Field of the Invention

This invention relates to water storage and dams and reservoirs for water storage, and in particular to a system and method for mitigating losses through evaporation from open topped dams and reservoirs.

Background Art

The following discussion of the background art is intended to facilitate an understanding of the present invention only. .It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge as at the priority date of the application.

In Australia and in many other dry regions in the world, there is a high rate of water evaporation from open storage reservoirs, dams and lakes. Per year the loss of water could exceed 2 m of the water column. For a typical reservoir size with a surface area of about 1 million m2 (1 km * 1 km) this amounts to a loss of around 2 million tonnes of water, rendering a gross financial loss in the order of $ 4 M per year, at an assumed domestic sales price of potable water of about $ 2 per tonne.

At increasing scarcity of fresh water, worldwide, it is anticipated that losses of such magnitude will not be accepted for much longer and that, as a consequence, effective measures to prevent evaporation will need to be enforced.

To accomplish this, the preferred (low-cost) solution would be to cover the water with a thin layer of buoyant, water-impermeable and flexible, plastic or fabric (hereafter called 'fabric'). Indeed this solution has been applied domestically in swimming pools and spa pools, where initially covers for such pools were used as an insulator to retain heat, and increasingly the use of such covers has been to reduce loss of water through evaporation. The scaling up of such an arrangement to cover dams and reservoirs presents some additional challenges. This invention seeks to provide a method, and an arrangement for deploying a cover for dams and reservoirs to mitigate (reduce) losses through evaporation.

Throughout the specification unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Throughout the specification unless the context requires otherwise, the word "include" or variations such as "includes" or "including", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Disclosure of the Invention

In accordance with one aspect of the present invention there is provided a connector for buoyant sheeting used to mitigate evaporation from a body of water, said connector being elongate to extend along an edge of buoyant sheeting or between edges of adjacent buoyant sheeting and having a plurality of fixing means located along the longitudinal extent of said connector, said plurality of fixing means being located on an upper surface thereof, to secure edges of said buoyant sheeting thereto.

Preferably said plurality of fixing means are located in a position recessed from an upper surface of said connector, in order to provide greater streamlining of said connector against forces imparted by wind, when in use.

Preferably said plurality of fixing means comprises fixings each spaced apart from each other by a predetermined distance. The buoyant sheeting is provided with complementary fixings along its edges, aligned with the fixings of said connector, so a plurality of said buoyant sheeting can be secured along its edges to a plurality of said connectors extending therebetween.

Preferably each fixing is selected from one of the following:

• a fastener located along the central longitudinal axis of said connector, or a pair of fasteners one located each side of the central longitudinal axis of said connector, • a bolt located along the central longitudinal axis of said connector, or a pair of bolts one located each side of the central longitudinal axis of said connector, either with or without an eyenut or pair of eyenuts respectively,

• an eyebolt located along the central longitudinal axis of said connector, or a pair of eyebolts one located each side of the central longitudinal axis of said connector,

• a loop located along the central longitudinal axis of said connector, or a pair of loops one located each side of the central longitudinal axis of said connector, or

• a pair of clip fasteners, one located each side of the central longitudinal axis of said connector.

Preferably said connector is neutrally buoyant or slightly heavier than water. The connector is preferably of a specific gravity so that it is restrained against sinking by the buoyant sheeting, but not sufficiently light that the connector sits higher in the water than the buoyant sheeting. This arrangement ensures that the connector does not produce any lift through sitting proud in windy conditions.

Preferably said connector has a specific gravity of from 1.0 to 1.1.

Preferably said connector has a specific gravity of from 1.0 to 1.075.

Preferably said connector has a specific gravity of from 1.0 to 1.05.

Preferably said connector has a specific gravity of from 1.0 to 1.025.

Preferably said connector includes an opening or a plurality of openings along the longitudinal length thereof, extending from said upper surface of said connector to a lower surface of said connector. With such an arrangement, any water lying on the buoyant sheeting may run off into the main body of water comprising the reservoir. This water may be collected from rainfall or from the reservoir itself due to disturbance such as wind. The openings also allow contact with air to assist in aeration of the water in the reservoir.

