Whichford Mill, Stratford-upon-Avon

Executive Summary
Air & Flood Consultants undertook a detailed Flood Risk Assessment for a proposed residential redevelopment at Whichford Mill, a brownfield site located within Flood Zone 3. The project required careful analysis of multiple flood sources and topographical constraints to demonstrate compliance with National Planning Policy Framework requirements whilst supporting the client's planning application for full demolition and reconstruction of an existing dwelling.
Site Context and Constraints
Location and Setting
The site occupies a valley floor location within a predominantly rural area of Warwickshire, bounded by the River Stout and associated sluice infrastructure. The approximate central grid reference is E: 432342; N: 236974. The existing site comprises previously developed brownfield land currently occupied by a residential building and communal sauna.
Topographical Characteristics
Analysis of LiDAR survey data revealed that ground levels across the site exhibit a northward gradient, with the site occupying a valley floor location within the local catchment. This topography presented specific challenges for surface water management and flood risk assessment.
Geological and Hydrological Setting
British Geological Survey mapping identified the underlying geology as Dyrham Formation (siltstone and mudstone, interbedded), with no superficial deposits. Nearby borehole data (reference SP33NW12, approximately 1,700 m north) indicated sandstone, claystone, clay, and limestone formations. Soilscapes mapping characterised the site as having slightly acid loamy and clayey soils with impeded drainage, indicating that surface water infiltration may not be feasible.
Regulatory Framework and Policy Context
The assessment was prepared in full accordance with:

National Planning Policy Framework (NPPF)
Planning Practice Guidance (PPG)
Stratford-on-Avon District Core Strategy 2011-2031 (adopted 2016)
Stratford-on-Avon District Level 1 SFRA (2020)
Stratford-on-Avon District Level 2 SFRA (2021)

The development classification as small-scale rural development meant that Sequential and Exception Tests were not required under NPPF paragraph 93, providing a pragmatic pathway for planning approval.
Multi-Source Flood Risk Assessment
Fluvial Flooding (High Risk)
Environment Agency Flood Map for Planning confirmed the site's location within Flood Zone 3, indicating land with a greater than 1% annual probability of flooding. Detailed analysis of EA flood mapping demonstrated that whilst the site boundary lay within Flood Zone 3, the proposed building location remained outside the design flood extent for the 1 in 100-year plus climate change event. Critically, no formal flood defences provide protection to the site, necessitating careful consideration of residual risk.
Pluvial Flooding (Low Risk)
EA surface water flood risk mapping for 1 in 30-year, 1 in 100-year, and 1 in 1000-year return periods indicated that whilst some site areas exhibited localised surface water flood risk, the proposed dwelling location remained outside modelled pluvial flood extents. The valley floor topography required careful surface water management design to prevent off-site impacts.
Groundwater Flooding (Low Risk)
The predominantly clay geology provided inherent protection against groundwater emergence. SFRA groundwater flood mapping confirmed no risk of groundwater flooding at the site in a 1% annual exceedance probability event. No historical groundwater flooding incidents were identified.
Sewer Flooding (Low Risk)
Review of the Stratford-on-Avon SFRA identified 1-5 recorded sewer flooding incidents in the wider area. Historic flood mapping confirmed flood incidents in the near proximity of the site. However, site-specific risk was assessed as low due to the redevelopment nature of the proposal and opportunities for drainage improvements.
Artificial Sources (Low Risk)
SFRA reservoir breach flood risk mapping confirmed that Whichford Mill lies outside the inundation extent from reservoir failure. The risk from canals and other artificial sources was assessed as negligible.
Historic Flooding
No Environment Agency or local authority records of past flood events were identified at the specific site location.
Technical Methodologies Employed
The assessment utilised:

High-resolution LiDAR topographical data analysis
Environment Agency Flood Map for Planning (2025)
Environment Agency detailed flood modelling outputs
DEFRA Magic mapping for designated site screening
British Geological Survey drift and bedrock geology mapping
Soilscapes web-based soil classification
Stratford-on-Avon SFRA Level 1 (2020) and Level 2 (2021) datasets
Site-specific topographical survey data

This multi-layered approach ensured robust evidence-based conclusions regarding flood risk from all sources.
Key Findings and Recommendations
Risk Classification Summary:

Fluvial flooding: High risk (Flood Zone 3)
Surface water flooding: Low risk
Groundwater flooding: Low risk
Sewer flooding: Low risk
Artificial sources: Low risk

Critical Technical Finding
Despite the Flood Zone 3 classification, detailed flood modelling analysis demonstrated that the proposed building footprint remained outside the 1 in 100-year plus climate change flood extent. This finding proved essential in demonstrating development acceptability.
Mitigation Strategy
The FRA outlined specific flood mitigation measures including:

Finished floor levels set above modelled flood levels
Flood-resilient construction techniques
Surface water management strategy to prevent increased runoff
Maintenance of floodplain storage capacity
Flood evacuation and emergency planning provisions

Project Outcomes and Benefits
Planning Support
The comprehensive FRA provided the technical evidence base required to support the planning application, demonstrating NPPF compliance and addressing Environment Agency consultation requirements.
Risk Management
The assessment enabled informed decision-making regarding flood risk, ensuring future occupants would remain safe throughout the development lifetime whilst demonstrating no increase in flood risk to surrounding areas.
Sustainable Development
By facilitating redevelopment of brownfield land in a challenging flood risk location, the project supported sustainable development principles and rural community regeneration.
Professional Standards and Quality Assurance
The assessment was prepared by chartered professionals with extensive experience in flood risk assessment and hydraulic modelling. All technical analysis underwent rigorous internal quality assurance procedures, with peer review by senior flood risk specialists.
Conclusions
This project exemplifies the value of detailed, evidence-based flood risk assessment in facilitating appropriate development within challenging Flood Zone 3 locations. Through comprehensive multi-source flood risk analysis and careful site-specific assessment, Air & Flood Consultants demonstrated that redevelopment could proceed safely and sustainably, supporting both client objectives and regulatory requirements whilst protecting future occupants and the wider community from flood risk.