Flood Risk Assessment in Blandford Forum

Our team at Unda prepare comprehensive flood risk assessments and drainage strategies for residential and commercial sites across Blandford Forum and the wider Stour valley. A flood risk assessment in Blandford Forum shows Dorset Council that a development will stay safe from flooding for its whole lifetime, and that it will not push flood risk onto neighbouring land or properties downstream.

Blandford Forum sits in the floodplain of the River Stour, where the river is fed by the chalk of Cranborne Chase and the Dorset Downs. We assess every source that matters here — the Stour itself, the surface water that runs off the surrounding slopes, and the groundwater that rises through the chalk and valley gravels — then deal directly with the Environment Agency and Dorset Council, the Lead Local Flood Authority, on your behalf. We work for architects, planning consultants, developers, landowners, home buyers and businesses, whether the report is for planning, a property purchase, a mortgage or insurance, BREEAM, or a surface-water drainage strategy.

If you need a quote or want to talk a site through, contact one of our experienced flood risk consultants on 01293 214444.

Blandford Forum grew up beside the River Stour, and the town-centre flood defences are the main reason the Market Place and East Street now stay dry — which is exactly why the Environment Agency still maps much of the town as flood zone 3 and looks closely at any development behind the wall.

Flood risk assessment in Blandford Forum at a glance

Blandford Forum is a market town on the River Stour in north Dorset, with a long, well-documented flood history and a flood defence scheme that protects the historic centre. That combination shapes nearly every assessment here.

• The River Stour is the main flood source. The Stour is a designated main river and runs through the centre of the town, with a broad floodplain on both banks. The Environment Agency leads on this river; Dorset Council leads on surface water, groundwater and ordinary watercourses.
• The defences do not remove the flood zone. The town-centre flood wall reduces the chance of flooding but the Flood Map for Planning is drawn as if defences are not there, so much of central Blandford Forum remains in flood zone 2 or 3.
• Groundwater is a genuine local source. The town sits on chalk, so the Stour is groundwater-fed and the water table can rise after prolonged wet weather — the winter of 2025–26 brought the worst groundwater flooding in the Dorset and Wiltshire chalk for over a decade.
• Dorset Council is your Lead Local Flood Authority. Dorset Council is the unitary authority and LLFA for the area, and a statutory consultee on surface water drainage for major development.
• Growth is planned. The Blandford+ Neighbourhood Plan provides for around 1,400 new homes to 2033, much of it on the edges of the town where surface water and drainage are decisive.

Check the flood risk for any address in Blandford Forum

Blandford Forum is outlined below. Screen any postcode in and around the town against Environment Agency data for rivers and sea, surface water and the planning flood zones, with a climate outlook to 2125. It is an indicative first pass — useful for an early read on a site, but not a substitute for a site-specific flood risk assessment.

What is the flood risk in Blandford Forum?

The dominant flood risk in Blandford Forum is the River Stour, which flows through the middle of the town and spreads across a wide floodplain in a large flood. Surface water and groundwater add to that picture: rain runs off the surrounding chalk slopes into the valley, and the chalk aquifer that feeds the Stour can push the water table up after a wet winter. Most sites near the river face more than one of these sources at once, which is why a generic, single-source report rarely satisfies the regulators here.

The town itself is an unusual case. Much of historic Blandford Forum was rebuilt on slightly higher ground after the great fire of 1731, set back from the river on a low chalk bluff, while the floodplain on the south bank around Langton Meadows stays as open ground. Read the area against the Unda flood risk map and the accuracy of national flood maps together, because the difference between the mapped floodplain and the ground a building actually sits on is often what an assessment turns on.

For an early steer you can use Unda's free screening tools alongside this page: the live river levels map shows where the Stour sits right now against its usual range, and the geology and ground conditions checker gives an indicative read on whether the chalk and valley deposits beneath a site are likely to take a soakaway. Both are a starting point, not a Flood Risk Assessment.

A history of flooding in Blandford Forum

Blandford Forum has one of the better-documented flood records in Dorset, and those events are why Dorset Council and the Environment Agency scrutinise development here so closely. Each flood reshaped local memory and, eventually, the defences a developer now has to design around.

