Abstract:
According to a first aspect, the invention relates to a container ( 10 ) for temporarily holding water on the roof of a building, including a bottom ( 11 ), a side wall ( 12 ) surrounding the bottom ( 11 ) and an overflow opening ( 14 ) for draining surplus water when the volume of water collected in the container ( 10 ) exceeds a buffer volume, characterised in that the container ( 10 ) includes a water-draining means configured to force water with a temporary storage volume which is lower than the buffer volume to flow according to a regulated leakage rate ( 13 ), and in that the dimensions of the bottom are smaller than the dimensions of a sloping roof on which the container ( 10 ) can be placed so that the water load is distributed evenly on the surface of the roof when a plurality of containers ( 10 ) of the same size cover the surface of the roof.

Description:
FIELD OF THE INVENTION 
       [0001]    The field of the invention is that of the management of rainwater. 
         [0002]    The invention concerns more precisely a device for controlling the discharge of rainwater on roofs, in particular on sloping roofs. 
       BACKGROUND OF THE INVENTION 
       [0003]    Because of the increasing rain-proofing of urban ground and roofs, the management of rainwater is becoming a major problem. 
         [0004]    This is because the water cannot infiltrate into rain-proofed ground or on roofs. A major part of the rainwater must therefore be collected and treated. This collection has a financial cost (pipes, retention basins, water treatment plants), and an ecological cost since the water is soiled by numerous pollutants on its travel (waste, hydrocarbons, heavy metals, etc.). 
         [0005]    In addition, a second problem related to the rain-proofing of ground is the increase risk of flooding. During violent storms, greater and greater volumes of rainwater run off, giving rise to a saturation of sewers and overflowing. 
         [0006]    Planted roofs afford concrete responses to these two problems since they offer a real management of rainwater. 
         [0007]    Planted roofs firstly afford management of infiltration. 
         [0008]    The planting complex (substrate and plants) in fact captures a major part of the annual rain (around 50% according to many tests). The water stored then returns to the atmosphere by evapotranspiration. 
         [0009]    Planted roofs therefore reduce the rain-proofing coefficient of the surfaces. 
         [0010]    In this regard, pre-cultivated containers with no water reserve, such as Hydropack® containers from the company Le Prieuré, a description of which will be found in the patent EP 1 044 599 B1, further improve this function. The water reserve contained in the alveoli of such a cell in fact increases the retention capacity. The stagnant water will then be “pumped” by the roots of the plants that have developed in these alveoli. 
         [0011]    Planted roofs also allow management of the retention by fulfilling a buffer role (delay effect) during violent storms. 
         [0012]    The water accumulates in the planted complex (substrate and plants) until it is saturated with water. Once the complex is saturated, it “salts out” the excess water, like a sponge. 
         [0013]    Many tests have proved the advantage of planted roofs in this field. A good part of the storm waters will therefore be captured by the planted complex. The other part will be “salted out”, once the complex is saturated, a few tens of minutes or even a few hours later. Saturation of sewers is therefore largely attenuated. 
         [0014]    Planted roofs thus reduce what is called the run-off coefficient (test show that this coefficient is 0.4 to 0.6 for a planted roof instead of 1 for an impermeable cladding). 
         [0015]    The current systems on planted roofs do however have certain limitations. 
         [0016]    Though planted roofs significantly reduce run-off, the coefficient could be further reduced. 
         [0017]    In addition, though planted roofs reduce the annual mean run-off coefficient by approximately 50%, they do not provide systematic reduction of each rainy event. This is because the run-off coefficient is not truly mastered but varies substantially according to the characteristics of the rainy event and the hydric state of the planted roof. Thus a planted roof already saturated by previous rain will have a run-off coefficient almost equal to 1 and a zero delay effect, which results in a non-reduced leakage rate. 
         [0018]    Storing roofs have thus been developed in order to very greatly reduce and control the leakage rate. These storing roofs provide a temporary retention of the rainwater in order to discharge it at a certain leakage rate. 
         [0019]      FIG. 1  shows in this regard a schematic view in section of a possible example embodiment of such a storing roof with a zero slope. 
