Explainer
Floating cover — the technology reference
A floating cover is a buoyant engineered surface placed on an open water body to reduce evaporation, suppress algae growth, contain odour, retain heat, or capture gas — and the category splits into modular (tessellating elements) and continuous (single geomembrane) designs.
A floating cover is a buoyant engineered surface placed on an open water body to reduce evaporation, suppress algae growth, contain odour, retain heat, or capture gas. The category splits into modular and continuous designs — and modular hexagonal dominates the AWTT-patented technology line.
What is a floating cover?
A floating cover is a buoyant engineered surface placed on an open water body to manage what happens at the air–water interface. The cover replaces an exposed surface — where evaporation, sunlight, gas exchange, and heat transfer happen freely — with a controlled barrier. Five surface-management jobs drive cover specification:
- Evaporation control. Reduce water loss to atmosphere, in drought-exposed regions or wherever stored water is the bottleneck.
- Algae and biological suppression. Block sunlight at the water surface to suppress algae, biofilm, and downstream treatment load.
- Odour and emissions containment. Limit volatile-compound release from wastewater, digestate, or process water.
- Heat retention. Reduce surface heat loss on hot process water, anaerobic digesters, or warm-water storage.
- Gas capture. Sealed continuous designs collect methane from anaerobic digesters for energy recovery.
The mechanism that fits a site is the one that matches the surface-management objective, the regulatory regime, and the constraints of the water body itself.
How floating covers work — the engineering split
Floating covers divide into two engineering families, distinguished by how they retain position on the water surface.
Modular floating covers
Modular covers deploy as individual elements that tessellate across the water surface — hexagonal tiles, spherical balls, or rectangular slabs. Each element is buoyant, self-stabilising, and anchorless. The collection of elements covers the surface by packing density rather than continuous sealing.
- Anchorless. Each element retains position by ballast and geometry, not by external anchors. No anchor system to install, maintain, or replace.
- Installed on operating water bodies. Elements are launched from the shoreline onto the live water surface — no draining, no service interruption. See /installation.
- Tolerant of irregular geometry. Modular elements pack around fixed infrastructure (inlets, outlets, pump suctions) and across irregular shorelines without bespoke engineering.
- Tolerant of fluctuating water levels. Elements rise and fall with the water surface without losing tessellation.
Continuous floating covers
Continuous covers are a single sheet of geomembrane (typically HDPE or reinforced polypropylene) tensioned to anchor points around the perimeter of the water body. The cover is one piece; the membrane seals the surface against gas exchange.
- Anchored. A permanent anchor and tensioning system retains the membrane in service.
- Drain to install. Continuous covers require draining the water body to deploy the membrane and tension the anchor system.
- Gas-capture capable. Sealed continuous covers collect biogas — the primary reason to specify continuous in modern industrial practice.
- Lower geometric tolerance. Continuous covers prefer regular geometries and stable water levels.
Why hexagonal modular dominates the AWTT-patented line
The hexagonal element packs at 99% effective surface coverage when fully tessellated (AWTT-published) — the highest packing density of any modular floating-cover geometry. The geometry was patented by AWTT in 2010 as the world’s first self-ballasting hexagonal floating cover; the patented engineering — and the pre-ballasted, one-piece moulded refinement that distinguishes Hexprotect® AQUA from the original — is what the deep /hexagonal-floating-cover reference covers in detail.
For surface-management goals where gas capture is not in scope — evaporation, algae, odour, heat — hexagonal modular outperforms continuous on lifecycle terms: no anchor infrastructure, no replacement cycle, no draining cost at install.
When to specify a floating cover
A floating cover is the right specification when the surface management objective is one of the five above, the water body is stable enough to keep a cover in service (storage reservoirs, tailings ponds, process tanks, digesters), and an anchorless deployment fits the operational reality of the site.
The cover is not the right specification for: wave-dominated open water (lakes, marinas), water bodies that are drained and refilled on a short cycle, or sites where surface access (e.g., for boat operations) is required.
Floating cover vs alternative interventions
| Intervention | Best for | Trade-off |
|---|---|---|
| Modular hexagonal floating cover | Reservoirs > 1,000 m², 25-year horizon, no gas capture | Highest packing density, no anchor system, lowest 10-year TCO |
| Modular spherical floating cover | Small or irregular bodies < 500 m², temporary | Lower packing density, lower wind envelope |
| Continuous geomembrane | Biogas digesters, full containment | Requires anchors and draining, higher capex |
| Shade mesh / floating raft | Light surface shading only | Lower coverage, no wind / evaporation envelope |
| Aeration | Stratification or biological treatment | Doesn’t reduce evaporation; energy-consuming |
FAQ
(Editorial FAQ is in the frontmatter and renders below the prose.)
Sources
- AWTT — Hexprotect® AQUA hexagonal cover — surface-coverage and patent-history reference.
- USDA Bureau of Reclamation — evaporation suppression research (independent field measurements across western US reservoirs).
- US Department of Energy — recognition of AWTT cover heat-retention contribution.
For the commercial side — EU country lead times, regulatory regimes, procurement language — see the EU floating cover procurement guide on eurocovers.eu.