17.3 - How to Increase Water Supply
The role of dams and reservoirs in managing water supply
Dams and reservoirs are critical large-scale solutions for addressing water shortages, particularly in areas with unpredictable rainfall or seasonal variations. They help store water during times of surplus and release it during deficits, ensuring a steady supply throughout the year.
How dams and reservoirs function
- Water storage mechanism - A storage dam is constructed across a river, creating a reservoir that traps water behind it. This stored water accumulates during periods of high rainfall.
- Regulated water release - During dry spells or water deficits, the reservoir releases water to maintain a consistent flow in the river, supporting communities and agriculture downstream.
Challenges associated with dams and reservoirs
- Flooding of land - Reservoirs often submerge valuable agricultural land, reducing available farmland.
- Displacement of communities - Settlements may be flooded, forcing residents to relocate to new areas.
- High financial costs - Building and maintaining dams is expensive.
The use of water diversion for irrigation and power generation
Water diversion is another method to manage water resources by redirecting river flow to areas where it is needed most. This approach is often less invasive than storage dams as it focuses on rerouting rather than long-term storage.
Mechanics and benefits of water diversion
- Raising water levels - A diversion dam is built to elevate a river's water level, allowing water to be channelled to a specific destination.
- Key applications - Commonly used to supply water to agricultural canal systems for irrigation or to generate hydroelectric power by directing water through turbines.
Advantages over storage dams
- Reduced disruption - Unlike storage dams, diversion dams typically do not create large reservoirs, minimising the flooding of land and displacement of people.
- Targeted water delivery - Allows precise allocation of water to areas of need, enhancing efficiency in water-scarce regions.
The impact of water transfer schemes on water security
Water transfer schemes are extensive engineering projects designed to move water from regions of surplus to those experiencing shortages. While they can alleviate water insecurity, they also bring significant challenges.
Operation of water transfer schemes
- Infrastructure involved - Water is transported using canals, pipes, pumping stations, and aqueducts (artificial channels) to navigate geographical barriers like hills and valleys.
- Purpose and benefit - These schemes aim to reduce water insecurity in deficit areas by redistributing resources from water-rich regions.
Potential problems with water transfer
- Environmental impact - Altering natural water flows can disrupt ecosystems, affecting aquatic life and river health in both donor and receiving areas.
- Social consequences - Communities in surplus areas may resent losing water resources, leading to conflicts over allocation.
- Economic burden - The construction and maintenance of transfer infrastructure require substantial investment, which can strain public finances.
The process and challenges of desalination for producing freshwater
Desalination offers a solution for water scarcity by converting seawater into usable freshwater. It is particularly vital in arid regions with limited natural water sources, though it comes with notable drawbacks.
Methods of desalination
- Thermal distillation - Seawater is heated until it evaporates, leaving salt behind. The vapour is then condensed back into freshwater.
- Reverse osmosis - Seawater is forced through a semi-permeable membrane that filters out salt and impurities, producing clean water.
Evaluation of desalination
- Reliable water source - Provides a consistent supply of drinking water in water-scarce regions.
- High energy costs - The process is energy-intensive, whether through heating water or powering membrane filtration, making it expensive to operate.
- Environmental concerns - Most plants currently use fossil fuels, contributing to greenhouse gas emissions. However, innovations like solar-powered facilities are emerging, as seen in projects in certain Middle Eastern countries.
- Economic barrier - The high cost of setup and operation limits its feasibility to wealthier nations or regions with significant financial resources.