Question: What is a Flood Risk Assessment (FRA)?
Answer: A Flood Risk Assessment (FRA) is a technical planning report that evaluates the risk of flooding to and from a proposed development. The assessment considers a range of flood sources including river flooding (fluvial), surface water flooding (pluvial), groundwater flooding, sewer flooding, reservoir flooding and tidal flooding where relevant. The purpose of an FRA is to demonstrate that a development can be designed safely without increasing flood risk elsewhere. Planning authorities use Flood Risk Assessments to determine whether proposals comply with the National Planning Policy Framework (NPPF), Planning Practice Guidance (PPG), Environment Agency requirements and local flood risk policies. A professionally prepared FRA can help identify mitigation measures, drainage strategies and design solutions that support planning approval whilst ensuring long-term resilience to flooding and climate change.
Question: When is a Flood Risk Assessment required for planning permission?
Answer: A Flood Risk Assessment is normally required where development is proposed within Flood Zone 2 or Flood Zone 3, within a Critical Drainage Area, or where a site exceeds one hectare in Flood Zone 1. Additional requirements may also apply where developments are located near Environment Agency Main Rivers or in areas affected by significant surface water flood risk. Many local planning authorities now request FRAs even for smaller developments where local drainage constraints, historical flooding records or climate change considerations are relevant. Producing an FRA at an early stage can significantly reduce planning risk, particularly for developments involving residential accommodation, care facilities, educational buildings or critical infrastructure.
Question: What does a Flood Risk Assessment include?
Answer: A typical Flood Risk Assessment includes a detailed review of the site and surrounding area together with an assessment of all relevant flood risks. The report evaluates existing conditions, identifies constraints and recommends mitigation measures where necessary. Key elements often include:
- Flood Zone classification
- Environment Agency flood mapping review
- Surface water flood risk assessment
- Groundwater flood risk assessment
- Sewer flood risk assessment
- Climate change allowances
- Site levels and topography review
- Safe access and egress assessment
- Flood mitigation measures
- Drainage strategy recommendations
The assessment provides planners, consultees and developers with a comprehensive understanding of potential flood risks and how these can be effectively managed.
Question: What is the difference between a Flood Risk Assessment and a Drainage Strategy?
Answer: Although often submitted together, a Flood Risk Assessment and a Drainage Strategy serve different purposes.
A Flood Risk Assessment focuses on understanding flood risk from external and internal sources and demonstrating that the development can be safely accommodated within its location. A Drainage Strategy focuses specifically on how surface water and foul water will be managed across the development through the implementation of Sustainable Drainage Systems (SuDS) and other drainage infrastructure. Many planning applications require both documents because flood risk and drainage performance are closely linked. Together they provide the evidence required to demonstrate compliance with planning policies and flood management objectives.
Question: What are Sustainable Drainage Systems (SuDS)?
Answer: Sustainable Drainage Systems (SuDS) are drainage solutions designed to mimic natural drainage processes and reduce the risk of flooding. Rather than rapidly directing water into sewers, SuDS aim to slow, store, filter and manage surface water more sustainably. Examples of SuDS features include:
- Permeable paving
- Attenuation tanks
- Swales
- Rain gardens
- Green roofs
- Blue roofs
- Infiltration systems
- Detention basins
National planning policy strongly encourages the use of SuDS on most developments. They help reduce flood risk, improve water quality, enhance biodiversity and support climate resilience objectives.
Question: What is a Drainage Strategy Report?
Answer: A Drainage Strategy Report sets out how surface water and foul water will be managed throughout the lifetime of a development. It considers existing site conditions, future drainage requirements and opportunities to incorporate Sustainable Drainage Systems. The strategy typically includes:
- Existing drainage review
- Application of the drainage hierarchy
- SuDS assessment
- Attenuation requirements
- Surface water discharge calculations
- Climate change allowances
- Exceedance flow routes
- Drainage maintenance requirements
Local Planning Authorities and Lead Local Flood Authorities frequently require drainage strategies to accompany planning applications, particularly for larger developments or those within flood-sensitive areas.
