AU2008200778A1 - Improvements in evaporation control systems - Google Patents

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: "IMPROVEMENTS IN EVAPORATION CONTROL SYSTEMS" The following statement is a full description of this invention, including the best method of performing it known to me: r 00 O TITLE S"IMPROVEMENTS IN EVAPORATION CONTROL SYSTEMS" FIELD OF THE INVENTION This invention is concerned with improvements in evaporation control systems for exposed water storage sites.

o00 The invention is concerned particularly with improvements in membrane evaporation control systems and methods of anchoring same Sover the surface of a body of water.

oo 0BACKGROUND OF THE INVENTION c 10 In an era where shortages of water suitable for horticulture, domestic consumption and industrial use, particularly for power station coolant use, are being blamed on the combined effects of climate change, population growth and increased energy consumption, there is a need in arid countries like Australia to conserve water by limiting wasteful usage and otherwise avoiding evaporation losses from water storages facilities such as dams and reservoirs.

In many regions of Australia and elsewhere in the world, the capacity to support increased regional population densities and for sustainable horticulture is dependent on the availability of water.

In arid and semi-arid regions, a level of sustainable horticulture has been achieved by building large but relatively shallow water storage dams covering many hectares.

Similarly, water for domestic and industrial use is stored in reservoirs, which while usually quite deep, have an exposed water surface and are of many hundreds or thousands of hectares.

Water levels in such storage facilities can be topped up in rainy seasons by drainage from catchment areas where the topography is appropriate or otherwise by pumping water from creeks or rivers when water is flowing therein. Even in reduced rainfall areas, water storages may be topped up by the introduction of recycled or treatment water or even desalinated water. In any event, it is considered likely that the cost of water 00 Sfor domestic, industrial and horticultural use will increase dramatically in C future.

A major disadvantage of such water storage systems is the high rate of water loss from to evaporation due to the combined effects of wind and water surface temperature. Evaporative losses are generally oo 0- measured in megalitres/hectare where a 100mm reduction in water depth per hectare equals one megalitre.

c In semi-arid areas where average annual rainfall may be of the 00oo order of 600mm, evaporative losses during the summer are typically of the C 10 order of 18 megalitres/hectare or a reduction in water depth of 1.8 metres. In more arid areas where average annual rainfall may be 200 mm or less, evaporative water losses of up to 30 megalitres/hectare have been recorded.

While the proportion of water lost by evaporation in water storage facilities can be reduced by increasing the depth/surface area ratio, this is generally uneconomical and the rate of loss per hectare will remain the same. For large capacity water storage dams of many hectares in surface area, these are usually constructed on flat land (without a surrounding catchment area) by pushing up a perimetral wall of 2-3 metres in height with a bulldozer. It generally is not economically feasible to excavate large volumes of earth to form a water storage facility. As far as the cost of evaporative losses are concerned, these may be measured by the cost of water purchased and/or the value of lost agricultural production. Typically, in an irrigation area where water is pumped from a stream, the current cost of a water allocation licence may cost from $1000-$3000 as an initial fee and a seasonal pumping cost of about $25 per megalitre subject to volumetric limits where the pumping distance or height is great, pumping costs can add substantially to the cost of water. These costs are steadily increasing as water becomes scarcer due to climatic changes, seasonal variations and increased levels of horticulture.

If evaporative losses were to be measured in terms of lost agricultural production otherwise possible, the value per megalitre of water could range between $500 for a cotton crop up to $1000 or even higher for 00 high value crops such as vegetables or the like. Similarly, even on current prices, the value per megalitre of water for urban use could be greater by an order of magnitude or more whereas the value for commercial usage could increase by several orders of magnitude.

5 Another problem associated with evaporative losses from open 00 0 storage facilities is the risk of increased salinity in water as water levels diminish due to evaporation. This problem can be exacerbated where the Nwater is constantly held in storage the storage facility is never completely 00

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Semptied or effectively flushed out to remove accumulated salt concentrations.

Over the years there has been extensive research into reduction of evaporative water losses. Prior art proposals have included chemical, physical and structural methods. Typically, chemical methods comprise the use of a chemical monolayer on the water surface to reduce the evaporation rate. The most well known of these is the use of cetyl alcohol. While chemical monolayers have proven useful in pilot studies on small surface areas, there are real practical difficulties in maintaining the integrity of the monolayer due to wind action as well as contamination and biodegradation of the monolayer.

