GB2417733A

GB2417733A - Water drainage system

Info

Publication number: GB2417733A
Application number: GB0419642A
Authority: GB
Inventors: Roland Frederick Potts
Original assignee: Marley Extrusions Ltd
Current assignee: DHM Plastics Ltd
Priority date: 2004-09-03
Filing date: 2004-09-03
Publication date: 2006-03-08
Anticipated expiration: 2024-09-03
Also published as: GB0419642D0; GB2417733B

Abstract

A water drainage system 10 having a water storage unit 12 comprising a plurality of adjoining vertical cells 121, wherein the water storage unit is provided on a lattice panel 14b that allows horizontal flow of the water between adjoining vertical cells. Preferably, the vertical cells can form a hexagonal structure, which provides a strong storage unit. The lattice panel 14b also provides additional stiffness to the water drainage system and reinforces the storage unit against lateral forces. The lattice panel has at least one spigot 141 shaped for insertion into a vertical cell so as to position and hold the water storage unit on the lattice panel. Preferably, two lattice panels 14a, 14b are provided to sandwich the water storage unit, each including rounded shoulders for use with fastening straps (16, Fig 1).

Description

24 1 7733 Water Drainage System This invention relates to a water drainage

system having a water storage unit, for example, for temporarily storing storm water while it is allowed to seep into the ground The system may also be provided for attenuation of the water, by substantially lengthening the period during which the water is held for dispersal into the ground The water drainage system could also be used to store water for use in other applications, for example, as an underground reservoir or other more permanent storage facility for the source of water In built up areas rain water is directed into gutters and underwater drains to be transported to rivers, water processing plants, reservoirs, the sea etc However, sporadic downpours can often overload the existing infrastructure. In addition drains can become silted up or blocked which can result in flooding, particularly during periods of heavy rain It is therefore often desirable to control the release of this rain water (sometimes referred to as "run-offwater") into the drainage courses.

Water drainage systems containing reservoir cells or reservoirs to divert the release of the run-offwater (sometimes referred to as "storm water cells" or "soakaways"), are used to prevent overloading of the drainage courses These devices generally consist of a perforated box that is placed underground to provide a storage reservoir or tank for rain water to be fed into. Usually these boxes are housed within some type of filtering system, such as pebbles or a geotextile covering Rainwater is directed into the cell via the filtering system, where it is stored and gradually released into the surrounding soil Alternatively the water collected in the water storage unit can be recycled Such storage units can be used both domestically, e.g. in people's gardens, or commercially, such as under football pitches EP-A-024465 1 is an example of one such water drainage system It comprises a rigid cell structure having perforated upper and lower surfaces separated by spacer members to allow the water to flow freely through the cell structure A development on the system of EP-A-024465 1 is described in WO-A 01/53608, in which the water drainage system is designed for use adjacent to the - 2 foundations of a building and is made up of modules that that can be locked together at angles of 90 degrees to each other The structure of these cells requires a complicated manufacturing process.

EP-A- 1416099 is an example of a crate-like moulded box which is used for a water drainage system. This device consists of two perforated water storage units, each containing supporting columns and open at one side The cells are sandwiched together along their open sides using a central grid member, in order to forth a single cell The supporting columns within the structure are necessary to provide the cell with enough strength to withstand the load to be placed on the system, which may of course include vehicles and pedestrians. The boxes may be mounted on a base element in the form of a lattice panel Despite their necessity, the columns can also be seen as a disadvantage as they take up approximately 10-30% of the volume within the cell, thus reducing the amount of water which can be stored by the cell In addition, the perforated cells must be made by injection moulding using complex multipart tools, which leads to high manufacturing costs The boxes are, however, strong and resistant from loading in all directions.

Another water drainage system using a plurality of perforated boxes is disclosed in WO-A-01/29334. Again the complex structure ofthe perforated box, which is able to withstand loading in all directions, dictates high manufacturing costs.

