How does urbanisation change drainage and generate waste, and how are these managed?
The impact of urbanisation on catchment hydrology and flood risk; sustainable urban drainage systems and river restoration; the generation of urban waste; and the options and issues of urban waste disposal.
A focused answer to the AQA A-Level Geography 3.2.3 content on urban drainage and waste, covering the impact of urbanisation on catchment hydrology and flood risk, sustainable urban drainage systems and river restoration, urban waste generation, and waste disposal options and issues.
Reviewed by: AI editorial process; not yet individually human-reviewed
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What this dot point is asking
AQA section 3.2.3 wants you to explain how urbanisation changes catchment hydrology and flood risk, the role of Sustainable Urban Drainage Systems (SUDS) and river restoration, the generation of urban waste, and the options and issues of waste disposal. It links the urban topic back to the water cycle and forward to sustainability.
Urbanisation, hydrology and flood risk
The result is that intense rainfall over a city produces faster, higher flood peaks than the same rainfall over countryside, and surface-water (pluvial) flooding becomes a serious urban hazard.
SUDS and river restoration
To counter this, cities increasingly use Sustainable Urban Drainage Systems (SUDS):
SUDS slow and store runoff, lengthening lag time and lowering the peak, while improving water quality (filtering pollutants) and adding amenity and biodiversity. River restoration and conservation (re-naturalising channels, removing culverts, re-creating floodplain storage) reverse past hard engineering. Both need space and maintenance, but are more sustainable than simply moving water away faster.
Urban waste generation
Cities generate large and rising volumes of waste: solid (household, commercial, construction), liquid (sewage, industrial effluent) and atmospheric (emissions). Affluent, high-consumption cities produce the most waste per person, while rapidly growing cities in the developing world struggle with collection and disposal capacity.
Waste disposal options and issues
Each disposal route has trade-offs:
- Landfill: cheap and simple, but uses land, generates methane (a greenhouse gas) and leachate (contaminating groundwater), and is filling up.
- Incineration: reduces volume and can recover energy (energy-from-waste), but emits pollutants and discourages recycling.
- Recycling, re-use and recovery: cut the volume needing disposal and conserve resources, but depend on participation, collection systems and end markets.
The waste hierarchy (reduce, re-use, recycle, recover, then dispose) sets the sustainable order, prioritising reducing waste at source over end-of-pipe disposal.
Try this
Q1. Explain why urbanisation increases peak discharge. [3 marks]
- Cue. Impermeable surfaces cut infiltration and raise runoff; drains deliver it quickly, shortening lag time and raising the flood peak.
Q2. Define Sustainable Urban Drainage Systems. [2 marks]
- Cue. Systems that manage rainwater near where it falls (permeable paving, swales, ponds, green roofs) to slow runoff, reduce flooding and improve water quality.
Q3. Outline one advantage and one disadvantage of landfill. [3 marks]
- Cue. Advantage: cheap and simple. Disadvantage: uses land and produces methane and leachate that pollute groundwater.
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 2019 (style)6 marksExplain how urbanisation increases flood risk within a drainage basin.Show worked answer →
A 6 mark "explain" question (AO1) linking to the water cycle. Urbanisation replaces permeable vegetated ground with impermeable concrete, tarmac and roofs, so infiltration falls and surface runoff rises.
Drains, gutters and culverts deliver this runoff to rivers quickly and efficiently, shortening lag time and raising peak discharge on the storm hydrograph. Removing vegetation also cuts interception and evapotranspiration. The result is a flashier hydrograph and a higher, faster flood peak, especially after intense rainfall.
Markers reward the chain: impermeable surfaces and drains cut infiltration and speed runoff, shortening lag time and raising the peak, increasing flood risk. Top answers link this directly to the storm hydrograph from the water-cycle topic.
AQA 2021 (style)9 marksAssess the effectiveness of strategies to manage urban drainage and waste.Show worked answer →
A 9 mark "assess" question (AO1 plus AO2): reach a judgement. Drainage: traditional hard drainage moves water away fast but can transfer flooding downstream; Sustainable Urban Drainage Systems (SUDS) (permeable surfaces, swales, retention ponds, green roofs) and river restoration slow runoff, improve water quality and add amenity and biodiversity, but need space and maintenance.
Waste: landfill is cheap but produces methane and leachate and uses land; incineration reduces volume and recovers energy but emits pollutants; recycling, re-use and recovery cut waste but depend on participation and markets.
The judgement: the most effective approach is the sustainable hierarchy, reduce, re-use, recycle, recover, dispose, paired with SUDS and restoration, rather than relying on landfill and hard drainage; effectiveness depends on funding, space and behaviour. Reward a calibrated conclusion with named methods.
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Sources & how we know this
- AQA A-level Geography (7037) specification — AQA (2016)