Physical methods of evaporation control include destratification to bring cooler water to the surface however this is of little value in reducing evaporative losses to wind action.

Other physical methods have involved floating covers made from: expanded perlite ore polystyrene beads foamed wax blocks white spheres butyl rubber sheets painted white polystyrene sheets and rafts white foamed wax in continuous layers 00 O foamed butyl rubber 3 light grey asphaltic concrete blocks.

While encouraging results have been obtained with some of these systems (up to 80% reduction with floating concrete rafts) none are suited to very large water storages having a surface area of many hectares oO due to cost.

Structural methods including roofing of reservoirs have shown Sevaporation reductions of up to 90% but again, the cost of such structures is 0 not feasible for large surface areas.

United States Patent 6,517,285 describes a membrane based water conservation system conceived by the present inventor and Australian Patent 2002300784, also to the same inventor, describes a membrane jointing system.

Accordingly, the present invention seeks to overcome or ameliorate at least some of the disadvantages of prior art water evaporation control systems and to provide, if not a more efficient and cost effective system, at least a useful alternative choice.

SUMMARY OF THE INVENTION According to one aspect of the invention, there is provided an evaporation control system for a body of water, said system comprising: one or more membrane modules, each module having a buoyant membrane reinforced adjacent its perimetral edge with one or more flexible tensile members; and, a plurality of spaced tendons anchored adjacent opposite ends thereof, said tendons being mechanically coupled to said one or more flexible tensile members.

Suitably, said one or more membrane modules each comprise a membrane having a plurality of spaced buoyancy chambers.

Preferably, said one or more membrane modules each comprise one or more downwardly depending skirt members located adjacent a perimetral edge thereof.

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If required, said one or more skirt members may include ballast.

Suitably, said system comprises coupling members to form mechanical junctions between said flexible tensile members and said tendons.

00 If required, said system may comprise coupling members to form mechanical junctions between flexible tensile members of adjacent (buoyant membranes.

0 0 The tendons may be anchored adjacent opposite ends by fixed and/or movable anchor members.

If required, one or more of said anchor members may include tensioning means to tension said tendons to a predetermined tensile load.

If required, said tendons may extend adjacent perimetral edges of said one or more membrane modules.

The tendons may extend transversely of said one or more membrane modules above and/or below said one or more membrane modules.

Preferably, said tendons are arranged in a grid-like array.

If required, either or both of said flexible tensile members and tendons may have buoyancy members coupled thereto.

The buoyant membrane may comprise a multi-layered plastics sheet structure with a plurality of spaced buoyancy chambers formed on an undersurface thereof.

If required, said buoyant membrane may comprise a mechanically reinforced layer.

If required, said system may include a buoyant protective perimeter barrier extending about said one or more membrane modules.

Suitably, said tendons are anchored to posts inserted into a bed of a storage structure for said body of water.

If required, said tendons may be anchored to one or more perimeter walls or banks of a storage structure for said body of water.

Preferably, said system includes tendon tensioning means adapted to maintain a substantially constant tension in said tendons with fluctuations in an upper level of said body of water.

The perimetral tendons may be ballasted at selected intervals to resist wind lift in said one or more membrane arrays.

Suitably, said one or more membrane arrays include spaced drainage apertures.

According to another aspect of the invention there is provided a method of installation of an evaporation control system wherein a grid-like array of tendons is anchored at opposite ends of each respective tendon and a membrane module is floated on a surface of said body of water into an aperture in said grid-like array prior to securing said membrane module to respective adjacent tendons.

BRIEF DESCRIPTION OF THE DRAWINGS.

In order that the invention may be fully understood and put into practical effect, preferred embodiments will now be described with reference to the accompanying drawings in which:- FIG. 1 shows a single module system in a raised wall earth dam; FIG. 2 shows an enlarged view of a membrane module; FIG. 3 shows a plurality of mechanically coupled membrane modules; FIG. 4 shows a cross-sectional view of a membrane module through A-A in FIG. 2; FIG. 5 shows a mechanical coupling member; FIG. 6 shows a partially buoyant ballasting system; FIG. 7 shows an alternative embodiment of the invention; FIG. 8 shows a protective barrier system; and FIG. 9 shows yet another embodiment of the invention.

For the sake of clarity, like reference numerals are employed for like features throughout the drawings.

