BACKGROUND OF THE INVENTION There are many situations in which there is a need for easily installed dam structures, particularly as part of temporary works during construction or in farming practice, or in response to flooding, whether natural or accidental.

There have been many proposals to construct temporary dams using flexible materials to contain a fluid, preferably utilising the dammed fluid itself to form a part of the resulting structure. For example, one previous device makes use of two elongated polyethylene tubes which are impermeable to water and which are contained within an outer tube made of woven polypropylene material. When the inner bags are filled with water and the ends of the tubes are elevated above the level of the water to be contained so as to keep the contents therein, the apparatus forms a stable structure able to resist rolling under pressure from the water to be contained, thereby acting as an effective dam or breakwater.

This device however has the disadvantage of requiring the two inner tubes to be filled simultaneously to prevent rolling of the structure during filling. This requires, in practice, either two supplies of water to fill the structure or some additional external piping to enable inflation. A further disadvantage is that the apparatus does not generally incorporate a valve or valves to prevent the water, or other fluid, from escaping, necessitating either the elevation of the ends or sealing of the structure by some suitable means. A further disadvantage is that in practice, when the apparatus is either deflated or only partially inflated and is being deployed or handled, it is possible for the inner tubes to become twisted within the outer tube necessitating that the apparatus be removed and made good.

A further disadvantage of the apparatus is the cost of construction, since the structure comprises three or more separate tubes, one of which must encompass at least two of the others.

OBJECT OF THE INVENTION The present invention has therefore been conceived out of the need to provide an improved and cost effective means of containing water or other fluid which overcomes some or all of the foregoing disadvantages. At the very least, the invention provides an alternative to presently known means of providing temporary dams or breakwaters.

DISCLOSURE OF THE INVENTION According to one aspect of the present invention, there is provided a temporary dam or breakwater, comprising a number of cells formed by joining longitudinally (ie along their length) two or more tubes made of flexible impermeable material, which tubes are to be filled with water or other fluid in use, and wherein the tubes are provided with means for fluid to migrate between adjacent tubes whilst the tubes are being filled with water or other fluid when being deployed for use, but which become effectively sealed when fully inflated with fluid, thereby preventing migration of fluid between the tubes and thereby making the temporary dam or breakwater a stable structure for the containment of water or other fluid when filled. According to another aspect of the invention, there is provided a method for deploying such a temporary dam or breakwater.

In one form of the invention, two large diameter thin-walled tubes (eg of polyethylene) of similar dimensions are joined along their length by welding the tubes to each other along a pair of lines that are distant from each other by approximately 1/4 of the circumference of the tubes. This results in an elongated tube-like structure comprising three cells, being two outer cells, each of large diameter corresponding to each original tube, joined to and either side of a central cell of smaller diameter formed between the pair of lines where the two tubes are joined.

Prior to the joining of the two tubes, a plurality of slits or holes is made in the side of each tube at approximately regular intervals along the length of each tube in the region between the lines where the two tubes are to be joined. After joining, these slits or holes permit the flow of fluid between the smaller central cell and the adjoining larger outer cells during filling of the structure. However, when the two tubes are to be joined, they are aligned lengthwise in such a manner that the slits or holes in their sides do not align but are alternately staggered, so that a hole in one tube is located approximately centrally between a pair of holes in the other side and so on along the length of the structure (excepting of course for the last hole at each end of the structure).

To facilitate inflation of the structure, a simple valve is incorporated into the join which will become the upper join in use between the two tubes. This valve communicates between the outside of the structure and the smaller central cell formed between the two tubes and is itself preferably constructed by forming a flat tube in flexible impermeable material, eg polyethylene, sufficiently large enough to accommodate the end of a hose or similar used to inflate the structure. The tube forming the valve also needs to extend sufficiently far into the smaller inner cell, so that when collapsed under pressure from water contained therein or as described below by collapse of the inner cell itself, it will act as a one-way valve preventing water or other fluid from escaping.

The ends of the structure are sealed so that the ends do not have to be elevated above the level of water to be contained in order to prevent the escape of the water or other fluid.

During filling of such a structure, water or other fluid will easily permeate or find its way throughout the entire structure as the walls of the tubes will be in a relatively relaxed state.

In other words, water will be free to flow through the inlet valve which is itself kept open by the hose or the like which has been inserted therethrough. The water will pass into the smaller central cell and make its way through the slits or holes in the walls of each tube and thus fill the tubes simultaneously. As the water fills the structure, it will cause the tubes (ie the two larger outer cells) to swell or inflate and because of the inherent geometry involved will cause the smaller inner cell (due to the pressure of water contained in each of the larger tubes) to decrease in size as the portions of the wall of each tube between the two joins are caused to be pulled taut as the outer tubes attempt to form circular cross-sections.

