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Component Design CIRIA C753 §15

Filter Strip Calculator

CIRIA C753 §15: vegetated filter strip sizing for treatment and pre-treatment.

1 Source & Flow
2 Strip Design
3 Results

Step 1: Source Area & Flow

Project Information

Total area of roads, car parks, roofs etc.
Length of strip perpendicular to sheet flow
Typical lowland UK values for SAAR ~700 mm (FSR Vol II / FEH22). For detailed design, override with site-specific FEH22 DDF lookup.
Source: EA May 2022 Climate Change Allowances Table 3 (peak rainfall intensity, surface water). Choose by time horizon + band: 2050s central 20 % / higher 25 % / upper 35 %, 2080s central 25 % / higher 30 % / upper 40 %, for 3.3 % AEP (30-year) sizing. For 1 % AEP (100-year) use the higher column (e.g. 2080s upper = 50 %). Check EA guidance for your river-basin district.
Typical range: 1–5%
Auto-calculated from land use

Step 2: Strip Design

Minimum 5m recommended, 6m for roads. Wider = better treatment.
Ideal range: 2–5%
Optional. Leave blank for none. 20m typical for slopes >3%.

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