Abstract:
Embodiments described herein are related to water management units for extracting water from moist soil. The units extract water and collect it to be siphoned away as waste water or for later use. A water management unit comprising: an elongate collection portion; and an extraction portion arranged to discharge extracted water into the collection portion, wherein the extraction portion comprises at least one rib extending laterally from the collection portion along a length of the collection portion. Water is collected by capillary action.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus and method for collecting and channeling ground water, and more particularly, to a unit for water management that combines an extraction unit to absorb liquid from the ground, a method to transfer the liquid into a conduit, and a conduit system to carry the water away, without the need for separate components. The apparatus may be used for drainage or as an irrigation system. 
     2. Description of Related Art 
     Conventionally, most drainage systems used for water management for example on farms, sports fields, golf courses, civil engineering projects such as tunnels, road beds and retaining walls are primarily comprised of permeable drain pipes which have a number of small openings or pores distributed over the upper portion of the pipe so that water may enter through the upper portion and collect in the lower portion of the pipe. However, such systems are prone to becoming clogged with soil particles and the collection capability quickly becomes reduced. Various additions such as filters have been tried to prevent soil from entering the pipe. However, clogging still tends to occur. 
     To overcome this, a drain belt was developed as disclosed in U.S. Pat. No. 5,934,828 and sold as Capiphon drain belt. The drain belt is an efficient method for ground water collection without transferring soil particles into the drainage system. Thus, the drain belt does not become clogged and the collection capacity is not reduced over time. Further, the system does not require maintenance to de-clog pipes. 
     Such a drain belt  10  is shown schematically in  FIG. 1 . The surface of the belt  10  has a plurality of parallel slots  12  of generally rectangular cross-section which extend along the length of the belt  10 . Each slot  12  communicates with a corresponding notch or channel  11  of generally circular cross-section forming, in combination, key-hole shaped cross-section extending along the length of the belt  10  and into the interior of the belt. The slots  12  and channels  11  are sized such that water is drawn into channels  11  via the slots  12  by capillary action so that it can be channelled along the length of the belt  10  and subsequently delivered into a pipe system to be drained away. When the belt  10  is installed in soil and the soil becomes saturated, water fills the spaces between the soil particles and also fills the channels of the drain belt  10  by capillary action. 
       FIG. 2 a    shows an end view of drain belt  10  in dry soil. Air fills the slots  12  and channels  11 .  FIG. 2 b    shows the drain belt  10  in saturated soil. Water fills the space between the soil particles and the slots  12  and channels  11 . The water may flow along the channels  11  in the belt  10  to be discharged. The drain belt  10  construction means that water will be collected from any saturated soil in which it is installed. 
       FIG. 3  illustrates the collection area of a width of drain belt  10 . As the water in the immediate vicinity of the drain belt moves into the channels  11  through the slots  12 , and is removed, it is replaced with additional water moving in to fill the area vacated by the collected water. The speed of water movement towards the collection area is limited by the size of the pore spaces between the soil particles (hydraulic conductivity of the soil) and the pressure (head). 
     The efficiency of a drainage system is improved when the collection and discharge rate is greater than the ability of the soil to provide water for collection. The collection rate of drain belt can be increased or decreased by increasing or decreasing the length of the drain belt, since increasing the length provides a larger surface area for collection. Increasing the collection capacity is effective only if the additional water collected can flow through the channels  11  easily and can be discharged at the same rate as collection. The small size of the channels  11  create resistance to flow along the length of the belt, and since the drain belt must discharge through one end the drainage capacity is reduced to a small amount even though the collection capacity has been increased. 
     A functional drainage system requires efficient collection of the water, but also efficient transport of the water to the evacuation point. The small size of the channels  11  are not a practical transport mechanism for the collected water, and as such, the drain belt must be connected to a pipe network. The combination of the drain belt for water collection and the pipe network to transport the water, forms an effective drainage system, but is complicated, expensive, and prone to workmanship error. 