00 SThroughout this specification and claims which follow, unless Sthe context requires otherwise, the word "comprise", and variations such as T "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers or steps but not the exclusion of any other integer or group of integers.

00 DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 shows a single module system located in a typical S"turkey's nest" dam created by bulldozing a perimeter embankment to create 00 a large relatively shallow water storage facility.

c 10 About the embankment 1 forming the retaining walls for the dam are located spaced anchoring posts 2 which may be located in a posthole with rammed earth or they may include a concrete foundation 3.

Posts 2 are aligned with corresponding posts 2 on an opposite bank to support steel cables 4 in a rectangular grid array. If required, at least one of each pair of opposed posts may support a tensioning device such as a cable winch or the like (not shown). If required, an automatic or semi-automatic tension device which operates on a similar principle to a "snubber" in a boat mooring line may be employed to apply a constant tension to the cable array as it rises and falls with changing water volume within the dam.

A buoyant membrane module 5 is secured at its corners and intermediate each side to the grid-like array of cables by coupling members 6 which enable the anchoring cables 4 to be tensioned without applying undue tension to the membrane module. The membrane module may be constructed from a weather resistant multi-layer flexible laminate of a polymeric sheet with sealed thermoformed air compartments to provide buoyancy. Such a buoyant membrane material is described in International Publication WO 02/086258. The buoyant membrane material may also include a glass or plastics fibre woven reinforcing layer. A module may be formed by fusing adjacent edges of 2-3 m wide rolls of the membrane material to form a single membrane measuring, say, 50 m x 100 m, or even 100 m x 100 m with a reinforced edge, details of which will be discussed 00 8 Slater.

SThe membrane module may be located on the surface of a body of water 7 in the dam by coupling the anchoring cables 4 to the coupling members 6 and then with the aid of the cables 4, to pull the membrane into position before tensioning the anchoring cables 4.

00 0 Alternatively, the cables may be installed first and the membrane positioned thereafter by floating the membrane into position and carefully easing the N membrane over one of the perimeter cables 4. This may be assisted by 00oo reducing the tension in perimeter cable 4 to allow the cable to sag below the C 10 water surface.

If the membrane module 5 is subject to lifting due to wind and/or wave action, a downwardly depending perimeter skirt 8 of flexible polymeric sheet may be located about the perimeter of the membrane module 5. The skirt 8 may be ballasted adjacent its lower edge by, say, a length of steel chain located in a pocket (not shown) formed along the lower edge of the skirt 8. If required, cables 4a and 4b may be arranged to lie on the upper surface of membrane module 5 to restrain "ballooning" of the membrane due to a region of reduced air pressure being formed above the membrane as a prevailing wind passes over the surface of the membrane Potentially damaging wave action is largely ameliorated by the combination of the skirt 8 and cables 4, the latter serving to disturb the integrity of waves as they pass thereover. In addition, either or both of cables 4a,4b may have secured thereto buoyancy members such as spherical bodies 4' or rectangular or circular cross-section tubular foam plastics bodies 4" attached over the cables for added buoyancy and also to act as a "spoiler" to wind and wave action.

Water may be introduced into the dam from a nearby river by a pump (not shown) coupled to a fluid inlet conduit 9.

FIG. 2 shows an enlarged view of a buoyant membrane module 5 with a downwardly depending perimeter skirt 8 which may include slits to accommodate an intermediate transverse cables 4a, in this case 00 extending beneath the membrane 5. Alternatively, cables 4a may rest on the surface of membrane module 5 as shown in FIG. 1.

As shown, the grid-like array of cables shown in FIG. 1 is formed by coupling the steel cables 4 to each coupling member 6 whereby the two dimensional grid-like array can be tensioned in a two dimensional OO plane as required. The corners of membrane module 5 are also coupled to rcoupling members 6 as are the intermediate regions of membrane 5 coupled 0to respective coupling members 6 in such a fashion as to prevent undue

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tension being introduced into the membrane module 5. Where the level of water in the dam is subject to considerable variations, a substantially constant tension may be maintained in cables 4 by automatic or semiautomatic tensioning devices similar to resilient boat mooring line snubbers or mechanically equivalent devices.

