Suspended Shade Covers & Structures
Shade cloth and structures suspended above water can cut evaporation ~85% while keeping the surface clear — at the cost of structural engineering.
What it is
A suspended cover is shade cloth, fabric, or a light roof structure held above the water on poles, posts and tensioned cables — never touching the surface. It shades the water and shelters it from wind without floating on it, so the surface underneath stays open.
How it works
Suspending a cover attacks two of the main evaporation drivers at once (see what is evaporation): it blocks much of the solar radiation that warms the water, and the overhead canopy reduces wind speed across the surface. Cooler water has a lower saturation vapour pressure, and slower wind leaves a more humid boundary layer in place — both narrow the vapour-pressure deficit.
How well it works
Field and manufacturer data put suspended covers around ~85% (field/manufacturer) reduction at good coverage, with the higher figures tied to denser, more complete canopies — consistent with the broader review of suspended and floating covers in Yao et al. (2021). Lighter or partial shade cloth delivers less, so the reduction scales with how much radiation and wind the canopy actually blocks.
A notable advantage over floating methods is that the water surface remains clear: no material to scoop, no displacement risk, and unobstructed access for pumps, aerators or sampling.
Trade-offs
- Structure and cost. The reduction comes from an engineered overhead structure. Spanning large open reservoirs becomes expensive and structurally demanding, so suspended covers are most practical at small to mid-size scale.
- Light and oxygen. At full coverage the same shading that suppresses evaporation also limits photosynthesis and gas exchange in the water below — good for algae control, but a consideration for living water bodies.
- Wind loading. The canopy acts as a sail; mounting and cabling must be engineered for local wind.
Where it fits
Suspended covers suit small to mid-size storages and tanks in hot, sunny climates where high reduction and clear surface access both matter. Where the goal is also to generate energy, compare floating solar; where a near-total surface seal is acceptable, see geomembrane covers. The full methods comparison sets the trade-offs side by side.