Flood Risk & Drainage Requirements for Cambridgeshire County Council

In Cambridgeshire the two questions that decide a planning application — is the site safe from flooding, and where does its surface water go — are answered by different bodies. One of five district councils determines the application, while Cambridgeshire County Council sits behind all of them as the Lead Local Flood Authority, setting the surface water drainage and sustainable drainage (SuDS) standards a scheme has to meet. On a fen county drained by pumps and criss-crossed by internal drainage boards, the drainage half of that test is often the harder one to pass.

Knowing which body wants what, and what the County requires before it will accept a drainage strategy, is the difference between a clean submission and one that stalls on a Lead Local Flood Authority objection. We prepare the flood risk assessments and drainage strategies that get schemes across Cambridge, South Cambridgeshire, Huntingdonshire, East Cambridgeshire and Fenland through validation and past the County's drainage team, for planning, property purchase, mortgage and insurance, and BREEAM, alongside sequential and exception tests and surface water drainage strategies.

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

Cambridgeshire County Council is the Lead Local Flood Authority for the whole county, so on almost every major site the drainage case is judged by the County against a fixed set of discharge rates and a strict drainage hierarchy — get that wrong and the district council cannot approve the application, however sound the flood risk assessment.

Flood risk and drainage in Cambridgeshire at a glance

• Two tiers, two jobs. The district or city council (Cambridge, South Cambridgeshire, Huntingdonshire, East Cambridgeshire or Fenland) is the local planning authority; Cambridgeshire County Council is the Lead Local Flood Authority for surface water, groundwater and ordinary watercourses across all five.
• Greenfield discharge rates apply. New development must limit surface water runoff to the greenfield (QBAR) rate or lower, and previously developed sites must reduce their existing runoff — set out in the County's Surface Water Planning Guidance (May 2025).
• The Cambridgeshire Flood and Water SPD is the shared rulebook. Adopted across the districts, it and the May 2025 guidance are what a drainage strategy is actually measured against.
• Internal drainage boards add a second consent. Much of the county sits within the Middle Level, the Ely Group and the North Level boards, whose byelaws require separate discharge consent on top of planning.
• Water scarcity is now a planning constraint. Cambridge is one of the most water-stressed places in England, so water efficiency and reuse increasingly sit alongside flood risk and drainage in a submission.

Who decides flood risk and drainage on a Cambridgeshire planning application?

On a Cambridgeshire application the planning decision is taken by the district or city council, but the surface water drainage is judged by Cambridgeshire County Council as the Lead Local Flood Authority, and the main rivers are the Environment Agency's responsibility. The County is a statutory consultee on surface water drainage for every major application, so on most sites you are answering to two councils at once — and often an internal drainage board as well.

This split is the single most common thing applicants get wrong here. The district council validates and determines the application against its own Local Plan; the County reviews the drainage strategy against the County's developer requirements and the Cambridgeshire Flood and Water SPD; and the Environment Agency advises on the Great Ouse, the Nene, the Cam and the other main rivers. Our explainer on the role the Lead Local Flood Authority plays sets out where each body's remit begins and ends.

Cambridgeshire's surface water drainage and SuDS requirements

Cambridgeshire County Council expects new development to control surface water to the greenfield runoff rate, follow the drainage hierarchy from infiltration downwards, and treat water quality before it leaves the site. These standards come from the Cambridgeshire Flood and Water SPD and the County's Surface Water Planning Guidance (May 2025), and they are the part of a submission an applicant is most likely to get an objection on. Below is what the County actually asks for, pulled out of documents that together run to well over a hundred pages.

The Cambridgeshire Flood and Water SPD

The Cambridgeshire Flood and Water Supplementary Planning Document is the shared guidance the districts adopted to explain how flood risk and the water environment must be handled in new development. First adopted in 2016 and re-adopted across the councils, it supplements the district Local Plans and is a material consideration when an application is decided, so a drainage strategy that follows it is far harder to object to. It sits alongside the published SPD and the County's own developer guidance.

The Surface Water Planning Guidance (May 2025)

The County's Surface Water Planning Guidance, updated in May 2025, is the document its drainage officers actually check a strategy against. It is where the discharge rates, the drainage hierarchy, the infiltration standard and the storm events in the table above are set, and it asks all developers and their consultants to design to it. Following its drainage hierarchy and completing the surface water pro-forma for a major application from the outset is the surest way to avoid an objection from the Lead Local Flood Authority. A drainage strategy for a Cambridgeshire site is a distinct piece of surface water engineering; our sustainable drainage strategy service explains what one involves, and the 2025 national SuDS standards and the four pillars of SuDS shape what the County will accept.

Where the County most often objects — and how to pre-empt it

From taking drainage strategies through Cambridgeshire County Council as Lead Local Flood Authority, an initial holding objection is common, and is usually lifted once the strategy answers a familiar set of points. Designing for them from the outset is what turns a first response of "object" into a "no objection" with conditions.

