Basement Impact Assessments (BIA)

The development of basements beneath an existing property is an increasingly common way to extend, particularly in central London where other options are limited. New basement development, or extension of existing ones, has been recognised as a potential problem in terms of local flooding, groundwater flow and ground movements. These issues can impact upon neighbouring properties and multiple basement developments in the same area can have a cumulative effect.

Many of the London boroughs now require completion of Basement Impact Assessments (BIA) for all planning applications proposing basement development. Initially, a Stage 1 Screening assessment is required, which is followed by more in-depth investigation and more detailed analysis if problems are encountered.

In order to complete a full BIA, three assessments are typically required:

• Surface Flow and Flooding – which must be completed by a hydrologist or specialist engineer, with appropriate chartered status
• Subterranean (Groundwater) Flow – which must be undertaken by a hydrogeologist with chartered geologist status
• Land Stability – to be completed by a ground engineer with adequate chartered status

At Water Environment, our chartered engineers can complete and sign off all levels of Surface Flow and Flooding assessment. We regularly work with groundwater flow specialists and structural engineers, and can put together an appropriately qualified team to complete the full BIA. Please contact us to discuss your requirements.