Every time you turn on the tap during a dry summer, you are relying on large-scale engineering to keep the water flowing. When a region's water supply falls below per person per year, it reaches a threshold known as water stress. To combat this, governments use massive infrastructure projects to move, store, or create freshwater.
A dam is a huge concrete or steel barrier constructed across a valley to block river flow. This creates an artificial lake behind it, known as a reservoir.
The primary function of a reservoir is to store water during times of water surplus (when rainfall and supply exceed demand). This stored water is then released during times of water deficit (when demand outpaces the available supply).
Large-scale dams have monumental impacts. For example, China's Three Gorges Dam cost approximately $37 billion and protects 25,000 hectares of farmland from flooding. In the UK, Kielder Water holds 200 billion gallons to regulate the River Tyne. However, dams do not come without costs; the Three Gorges Dam displaced 1.3 million people, and dams can severely restrict downstream water flow, as seen when Turkey's Ilisu Dam reduced flow into Iraq by 50%.
Water diversion involves redirecting a portion of a river's flow or groundwater to another location for storage or immediate use. One innovative method is storing this diverted water underground inside an aquifer (a body of permeable rock that holds groundwater).
Unlike surface reservoirs, underground storage does not suffer from high evaporation rates and does not permanently flood valuable land. For example, Arizona in the USA stores 600 million of water underground to protect it from the intense desert sun.
Step-by-Step Mechanism of Underground Storage:
Step 1: Water is diverted from a river during high-flow (surplus) periods.
Step 2: The diverted water is filtered to remove heavy sediment.
Step 3: The clean water is pumped deep underground into permeable rock layers.
Step 4: Water is extracted via boreholes during dry seasons when the surface is in deficit.
Desalination is the industrial process of removing salt and minerals from seawater to produce potable water (water safe for human consumption). It is unique because it does not rely on rainfall, making it entirely drought-proof.
Most modern plants use reverse osmosis, where seawater is forced through semi-permeable membranes at extremely high pressure to filter out salt molecules. The Beckton plant in the UK Thames Gateway cost £270 million and uses a four-stage reverse osmosis system. It operates at 85% efficiency to produce 150 million litres of drinking water per day, enough for 1 million people.
However, desalination is usually only viable for High Income Countries (HICs) or wealthy Newly Emerging Economies (NEEs). The Beckton plant is highly energy-intensive, using per , giving it a massive carbon footprint. It also produces a toxic, highly concentrated salt byproduct called brine, which must be carefully diluted with treated sewage effluent before being discharged to avoid creating marine "dead zones".
A water transfer scheme is a large-scale project that moves water from an area of surplus to an area of deficit via networks of canals, tunnels, and pipelines. In the UK, the North and West are areas of surplus, while the densely populated South and East are areas of deficit.
While a national UK water grid has been proposed, it remains unbuilt due to immense costs and environmental concerns. Existing regional transfers include gravity-fed pipes from the Lake District and Wales to Manchester and Liverpool. A major drawback of these schemes is inefficiency; up to 40% of the water can be lost through leakage in aging pipe networks.
The SNWTP in China is the world's largest transfer scheme, moving 44.8 billion of water annually from the Yangtze River in the south to the Yellow River basin in the north. Costing roughly $79 to $80 billion, it serves 200 million people across three routes (Eastern, Central, and a proposed Western route).
Economic Impacts:
Social Impacts:
Environmental Impacts:
Overall Judgement: While the environmental disruption and mass displacement of the SNWTP are severe, the scheme is arguably essential for China's continued economic survival. Without it, the industrial north would face catastrophic water shortages, meaning the national economic and health benefits currently outweigh the localised environmental costs.
Students often confuse a "water transfer scheme" with "water diversion". Remember that a transfer involves moving water across regions (e.g., via large pipelines), whereas diversion redirects local river or groundwater flow.
In 9-mark "Evaluate" questions on large-scale water schemes, examiners expect a balanced judgement; always conclude your answer by explicitly stating whether the social and economic benefits outweigh the environmental costs.
When outlining the impacts of dams, mark schemes frequently reward specific mentions of negative downstream impacts, such as reduced cross-border water flow and resulting diplomatic tensions.
To access the top-tier marks in case study questions, always use specific place names (e.g., Danjiangkou Reservoir, Han River) and specific data (e.g., 350,000 displaced) rather than vague statements.
Water stress
A situation where the available clean water supply falls below 1,700 cubic metres per person per year.
Dam
A large concrete or steel barrier constructed across a valley to hold back river water.
Reservoir
A large natural or artificial lake created behind a dam, used as a source of water supply.
Water surplus
A situation where the water supply exceeds the demand from the population, industry, and agriculture.
Water deficit
A situation where water demand exceeds the available supply, leading to water insecurity.
Water diversion
Redirecting a portion of a river's flow or aquifer water to another location for storage or use.
Aquifer
A body of permeable rock underground which can contain or transmit groundwater.
Desalination
The industrial process of removing salt and minerals from seawater to produce drinking water.
Potable water
Water that has been treated and is safe for human consumption.
Reverse osmosis
A desalination technique that forces seawater through semi-permeable membranes at high pressure to remove salt molecules.
Brine
A highly concentrated toxic salt solution produced as a byproduct of the desalination process.
Water transfer scheme
The large-scale movement of water from an area of surplus to an area of deficit via canals, tunnels, and pipelines.
Over-abstraction
The process of extracting groundwater from aquifers faster than it can be naturally replenished by rainfall.
Subsidence
The sinking of the Earth's surface, often caused by the excessive removal of groundwater from aquifers below.
Put your knowledge into practice — try past paper questions for Geography
Water stress
A situation where the available clean water supply falls below 1,700 cubic metres per person per year.
Dam
A large concrete or steel barrier constructed across a valley to hold back river water.
Reservoir
A large natural or artificial lake created behind a dam, used as a source of water supply.
Water surplus
A situation where the water supply exceeds the demand from the population, industry, and agriculture.
Water deficit
A situation where water demand exceeds the available supply, leading to water insecurity.
Water diversion
Redirecting a portion of a river's flow or aquifer water to another location for storage or use.
Aquifer
A body of permeable rock underground which can contain or transmit groundwater.
Desalination
The industrial process of removing salt and minerals from seawater to produce drinking water.
Potable water
Water that has been treated and is safe for human consumption.
Reverse osmosis
A desalination technique that forces seawater through semi-permeable membranes at high pressure to remove salt molecules.
Brine
A highly concentrated toxic salt solution produced as a byproduct of the desalination process.
Water transfer scheme
The large-scale movement of water from an area of surplus to an area of deficit via canals, tunnels, and pipelines.
Over-abstraction
The process of extracting groundwater from aquifers faster than it can be naturally replenished by rainfall.
Subsidence
The sinking of the Earth's surface, often caused by the excessive removal of groundwater from aquifers below.