Introduction: The Challenge of Water Loss in Dams
Dams are essential for farming, industry, and community water supply. However, one of the main ways water is lost is through evaporation—especially in dry and semi-dry regions. In Australia, for example, climate change has led some places to receive 20% less rain per year since the 1970s. This means every drop of stored water is more valuable than ever. Evaporation can cause significant water loss from lakes, reservoirs, and farm dams, particularly during hot and windy conditions.
Traditional water management methods are no longer sufficient. This has led to the adoption of innovative solutions like windbreaks and floating covers. These approaches not only reduce evaporation but also improve water quality and promote sustainable water use.
1. Floating Covers: How They Work
Floating covers are modular or continuous barriers that float on the water’s surface, shielding it from the sun and wind. They are typically made from geomembrane materials, high-density polyethylene (HDPE), or recycled polymers designed for durability and UV resistance.
Mechanisms of Evaporation Reduction
- Blocking Solar Radiation: Covers reflect sunlight, preventing the water from heating up and slowing the rate at which water molecules escape into the atmosphere.
- Reducing Wind Exposure: By covering the water surface, floating covers minimize the effect of wind, a major driver of evaporation.
- Limiting Water Vapor Loss: The physical barrier prevents water vapor from escaping, especially when the cover is nearly complete.
Types of Floating Covers
- Hexagonal Modular Covers: Examples include Daisy Dam Covers and HexaCover. These consist of interlocking plastic discs that float on the water. They are easy to install and can cover up to 99% of the dam’s surface, depending on water levels.
- Continuous Geomembrane Covers: These are large sheets of material that float on the water’s surface, usually anchored at the edges. They provide a more complete barrier but can be more challenging to install and maintain.
- Floating Bubble Covers: Similar to swimming pool covers, these are multi-layered, bubble-wrap-like sheets that float on the water and reflect sunlight.
Effectiveness
Floating covers can reduce evaporation by 70% to 99.98%, depending on the type and coverage. For example, HexaCover installations in Western Australia reduced evaporation by 73%, saving over 1.6 million litres of potable water in a recent trial. Daisy Dam Covers claim to stop evaporation by 99.98% where the cover is in direct contact with the water.
Additional Benefits
- Improved Water Quality: Covers prevent debris, dust, and contaminants from entering the water. They also block sunlight, reducing algae growth and improving water clarity.
- Reduced Maintenance: Less algae and debris mean less clogging of pumps, pipes, and valves, leading to lower maintenance costs.
- Sustainable Materials: Many covers are made from recycled plastics, supporting circular economy principles.
Limitations
- Cost: Initial investment can be significant, especially for large dams.
- Installation and Removal: Some covers require careful installation and must be removed before the dam dries out to avoid damage or contamination.
- Wind Vulnerability: Floating covers can be lifted or displaced by strong winds, although many designs include wind-skirting or ballast systems to mitigate this.
2. Windbreaks: How They Work
Windbreaks are barriers—usually rows of trees or shrubs—planted around the perimeter of a dam to reduce wind speed over the water surface.
Mechanisms of Evaporation Reduction
- Slowing Wind Speed: Windbreaks disrupt airflow, decreasing the rate at which water vapour is carried away from the water’s surface.
- Creating a Humid Microclimate: The sheltered area behind a windbreak becomes more humid, reducing the humidity gradient between the water and the air, which further slows evaporation.
- Shading: Tall windbreaks can provide some shade, reducing water temperature and evaporation1.
Types of Windbreaks
- Tree Windbreaks: Commonly used species include pines, acacias, and eucalypts. These are planted in rows perpendicular to the prevailing wind direction.
- Artificial Windbreaks: Fences or screens can be used where tree growth is not feasible, though they are less common.
Effectiveness
Windbreaks can reduce evaporation by 20% to 35% under typical conditions, with some studies reporting higher reductions in specific circumstances. For example, Hipsey et al. (2004) found a 30% reduction in evaporation from small dams behind an 8m high tree windbreak. In some cases, with optimal design and placement, evaporation reductions of up to 50% have been modelled.
Additional Benefits
- Habitat Creation: Windbreaks provide habitat for wildlife and support biodiversity.
- Erosion Control: They reduce wind erosion and protect dam banks from wave action.
- Shelter for Livestock: Windbreaks can provide shade and shelter for animals, improving animal welfare.
Limitations
- Space Requirements: Windbreaks require land and can compete with other land uses.
- Time to Maturity: Trees take several years to grow tall enough to be effective.
- Maintenance: Windbreaks require ongoing management, including pruning and weed control.
