Flood Risk Assessments in Somerset

Around 18 per cent of Somerset lies below average tide level. The Somerset Levels and Moors are one of the lowest areas in the UK and have been managed for agriculture and settlement for centuries through a network of rivers, rhynes, pumping stations and sluices. This network is maintained by the Parrett Internal Drainage Board and the Axe Brue Internal Drainage Board alongside Somerset Rivers Authority. Development anywhere near this managed drainage network requires specific IDB consultation and must address the IDB drainage system as a distinct flood source. This is not optional – it is a fundamental requirement of planning applications across the Levels.

The River Parrett is tidal as far upstream as Oath Lock near Langport, and tidal water levels in the Parrett directly influence the ability of the managed drainage system to discharge. When the Parrett is high, pumping stations cannot discharge and moor water levels rise. This interaction between the tidal Parrett and the managed Levels drainage is central to understanding flood risk for any development in the central Somerset Levels. The Bridgwater Tidal Barrier is currently under construction and is expected to be operational by 2027. It will provide protection for at least 11,300 homes and 1,500 businesses from tidal flooding when complete – but at present its defences cannot be relied upon in planning FRAs.

The upland fringes of the county – the Quantock Hills, Mendip Hills, Black Down Hills and Exmoor edges – generate rapid overland flow into the river valleys. The Tone floods Taunton. The Brue affects Glastonbury, Street and Wells. The Axe and its tributaries affect Shepton Mallet, Wookey Hole and the limestone areas of central Mendip, where groundwater flooding from cave systems and spring lines is a specific local issue. Somerset Council as LLFA for the whole unitary authority area applies its own drainage requirements alongside the IDB framework.

• Development on or near the Somerset Levels and Moors where IDB drainage network consultation is required
• Development in Flood Zone 2 or 3 along the Parrett, Tone, Brue, Axe, Yeo or any main river
• Development near the tidal River Parrett where tidal influence must be assessed alongside fluvial risk
• Development of 1 hectare or more in Flood Zone 1
• Development in Taunton, Bridgwater, Glastonbury, Street or Wells where fluvial and surface water risk combine
• Development requiring a surface water drainage strategy under Somerset Council LLFA guidance

We understand the Somerset Levels’ managed drainage system, the IDB network, the tidal Parrett and the specific planning requirements that apply to development in this part of England. The IDB consultation requirement and the interaction between tidal conditions and managed drainage are not standard national planning knowledge – they require specific local understanding.

Our FRAs for Somerset applications address the Levels drainage system, the Bridgwater Tidal Barrier’s current limitations and the specific upland catchment characteristics of the Tone, Brue and Axe. We prepare FRAs and drainage strategies together for Somerset applications.

We cover all Somerset Council planning areas including Taunton, Bridgwater, Yeovil, Glastonbury, Wells, Frome and the wider county.