Glossary of Terms: Flooding, Drainage, Sustainable Drainage, Natural Flood Management, and Property-Level Flood Resilience

• Attenuation – The slowing down or reduction of the peak flow of water. In drainage systems, this means temporarily storing water to reduce the risk of flooding downstream.

• Amphibious House – A building designed to sit on the ground under normal conditions but float during flooding, using guideposts and flexible connections.

• Blue-Green Infrastructure – A network of natural and semi-natural features (like parks, ponds, and swales) designed to manage water sustainably and provide environmental benefits.

• Bund – An embankment built to contain or direct water, used as a flood defence.

• Catchment – The area of land where rainfall collects and drains into a river, lake or other body of water.

• Combined Sewer System – A drainage system where surface water (from rain) and foul water (from toilets, sinks) share the same pipes. Common in older urban areas and prone to overflows during heavy rainfall.

• Detention Basin – A dry basin designed to temporarily store stormwater and release it slowly. Often used in SuDS.

• Exceedance Flow – Water that exceeds the design capacity of a drainage or flood management system, needing controlled overland flow paths to minimise damage.

• Floodplain – The natural area adjacent to a river that floods when the river overflows. Can be used intentionally for flood storage.

• Flood Resistance – Measures that prevent water from entering a property, such as flood doors and airbrick covers.

• Flood Recoverability (or Resilience) – Measures inside a property that minimise damage if water enters, such as waterproof flooring or raised electrics.

• Foul Drainage – The system of pipes that carries wastewater from toilets, sinks, showers, and washing machines to a treatment facility or sewer.

• Green Roof – A roof covered with vegetation that absorbs rainwater and reduces runoff.

• Infiltration – The process of water soaking into the ground. SuDS often encourage this to reduce runoff.

• Leaky Dam – A natural flood management feature made from logs or brushwood that slows the flow of water in a stream, allowing it to back up and infiltrate.

• Natural Flood Management (NFM) – Using natural processes and features (like wetlands, woodland, and leaky dams) to slow, store and filter water in the landscape.

• Non-Return Valve (NRV) – A valve that allows water to flow one way (out of a property) and prevents it from flowing back in, often used in sewers and drains.

• Permeable Paving – Surfaces that allow rainwater to soak through into the ground, reducing runoff.

• Property Flood Resilience (PFR) – Measures taken at the household level to reduce flood risk and damage, both outside (barriers, doors) and inside (resilient finishes, raised services).

• Rain Garden – A shallow planted depression that collects and filters rainwater from roofs or paving.

• Retrofit – The addition of new flood or drainage measures to existing buildings or infrastructure.

• Smart Airbrick – An airbrick that seals automatically when submerged to prevent floodwater entering through ventilation gaps.

• Airbrick – A vent, usually located low on external walls, that allows air to circulate under floors. Can be a flood entry point if not protected.

• Soakaway – An underground pit filled with gravel or crates that allows rainwater to drain slowly into the ground.

• Storm Overflow – The release of untreated sewage and rainwater into rivers or the sea when combined sewers are overwhelmed.

• SuDS (Sustainable Drainage Systems) – A set of techniques that mimic natural drainage to manage rainwater close to where it falls. Includes features like swales, rain gardens, ponds, and permeable surfaces.

• Surface Water Flooding – Flooding caused by heavy rainfall overwhelming drains and flowing over land.

• Swale – A shallow, vegetated channel that slows and filters rainwater runoff.

• Washland – An area (often rural) that is intentionally allowed to flood during high river flows to protect downstream areas.

• Wetland – A low-lying area saturated with water, either permanently or seasonally, that can absorb floodwater and filter pollutants.

• Water Square / Floodable Plaza – A public space designed to temporarily store stormwater during intense rainfall while functioning as a recreational area during dry weather.

• Woodland Creation (for NFM) – Planting trees and restoring woodlands to slow runoff and improve water infiltration in a catchment.

• Downspout – A vertical pipe attached to gutters that channels rainwater from the roof to the ground or drainage system.

• Water Butt – A container used to collect and store rainwater from roofs for later use, such as watering gardens.

• Flow Control – A device used to regulate the rate at which water is released from storage areas like ponds or tanks to prevent overwhelming downstream drainage.