     Efficiency of the drainage system can be improved by increasing the frequency of drain belts, and thus, the frequency of discharge points, and by limiting the length of the drain belt so that the transport distance is short and the water is discharged into the pipe sooner.  FIG. 4  shows a drainage system which can collect and discharge water rapidly, but is complicated and labor intensive to assemble and install. Both the pipe  20  and drain belts  10  must be sloped to drain by gravity, requiring extensive and careful excavation and backfilling. The areas surrounding the pipe  20  and drain belts  10  must be carefully hand compacted to prevent a U-bend joint so that water from the drain belt no longer discharges from the belt into the pipe.  FIG. 5 a    shows, in cross section, a belt  10  joined to a pipe  20 , arranged so that water may flow from the belt  10  into the pipe  20 .  FIG. 5 b    shows, in cross section, a joint where the surrounding ground has settled resulting in a U-bend preventing water from being discharged into the pipe  20 . 
     Further, installing the drain belt in damp, wet, and muddy conditions has increased difficulties. A small amount of weight applied to the top surface can easily push the bottom surface into the soft earth and completely clog the slots  12  and channels  11 , rendering the drain belt inoperative. Also, since the drain belt is installed in low areas where water collects, in trenches, the likelihood of foot traffic on the surface of the belt is unavoidable. Even installations over a layer of sand will display some obstructions in the slots  12  and channels  11 . 
     As such, installation of a drain belt system is expensive because it requires careful supervision. 
     SUMMARY OF THE INVENTION 
     In one embodiment a water management unit comprising: an elongate collection portion; and an extraction portion arranged to discharge extracted water into the collection portion, wherein the extraction portion comprises at least one rib extending laterally from the collection portion along a length of the collection portion is disclosed. 
     In another embodiment, the water management unit further comprises a water extraction formation located on the underside of the at least one rib. 
     In another embodiment, the water extraction formation is arranged to extract water by capillary action. 
     In another embodiment, the capillary action method uses an array of rods. The array may be arranged in a number of layers, where the layers are rotated relative to each other. The rods may be directed or sloped towards a collection portion of the unit. 
     In another embodiment the extraction portions may be interrupted with each extraction sub-portion directing water into a collection portion. Adjacent extraction sub-portions may be substantially parallel to each other or they may have surfaces sloped in opposing directions. 
     In another embodiment, the extraction portion formation has a plurality of channels for water to flow along. 
     In another embodiment, the at least one rib extends along the length of the collection portion. 
     In another embodiment, the at least one rib slopes in a downward direction from an upstream end of the unit. 
     In another embodiment, the at least one rib slopes at an angle in the range of 2°-30°, more particularly in the range of 5°-20°, and preferably at approximately 15° relative to the collection portion. 
     In another embodiment, the rib has a triangular cross section where the upper surface is angled and the underside is approximately horizontal. 
     In another embodiment, the unit has a plurality of parallel ribs arranged on at least one side of the unit. 
     In another embodiment, the unit is rectangular and relatively narrow laterally in cross-section profile or the unit may be relatively low and broad in cross-section. 
     In another embodiment, the collection portion has dimensions in the range of height of 10-40 cm, a width of 5-15 cm and a length of 20-60 cm; and the ribs are 1-5 cm wide or the until may be 3-4 cm in height with a width of approximately 50 cm. 
     In another embodiment, an upstream end of the unit is shaped to cooperate with a downstream end of a second unit. 
     In another embodiment, the upper surface of the unit is shaped to cooperate with the lower surface of a second unit. 
     In another embodiment, the unit may have a lid or cover. Alternatively, the unit may be covered with geotextile. 
     In another embodiment, the unit is adapted to connect to interlocking fittings of drainage systems. 
     In another embodiment, the unit is made from a semi-rigid material. 
     In another embodiment, the unit is made from plastic. 
     In another embodiment, the unit is manufactured in a moulding process as a single part. 
     In another embodiment, a water management system comprises at least one water management unit and a discharge pipe located downstream of the at least one unit is disclosed. 
     In another embodiment, the drainage system further comprises a plurality of connected units. 
     In another embodiment, the plurality of units are connected by vertically stacking. 
     In another embodiment, the plurality of units are connected horizontally with the upstream end of a first unit connected to the downstream end of a second unit. 