Membrane module 5 includes flexible tensile members 11 such as rope or steel catenary cables (not shown) located in pockets (also not shown) about the upper perimeter of the membrane module. These catenary cables 11 are coupled to coupling members 6 and are the same length or slightly longer than the adjacent sections of tensioning cables 4 to avoid placing undue tension in membrane module 5. Alternatively, where catenary cables 11 are comprised of steel cables capable of withstanding applied tensions, tensile members 1 la, coupled intermediate the length of membrane module 5, may be coupled at opposite ends by coupling members 6 directly to tendons 4 to form a composite tensionable tendon structure anchored at opposite ends thereof by anchors (not shown).

Generally, such a structure would be employed for relatively small evaporation control systems as a large system preferably relies upon the structural integrity of a rectangular grid array of tendons anchored under tension with the membrane arrays loosely located without undue edge tension in each aperture of the grid array of tendons.

FIG. 3 shows schematically an array of six membrane modules located in abutting relationship to cover a much larger surface area of a 00 IU body of water such as a conventional water storage dam or reservoir. Such San array is formed in substantially the same manner as described with reference to FIGS. 1 and 2 and can be constructed to cover very large surface areas as a single integrated grid-like array of tensioning cables extending between coupling members 6, in turn supporting membrane 0O modules FIG. 4 shows a cross-sectional view of the module 5 of FIG. 2 (Ni through A-A.

0Skirt 8 will typically have a depth of between 200-1500 mm but c 10 this depth may be varied depending upon the ambient wind and wave patterns. A ballast 12 such as steel chain or the like is located in a generally tubular pocket 13 formed in the lower edge of skirt 8.

FIG. 5 shows one embodiment of a coupling member 6.

Coupling member 6 is a metal ring to which tension cables 4 and catenary cables 11 may be connected by conventional cable clamps 13.

As shown, catenary cables 11 are located in pockets 14 formed in the perimeter edges of membrane module 5. Coupling members 6 may also accommodate attachments or clamps 15 for securing other members to all or selected ones of coupling members 6 in a membrane module or an array of membrane modules.

FIG. 6 shows a semi-buoyant ballast system 16 which may be coupled to selected coupling members in an array of buoyant membrane modules.

As shown, the ballast system 16 comprises one or more hollow buoyancy members such as drums 17 partially filled with water until they float just below the surface 18 of a body of water. Drums 17 are tethered to a coupling member 6 by a rope, cable or chain tether 19. If due to wind and/or wave action, there is a tendency of an edge of a membrane module to lift, ballast system 16 changes rapidly from a neutral ballast influence to a substantial mass under any vertical movement of coupling member 6.

Alternatively, the buoyancy members may comprise hollow flexible walled 00 11 N sealed bladders (not shown) which are collapsible when the membrane modules approach the floor of the water storage facility to avoid placing the system into unnecessary tension.

It readily will be apparent to a person skilled in the art that many modifications or variations may be made to the various aspects of the 0 invention without departing from the spirit or scope thereof.

For example, in a very large body of water such as a reservoir, N it may not be practical to anchor support cables at opposite sides of a 00 0 waterway. In this case, an array of membrane modules may be tethered by a S 10 number of anchors located on the floor of the water storage facility. These anchors may include static masses such as large concrete blocks, marine anchors, screw piles, pylons or any other suitable earth anchoring system.

Ideally, the anchors are located at a sufficient distance from the tethered coupling to the membrane module array to permit accommodation of substantial variations in water depth due to fluctuations in seasonal and other flows of water into and out of the water storage facility.

As shown in FIG. 7, evaporation control system 30 comprises an array of buoyant membrane modules 5 with tensionable tendons 4 coupled to coupling members 6 spaced about the perimeter of array Located at the corners of each membrane module 5 are pylon anchors 31 driven into the bed of the water storage facility. Coupling members 6 are anchored to pylon anchors 31 by tethers 32 coupled to a sliding or roller ring coupling 33 secured about each pylon anchor 31 to enable the array 30 to move up and down with the level of the body of water upon which the array 30 floats. At the inner corners of membrane modules 5, tendons 4 may be coupled directly to each other by a coupling member 6 (not shown) or alternatively, to slide on roller ring couplings 33 engaged about central pylons 31a as shown. Tendons 4 and tethers 32 together may be tensioned to form a rectangular grid array of tensile members with membrane arrays 5 located in each aperture of the grid array, the grid array supporting each membrane array at respective corners on coupling members 6 and straps 6a if required.