• Source control on every site. The County expects interception SuDS — permeable paving, rain gardens, bioretention or swales — as the first stage of the treatment train, and does not accept "site constraints" or a pumped site as a reason to leave them out without evidence.
• Greenfield-equivalent discharge, even when pumped. On a fen site drained by pump the County still expects runoff held to greenfield (QBAR) equivalent rates, often only a few litres per second, with a flow control on each catchment.
• The attenuation basin counts as impermeable. Its surface area has to be included in the impermeable total, because it drains positively into the system — a common gap in the calculations.
• Prove the outfall works. You must show the receiving watercourse has capacity for the extra flow, assessed at its narrowest worst-case section, and identify a genuine final outfall; a desktop trace is accepted.
• Settle watercourse maintenance. Where boundary ditches would fall behind private gardens, the County objects to maintenance being fragmented across many owners — it wants a maintenance strip or easement and a single management body named.
• Water quality by the Simple Index Approach. Treatment has to be demonstrated against the CIRIA SuDS Manual, not simply asserted.

Does a Cambridgeshire application need a flood risk assessment or a drainage strategy?

Most Cambridgeshire sites need one or both. A flood risk assessment is required for development in Flood Zones 2 and 3, for sites of one hectare or more in Flood Zone 1, and, since the 2025 Planning Practice Guidance update, for smaller Flood Zone 1 sites where the mapping shows surface water risk. A surface water drainage strategy is expected on all major development and on many minor schemes, because the County reviews drainage separately from flood risk. They are two different reports answering two different questions, and on a fen site you very often need both.

If you are unsure which you need, our note on when a flood risk assessment is required and our guide to flood zones 1, 2 and 3 are a good start, or send us the address and we will tell you quickly. Getting the scope right first time is how you avoid the kind of invalidation on flood risk or drainage grounds that holds an application up for weeks.

The district Local Plans and their flood and drainage policies

Because Cambridgeshire is two-tier, the Local Plan flood and drainage policy that binds your application is the district council's, not the County's, though the County's drainage standards apply underneath all of them. Each district judges flood risk against its own adopted plan, and those policies name the tests a scheme must pass. The table below shows where each district's flood and drainage policy sits; the detail of each is covered on that district's own page.

Cambridge Local Plan Policy 32 is the source of the 2 litres per second per hectare discharge floor the County applies, and Huntingdonshire's Policy LP5 sets that district's flood-risk test. Fenland's Policy LP14 governs the almost entirely low-lying Fenland district — we cover it in full on the Fenland District Council page. We are building out the same detail for each of the other Cambridgeshire authorities. Whichever district you are in, the assessment still has to satisfy the district's plan, the County's drainage standards and, where a higher-risk site is involved, the sequential and exception tests.

Internal drainage boards and Anglian Water in Cambridgeshire

Across much of Cambridgeshire the watercourse a site drains into is managed not by the County but by an internal drainage board, and discharging to it needs the board's consent as well as planning permission. The Middle Level Commissioners and their constituent boards, the Ely Group of internal drainage boards and the North Level District board between them manage the pumped fen drainage that keeps large parts of the county dry, and each sets its own discharge expectations under its byelaws.

• Separate consent, not a formality. A board can require a lower discharge rate or a contribution to pumping costs, so the board's position needs settling early, not after the drainage strategy is fixed. Our note on why internal drainage boards matter for planning explains how they fit in.
• The Middle Level. One of the oldest and largest drainage systems in the country, draining a swathe of the fens between the Nene and the Ouse through Wisbech, March and Whittlesey.
• Ordinary watercourse consent. Any works in or affecting an ordinary watercourse — a culvert, headwall or outfall — need the County's consent under the Land Drainage Act 1991, separate from planning permission and from any board consent.
• Anglian Water. The sewerage undertaker for the county and, with Cambridge Water, its water supplier — relevant both to a sewer connection and to the water-efficiency expectations below.

Water scarcity: the extra test Cambridgeshire drainage now has to answer

Cambridge and the surrounding area is one of the most water-stressed places in England, and that now shapes what a planning application has to show. Cambridge City Council has declared a water emergency, and the emerging Greater Cambridge plan sets a demanding water-efficiency target for new homes. For a drainage designer this pushes rainwater harvesting and water reuse up the agenda, because holding and reusing rainfall on site helps answer both the surface water and the water-supply questions at once.

It means a Cambridgeshire drainage strategy is increasingly read against two objectives: controlling runoff to the County's discharge rates, and reducing how much mains water the development draws. Designing the two together, rather than bolting water efficiency on at the end, is what keeps a scheme moving through a system under real supply pressure.

