It is known from European Patent No 0 786 034 to provide a paving system for spillage or floodwater management comprising a permeable layer providing an upper surface; at least one supporting substrate layer thereunder which is permeable to liquid and a containment membrane of impermeable material containing said substrate layer for controlled retention of liquid therein. In a preferred embodiment of the paving system described in that specification, the paving system is provided with valves and discharge ducts for drainage. The paving system according to European Patent No 0 786 034 is particularly suitable for use in areas where there is a risk of spillage of fluids which must be prevented from entering the environment before treatment. It is a disadvantage of the paving system according to European Patent No 0 786 034 that it is not suitable for use in areas where there is a slope.

It is an object of the present invention to provide a paving system in which the above disadvantages are reduced or substantially obviated.

Accordingly, the present invention provides a paving system for controlling drainage and/or flow of water on a slope, the system comprising: a permeable layer providing an upper surface; at least one supporting substrate layer thereunder which is permeable to liquid; a containment layer containing said substrate layer for restricting release of water from said supporting substrate layer into surrounding ground; and weir means for controlling the flow of water down the slope.

In a preferred form of the invention the containment layer comprises a water impermeable membrane or material layer beneath the supporting substrate layer which prevents the flow of liquid vertically from the substrate layer into the ground beneath the containment layer.

In a further preferred form of the invention, the weir means comprises one or more trenches extending laterally across said slope. The trenches are preferably approximately 0.5m wide and 0.5m deep, and are preferably spaced at 10m intervals measured in the direction of the slope. The lowermost trench is preferably deeper than the previous trenches.

In an alternative preferred form of the invention, the weir means may comprise barriers which extend laterally across the slope. The barriers preferably comprise folds formed in the containment layer and are preferably provided with openings to allow restricted flow of liquid down the slope. The openings are preferably staggered along consecutive barriers to provide a meandering path for said liquid thereby to restrict the flow of liquid down the slope.

The present invention is further described hereinafter by way of example, with reference to accompanying drawings, in which: Figure 1 is a sectional side elevation, of a first embodiment of a system according to the present invention and Figure 2 is a view similar to that of Figure 1 of a second preferred embodiment of a system according to the present invention and Figure 3 is a plan view of the system of Figure 2.

Referring first to Figure 1, this shows a system for controlling or regulating the flow of water down a slope. The system has a surface layer 12 which is a permeable layer to allow liquid such as rain water to run through into a channel 14 formed by a containment layer 16 and the arrangement of layers is described in detail in European Patent No 0 786 034 In the system shown in Figure 1, a number of trenches 50 are provided which extend generally along contour lines of the slope. Each trench is typically 0.5 m deep by 0.5 m wide and the trenches are typically spaced at 10 m intervals. A trench having these dimensions

will hold the equivalent of 7.5 mm rainfall from a 1 Om pavement, assuming 30% void in the subbase stone. The lower most trench is conveniently 1.0 m deep to avoid the risk of surface flooding if the soil infiltration rate is greater than 10-5 m/s.

Figure 2 is a view similar to that of Figure 1 of a similar system in which the containment layer is formed by a water impervious membrane. Barriers 60 are provided at intervals down the slope, the barriers extending along contour lines of the slope. The barriers are conveniently at regular intervals and typically at 9 m or 10 m intervals. The barriers 60 are in the form of upstands and are conveniently formed by folds in the membrane 16, stapled along the top edge and held up by steel pins.

Figure 3 is a plan view and shows that the barriers 60 are provided with gaps or openings 62 to allow the flow of water down the slope. However, the gaps or openings 62 are staggered to provide a tortuous path for the water and assist its dispersion.

The openings may conveniently be formed by pipes, with sealed flanged pipe connections between the panels.

Alternatively, the barriers may be of more substantial construction, for example in the form of small walls covered by the membrane.