London is forever changing above ground, but it is essential to understand what lies beneath to ensure we are developing in sync with the hydrogeology. Our extensive experience and market leading scientific analysis ensures we are the right choice for property and infrastructure projects. In particular ESI wrote the definitive report on the groundwater systems under London for the Environment Agency and developed a region wide groundwater model that is the technical basis for all major water resource schemes in the capital.
For more information, call us on 01743 276100 or email email@example.com