         [0020]    The roof  1  has two rain discharge orifices  2 ,  3 . 
         [0021]    The first orifice  2  is disposed at the bottom part of the roof  1  so as to afford permanent discharge. The diameter thereof is relatively small so as to greatly reduce the discharge of water. The diameter is thus calibrated according to the maximum acceptable leakage rate. 
         [0022]    The second orifice  3  fulfils the role of an overflow orifice and has a relatively large diameter. The second orifice  3  is disposed several centimetres above the first orifice  2 , according to the buffer volume necessary (as determined statistically by local meteorological recordings, for example, ten-year rain). 
         [0023]    Such a storing roof can advantageously also be equipped with pre-cultivated containers with a water reserve, such as the Hydropack® containers presented above. The pre-cultivated containers  4  can for that purpose be raised on a honeycomb structure  5  into which the water will infiltrate. 
         [0024]    However, the model of storing roofs cannot at present find application except for roofs with a zero slope. 
         [0025]    This is because, on large roofs, even a small slope (2% or more, as is the case with industrial, commercial, transport, etc. buildings) represents a significant difference in level. Very high watertight walls would therefore be necessary to ensure temporary retention of the water. Moreover, the weight distribution would not be even, which would make it necessary to significantly reinforce the structure of the building at the slope bottoms. 
         [0026]    By way of example, for a building 20 m long, a slope of 3%, represents a difference in level of 60 cm between the top part and the bottom part of the roof. In order to store 50 litres of water per m 2  (on average) on such a roof, it is necessary to provide a wall of a minimum of 24.5 cm at the slope bottom. For a building 30 m long and a slope of 3% also, it is necessary to provide a wall 30 cm in height. As for the distribution of weight, the extra load relating to the temporary storage of water at the slope bottom would be approximately 245 kg/m 2  in the first case and 300 kg/m 2  in the second case. 
         [0027]    Technical constraints (height of roof elevations and extra loads at the slope bottom) thus make it possible to temporarily retain water on roofs even with a low slope. 
       DISCLOSURE OF THE INVENTION 
       [0028]    The objective of the invention is in particular to make it possible to temporarily retain rainwater on roofs having a slope in order to reduce and control the leakage rate thereof. 
         [0029]    In this regard, the invention proposes, according to a first aspect, a container for temporarily holding water on the roof the building, comprising a bottom, a side wall surrounding the bottom and an overflow orifice for draining surplus water when the volume of water collected by the device exceeds a buffer volume, characterised in that it comprises water discharge means configured to force water with a temporary storage volume that is less than the buffer volume to flow at a regulated leakage rate, and in that the dimensions at the bottom are small vis-à-vis dimensions of a sloping roof on which the device can be positioned so that the water load is distributed evenly on the surface of the roof when a plurality of containers with the same size cover the surface of the roof. 
         [0030]    Certain preferred but non-limitative aspects of this container for the temporary holding of water are as follows:
       the means of discharging water at a regulated leakage rate comprise an obturator controlled so as to adjust the opening of a discharge orifice according to the temporary storage volume;   the obturator is associated with a float by means of an arm, the arm being able to pivot in response to the change in the temporary water storage volume detected by the float in order to cause a rotation of the obturator in front of or through the discharge opening;   the obturator is a disc portion able to be rotated in front of the discharge orifice and in which a slope with a progressive opening is provided, ensuring a constant leakage rate independent of the height of water in the container;   the obturator is a horn able to be rotated through the discharge orifice, the horn being conformed so as to provide a constant leakage rate through the discharge orifice, independently of the height of water in the container;   the obturator is a cone able to be driven in translation by a float through the orifice, the cross-section of the cone decreasing as the float is approached so that the opening of the discharge orifice decreases as the water level increases in the container, thus ensuring a constant leakage rate;   the overflow orifice constitutes the discharge orifice;   the discharge orifice is distinct from the overflow orifice, the overflow orifice being arranged above the discharge orifice at a distance defining the buffer volume;   the container also comprises permeable means of supporting a vegetation complex;   the permeable support means are formed a grid supported by one or more support services defined by little islands extending from the bottom;   the permeable means of supporting the vegetable complex are formed by a pre-cultivated container conformed so as to fit in the temporary water holding container, or made in one piece with the temporary water holding container;   the pre-cultivated container has a base in which a plurality of alveoli are formed, the alveoli being separated by separation partitions consisting of walls of alveoli extending from the base and a support surface connecting the top edges of the walls, a plurality of drainage holes being formed through the support surfaces;   the temporary water holding container comprises a plurality of separation partitions consisting of walls of alveoli extending from the bottom and a support surface connecting the top edges of the walls, forming a plurality of alveoli with the bottom, a plurality of drainage holes being formed through the support surfaces in order to form said permeable means of supporting a vegetation complex;   it comprises a permeable bearing slab arranged parallel to the bottom;   it comprises a partial sealed closure extending parallel to the bottom from the top part of the side wall;   the surface area of the bottom is less 2 m 2 , preferably less than 1 m 2 ;   the regulated leakage rate is no more than 10 l/s/ha, and preferably no more than 5 l/s/ha.       
