The SWDC represents a proportionate contribution towards the increased maintenance and management costs arising from new impermeable surfaces within an Internal Drainage District. SWDC is based upon the net increase in impermeable area over an assumed development lifespan of 100 years and is influenced by factors such as pre-development greenfield run off rates for various rainfall events and whether the site falls within a pump-served or gravity discharge catchment. The charge is designed to ensure that most of the Board’s costs of dealing with the surface water legacy of developments are met.

SWDC is levied on applicants with projects falling into the following categories:

• Windfall development (sites of 2-9 houses).
• Large scale development (10 or more houses).
• Commercial development on greenfield sites.
• Commercial development on brownfield sites resulting in net increase in runoff.
• Infrastructure projects on greenfield sites.
• Infrastructure projects on brownfield sites resulting in net increase in runoff.