Flood risk assessments, river by river

Unda provides flood risk assessments and drainage strategies for sites across England and Wales, and a great deal of that risk comes down to a single watercourse. For the rivers we know best we have published a dedicated guide — how the river behaves, where it has flooded, the towns strung along it, and what all of that means for a planning application on its floodplain.

Whether your site sits beside a major river like the Thames or Severn, or a small urban brook that only appears on the surface-water map, understanding the specific watercourse is where a credible flood risk assessment begins. Explore a published river guide below, or start a quote and one of our experienced flood risk consultants will talk through your site.

Flood risk is local to the river: the same rainfall produces very different flooding on a steep, flashy catchment than on a slow, wide floodplain — and every river carries its own history, gauges and hydraulic modelling.

Find your river

Search a postcode, town or city to drop a pin on the map and find the nearest river guide. Where we have published a guide for the watercourse near your site, we will point you straight to it. Otherwise, we will show the closest guide we have, or route you to a quote.

Browse flood risk guides by river

Prefer to browse? The rivers below are grouped by region, and by the county each one flows through. Select a river for its full flood risk guide, or a county to open our local area guides.

Flood risk assessments for every situation

People come to us for a flood risk assessment for many reasons — securing planning permission, buying a home, satisfying a mortgage lender or insurer, achieving a BREEAM rating, or designing the drainage for a new scheme. We prepare the right report for each.

It helps to keep three things separate: a flood risk assessment, a sequential or exception test, and a drainage strategy are three distinct 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. Groundwater and flood modelling aren’t separate reports: groundwater is a source every assessment considers, and modelling is a technique that feeds one.

• Flood risk assessment for planning. The site-specific report that satisfies the NPPF in England, or TAN15 in Wales, and shows your development is safe for its lifetime without increasing risk elsewhere.
• Flood consequence assessment (Wales). The TAN15 assessment for Welsh sites, demonstrating the consequences of flooding can be safely managed over the development’s lifetime.
• Flood risk survey for property purchase. An independent, property-specific survey for buyers and their advisers, going beyond the conveyancing search to assess the actual building.
• Flood risk assessment for insurance. Property-level evidence for brokers and underwriters where cover has been restricted, declined or priced on flood risk.
• Flood risk assessment for BREEAM. The assessment structured around BREEAM Pol 03 so a scheme keeps its flood and surface-water credits.
• Sequential and exception tests. The locational justification that a higher-risk site is the most appropriate available, prepared alongside the assessment.
• Groundwater flood risk. A defensible design groundwater level, tested against floor levels, basements and drainage.
• Flood modelling. 1D and 2D hydraulic modelling for sites where national mapping doesn’t reflect how water actually behaves on the ground.
• Surface-water drainage strategy (SuDS). A scheme that manages runoff to the local SuDS standard, following the four pillars of SuDS and the drainage hierarchy.
• Discharge of drainage conditions. The detailed design that discharges a pre-commencement or pre-occupation drainage condition on a permission.