5.11 - Managing Water Supply: Hard Engineering
Hard engineering approaches to managing water supply
Water supply can be managed through a range of strategies designed to increase the amount of water available in areas facing water deficit. Hard engineering approaches involve large-scale infrastructure and technological solutions to improve water security.
Three main hard engineering strategies
- Water transfer schemes - Moving water from areas of surplus to areas of deficit
- Mega dams - Storing water during periods of surplus for use during periods of deficit
- Desalination plants - Converting seawater into freshwater for human use
Selecting the most appropriate strategy is complex, as different stakeholders and players have competing interests and priorities.
Water transfer schemes
Water transfer schemes involve transporting water from regions where it is abundant to regions where it is scarce. This is typically achieved by pumping water through infrastructure such as pipes, channels, canals, and aqueducts.
How water transfer schemes work
- Water is pumped through engineered channels from a source area to a receiving area
- In some cases, entire river courses are redesigned so that water flows into the required region
- Transfers can operate at a range of scales, from local redistribution to transfers between whole regions or even between countries
Advantages and disadvantages of water transfer schemes
| Advantages | Disadvantages |
|---|---|
| Water security is increased in the receiving area | Water stress may be increased in the source area |
| The volume of water transferred can be adjusted to suit seasonal demand | The receiving area may develop water-intensive land uses (e.g. golf courses), increasing long-term demand |
| Schemes can be highly effective at a small scale | Infrastructure is expensive to construct and maintain, and environmentally damaging |
| Can promote greater political cooperation between regions and countries | Decreased river discharge can alter freshwater ecosystems and increase saltwater intrusion |
| Provides greater security against minor imbalances between supply and demand | Rivers can become heavy with sediment, further changing the rate of flow |
Mega dams
Mega dams are large-scale structures built across rivers to trap and store water, creating reservoirs. These reservoirs fill during periods of extended rainfall, and water is released during drier periods. This ensures a more consistent flow of water throughout the year.
There are many large-scale dams around the world, including the Three Gorges Dam on the Yangtze River in China and dams on the Colorado River in the United States.
Advantages and disadvantages of mega dams
| Advantages | Disadvantages |
|---|---|
| Large dams can increase water security for many people | Reservoirs often flood agricultural land and cause displacement of settlements |
| Construction employs many people over many years | Construction frequently causes local conflicts and mistrust between displaced communities and national authorities |
| Reservoirs can be used for recreational activities such as sailing | Dams are extremely expensive and often require international loans |
| Dams can generate hydroelectric power (HEP) for local communities | Evaporation from the large reservoir surface reduces the amount of water available for human use |
| Dams help control flooding by regulating the rate of water flow | Dams hold back silt - an important natural fertiliser for farmland further downstream |
Desalination plants
Desalination is the process of removing salt from seawater so that it can be used as a freshwater source. Seawater is abundant in many coastal areas that lack sufficient freshwater, making desalination a valuable tool for increasing water security.
Methods of desalination
- Seawater is heated until the water evaporates, leaving the salt behind. The water vapour is then condensed to produce freshwater
- Reverse osmosis - Seawater is passed through a series of membranes that filter out the salt, producing freshwater
Saudi Arabia operates over three dozen desalination plants - more than any other country. Desalination is also particularly suited to island nations, such as the Maldives, where tourism drives high water demand but river systems are limited.
Advantages and disadvantages of desalination plants
| Advantages | Disadvantages |
|---|---|
| Uses a plentiful resource (seawater) | Extremely expensive to set up |
| Suitable for island countries with high water demand from tourism | Requires large amounts of energy, most of which comes from fossil fuels, contributing to pollution and climate change |
| Viable in areas with few river systems | Discharging concentrated salt back into the sea can harm marine life |
| Less viable for landlocked countries without coastal access |
Case study: The South-North Water Transfer Project, China
The South-North Water Transfer Project (SNWTP) is a major water transfer scheme in China, costing an estimated $79 billion. It was designed to increase water security in China.
Overview of the project
- The scheme involves a network of tunnels and canals that divert approximately 45 billion cubic metres of water per year from the Yangtze River and its tributaries in the south to the Yellow River basin in the north
- Three routes were planned - the Central Route, the Eastern Route, and the Western Route
- The Central and Eastern Routes have been completed, while the Western Route is planned for completion by 2050
Advantages of the SNWTP
- Improved urban water supply - The project provides clean water to over two dozen cities, including Beijing and Tianjin. The Chinese government estimates that nearly 100 million people have benefited
- Support for industrial and agricultural development - An increased water supply allows industrial development to continue in the north, boosting the country's wealth. The scheme also provides water for irrigating farmland, enabling crop production
- Reduced over-abstraction - The project helps to prevent the excessive extraction of groundwater in the north, reducing the risk of land subsidence
Disadvantages of the SNWTP
- Habitat destruction and biodiversity loss:
- As part of the Central Route construction, the height of the existing Danjiangkou Dam on the Hanshui River (a tributary of the Yangtze) was raised by approximately 15 metres to increase reservoir storage capacity
- This flooded additional land, destroying habitats and reducing biodiversity
- Algal blooms and ecological damage:
- Raising the dam height decreased the velocity of the Hanshui River downstream
- This slower flow contributed to an increase in algal blooms - thick blankets of algae on the water surface
- These blooms prevent light from penetrating below the surface, causing aquatic plants to die
- The resulting oxygen shortages in the water lead to the death of organisms that depend on dissolved oxygen, such as fish and amphibians