Sloping Site Design

Sloping Sites

Permeable paving can be successfully installed on sloping sites, dependent upon the gradients it may be necessary to construct devices within the sub-base layer to control the flow of water down the slope.
Whilst it is preferable to construct permeable paving on level sites, it is often unavoidable as expansion of urban growth takes construction onto more difficult sites. On sites where the gradient exceeds 2%, without control mechanisms within the sub-base, water will simply follow the gradient, collect at the lowest point and issue onto the surface. Due to the speed of flow the expected water treatment capabilities would be diminished and maximum pollutant removal would not be achieved. In any case, the gradient of the surface should not exceed 5% to prevent water flowing across the surface and not entering the joints. There are a number of ways in which sloping sites can be addressed, as discussed below.

Dams / Baffles

By installing dams or baffles at points across the slope, the sub-base is compartmentalised and therefore the flow is controlled within each of the compartments. It is important that drain down pipes are inserted within the baffles to prevent water remaining in each area after the rainfall event has passed.
These dams or baffles are simple structures, formed with concrete, concrete kerbs, blockwork or geo-membranes.

Terracing

 

This can be carried out by terracing the sub-base whilst having a sloping surface, or indeed terracing the surface and the sub-base. Again the structures tend to be simple in construction as previously mentioned. Flow control between the terraces is again required.

As with all permeable pavement design, the approach taken will depend upon specific site criteria, and therefore there is no such thing as a standard approach.