These high manufacturing costs have already been overcome to an extent by systems such as that described in an earlier patent of EP-B-0286662. The patent discloses an underground tank for retention and control of water which includes a honeycomb layer consisting of adjacent vertical cells resting on a draining structure, the draining structure permitting a horizontal flow of water The draining structure is preferably a layer of coarse alluvial gravel The honeycomb structure can be made easily and cheaply using extrusion techniques The strength of the honeycomb structure allows it to withstand a high load in the vertical direction without the need for extra support The honeycomb structure also means that all the space within the cells can be used to store water with just a small fraction of the internal volume bemg taken up by the thin walls ofthe vertical cells As such the storage capacity of - 3 the honeycomb system is greater than that of the more complicated, but overall stronger, water drainage systems described above Further developments on the idea of using a honeycomb storage cell are described in EP-A-0607349 and EP-A- 0770735. All these systems recognise that a porous layer, for example, of coarse gravel, must be provided in order to allow for horizontal transfer of water to occur as the water in the vertical cells can only permeate in the vertical direction Without the horizontal flow of water, the dispersion of the water into the ground would be uneven and dependent on the local absorption properties of the ground beneath the columns Whilst a honeycomb structure is strong in its direction of the cell walls (the vertical direction of the honeycomb material described above), it is comparatively weak in the transverse directions One of the problems with the known honeycomb systems is that they require a bed of coarse gravel to be laid first. The gravel may be uneven if insufficient care is taken or subsequently there may be localised movement or subsidence which could cause distortions in the honeycomb, thereby reducing the load the honeycomb might be capable of carrying.

The present invention therefore recognises that there is a need for a water drainage system that is relatively cheap and easy to manufacture as well as to install in the ground, and that such a system should also be sufficiently rigid to withstand non-vertical loading.