 
         [0047]    According to another aspect, the invention concerns a system for temporarily holding water on the roof of a building consisting of a plurality of containers intended to be attached to one another, at least one of which is a container according to the first aspect of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0048]    Other aspects, aims and advantages of the present invention will emerge more clearly from a reading of the following detailed description of preferred embodiments thereof, given by way of non-limited example and made with reference to accompanying drawings, in which: 
           [0049]      FIG. 1 , already commented on, is a schematic view section of a storage roof with zero slope; 
           [0050]      FIG. 2  shows a possible embodiment of a container according to a possible embodiment of the invention; 
           [0051]      FIGS. 3   a - 3   b ,  5   a - 5   b  and  6   a - 6   b  show different possible embodiments of means of discharging water with a constant leakage rate; 
           [0052]      FIG. 7  illustrates a possible embodiment of a container according to an invention having a residual water storage volume; 
           [0053]      FIG. 8  illustrates a possible embodiment of a container according to the invention having a partial sealed closure; 
           [0054]      FIGS. 9   a - 9   c  illustrate the different possible connections of containers to one another. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0055]    Referring to  FIG. 2 , this shows a container for the temporary holding of water on the roof of a building in accordance with a possible embodiment of the invention. 
         [0056]    The container  10  comprises a bottom  11 , rectangular in shape in the example shown, and a side wall  12  surrounding the bottom. 
         [0057]    According to the invention, the dimensions of the bottom are small vis-à-vis the dimensions of a roof, in particular a sloping roof, on which the container is intended to be positioned. In this way, the water load liable to accumulate in the container at the slope bottom is substantially equivalent to that liable to accumulate in the container at the top of the slope. 
         [0058]    More particularly, the advantage of containers of small size is to be able to distribute the mass of water evenly over the surface of the whole of the roof. This is because all the containers will routinely and automatically carry the same mass, at the slope bottom as at the slope top. 
         [0059]    The invention thus proposes to equip a roof by means of a plurality of small temporary water-holding containers, independent of one another. The problem of the distribution of the rainwater (which accumulates at the slope bottom) and therefore the constraints of excess loads and high wall heights are dispensed with. 
         [0060]    The surface area of the solid bottom is for example less than 2 m 2 , preferably less than 1 m 2 . By way of example, the bottom  11  is rectangular and measures 60 centimetres and 40 centimetres wide. 
         [0061]    The container is preferably produced from inert and non-deteriorating material, plastic for example. 
         [0062]    The container  10  also comprises an overflow orifice in order to discharge surplus water when the volume of water collected by the device exceeds a buffer volume, as well as water discharge means configured to force water with a temporary storage volume less than the buffer volume to flow at a regulated leakage rate. 
         [0063]    In the context of the invention the leakage rate is preferentially no more than 10 l/s/ha, even more preferentially no more than 5 l/s/ha. In general terms, the leakage rate is adapted to the building and the location thereof, so as to meet local directives relating to water management. The leakage rate can ideally be reduced to 1 l/s/ha. 
