Pol 03 Flood and Surface Water Management | BREEAM UK New Construction 2018

Pol 03 represents one of the most significant credit opportunities in BREEAM's Pollution category, offering up to 5 credits plus 1 exemplary for developments that demonstrate proper flood risk management and sustainable surface water control. For projects on constrained urban sites or in flood-prone locations, these credits often determine whether you achieve Good or Very Good ratings.

This credit appears across BREEAM UK New Construction 2018 schemes and rewards three distinct but interconnected environmental outcomes: avoiding inappropriate development in flood risk areas, reducing surface water discharge through sustainable drainage, and preventing pollution of watercourses from contaminated run-off. With the Pollution category weighted at 8% of overall score for fully-fitted buildings, Pol 03's 5 credits contribute approximately 4% to your final BREEAM rating—enough to shift you between rating bands.

What is BREEAM Pol 03?

Pol 03 tackles the growing problem of urban flooding and water pollution through three assessment areas. The credit structure recognises that poor surface water management doesn't just cause flooding—it overwhelms drainage infrastructure, degrades water quality, and creates environmental damage that proper design can prevent.

Flood Risk Management (2 credits) rewards developments located in appropriate flood zones or designed with comprehensive resilience measures where flood risk cannot be avoided. Sites in Flood Zone 1 achieve maximum credits straightforwardly. Higher-risk sites need demonstrating proper protection.

Surface Water Run-off (2 credits) acknowledges sustainable drainage systems that reduce both the rate and volume of water leaving the site. Brownfield developments must show 30% improvement over pre-development conditions. Greenfield sites must maintain their natural run-off characteristics despite development.

Water Quality Protection (1 credit) recognises pollution prevention measures that stop contaminated run-off reaching watercourses. This includes treatment for oils and sediments from car parks, emergency containment for chemical storage areas, and general treatment through sustainable drainage features.

The credit assessment links directly to planning policy requirements—your flood risk assessment serves both NPPF compliance and BREEAM evidence. Similarly, SuDS designs satisfy both statutory consultees and BREEAM assessors when done properly.

Pol 03 Requirements for UK New Construction 2018

Flood Risk Credits (Up to 2 Credits)

Two Credits - Low Flood Risk Sites

Sites in Environment Agency Flood Zone 1 achieve 2 credits when your site-specific flood risk assessment confirms low annual probability of flooding from all sources. This means assessing fluvial flooding from rivers, pluvial flooding from surface water, groundwater flooding, and sewer flooding. Simply referencing EA flood maps isn't sufficient—you need a professional assessment considering local conditions, flow paths, and climate change impacts.

The FRA must include climate change allowances appropriate for your development lifetime and location. For most of England, this means applying +40% to peak river flows for developments designed to 2080s standards. Peak rainfall intensity increases vary by location but typically range from +20% to +40%.

One Credit - Medium or High Flood Risk with Resilience

Sites in Flood Zones 2 or 3 can still achieve 1 credit (rather than 2) by implementing comprehensive flood resilience measures. Functional floodplains (Zone 3b) typically cannot achieve BREEAM certification unless only water-compatible development is proposed.

Two routes exist for demonstrating resilience:

Option A: 600mm Freeboard - Design finished floor levels and all access routes at minimum 600mm above the design flood level for your site's flood zone. This applies to both 1-in-100 year fluvial events or 1-in-200 year coastal events, with climate change factors applied. Where the Environment Agency has set more onerous local requirements, follow those instead.

Option B: BS 8533:2017 Compliance - Implement a full flood resistance and resilience strategy following the hierarchy approach in BS 8533. This means addressing:

• Building fabric with flood-resistant materials (concrete floors, impermeable membranes, water-resistant finishes)

• Core services positioned above flood levels or protected through design (non-return valves, protected cable routes, elevated plant)

• Local services relocated appropriately (sockets, vents above flood level)

• Emergency planning including safe access and egress during flood events

Both options require your site-specific FRA demonstrating that residual risks are properly managed. Simply meeting planning requirements doesn't automatically secure BREEAM credits—you need evidence of design responses to flood risk.