• The nineteenth century. The Stour flooded the town in 1882 and again in 1894, part of a long pattern of the river spilling into the low-lying streets near the bridge.
• 1966, 1974, 1979 and 1990. A run of post-war floods affected the town; older residents recall the 1970s, when the only way through parts of Blandford Forum was by boat.
• December 2013. The River Stour at the Blandford gauge reached a record 2.78 metres on 24 December 2013, at the start of the very wet winter of 2013–14 that tested defences across southern England.
• Winter 2025–26. Sustained rainfall through January and February 2026 drove the worst groundwater flooding in the Dorset and Wiltshire chalk catchments for more than a decade, prompting a dedicated Environment Agency groundwater flood warning service for the area.

Behind the dated events is a catchment statistic worth keeping in mind: the Environment Agency's Dorset Stour Catchment Flood Management Plan put around 780 properties at risk across the catchment in a 1% (1-in-100-year) event even with the existing defences in place, a figure expected to rise to more than 2,900 as the climate changes.

The Blandford Forum flood defences — and why your site can still be in a flood zone

Blandford Forum is a defended town. A flood wall and embankment run from the water meadows, across the Ham car park, and behind the properties of the Market Place and East Street, with removable stop-log barriers closing the gaps when a flood is forecast. Floodwater is pumped from behind the wall — including from the Langton Meadows area and the Pimperne stream — and the open floodplain on the south side of the river is kept as washland to take excess water. Since the scheme was completed there have been no serious floods in the town centre.

A wall that keeps the river out on the day is not the same as a site that planning policy treats as low risk — the two are assessed quite differently.

This is the single most important point for anyone developing in Blandford Forum. The Environment Agency's Flood Map for Planning shows the floodplain as if the defences were not there, so a site protected by the town's wall can still sit firmly in flood zone 2 or 3. National policy then requires the residual flood risk — the risk that remains if a defence is overtopped or breached — to be assessed over the development's lifetime, including climate change. A defended site in Blandford Forum almost always still needs a flood risk assessment, and often a finished-floor-level and safe-access case to go with it. Our note on the long-term flood risk map versus the Flood Map for Planning explains why the public "check your risk" service and the planning dataset give different answers for exactly this kind of defended town.

Planning policy and your Lead Local Flood Authority in Blandford Forum

Two authorities set the rules. The Environment Agency leads on the River Stour as a main river. Dorset Council is the Lead Local Flood Authority, leading on surface water, groundwater and ordinary watercourses, and acting as a statutory consultee on surface water drainage for major development. A development in Blandford Forum is assessed by Dorset Council alongside the Environment Agency, and the two look at different things.

Dorset Council has prepared a Level 1 Strategic Flood Risk Assessment covering its whole area, and publishes surface water planning guidance and groundwater drainage guidance that an application here has to follow. Our overview of the role the LLFA plays and of who manages flood risk in England explains how the pieces fit together.

Your assessment and drainage strategy must satisfy national policy — the NPPF and its Planning Practice Guidance — and the local framework. Where a higher-risk site is involved, the Sequential and Exception Tests apply, and the right vulnerability classification has to be argued. On drainage, the 2025 national SuDS standards and the four pillars of SuDS shape what Dorset Council will accept, with surface water steered down the drainage hierarchy and runoff held back to greenfield rates wherever the ground allows.

What your flood risk assessment in Blandford Forum must show

• Every relevant source. The River Stour, surface water, groundwater, ordinary watercourses and sewers — assessed together, not just the river.
• Design flood levels with climate change. The 1% (1-in-100-year) river event plus an Environment Agency climate change allowance over the development's lifetime, generally 100 years for housing.
• Safe floor levels and access. Finished floor levels set above the design flood level with freeboard, and safe access and egress in a flood.
• Residual risk behind the defences. What happens if the town's flood wall is overtopped or breached, where the site relies on it.
• No increase in risk elsewhere. Compensatory storage and a drainage strategy so the scheme does not push water onto neighbours.

Development and flood risk assessment in Blandford Forum

The kind of site you bring forward shapes the assessment you need, and Blandford Forum offers most of them — from infill and conversions in the historic centre to the larger edge-of-town allocations in the neighbourhood plan. The right scope is the difference between a clean approval and a flood or drainage objection that holds an application up for months.

