Station Road, Crewkerne - Comprehensive Flood Risk Assessment & Drainage Strategy

Enviren prepared a comprehensive Flood Risk Assessment and Drainage Strategy in support of a planning application for 325 dwellings and associated infrastructure on land west of Station Road, Crewkerne.

The assessment demonstrates that, with appropriate mitigation, the scheme is safe from flooding and will not increase flood risk elsewhere.

Site Overview

Site characteristics

• Location: West of Station Road, Crewkerne, Somerset
• Site area: 16.532 ha
• Existing land use: Agricultural (less vulnerable)
• Proposed use: Residential (more vulnerable)

Topography & Hydrology

Runoff flows north toward the River Parrett

A watercourse runs along the west of the site, eventually discharging to the River Parrett

Flood Zone Status

The entire site lies within Flood Zone 1 (lowest fluvial/thalassic risk)

Sources of Flood Risk

The FRADS assesses all flooding mechanisms as required by the National Planning Policy Framework (NPPF).

Fluvial flooding

Very low risk — site is entirely Flood Zone 1

Surface water (pluvial)

Very low risk across the developable area

Groundwater flooding

Low risk, but the report identifies the need for ongoing groundwater monitoring

Sewer flooding

Very low risk

Reservoir flooding

Very low risk, reservoir flooding does not reach the site

Surface Water Drainage Strategy

Core principles

The drainage strategy adheres to:

• The SuDS hierarchy
• Somerset Council requirements
• NPPF and Planning Practice Guidance

Primary discharge option — infiltration

The report recommends infiltration-based drainage where viable.

Evidence for infiltration viability

A separate supported soakaway investigation confirms:

• No groundwater encountered in any trial pits
• Limestone and clay strata across the site
• Infiltration rates were successfully established in several pits.



Fallback strategy

If further sitewide infiltration testing finds areas unsuitable or if groundwater rises:

• An alternative drainage layout has already been prepared

This ensures the scheme can manage runoff under all expected conditions.

Foul Water Strategy

The FRADS confirms:

• Foul water will discharge to the main foul sewer along Station Road

 There is no reference to requiring on-site treatment or alternative foul measures in this document.

Flood Risk Mitigation Measures

The FRADS prescribes the following:

Groundwater monitoring

• Required to track seasonal variations and identify potential rising trends

SuDS features

The strategy incorporates:

• Swales
• Attenuation basins
• Porous surfaces
• Rainwater harvesting
• Greenfield runoff compliance



All surface water discharge is constrained to greenfield runoff rates and volumes.

Catchment impact

Runoff will be managed entirely on-site through infiltration, ensuring no downstream flood risk.

Summary of Post-Mitigation Flood Risk

Table 8.1 shows:

Final Conclusion

According to the FRADS:

“Providing the flood mitigation strategies outlined in this document are implemented, flood risk should not prevent approval being granted to this development.”

The site is demonstrably safe from all key flood sources, and the drainage strategy—primarily infiltration—ensures no increase in flood risk to the wider catchment.