         [0064]    According to a first variant shown in  FIG. 2 , the container  10  comprises, at a first height from the bottom  11 , discharge means  13  configured to allow a discharge of a volume of water less than the buffer volume at a very low rate and, at a second height from the bottom  11 , a high-rate overflow orifice  14 , the second height being greater than the first height so as to define the temporary buffer water storage volume able to collect storm rain. 
         [0065]    These regulated leakage rate discharge means comprise at least one low rate discharge orifice  13  passing through the side wall at the first height, the diameter which is chosen to allow a discharge at low rate, known and controlled. In a variant, these discharge means can be formed by a porous membrane or by a regulator. 
         [0066]    The overflow orifice  14  for its part allows high-rate discharge. The diameter of the overflow orifice is typically greater than that of the low-rate discharge orifice  13 . 
         [0067]    The difference in height between the discharge means with a regulated leakage rate  13  and the overflow discharge means  14  determines a water storage buffer volume able to collect storm rain, even of high intensity. The buffer volume will drain away gently after the storm, at a (leakage) rate determined by the rate of the discharge means (for example by the diameter of the low-rate discharge orifice or orifices  13 ). The buffer volume will once again be empty for a few minutes or a few hours after the storm and will once again be able to completely fulfil its buffer role during further precipitations. 
         [0068]    It should be noted that the first height may be zero (the first water discharge means then being arranged in the bottom  11  of the container  10 ). In this case, the container  10  may be raised by legs so that the water discharge means  13  emerge above any puddles of water present on the roof. 
         [0069]    The first height may also be situated at a few centimetres (by way of example, the low-rate discharge orifice  13  is then pierced in the side wall  12 , or in a partition separating alveoli formed in the bottom  11 ), for example less than 3 centimetres, so as to constitute a small residual water storage volume at the bottom of the container (cf.  FIG. 5   a  for example). 
         [0070]    It will be noted that, if the discharge means  13  consisted of a simple orifice, the leakage rate would not be constant. The rate effectively decreases as the water height decreases in the container according to the following mathematical formula: Q=Ω×outlet surface×(2×g×h) 0.5 , where Q designates the leakage rate, Ω is a coefficient relating to the geometry of the orifice, g designates acceleration due to gravity and h represents the water height. By way of example, between water heights of 100 mm and 10 mm, the rate could be divided by three. 
         [0071]    The invention provides that the opening of a discharge orifice is modified when the water level decreases or increases, by means of a mechanism that adjusts the opening of the orifice according to the water height in the container. The means of discharging water at a regulated leakage rate according to the invention can in particular be configured so as to close off part of an orifice to a greater or lesser extent according to the temporary volume of water so as to discharge water from the buffer space according to a constant leakage rate. 
         [0072]    In the context of a first variant, the orifice the opening of which is adjusted is a low-rate discharge orifice  13 , distinct from the overflow orifice  14 , and the surface of which is determined by the buffer volume and the leakage rate sought. 
         [0073]    According to a second variant that will be detailed in more detail hereinafter, the overflow and the temporary water volume are discharged by one and the same orifice. In this second variant, the orifice the opening of which is adjusted is the overflow orifice itself, the surface of which is determined by the overflow rate sought. 
         [0074]    Different embodiments of means for discharging water at a constant leakage rate are shown in  FIGS. 3   a - 3   b ,  4   a - 4   b ,  5   a - 5   b  and  6   a - 6   b . These figures show more particularly the second variant presented above but it will be understood that the principles that are shown therein can easily be used in the context of the first variant, in particular modifying the form of the obturator. 
         [0075]    In each of the variants shown in  FIGS. 3   a - 3   b ,  4   a - 4   b  and  5   a - 5   b , the means of discharging water at a constant leakage rate comprise a float  30  connected to an arm  34  pivoting about a spindle  33  perpendicular to the wall ( FIGS. 3   a - 3   b  and  FIGS. 5   a - 5   b ) or to the bottom ( FIGS. 4   a - 4   b ) of the container and to which an, obturator  32 ,  37 ,  38  is connected. The arm  34  pivots in response to the change in height  40  of temporary holding of water detected by the float  30  and rotates the obturator  32 ,  37 ,  38  about the spindle  33  in front of or through the orifice  14 . 
