VCE Environmental Science (Year 11) · Unit 2 — Pollution, Food and Water Security · 16m read

Water Systems and Management

Ever wondered why water shortages happen in some places while others have plenty? You'll explore how water actually moves through our planet (the water cycle), how human activities strain these systems, and what strategies—from dam building to recycling—can help us use water more wisely. This matters for your VCE studies and your future, since water security is shaping everything from agriculture to where people can live.

Learning objective: Analyse water systems, the water cycle, and evaluate strategies for sustainable water management.

By the end of this lesson you can:

• I can describe the water cycle and explain how human activities disrupt it.
• I can analyse causes and effects of water scarcity, flooding, and water pollution.
• I can evaluate water management strategies including dams, desalination, and water recycling.

Water systems are a leaky bucket. Rain fills it; overuse, pollution and drought punch holes.

Water systems, disruption, and management

### The water cycle

Water cycles continuously through the Earth system:

Evaporation: Solar energy converts liquid water (from oceans, lakes, rivers) to water vapour. Oceans contribute ~86% of evaporation.

Transpiration: Plants release water vapour through their leaves. A single large eucalyptus tree can transpire 200+ litres per day.

Condensation: Water vapour cools and forms clouds (tiny water droplets or ice crystals around particulate nuclei).

Precipitation: Water returns to Earth as rain, snow, sleet, or hail.

Infiltration: Water soaks into soil and rock, recharging groundwater (aquifers).

Runoff: Water flows over land surface into rivers, lakes, and eventually oceans.

### Human disruption of water systems

Over-extraction: Groundwater pumped faster than it recharges → water table falls → wells dry up → land subsidence. Murray-Darling Basin: over-allocation for irrigation.

Land clearing: Reduces transpiration and interception → increased runoff → reduced infiltration → water table rises → salinisation.

Urbanisation: Impervious surfaces (concrete, asphalt) prevent infiltration → increased runoff → flooding → reduced groundwater recharge.

Pollution: Agricultural runoff (nutrients, pesticides), industrial discharge, sewage → water quality degradation.

Climate change: Altered precipitation patterns — some regions drier, others wetter. More intense rainfall events but less total rainfall. Earlier snowmelt → reduced summer water supply.

### Water management strategies

Dams and reservoirs: Store water for supply and flood control. Advantages: reliable supply, hydroelectric power. Disadvantages: disrupts river ecology, displaces communities, traps sediment, evaporation losses.

Desalination: Removes salt from seawater (reverse osmosis). Advantages: unlimited source. Disadvantages: energy-intensive, brine discharge, expensive.

Water recycling: Treating wastewater for reuse (irrigation, industrial, or potable). Australia leads in recycled water use. Reduces demand on freshwater sources.

Rainwater harvesting: Collecting rainwater from roofs. Simple, low-cost, reduces stormwater runoff.

Demand management: Water restrictions, pricing signals, efficient appliances, drought-resistant landscaping. Reduces consumption without increasing supply.

Quick reference

| Issue | Response |
|---|---|
| Over-allocation | Murray–Darling Basin Plan |
| Salinity | Revegetation |
| Pollution | Riparian buffers |
| Scarcity | Recycling, desalination |
| Water cycle | Evaporation, condensation, precipitation |

Key ideas at a glance

• Catchment management: Whole system.
• Environmental flows: River health.
• Water quality indicators: pH, turbidity, DO.
• Equity: Shared use.

Worked example (Medium)

Explain how urbanisation disrupts the natural water cycle in a catchment.

