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.
When is a Basement Impact Assessment required?
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.
What a full BIA involves
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.
How we work
- Stage 1 Screening — we carry out the initial screening assessment to establish which of the surface flow, groundwater and stability issues are relevant to your site, and whether further investigation is needed.
- Scoping and team — where a fuller assessment is required, we scope the work and assemble an appropriately qualified team, leading the surface flow and flooding element ourselves.
- Assessment — we complete the detailed Surface Flow and Flooding assessment and coordinate the groundwater and land stability inputs into a single, consistent BIA.
- Reporting and planning support — we produce the BIA report for submission and respond to queries from the borough's technical reviewers through to approval.
Why Water Environment?
Our directors have a combined 40+ years of specialist experience in flood risk and hydrology, and our chartered engineers can complete and sign off the Surface Flow and Flooding element of a BIA to the standard the London boroughs require. Because we routinely coordinate multi-disciplinary flood and ground assessments, we can lead the whole BIA and bring in the right groundwater and structural specialists, giving you a single point of responsibility for the report.
We are members of the Chartered Institution of Water and Environmental Management (CIWEM) and hold professional qualifications with the Institution of Civil Engineers (ICE).