         [0076]    According to a first embodiment shown in  FIGS. 3   a  and  3   b , the obturator  32  is rotated in front of the orifice  14 . The obturator is for example in the form of a portion of a disc  32  in which a slot  31  with progressive opening is formed. This progressive opening ensures a constant leakage rate when the temporary volume of water decreases or increases by rotating the disc  32  and therefore modifying the position of the slot in front of the orifice. 
         [0077]    In a variant, it is possible to provide, in place a slot formed in a disc portion, a blade the thickness of which varies progressively in order to ensure a constant leakage rate when the blade closes off the opening. 
         [0078]    With reference to  FIG. 3   a , the orifice  14  is formed through the wall of the container close to the bottom  11  of the container. The progressive-opening slot  31  is formed in a disc  32  mounted so as to rotate about the rotation spindle  33  perpendicular to the wall. The disc is connected to the float  30  via the arm  34  pivoting about the spindle  33 , so as to pivot against the wall  12  having the orifice in response to changes in water level in the container as detected by the float. The opening of the slot  31  widens on approaching the float so that the obturator covers the orifice to a greater extent when a large volume of water is to be drained (high pressure) that when a small volume has to be drained (low pressure). The progressiveness of the opening ensures a constant leakage rate whatever the volume of water remaining to be drained. 
         [0079]    In order to minimise the risks of clogging, it is also possible to make provision for attaching, by adhesive bonding for example, a rod  35  to the rim of the orifice, the rod being directed towards the inside of the container so as to enter inside the slot  31 . 
         [0080]    According to a second embodiment shown in  FIGS. 4   a - 4   b  and  FIGS. 5   a - 5   b , the obturator  37 ,  38  is rotated about a spindle  33  through the orifice  14 . 
         [0081]    The obturator for example takes the form of a horn  37 ,  38  associated with an arm  34  pivoting about the spindle  33  under the action of a float  30  to which it is connected. The horn, the diameter of which increases progressively, thus adjusts the opening of the orifice according to the volume of water remaining to be drained in the container. The orifice can be formed in the bottom of the container ( FIGS. 4   a - 4   b ) or through a wall of the container ( FIGS. 5   a - 5   b ), which creates a residual volume of water  42 . 
         [0082]    In the variant shown in  FIGS. 6   a - 6   b , the means of discharging water with a constant leakage rate comprise an obturator  43  directly driven by a float  30  in translation through the orifice  14 . 
         [0083]    The obturator is for example formed by a cone  43 , at the head of which a float  30  is provided. The orifice  14  is here formed in the bottom of the container, while the cross-section of the cone decreases on approaching the float. In this way, the opening of the orifice decreases as the water level increases in the container. 
         [0084]    The base of the cone can be sufficiently wide vis-à-vis the surface of the orifice in order to hold the obturator in place when the buffer volume (the maximum temporary holding volume) is reached. In this case, the orifice  14  is blocked when the buffer volume is reached and it is therefore necessary to provide a separate overflow orifice in order to discharge the surplus water. 
         [0085]    In a variant (cf.  FIG. 6   b ), it is possible to associate with the base of the cone a support  46 , for example cruciform, carrying vertical lugs  47  bearing against the bottom  11  of the container when the buffer volume is reached, thus holding the obturator in place. In this case, the orifice  14  is completely open when the buffer volume is reached. This orifice can therefore also fulfil the role of an overflow orifice. 
         [0086]    The reciprocating movement of the obturator can also be guided by means of a porous pipe  45  that is disposed vertically above the orifice and the diameter of which exceeds that of the float and obturator, by a few millimetres only. 
         [0087]    In addition, the float  30  is sized so as to be sufficiently large vis-à-vis the surface of the orifice in order to remain locked inside the container when the latter is empty, thus holding the obturator. 
         [0088]    It will also be noted that the container must be raised by a height at least equal to the height of the cone. 