     In another embodiment, a method of installing a water management unit or water management system, wherein the water management unit is connected to a pipe network and placed in a trench and the trench is backfilled is disclosed. 
     Aspects of the invention are defined in the accompanying independent claims. 
     The invention meets a need for a drainage system which is effective, durable, simple to install, and has a large collection and discharge capacity, and can operate without a separate pipe network. Preferably this does not become clogged with debris during installation or during use, and does not require maintenance after installation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which like reference numerals are used to depict like parts. In the drawings: 
         FIG. 1  shows a perspective schematic diagram of a drain belt; 
         FIG. 2 a    shows a cross sectional view of a drain belt in dry soil; 
         FIG. 2 b    shows a cross sectional view of a drain belt in saturated soil; 
         FIG. 3  shows a plan view of the collection area of the drain belt; 
         FIG. 4  shows a plan view of a drainage system that incorporates the drain belts; 
         FIG. 5 a    shows a cross sectional view of a joint between a drain belt and a discharge pipe; 
         FIG. 5 b    shows a cross sectional view of a joint between a drain belt and a discharge pipe; 
         FIG. 6  shows a schematic diagram of a water management unit; 
         FIG. 7  shows a schematic diagram of two water management units; 
         FIG. 8  shows two water management units connected to a pipe; 
         FIG. 9  shows a cross sectional view of a water management unit; 
         FIG. 10  shows a cross sectional view of an extraction formation; 
         FIG. 11  shows a schematic diagram of a low profile water management unit; 
         FIG. 12  shows a detailed cross-section view taken through section B-B of  FIG. 13 ; 
         FIG. 13  shows a schematic diagram of a low profile water management unit; 
         FIG. 14  shows a detailed view of a capillary extraction arrangement; 
         FIG. 15  shows a schematic diagram of a low profile water management unit; 
         FIG. 16  shows a detailed view of the embodiment shown in  FIG. 15 ; 
         FIG. 17  shows an alternative arrangement to  FIG. 16 ; 
         FIG. 18  shows a detailed view taken through section A-A of  FIG. 11 ; 
         FIG. 19  shows a detailed view of capillary rods; 
         FIG. 20  shows a detailed view of capillary rods; 
         FIG. 21  shows a detailed view of capillary rods. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the invention are now described with reference to the drawings. 
     An embodiment of the invention is shown in  FIG. 11 . The arrangement uses an alternative capillary action water collection method and the water management unit has a relatively broad and low or flat profile. The unit  200  has a main water flow channel  210 , a number of collection portions  212  and a number of extraction portions or sub-portions  214 . The extraction portions  214  comprise ribs extending from the main water flow channel  210 . Water extraction material is located on the underside of the ribs. The collection portions  212  also extend from the main water flow channel  210  and are parallel and below the extraction portions  214  so that water may be deposited from the extraction portion  214  into the collection portion  212 . The extraction portions  214  are sloped and are directed to deposit extracted water directly into the collection portions  212  which are located in the troughs between extraction portions. In the embodiment shown in  FIG. 11 , the extraction portions  214  form a peak between adjacent collection portions  212  such that the extraction portions  214  are sloping in two opposing directions relative to the length of the unit  200 . In other embodiments the adjacent extraction sub-portions are substantially parallel. The extraction portions  214  are interrupted at intervals so that they discharge directly into collection portions  212 , where extracted water has travelled only a short distance. 
     The unit  200  in the embodiment shown does not have a defined nor required upstream or downstream direction. This may be determined during installation of the unit  200  by the water flow direction in the main water flow channel  210 . The collection portions  212  also provide supports for the unit  200 , akin to feet, which may be directly placed in a trench during installation. More details of installation of water management units are given below in relation to other embodiments. 
     The collection portions  212  extend below the extraction portion  214 . When placed in a trench, the collection portions or feet, ensure that the water management unit is supported and that the extraction portions  214  are raised. This helps to ensure that the extraction portions are clear from soil and soil is not extracted with water, which would clog the capillary extraction material. Having the water management unit raised by the collection portions  212  also allows water to follow to an area where it may be easily extracted from. 
