Understanding Flood Risk Assessment for Planning Applications
A Flood Risk Assessment (FRA) for planning is a critical, evidence-based report that evaluates the potential flood risks associated with a proposed development site. We prepare a comprehensive FRA to demonstrate to planning authorities that a project is safe, sustainable, and compliant with national and local flood risk policies.
In areas vulnerable to flooding, local planning authorities require a site-specific flood risk assessment to ensure that new developments do not increase flood risk elsewhere and remain safe for their lifetime. Our approach integrates hydrological data, flood risk assessment for planning topographical analysis, drainage strategies, and climate change projections to provide a fully compliant and technically robust submission.
By delivering a precise and professionally structured flood risk assessment, we strengthen planning applications and significantly improve the likelihood of approval.
When Is a Flood Risk Assessment Required?
A flood risk assessment for planning permission is typically mandatory when:
The development site lies within Flood Zone 2 or Flood Zone 3
The proposal involves a site larger than 1 hectare in Flood Zone 1
The development may affect existing drainage systems or watercourses
There is a known history of surface water or groundwater flooding
We ensure that every assessment aligns with national planning policy frameworks and local authority guidelines. Early identification of flood risk constraints allows us to design mitigation strategies that are both practical and policy-compliant.
Key Objectives of a Flood Risk Assessment
Our flood risk assessment achieves several core objectives:
Identify all potential sources of flooding, including river (fluvial), coastal, surface water, groundwater, sewer, and artificial sources.
Assess the probability and severity of flood events affecting the site.
Evaluate the impact of the proposed development on flood risk elsewhere.
Recommend mitigation measures to reduce or eliminate flood risk.
Demonstrate compliance with national and local planning policy.
We present clear calculations, modelling outputs, mapping analysis, and drainage proposals to provide planning officers and statutory consultees with complete confidence in the development’s safety.
Types of Flood Risk Considered in Planning
Fluvial Flood Risk
Fluvial flooding occurs when rivers exceed their capacity during periods of prolonged rainfall. We analyse:
Flood Zone classification
Modelled flood levels
Floodplain storage capacity
Impact of development on flood flow routes
We use hydraulic modelling outputs and Environment Agency datasets to determine predicted flood depths and velocities, ensuring development layouts avoid high-risk areas.
Surface Water Flood Risk
Surface water flooding results from intense rainfall overwhelming drainage systems. We evaluate:
Topographical flow paths
Existing drainage infrastructure
Impermeable surface coverage
Climate change rainfall allowances
By modelling runoff rates and volumes, we design attenuation systems that restrict discharge to greenfield runoff rates, ensuring no increase in downstream flood risk.
Groundwater Flood Risk
Groundwater flooding can occur in areas Acoustic surveys with high water tables or permeable geology. We assess:
British Geological Survey mapping
Historic groundwater flood incidents
Site investigation borehole data
Where necessary, we recommend structural waterproofing and raised floor levels to mitigate groundwater intrusion.
Sewer and Artificial Source Flooding
We review local sewer capacity data and proximity to reservoirs or canals. We ensure that developments incorporate backflow prevention and resilient drainage strategies to eliminate internal flood risk.
Flood Zones and Their Impact on Planning
Flood Zones are central to the planning decision-making process:
Flood Zone 1: Low probability of flooding
Flood Zone 2: Medium probability
Flood Zone 3a: High probability
Flood Zone 3b: Functional floodplain
We apply the Sequential Test to steer development toward areas of lowest flood risk. Where necessary, we support the planning process with an Exception Test, demonstrating sustainability benefits and site safety through detailed mitigation proposals.
Climate Change and Long-Term Resilience
Modern flood risk assessments must incorporate climate change allowances. We integrate projected increases in peak river flows and rainfall intensity into hydraulic and drainage modelling.
By designing for the development’s lifetime—often 100 years for residential projects—we ensure resilience against future flood scenarios. Our assessments include:
Raised finished floor levels
Compensatory floodplain storage
Oversized attenuation basins
Sustainable drainage systems (SuDS)
This proactive approach safeguards property value, infrastructure integrity, and occupant safety.
Sustainable Drainage Systems (SuDS) in Flood Risk Assessment
A high-quality flood risk assessment for planning includes a detailed Sustainable Drainage Strategy. We prioritise:
Permeable paving
Swales and filter drains
Detention basins
Underground attenuation tanks
Green roofs
These systems manage runoff at source, reduce peak discharge rates, and improve water quality. We provide hydraulic calculations demonstrating compliance with allowable discharge limits and storage requirements.
Our drainage strategies are engineered for adoptability, maintainability, and long-term performance.
Site-Specific Data Collection and Analysis
A robust flood risk assessment is built on accurate site data. We conduct:
Topographical surveys
Ground investigations
CCTV drainage surveys
Watercourse condition assessments
We integrate survey findings into hydrological and hydraulic models to simulate realistic flood scenarios. Our evidence-based methodology eliminates uncertainty and strengthens planning submissions.
Mitigation Measures for Safe Development
Where flood risk exists, we design targeted mitigation measures, including:
Raising floor levels above modelled flood levels
Flood-resistant construction materials
Safe access and egress routes
Flood warning and evacuation plans
Compensatory flood storage areas
Each recommendation is supported by quantitative modelling and policy justification, ensuring approval authorities recognise the scheme’s compliance and safety.
The Planning Authority Review Process
Local planning authorities and statutory bodies rigorously examine flood risk assessments. We prepare documentation that includes:
Detailed flood maps
Hydraulic model outputs
Drainage calculations
Sequential and Exception Test statements
Maintenance and management plans
By anticipating technical queries and addressing them proactively, we streamline the review process and minimise delays.
Common Challenges in Flood Risk Assessment for Planning
We frequently encounter complex scenarios such as:
Development within functional floodplain
Brownfield redevelopment in urban flood zones
Sites with culverted watercourses
High groundwater tables
Limited discharge points
Our technical expertise enables us to deliver innovative engineering solutions that unlock constrained sites while maintaining strict policy compliance.
Benefits of a Professionally Prepared Flood Risk Assessment
A comprehensive flood risk assessment for planning provides measurable advantages:
Accelerated planning approval
Reduced risk of costly redesign
Improved stakeholder confidence
Enhanced long-term asset resilience
Compliance with environmental legislation
We approach each project with precision, ensuring documentation is clear, technically rigorous, and aligned with planning authority expectations.
Flood Risk Assessment and Sustainable Development
Responsible development requires balancing growth with environmental stewardship. Through careful flood risk management, we:
Protect communities from increased flood exposure
Preserve natural floodplains
Support biodiversity enhancement
Reduce pressure on public drainage infrastructure
Our assessments integrate engineering excellence with environmental sensitivity, ensuring developments contribute positively to their surroundings.
Conclusion: Delivering Planning Success Through Expert Flood Risk Assessment
A well-prepared Flood Risk Assessment for planning is not simply a regulatory requirement—it is a strategic tool that secures development viability and protects future occupants. By combining hydrological expertise, drainage engineering, climate resilience planning, and policy compliance, we deliver authoritative, approval-ready assessments.