         [0089]    It should be noted that, in the embodiment shown in  FIGS. 4   a - 4   b ,  5   a - 5   b  and  6   a - 6   b , the obturator  37 ,  38 , passes through the orifice. The coming and going thus created through the orifice minimises the risks of clogging. The body of the through obturator can also be provided with roughnesses that facilitate the discharge of particles out of the container. 
         [0090]    It was seen previously that, according to a variant embodiment, the overflow and temporary water volume are discharged through one and the same orifice. This variant is advantageous in that it makes it possible to discharge the particles issuing from vegetation complexes associated with the temporary water-holding container on a building roof (see below). This variant also proves to be advantageous in that it avoids having to create upright an overflow orifice, the position of which will vary according to the permissible excess load. 
         [0091]    In the context of this variant, the obturator  37 ,  38 ,  43  is conformed so as to allow maximum opening of the discharge orifice  14  when then float reaches its maximum height  41  corresponding to the buffer volume of water. The orifice here has a large surface area, for example a diameter of at least 1 cm. 
         [0092]    In the context of the embodiment illustrated in  FIGS. 3   a  and  3   b , the slot  31  formed in the disc is extended by a piercing  36 , the surface of which is at least equal to that of the opening  14  so that said piercing coincides with the orifice when the float  30  reaches its maximum height  41 . 
         [0093]    In the context of the embodiment illustrated, in  FIGS. 4   a - 4   h  and  5   a - b , the horn  35  has a recess  39  coming through the orifice when the float reaches its maximum height  41 . 
         [0094]    In the context of the embodiment illustrated in  FIGS. 6   a - 6   b , a recess  44  is hollowed out in the base of the cone, which makes it possible to discharge the overflow through the entire surface of the orifice when the base of the cone is upright with respect to the bottom of the container (cf.  FIG. 6   b ). 
         [0095]    It should be noted that, by integrating the low-rate discharge with the overflow, it is possible to vary the buffer volume according to the permissible excess load on the roof, while still keeping the same container: the height of the container and the surface area of the discharge orifice effectively remain the same. This is because, whatever the obturator in question (disc with slot, horn or cone), it is possible to adapt the sizing thereof (width of the slot, length of the cone, thickness of the cone or horn, positioning of the overflow recess) to the required leakage rate and to the permissible maximum excess load. 
         [0096]    In the context of a possible embodiment of the invention, a small residual water storage space is formed at the bottom of the container, in particular in order to ensure, via synthetic wicks, the supply of water to a vegetation complex that will be associated with the temporary retention container. 
         [0097]    To do this, the discharge orifice can be positioned at a certain distance from the bottom of the container, through a wall (cf.  FIGS. 5   a - 5   b ). As shown in  FIG. 7 , it is also possible to provide one or more partitions  49  starting from the bottom of the container and extending over a height less than that of the side wall, the partition or partitions dividing the container into one or more regions, at least one of which is not connected to water discharge means and can thus form a water reserve  42 . 
         [0098]    The stagnant water is then available for the plants in the vegetation complex. Synthetic wicks  48  (cf.  FIGS. 5   a - 5   b  and  FIG. 7 ) attached to the bottom of the container and passing through a vegetation support  49  through drainage orifices are connected to a filter  21  (cf.  FIG. 5   a ) on which the vegetation complex rests and conduct the water thereby capillarity. 
         [0099]    In addition to control of the leakage rate, the container for temporary holding of water on the roof of a building according to the invention can effectively also allow management of infiltration by providing the use of a vegetation complex. Some of the rainwater can thus be absorbed by the vegetation complex and then returned to atmosphere by evapotranspiration, which appreciably reduces infiltration. 
         [0100]    The rainwater that is not absorbed by the vegetation complex for its part descends into the container, where the leakage rate of this excess water will be regulated. 
         [0101]    As shown in  FIG. 2 , the container can for this purpose comprise permeable means of supporting a vegetation complex  20 , where said vegetation complex is for example formed by a microporous filter  21 , a layer of cultivation substrate  22  deposited on the filter  21  and vegetation  23  sown and cultivated on the substrate layer  22 . 