     The unit  200  may be covered with a cover  216 . The cover  216  may be made from a semi-rigid plastic material, or an equivalent material, which is welded to the main body of the extraction unit. Alternatively, the cover may be a snap fit cover. Alternatively, the unit may be covered by a geotextile material  218 , suitable for use in conjunction with SubAir applications. The cover  216  or geotextile  218  assist in providing rigidity to the unit and also help to prevent soil from clogging the capillary collection structure of the extraction portions  214 . The skilled person will be familiar with SubAir systems. A SubAir system allows for compressed air or gas to be inserted into the sub grade and defused through the top and bottom of the unit. Use of a geotextile cover allows for easier diffusion through the top of the unit, and less pressure is required when compared to using a perforated pipe arrangement. 
     The method of capillary action extraction of water used in the present embodiment is more effective than that previously described in relation to the prior art as it is not influenced by the resistance of water already in the extraction material. 
       FIG. 18  shows a detailed view taken through section A-A of  FIG. 11 . The detail shows the extraction portion  214  and the collection portion  212 . The extraction portion comprises an array of capillary rods  284  arranged in parallel as shown in  FIG. 19 . The rods may be fixed in layers by setting one end of the rods in resin, fixing in an open frame or otherwise holding the rods in place. In  FIG. 18 , two layers are shown where the direction of the rods are at 90° to each other. The upper layer of rods is directed towards the collection portion  212 . In general, each layer of rods  284  should have a different orientation, for example rotated by 90° or 45°. Only one layer of rods is required, however, two or more layers provide additional benefits. As the water management unit is placed directly in the ground, the underside of the rods is exposed to the soil  213 . Rising water in saturated soil, shown by the broken line  282 , is taken up by the rods by capillary action. 
       FIG. 20  shows an end view of the rods in detail. The rods  284  are spaced apart by a suitable distance such that water  285  is drawn up between the rods  284 . Where the rods  284  are sloped water  285  may flow between the rods  284  as shown in  FIG. 21 . The flow of water is according to the slope of the rods  284  in the extraction portion  214 . Thus, water may be extracted from the surrounding soil and deposited directly in the collection portion  212  of the water management unit. 
     The capillary collection method benefits where more than one layer of capillary rods are present. An increased number of layers provide an increased water capacity. Further, where a single layer is used, water may spurt through the capillary rods. A second layer helps to block this. Further, soil particles are less likely to enter the water management unit with an increased number of rod layers. 
     As each layer of rods will have draining capacity, it is preferable to direct each layer of the rods towards a collection portion. For example, two layers of rods may be arranged at 45° to the edge of the collection portion so that both layers are directed towards the collection portion. 
     The capillary extraction rods may be made from rigid plastic, heavy gauge copper wire or any other suitable material. 
     Referring again to  FIG. 11 , water is extracted from the soil in the gaps between the collection portions  212 , and surrounding area. In this embodiment, once water has been extracted from the surrounding soil, it does not need to be transported through a long length of capillary channels. Water is quickly deposited in the larger channels of the collection portion  212  and the main water flow channel  210 . Thus, the flow of water through the extraction portion  214  does not limit the water extraction capability of the unit  200 . Water extraction is not affected by water already in the collection portions  212  or main water flow channel  210 . The collected water may be removed by connecting the unit  200  or the main water flow channel  210  to a drainage system. 
     The embodiment shown in  FIG. 13  shows a similar arrangement to that of  FIG. 11  where the water management unit has a relatively broad and flat profile. However, this embodiment uses a different capillary action collection method. The unit  300  has a main water flow channel  240 , a number of collection portions  242  and a number of extraction portions  244 . The extraction portions  244  form ribs extending from the main water flow channel  240 . The collection portions  242  also extend from the main water flow channel  240  and are parallel with the extraction portions  244 . In this embodiment, the extraction portions  244  are substantially horizontal as the extraction material does not require a slope to deposit water directly into the collection portions  242 . The unit  300  may be covered with a cover  246  or geotextile  248 . The cover  246  may be attached to the unit  300  at points  247 . When installed, water is collected from the gaps  243  between the collection portion  242  and surrounding area. Again, the collection portions  242  may also provide supports for the unit  300 . The unit may be placed directly in a trench during installation. 
