Flood Risk Assessment in Derbyshire

Our team at Unda prepares comprehensive flood risk assessments and drainage strategies for residential and commercial sites right across Derbyshire, from the Derwent valley and the Peak District to the former coalfield towns of the north east. A flood risk assessment in Derbyshire shows your local planning authority that a development will stay safe from flooding for its whole lifetime, without pushing flood risk onto anyone else.

Derbyshire is a county of fast-responding upland rivers and tightly constrained valley towns. We assess every source that matters here — the River Derwent and its tributaries the Wye, Dove, Amber and Ecclesbourne, the Rother and Hipper around Chesterfield, the Goyt and the Sett in the High Peak, the surface water that sheets off steep ground, and the groundwater that moves through the limestone of the White Peak — then deal directly with the Environment Agency and the relevant Lead Local Flood Authority on your behalf. We guide architects, planning consultants, developers, landowners, home buyers and businesses through to a decision, whether the report is needed 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.

Derbyshire's rivers rise fast off steep upland catchments, so a flood here can arrive within hours of the rain — the river, the surface water that sheets off the hills and the groundwater moving through the limestone all have to be read together, or an assessment will not stand up to the Lead Local Flood Authority.

Flood risk assessment in Derbyshire at a glance

• The Derwent runs the length of the county. Derbyshire's longest river drains the Peak District through Matlock and Belper to Derby, so heavy rain on the moors becomes a flood peak in the valley towns hours later.
• Storm Babet flooded 1,647 properties in October 2023. Of those, 1,251 were homes and 396 were businesses, with Chesterfield, Long Eaton and Sandiacre among the worst hit — the benchmark recent event for the county.
• Two Lead Local Flood Authorities. Derbyshire County Council is the LLFA for the county; the City of Derby is a separate unitary authority and its own LLFA. We work with both.
• Flood Zone 1 is not a free pass. Since the 2025 PPG update, surface water risk can trigger an assessment even on a Flood Zone 1 site — common on Derbyshire's steep ground.

Check flood risk anywhere in Derbyshire

Derbyshire and the City of Derby are outlined below. Screen any postcode in the county 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, not a substitute for a site-specific assessment.

Flood risk in Derbyshire: rivers, surface water and the Peak District

River flooding leads in Derbyshire, but it rarely acts alone. The county's rivers rise on steep, often impermeable upland and reach their valley towns quickly, while surface water sheets off the hills and groundwater moves through the limestone of the White Peak. Most sites here face more than one source at once.

The Derwent gathers the Wye, Amber, Ecclesbourne and Dove as it runs south through Matlock, Belper and Darley Abbey to Derby, where it meets the Trent. In the north east the Rother and its tributary the Hipper drain Chesterfield towards the Don, and in the High Peak the Goyt and the Sett fall steeply through Whaley Bridge and New Mills. Working out which watercourse drives the risk on a given site, and how fast it responds, is the heart of a credible fluvial flood risk assessment.

• Rivers (fluvial). The Derwent and its tributaries, the Rother and Hipper at Chesterfield, and the Goyt and Sett in the High Peak flood the valley floors. Land in Flood Zones 2 and 3 along these corridors almost always needs an FRA.
• Surface water (pluvial). Now the most widespread flood risk in England. On Derbyshire's steep ground intense rain runs off fast and overwhelms drains. Since the 2025 PPG update, surface water on the Flood Map for Planning can trigger an assessment even on a Flood Zone 1 site.
• Groundwater. The Carboniferous limestone of the White Peak and the Sherwood Sandstone in the east are productive aquifers, so water tables can rise and feed springs and valley flooding without ever showing on a river map — critical for any soakaway or basement. See groundwater flooding.
• Reservoirs. Derbyshire holds many large upland reservoirs, including Howden, Derwent and Ladybower in the upper Derwent and Toddbrook above Whaley Bridge. They are well managed, but the worst-case failure extent is an emergency-planning consideration on some valley sites — see reservoir flooding.
• Sewers and ordinary watercourses. Smaller brooks and the surface-water sewer network back up in heavy rain. This is the Lead Local Flood Authority's responsibility rather than the Environment Agency's — see the role the LLFA plays.

Matlock is the textbook case for why a single map is never enough: the Derwent rises quickly through a narrow valley with little room to spread, so the town centre and the A6 corridor flood while surface water pours off the surrounding hills at the same time. A scheme there has to reconcile both. Our notes on the sources of flood risk and on surface water and planning set out how these sources interact.

A history of flooding in Derbyshire

These dated events are why local authorities here scrutinise development so closely, and why a flood risk assessment in Derbyshire has to be evidence-led rather than generic. Each one reshaped local policy and the flood defences a developer now has to design around.

