Technical
Infiltration measuring equipment
“The planners will need this information and the client will be more reassured, when comparing two or more proposals in a competitive tendering situation, that one or other is going to deliver the same quality of surface whilst being of a lesser overall cost”
Pipe drains prior to surface preparation for natural turf
water by the subsoil surface may be unavailable to us, this storage capacity is. Indeed, if a stone layer, say 300mm deep, underlies an artificial surface, with 30% void space within it, this could very well provide most, if not all, of the necessary storage volume needed to cope with the critical storm. A shock pad, a porous macadam layer and even a sports carpet itself will have the capacity to retain some water, and that capacity can also be incorporated into these calculations, provided the connection with the soakaway system is maintained.
The materials beneath an artificial sports surface provide many of the structural properties that are, of course, also required for the sports concerned, but there is considerable diversity in how deeply these are laid down and of what material they are actually composed. In terms of the design, however,
provided the structural requirements of the surface is met by the layers beneath, there will be in each circumstance a particular depth, choice and arrangement of materials that will provide the necessary storage volume in relation to a particular soakaway design. It is then simply (!) a matter of determining the most cost effective means of delivering this. For any particular design, the client, and the planners, should be made aware of the figures and the thinking that has gone into this. The planners will need this information anyway and the client will be more reassured, when comparing
two or more proposals in a competitive tendering situation, that one or other is going to deliver the same quality of surface whilst being of a lesser overall cost. That is how free markets should apply to the design and construction of artificial surfaces. There is, unfortunately, some confusion over how these features relating to flood prevention apply to natural turf situations. For example, I have been asked by planning authorities to design soakaway systems for natural turf facilities that conform to the stipulations applicable to totally impermeable surfaces, such as a supermarket roof! This is clearly ludicrous and this less than enlightened approach, or less extreme versions of it, can lead to perfectly good natural turf development projects being prevented from going ahead due to the excessive cost of the soakaway system that is supposedly required in association with it.
The problem is that there is, as yet, no technical protocol for relating the improved performance in terms of surface water dispersal that newly constructed, or improved natural turf sports surfaces, may have and their impact on flood risk.
But the situation I describe above concerning artificial surfaces, though not identical, has many parallels with natural turf systems, and this may provide the way into achieving that protocol. Improving soil conditions, for example by incorporating sand carpets or sand
116 PC JUNE/JULY 2013
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