Maerkle Reservoir Floating Cover Project

Floating cover and chafer for drinking water distribution reservoir
45mil, scrim reinforced CSPE geomembrane - beige material for floating cover , 45mil, scrim reinforced CSPE geomembrane - black material for chafer
Hilts Consulting Group and Raven Industries

The reservoir stores treated potable water as part of a water distribution system and provide a 10-day operation storage of 200 million gallons. The reservoir covers 17 acres and has a maximum depth of 60 ft.  Interior side slopes range from 2H:1V to 4.5H:1V.  The reservoir geometry is complex, consisting of eight curves and eight tangent sections.

The project components include removing the 20-year-old existing reinforced polypropylene floating cover and existing partial HDPE geomembrane chafer. The replacement floating cover system consists of a new 45-mil,scrim reinforced CSPE geomembrane, weight tensioned floating cover.  The floating cover features include access hatches, air/vacuum vents, remote water quality sampling capabilities, four submersible rainwater removal pumps, and walkaway access paths.  A new 45-mil, scrim reinforced, CSPE geomembrane chafer strip was installed covering approximately two-thirds of the reservoir side slopes.

The floating cover and chafer materials were prefabricated into large panels based on site specific geometry and location within the reservoir.  A total of 117 prefabricated panels were required for the floating cover system and 101 prefabricated panels for the chafer. The panels are approximately 34 feet wide with custom lengths up to over300 feet long.

Additional site improvements include new storm water discharge laterals for the floating cover, rainwater removal pumps, discharge points, new electrical power distribution system, replacement of three submerged valves at the outlet structures within the reservoir, and perimeter site fencing.


Floating cover designs are typically performed while a reservoir is in service. Accurate as-built drawings and underwater dive inspection photos and videos are essential to document and verify actual existing conditions for the design. One lesson learned is the information shown on as-built drawings may not always be accurate so underwater dive inspections during design are important. Existing conditions should be documented and reviewed by the design engineer once the reservoir is dewatered, and the existing floating cover is exposed before removal. Any unforeseen conditions revealed during this process should be addressed early in the design and construction phases to avoid potential project delays and costs.

Long lead-time components must be identified early to prevent project delays. On this project, the CSPE geomembrane for the floating cover and chafer, along with the outlet valves, actuators, and hydraulic power unit, were all identified as long lead-time items.  The CSPE geomembrane manufacturing supply chain for large quantities requires highly coordinated schedules and upfront time to facilitate.  This process guarantees the project-specific sized panels delivered to the job site on time and ready for installation.

Coordination with the valve manufacturer along with the actuator and hydraulic power unit manufacturer proved to be critical in the timing of this long lead-time item.  Manufacturing was performed in multiple locations both domestically and abroad.

During this project, lessons learned include the sheer-importance of preparation through the coordination of shop drawing submittals, fabrication schedules, different contracting entities, and subcontractors, which all proved to be essential components of success.  All of these components should be aggressively pursued right at the project onset.

On a complex project, such as this one, coordinating with vendors both domestically and abroad is essential for both the design, approval, and construction processes.  Sequence of construction required close collaboration with material suppliers, fabricators, and field installation crews.


Large panel fabrication for this project and appurtenances dramatically reduced the field installation time on this project with a tight schedule. This ensured no startup delays for the owners and the reservoir was back online per schedule.

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