00 1L In the embodiment shown in FIG. 7, each membrane module has an edge reinforcement in the form of a catenary rope or cable 11 and between the outer edges of array 30 and respective pylon anchors 31 the tethers 32 comprise flexible tensile members coupled at one end to the interconnected tendons 4 and the pylon anchor 31. Automatic or semi- 00 0 automatic tensioning devices (not shown) such as that identified by reference numeral in FIG. 1 may extend between the module array 30 and Srespective pylon anchors 31 in conjunction with or in lieu of tethers 32. If 00 Srequired, some or all of pylon anchors 31 may be further secured by screw anchors 34 or the like tethered directly to pylon anchors 31 by guy ropes or the like secured above the travel path of slide on roller rings 33 or otherwise to slide on roller rings 33 via a tension compensating device to allow for changing water levels. The tendons 11, tethers 32 and guy ropes may be selected from any suitable material such as stainless steel wire, synthetic or natural cables, ropes or the like or any combination thereof.

For very large water surface areas, a plurality of membrane module arrays, each with its own submerged anchoring system, may be interconnected via respective coupling members thereby permitting individual membrane module arrays or even individual membrane modules to be readily replaced and removed in the event that maintenance or repair is necessitated.

FIG. 8 shows an alternative embodiment of an evaporation control system 40 according to the present invention which may be subject to damage by flotsam and jetsam in seasonal flood conditions wherein a buoyant or semi-buoyant protective barrier 41 may be positioned adjacent selected edges of a membrane module array to prevent contact from floating logs or the like. By way of example, lengths of large diameter plastics pipe 41a, sealed at opposite ends and coupled in an end to end manner may be anchored or otherwise tethered at a distance from the membrane module array 40. The pipe lengths may be partially filled with water ballast if required. A steel mesh barrier or the like (not shown) may be suspended 00 13 from below the buoyant barrier structure to engage semi-buoyant objects.

rF Another alternative may be a protective barrier comprising a plurality of hollow plastics traffic barriers 41b, coupled in end to end configuration, and partially filled with water to provide protection from semisubmerged as well as floating articles. These barriers may be placed o upstream of the membrane array and angled to deflect floating objects around the array. Such protective barriers, having an upper surface located 0 above the water level, also provide a wave dampening effect and an air flow 0 0spoiler.

c 10 FIG. 9 illustrates schematically yet another embodiment of the invention.

In FIG. 9, a grid-like array of tendons 4 with associated coupling members 6 forms an array of adjacent rectangular apertures 50 as generally described hereinbefore. Located within each aperture 50 is a membrane module 5 secured at the corners thereof to coupling members 6 by flexible tensile members such as cords or ropes of synthetic or natural fibres or steel cables. Membrane module 5 has perimetral edges 51 reinforced with a flexible tensile member (not shown) secured to the perimetral edge 51 by any suitable means such as a locating pocket (not shown). Each corner of membrane module 5 is reinforced with a stiff or rigid reinforcing member 52 in a manner similar to a sail corner reinforcing board and has a eyelet or the like (not shown) for connection to an adjacent coupling member 6 by a flexible tensile member 53.

Depending upon the size of membrane module 5 and/or the risk of wind lift under the edges of membrane module 5, one or more of perimetral edges 51 may be secured to an adjacent tendon 4 by further flexible tensile members in the form of straps 54.

In the embodiment shown in FIG. 9, the membrane module preferably comprises a multi-layered laminated or co-extruded membrane having at least one layer formed from a reinforcing material such as a woven plastics sheet or a fibreglass cloth reinforced plastics sheet.

00 14 SEach of the embodiments described herein may include spaced ,F drain apertures 45 to allow drainage of rainwater collected on the top surface of membrane array 5. Alternatively, for applications other than evaporation control such as tailings dams, where dilution of the contents of the dam is to be avoided, or biomass digesters where escape of malodorous gases is to 0 be avoided, the membrane may form a contiguous seal over the storage facility. To avoid accumulation of rainwater, a sump depression 46 may be Sformed in the membrane by the weight of an electric or gasoline powered 00oo 0pump 47 resting on a base frame 48. A float valve or the like (not shown) C 10 actuates the pump 47 to pump accumulated rain water away via conduit 49.