Surface Water Run-off Credits (Up to 2 Credits)

Prerequisite for All Surface Water Credits

Before any credits can be awarded, your drainage design must follow the SuDS hierarchy with bespoke solutions appropriate to your site. The priority order is:

1. Infiltration at source

2. Attenuation with surface features

3. Controlled discharge to watercourse

4. Controlled discharge to sewer

You need documented justification for why you cannot move up this hierarchy. Saying infiltration is "inconvenient" doesn't satisfy BREEAM. Demonstrating contaminated ground conditions, clay soils with failed infiltration testing, or high groundwater levels does.

One Credit - Run-off Rate Control

For brownfield sites: Drainage measures must demonstrate 30% improvement in peak run-off rate compared to pre-development conditions. This applies at both 1-year and 100-year return period events, calculated at each discharge point.

Note this is 30% improvement over what was there before, not 30% reduction from theoretical maximum. If you're redeveloping a fully paved car park, you might need 70-80% reduction to achieve greenfield rates, not just 30%.

For greenfield sites: Peak run-off rate must be no greater than pre-development greenfield run-off. This typically requires significant attenuation storage when you're adding buildings and hardstanding.

Both calculations must include climate change allowances applied to post-development scenarios only. If your pre-development site would discharge 5 l/s in a 100-year event, and your post-development site (with climate change) would discharge 3.5 l/s, you've achieved the 30% improvement.

One Credit - Run-off Volume Control

Demonstrate reduction in annual run-off volume through SuDS features that intercept rainfall before it becomes run-off. This typically means:

• Green roofs capturing and evapotranspiring rainfall

• Rain gardens and bioretention absorbing water

• Permeable paving allowing infiltration

• Rainwater harvesting for reuse

Alternatively, demonstrate no increase in run-off volume through infiltration-based drainage maintaining the site's natural hydrology.

Additional Requirements for Surface Water Credits

Both credits require:

• Relevant maintenance agreements in place for all SuDS (Section 38/104 adoption, management company specifications, or homeowner guidance)

• Climate change allowances following current EA guidance

• Professional hydraulic calculations using recognised software (MicroDrainage, InfoWorks, or equivalent)

For derelict sites vacant over 5 years, you need professional assessment of the previous drainage network to establish probable historic flow rates. Without this, BREEAM treats the site as greenfield.

Water Quality Credit (1 Credit)

Achieve appropriate pollution prevention based on risk level:

• Low-risk sources (roofs, landscaping): Basic SuDS treatment through vegetated features providing sedimentation and filtration. Typical treatment train might be grass swale followed by infiltration basin.

• High-risk sources (car parks, service yards, delivery areas): Petrol interceptors (Class 1 full retention or equivalent) treating potential oil contamination before discharge. Must meet relevant standards and include bypass arrangements preventing flooding.

• Chemical/fuel storage areas: Emergency shut-off valves or containment preventing chemicals reaching watercourses in the event of spillage or bunding failure.

• Vehicle washing areas: Pollution prevention systems following Environment Agency PPG13 guidance, with appropriate separation and treatment.

The first 5mm of rainfall should be prevented from leaving site untreated where practically achievable. On very constrained sites where this proves impossible, you need professional justification explaining why and demonstrating you've minimised discharge as far as possible.

Exemplary Credit (1 Additional Credit)

Available through either:

Option 1: Brownfield sites achieving greenfield run-off rates (rather than just 30% improvement). This represents exceptional performance, essentially restoring the site's natural drainage despite adding buildings.

Option 2: Developments discharging directly to tidal estuary or sea where uncontrolled discharge causes no flood risk downstream. Drainage must only carry site run-off and cannot cross third-party land.

How to Achieve BREEAM Pol 03

Early Stage Planning Decisions

Commission your flood risk assessment during feasibility, not at planning submission. FRA findings affect fundamental design decisions: site layout, finished floor levels, access arrangements, building positioning. Making these decisions early means they're embedded in the concept rather than awkward retrofits.

Similarly, SuDS should influence landscape strategy from project inception. The best schemes integrate drainage with public realm, providing amenity value and biodiversity benefit alongside flood management. Rain gardens become attractive planted features. Swales provide green corridors. Attenuation basins become landscape ponds. This integration works when conceived early; it fails when drainage is an afterthought.