Question: What is the drainage hierarchy?
Answer: The drainage hierarchy is a planning principle that prioritises the most sustainable methods of managing surface water runoff. The hierarchy requires development teams to consider drainage options in a specific order before discharging to public sewers. The hierarchy generally prioritises:
Infiltration into the ground.
Discharge to a watercourse.
Discharge to a surface water sewer.
Discharge to a combined sewer as a last resort.
Planning authorities expect developers to demonstrate that each stage of the hierarchy has been properly considered before selecting a drainage solution.
Question: What is the Sequential Test in flood risk planning?
Answer: The Sequential Test is a planning tool used to direct development towards areas of lower flood risk wherever possible. It forms a key part of national flood risk policy under the National Planning Policy Framework. The principle is that new development should be located in areas with the lowest probability of flooding before considering higher-risk locations. Where development in higher-risk zones cannot reasonably be avoided, additional justification and supporting assessments may be required.
The Sequential Test is frequently required for developments proposed within Flood Zones 2 and 3 and can be a critical part of the planning process.
Question: What is the Exception Test?
Answer: The Exception Test is sometimes required where development is proposed in areas of higher flood risk and the Sequential Test alone is not sufficient to justify the proposed location.
The Exception Test typically requires developers to demonstrate:
- The development delivers wider sustainability benefits that outweigh flood risks.
- The development will remain safe for its lifetime without increasing flood risk elsewhere.
The specific requirements depend on the development type, vulnerability classification and flood zone designation. A Flood Risk Assessment often forms an integral part of the evidence required to support the Exception Test.
Question: How does climate change affect Flood Risk Assessments?
Answer: Climate change is now a fundamental consideration within modern flood risk assessments. National guidance requires flood risk evaluations to consider future increases in rainfall intensity, peak river flows and changing flood patterns over the lifetime of the development. Climate change allowances influence drainage sizing, attenuation requirements, discharge calculations and site layout recommendations. Failure to adequately address climate change can result in planning objections or requests for additional information from consultees.
By incorporating future climate scenarios into the assessment, developments can be designed to remain safe, resilient and compliant throughout their operational lifespan.
Question: Why choose Syntegra Group for a Flood Risk Assessment or Drainage Strategy?
Answer: Syntegra Group provides flood risk, hydrology and drainage consultancy services for developments across the UK. Our expertise includes Flood Risk Assessments, Drainage Strategies, Sustainable Drainage System (SuDS) design, highway drainage, below-ground drainage, drainage impact assessments and planning-stage flood risk consultancy. Our team works closely with developers, architects, planning consultants, local authorities and the Environment Agency to develop practical and policy-compliant drainage solutions. By combining technical expertise with a strong understanding of planning requirements, we help clients secure planning approval whilst creating sustainable, resilient and future-proof developments.
Question: How much does a Flood Risk Assessment cost?
Answer: The cost of a Flood Risk Assessment (FRA) depends on the size, location and complexity of the proposed development. Factors that can influence the scope of work include the site's Flood Zone designation, the presence of nearby watercourses, the need for drainage strategies, climate change assessments, hydraulic modelling or supporting technical studies. Simple developments in Flood Zone 1 typically require less detailed assessment than developments within Flood Zones 2 and 3, Critical Drainage Areas or sites affected by multiple flood risk sources. Obtaining a planning-stage FRA early can often identify potential issues before they become costly planning delays.
Question: How long is a Flood Risk Assessment valid for?
Answer: There is no fixed statutory expiry period for a Flood Risk Assessment. However, planning authorities generally expect FRAs to reflect the most up-to-date flood mapping, climate change guidance, planning policy and site conditions available at the time of submission. Where a planning application has been delayed for an extended period, it may be necessary to review or update the original assessment to ensure it remains compliant with current Environment Agency guidance, climate change allowances and local planning policies.
Question: Do I need a Flood Risk Assessment in Flood Zone 1?
