Modular Floating Covers vs.
Geomembrane Covers
A detailed engineering analysis of operating principles, self-interlocking mechanics, performance advantages, and total cost of ownership — with a focus on the Hexprotect® AQUA system by AWTT.
Operating Principles
Both cover types aim to reduce evaporation, block UV light, suppress algae, deter wildlife, and insulate liquid surfaces — but they achieve these goals through fundamentally different engineering approaches.
Hexprotect AQUA — Modular
The Hexprotect AQUA system consists of thousands of individual, hollow hexagonal tiles made from UV-resistant virgin HDPE. Each tile is poured directly onto the liquid surface where natural wave motion distributes the elements automatically. The tiles self-ballast by admitting water into their lower chambers, increasing their effective weight by over 260%, which anchors them against wind forces.
Roughly 50% of each tile sits above the waterline, creating a combined thermal barrier: the trapped air inside each tile insulates, while the HDPE shell itself has poor heat conductivity. Small gaps between tiles allow rainwater and snowmelt to drain through to the reservoir below — eliminating the need for sump pumps or drainage infrastructure entirely.
Because the tiles are discrete and free-floating, they part around any static or moving equipment (mixers, dipping probes, aerators) and automatically reform coverage behind it. They also track water level changes by rising, falling, and even stacking at the basin edges as the level drops.
Geomembrane — Monolithic
A geomembrane floating cover is a single continuous sheet of synthetic polymer (HDPE, RPE, CSPE, or PVC) laid across the entire liquid surface. Buoyancy is provided by ethylene foam float tubes that are welded or mechanically attached to the underside of the membrane. The cover is anchored at the pond perimeter — typically bolted to concrete curbing or trenched into earthen embankments.
Because the membrane is impermeable and continuous, rainwater that lands on it cannot drain through. This requires an engineered network of defined sumps — troughs created by strategically placed ballast weights and floats that channel water toward submersible sump pumps. These pumps must run continuously during rain events.
Geomembrane covers rise and fall with the water level by virtue of excess material that folds and unfolds. Accessing the liquid below requires hatches, ports, or physically cutting and re-welding the membrane.
Self-Interlocking Mechanics of Hexprotect AQUA
The Hexprotect AQUA system uses a patented geometry and ballasting strategy that turns loose tiles into a cohesive floating mat — without any fasteners, clips, or manual assembly. Three mechanisms work in concert:
Hexagonal Tessellation
Hexagons are the most efficient shape for tiling a plane with minimal perimeter-to-area ratio. When poured onto water, the tiles naturally orient and nestle against their neighbors under wave action, achieving up to 99% surface coverage. Unlike circles (which leave ~9% gaps), hexagons eliminate dead space.
Side-Locking Tabs
Each tile features proprietary locking mechanisms on its six edges. As tiles press together under wave motion, these tabs engage, preventing tiles from overlapping or climbing over one another — a problem common with low-draft covers. The deep draft ensures stable vertical engagement.
Water Self-Ballasting
Each tile admits water into its lower cavity through calibrated openings. This increases the tile's effective weight by over 260%, dramatically lowering its center of gravity. The result: tiles resist wind uplift far beyond what their dry weight would suggest — rated to 130+ MPH sustained winds.
Key Advantage: Self-Organizing Coverage. Once deployed, the interlocking mat requires zero maintenance to sustain coverage. As water levels change, tiles at the edge automatically stack or unstack. If equipment passes through, displaced tiles regroup and re-lock behind it. This passive self-healing is something no monolithic geomembrane can replicate without manual intervention.
Performance Comparison
Head-to-head comparison across the criteria that matter most for liquid storage applications.