• 2007 — the summer floods. The June and July 2007 floods were among the most damaging in modern British history and hit the East Midlands hard, reshaping how flood risk is reported and managed and prompting the Pitt Review. Many Chesterfield properties flooded in 2007 would flood again in 2023.
• July 2019 — the Whaley Bridge dam crisis. After intense rain, several spillway panels on Toddbrook Reservoir collapsed and around 1,500 residents were evacuated for up to six nights. Over a billion litres were pumped out; the rebuilt spillway was certified complete in 2026, with the total cost put at around £50 million.
• November 2019 — record Derwent flows. The Derwent at Chatsworth set a new peak in a record running from 1975, exceeding 2000/01 and 2007. Matlock and Matlock Bath were sandbagged, schools closed, and a woman died in the Derwent at Darley Dale.
• February 2020 — Storms Ciara and Dennis. The second main wave of the 2019–20 winter floods closed the main road through Repton and brought further Derwent flooding in Derby.
• October 2023 — Storm Babet. Derbyshire County Council recorded 1,647 properties internally flooded between 18 and 21 October — 1,251 homes and 396 businesses — with more than 400 homes flooded in Chesterfield as the Rother and Hipper burst their banks. The county's Section 19 investigation reported 35 communities where five or more homes flooded.

A pattern runs through all of it: ground that flooded once tends to flood again. A robust assessment treats this recorded history as evidence, not background colour.

Flood defences and schemes protecting Derbyshire

Major investment has followed these events, and the schemes change what a development next to them has to prove. A new defence reduces the chance of flooding, but it never removes it, and planning policy still expects the residual risk to be assessed.

• Our City Our River, Derby. A multi-phase programme of more than £95 million along the lower Derwent. The first phase protected over 1,100 homes and 400 businesses; later phases, including the £35 million Derby Riverside works, extend cover towards around 2,000 properties and safeguard critical infrastructure in the city.
• Toddbrook Reservoir, Whaley Bridge. The spillway that partly failed in 2019 has been rebuilt and certified complete, with the reservoir refilling under a specialist reservoir engineer's supervision.
• Chesterfield and the Rother. A 250,000 cubic-metre flood-storage scheme on the Rother at Wingerworth helps protect the town, and around £400,000 has been secured to develop the business case for a River Hipper scheme supporting regeneration at Brampton.
• Matlock property flood resilience. An £84,000 scheme is providing property-level protection to repeatedly flooded homes in the town, alongside a town flood warden scheme.

The catch for developers is the one we set out in residual flood risk and why a site stays in a flood zone after defences are built: the Flood Map for Planning is drawn as if the defences are not there, so a defended site can still sit in Flood Zone 3. Climate change makes this sharper still, which is why an assessment applies the Environment Agency's allowances over the development's lifetime.

Planning policy and your Lead Local Flood Authority in Derbyshire

Two kinds of authority set the rules. The Environment Agency leads on the Derwent and the other main rivers. A Lead Local Flood Authority (LLFA) leads on surface water, groundwater and ordinary watercourses — and Derbyshire has two: Derbyshire County Council for the county and Derby City Council for the city.

Across the county, Derbyshire County Council is the LLFA and reviewed its Local Flood Risk Management Strategy in 2023; within the city boundary, the City of Derby is a unitary authority and its own LLFA with its own Strategic Flood Risk Assessment. A developer here deals with whichever applies, alongside the Environment Agency and the relevant district or borough council as the local planning authority. Our overview of who manages flood risk in England explains how the pieces fit together, and our note on the role of the LLFA covers its part as statutory consultee on surface water drainage.

Your assessment and drainage strategy must satisfy national policy — the NPPF and its Planning Practice Guidance — and the local framework: Derbyshire's Local Flood Risk Management Strategy, the relevant Strategic Flood Risk Assessment and the adopted Local Plan flood policies of the district covering your site. 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 the LLFA will accept.

What your flood risk assessment in Derbyshire must show

• Risk assessed from every credible source, using the Flood Map for Planning flood zones and local data.
• An appropriate location, tested against the Sequential Test where policy requires it.
• Safe for its lifetime, once the climate change allowances are applied.
• No increase in flood risk elsewhere, with attenuation and, where needed, compensatory storage.
• Residual risk managed, with safe access, egress and finished floor levels. Get one of these wrong and the application stalls, as our note on LLFA drainage objections shows.

Development and flood risk assessment in Derbyshire

Derbyshire's geography pulls development in very different directions, and the kind of site you bring forward shapes the assessment you need. The right scope is the difference between a clean approval and a drainage objection that holds an application up for months.

• Riverside regeneration in Derby. Schemes along the lower Derwent frequently sit in Flood Zones 2 and 3, needing finished floor levels, safe access and egress, and often compensatory flood storage even behind the Our City Our River defences.
• Peak District and dales sites. Development in the national park and the central dales is tightly constrained, with narrow valleys, steep surface-water runoff and limestone ground conditions that change how drainage can work.
• Former coalfield brownfield in the north east. Regeneration around Chesterfield and north-east Derbyshire often turns on the Rother and Hipper, made ground and surface water, and on the right drainage information for planning.
• Market towns and rural schemes. Conversions and new builds in towns such as Bakewell, Belper, Ashbourne and Wirksworth often turn on a single watercourse and ordinary watercourses rather than a major river, and on a proportionate screening-level assessment.