3. Comparing Floating Covers and Windbreaks
| Feature | Floating Covers | Windbreaks |
|---|---|---|
| Evaporation Reduction | 70–99.98% | 20–35% (up to 50% in ideal cases) |
| Installation | Modular, quick to deploy | Requires planting, years to mature |
| Cost | High initial cost, low maintenance | Low initial cost, ongoing maintenance |
| Water Quality Impact | Reduces algae, debris, and contamination | Minimal direct impact |
| Ecological Benefits | Limited | Supports biodiversity, habitat creation |
| Wind Vulnerability | Can be displaced by strong winds | Reduces wind speed, protects dam |
| Aesthetics | May be visually intrusive | Enhances landscape, provides shade |
4. Practical Considerations for Dam Owners
When to Choose Floating Covers
- High Evaporation Rates: Floating covers offer the greatest water savings in regions with intense sun and wind.
- Small to Medium Dams: Modular covers are particularly effective for farm dams and community water supplies.
- Need for Rapid Deployment: Covers can be installed quickly and provide immediate benefits.
- Priority on Water Quality: Covers significantly reduce algae and contamination.
When to Choose Windbreaks
- Large Dams or Reservoirs: Windbreaks are more practical for large water bodies where floating covers may be cost prohibitive.
- Long-Term Planning: Windbreaks require time to establish but provide lasting benefits.
- Desire for Ecological Benefits: Windbreaks support wildlife and improve the local environment.
- Limited Budget: Windbreaks have lower upfront costs compared to floating covers.
Combining Both Approaches
For optimal water conservation, consider combining floating covers and windbreaks. For example, use floating covers on the main water storage area and plant windbreaks around the perimeter to further reduce wind exposure and evaporation. This hybrid approach maximises water savings and ecological benefits.
5. Real-World Examples and Case Studies
Western Australia: HexaCover Trial
In 2024, a $2.8 million project saw the installation of HexaCover floating covers on three dams in southern Western Australia. The covers, made from 100% recycled plastic, reduced evaporation by 73%, saving over 1.6 million litres of drinking water and reducing the need for water carting by up to 700 truck movements annually. The project highlights the effectiveness of modular floating covers in securing water supplies for remote communities.
Queensland: Windbreak Effectiveness
Research in South East Queensland found that tree windbreaks can reduce evaporation from small dams by up to 30%. The study highlighted the importance of windbreak height, density, and placement relative to prevailing winds. Medium-density windbreaks were found to be most effective, balancing wind reduction with minimal turbulence.
6. Challenges and Solutions
Floating Covers
- Wind Displacement: Use wind-skirting or ballast systems to anchor covers.
- Cost: Seek government grants or subsidies for water conservation projects.
- Maintenance: Choose low-maintenance designs and monitor for debris accumulation.
Windbreaks
- Space and Competition: Select narrow, tall windbreaks and consider species with dual benefits (e.g., timber production).
- Time to Maturity: Plan ahead and use fast-growing species where possible.
- Maintenance: Implement regular pruning and weed control.
7. Environmental and Economic Impacts
Environmental Benefits
- Water Conservation: Both methods significantly reduce water loss, supporting sustainable water use.
- Habitat and Biodiversity: Windbreaks provide habitat for wildlife and support ecosystem health.
- Reduced Carbon Footprint: Using recycled materials in floating covers and planting trees for windbreaks contribute to carbon sequestration and circular economy principles.
Economic Benefits
- Reduced Water Carting: Less evaporation means fewer truck movements and lower costs for water supply.
- Lower Maintenance Costs: Improved water quality reduces the need for cleaning and repairs.
- Increased Agricultural Productivity: Reliable water supplies support crop and livestock production.
8. Future Directions
As climate change intensifies, the need for innovative water conservation solutions will only grow. Future developments may include:
- Smart Covers: Integration of sensors to monitor water levels, temperature, and cover integrity.
- Hybrid Systems: Combining floating covers, windbreaks, and other technologies (e.g., solar panels) for maximum efficiency.
- Community Engagement: Educating dam owners and communities about the benefits and best practices for water conservation.
Conclusion
Installing floating covers or windbreaks is a proven and effective way to conserve water in dams. Floating covers offer rapid, high-impact evaporation reduction and improved water quality, while windbreaks provide long-term ecological and water-saving benefits. By understanding the strengths and limitations of each approach, dam owners can make informed decisions to secure their water supplies, support local ecosystems, and build resilience against climate change.
For most dam owners, a combination of both strategies—tailored to their specific needs and conditions—will deliver the best results. As water becomes an increasingly precious resource, investing in these solutions is not just prudent; it is essential for the future of agriculture, industry, and communities across Australia and beyond