| Criterion | Modular Floating Cover | Solid Geomembrane Cover |
|---|---|---|
| Installation | Tiles are poured directly onto the liquid — no specialized crew, no welding, no anchoring hardware. Can be installed on a full pond in hours to days. | Requires certified welding crews, foam floats, perimeter anchoring, and often a dry installation (pond must be emptied). Complex, multi-week process. |
| Surface Coverage | Up to 99% via hexagonal tessellation and locking tabs | 100% — fully impermeable continuous sheet |
| Rainwater Handling | Rain and snowmelt pass through gaps between tiles directly into the reservoir. No pumps, no sumps, no power needed. | Rainwater accumulates on the surface. Requires defined-sump design with submersible pumps, power supply, and ongoing monitoring. |
| Evaporation Reduction | Up to 98% (Rhombo Hexoshield® 189) | Up to 100% when intact and properly maintained |
| Maintenance | Essentially zero. No moving parts, no pumps, no anchors. 10-year warranty. Periodic visual inspection only. | Annual deep cleaning, sump pump maintenance ($200–$500/yr each), seam inspections, tear repairs, and ballast/float checks. |
| Gas Containment | Not gas-tight. Small gaps between tiles allow gas to escape. Not suitable for biogas capture. | Fully impermeable — can capture methane and other gases for collection or flaring. Essential for anaerobic digesters. |
| Equipment Access | Tiles part around mixers, aerators, and probes, then self-heal behind them. Full, unrestricted access to the liquid. | Equipment access requires pre-installed hatches, ports, or cutting/re-welding the membrane. Disruptive and expensive. |
| Wind Resistance | Self-ballasting tiles (260%+ weight increase) resist winds >130 MPH. No anchors required. | Anchored at perimeter but center can billow and flap. Prone to tearing and fatigue cracking from constant wind movement. |
| Water Level Changes | Auto-adjusts — floats at any level, tiles stack/unstack at edges | Must accommodate level changes in design; excess material folds/unfolds; risk of tearing |
| Snow & Ice | Frost-resistant to −70°F (−57°C). No structural damage from freeze/thaw. Snow melts through gaps. No collapse risk. | Snow and ice loads can stress the membrane, especially at seams. Pumps may freeze. Ice can rip or deform the surface. |
| Damage & Repair | If a tile is damaged, replace that single tile. No downtime, no welding, no draining. Non-adjacent tiles are unaffected. | A tear can propagate. Repairs require patching or re-welding in the field by certified crews. May require partial draining. |
| Reusability | Fully reusable — tiles can be removed, transported, and redeployed on a different pond with zero modification. | Custom-fabricated for a specific pond shape. Cannot be reused on a differently shaped or sized basin. |
| Lifespan | 25+ years (UV-stabilized HDPE, 10-year warranty) | 20–30+ years (high-quality CSPE/RPE with proper maintenance) |
| Scalability | Add more units as needed; phase deployment across cells | Must fabricate full cover per cell |
Where Geomembrane Still Wins: If your application requires gas capture (biogas, methane harvesting from anaerobic digesters), vapor containment, or a 100% impermeable seal to prevent rainwater dilution, a monolithic geomembrane is the only viable choice. Modular covers are permeable by design and are not suitable for these specialized applications.
Cost Comparison
Estimated cost model for a representative 1-acre (43,560 sq ft / ~4,050 m²) municipal wastewater lagoon. All figures are approximate ranges and should be confirmed with project-specific quotes.
Installed Capital Cost
| Cost Category | Hexprotect AQUA (Modular) | Geomembrane (HDPE/RPE) |
|---|---|---|
| Cover Material | ~$104,500 $2.40/sq ft × 43,560 sq ft — pre-fabricated HDPE tiles | $15,000 – $55,000 $0.30–$1.25/sq ft HDPE film; $1.50–$3.50/sq ft RPE/CSPE |
| Float & Ballast System | $0 Self-ballasting — no floats needed | $8,000 – $20,000 Ethylene foam tubes, sand tube ballasts, sump hardware |
| Sump Pumps & Drainage | $0 Rain flows through — no pumps needed | $5,000 – $15,000 Submersible pumps, piping, power supply, controls |
| Perimeter Anchoring | $0 No anchors required | $4,000 – $12,000 Concrete curbing, batten bars, or anchor trenches |
| Installation Labor | $2,000 – $5,000 Unskilled crew — pour tiles onto surface over 1–2 days | $15,000 – $40,000 Certified welding crews, 1–4 weeks, field seaming, QA testing |
| Engineering & Design | $0 – $2,000 Minimal — standard product configuration | $5,000 – $15,000 Custom: sump layout, float spacing, anchor design, wind analysis |