         [0102]    According to the preferential embodiment of the invention shown in  FIG. 2 , the permeable means of supporting a vegetation complex  20  are formed by a pre-cultivated container, more particularly by a Hydropack® container from the company Le Prieuré (a description of which will be found in the patent EP 1 044 599 B1). 
         [0103]    In this  FIG. 2 , the pre-cultivated container  20  is conformed so as to fit in the temporary water holding container  10 . 
         [0104]    According to a variant, the pre-cultivated container  20  is made in one piece with a temporary water holding container  10  so as to form a double-bottom container. The lower bottom is formed by the bottom  11  while the upper bottom is formed by a bottom (base  24  hereinafter) identical to that of the pre-cultivated Hydropack® container. 
         [0105]    In these two cases, the pre-cultivated container has a base  24  from which a plurality of alveoli extend. 
         [0106]    Each alveolus is closed by a side alveolus wall  25  so as to constitute a water reserve space in which mineral aggregates  26  can be arranged. 
         [0107]    The alveoli are preferably connected together by water communication means so that the network of alveoli defines a water reserve, for example of around 8 litres/m 2 . 
         [0108]    The height of the side wall  25  of the alveoli is preferably less than the height of the side wall  27  surrounding the base  24  of the pre-cultivated container so that the vegetation complex can be accepted in the pre-cultivated container  20 . 
         [0109]    The alveoli are separated by separation partitions consisting of alveolus side walls  25  extending from the base  24  of the container  20  and a support surface  28  connecting the top edges of the alveolus walls  25 , roughly parallel to the base  24 , and on which the vegetation complex  21 - 23  can be arranged. 
         [0110]    Drainage holes  29  are pierced in the support surfaces  28  in order to ensure permeability of the vegetation complex support means and thus allow rapid discharge of the excess water to the bottom  11  of the temporary water holding container  10 . By way of example, 500 drainage holes  29  per m 2  are provided, make it possible to sort out the excess water once the vegetation complex is saturated with water and the alveoli filled with water. 
         [0111]    According to another possible embodiment of the invention (not shown), the permeable vegetation complex support means are formed by a grid supported by one or more support surfaces defined by small islands extending from the bottom  11  of the temporary water holding container  10 . 
         [0112]    According to yet another embodiment of the invention, the temporary water holding container  10  itself forms a pre-cultivated container. The container  10  is for example a Hydropack® container of the type described previously, modified in order to control the leakage rate. 
         [0113]    The means of discharging water at a constant leakage rate can thus be arranged at the base  24  of the pre-cultivated container (the base  24  here forming the bottom  11  of the temporary holding container) or in the lower part of an alveolus side wall  25 . 
         [0114]    The height of the alveoli can moreover be modified with respect to that of a standard Hydropack® container in ardor to increase the water reserve volume to 50 litres/m 2  (rather than 8 litres/m). It should be noted that the water reserve no longer exists because of the continuous discharge: the volume of 50 litres/m 2  thus corresponds to the buffer volume of the temporary water holding container that will drain out at the low leakage rate. 
         [0115]    The temporary holding container according to the invention is however not limited by its use in conjunction with a vegetation complex to allow management of infiltration. The container  10  can thus comprise, instead of the permeable means of supporting a vegetation complex, a permeable bearing slab arranged parallel to the bottom. The permeable bearing slab is for example a porous slab, in particular a slab made from porous cement. 
         [0116]    It will also be noted that, when the temporary water holding container is disposed on a steep slope, the holding volume is drastically reduced. In an advantageous embodiment of the invention shown in  FIG. 8 , the container is provided with a partial top sealed closure  50 , which extends for example parallel to the bottom from the upper part of the side wail. 
         [0117]    This partial top closure makes it possible to keep a holding volume that is as great as in the case where the container is disposed on a fiat roof. Moreover, the water issuing from a pre-cultivated container positioned above this partial closure, which optionally serves a support for it, will pour onto this closure, where it will run off while being brought, via the opening  50 , into the underlying holding container on the slope. The pouring of the water from the surface of a container to the inside of the underlying container is provided by an overflow  52  from the partial closure of the first container into the opening  51  of the second container (in other words, the water may percolate between the two containers). 
