FLOATING COVER DESIGN AND MAINTENANCE
Printable Floating Cover Project Evaluation Sheet
Proper design and maintenance are critical to the success of any floating cover installation. According to the American Water Works Association, this design process should begin with site selection.
For security reasons, floating cover facilities should be out of view. Cut-and-fill type reservoirs should have high perimeter berms to prevent people from easily seeing the cover. A security fence is also recommended for these and other floating cover facilities. Again, this helps keep the cover out of sight. At the same time, it prevents damage from animals walking on the cover. Such a fence should be placed far enough away from the cover to discourage rock throwing.
In areas where vandalism is a real problem, other security measures may be required. These can include alarms, television surveillance and guards.
Floating cover facilities should be positioned to minimize the effects of prevailing winds. Stabilizing floats and other special wind-resistant design features may have to be incorporated into the design as well.
In hot climates, or where sunlight exposure is severe, a light-colored fabric should be used. This results in a lower surface temperature.
In cold areas, the design must take into account the need to remove surface water before ice forms on top of the cover. Removing excess surface water is a good idea in all regions, however, because this water can reduce the usable storage capacity of a reservoir and increases stresses due to the submergence floats. Water removal can be accomplished by pumping, siphoning or gravity flow.
If floating covers are properly designed, installed and operated, the contents of the containment structure generally provide most of the support cover. It essentially floats on the surface with little if any stress on the cover material. Floating covers should be designed, however, with sufficient slack to accommodate fluctuations in the level of reservoir contents.
Flexible membrane covers have the ability to automatically adjust to forces exerted on them by either static loads (such as an inactive weight) or dynamic loads (walking person). The weight of theses loads is buoyed up by a force equal to the weight of the water displace, thereby redistributing the load into a uniform pattern of minimum stress. However, while flexible membrane covers redistribute stresses as they occur, they are not designed to handle point stresses.
Point stresses are potential sources of mechanical damage and must be avoided in designing the floating cover.
For example, protruding walls, structures and pipes should be avoided. The cover must be able to rise and fall without restriction or interference. If such problems cannot be avoided, the cover material must be protected to prevent puncture, tearing and other types of damage.
INLET AND OUTLET PIPING
Engineer inlet and outlet piping to minimize its impact on the cover. Inlet piping should be placed to avoid hitting the cover with incoming liquids. Avoid high flow velocities. Outlet piping should be placed so that the cover is not sucked into the pipes at low reservoir levels.
An overflow system must be included in any floating cover design to prevent overfilling of the reservoir.
Another vital feature of any floating cover design is the drainage channel which is formed by securing either sand tubes or a wrapped galvanized chain to the exposed side of the floating cover. The weight of this static load will form a depression in the cover where rain water will collect. This water can be subsequently removed through the use of a pumping device.
Fire hydrants, or similar source of washdown water for cleaning the cover, should be included in the design.
MAINTENANCE IS THE KEY TO LASTING COVER PERFORMANCE
Floating covers feature excellent tensile strength and tear properties, and are relatively maintenance free. However, it is essential to the performance of the floating cover that excessive amounts of rainwater be continually removed. The cover drainage channels described above have a finite capacity which, if exceeded, can cause mechanical damage. Other precautions to take in maintaining a floating cover are:
- Avoid fluctuating the contents level of the containment structure during freezing weather to avoid possible ice damage.
- Employ professional certified divers if periodic cleaning of the reservoir interior is required. They can enter the reservoir through access hatches strategically placed on the floating cover itself. It is generally recommended that the reservoir be drained in order to air inflate the cover for interior access. This practice can be dangerous and can result in mechanical damage to the cover.
In some cases, air may penetrate beneath the floating cover either through overflow pipes or while entrapped in fluid entering the reservoir. If a substantial amount of air continues to build beneath the cover, the cover may be subject to wind damage. If air build-up becomes a problem, install air vents. They will allow entrapped air to escape while ensuring that no rainwater can enter the reservoir.
Printable Floating Cover Project Evaluation Sheet
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10/17/2013 01:13 PM