Preferably said connector comprises a pair of parallel members extending along the longitudinal axis, and each fixing comprises a pair of said fasteners, one located on each member, said members being spaced apart and rigidly joined by a plurality of transverse struts. Alternatively said connector comprises a pair of parallel tubular members extending along the longitudinal axis, and each fixing comprises a pair of said fasteners, one located on each member, said members being spaced apart and rigidly joined by a plurality of transverse struts.

Preferably each said tubular member is formed from plastic pipe, and is partially filled with a settable composition leaving an air space thereabove to provide the required buoyancy in said connector.

In accordance with a second aspect of the invention there is provided a system for reducing evaporation from a body of water in a reservoir or dam, the system comprising pieces or lengths of buoyant sheeting provided with connection means along edges thereof, said system including connectors as described above for connecting to said connection means by said plurality of fixing means of said connectors, said connectors being provided to join said pieces or lengths of buoyant sheeting to adjacent pieces or lengths of buoyant sheeting.

Preferably said connection means comprise a plurality of eyelets spaced apart from each other by a predetermined distance, corresponding to the predetermined distance the fixings are spaced apart on said connector.

Preferably in said system, a plurality of said connectors extend continuously along edges of said buoyant sheeting to connect to edges of adjacent lying buoyant sheeting on the surface of the body of water.

Preferably in said system, outer edges of said buoyant sheeting on the surface of the body of water are provided with connectors as described above extending along the outer edges, to provide a tether point to anchor the system to a shore or edge surrounding the body of water.

Preferably said buoyant sheeting comprises a length of buoyant sheeting dispensed from a roll.

Preferably said buoyant sheeting has a light coloured or reflective upper surface, to reflect light and minimise heating of water that it overlies when in use.

Preferably said buoyant sheeting is flexible. Preferably said buoyant sheeting is impermeable to water.

Preferably said buoyant sheeting is formed with apertures extending from one surface to the other to release any gas forming therebelow.

In accordance with a third aspect of the present invention there is provided a method for reducing evaporation from a body of water in a reservoir or dam, the method comprising providing pieces or lengths of buoyant sheeting provided with connection means along edges thereof, and providing connectors as described above for connecting to said connection means by said plurality of fixing means of said connectors, said connectors being provided to join said pieces or lengths of buoyant sheeting to adjacent pieces or lengths of buoyant sheeting to form a two dimensional array of pieces or lengths of buoyant sheeting joined along their edges by said connectors extending across substantially the surface of the body of water. The connectors provide rigidity to the array and resistance against drift due to forces which may be imparted by windy conditions that the array might be subjected to. The array may not necessarily extend across the entire surface of the body of water, and indeed the edges of the body of water may remain exposed to provide space for anchoring ropes and tensioning arrangements which may otherwise damage or be impeded by any buoyant sheeting that extends thereacross.

Preferably in the method, said connection means (of said buoyant sheeting) comprise a plurality of eyelets spaced apart from each other by a predetermined distance, corresponding to the predetermined distance the fixings are spaced apart on said connectors.

Preferably in the method, a plurality of said connectors extend continuously along edges of said buoyant sheeting to connect to edges of adjacent lying buoyant sheeting on the surface of the body of water.

Preferably in the method, outer edges of said buoyant sheeting on the surface of the body of water are also provided with connectors as described above extending along the outer edges, to provide a tether point to anchor the system to a shore or edge surrounding the body of water. This arrangement is preferred as it assists in spreading the load between the tethering ropes and the buoyant sheeting. Preferably said buoyant sheeting comprises a length of buoyant sheeting dispensed from a roll.

Preferably in said method, said buoyant sheeting is flexible.

