SuDS (General)
Key Benefits
- Water Management: Conveyance; Attenuation (esp. with check dams); Water Quality Improvement (TSS, Nutrients, Metals via filtration/sedimentation); Infiltration (if unlined); Interception. (C753 Ch 3, Ch 4, Ch 15, Ch 17)
- Environmental: Carbon Sequestration & Storage; Potential for Urban Cooling (evapotranspiration).
- Biodiversity: Creates linear habitat (grassland, wetland edge); Supports invertebrates, potentially amphibians/reptiles; Improves habitat connectivity. (C753 Ch 6; GI Guide)
- Amenity: Enhances landscape/streetscape visual quality; Can be integrated with paths/recreation areas. (C753 Ch 5; GI Guide)
- Metrics: Rainwater Runoff Retained: 69%; Stormwater Runoff Delay: 57%; Water Quality Improvement (TSS, NO3, P - variable); Carbon Sequestered: 0.27 kg/m²/yr; Carbon Stored: 3.05-5.04 kg/m²; Amenity & Biodiversity Enhancement; Property Value Uplift (Nearby Water): 0.9-3.6%.
Technical Guidance
Filter Strips (C753 Ch 15)
Function: Pre-treatment via filtration/sedimentation for sheet flow from adjacent impermeable areas (roads, car parks). Some infiltration/Interception.
Design: Gentle slope (1-5%, 1:100-1:20), dense vegetation (grass). Min. 5m flow path for treatment (C753 S15.5). Requires level spreader inlet for sheet flow (C753 S15.8.1), ensure min. 50mm drop from hard surface to prevent sediment blocking inflow.
Maintenance: Regular mowing, sediment removal from upstream edge (C753 S15.12).
Swales (C753 Ch 17)
Function: Conveyance, attenuation, treatment (filtration/sedimentation), infiltration (if unlined), biodiversity. Types: Conveyance, Dry/Enhanced (underdrained), Wet.
Design: Shallow, broad channel (base 0.5-2m typ.), gentle longitudinal slope (0.5-3% typ., max 6%). Use check dams >3% slope (C753 S17.2, S17.9.2) to slow flow, increase residence time & infiltration. Side slopes max 1:3 for maintenance/safety (C753 S17.2). Ensure capacity for design flow (e.g., 1:30yr) & safe exceedance (Ch 24.12). Underdrains for slopes <1.5% or poor infiltration (dry swale - C753 S17.1.2). Wet swales for flat sites/high water table (C753 S17.1.3).
Treatment: Requires flow velocity <0.5 m/s & residence time >9 mins for water quality event (C753 S17.4.1).
Vegetation: Dense grass cover essential (C753 S17.10). Species tolerant of periodic inundation (dry swales) or permanent wetness (wet swales). Native species enhance biodiversity (GI Guide).
Maintenance: Regular mowing (dry swales), vegetation management (wet swales), inspection/clearing of inlets/outlets/check dams, sediment removal (C753 S17.12).
General Considerations (C753 & GI Guide)
Assess site suitability (slope, soils, groundwater - C753 Ch 8). Integrate into landscape design and GI network. Protect during construction (C753 Ch 31). Ensure correct soil specification/handling (C753 Ch 29.5, Ch 30.4). Design inlets/outlets carefully (C753 Ch 28). Consider long-term management (C753 Ch 32).