Climate change is not optional here. A Derbyshire assessment must apply the Environment Agency's allowances for higher river flows and rainfall over the development's lifetime — generally 100 years for housing — which sets floor levels, freeboard and how much attenuation a drainage scheme needs.

Home buyers and businesses come to us too. A flood risk question can affect a purchase and house prices, and a conveyancing search is not the same thing as a planning-grade assessment. Knowing which you actually need saves time and money, and our guide on how a flood risk assessment is done explains where the line falls.

How Unda helps with flood risk assessment in Derbyshire

We act as the accurate translation layer between your scheme and the requirements set by the Environment Agency, the relevant Derbyshire LLFA and national planning policy. We are experts on the county's flooding, not a generic report mill.

A flood risk assessment in Derbyshire from Unda assesses every credible source — the Derwent and its tributaries, the Rother and Hipper, surface water, groundwater through the limestone, 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. We are a CIWEM Business Partner with chartered members, and a senior consultant signs off every report. Where the 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.

Flood risk assessments and related reports for every situation in Derbyshire

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. We prepare all three, alongside the right form of assessment for buyers, lenders and BREEAM.

Flood risk assessments

• Flood risk assessment for planning. The core report, site-specific and prepared to satisfy the NPPF, the Environment Agency and your Derbyshire planning authority. Groundwater and, where needed, flood modelling are assessed within it rather than as separate reports.
• Homebuyer and property-purchase survey. For conveyancing, where a search has flagged Derwent-valley or surface-water risk and you need the actual building assessed, not a broad map.
• Flood risk assessment for insurance. Property-specific evidence for brokers and underwriters where premiums have risen or cover has been restricted.
• Flood risk assessment for BREEAM. Structured around BREEAM Pol 03, which is credit-driven rather than safety-driven, so a planning FRA alone rarely satisfies it.
• Groundwater flood risk. A defensible design water table for limestone and sandstone sites and any basement — assessed as a source within the FRA, or as a standalone hydrogeological assessment on complex sites.

Sequential and Exception Tests

The Sequential and Exception Tests are a separate, locational report about whether a development should be in a higher-risk location at all. The Sequential Test defines an area of search, identifies reasonably available lower-risk sites and justifies the proposed site; the Exception Test is the second gate where development still needs to proceed. A clean site-specific assessment showing the development is not actually within an area at risk can sometimes remove the need at application stage — a live policy area, as our explainer on the Sequential and Exception Tests sets out.

Drainage strategy and SuDS

• Sustainable drainage strategy (SuDS). Surface-water engineering — calculates existing versus proposed runoff and proposes SuDS to hold discharge within the required rates.
• Preliminary drainage design. The early, outline read that flags infiltration issues before they affect layout and land value.
• Discharge of drainage conditions. The detailed stage to discharge a pre-commencement or pre-occupation drainage condition.
• Flood modelling. 1D and 2D hydraulic modelling — a technique that feeds the assessment, Sequential Test or drainage design where national mapping is not enough.

Early in a drainage strategy it helps to know whether the ground will take water: our free geology and ground conditions map and BRE 365 infiltration rate calculator give an indicative read before a trial pit — useful over Derbyshire's limestone and made ground — and the drainage calculators help size the scheme. You can screen a postcode on our flood risk map or see our wider drainage assessment and flood risk assessment services, all overseen by a chartered consultant who stays involved past the report to answer objections.

Derbyshire flood resources and contacts

The most reliable Derbyshire flood information comes from the lead authorities. For an immediate threat to life during a flood, always call 999; for a power cut during flooding, call 105.

• Check for flooding in Derbyshire. 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.
• Derbyshire County Council flood risk. The Local Flood Risk Management Strategy, how to report flooding and developer guidance at derbyshire.gov.uk, plus its groundwater flood risk guidance.
• Derby City Council and Our City Our River. The city's flood defence programme and flood risk role at derby.gov.uk.
• Storm Babet Section 19 investigation. The county's statutory flood investigation into the October 2023 flooding, via Derbyshire County Council.
• Derbyshire Prepared. The county's Local Resilience Forum, with community flood advice, at derbyshireprepared.org.uk.
• Trent Regional Flood and Coastal Committee. Regional investment and priorities via the Trent RFCC.
• Live river levels. Whether the Derwent, Wye or Rother are running high right now via our live river levels map.

For flooding from blocked or burst sewers, contact your water company — Severn Trent serves most of Derbyshire and the city of Derby, while parts of the north of the county are served by Yorkshire Water. For broader policy context, our notes on the Environment Agency's planning role and on flood zones 1, 2 and 3 are a good starting point.

Flood risk assessment in Derbyshire: frequently asked questions