Sustainable drainage approval bodies in Wales

This article covers Wales only. Schedule 3 to the Flood and Water Management Act 2010 came into force in Wales on 7 January 2019. Since then, construction work in Wales on an area of 100m² or more, or involving one or more houses, needs approval of its surface water drainage from a SuDS Approving Body before work starts. The SAB is the unitary authority in its role as lead local flood authority. It is a separate consent from planning permission, with its own application, its own standards and its own determination period, and no equivalent exists in England, where Schedule 3 has never been brought into force and drainage is handled through planning conditions instead.

Developers who treat SAB approval as a condition to discharge after permission lose weeks. It is a consent in its own right, and it has to be in place before work starts.

What Schedule 3 requires in Wales

Schedule 3 makes the drainage system the subject of an approval rather than a planning judgement. The SAB assesses the design against national statutory standards published by the Welsh Government, approves or rejects it, and then has a duty to adopt drainage that serves more than one property once it has been built and checked.

That adoption duty is the structural difference from England. In England a management company or a resident-owned arrangement usually ends up maintaining the basin in perpetuity. In Wales, systems that meet the standards and serve more than a single property pass to the SAB, which changes the whole-life cost conversation and the way the layout is drawn.

The trade-off is that the SAB is buying a liability, so it scrutinises construction detail, access for maintenance vehicles, and long-term silt management with more care than a planning officer would.

The threshold and what counts as construction work

The trigger is construction work with drainage implications on an area of 100m² or more, or construction of one or more houses. Read "area" as the area of the construction work rather than the site area, which catches a surprising number of commercial hardstanding and yard projects that were never thought of as development with a drainage dimension.

Some work is outside the regime, including certain highway drainage and single-building projects below the threshold. A change of use with no construction work does not engage it. Where a scheme is phased, each phase needs its own approval, and the phasing plan has to be agreed early because the interim drainage arrangements for phase one have to work while phase two is a building site.

The statutory standards and how they are applied

The Welsh Government standards run in a hierarchy, and the SAB works through them in order:

• The destination of surface water runoff, following a hierarchy that puts infiltration and discharge to a watercourse well ahead of any connection to a sewer.
• Hydraulic control, covering runoff rates and volumes against greenfield or existing rates, with allowances for climate change.
• Water quality, sized by the pollution risk of the contributing surface rather than by a single blanket treatment train.
• Amenity, meaning the drainage has to contribute something to the place rather than sit behind a fence.
• Biodiversity, which overlaps with the habitat work but is assessed here as a drainage standard.
• Design for construction, operation, maintenance and structural integrity across the design life.

The amenity and biodiversity standards are where English design teams come unstuck. A deep-sided attenuation basin in a corner, fenced off, satisfies the hydraulic standard and fails two others. Rethinking that at SAB stage means redrawing the plot layout, which means a planning amendment, which means the programme slips twice.

Infiltration testing is the other early task. Without ground investigation results, the drainage hierarchy cannot be evidenced, and a SAB is entitled to reject a design that assumes a sewer connection without demonstrating that infiltration was tested and ruled out.

Running SAB approval alongside planning permission

The two consents are legally independent, which is an opportunity rather than a problem. The drainage layout that satisfies the SAB has to be the same layout shown on the approved planning drawings, so the sequencing matters more than the order.

1. Do the ground investigation and infiltration testing before the layout is fixed.
2. Design the drainage into the masterplan, with the attenuation features as usable space rather than leftovers.
3. Hold a pre-application discussion with the SAB. Most Welsh authorities offer one, and it costs far less than a rejection.
4. Submit the planning application with a drainage layout you are confident the SAB will approve.
5. Submit the SAB application in parallel or immediately after, rather than waiting for the decision notice.
6. Reconcile any changes required by either body across both sets of drawings before construction.

Foul drainage runs on a third track again, through the sewerage undertaker's adoption process, so a Foul Sewage Assessment and the surface water case need to be consistent about connection points and capacity.

Adoption, maintenance and the construction bond

Adoption is not automatic on completion. The SAB inspects against the approved drawings, and it can require a bond or other security to cover the cost of finishing the system if the developer fails partway through. Budget for that as a cash-flow item.

Between practical completion and adoption there is a maintenance period, during which the developer keeps the system working and the planting establishes. Poorly specified planting is a common reason adoption is delayed, because a basin that has not vegetated does not deliver the water quality or biodiversity performance that was approved.

Keep as-built records. Manholes that moved 300mm on site, a flow control that was substituted for an equivalent, a headwall built to a different detail: each of those needs recording and agreeing, or adoption stalls while someone surveys the site again.

Timescales and the things that cause delay

The statutory determination period for a SAB application is seven weeks for most schemes, and longer where an environmental statement accompanies the proposal. Check the current period and the extension arrangements with the authority, since an agreed extension in writing is common on larger sites.

What actually causes delay is rarely the SAB. It is missing infiltration data, a layout that cannot accommodate the features the standards require, unresolved third-party land for an outfall, or a discharge consent from the watercourse owner that nobody chased. Outfall rights in particular can take months and sit entirely outside the consenting process.

Designing to avoid a rejection

Treat the drainage designer as part of the masterplanning team from the first layout, not a consultant who tidies up afterwards. Evidence the hierarchy properly, with test results and dates. Size the treatment train against the actual risk of each surface. Show maintenance access for a vehicle to every structure. And give the attenuation features a second function, whether that is public open space, a play setting or a habitat corridor, because that is what the amenity and biodiversity standards are asking for.

Where a scheme in Wales also needs a flood case, the Flood Risk Assessment work follows Welsh national policy and Technical Advice Note 15 rather than the English sequential and exception tests, and the comparison with the avoidance principle under NPF4 in Scotland shows how far the three frameworks have diverged.

PlanScope can produce an AI-assisted draft Drainage Strategy to support the planning application, and its drafting is grounded in English national policy and local plans, so a Welsh scheme needs the reviewer to check Planning Policy Wales, the statutory SuDS standards and the SAB's own guidance. PlanScope does not produce the SAB application itself. Reports should be reviewed before submission, and PlanScope does not guarantee planning approval. For specialist technical reports, qualified professional input may be required. This is general guidance, not legal advice; check the position with the relevant authority or a qualified professional before relying on it.