For applications where accumulated gases are to be collected, a skirted membrane array such as that shown in FIGS. 1 and 2 is preferred with a floating device (not shown) supporting an outlet port of a collection conduit (also not shown) under the membrane array Membrane modules may be pre-fabricated at a remote location and transported on to site for installation. Alternatively, membrane subassemblies may be pre-fabricated at a remote location and assembled onsite utilizing the method and/or apparatus described in Australian Patent 2002300784, the content of which is incorporated herein by cross-reference.

In man made water storages such as a "turkey's nest" dam comprising a generally flat inner floor surface surrounded by a raised perimetral wall, the expression "floor", "bed", "base" and "wall", "bank" or the like have a clear structural distinction. Where a water storage is formed from a natural structure such as a flooded river valley or the like, the structural distinction between the expressions "floor", "bed" or "base" on the one hand and "wall" or "bank" on the other hand is not as clear, particularly when the water level in such a storage facility can fluctuate greatly. Accordingly, for the sake of clarity, the expressions "floor", "bed" or "base" as they may apply to a water storage facility is to be taken as the lowest cross-sectional portion of a geological or earth formation and "wall" or "bank" is that portion rising above the "floor", "bed", or "base" and which functions to constrain a body of 00 0 Swater within the geological or earth formation.

f The various embodiments of the invention described herein t incorporate differing features by way of example. It is to be understood that the various individual features described herein, alone or in any combination 5 thereof, may be utilized with any or all of the evaporation control system oo 0 embodiments described herein.

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Claims (15)

1. 3. A system as claimed in claim 1 or claim 2 wherein said one or more membrane modules each comprise one or more downwardly depending skirt members located adjacent a perimetral edge thereof.
2. 4. A system as claimed in claim 3 wherein said one or more skirt members includes ballast. A system as claimed in any preceding claim wherein said system comprises coupling members to form mechanical junctions between said flexible tensile members and said tendons.
3. 6. A system as claimed in claim 5 comprising coupling members to form mechanical junctions between flexible tensile members of adjacent buoyant membranes.
4. 7. A system as claimed in any preceding claim wherein said tendons are anchored adjacent opposite ends by fixed or movable anchor members or a combination thereof.
5. 8. A system as claimed in claim 7 wherein said one or more of said anchor members includes tensioning means to tension said tendons to a predetermined tensile load.
6. 9. A system as claimed in any preceding claim wherein said tendons extend adjacent perimetral edges of said one or more membrane O 0 modules. A system as claimed in any preceding claim wherein said tendons extend transversely or longitudinally of said one or more membrane modules adjacent an upper or lower surface thereof.
7. 11. A system as claimed in any preceding claim wherein said 0 tendons are arranged in a grid-like array.
8. 12. A system as claimed in any preceding claim wherein either or both of said flexible tensile members and tendons have buoyancy members 00 Scoupled thereto. c, 10 13. A system as claimed in any preceding claim wherein said one or more membrane modules comprise a multi-layered plastics sheet structure with a plurality of spaced buoyancy chambers formed on an undersurface thereof.
9. 14. A system as claimed in claim 13 wherein said membrane module comprises a mechanically reinforced layer. A system as claimed in any preceding claim wherein said system includes a buoyant protective perimeter barrier extending about said one or more membrane modules.
10. 16. A system as claimed in any preceding claim wherein said tendons are anchored to posts inserted into a bed of a storage structure for said body of water.
11. 17. A system as claimed in any one of claims 1 to 15 wherein said tendons are anchored to one or more perimeter walls or banks of a storage structure for said body of water.
12. 18. A system as claimed in any preceding claim including tendon tensioning means adapted to maintain a substantially constant tension in said tendons with fluctuations in an upper level of said body of water.
13. 19. A system as claimed in any preceding claim wherein perimetral tendons are ballasted at selected intervals to resist wind lift in said one or more membrane arrays. A system as claimed in any preceding claim wherein said one 00 18 Sor more membrane arrays include spaced drainage apertures.
14. 21. A method of installation of an evaporation control system according to any preceding claim wherein a grid-like array of tendons is anchored at opposite ends of each respective tendon and a membrane module is floated on a surface of said body of water into an aperture in said 0 grid-like array prior to securing said membrane module to respective adjacent tendons.
15. 22. A method of controlling evaporation in a body of water wherein 00oo an evaporation control system as claimed in any one of claims 1 to 20 is c 10 secured on a surface of a body of water.