The invention can, in its most preferred form, be described as a modular system of interconnected floating fabric sheets covering a water body with the following capabilities:

- to withstand severe storm-induced wind forces without risk of dislodging;

- to cope with large water level fluctuations without risk of failure;

- to allow removal of debris from its surface in a relatively easy, low cost, manner;

- to provide for aeration of the water, to benefit aquatic life in the reservoir

Brief Description of the Drawings

A preferred embodiment of the invention will now be described in the following description of a connector, a system and method for reducing water loss from a reservoir due to evaporation using buoyant sheeting secured using the connector, made with reference to the drawings in which:

Figure 1 is a plan view of a connector according to the embodiment;

Figure 2 is a cross section of the connector of figure 1 , showing it connected to buoyant sheeting adapted for use therewith;

Figure 3 is a plan view showing one deployment an array of buoyant sheeting according to the method and system of the invention;

Figure 4 is a plan view showing another deployment an array of buoyant sheeting according to the method and system of the invention;

Figure 5 is a longitudinal elevation showing deployment of the array of figure 3;

Figure 6 is a plan view corresponding to figure 5;

Figure 7 is a longitudinal elevation showing an alternative installation of the system of the invention; and

Figure 8 is a longitudinal elevation showing another alternative installation of the system of the invention.

Best Mode(s) for Carrying Out the Invention

The embodiment is a system and method for reducing loss of water through evaporation from reservoirs, and a connector for used with buoyant sheeting in the system and method. Referring to figure 1 , the connector is illustrated. The connector is in the form of a float 11 of neutral buoyancy and elongate construction, being a nominal 970 mm long, a nominal 360 mm transverse width, and a nominal 140 mm vertical height. The float 11 has two parallel members each in the form of tubular members being ultra violet stabilised plastic pipe 13 and 15. The plastic pipes 13 and 15 are spaced apart and joined by transverse struts in the form of transverse rods 17 made of steel which is galvanised or otherwise coated to prevent rusting. The transverse rods 17 are spaced apart from each other to support the pipes 13 and 15 relative to each other. The spacing apart of the pipes 13 and 15 by the transverse rods 17 provides an opening 19 between the pipes 13 and 15, which extends all the way through from an upper surface or extent 21 to a lower surface or extent 23 of the float 11. The plastic pipes 13 and 15 are sealed at their opposed ends by caps 25. In an alternative embodiment other means such as foam plugs could be employed instead of caps.

The plastic pipes 13 and 15 are provided with a plurality of fixing means in the form of fixings 27 29 31 and 33 which are spaced apart from each other along the longitudinal extent of the float 11 , by a predetermined distance. Each of the fixings 27 29 31 and 33 comprises a pair of fasteners in the form of bolts or studs 35 37, provided one bolt or stud 35 37 extending out of each plastic pipe 13 15 respectively (spaced apart longitudinally along each plastic pipe 13 15 by the predetermined distance). As can be seen in figure 2, the fixings 27 are located below the upper surface or extent 21 of the float 11.

The pipes 13 and 15 with assembled transverse rods 17 are partly filled with concrete 39 or another settable substance heavier than water, to an extent sufficient to render the float almost neutrally buoyant when placed in a water body. The concrete 39 or other settable composition must be sufficiently rigid to prevent the transverse rods 17 being pulled out, or alternatively the transverse rods 17 can be formed with a kink which rests within the settable composition to prevent disengagement. The extent that the settable composition fills the float will depend on its specific gravity. The float 11 should be buoyant to the extent that it floats just contacting the surface of the water. It may be slightly heavier than water, as any tendency to sink will be countered by the buoyancy of the buoyant sheeting to which the floats 11 are to be attached, as will be described hereunder. The reason for this arrangement, and the fixings 27 being located below the upper surface or extent 21 of the float 11 , is so that the float when connected to fabric/buoyant sheeting presents the minimum profile to wind which might cause the float and sheeting assembly to be deflected or otherwise disturbed under windy conditions.