       FIG. 12  shows the extraction portion  214  of  FIG. 13  in more detail, taking a section through B-B of  FIG. 13 . The method of extraction is by capillary action. However, the arrangement is different to that previously described herein. In the present arrangement, water is extracted from the soil under the ribs through slots  220  between “m”-shaped mini-channels located on the bottom side of the ribs. A number of mini-channels are located along the width of the ribs with a gap between each of the channels. The slots  220 , through which the water is extracted, are suitably sized for the water to enter the extraction portion  214  by capillary action. Extracted water is then deposited in the “U”-shaped bends  222  of the m-shaped mini-channel and the mini-channel to the collection portion  210  of the unit  200 . The collection portion  212  of the unit is shown by the broken line  224  and is located at the end of the mini-channels. Thus, water may flow into the unit from the surroundings in a direction as indicated by arrow  226 . 
     As can be seen in  FIG. 12 , the unit cover  228  is attached to the unit  200  on a number of supports located to the side of the “m”-shaped mini-channels. 
       FIG. 14  shows an enlarged portion of the slots made by two ends of the “m”-shaped mini-channels. The slot has substantially parallel elongate sides and each side curves away from the other at the top. The rounded shape allows for easier access into the collection portion as water is extracted by capillary action through the width of the slots and deposited in the “U”-shaped bends of the “m”-shaped mini-channels. There is no need for the extraction portion  244  to slope as water cannot build up before it flows into the collection portion  242  of the unit  300 . 
     The skilled person will realise that any of the described extraction methods and materials may be used with any of the water management units described herein. 
     Another embodiment is shown in  FIG. 15  which has extraction portions  254 . The extraction portion  254  comprises ribs with extraction material on the underside. The extraction material may be the extraction material as described in relation to any of the previous embodiments or any other suitable arrangement. The sloped extraction portions  254  discharge into a main water flow channel  250  along the length of the unit via a collection portion located between the sloped ribs. As with previous embodiments, water is collected from the soil from the underside of the sloped ribs and surrounding area and transferred to the inside of the unit via the extraction portion for transport and removal via the main water flow channel  250 . In this embodiment a snap fit cover  256  is also provided in order to prevent soil particles from entering the unit. 
       FIG. 16  shows a detail of the rib sections of the embodiment shown in  FIG. 15 . Extraction material  260  is located on the under side rib  262  and passes over the edge of the rib  262  so that water may be collected in the water management unit  264 . Alternatively, as shown in  FIG. 17 , a slot may be cut in the rib  272  so that the extraction material  270  passes through the rib  272  for depositing water in the unit  274 . 
     These low profile embodiments may be installed in an area needed to be drained without a trench, however, a trench will give better efficiency and performance. Generally, these embodiments have a profile where the water management unit is only 3 or 4 cms tall so they require a shallow trench and hence little excavation. Such a trench may easily be dug by hand and requires a minimal quantity of material for back filling. This results in substantial cost savings in both labour and materials. The unit may be made in any suitable length or width. For example, approximately lm in length and 50 cm in width. 
     Another embodiment is shown in  FIG. 6  which provides a schematic diagram of a water management unit  4 . The water management unit  4  comprises an elongate collection portion  16  and an extraction portion  18 . Extraction portions  18  may be located on one or more sides of the collection portion  16 . The collection portion  16  has a plurality of ribs  8  located on the exterior which extract water from the surrounding area. 
     Water is extracted from the surrounding ground by the extraction portion  18  of the water management unit  4  and is made up of the plurality of ribs  8 . The extracted water flows along the ribs  8  on the exterior of the collection portion  16 . The collection portion  16  provides a conduit for extracted water. Water is transferred from the extraction portion  18  to the collection portion  16  and subsequently water is transferred to the drainage system. 
     The collection portion  16  has an upstream end  6 , a downstream end  5  and in some embodiments it is generally rectangular and narrow in cross-sectional profile, elongate and T-shaped in plan view, the cross bar being at the downstream end  15 . It has a box shape so that the ribs  8  may be conveniently located along the sides. When installed in saturated ground, water is extracted from the surrounding ground along the ribs  8  and flows along the ribs  8  into the collection portion  16  at the wider section  7 . 
