Flood Risk Assessment in Derby

Our team at Unda prepares clear, policy-compliant flood risk assessments and drainage strategies for commercial and residential sites across Derby. A flood risk assessment in Derby shows the city council and the Environment Agency that a development will stay safe from flooding for its whole lifetime, without pushing flood risk onto anyone else. We have years of experience of the way the River Derwent, the culverted Markeaton Brook and Derby's surface-water network behave, and we deal directly with the regulators on your behalf.

Derby is a river city. The Derwent runs straight through it on its way to the Trent, the Markeaton Brook arrives from the north-west and disappears into a Victorian culvert beneath the shopping streets, and the low ground at Pride Park, Chaddesden and Alvaston sits where that water wants to spread. We read every source that matters here — the Derwent and its tributaries, the brooks and the culverts, the surface water that overwhelms the drains, and the groundwater in the valley gravels — then translate it into a report the regulators will accept. We guide architects, planning consultants, developers, landowners, home buyers and businesses through to a decision, whether the report is for planning, a property purchase, a mortgage or insurance, BREEAM, or a surface-water drainage strategy.

Derby's worst floods have come not from the Derwent but from the Markeaton Brook, which was buried in a culvert through the city centre after the 1842 flood and still overwhelmed it in 1932 — which is why an assessment here has to read the brooks, the culverts and the river together, not just the headline river map.

Flood risk assessment in Derby at a glance

• The River Derwent runs through the heart of the city. Its lower reach through Derby has long carried a roughly 1 in 25 year chance of flooding, which is why the city is delivering one of the largest flood defence schemes in its history.
• The Markeaton Brook is culverted beneath the centre. A main river that vanishes underground through the shopping quarter, it caused Derby's catastrophic 1932 flood and remains a surface-water and culvert-capacity risk today.
• Derby City Council is the Lead Local Flood Authority. As a unitary authority, the council handles surface water, groundwater and ordinary watercourses, while the Environment Agency manages the Derwent and the Markeaton Brook.
• One quote, 60-minute reply. Tell us about your Derby site and one of our experienced flood risk consultants will get back to you within 60 minutes.

Check flood risk anywhere in Derby

Derby is outlined below. Screen any postcode in the city 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 — for that, start a quote and we will assess the property itself.

Flood risk in Derby: the Derwent, the Markeaton Brook and surface water

Derby faces flooding from more than one direction at once. The River Derwent is the obvious threat as it cuts through the city, but the Markeaton Brook — culverted beneath the centre — and the surface water that collects in the low ground at Pride Park, Chaddesden and Alvaston are just as important. A credible flood risk assessment in Derby has to weigh all of them against the specific site.

The Derwent enters from the north past Darley Abbey, runs through the city centre and Pride Park, and joins the River Trent a few miles south. The Markeaton Brook comes in from the north-west, is taken underground in a Victorian culvert through the shopping streets, and re-emerges to meet the Derwent. Both are designated main rivers managed by the Environment Agency, while the surface water and ordinary watercourses are the city council's responsibility. Knowing which one drives the risk on a given plot is the heart of the work.

• Rivers (fluvial). The Derwent through the city centre and Pride Park, and the Trent to the south, put land along their corridors in Flood Zones 2 and 3, where an assessment is almost always required.
• The culverted Markeaton Brook. A main river that runs underground through the centre. When the culvert cannot take the flow, water surcharges into the streets above — the mechanism behind Derby's historic city-centre floods.
• Surface water (pluvial). Now the most widespread flood risk in England. Since the 2025 update to Planning Practice Guidance, surface water on the Flood Map for Planning can trigger an assessment even on a Flood Zone 1 site in Derby.
• Groundwater. The sand-and-gravel deposits of the Derwent valley can hold a high water table that floods low ground and basements without ever appearing on a river map — decisive for any soakaway or below-ground level. See groundwater flood risk.