According to the present invention there is provided a drainage system having a water storage unit comprising a plurality of adjoining vertical cells that store water as vertical columns of water, wherein the water storage unit is provided on a lattice panel that allows horizontal flow ofthe water between adjoining vertical cells This invention incorporates the strength and ease of manufacture of the honeycomb design while allowing for horizontal flow of water via the lattice panel A bed of coarse gravel does not have to be laid first, though it can if so desired The system has substantially no dead volume within the structure and so no loss of storage capacity The lattice panel provides additional stiffness to the water drainage system by distributing forces and reinforcing the storage unit, which is preferably a honeycomb, against lateral forces, e g resulting from locahsed - 4 movement or subsidence It also provides additional strength for stacking the system on top of additional drainage systems Preferably the water drainage system comprises a water storage unit sandwiched between two lattice panels The lattice panels may be injection moulded from plastics or other rigid material (e g a metal, ceramic or composite), such that the lattice panels form rigid plates extending along the top and bottom of the water storage unit The stiffness of the lattice panel may be a result of the inherent stiffness of the material, the structure of the lattice panel creating rigidity or more preferably both In one embodiment, polypropylene is used for the lattice panels. The rigidity of the lattice panels adds significantly to the stiffness of the water drainage system and its ability to cope with the loading that may be applied to the structure. The stiff lattice panels separated by a honeycomb storage unit thus create a girder like effect Thus viewed from another aspect, the present invention provides a water drainage system comprising an extruded water storage unit of cells that is sandwiched between upper and lower, substantially parallel, lattice panels that are secured to upper and lower surfaces respectively of the water storage unit This provides the advantage that the bulk of the storage volume of the water drainage system is provided by an extruded unit or units that can be manufactured cheaply and easily in long sections that are cut to size. The lattice panels can be manufactured easily by injection moulding using a two part tool. This avoids the complicated tooling required to form the box-like water drainage systems of the prior art, thereby significantly reducing production costs The lattice panels preferably include attachment means that prevents relative transverse movement of the water drainage unit with respect to the lattice panel The lattice panels therefore act as a hard skin which is provided on the honeycomb layer and greatly improves stiffness in the same way as the layers on the side of honeycomb panels for modern aircraft flooring add significantly to the stiffness of those flooring panels The water storage unit can be attached to the lattice panel by numerous means, such as clips, ties, pegs, collars, protrusions, fastening straps, mechanical engagement means, bonding agents, heat welding, etc However, it is preferable that the attachment means is integral to the lattice panel m order to reduce the number of - s - parts associated with the system and to allow the parts to be connected together easily in a locking manner Preferably therefore the lattice panel has at least one protrusion or other attachment means providing mechanical engagement, which is preferably in the form of a spigot for insertion into a vertical cell, so as to correctly position the water storage unit on the lattice panel and prevent any sideways movement between the two components In this way the water storage unit can be fixed to the lattice panel without the need to manipulate clips or fasteners Having a spigot for the attachment means allows the water drainage system to be assembled easily, for example, on-site, but more preferably in a factory, by simply engaging the vertical cells of the water storage unit on the spigot or spigots of the lattice panel This method of construction allows a plurality of water storage units, for example, in the form of blocks of vertical cells (e.g., blocks of honeycomb section) to be sandwiched between two lattice panels. This enables the individual blocks to be made smaller, facilitating easier fabrication and manipulation of the components, without significant loss of stiffness to the overall structure The blocks can each be secured against relative transverse movement using spigots formed integrally with the lattice panel or panels Unlike the honeycomb drainage systems of the prior art, gaps may be provided between the blocks of honeycomb because transverse loading is taken up by the lattice panels Such gaps may assist in the horizontal distribution of water within the drainage system. The water storage units act as structural columns extending between the lattice panels which also serve to store water within their cell-like structure Preferably each "structural column", i e each water storage unit, is prevented from moving sideways on the lattice panel through the mechanical engagement of two or more attachment means in the form of spigots Conceivably, if desired, a water storage unit could be produced having two or more different shapes or sizes of cell, such that the spigot could only be correctly inserted into one type of vertical cell In this way different honeycombs or other cell structures could be chosen to optimise cell location of the loading requirements with the different sizes of spigot ensuring that the water drainage system could only be fixed together in one configuration. However this is seen as being less desirable as - 6 it complicates the manufacture of the system and the beauty of the present invention is the simplicity of the water drainage system it provides Preferably the spigot is shaped so as to substantially fill the entire cross sectional area of the vertical cell and thus provide a snug and secure connection through frictional engagement with the vertical cell walls Preferably the spigot is formed to allow water to escape from the bottom of the cell In one embodiment, the spigot includes formations to allow water to escape between the side of the spigot and the wall of the vertical cell. In more preferred embodiments, the spigot is hollow to allow water to escape to the lattice panel where channels can be provided to allow horizontal flow of the water between adjoining vertical cells Preferably the lattice panel includes a spigot hole which is of a shape and size to allow the insertion within it of an identical spigot. In this way the lattice panels can be stacked securely on top of each other during storage and transportation One of the advantages of using spigots instead of other types of attachment means is that it facilitates the stackability of the lattice panels Preferably the distal end of the spigot is also tapered to make it easier to locate the lattice panels together. This feature also makes it easier to connect a lattice panel to the vertical cells of the water storage unit The lattice panel having such a spigot feature is considered inventive in its own right and therefore, viewed from a further aspect there is provided, a lattice panel for a water drainage system having upper and lower surfaces separated by a lattice structure of walls extending between the upper and lower surfaces in a thickness direction, the walls defining a plurality of through-holes through the lattice panel, wherein the upper surface of the lattice panel is provided with attachment means for mechanical engagement with a water storage unit of a water drainage system In one preferred embodiment, the attachment means comprises a plurality of integrally moulded spigots which are provided for engagement with vertically extending cells of a water storage unit Preferably the spigots are hexagonal in cross-section with a tapered distal end and are hollow to allow passage of water therethrough. However other polygonal shapes are envisaged to accommodate shapes of vertical cells other than hexagonal, for example triangular, square, rectangular, pentagonal etc The spigots may also be circular or oval in cross-section to accommodate a range of different cell shapes Preferably the lattice panel includes spigot holes in its lower surface to allow the lattice panels to be stacked one on top of the other Preferably the lattice panel also has channels in its lower surface linking each spigot to a neighbouring through hole so that water can flow horizontally from said spigot to said neighbouring through-hole In one preferred embodiment the only channels provided in the lower surface of the lattice panel extend in straight lines passing through the through-holes at the base of the spigots, to link the spigots with neighbouring through-holes. Other lattice panels not having spigots are known from EP-A- 1416099, in which channels are provided in the lower surface of the lattice panel to link every through- hole with its neighbouring through-hole Whilst such an extensive channel system could be adopted in the present invention, preferably the number of channels is kept to a minimum (i.e. just those linking spigots) in order to maximise contact area for transmitting load as well as minimising production complexity The same lattice panel design can be used for the top and bottom of the water storage unit or different designs can be used as desired Preferably the same design is used in order to minimise the complexity of the components The vertical cells of the water storage unit, could conceivably be a number of different shapes, such as circular, oval, triangular, square or rectangular, pentagonal, hexagonal, or some other more complex pentagonal close packing shape. The cells could also be a mixture of these shapes However, preferably hexagonal cells are used for the inherent good ratio of stiffness to weight of material this provides In one preferred embodiment a vertical side of the or each of the water storage units is substantially planar through the formation of a line of pentagonal cells along said side Where the cells are mostly hexagonal in shape, this planar side created by the pentagonal cells stiffens that side of the water storage unit by acting as a skin to transmit tensile forces Preferably the or each of the water storage units has two such substantially planar vertical sides on opposed surfaces of the unit The water storage unit can be formed by extrusion, e g in plastics or other inexpensive material, and cut to length. In a hexagonal arrangement, the triple points, where the walls from three cells join, act to stabilise the transmission of the load through the unit and thereby carry the load placed on the system (together with - 8 some transfer of the load via the cell walls) Therefore it is preferable that the lattice structure of the lattice panel is arranged such that it supports the majority of these triple points or a region of the cell wall adjacent the triple point, thus increasing the strength of the system by providing a direct vertical transfer of the load through the triple points and the vertical walls of the lattice panel to the ground it rests on In one preferred embodiment, the walls of the through-holes of the lattice panel generally define a grid of perpendicular walls interspersed with hexagonal (or other polygonal, circular or oval) through-holes at the location of the spigots The through-holes are preferably of varying cross-sectional area, the majority being rectangular though preferably the width of the different through-hole shapes is approximately the same and corresponds to roughly the width across the flats of the honeycomb cells. In this way the walls of the lattice panel can be arranged to provide a good transfer of the load, e g via a triple point or a cell wall, whilst also leaving a portion of the cell perimeter unsupported This allows stored water to flow under and over the edges of the walls in an overall horizontal direction, thereby permitting the transfer of water in the horizontal direction for those cells not connected by channels.