     The downstream end  5  of the collection portion  16  has a wider section  7 . The end of the ribs  8  abut the collection portion  16  at the wider section  7 , the cross-bar of the T-shape, and the ribs  8  are molded into the outer frame of the wider section  7 , while the water extraction material  14  extends through the walls of the wider section  7  so water collected by the water extraction material  14  can be effectively transferred to the inside of the wider section  7  for removal by the collection portion  16 . 
     Optionally, the downstream end  5  of the collection portion  16  is shaped so that it may cooperate with the upstream end  6  of an adjacent collection portion  16 . The downstream end  5  of a first unit  4  may be inserted into the upstream end  6  of a second unit  4 . Thus, several units  4  may be connected together to extract water over a larger area.  FIG. 7  shows a schematic diagram of two water management units  4  fitted together. As can be seen, the downstream end  5  of the first unit  4  is sized and shaped so that it may be inserted into the upstream end  6  of the second unit  4 . 
     The ends  5 , 6  of the unit  4  may alternatively be shaped to connect to a pipe  20  of a drainage system. Alternatively, the upstream end  6  of the unit  4  may be capped as a terminus of the drainage system. Thus, the unit  4  may be placed in any position within a drainage system, for example, next to another unit  4 , at the end of pipe  20  branch, at any position along a length of pipe  20  or at a pipe junction. 
     An example of a water management system is shown in  FIG. 8  before it is inserted in the ground. Two units  4  are connected by their respective upstream  6  and downstream ends  5 . The first unit  4  is also connected to a pipe  20  at the downstream end  5 . The upstream end  6  of the second unit  4  is capped. 
     Although not shown in the drawings, the top and bottom of the collection portion  16  may also be shaped so that a first unit  4  cooperates with a second unit  4  such that the units  4  may be stacked vertically. For example, the units may be stacked, increasing the overall height of the system, for use against a retaining wall. 
     According to the example shown in  FIG. 8 , the unit  4  may have dimensions in the range of height of 10-40 cm, a width of 5-15 cm and a length of 20-60 cm; and the ribs are 1-5 cm wide. The width (not shown) between extraction portion  18  on either side of the collection portion  16  may be approximately 5 cm. However, any suitable dimensions may be used and the foregoing is merely a suggestion of suitable dimension. 
     Joints between units  4 , pipes  20  and other parts of the drainage system are preferably such that water does not leak. For example, they might include rubber parts with interference fit ribs so that a seal is formed. However, even if some leakage between parts does occur, the water will be collected again by the extraction portion  18  of the unit  4 . 
     Further, the unit  4  may have additional openings to connect with other parts of a drainage system. For example, a side or top opening may be suitable to form a connection with additional drain belts to increase the effective water collection area of the unit  4 . Thus, the drain belts may drain into the collection portion  16  of a unit. 
     The water extraction portion  18  of the unit  4  comprises at least one rib  8  arranged along the length  3  (see  FIG. 6 ) of the collection portion  16 . Optionally there is a plurality of parallel ribs  8  arranged on the side of the collection portion  16 . The ribs  8  are arranged along the length  3  of one or both vertical sides of the collection portion  16  and optionally slope down from the upstream end  6  of the collection portion  16  to the collection point at the wider point  7  of the collection portion  16  at the end of the ribs  8 . At the downstream end of the ribs  8 , they abut with the wider section  7  of the collection portion  16  where the ribs  8  are molded into the outer frame and the water extraction material  14  extends through the walls of the wider point  7  so extracted water is discharged into the collection portion  16 . 
     Referring to  FIG. 9 , a formation or water extraction material  14 , of the type described above, is located on the bottom of the ribs  8 . The water extraction material  14  is a plurality of slots  12  which extend along the length of the rib  8 . Each slot  12  has a corresponding notch  11  extending into the rib. The channels  11  are wider than the slots  12  to hold water in the material  14 . The slots  12  and channels  11  are sized so that water is extracted from the surrounding area by being drawn up into the channels  11  through the slots  12  by capillary action. Water extracted from the surrounding area can flow along the channels  11 . At the downstream end of the rib  8 , the end of the water extraction material  14  is open so that water can flow out of the channels  11 . 