• Town-centre infill and change of use. Sites behind the flood defences, where residual risk, finished floor levels and safe access usually drive the assessment.
• Edge-of-town housing. The Blandford+ allocations, including land to the north and east of the town, where surface water and the drainage strategy often decide the outcome.
• Riverside and floodplain sites. Plots close to the Stour, where flood modelling and floodplain compensation may be needed.
• Rural and agricultural schemes. Conversions and new builds in the surrounding villages, often turning on ordinary watercourses, infiltration and the right drainage information for planning.
• Property purchase and due diligence. Buyers and lenders needing a clear, site-specific read on flood risk before they commit.

Riverside and edge-of-town sites also raise riparian responsibilities where a watercourse runs along a boundary, which Dorset Council and the Environment Agency routinely raise in planning. Climate change is not optional in any of this: an assessment in Blandford Forum has to apply the Environment Agency's allowances for higher river flows and heavier rainfall over the development's lifetime, which is what sets floor levels, freeboard and how much attenuation a drainage scheme needs.

How Unda helps with flood risk assessment in Blandford Forum

We act as the accurate translation layer between your scheme and the requirements set by the Environment Agency, Dorset Council and national planning policy. We are experts on this part of the Stour valley and its flood history, not a generic report mill.

A flood risk assessment in Blandford Forum from Unda assesses every credible source — the River Stour, surface water, groundwater, sewers and any ordinary watercourse on the boundary — compares modelled flood levels against your proposed floor levels, sets safe access and egress, and recommends mitigation the regulators will accept. Groundwater here is treated as a real source rather than an afterthought, which matters on a chalk catchment. We are a CIWEM Business Partner with chartered members, and a senior consultant signs off every report. Where Dorset Council needs it, a surface-water drainage strategy sits alongside the assessment as a separate report so the two cases stay consistent and an objection has nowhere to land. You can read more about Unda and our flood risk consultants.

Start a quote for your site, or see the full flood risk assessment service and our wider work across flood risk assessment in Dorset.

Flood risk assessments and related reports for every situation in Blandford Forum

A flood risk assessment, a sequential or exception test and a drainage strategy are three different reports. They often travel together in a planning submission, but they answer different questions: is the site safe, should the development be here, and where does the surface water go. We prepare all of them for sites in Blandford Forum.

• Flood risk assessment for planning. The site-specific report prepared to satisfy the NPPF, the Environment Agency and Dorset Council. Groundwater and, where needed, flood modelling are assessed within it rather than as separate reports.
• Flood risk survey for property purchase. An independent, property-specific survey for buyers and their advisers when a search flags risk or a lender asks questions.
• Flood risk assessment for insurance. Property-level evidence where premiums rise, cover is restricted, or you need to understand risk after a flood.
• Flood risk assessment for BREEAM. Structured around BREEAM Pol 03 so a scheme earns its flood and surface water credits.
• Sequential and Exception Tests. The locational case for development in a higher-risk part of the floodplain.
• Surface water drainage strategy (SuDS). How runoff is managed to the 2025 national standards, with preliminary drainage design at outline stage and discharge of drainage conditions later.
• Groundwater flood risk. Specialist input where the chalk water table is a credible issue — common on this catchment.

For drainage design you can also use our free drainage calculators and the BRE 365 infiltration rate calculator to sanity-check soakaway and attenuation figures before they go into a strategy.

Flood resources and contacts for Blandford Forum

The most reliable flood information for Blandford Forum comes from the Environment Agency and Dorset Council. For an immediate threat to life during a flood, always call 999; for a power cut during flooding, call 105.

• Check for flooding. Environment Agency live warnings, river levels and maps at check-for-flooding.service.gov.uk; sign up for flood warnings or call Floodline on 0345 988 1188.
• River Stour at Blandford. The Environment Agency river-level gauge for the town is at check-for-flooding.service.gov.uk/station/3305.
• Dorset Council flood risk. Reporting, strategy and developer guidance at Dorset Council, including the Level 1 Strategic Flood Risk Assessment.
• Local growth framework. Site allocations and policy in the Blandford+ Neighbourhood Plan.

Flood risk assessment in Blandford Forum: frequently asked questions