Preferably, in order to secure the water storage unit and the lattice panel together, at least one fastening strap is used. This preferably extends right around the periphery of the water drainage system. This ensures the elements do not become disconnected, particularly during installation in the ground. It also helps to clamp the components together, to resist distortion resulting from vertical and non vertical loading Preferably the water storage unit is sandwiched between two lattice panels and at least two straps are used to clamp the components together, more preferably three straps The lattice panels, being the more rigid component but clamped in a spaced parallel relationship by the water storage unit and prevented from sideways relative movement through the attachment means that is preferably in the fonn of spigots, creates an exceedingly stiff water drainage system that can carry significant loads even if the ground is slightly uneven or if there is localsed ground movement The lattice panel preferably includes rounded shoulders at the edges where the fastening straps cross The rounded edge of the lattice panel ensures an even tension throughout the strap and minimises wear, e g. through rubbing during - 9 - transit Preferably, curved guiding walls are placed on either side of the shoulders to create valleys to help with the correct positioning of the straps during attachment, which can be an automated process Preferably a channel is provided in the lattice panel for recessing the fastening strap below the level of the lattice panel surface The shoulder feature on the lattice panel is considered inventive in it's own right and therefore, viewed another aspect the invention provides, a water drainage system having a water storage unit sandwiched between upper and lower lattice panels, wherein a fastening strap is used to clamp the lattice panels to the water storage unit, the fastening strap forming a loop which passes over the uppermost O surface of the upper lattice panel and the lowermost surface of the lower lattice panel to encircle the water drainage system, and further wherein the lattice panels are moulded to include a region where the edge is rounded off for the fastening strap to pass over. Viewed from another aspect there is provided a lattice panel for a water drainage system which comprises a lattice structure having a plurality of spigots integrally moulded on a first surface thereof for engagement with a water storage unit, wherein opposed edges of the opposite surface of the lattice panel are formed with a region where the edge has been rounded off to accommodate a fastening strap The idea of using stiff lattice panels strapped either side of one or more water storage units is not limited to the applications where the water storage units are a plurality of vertical cells, for example, of an extruded section, but applies to all forms of water storage unit which includes injection moulded crate-like boxes and other lattice panel separating devices The stiff lattice panels and fastening straps would enable less substantial boxes to be used because of the "girder effect", or if it was used in conjunction with the existing water storage units then it may increase the loading properties of the system It is also envisaged that the fastening straps could be used to secure a sandwich of more than three layers, i.e. five layers in the case of lattice panel, water storage unit, lattice panel, water storage unit, lattice panel The water drainage system may be used individually but is preferably used in conjunction with other water drainage systems (i e, there are a plurality of these storm water cells) which are arranged stacked beside one another or on top of each - 10 other within a hole in the ground to create a much larger water storage assembly For such situations it is desirable to fasten the water drainage systems together.