How national flood and drainage policy applies in Cambridgeshire

National policy sets the framework the County and the districts apply. The National Planning Policy Framework and its Planning Practice Guidance require development to be steered to the lowest flood-risk land through the sequential test, to be safe for its lifetime once climate change is allowed for, and not to increase flood risk elsewhere. The September 2025 guidance update widened the sequential test to all sources of flooding, including surface water, which matters in a county where surface water and groundwater are as much of a threat as the rivers.

On drainage, the 2025 national SuDS standards and the Environment Agency's climate change allowances set the baseline the County builds on. Where a site sits in a higher flood zone, the NPPF flood-risk approach and the right vulnerability classification decide whether the development is acceptable at all, and the strategic flood risk assessments the councils hold define the functional floodplain locally.

Flood risk across Cambridgeshire's area

Cambridgeshire floods in almost every way a place can. Much of the county is low-lying fenland at or below sea level, drained by pumps and defended by embankments, so tidal and fluvial flooding from the Great Ouse, the Nene and the tidal system runs alongside surface water that has nowhere to drain by gravity and groundwater rising through peat and silt. The higher ground around Cambridge and Huntingdon behaves differently again, with the Cam and the upper Great Ouse driving the risk. This is a compact summary — the full local flood-risk picture, river by river, is on our Cambridgeshire area page and the Cambridge page.

• The Great Ouse. Drains a large clay-and-fen catchment through Huntingdon, St Neots and Ely; read the River Great Ouse page for how it floods.
• The River Nene. Runs through the northern fens and Peterborough's edge to the Wash; see the River Nene page.
• The River Cam. Threads through Cambridge itself; our River Cam page covers the city's fluvial risk.
• Surface water and groundwater. The most widespread risks across the built-up and low-lying parts of the county, and the ones the County's drainage standards are written to control. Check live warnings and river levels on the Environment Agency's flood service.

How Unda helps with flood risk and drainage in Cambridgeshire

Our job is to make your scheme legible to the bodies that decide it — the district council, Cambridgeshire County Council as Lead Local Flood Authority, the internal drainage boards and the Environment Agency — and to answer each of them in the terms it uses. We know how this county's authorities read a flood risk assessment and a drainage strategy, and we write reports built to be approved the first time.

A flood risk assessment from Unda reads every credible source on a Cambridgeshire site — the rivers, the tidal system, surface water, groundwater and any board watercourse on the boundary — compares modelled levels against your proposed floor levels, and sets mitigation the regulators will accept. Where the County needs it, a surface water drainage strategy sits alongside as a separate report built to the discharge rates and hierarchy above, so the two cases stay consistent and an objection has nowhere to land. We are a CIWEM Business Partner with chartered members, and a senior consultant signs off every report.

That approach is what clears objections. On a recent outline application for a major housing scheme in the county, the County's first drainage response was an objection — on source-control SuDS, and on how the boundary watercourses would be maintained. We revised the strategy around a full treatment train, pumped discharge held to greenfield-equivalent rates and a defined maintenance easement, and the objection was withdrawn, subject to the usual pre-commencement drainage conditions.

Flood risk and drainage reports for every situation in Cambridgeshire's area

A flood risk assessment, a sequential or exception test and a drainage strategy are three distinct reports. They often travel together in a Cambridgeshire 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 site-specific report prepared to satisfy the NPPF, the Environment Agency and your district planning authority. Groundwater and, where needed, flood modelling are assessed within it.
• Homebuyer and property-purchase survey. For conveyancing, where a search has flagged fen 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 narrowed.
• Flood risk assessment for BREEAM. Built around BREEAM Pol 03, which is credit-driven rather than safety-driven, so a planning report alone rarely satisfies it.
• Groundwater flood risk. A defensible design water table for fen, peat and silt sites and any basement — assessed within the flood risk assessment, or as a standalone study on complex ground.

Sequential and exception tests

The sequential and exception tests are a separate, locational report about whether a development should be in a higher-risk place at all — a live issue across a county where so much land sits in Flood Zone 3. The sequential test identifies reasonably available lower-risk sites and justifies the proposed one; the exception test is the second gate where development still needs to proceed. The September 2025 guidance now applies that scrutiny to surface water too.

Drainage strategy and SuDS

• Sustainable drainage strategy (SuDS). The surface water engineering that holds discharge to Cambridgeshire's greenfield rates and follows the County's hierarchy.
• Preliminary drainage design. The early, outline read that flags infiltration and board-consent 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 where national mapping is not enough to settle the levels on a fen or river-valley site.

Early in a drainage strategy it helps to know whether the fen or clay 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, and the drainage calculators help size the scheme. You can screen a postcode on our flood risk map, check whether the rivers are running high on the live river levels map, and every report is overseen by a chartered flood risk consultant who stays involved past the report to answer objections.

Cambridgeshire flood risk and drainage: frequently asked questions