Answer: Possibly. Whilst Flood Zone 1 is considered to have the lowest probability of flooding from rivers and the sea, an FRA may still be required in several circumstances.
A Flood Risk Assessment is often required where:
- The site is one hectare or greater in size.
- The site lies within a Critical Drainage Area.
- Significant surface water flood risk exists.
- Local planning policy specifically requires an assessment.
- Development is proposed adjacent to an Environment Agency Main River. Flood Zone 1 does not automatically remove the requirement for flood risk and drainage assessments.
Question: What is a Critical Drainage Area?
Answer: A Critical Drainage Area (CDA) is an area identified by local flood authorities where flooding issues are known to occur and where development has the potential to exacerbate existing drainage problems.
Developments within Critical Drainage Areas often require additional flood risk and drainage information to demonstrate that runoff is appropriately managed and that flood risk will not increase elsewhere. Local Planning Authorities and Lead Local Flood Authorities may impose specific requirements relating to drainage design and SuDS implementation within these areas.
Question: What is the difference between Flood Zones 1, 2 and 3?
Answer: The Environment Agency classifies land into Flood Zones according to the likelihood of river and coastal flooding.
- Flood Zone 1: Lowest probability of flooding.
- Flood Zone 2: Medium probability of flooding.
- Flood Zone 3: Highest probability of flooding.
The flood zone designation helps inform planning decisions and determines whether further assessments, Sequential Testing or Exception Testing may be required. Flood zone classification is one of the first considerations within a Flood Risk Assessment.
Question: What is a Lead Local Flood Authority (LLFA)?
Answer: A Lead Local Flood Authority (LLFA) is the local authority responsible for managing local flood risk arising from surface water, groundwater and ordinary watercourses.
LLFAs are often statutory consultees during the planning process and frequently review Flood Risk Assessments and Drainage Strategies submitted alongside planning applications. Their objective is to ensure developments properly manage drainage, surface water runoff and flood risk in accordance with national and local policy requirements.
Question: What is a SuDS Strategy?
Answer: A Sustainable Drainage System (SuDS) Strategy is a technical document that explains how surface water runoff will be managed across a development using sustainable drainage techniques.
The strategy assesses available drainage options while following the recognised drainage hierarchy. It typically includes attenuation, water quality treatment, runoff reduction measures and climate change resilience considerations.
Well-designed SuDS schemes can reduce flood risk, improve water quality, support biodiversity and contribute towards wider environmental objectives.
Question: Do I need infiltration testing for planning permission?
Answer: Not always. At planning stage, infiltration feasibility is often assessed using available geological and drainage information. However, where infiltration-based drainage solutions are proposed, site-specific infiltration testing may be required to demonstrate that the ground can effectively absorb water. Many detailed drainage designs rely upon infiltration testing performed in accordance with recognised industry guidance before final drainage solutions are confirmed.
Question: What is BRE 365 testing?
Answer: BRE Digest 365 is the standard methodology used within the UK to assess infiltration rates and determine whether infiltration drainage systems are feasible.
The testing helps establish whether techniques such as soakaways, infiltration basins and other infiltration-based SuDS solutions can operate effectively on a particular site. Results are commonly used during detailed drainage design and can support planning submissions where infiltration drainage is proposed.
Question: What are climate change allowances in drainage design?
Answer: Climate change allowances are adjustments applied to rainfall and flood calculations to account for the predicted effects of future climate change over the lifetime of a development.
Modern Drainage Strategies and Flood Risk Assessments are expected to consider increased rainfall intensity and changing weather patterns when sizing attenuation systems and calculating runoff rates. Incorporating these allowances helps ensure developments remain resilient throughout their design life and comply with current planning guidance.
Question: Can a Flood Risk Assessment prevent planning refusal?
Answer: A well-prepared Flood Risk Assessment cannot guarantee planning approval, but it can significantly reduce planning risk by identifying potential flood-related issues and demonstrating how those risks will be managed.