| Total Installed Cost | $106,500 – $111,500 | $52,000 – $157,000 |
Ongoing Annual Costs (Years 1–10)
| Ongoing Cost | Hexprotect AQUA | Geomembrane |
|---|---|---|
| Pump Maintenance | $0 | $1,000 – $3,000/yr Multiple pumps × $200–$500 each; replacement every 7–10 yrs |
| Pump Electricity | $0 | $500 – $1,500/yr Continuous operation during rain/snow events |
| Cleaning & Inspection | $0 – $500/yr Visual inspection only | $2,000 – $5,000/yr Annual deep clean, seam inspections, debris removal |
| Tear / Damage Repairs | $0 – $200/yr Replace individual tiles if damaged | $1,000 – $8,000/yr Patch welding by certified crews; potential for cascading failure |
| Total Annual O&M | $0 – $700/yr | $4,500 – $17,500/yr |
10-Year Total Cost of Ownership
| Component | Hexprotect AQUA | Geomembrane |
|---|---|---|
| Installed Capital | $106,500 – $111,500 | $52,000 – $157,000 |
| 10 Years O&M | $0 – $7,000 | $45,000 – $175,000 |
| 10-Year TCO | $106,500 – $118,500 Up to 64% savings | $97,000 – $332,000 |
Note: These are representative estimates for a 1-acre lagoon. Actual costs vary significantly based on geography, pond geometry, local labor rates, material selection (basic HDPE film vs. premium RPE/CSPE), and site-specific conditions. Contact AWTT for project-specific pricing.
When to Choose a Modular Floating Cover
For the majority of ponds, reservoirs, and lagoons, a modular floating cover delivers superior long-term value with lower risk and near-zero maintenance. Modular covers are the preferred solution when any of the following conditions apply:
Most ponds and reservoirs — evaporation control, algae prevention, odor suppression, or bird deterrence where a hermetic gas-tight seal is not required.
Exposed or windy sites — self-ballasting modular covers (Hexprotect® AQUA) resist winds exceeding 130 MPH without anchors or ballast tubes.
Sites with in-pond equipment — aerators, mixers, sensors, or piping that require periodic access. Tiles part and self-reform around obstructions.
Limited maintenance budget — no pumps, no inspections, no mechanical components, eliminating ongoing operational expense.
Remote sites with no power supply — no electricity needed for sump pumps or monitoring. Fully passive operation.
Phased deployment or reusability — cover can be installed in stages, moved between ponds, or redeployed on a different site with zero modification.
Irregular pond shapes — modular units conform to any geometry without custom fabrication, panel welding, or perimeter engineering.
Rainwater ingress is acceptable — applications where rain draining into the reservoir is neutral or beneficial (most ponds and lagoons).
When to Choose a Solid Geomembrane Cover
Solid geomembrane covers are justified in a narrower set of applications where a complete hermetic seal is a non-negotiable engineering requirement:
Gas collection applications — biogas or landfill gas systems requiring a sealed headspace for methane capture, routing, and flare or engine feed.
Zero-emission containment required — applications where regulations mandate 100% vapor seal with no allowable surface exposure, such as certain hazardous waste impoundments.
Rainwater dilution must be prevented — chemical storage or process water where any rainwater contamination is unacceptable.
Regulatory mandate for sealed barrier — potable water protection under AWWA M25 standards or odor containment requiring zero gap tolerance.
Bottom line: For the majority of municipal wastewater, agricultural, industrial water storage, frac pit, and raw water reservoir applications — where the cover's job is to reduce evaporation, prevent algae, and keep wildlife out — modular systems like Hexprotect AQUA offer a compelling advantage. The lower total cost of ownership, near-zero maintenance, tolerance of water level fluctuations, and full equipment compatibility make them the practical choice for most non-gas-capture scenarios.
Frequently Asked Questions
Common engineering and procurement questions about modular versus solid geomembrane floating cover systems.
Can modular floating covers achieve 100% evaporation reduction?
Do solid geomembrane covers last longer than modular floating covers?
Can I convert from a solid geomembrane cover to a modular floating cover?
Which cover type is better for windy or exposed sites?
How does the self-interlocking mechanism work on Hexprotect AQUA tiles?
Not Sure Which Approach Is Right?
Our engineering team can evaluate your site conditions, water chemistry, wind exposure, and operational requirements — then recommend the cover system that delivers the best long-term value for your application.