Design Stage Technical Requirements

For Flood Risk Credits:

Engage a competent flood risk consultant—typically chartered engineer with specific flood risk expertise. They need familiarity with Environment Agency guidance, local planning requirements, and BREEAM evidence standards.

Your FRA must assess all sources: fluvial, pluvial, groundwater, and sewer flooding. Relying solely on EA river flood mapping misses surface water flooding, which affects more properties in England than river flooding.

Apply appropriate climate change factors. These vary by location, development type, and assessment period. Check EA guidance for your specific catchment—don't assume national averages apply everywhere.

For sites in Zones 2 or 3, design flood resilience into the scheme from the outset. Specifying flood-resistant materials costs little more than standard construction when decided early. Retrofitting resilience measures after design is complete becomes expensive and often compromises architecture.

For Surface Water Credits:

Appoint a suitably qualified drainage consultant capable of CIRIA C753 design. BREEAM defines this as someone with skills and experience to champion SuDS within overall design, with knowledge of infiltration-based solutions and capability to produce robust hydraulic calculations. This typically means chartered engineer with drainage specialism or landscape architect with specialist SuDS training.

Conduct infiltration testing to BRE Digest 365 standards if you're proposing infiltration-based drainage. Testing confirms whether soils can accept water at sufficient rates. Typical minimum infiltration rate for SuDS is 1×10⁻⁶ m/s. Failed infiltration tests don't prevent achieving credits but require justification for moving down the SuDS hierarchy.

Model pre-development run-off using appropriate methodology. For brownfield, this means assessing what drainage was there before, not assuming 100% run-off. For greenfield, use soil type and land use to calculate natural run-off characteristics.

Design your SuDS following the hierarchy. Start by maximising infiltration at source through permeable paving, rain gardens, and soakaways. Where infiltration is not viable, use surface attenuation features before resorting to underground tanks. Document why you cannot achieve higher hierarchy solutions.

Size attenuation for 100-year plus climate change event. Your storage must accommodate the rainfall that would occur once every 100 years, increased by climate change factors, without flooding. This typically requires significant storage volumes on constrained sites.

Design exceedance routes for flows exceeding your drainage system capacity. During extreme events beyond your design standard, water needs safe pathways that don't flood buildings or critical infrastructure. Route exceedance flows along roads, through swales, or via designated flood pathways.

Specify your treatment train for water quality. This typically means two or three stages: grass swale providing initial settlement, followed by infiltration basin or filter drain providing secondary treatment, with final polishing through infiltration to ground. For high-risk areas, add petrol interceptor before other treatment stages.

Arrange maintenance agreements before final BREEAM assessment. This is not optional—2 credits depend on having agreements in place. For residential schemes with private SuDS in gardens, provide homeowner guidance. For communal areas, secure management company specifications. For adopted drainage, obtain Section 38 or Section 104 agreements with commuted sums.

Evidence Requirements for BREEAM Assessor

Your BREEAM assessor needs specific documents:

Flood Risk:

• Site-specific FRA covering all sources with climate change allowances

• Clear statement of flood zones from EA mapping

• Design flood levels for the site

• Demonstration of resilience measures (if Zones 2/3)

• Specification of flood-resistant materials (if applicable)

Surface Water:

• Drainage strategy drawings showing SuDS locations and catchments

• Hydraulic calculations for pre and post-development scenarios

• Attenuation storage calculations for 100-year plus climate change event

• Cross-sections of SuDS features with material specifications

• Infiltration test results or justification for why infiltration not viable

• Climate change factors used with reference to EA guidance

• Maintenance and adoption agreements

Water Quality:

• Treatment train description

• Petrol interceptor specifications (for high-risk areas)

• Shut-off valve details (for chemical storage)

• Confirmation first 5mm rainfall managed on-site

Common Challenges with Pol 03

Brownfield Run-off Baseline Confusion

The 30% improvement for brownfield sites catches many projects out. It's 30% better than whatever was there before, not 30% reduction from theoretical maximum discharge. If you're redeveloping a site that was 80% hardstanding discharging at near-100% run-off, greenfield rates might represent 90% reduction, not 30%.