Each float 11 is used to connect to adjacent buoyant sheeting 41 and 43. The portion of the buoyant sheeting along and adjacent to the edges 45 are provided with connection means in the form of eyelets 47 spaced according to the same predetermined distance as the spacing of the fixings 27 29 31 and 33 on the float 11. Each eyelet 47 is connected to a bolt or stud 35 37 and secured by a locking nut such as a nylock nut 49 (and washer 51 ), thus securing each buoyant sheet 41 and 43 to a respective pipe 13 and 15.

The floats 11 shown in figures 1 and 2 are used fitted along both the longitudinal edges 53 and transverse edges 55 of adjoining buoyant sheeting, fusing/forming them into one large 'blanket' 57 which would cover most of water surface of a typical reservoir 58 as shown in figure 3.

To prevent the completed 'blanket' from being shifted by wind forces, its edges would be anchored at regular intervals by means of ropes or cords 59 which may be elastic or inelastic, connected to onshore pins or small anchor piles 61.

In areas where the reservoir's embankment has a gentle gradient, as shown in zone 63, the edge of the 'blanket' could be anchored directly onshore by a row of anchor pins 65, driven into the bank material through eyelets in the fabric.

The first sheeting 41 (a) would be installed, and successive sheets would be installed, commencing with sheeting 43 (b) and sheeting 43' (g), on either edge of sheeting 41. This makes it possible to operate two crews, one of which would install the buoyant sheeting 43 (b) and further sheeting (c to f) outward (away from sheeting 41) and the other crew would install the buoyant sheeting 43' (g) and further sheeting (h to 1) extending outward in the opposite direction.

In the case of a relatively small -man made- reservoir or basin as shown in figure 4, anchoring would not be required. Note that in this application the 'blanket' 57 would be free floating, kept fully stretched by its longitudinal and transverse rows of floats 11. Referring to figures 5 and 6, the installation procedure is illustrated. The buoyant sheeting 41 is provided on a roll 67, which is mounted on a spindle 69 for dispensing. The buoyant sheeting 41 is pulled off the roll 67 in the direction indicated by arrow 71 by a small - trailerable - craft 73, connected by tow ropes array 75 which are secured to end floats 11. During the towing process, further floats 11 are fixed to the side edges 77 of the buoyant sheeting 41 as soon as it makes contact with the water surface 79. Once the buoyant sheeting reaches the shore opposite the roll, it is secured in position. An adjacent roll of buoyant sheeting 43 is unrolled and floats are affixed along the edge thereof, opposite the buoyant sheeting 41 already in position, as the buoyant sheeting 43 is being extended. Once fully extended, the buoyant sheeting 43 is secured to the floats already in position attached to the buoyant sheeting 41. Further buoyant sheeting is added in similar fashion until the reservoir is covered to the desired extent, forming a blanket of buoyant sheeting connected by floats.

Referring to figure 7 to ensure that installed 'blanket' 57 can not be dislocated by the substantial drag force caused by storm wind conditions, its ends 81 are anchored onshore by means of anchor pins 65 driven through the buoyant sheeting's eyelets 47. To increase pull-out resistance, the buoyant sheeting can be placed in a pre-dug trench 83 which would subsequently be filled by compacted soil, crushed rock, limestone, cemented sand or concrete 85. Optional weights 87 can be placed at regular intervals to hold down the buoyant sheeting and/or to keep it under some tension.

Referring to figure 8, at its opposing end 89, the 'blanket' 57 is anchored by ropes or cords 91 , connected to small anchor piles or stakes 93. The 'blanket' 57 would be kept under constant tension, irrespective of the fluctuating water levels in the reservoir, by means of weights 95 which are hung from the ropes 91. The downward force of the weights 95 is compensated by the buoyancy of special end floats 97 which are more buoyant than the other floats 11 through not being filled with concrete. In figure 8, a higher water level in the reservoir is illustrated, along with the configuration of the system of this embodiment, in dashed outline. It should be noted that only limited tension in the buoyant sheeting is required to prevent significant downwind shifting of the blanket, even during the most severe storm conditions.

