Design Workflow Tutorial

Establish Baseline

Calculate the greenfield runoff rate for your site, the peak discharge rate as if the site were entirely undeveloped. This is the anchor point for all downstream calculations and the compliance benchmark for S3.

Define Discharge Strategy

Determine your preferred runoff destination following the S1 hierarchy: harvesting for reuse, infiltration to ground, surface water discharge, or sewer discharge. Assess site constraints (soil infiltration capacity, groundwater proximity, receiving watercourse availability) to establish which destinations are feasible.

Consult with statutory bodies (Environment Agency, LLFA, sewerage undertaker) and review site investigation data to guide your S1 hierarchy decision.

Manage Everyday Rainfall

Design features to achieve S2 compliance: at least 5 mm of rainfall from the site must be captured, infiltrated, or evaporated without resulting in runoff. Calculate interception storage requirements for green roofs, rainwater harvesting tanks, permeable pavements, swales, or bioretention.

Size Attenuation Storage

Calculate storage volume and orifice (outlet) sizing for detention basins, retention ponds, and other attenuation features to meet S3 discharge limits: 50% AEP and 1% AEP events, including climate change uplifts and urban creep adjustments.

Assess Water Quality

Design a treatment train using the Simple Index Approach to achieve S4 compliance. Identify the site's pollution hazard, select SuDS features with appropriate treatment efficiency, and demonstrate that the combined train achieves adequate removal of sediments, metals, and hydrocarbons.

Design Individual Components

Now that the overall strategy is set (S1–S5), design each individual SuDS component to detailed engineering standard. Sizing, materials, construction details, and maintenance access requirements must be specified.

Size Building Drainage

Design the guttering and downpipe system for the building itself, sized to convey the design rainfall to collection points or downpipe outlets. Building drainage is distinct from site SuDS but must interface correctly.

Full Compliance Audit

Once all components are sized and integrated, conduct a master compliance check against all seven National Standards (S1–S7). Confirm that the overall design strategy meets S1 (hierarchy), S2 (interception), S3 (peak discharge), S4 (water quality), S5 (amenity), S6 (biodiversity), and S7 (constructability and maintenance). Generate a planning submission PDF documenting compliance with evidence and calculations.