Low Cost Water Storage & Evaporation Covers

Inground floating roof water storage is now a genuine alternative to steel water tanks when considering larger installations.

Floating roof structures have advantages over steel tanks:

• Where a large volume of water is to be stored.
• Where ample land is available for the storage.
• Where it is desired to prevent exposure of the stored water to the environment and to eliminate evaporation.
• Where an off peak storage is required and it is desired to minimise pump and delivery line size and expense.
• Where it is required to construct a large capacity storage in a short period of time.
• Where it is required to use the floating roof structure as part of a lined catchment to collect rainfall.
• Where the required location of the reservoir is remote and transport of structural steel plate and members will be a high cost.

The construction costs of an inground floating roof reservoirs dramatically reduces, as the stored volume and the depth of the storage increases. The following is an indication of costs:

.The above costs include earthworks, floating roof and lining systems, roof drainage pumps
and immediate inlet and outlet pipe work. Costs of pumping and delivery lines from the source
and to the point of delivery are not included.

The development of high strength, UV resistant, polymer materials used in the construction of floating roof storage’s has progressed rapidly in the last 10 years. A wide variety of polypropylene, elvaloy and polyethylene sheet is available with tensile strengths up to 8000kg/m width. Materials typically come with a manufacturers 20 year guarantee against UV degradation.

Installation of lining systems is a matter of science. Installation procedures and Quality Assurance procedures are set out in American Standards (ASTM) and have been the subject of wide research and development activity. Destructive and None-destructive test methods are widely recognised for the verification of weld integrity. The floating roof installation team is accompanied by a mobile laboratory and testing technician.

1. Investigation. Site investigation is carried out comprising, site survey and geotechnical investigation. The results of the investigation stage are presented in a report. A firm offer to construct the storage, on a design and construct basis, is given at the completion of this stage.
2. Detailed Design. Detailed design drawings for earthworks and structural items and workshop drawings for the lining systems and floating roof are compiled and technical specifications are prepared. A Quality Plan is developed.
3. Construction. Construction of earthworks is carried out to AS 3798-1996. The surface finish to the earthworks is of highest importance for a lined structure and is closely monitored. The installation of the lining systems is carried out in accordance with relevant United States standards and accepted practice.
4. Commissioning. The first filling of the structure is required to be monitored. The ballasting and floatation of the cover is required to be adjusted as it rises.

A floating roof has a greater surface areas when the cover is low in the storage compared to when the cover is fully floating. The cover must fold along designed lines in order to remain orderly and facilitate free drainage of rain water to the drainage sumps on the cover. The cover is also provided with two way tension in order to eliminate low spots and reduce the creation of ponds on the cover which are a maintenance problem. The cover is fitted with pump sumps to dispose of rain water. Where required the rain water can be sent through a filter and discharged under the cover. Manholes are incorporated into the cover to allow entry by divers and allow sampling and inspection of the stored water.

If you have a need for a floating roof reservoir and would like to commence the investigation process for a proposed structure please give our engineer a call to discuss your requirements.