Basement Impact and Flood Risk Assessment in Notting Hill

Lustre Consulting was appointed by Schneider Designers to conduct a detailed Basement Impact Assessment (BIA) and Flood Risk Assessment (FRA) for a proposed residential development in Notting Hill. The project involved the extension of a basement beneath an existing property within the Royal Borough of Kensington and Chelsea. Our service aimed to address concerns related to structural integrity, flood resilience, and environmental impact while satisfying planning requirements.

Understanding the Challenges

The development was situated in a Critical Drainage Area (CDA), classified as “high risk” for surface water flooding. Coupled with the site’s underlying geology of London Clay, known for its shrink-swell properties, these challenges required a tailored approach to ensure compliance with local planning policies and environmental standards. Additionally, the basement’s proximity to neighbouring properties demanded careful assessment to mitigate any potential impact on adjacent structures.

Basement Impact Assessment

Our Basement Impact Assessment focused on identifying risks associated with groundwater, soil stability, and drainage while proposing practical solutions to address these issues. Key aspects of the assessment included:

• Ground Stability and Structural Integrity: London Clay, the primary stratum beneath the site, is known for its reactivity to moisture changes, posing risks of ground movement. To address this, we recommended traditional underpinning techniques for the retaining walls to minimise any disturbance during excavation. These techniques were specifically designed to protect both the proposed basement and neighbouring properties from structural instability.
  
• Groundwater and Drainage Solutions: The BIA identified potential risks of groundwater ingress due to the basement excavation. To mitigate this, we proposed a waterproofing system, incorporating sump pumps and tanking to manage potential water intrusion effectively. These measures not only addressed current groundwater risks but also enhanced the long-term resilience of the structure.
  
• Neighbouring Properties: The assessment also included detailed modelling to evaluate how the excavation could affect nearby properties. By incorporating conservative construction techniques, we ensured minimal disruption to surrounding structures.

Flood Risk Assessment

As the site was situated in a high-risk flood zone, our FRA focused on reducing surface water flood risks while ensuring compliance with the borough’s planning policies. Highlights of our flood mitigation strategy included:

• Surface Water Mitigation Measures: The FRA recommended the use of Sustainable Drainage Systems (SuDS), such as permeable paving and green roofs, to manage runoff efficiently. These measures were designed to reduce surface water discharge by at least 50%, as required by the Royal Borough of Kensington and Chelsea’s policies.
  
• Flood Resilience and Resistance Features: To safeguard the proposed basement, the design included raised thresholds, flood-resistant materials, and advanced drainage systems to direct water away from the structure during extreme rainfall events.
  
• Drainage Strategy: A detailed drainage strategy was devised to complement the SuDS measures. By improving site-wide drainage capacity, we ensured that both the property and its surroundings would remain resilient to surface water flooding.

Delivering Value Through Tailored Solutions

The combined findings of the BIA and FRA provided the client and the planning authority with a clear roadmap for achieving a safe and sustainable development. Key outcomes of our work included:

• Demonstrating compliance with strict local planning requirements, enabling smooth progression through the planning process.
  
• Mitigating risks associated with both groundwater ingress and surface water flooding.
  
• Protecting neighbouring properties through advanced structural and drainage solutions.
  
• Adding long-term value by integrating sustainable and resilient design measures.

By addressing these challenges comprehensively, Lustre Consulting played a pivotal role in ensuring the development’s success, from securing planning approval to laying the groundwork for safe and sustainable construction.

For more information on how Lustre Consulting can assist with similar projects, contact us today.