With the arrangements of covers for reservoirs as illustrated in the embodiments, leaves and any other forms of debris heavier than water can be brushed or hosed into the water through the openings 19 between the pipes 13 and 15 of the floats 11. Man-made rubbish such as, for example, plastic bags and natural materials lighter than water, such as twigs and branches, would be manually collected and removed. This can be done by workers traversing the buoyant sheeting on short skis or in pontoons, punts, shallow inflatables or canoes of a type with rounded hulls which allow them to traverse in any direction, across both the buoyant sheeting and the floats 11. The load spreading effect of skis, in combination with the trampoline effect of fabric tension and the tension introduced through the rope anchoring, would reduce foot (or hull) subsidence to, at most, a few inches. The most effective arrangement for cleaning and maintenance would be a small portable pontoon of light material with little draught (ideally not exceeding 50 mm) would be most effective. It could be pulled lengthwise along a blanket sheet via auxiliary pull rope, which while being used could be sufficiently tensioned at both shore ends to prevent the pontoon from being shifted sideways by any strong cross winds. It would easily slide over the buoyant sheeting and floats and would provide a rotationally stable platform for the cleaner or cleaners. In order to remove debris from the surface of the buoyant sheeting, a compact water jetting unit with its intake alongside the pontoon could be utilised to jet debris off the buoyant sheeting and onto the floats, where it may pass through the apertures in the floats. Larger or floating debris can be manually retrieved and transported on the pontoon.

The buoyant sheeting is a woven polypropylene that is treated to be waterproof and ultraviolet stable. Such sheeting is buoyant and flexible. The polypropylene sheeting or a covering layer is light in colour or reflective, so as to minimise heating of the water through incident sunlight. While other flexible sheeting known in the art for covering domestic swimming pools and domestic spa pools may be used, this is more expensive than the polypropylene product.

Other arrangements may be utilised including a composite including polypropylene or another buoyant material. The upper face or layer of the material is one which is light in colour or reflective, so as to minimise heating of the water through incident sunlight. The polypropylene layer may be bonded to overlie a layer of buoyant sheet which may be a foamed plastic sheet or plastic sheet incorporating an array of air bubbles. With the upper layer of the buoyant sheeting being of polypropylene, this minimises friction, easing the sliding of watercraft thereover. The buoyant sheeting should be waterproof to minimise losses due to evaporation. While the sheeting is most preferably waterproof to minimise losses through evaporation, fabrics that are not waterproof would be expected to have some effect in reducing evaporative losses, as there would still be the effect of the fabric damping down rippling and wave action which in turn would minimise the surface area from which evaporation takes place.

The buoyant sheeting requires sufficient tensile strength to be able to safely cope with the maximum drag force induced by storm winds and/or the weight of maintenance personnel. For long life, the buoyant sheeting needs a high level of UV light protection. It is recommended that the upper surface of the buoyant sheeting is pale, preferably white or silver, in order to maximize sunlight reflection. This keeps the covered water body relatively cool, and could compensate for thermal losses that would otherwise occur through evaporation, minimising the impact on aquatic life in the reservoir. This, and the effective shielding from sunlight, can assist in minimising algal growth. Part of the water surface would remain uncovered, to the extent that natural aeration of the water body either through edges that are uncovered, and/or via the openings 19 in the floats 11 would remain high enough to ensure the well being of fish and other forms of aquatic life.

At regular intervals, in perpendicular directions, the buoyant sheeting can be perforated with small vent holes in order to allow the escape of gasses generated during the anaerobic decay of organic material in the reservoir or at the base at the reservoir. This would effectively prevent the formation of gas pockets below the buoyant sheeting, ensuring that the buoyant sheeting material would remain in direct contact with the water at all locations at all times.

It should be noted that the invention is not limited to the configurations of the described embodiments, and that changes may be made from these embodiments, within the scope of the invention as described, without departing from the spirit and scope of the invention. Particularly, dimensions given in connection with the embodiments are given by way of example, and changes may be made to accommodate whatever materials are readily available to implement the invention in a cost effective manner.