The reason a single national map is never enough in Derby is that these sources interact. A site can sit in Flood Zone 1 for the river yet still flood from the brook culvert or from surface water with nowhere to drain. Our note on whether flood maps are accurate explains why a property can flood when the map says low risk — and why the regulators expect a site-specific reading.

A history of flooding in Derby

Derby's flood history is written into the city's streets and its drains. The dated events below are why the council and the Environment Agency scrutinise development so closely, and why a flood risk assessment in Derby has to be evidence-led rather than generic. Each one shaped the defences and the policy a developer now designs around.

• 1842 — the flood that buried the brook. After serious flooding from the Markeaton Brook, the town built a large culvert to carry it underground through the centre, in the hope of preventing a repeat. It is still there today.
• September 1931 and May 1932 — the Great Flood. Intense rain overwhelmed the culvert and the Markeaton Brook burst through the centre. Water filled shops and houses up to six or seven feet deep along the Cornmarket, St Peter's Street and St James's Street, with damage estimated at around £400,000 at the time — equivalent to roughly £35 million today.
• 1938 — the flood-relief culverts. In response, the borough opened the Northern Flood Relief Culvert to drain excess flow from the Markeaton and Mackworth brooks, plus the Bramble Brook culvert for that tributary. Much of Derby's centre still relies on this hidden network.
• 2000 and 2007 — the Derwent returns. More recent flooding from the river caused significant disruption and flooded a number of properties, with emergency flood protection installed in parts of the city — the events that built the case for the current defence scheme.

That long memory is exactly why an assessment here cannot lean on the headline river map alone. The culvert system, the historic flood outlines and the defended status of the Derwent all have to be read together, which is where residual flood risk — the risk that remains even behind defences — becomes central to a Derby submission.

Our City, Our River: Derby's flood defences — and why your site still needs an assessment

Derby is delivering one of the largest flood schemes in its history, but new defences do not remove the need for a flood risk assessment. They change the question from “is this site in the floodplain?” to “is this site safe behind the defences, for its whole lifetime, allowing for climate change?” — which is precisely what an assessment has to answer.

The Our City, Our River programme is led by Derby City Council on behalf of the Environment Agency, building on the Lower Derwent Flood Risk Management Strategy adopted in 2011. It set out to reduce flood risk to around 2,250 properties along the lower Derwent — more than 1,450 homes and nearly 800 businesses — by realigning and raising the defences through the centre to a 1 in 100 year standard. Early packages are complete and further phases, including the Derby Riverside works begun in 2025, bring the total number of properties benefiting closer to 2,000.

• Defences reduce probability, not possibility. The Derwent's defences are designed to a standard; flows above that standard, or a defence failure, still leave a residual risk that an assessment must characterise.
• The maps still show the undefended floodplain. The Environment Agency's Flood Map for Planning ignores defences, so a defended Derby site can sit in Flood Zone 3 on the map and still need the full Flood Map for Planning treatment.
• Lifetime safety is the test. A scheme has to stay safe for its design life — usually 100 years for housing — using Environment Agency climate change allowances, not just present-day levels.

Flood risk and planning policy in Derby

In Derby, your application is judged by two bodies and one local plan. The Environment Agency advises on the Derwent and the Markeaton Brook; Derby City Council, as Lead Local Flood Authority, advises on surface water and drainage; and the council's adopted Core Strategy sets the policy your scheme must satisfy. Getting all three right at the first attempt is what keeps an application moving.

Derby City Council is a unitary authority, so it is both the local planning authority and the Lead Local Flood Authority. It maintains a Local Flood Risk Management Strategy and a Strategic Flood Risk Assessment, and it is a statutory consultee on surface-water drainage for major development — an unresolved drainage objection can stall a decision for months, as our piece on the LLFA objection explains.