For sites derelict over 5 years, you cannot rely on visible drainage infrastructure. You need a drainage consultant to assess the previous network and establish probable historic flow rates through hydraulic modelling. This requires site investigation of existing pipework, outlet locations, and historical drainage records if available. Without this assessment, BREEAM treats the site as greenfield, which may require even greater attenuation.

Contaminated Land Infiltration Issues

Sites with contamination—previous industrial use, fuel storage, chemical processing—typically cannot use infiltration drainage without remediation. Your site investigation must identify contamination extent and severity. Where contamination exists, drainage design needs impermeable liners preventing pollutant migration.

This doesn't prevent achieving BREEAM credits, but you need robust justification for not infiltrating. Document the contamination, explain why infiltration risks pollutant spread, and demonstrate you've maximised surface treatment features (lined swales, sealed bioretention) even though water ultimately discharges via pipes.

On partially contaminated sites, consider whether remediation allows infiltration in clean areas whilst sealed drainage serves contaminated zones. The cost of limited remediation might be justified by improved drainage performance and BREEAM credits.

Maintenance Agreement Timing Problems

Surface water credits require maintenance agreements at final BREEAM assessment, not just design intentions or draft agreements. For developments with phased handovers, this creates timing challenges. You cannot achieve final certification until agreements are legally complete.

For residential developments, this means:

• Management company formed with specifications in place

• Section 38/104 adoption agreements signed with authorities

• Homeowner guidance prepared and ready for handover packs

For commercial developments:

• Facilities management contracts including SuDS maintenance

• Adoption by local authority or water company confirmed

• Long-term maintenance funding secured

Start these arrangements early. Local authorities and water companies often take months to finalise adoption agreements. Leaving this to practical completion risks delaying BREEAM certification.

Climate Change Factor Application Errors

Climate change allowances apply to post-development calculations only, not pre-development baselines. This is logical—you're assessing future flood risk and drainage capacity—but it's frequently calculated incorrectly in BREEAM submissions.

Pre-development run-off represents historical site conditions without climate change. Post-development run-off includes climate change because your development will operate under future climate conditions. This means your attenuation must cope with more intense rainfall than the site experienced historically.

The specific percentage increase varies by location, development lifetime, and acceptable risk. For developments across most of England designed to 2080s, apply:

• +40% to peak river flows for fluvial flood risk

• +20% to +40% to peak rainfall intensity for surface water drainage (varies by catchment)

Check Environment Agency guidance for your specific location. Upland catchments often have different factors than lowland areas. Coastal sites have different allowances than inland sites.

Expert Support for Pol 03

Pol 03 requires specialist technical input that architects and general engineers typically don't provide. You need professionals with specific expertise in flood risk assessment and sustainable drainage design.

Flood Risk Assessment Expertise:

Your flood risk consultant should be a chartered engineer or equivalent with demonstrable flood risk experience. They need familiarity with:

• Environment Agency flood mapping and how to interpret it

• Hydraulic modelling of flood flows and levels

• Climate change allowance application

• Local planning policy requirements

• BS 8533:2017 resilience hierarchy

They should understand the difference between EA indicative mapping and site-specific risk. They should recognise when detailed hydraulic modelling is required rather than desktop assessment.

Sustainable Drainage Design:

Your SuDS consultant needs the competencies BREEAM specifies: capability to champion SuDS within overall design, knowledge of infiltration-based solutions, experience with treatment train design, and ability to produce robust hydraulic calculations following CIRIA C753.

This might be a chartered engineer with drainage specialism, a landscape architect with specialist SuDS training, or a civil engineer focusing on sustainable water management. Professional membership (ICE, CIWEM, Landscape Institute) provides evidence of competence, though specific drainage experience matters more than job title.

They should understand:

• Infiltration testing and interpretation

• SuDS Manual C753 methodology

• Hydraulic modelling software

• Treatment train design for water quality

• Integration with landscape architecture

• Long-term maintenance requirements

Integrated Approach:

Many flood risk consultants also provide SuDS design, which often delivers better outcomes. Using one consultant for both ensures:

• Consistent climate change assumptions across assessments

• Integrated solutions addressing both flood resilience and drainage

• Coordinated evidence for BREEAM submission

• Reduced risk of conflicting recommendations

• Single point of contact for the design team

For our clients, we provide this integrated service. Our CIWEM-qualified consultants deliver flood risk assessments and SuDS design from project inception, ensuring drainage strategy develops alongside architecture rather than being retrofitted later.

