Key Terms: Urban Drainage (AQA A Level Geography): Revision Note

Urban precipitation - key terms

Condensation nuclei – Small particles like dust and pollutants in urban air that promote condensation, increasing precipitation.

Evapotranspiration (EVT) – The combined process of water evaporating from surfaces and transpiring from plants; reduced in urban areas due to less vegetation.

Impermeable surfaces – Roads, pavements, and buildings that prevent infiltration and increase surface runoff.

Overland flow (surface runoff) – Water that flows over the ground surface, dominant in cities due to impermeable surfaces.

Pollution dome – A layer of polluted air over a city that traps heat and moisture, enhancing rainfall and thunderstorms.

Thunderstorms – More frequent in urban areas due to higher temperatures and uplift from built structures.

Urban heat island – A phenomenon where urban areas are warmer than surrounding rural areas, contributing to increased rainfall.

Urban hydrograph – A "flashy" hydrograph with short lag time, steep rising limb, and high peak discharge, caused by rapid runoff and low infiltration.

Urban water cycle – Modified by urbanisation, with reduced infiltration and storage, and increased runoff, transfers, and artificial inputs and outputs.

Drainage management - key terms

Catchment management – A holistic approach to managing the entire river basin to reduce flooding, drought, and pollution while improving ecosystems.

Channelisation – The engineering of rivers with straight channels and artificial linings (e.g. concrete) to speed up flow and reduce flood risk.

Floodplain zoning – Restricting development in flood-prone areas to reduce flood damage and maintain natural floodplains.

Hard engineering – Physical constructions like levees, dams, and concrete embankments to control water flow and reduce flooding.

Levees – Raised embankments (natural or artificial) used to increase river channel capacity and prevent overflow.

River straightening – Altering a river’s natural course to improve flow rate and reduce meandering; may increase erosion downstream.

Soft engineering – Using natural processes and materials (e.g. afforestation, wetland restoration) to manage water sustainably.

SuDS (Sustainable Drainage Systems) – Drainage methods that mimic natural processes to manage rainfall and improve water quality.

Swales – Shallow, vegetated channels used in SuDS to slow runoff and provide recreational green space.

Green roofs – Vegetated rooftop systems that increase evapotranspiration and reduce runoff.

Infiltration basins – Depressions that allow water to soak into the ground, reducing surface runoff.

Rain gardens – Shallow planted areas that slow and filter stormwater while creating green space.

Retention ponds – Permanent water bodies designed to store excess stormwater and improve water quality.

Permeable surfaces – Surfaces that allow water to pass through, reducing runoff and filtering pollutants.

River restoration - key terms

Conservation – Protecting and preserving natural environments, including river systems, to support biodiversity and ecosystem function.

Dam removal – Part of river restoration aimed at restoring natural flow, reducing evaporation, and improving aquatic connectivity.

Meander reintroduction – Recreating natural bends in rivers to slow water flow and reduce erosion.

Natural wetlands – Reinstated floodplains and marshlands that store water and reduce flood risk while supporting wildlife.

Partial restoration – Restoring some aspects of a river’s natural function and form where full restoration is not possible due to urban constraints.

Restoration – Returning a river or landscape to its original, natural state by removing previous human modifications.

Stakeholder conflict – Tensions between different groups, such as farmers and conservationists, regarding land use and river management.