Preferably the lattice panels are adapted to accommodate a clip to attach one water drainage system to the next In one preferred embodiment, the clip comprises a plate having four pegs extending from a surface thereof, each peg being split and including a catch member to enable the peg to snap-ft into locking engagement with a peg receiving hole of a lattice panel More preferably the clip includes corresponding male and female connecting features on the surface of the clip opposite the pegs to enable two clips to be joined together in back-to-back l O engagement The lattice panel may be formed at its corners with a lattice structure that can receive two pegs. This allows the clip to join two water drainage systems together at the sides of the water storage assembly without extending beyond the sides of that assembly. In most situations, the clip will be used to join water drainage systems together within the bulk of the water storage assembly and so each ] 5 clip will connect four water drainage systems together at the corners thereof, with each peg locating into a peg receiving hole of a different lattice panel Where water drainage systems are stacked on top of each other, two clips can be joined back-to back to locate pegs into eight different lattice panels of eight water storage systems Preferably the lattice panels include a portion of the corners thereof where the surface has been recessed to accommodate the thickness of the clip plate within the line of the lattice panel so that when the clip is in position, apart from the clip's male connecting feature if present, the clip does not protrude above the plane of the lattice panel surface Where spigots are present on the lattice panel, these recessed corner portions will be located on the surface of the lattice panel opposite that with the spigots The water drainage system may be laid within a permeable membrane which allows water to permeate out into the ground but prevents soil Prom entering the water drainage system, such as a permeable geotextile fabric. The membrane may be chosen so that the water can only seep out slowly and thereby provide a ground water attenuation system m which the water may be stored for a substantial time In other embodiments, the water drainage system can be laid within an impervious membrane to provide a more permanent storage solution Nor the water In these embodiments, the water may be used for other purposes (e g recycled) before it enters the normal ground water system. Preferably the corners of the water drainage system are rounded off to reduce the risk of puncturing the membrane For the avoidance of all doubt, it should be noted that each of the broad aspects of the invention described above are intended to apply equally in conjunction with all the preferred features ofthe invention described herein and not just features described immediately following the particular aspect.

The present invention also extends to a water storage assembly comprising a plurality of water drainage systems, each having a water storage unit located between two lattice panels, the components of the water drainage system being retained together with a strap extending, around the water drainage system, and wherein said plurality of water drainage systems are retained together in locking engagement by clips engaging the corners of lattice panels of adjacent water drainage systems.