Once the structure is fully inflated with water or other fluid, the walls between the joins will have thus come into contact with each other along their length, thereby excluding all the water therebetween and thus forming an effective seal between the tubes, since each hole or slit will then be covered by that portion of the corresponding wall of the adjacent tube, preventing flow of water therethrough.

When the structure is fully inflated, the hose is withdrawn and the pressure of water in the two tubes which has caused collapse of the inner cell also causes the inlet tube to collapse as well, thereby preventing egress of the water from the structure.

In other forms of the invention, there may be more that one filling valve and these may be located, for example, at the ends of the structure or in the bottom join between the two tubes. Still further, in other forms of the invention, the structure may be formed by the joining of more than two tubes to make a larger structure or a structure more suited to particular circumstances such as a change in river depth, where it is necessary to divert flowing water rather than containing relatively still water.

The invention may be made from any flexible impermeable material such as polyethylene or PVC. The structure according to the invention can be made, depending upon the particular material, by welding, sewing or gluing of the various parts to each other in known fashion.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention will now be described with reference to the drawings in which: Fig. 1 shows a perspective view, partially cut away, of one example of the temporary dam according to this invention; and Fig. 2 shows a schematic cross-section of the temporary dam structure according to Fig. 1, illustrating the structure just prior to joining the two tubes from which it is formed.

BEST MODE OF CARRYING OUT THE INVENTION Referring generally to Figs. 1 and 2, there is illustrated a structure generally referenced 11, which is a temporary dam structure according to the invention and which comprises two tubes 12 and 13 of flexible material that are joined together along their length, for example by heat welding, the upper join being designated 14 and the bottom join 15, to form a structure 11 comprising three cells, 16,17 and 18, of which the two larger outer cells 16 and 17 are the regions defined by and within the tubes 12 and 13 and the smaller inner cell 18 is defined as that region formed between the two joins 14 and 15 and is located between the two cells 16 and 17. Fig. 2 illustrates schematically the structure I I just prior to joining the two tubes 12 and 13 together in the direction of arrows"A"and"B"along the lines which are to form the respective joins 14 and 15.

The respective wall portions 19 and 20, of tubes 12 and 13, located between joins 14 and 15, are each perforated intermittently along their length by a plurality of holes, of which only one pair, holes 21 and 22 respectively, are illustrated. These holes 21 and 22, are offset from each other so that for a fluid to flow from cell 16 to 17 it would have to flow for a significant distance along the axis of the structure 11, ie along a portion of cell 18.

A filling valve 23 comprising a flat tube 24 of flexible material is located in a portion 25 of the upper join 14, so that there is communication between the outside of the structure 11 and the inner cell 18 to allow filling of the structure (and where required later release of the contained water). In other words, in the portion 25, the seal between the respective portions of the tubes 12 and 13 along join 14 is replaced by seals between the respective tubes 12 and 13 and opposite sides of the flat tube 24 comprising the filling valve 23.

In use, the structure 11 is inflated by inserting a hose-end or pipe-end or similar (not illustrated) into the filling valve 23, at its free outer end 26, thereby causing the valve 23 to open and remain open during filling. Water or other fluid then flows into cell 18 and makes its way along the axis of the structure 11 attempting to find an equilibrium and escaping to cells 16 and 17 by way of holes 21 and 22. When the structure 11 is fully inflated, wall portions 19 and 20 are drawn taut causing cell 18 to collapse and wall portions 19 and 20 to act as seals to holes 22 and 21 respectively, so that fluid cannot easily migrate between either cell 16 or 17 and cell 18, thereby providing a stable structure.

When the structure 11 is fully inflated, the filling hose or pipe or similar is withdrawn from the filling valve 23 and the internal pressure in cell 18, effectively because of its collapse under pressure from cells 16 and 17, in turn causes the filling valve 23 to collapse making an effective seal and thereby trapping the water or other fluid within the structure 11. In order release fluid, all that is necessary is that a hose be inserted into the valve 23 to open it and allow fluid to drain therefrom.

In use, the apparatus 11 is filled with water so as to cause the height of the dam structure 11 thus formed to be greater than the depth of water adjacent thereto. The weight of the water contained within the dam structure 11 gives rise to a frictional force along the line of contact between the dam 11 and the stream bed or other terrain on which the dam structure 11 is to be deployed. This frictional force resists the applied pressure of the dammed water.

Due to the applied pressure and the resisting frictional force not being co-linear there is a tendency for the structure 11 to rotate or roll over. However, this tendency to roll over is resisted in this structure 11 by the cells 16 and 17 of the structure 11 being interlocked making the structure 11 stable under normal operating conditions.

It will be realised that that the temporary dam or breakwater according to this invention is not restricted to this form alone but that a number of structures according to this invention may be used together to build a more substantial barrier by either placing them end to end and/or by placing them one upon the other, and/or by placing them side-by-side.

The foregoing describes only one embodiment of the present invention, and modifications obvious to those skilled in the art can be made thereto without departing from the scope of the present invention.