     The ribs  8  may be level or at any angle along the side of the collection portion  16 . Where the ribs  8  are sloped downward from the upstream end  6  to the downstream end  5 , water flows along the channels  11  into the collection portion  16  under gravity. Water pressure may be enough that water will flow along the ribs  8  even when, when installed, there is no overall downward slope of the extraction portion  18 . 
     Conveniently, the slope will be such that a plurality of ribs  8  can be arranged on one side of the collection portion  16  and so that they provide sufficient flow of water. For example the slope may be in the range of 2°-30°, preferably in the range of 5°-20° and more preferably 15°. 
     Installation of units  4  may be in a level trench. In some embodiments, the slope of the ribs  8  therefore provides a built-in downward slope in the extraction portion  18  from the upstream end  6  to the downstream end  5  so that water may be collected and taken away by the drainage network. The slope of the ribs  8  is independent to the slope of the network. 
     Further, the slope of the ribs  8  may be such that where the unit  4  is installed in a trench that does not have a level base, e.g. where the section of the trench is sloping up from the upstream end to the downstream end of the system, the slope of the ribs  8  is sufficient to compensate for a negative slope of the installation trench. Due to the slope of the ribs  8  on the collection unit  4 , sloping of the trench for installation is not critical and therefore it is much easier to install the water management unit  4  so that it is effective in use because the slope of the ribs  8  gives the unit  4  a greater tolerance. 
     Again referring to  FIG. 6 , the ribs  8  are located along the length  3  of the water management unit  4  and extend laterally from the side of the unit  4 . The width  2  of the ribs is not critical. However, the dimension will be chosen to keep the overall profile of the unit  4  narrow and to provide the desired extraction capacity. Suitable dimensions have been given above. However, the person skilled in the art will appreciate that these are not limiting. 
       FIG. 9  shows a cross section view of a water management unit  4 . Ribs  8  extend laterally from the side of the collection portion  16 . The ribs  8  have a triangular cross-section with a downwardly angled top surface and water extraction material  14  on the generally horizontal bottom of each rib  8 .  FIG. 10  shows an expanded view of the water extraction material  14 . Similarly to the drain belt  10 , the material has slots  12  and channels  11  which extract water by capillary action. 
     Optionally, the ribs  8  have triangular cross-section, with the water extraction material  14  on the bottom side of the triangle. The cross-section of the ribs  8  provides increased rigidity to the extraction portion  18  so that the extraction material  14  remains in place and facing down when installed and during compaction of the backfill. The ribs  8  may also provide increased rigidity to the collection portion. During installation the slope on the upper surface of the ribs  8  helps to deflect soil particles from the extraction material  14  so that there is less risk of small particles entering the slots  12  and clogging the water flow path. 
     Where a plurality of ribs  8  are located on the side of the collection portion  16 , the result is effectively a separated stack of thin strips of extraction material  14 . 
     Therefore, the effective width of the extraction material  14  is large enough to provide enough water extraction capacity, while maintaining a narrow profile of the unit. Further, the extraction capacity is increased as the total effective width of the extraction material is increased or the height of the water management unit  4  is increased. 
     The maximum distance that water has to flow along the ribs  8  to the discharge point in the collection portion  16  is limited by the length  3  of the collection portion  16 . The strips of extraction material  14  are limited in length to the length of the rib  8  on the collection portion  16 . Strips of extraction material  14  are thus preferably short enough that the flow of water through the channels  11  is not significantly impeded by resistance from the small size of the channels  11 , and optimally, the water flow and discharge will match the extraction capacity of the extraction material  14 . 
     If a greater length of water extraction is required along a greater length, several units  4  may be joined together, as described above. Along the length of the water extraction units  4 , water will be collected regularly into the collection portion of the units  4 . The collection portion  16  is large enough that it does not fill and prevent water from being extracted. Therefore, it is possible to extract water at rates as great as 20 lt per minute per meter in course sand, the limiting factor being the hydraulic conductivity of the sand, with a relatively small and narrow water management unit  4 . 