Certain preferred embodiments of the present invention shall now be described in greater detail by way of example only and with reference to the accompanying drawings, in which FIG 1 shows a preferred water drainage system in accordance with the present invention; FIG 2 shows an exploded view of the water drainage system; FIG 3 shows a lattice panel as used in the water storage system shown in FIG 1, FIG 4 shows the water storage system of FIG I from above, FIG 5 shows a detail of the corner of the lattice panel, FlGs 6A and B show connection clips for use with the water storage system shown in FIG.I, FIG 7 shows an enlarged view of the spigots in a stacked configuration, FIG 8 illustrates a different attachment means that could be used in conjunction with the present invention, and FIG 9 illustrates a further variation of the attachment means FIG I shows a water drainage system 10 comprising a water storage unit 12 that is sandwiched between upper and lower lattice panels 1 4a, 1 4b The system 10 - 12 isheldtogetherbyfasteningstraps 16 end spigots 141 (discussed belong) As can best be seen in FIG 2, there are twelve such water storage units, each in the form of a block of honeycomb elements 12a, 12b 121 comprising 23 hexagonal columns or cells 121 The water storage units 12 act as structural columns maintaining the separation of the lattice panels 14a, 14b to define a water storage volume. Other arrangements of honeycomb elements 12a- 121 and numbers of hexagonal cells 121 are also envisaged according to the dimensions of the water drainage system I O In one preferred embodiment which is not shown, along one or more oi'the vertical sides of the honeycomb elements 12a-121, some or all of the cells 121 may have a pentagonal cross-section creating a planar or substantially planar surface. In the prior art, these planar surfaces are used to bond honeycomb elements together, e g, through heat welding, to create larger blocks of elements. In the present invention, this planar surface acts as a band or skin to the honeycomb element to transmit tensile forces and thereby increases the stiffness of the honeycomb element Preferably the honeycomb elements 12a- 121 are arranged so that the planar surface forms an external surface of the water drainage system 10 to increase the stiffness of the system. Each element 12a-121 is formed by extrusion and can therefore be made simply and cheaply Any material having suitable extrusion properties which is sufficiently strong and resistant to prolonged exposure in water would be suitable, for example, most plastics, and indeed a more exotic material such as a ceramic, composite or metal could be used where financial viability allows The material can be extruded as long lengths that are cut to size to form the honeycombelements 12a 121 The honeycomb structure is very strong in the longitudinal direction of the cells 121, and able to withstand large loads It also has good stiffness properties through the arrangement of the honeycomb's walls at 120 to each other and via the triple points where these walls meet. As a consequence the hexagonal cells 121 are all hollow which allows the storage of water within them FIG 3 shows a lattice panel 14 Here it can be seen that the lattice panel 14 consists of a lattice structure providing a plurality of through-holes of dif'f'erent cross-section Despite its complex appearance, the lattice panel 14 can be injection moulded using a two-part tool In addition the lattice panel 14 contains 24 hexagonal spigots 141 As can be seen from FIG 2, each honeycomb element 12a - 13 121 is attached to the plate 14 by the insertion of two spigots 141 into two of the hexagonal cells 121 The spigots 141 are shaped so as to fit snugly within the cells 121 and provide a good hold on the honeycomb elements 12a-121 When the honeycomb elements 12a-121 have been attached to the lattice panels 14 via the spigots 141 it can be seen from FIG 4 that the lattice structure of the lattice panel 14 provides support for the majority of the triple points of the water storage unit 12 In addition the irregular shapes of the lattice structure allows for horizontal water transfer between ad jacent cells 121 This allows water within the water drainage system 10 to be distributed more evenly and thus leads to quicker drainage. It also allows the lattice structure to be designed to optimise its resistance to non-vertical loading in order to provide a stiff lattice panel 14 The lattice structure is preferably a grid-like structure of internal walls arranged at 90 to each other with interspersed hexagonal elements to accommodate the spigots 141 This is in contrast to the hexagonal structure of the honeycomb The spigots 141 are hol low to allow water to flow into and out of the hexagonal cells 121 to which the spigot 141 is attached. As the spigot 141 is shaped to create a snug fit within the hexagonal cells 121, water within the cells 121 cannot be transferred via the lattice structure as this part of the lattice panel 14 is in register with the hexagonal cells 121. Therefore, fluid channels 142 are provided to allow water to flow away from the base of the spigot 141. These channels 142 connect the spigots 141 along the lines 141 a - 141 e, which are shown on FIG 3 In the case of line 141a and 141fthe channels 142 are also used to locate fastening straps 16 Therefore additional channels 142 are provided to ensure that horizontal water transfer is not impeded by the fastening strap 16 These additional channels 142 extend from the spigot 141 at right angles to lines 141 a and 141 f to the closest edge of lattice panel 14 The fluid channels 142 can be seen best in FIG 5 FIG 5 also shows a region of rounded shoulder 143 These are provided in opposing pairs along lattice panel 14 As can be seen from FIG 1, these are used to position fastening straps 16 The rounded shape of the shoulder 143 helps to provide an even tension throughout the strap 16 Each shoulder 143 is provided, on both sides, with curved guiding faces 144 which help to guide the strap 16 into position during manufacture of the water drainage system - 14 As mentioned above, spigots 141 are hollow so that water can flow through them However this feature can also be used to allow the spigots 141 to be inserted into one another when the plates 14 are stacked (as shown in FIG 7). As can be seen in FIG 3, the tops of spigots 141 are slightly tapered In addition, the holes in the lattice panel 14 at their bases are widened (see FIG 5) This allows the tapered end of one spigot 141 to be inserted into the base of another spigot 141 such that the two lattice panels 14 can lie flush against each other in a stacked configuration This increases the ease with which the lattice panels 14 can be transported through this locking feature if they are moulded at a different site to the final assembly into a water drainage system 10 An individual water drainage system 10 preferably has dimensions of about a cubic metre and so can retain approximately the same volume of run -off water.