Related BREEAM Credits

LE 04 Ecological Change and Enhancement: Well-designed SuDS features contribute to biodiversity credits through habitat creation, native planting, and blue-green infrastructure provision.

Wst 05 Adaptation to Climate Change: Flood resilience measures demonstrate climate adaptation, contributing to this waste category credit through design for changing conditions.

Hea 07 Safe and Healthy Surroundings: Flood risk management and safe drainage design contribute to creating healthy surroundings free from flooding hazards.

Pol 03 Frequently Asked Questions

Can I achieve Pol 03 credits if my site is in Flood Zone 3?

Yes, provided you're not in the functional floodplain (Zone 3b). Sites in Zone 3a achieve 1 flood risk credit rather than 2 by implementing comprehensive resilience measures. You need demonstrating either 600mm freeboard above design flood level or a BS 8533:2017 compliant strategy addressing building fabric, services, and emergency access. Your site-specific FRA must show residual risks are properly managed and the development is appropriate for this location.

What if our sewerage undertaker won't accept greenfield discharge rates?

BREEAM expects following the SuDS hierarchy and minimising discharge where possible. If your local authority or sewerage undertaker specifies particular discharge rates through planning conditions or adoption agreements, provide their formal written requirements. BREEAM will assess against those requirements rather than standard benchmarks, but all other criteria still apply—treatment, maintenance agreements,

climate change allowances, and SuDS hierarchy justification.

Do we need separate consultants for flood risk and drainage?

Not necessarily. Many flood risk consultants also provide drainage design, which often works well as it ensures consistent climate change assumptions and integrated solutions. The key requirement is demonstrable competence. BREEAM specifies required skills and experience, not job titles. Whether you use one consultant or two, ensure they have appropriate qualifications and experience for their respective disciplines. Using one consultant for both often reduces coordination issues and conflicting recommendations.

Can rainwater harvesting help achieve surface water credits?

Yes. Rainwater harvesting reduces run-off volume by capturing roof water for reuse, contributing to volume reduction credits. Systems must be designed to BS EN 16941-1:2018 standards. However, your exceedance flow routes must be sized assuming the harvesting system is unavailable—it might be full when a storm arrives. Don't rely on harvesting tanks as your flood protection strategy; they're one component of a comprehensive SuDS approach.

How detailed do hydraulic calculations need to be?

BREEAM expects professional-standard drainage design using recognised modelling software—MicroDrainage, InfoWorks ICM, or equivalent. Your calculations must show:

• Pre-development run-off rates and volumes (1-year and 100-year events)

• Post-development rates with climate change applied

• Attenuation storage volumes and locations

• Discharge rates at each outfall

• Infiltration assumptions and test results

• Treatment provision and specifications

Hand calculations don't satisfy BREEAM requirements beyond very simple single-dwelling projects. For commercial developments, residential schemes, or anything with multiple buildings, professional hydraulic modelling is essential.

Get Expert Help with Pol 03

Achieving all 5 Pol 03 credits requires proper flood risk assessment and sustainable drainage design from project inception. Our CIWEM-qualified consultants provide integrated solutions addressing flood resilience and surface water management together, ensuring consistent climate change assumptions and coordinated design responses.

We work alongside your design team from feasibility stage, developing SuDS strategies that integrate with landscape architecture whilst maximising BREEAM credits. Our assessments serve dual purpose—satisfying statutory consultees for planning permission whilst providing the specific technical evidence BREEAM assessors require for certification.

Based in London and operating throughout Kent, Essex and Scotland, we deliver rapid turnaround for developments requiring BREEAM assessment support. Professional indemnity insurance exceeds £5 million, and we maintain robust quality assurance procedures for all technical work.

Contact us to discuss your project's Pol 03 requirements and how we can help maximise your BREEAM rating through expert flood risk and drainage assessment.