• Local Plan Core Strategy, Policy CP2. Adopted in 2017, it blends the national flood risk Sequential and Exception Tests with local requirements for sustainable drainage and access to watercourses for maintenance — the policy your application is weighed against.
• The Strategic Flood Risk Assessment. The council's Level 1 and Level 2 SFRA is the city-wide evidence base that drives the Sequential Test and shows where a site needs a full assessment.
• Local SuDS expectations. Derby has its own SuDS design and adoption guidance and a SuDS Approval Body, so your drainage has to follow the discharge hierarchy and the four pillars of SuDS to be acceptable.
• Critical drainage and surface water. Parts of low-lying Derby behave as critical drainage areas, where even a Flood Zone 1 site can need an assessment — see critical drainage areas.

Do you need a flood risk assessment in Derby?

You will usually need a flood risk assessment in Derby if your site is in Flood Zone 2 or 3, is one hectare or larger anywhere in the city, or is flagged for surface water on the Flood Map for Planning. A separate drainage strategy is triggered by the scale of the development. The table below shows the common situations and the report each one points to.

Even a small householder scheme can need one where surface water or the brook culvert is in play. If you are unsure, our guide to whether you can do your own flood risk assessment sets out where standing advice ends and a competent professional is required — and the Environment Agency's role in reviewing it.

How Unda helps with flood risk assessment in Derby

We are not based in Derby, but we know the city's flood behaviour well — the Derwent, the buried Markeaton Brook, the relief culverts and the low ground at Pride Park and Alvaston. We act as the accurate translation layer between your scheme and the Environment Agency, Derby City Council and national policy, and we stay involved past the report to answer objections.

Every project is overseen and signed off by a Senior Flood Risk Consultant. We have prepared more than 5,000 flood risk assessments since 2014, we are a CIWEM Business Partner with chartered members, and we reply to every quote request within 60 minutes. Where the national mapping is too coarse for a Derby site, we can build site-specific flood modelling to establish the real levels and flow routes.

You can read more about our team and track record, or see how we approach flood risk assessment for planning across England.

Flood risk assessments for every situation in Derby

People need flood risk work in Derby for many reasons, and we cover them all. 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.

• Flood risk assessment for planning. The site-specific report submitted with a planning application under the NPPF and its guidance — see flood risk assessment for planning and our NPPF guidance.
• Flood risk survey for property purchase. An independent, property-specific survey for buyers when a search or lender flags flood risk — see flood risk survey for property purchase and why flood risk affects house prices.
• Flood risk report for insurance. Property-level evidence where premiums rise, cover is restricted, or there has been a flood event — see flood risk assessment for insurance.
• Flood risk assessment for BREEAM. An assessment structured around BREEAM Pol 03 for schemes pursuing certification — see flood risk assessment for BREEAM.
• Sequential and Exception Tests. The locational justification under national policy when a site is in a higher-risk zone — see Sequential and Exception Tests and the lessons of the Yatton judgment.
• Surface-water drainage strategy (SuDS). The surface-water engineering that keeps discharge within limits — see drainage strategy and SuDS, with discharge of drainage conditions and preliminary drainage design at the right stages.

Groundwater and flood modelling sit inside this work rather than alongside it: groundwater is one of the sources every assessment examines, and modelling is the technique we use to pin down levels where the maps fall short. For the drainage side, our free drainage calculators and BRE 365 infiltration calculator give a quick first pass, and our notes on infiltration testing and permeable paving explain what the council will expect.

Local flood risk management and emergency contacts in Derby

If you need to report flooding, sign up for warnings or reach someone in an emergency in Derby, the bodies below are the right first call. Each has a defined responsibility — the council for surface water and drainage, the Environment Agency for the rivers, Severn Trent for the sewers — and knowing which is which saves time when water is rising.

To watch the rivers yourself, the Environment Agency gauges on the Markeaton Brook at Bridge Street and the River Derwent at Derby City update through the day, and our free live river levels map and flood risk map put them and the EA risk layers in one place. If your boundary contains a brook or ditch, you may also carry riparian responsibilities for keeping it clear.

Flood risk assessment in Derby: your questions answered