Usually several water drainage systems 10 are provided within a water storage assembly to Increase the water storage potential These individual units 10 are held together by clips 17. Each clip has four protrusions or pegs 171 which are pushed through peg receiving holes in the corners of the lattice panels 14. Therefore a single clip 17 can connect up to four separate water drainage systems 10. Each peg 171 has a slit 172 along its length to allow the two peg-halves to be pushed together, thereby reducing the diameter of the peg 171 as it is inserted through the lattice panel 14 The peg-halves are biased outwards so that the peg 171 maintains a good grip on the lattice structure to prevent the peg 171 from falling out once it has been inserted. In addition each peg 171 has a lip or catch 173 at its tip This co-operates with the opposite surface of the lattice panel 14 to increase the secureness of the connection Using these clips 17, individual water drainage systems 10 can be combined side-by-side and stacked on top of each other to increase the water storage potential Two clips 17 can be combined in a back-to-back configuration to connect two layers of water drainage systems 10 together using the indent 175 and detent 176 found on the back of each clip 17 The detent 176 of one clip can be inserted into the intent 175 of a second clip Detent 176 has teeth 176a that, once the two clips 17 are connected, sit on a rim within indent 175 (not shown) and oppose the release of the two clips 17 Once combined the pegs 171 of one clip 17 are used to connect - 15 together four water storage systems 10 on one level while the pegs 171 of the other clip 17 are used to connect together four water storage systems 10 on a second level In one preferred embodiment, the water drainage system 10 can withstand a loading of greater than 10 tonnes per square metre, more preferably 15 tonnes per square metre, still more preferably greater than 1 7'/z tonnes per square metre and in the most preferred embodiments it can withstand a loading of greater than 20 tonnes per square metre The water drainage system 10 could be made to any size but is preferably of dimensions 600 x 800 x 520 mm FIG 7 shows how the shape of spigots 141 allows for easy stacking of the lattice panels 14 during storage and transportation The spigots 14 i of lower panel 1 4b are inserted into the spigots 141 of upper panel 1 4a through the hexagonal hole in the lattice on which the spigot 141 sits. The tapered end 146 of the spigot 141 allows the spigots 141 to fit inside each other such that the base of upper panel 14a is flush with the top of lower panel 1 4b The entire length of the spigot can be inserted into another spigot, thus securing the panels together FIGs 8 and 9 show alternative ways of attaching the water storage unit 12 to the lattice panel 14. In the embodiment shown in FIG 8, corner bosses 80 are used to correctly position and hold the water storage unit on the panel In another embodiment (not shown) the corner bosses 80 may be replaced by bosses that just engage the sides of the water storage unit 12. In another embodiment (not shown) the corner bosses 80 may be replaced by a raised collar that extends around the perimeter of the water storage unit 12 The collar may be continuous or made up of several sections In FIG 9 the panel 14 contains a grid of upright clips 90 I he clips 90 have a central slit into which the cell walls can be inserted and securely held by the biasing force of the clip 90 These clips 90 can either be positioned all over the lattice panel 14 or only in specific areas so as to require that the water storage system is assembled in a particular way - 16

Claims

Claims: I A water drainage system having a water storage unit comprising a

plurality of adjoining vertical cells, wherein the water storage unit is provided on a lattice panel that allows horizontal flow of the water between adjoining vertical cells 2 A system as claimed in claim 1, wherein attachment means are provided to connect the water storage unit to the lattice panel 3 A system as claimed in claim 2, wherein the attachment means comprises a spigot.