1. Natural system. In a forested catchment: rainfall is intercepted by vegetation canopy → slowed → infiltrates soil → recharges groundwater → flows slowly to streams. Transpiration returns water to atmosphere. Runoff is slow and filtered.
2. Urbanised system. Impervious surfaces (roads, roofs, car parks) cover 50-90% of urban areas. Rainfall cannot infiltrate → rapid surface runoff via stormwater drains → directly to waterways.
3. Effects. Increased flood risk (rapid runoff peaks). Reduced groundwater recharge (less infiltration). Reduced baseflow to streams (less groundwater feeding rivers between rain events). Water quality decline (stormwater carries pollutants: oil, litter, heavy metals). Altered stream ecology (flashy hydrology, erosion, habitat loss).
4. Management. Water-sensitive urban design (WSUD): permeable pavements, rain gardens, detention basins, green roofs — mimicking natural infiltration and slowing runoff.

Answer: Urbanisation converts infiltration to runoff, disrupting groundwater recharge, increasing flooding, and degrading water quality. WSUD aims to restore natural water cycle processes in urban areas.

Worked example (Hard)

Evaluate desalination as a strategy for water security in Australia.

1. What it does. Reverse osmosis forces seawater through semi-permeable membranes, separating fresh water from salt. Australia has major desalination plants in Perth, Melbourne, Sydney, Adelaide, and Gold Coast.
2. Advantages. Climate-independent: unlike dams and rivers, desalination isn't affected by drought. Unlimited source: the ocean. Provides water security as a supplement to rainfall-dependent supplies. Crucial during the Millennium Drought (2001-2009) when dam levels fell below 30%.
3. Limitations. Energy-intensive: ~3-4 kWh per cubic metre of water (vs ~0.5 kWh for conventional treatment). Carbon emissions unless powered by renewables. Brine discharge: concentrated salt water returned to ocean may affect local marine ecosystems. Cost: $1-2 per cubic metre vs $0.20-0.50 for conventional supplies.
4. Evaluation. Desalination is valuable as insurance against climate variability but should not be the primary supply strategy due to energy cost and environmental impact. Best used as part of a diversified portfolio: dams + recycling + rainwater + demand management + desalination.

Answer: Desalination provides climate-independent water security but at significant energy and environmental cost. It is most effective as one element of a diversified water supply strategy.

Common mistakes

• Thinking the water cycle is only evaporation and rain This is a common error. Fix: The water cycle includes evaporation, transpiration, condensation, precipitation, infiltration, runoff, groundwater flow, and ocean currents. Human activities disrupt multiple processes simultaneously.
• Confusing water scarcity with water quality This is a common error. Fix: A region can have abundant water that is too polluted to use, or very clean water in insufficient quantity. Both are water management challenges, but with different causes and solutions.
• Treating dams as purely beneficial This is a common error. Fix: Dams provide reliable supply but disrupt river ecology (block fish migration, alter flow regimes, trap sediment), displace communities, and cause evaporation losses. Always discuss both benefits and costs.

Virtual water — the hidden water footprint

Virtual water is the water used to produce goods and services. A kilogram of beef requires ~15,400 litres of water (growing feed, drinking water, processing). A cotton T-shirt: ~2,700 litres. A cup of coffee: ~140 litres. When Australia exports agricultural products, it is effectively exporting water. When it imports manufactured goods, it is importing virtual water. Understanding virtual water reveals the true scale of water consumption — and shows that water management is a global, not just local, challenge.

Practice questions

1. Urbanisation primarily disrupts the water cycle by:

   1. Increasing evaporation
   2. Replacing permeable surfaces with impervious ones, reducing infiltration and increasing runoff
   3. Increasing transpiration from urban trees
   4. Reducing precipitation

   (1 marks)

2. Explain how land clearing contributes to both water table rise and reduced river flows in the Murray-Darling Basin.

   (3 marks)

Summary

• Water cycle: evaporation → condensation → precipitation → infiltration/runoff → groundwater → back to cycle.
• Human disruption: over-extraction, land clearing (salinity), urbanisation (runoff), pollution, climate change.
• Management: dams (reliable but ecological cost), desalination (climate-proof but energy-intensive), recycling, rainwater harvesting.
• Demand management: water restrictions, pricing, efficient appliances — reduce consumption rather than increase supply.
• Best approach: diversified portfolio of supply + demand strategies tailored to local conditions.