Planning officers, the Environment Agency and Lead Local Flood Authorities often rely upon Flood Risk Assessments when assessing whether development proposals are safe, sustainable and policy compliant. Robust technical evidence can frequently address concerns before they develop into planning objections.
Question: What is an Environment Agency Main River?
Answer: An Environment Agency Main River is a watercourse designated by the Environment Agency as having strategic importance for flood risk management.
Developments located close to Main Rivers may be subject to additional planning and environmental requirements. The Syntegra service page notes that an FRA is typically required where development is within 20 metres of an Environment Agency Main River, and separate permits may be required for works carried out close to these watercourses.
Question: Do I need a Drainage Strategy for planning permission?
Answer: Many developments now require a Drainage Strategy as part of the planning submission process. Planning authorities increasingly expect applicants to demonstrate how surface water and foul water will be effectively managed before consent is granted.
Drainage Strategies usually accompany Flood Risk Assessments and include consideration of SuDS, attenuation requirements, discharge rates, runoff calculations, climate change allowances and long-term maintenance arrangements.
Question: What is a Surface Water Flood Risk Assessment?
Answer: A Surface Water Flood Risk Assessment examines flooding caused by intense rainfall exceeding the capacity of drainage systems.
Unlike river flooding, surface water flooding can occur even in areas that are far from rivers or coastal flood zones. The assessment considers topography, runoff pathways, drainage infrastructure and mapping data to understand the likelihood of overland flooding affecting the development or surrounding areas.
Question: What is a Drainage Impact Assessment?
Answer: A Drainage Impact Assessment evaluates how a proposed development may affect the surrounding drainage network and flood risk conditions.
The assessment considers existing infrastructure, proposed discharge arrangements, capacity constraints and the effectiveness of planned drainage measures. It helps demonstrate that development will not overload local drainage systems or increase flood risk to neighbouring properties and land.
Question: Can flood risk stop a development?
Answer: Flood risk can present a significant planning constraint and, in some cases, may prevent certain forms of development from proceeding in specific locations.
However, many developments can still progress where suitable mitigation measures, drainage strategies and flood resilience measures are incorporated. Planning policies generally seek to ensure development is directed towards lower-risk areas wherever possible and that any residual risks are appropriately managed.
Question: What is flood compensation storage?
Answer: Flood compensation storage is a flood mitigation measure used where development removes or displaces existing floodplain storage capacity.
The principle is that any reduction in natural flood storage resulting from development should be offset by creating alternative storage capacity elsewhere. Flood compensation may be required for developments within higher-risk flood zones and is commonly reviewed in conjunction with flood modelling and Environment Agency requirements.
Question: How is runoff calculated for planning applications?
Answer: Runoff calculations are used to determine how much surface water will be generated by a development during rainfall events and how that water will be managed safely.
Calculations typically consider:
- Site area
- Existing land use
- Proposed impermeable surfaces
- Design rainfall events
- Climate change allowances
- Discharge restrictions
- Attenuation storage requirements
The outputs help inform the drainage strategy and demonstrate compliance with planning policy and flood risk management requirements.
Question: What are green roofs and blue roofs?
Answer: Green roofs and blue roofs are sustainable drainage features increasingly used within urban developments.
Green roofs include vegetation and planting layers that absorb rainfall, improve biodiversity and reduce runoff.
Blue roofs are designed to temporarily store rainwater on roofs before releasing it at a controlled rate into the drainage system.
Both systems can contribute towards SuDS objectives, improve climate resilience and assist developments in meeting planning policy requirements relating to sustainable drainage.
Question: How do I discharge a flood risk planning condition?
Answer: Many planning permissions include conditions requiring additional flood risk, drainage or SuDS information to be approved before construction begins.
To discharge the condition, applicants typically submit supporting technical information such as:
- Updated Flood Risk Assessments
- Drainage Strategies
- Detailed drainage calculations
- SuDS designs
- Maintenance schedules
- Supporting plans and drawings
The Local Planning Authority, often in consultation with the Lead Local Flood Authority, reviews the information before confirming the condition has been satisfied