4 A system as claimed in claim 3, wherein the spigot corresponds to the size of a vertical cell to provide a friction fit therewith A system as claimed in claim 4, wherein the spigot is hollow to enable water to escape from the bottom of the vertical cell that it engages 6. A system as claimed in claim 5, wherein at least one channel connects to a hole in the lattice panel associated with the spigot.

7 A system as claimed in any of claims 3 to 6, wherein the lattice panel includes a spigot hole which is of a size corresponding to the spigot such that a second of said lattice panels can be stacked on top of a first lattice panel for transportation thereof with a spigot of said first panel locating within a spigot hole of said second lattice panel 8 A system as claimed in any of claims 2 to 7, wherein attachment means comprises a strap 9 A system as claimed in claim 8, wherein the lattice panel is provided with curved valleys to seat the strap - 17 A system as claimed in any preceding claim, wherein the water drainage system includes a plurality of water storage units, each water storage unit taking the form of a block I I A system as claimed in claim 10, wherein gaps exist between ad jacent water storage units on said lattice panel 12 A system as claimed in any preceding claim, wherein the plurality of ] O adjoining vertical cells form a substantially honeycomb structure 13 A system as claimed in claim 12, wherein the vertical cells are mostly in the form of hexagonal prisms.

14. A system as claimed in any preceding claim, wherein the water storage unit is an extruded section of cells A system as claimed in any preceding claim, wherein said lattice panel defines an array of vertical holes therethrough which are sufficiently in register with the vertical cells of the water storage unit to support a predetermined load but sufficiently out of register to allow water to seep in a horizontal direction between adjoining vertical cells.

16 A system as claimed in any preceding claim, wherein channels are provided in the lattice panel to allow horizontal flow of the water between adjoining vertical cells 17 A system as claimed in any preceding claim, wherein a second lattice panel is provided on top of the water storage unit. - 18

18 A water storage assembly comprising a plurality of water storage systems of any preceding claims which are connected together using clips that engage with the lattice panels of adjacent water storage systems 19 A lattice panel for a water drainage system having upper and lower surfaces separated by a lattice structure of walls extending between the upper and lower surfaces in a thickness direction, the walls defining a plurality of through -holes through the lattice panel, wherein the upper surface of the lattice panel is provided with a plurality of integrally moulded spigots for engagement with vertically extending cells of a water storage unit A lattice panel as claimed in claim 19, wherein the spigots are hexagonal in cross -section.

21 A lattice panel as claimed in claim 19 or 20, wherein the lattice panel includes spigot holes for receiving the spigots of a further lattice panel to allow the panels to be stacked on top of each other 22. A lattice panel as claimed in any of claims 19 to 21, wherein the lattice panel includes channels in the surface which is opposed to that provided with said spigots.

23 A lattice panel as claimed in any of claims 19 to 22, wherein the surface of the lattice panel which is opposed to that provided with spigots includes regions where the edge of the surface is rounded to receive a fastening strap thereover 24 A lattice panel as claimed in claim 23, wherein the regions of rounded edge are bound by curved shoulders for locating the fastening strap A lattice panel as claimed in any of claims 19 to 24, wherein the surface of the lattice panel which Is opposed to that provided with spigots includes recessed portions for receiving connecting clips - 19 26 A system as claimed in claim 2, wherein the attachment means comprises a collar extending around or along a part of the perimeter of the water storage unit 27 A system as claimed in claim 2, wherein the attachment means comprises lugs or bosses which mechanically engage with the water storage umt 28 A system as claimed in claim 2, wherein the attachment means comprises a protrusion which mechanically engages with a vertical cell of the water storage unit 29 A water drainage system as substantially hereinbefore described with reference to FIG I of the accompanying drawings A lattice panel as substantially hereinbefore described with reference to FIGS 3 to 5 and 7 of the accompanying drawings.