Comment
“
HOST classifies the soils of the United Kingdom into twenty-nine
categories and the Wallingford
procedure uses this information to derive the greenfield runoff rate that can be anticipated for a particular site
distributions and, hence, differing hydraulic conductivity readings. Measurement of hydraulic conductivity and of the distribution of void space within an intact sample of soil needs to be undertaken in a laboratory and requires considerable expertise. Again, we have collected some data on this during the course of our work. In addition, methods exist that can derive, albeit theoretically, hydraulic conductivity from particle size distribution data (how much sand, silt and clay is present). This is something which can readily be established, although we have yet to test the practicality of this predictive approach. Nevertheless, bearing in mind that the
qualities of a topsoil are different in all these respects from those of the subsoil, it will be clear by now how un-enlightening a simple measure of infiltration rate, for example, can actually be. It is the product of so many factors, any one of which may be the primary determinant of the measured value and which may be effective at any depth within the soil profile. The upshot is that, because of the complexity of the real situation, the single measure of infiltration rate does not provide sufficient information to make a reliable judgement on the way forward. The interpretation of infiltration data and, more widely, the establishment and measurement of performance standards need to be accomplished in a much more nuanced and considered way.
Modelling the behaviour of water in natural turf
It will be becoming clear that the development of a predictive model that will describe the behaviour of water in natural turf systems, with sufficient accuracy to allow a fully supported design to be put before a planning authority or funding body, with the equivalent degree of confidence with which designs for artificial sports surfaces are
18 I PC AUGUST/SEPTEMBER 2016
presented, is some way away yet. However, I am convinced that it is possible and that it is a very worthwhile objective. One possible way in to all this, and that has
impressed me very much, is that of the HOST (Hydrology of Soil Types ) system. Published in 1995, this is now included in the methodology behind the estimation of greenfield runoff as established by HR Wallingford working with the Environment Agency and which, since 2013, is an approach increasingly required of developers in relation to planning and flood prevention . HOST classifies the soils of the United Kingdom into twenty-nine categories and the Wallingford procedure uses this information to derive the greenfield runoff rate that can be anticipated for a particular site. The twenty-nine categories are based on a series of conceptual models that simulate the hydrological behaviour of the soils and interpret soil physical properties and their effects on the behaviour of soil water. Each of the soil associations defined by the
Soil Survey of England and Wales are allocated to a particular HOST category, and it seems reasonable to me to suppose that natural turf sports surfaces in their various forms may be incorporated into the overall model in exactly the same way. We are currently testing real data from
sports grounds on total porosity, particle size distribution, hydraulic conductivity and infiltration rates etc. within models based on this approach. The aim is ultimately to enable the optimum natural turf drainage and attenuation system to be designed for any given situation and for the performance of the completed system to be predicted and described accurately. This would give planners a much clearer
indication of the likely consequences of any development in terms of flood prevention, and would also indicate to the end users of
the facility what level of performance they can look forward to with their new or improved installation.
Natural turf needs to fight back
I think that, from both a social and environmental point of view, it is vital that natural turf is restored to its status as the standard form of sport and amenity surface. The restricted accessibility and limited flexibility of most artificial surfaces may ultimately be to the detriment of sport itself. The casual ‘kicking about with friends’ approach, by which most of us were introduced to at least our national sports of football and cricket, are denied to young people in relation to the almost invariably fenced off artificial surfaces. If we can convince the authorities and sporting bodies that natural turf facilities of the highest standard can consistently be achieved, with designs supported by accurate data and sound calculations, what seems to be a relentless march of artificial surfaces may be halted. In order to achieve this, we must develop for natural turf behaviour models equivalent to those used to derive artificial pitch drainage, attenuation and storm water management systems. This must be achieved in order to deliver the optimum performance of sporting surfaces capable of being measured by appropriate and realistic standards. I believe all this is entirely possible, but it is by no means simple.
Dr Tim Lodge Agrostis Turf Consultancy Ltd
www.agrostis.co.uk 01359 259361
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