         [0118]    In this case, the regulation system will preferentially be arranged at the edge at the container bottom so that the arm connected to the float remains perpendicular to the surface of the water. 
         [0119]    The container according to the invention advantageously comprises means of attachment to a similar adjacent container. This facilitates the operations of placing the containers on roofs, terraces or balconies. 
         [0120]    When several containers are thus connected, it is also possible advantageously to provide that a single container fulfils the discharge function (low-rate and overflow discharge) for a set of containers. The number of discharge systems will thus be reduced. 
         [0121]    In addition, by thus connecting the containers, the temporary holding volume will be enlarged. It is then possible, for the same leakage rate in question, to enlarge the surface area of the discharge orifice, which reduces the risks of clogging. On the other hand, if the surface area of the discharge orifice is not modified, the leakage rate is reduced. 
         [0122]    The containers are connected so as to provide a communication of water over several square metres. 
         [0123]    As shown in  FIG. 9   a , the connection  53  can be provided at the container bottom if it is not wished for there to be any residual water volume. 
         [0124]    As discussed previously in relation to  FIG. 7 , provision can be made for equipping the container fulfilling the discharge function with a partition  49  starting from the bottom defining a residual storage volume  42 . As shown in  FIG. 9   b , the connection  53  between the containers can then be made at the container bottom. In a variant (cf.  FIG. 9   c ), the connection  53  can be arranged at a height determined by the required residual volume. 
         [0125]    Finally, it should be noted that the means of discharging water at a constant leakage rate are not necessarily integrated as such in a temporary water holding container but may form, as is the case in  FIGS. 9   a - 9   c , a separate piece able to be attached to such a container, and in particular to the container at the end of the line when several containers are connected. The use of such an attached piece facilitates in particular maintenance operations. 
       REFERENCE SIGNS IN THE DRAWINGS 
       [0000]    
       
         
           
               1 : roof 
               2 : leakage rate regulation orifice 
               3 : overflow orifice 
               4 : pre-cultivated containers 
               5 : honeycomb structure 
               10 : temporary holding container with controlled leakage rate 
               11 : bottom of temporary holding container with controlled leakage rate 
               12 : walls of temporary holding container 
               14 : overflow orifice in the bottom or wall the temporary holding container 
               20 : vegetation support 
               1 : microporous filter 
               22 : cultivation substrate 
               23 : vegetation 
               24 : base of pre-cultivated container 
               25 : side wall of alveoli 
               26 : mineral aggregates 
               27 : side wall surrounding base  24  of pre-cultivated container  20   
               28 : support surface connecting the upper edges of the alveolus walls 
               29 : drainage holes 
               30 : float 
               31 : slot in the “disc portion” obturator 
               32 : “disc portion” obturator 
               33 : obturator rotation spindle 
               34 : arm connected firstly to the float and secondly to the obturator 
               35 : rod serving to prevent clogging of the orifice 
               36 : overflow orifice in “disc portion” obturator 
               37 : “horn” obturator passing through the container bottom 
               38 : “horn” obturator passing through the container wall 
               39 : recess providing the overflow in the horn-shaped obturators 
               40 : any water level 
               41 : maximum water level, corresponding to maximum permissible excess load 
               42 : residual water volume, serving as reserve plants 
               43 : vertical obturator 
               44 : recess in vertical obturator 
               45 : porous pipe guiding obturator vertically 
               45 : cruciform support for vertical obturator 
               47 : lugs attached to cruciform support for vertical obturator 
               48 : synthetic wick for water to rise to plants by capillarity 
               49 : partitions serving to delimit a storage volume 
               50 : partial closure of containers to preserve retention capacity even on a slope 
               51 : opening of container by which run-off water enters coming from container above 
               52 : room providing run-off of water from container to container on a sloping roof 
               53 : connection between containers at container 
               54 : connection between containers upright with respect to container bottom