     The narrow profile makes installation of the unit  4  in the ground straightforward. A narrow profile allows for minimal disruption of the ground as one or more units  4  may be inserted in a trench which is only slightly wider than a unit  4  and connected to other units  4  or pipes  20 . The trench is then backfilled with the excavated soil or with sand with out the need for accurate positioning in view of the rigidity and inherent angle of the ribs. As will be apparent from the foregoing, the water management unit  4  is simple to install. In most embodiments the unit  4  will have a narrow profile. Further, as the ribs  8  do not extend from the unit  4  by a great distance, there is no need to excavate a wide area to accommodate the extraction portion  18 . The unit  4  can be installed in a trench which is approximately the same size as the drain pipe  20  trench. 
     Since the strips of extraction material  14  are oriented one above the other, for the height of the water management unit  4 , and the water management unit  4  is placed into the narrow trench with the strips of extraction material  14  facing down, in the opposite direction of the backfill sand, it is not probable that the extraction material  14  can be clogged from pressure on the surface, or foot traffic, or backfill operations. 
     Preparation of the trench is also simpler than for other drainage or water management systems. As a slope in the extraction portion  18  is built into the unit  4 , it is not necessary to ensure that the trench is sloped in a downward direction from the upstream end of the unit  4 . Normally, the unit  4  will be installed in a trench with a slight slope to drain the collection portion  16 , but can be installed in a level trench since the height of the unit  4  will allow for substantial drainage of the collection portion  16 , while the extraction portion  18  is sloped independent of the trench slope. 
     Indeed, it is possible that the slope of the extraction portion  18  of the unit will be sufficient even if the unit  4  is installed on a positive slope i.e. the trench slopes upwards from the downstream end  5  of the unit  4 , the unit  4  will still be able to extract water and deliver water into the collection portion  16  of the unit  4 . 
     The ends of the unit  4  are either capped or connected to pipes  20  in the drainage system. The units  4  may also be installed adjacent to each other along the trench. Once in place, the trench is backfilled using either the excavated soil, sand or other material. It is not necessary to use drain rock as a filter, as required by more conventional systems, since the soil particles are separated from the water by gravity before the water enters the water extraction material  14  by capillary action. 
     Further, it is not necessary to carefully compact the soil around the unit  4  because the joints between the extraction portion  18  and the collection portion  16  are fixed by the unit  4  itself, and the ribs  8  provide elongate rigidity. Therefore, faults arising from installation are unlikely. 
     As will be apparent, the unit  4  is suitable for use in a number of situations where water management is required. For example, it may be installed at a number of locations for managing water in a playing field, or, next to a retaining wall. In the situation where the unit is used directly next to a retaining wall, the ribs  8  may be located on just one side of the collection portion  16 . 
     As after installation the operation of the unit  4  does not depend on whether the ground around the installation has settled, small ground movement will not effect the collection of water. Further, even if the ground below the installation settles so that the unit  4  is no longer level, as noted above, the unit  4  will continue to operate in the desired way because the tolerance of the unit  4  is large enough that it may work. 
     Further, the design of the unit  4  is such that it is very unlikely that soil particles will enter the water extraction material  14  and the collection portion  16 . Therefore, it is unlikely that the water flow path will become clogged. This means that after installation, the unit  4  will continue to operate without the need for maintenance. This represents a significant advantage, as when a drainage system is installed in the ground, there is very limited access to it without re-excavating the area. 
     The unit  4  can be manufactured using a durable semi-rigid material, such as plastic. The unit may be manufactured by constructing several parts, or in a single part process with all of the different features integrated in a single part. 
     Collected water may be re-used or channelled so that it may be stored for other purposes. The unit  4  may alternatively be used for water irrigation systems. In this instance the ribs  8  would slope downwards from the openings in the collection portion  16  and water would flow from the collection portion  16  to the extraction portion  18 . 
     Embodiments of the invention have been described by way of example only. It will be appreciated that variation of the described embodiments may be made which are still within the scope of the invention. 
     For example, the dimensions of the collection portion may be varied. Any suitable shape of the collection portion  16  may be envisaged. Also, the width and number of the ribs may be varied. The unit may be constructed and fabricated from any suitable material.