Water detention system incorporating a composite draining membrane

Abstract

A water detention system comprises a sub-base of crushed rock or stone overlying an impermeable layer which may be naturally-occurring, as in an impermeable sub-grade, or may be formed by an impermeable membrane laid over the sub-grade prior to the sub-base layer. Over the sub-base layer is an incompletely impermeable layer the impermeability of which is compromised by openings in the form of slits or by spacing between adjacent strips forming the layer. These openings allow water to percolate downwardly through the layer into the sub-base, but substantially inhibit the escape of moisture by evaporation thereby serving to retain the collected water. Above the incompletely impermeable layer may be a laying course of finer particulate material such as pea gravel over which may be laid a wear surface of slabs or blocks to form an area for traffic, such as a roadway or parking area.

1 . A water detention system characterised by comprising at least a sub-base of particulate material in a layer having a substantial number of voids, an overlying permeable layer of particulate material, and a composite membrane comprising a first, permeable layer, a second impermeable layer and spacer means between the said first and second layer, the said spacer means acting to maintain at least part of the said first and second layers out of contact with one another and to allow the movement of liquid in the space between them, composite membrane being so positioned that water collecting on its surface can infiltrate into the sub-base from the edges of the composite drainage membrane or through openings formed in the second layer.  
     
     
         2 . A water detention system according to  claim 1 , wherein the sub-base overlies an impermeable or at least substantially impermeable underlying layer.  
     
     
         3 . A water detention system according to  claim 2  wherein said impermeable or at least substantially impermeable underlying layer is a sub-grade.  
     
     
         4 . A water detention system according to  claim 2 , wherein said impermeable or at least substantially impermeable underlaying layer is a membrane.  
     
     
         5 . A water detention system according to any of claims  1  wherein said underlying layer further comprises a cavity forming a sump.  
     
     
         6 . A water detention system according to  claim 1 , wherein the spacer means comprise a plurality of discrete elements in the form of stones or crushed rock in a given size range.  
     
     
         7 . A water detention system according to  claim 1 , wherein said second layer comprises a plurality of plastics membranes.  
     
     
         8 . A water detention system according to  claim 1 , wherein said membrane has a plurality of openings with a cross-sectional area of less than 7 mm 2    
     
     
         9 . A water detention system according to  claim 8 , wherein said overlying layer is a laying course for a wear layer.  
     
     
         10 . A water detention system according to  claim 9 , wherein said wear layer comprises a plurality of paving elements.  
     
     
         11 . A water detention system according to  claim 10 , wherein said paving elements are blocks or slabs having means defining openings between them when laid in juxtaposed relation.  
     
     
         12 . A water detention system according to  claim 9 , wherein wear layer comprises a substantially continuous layer of permeable material (such as asphalt, permeable on porous concrete, or the like).  
     
     
         13 . A water detention system according to  claim 1  wherein said overlying layer of particular material itself constitutes a wear layer.  
     
     
         14 . A water detention system according to  claim 1 , wherein said overlying layer is itself overlain by soil and/or vegetation.  
     
     
         15 . A water detention system according to  claim 1  wherein said membrane is laid in spaced strips over the said sub-base.  
     
     
         16 . A water detention system as claimed in  claim 15 , in which adjacent strips are spaced from one another.  
     
     
         17 . A water detention system as claimed in  claim 16 , in which further strips of permeable geotextile material overlie the spaces between adjacent said spaced strips.  
     
     
         18 . A water detention system as claimed in  claim 15 , in which adjacent said strips overlap one another.  
     
     
         19 . A water detention system according to  claim 1 , wherein the components of the said composite membrane, comprising the said first and second layers and the said spacer means, are located in unbonded juxtaposition.  
     
     
         20 . A water detention system according to  claim 1 , wherein the components of the said composite membrane are held together in fixed relation.  
     
     
         21 . A water detention system according to  claim 19 , wherein the components of the said composite membrane are held together by adhesive bonding.  
     
     
         22 . A water detention system according to  claim 19 , wherein the components of the said composite membrane are held together by fixing elements.  
     
     
         23 . A water detention system according to  claim 1 , wherein said spacer means comprises a mesh or grid having grid elements so formed as to define lateral transfer passages in the composite membrane.  
     
     
         24 . A water detention system according to  claim 20 , wherein said grid elements are elongate rods, bars or tubes.  
     
     
         25 . A water detention system according to  claim 1 , wherein said first layer comprises a woven or non-woven textile material the fibres or filaments of which are heat bonded.  
     
     
         26 . A method of forming a water detention system characterised by comprising the steps of: laying a sub-base of rigid insoluble hard particulars material of a defined size range over an at least substantially impermeable sub-grade or a preliminary positioned at least substantially impermeable membrane; 
 overlaying the sub-base with a substantially unidirectionally porous layer able to allow water to infiltrate from above into the sub-base but which is such as substantially to resist loss of water from the sub-base by evaporation; and overlaying the said substantially unidirectionally porous layer with a further layer of particulate material.    
     
     
         27 . A method according to  claim 26 , further comprising the step of compacting the material of the sub-base prior to application of the said substantially unidirectionally porous layer.  
     
     
         28 . A method according to  claim 26 , wherein said substantially unidirectionally porous layer is a composite membrane comprising at least an impermeable layer, a permeable layer and spacer means holding the said two layers apart over at least a part of their area, which are applied one at a time to the sub-base to build up the said at least substantially unidirectionally porous layer.  
     
     
         29 . A heat exchange structure comprising: 
 a substantially enclosed volume bounded by a lower water-impermeable stratum or layer and containing a sub-base of rigid substantially incompressible particulate material, overlain by an at least partly semi-permeable membrane which allows water to enter the said substantially enclosed volume but resists evaporative escape therefrom, and    one or more heat exchange pipes for directing a heat exchange fluid therethrough and located so as to pass through water trapped in the said substantially enclosed volume.    
     
     
         30 . A heat exchange structure according to  claim 29 , wherein the substantially enclosed volume includes a channel through which the or each heat exchange pipe passes.  
     
     
         31 . A heat exchange structure according to  claim 29 , wherein the channel is formed by the membrane defining the lower boundary of the said enclosed volume.  
     
     
         32 . A heat exchange structure according to  claim 31 , wherein the channel is formed as a sump in the bottom of the said enclosed volume.  
     
     
         33 . A heat exchange structure according to  claim 29 , wherein said rigid substantially incompressible particulate material comprises crushed rock.  
     
     
         34 . A pavement structure and water detection system comprising: 
 a pavement structure;    a water detention system underlying the pavement structure, the water detection system comprising at least a sub-base of particulate material in a layer having a substantial number of voids, an overlying permeable layer of particulate material, and a composite membrane comprising a first, permeable layer, a second impermeable layer and spacer means between the said first and second layer, the said spacer means acting to maintain at least part of the said first and second layers out of contact with one another and to allow the movement of liquid in the space between them, composite membrane being so positioned that water collecting on its surface can infiltrate into the sub-base from the edges of the composite drainage membrane or through openings formed in the second layer.