Increasingly we're being asked to undertake the analyses required in relation to the surface water drainage system designs of new developments. This is most usually necessary, and is required by planners, for new artificial surfaces, 3G pitches, athletics tracks, MUGAs and so on. The purpose is, of course, to minimise the risk of flooding arising as a consequence of the new development and we are required to demonstrate that the design will indeed achieve this. The process is extremely complex in that the existing drainage characteristics of the usually natural conditions of the site have to be precisely determined in order that they may be replicated in the development. This involves a concept called 'Greenfield runoff' and this is related to the soil type, geology, topography and so on, all the areas in which Agrostis has considerable expertise. Because the construction of natural turf sports pitches and surfaces often involves the incorporation of drain pipes into the ground, planners frequently require the equivalent demonstrations of the before and after drainage state of a site as one of the conditions of the project going ahead. The use of natural soils in most of these situations makes the prediction of runoff rates and volumes when pitch construction procedures are carried out rather more difficult and, unlike for artificial surfaces, the models do not currently exist that will allow these data to be accurately generated. With our experience in both these fields, however, we are continuing to refine our understanding of the behaviour of constructed sports surfaces in natural soils and we are usually able to incorporate the appropriate methods of flood prevention in all sports facility installations, natural and artificial, to the satisfaction of planners.
Effects of AGP slope on attenuation capacity
Flow restriction from artificial grass pitch (AGP)
Determining Greenfield runoff
The first requirement in any SuDS design process is to identify the 'natural' or greenfield runoff rate for the site. A very great deal of work has gone into determining this on the basis of soil type, location and topography and we work with the latest software programmes to do this; as the planning authorities expect of us.
Drainage and attenuation design
Using the greenfield runoff we are able to calculate how much water is likely to run off the area of the development during the course of the various storm events, with or without adjustments for climate change which are usually called for. With our understanding of construction and drainage methods for artifical surfaces and of soils, geology and hydrology for natural turf situations, we're then able to design the most appropriate systems (SuDS) that will replicate the 'natural' state of things.
'Common sense' approach
Misunderstandings in relation to the impact of, for example, a natural turf football pitch development on local flood risk can often lead to difficulties in obtaining planning permission. In several cases in our experience this has included the cancellation of projects as the mitigating procedures that have been considered necessary were so expensive. Such tragedies can usually be avoided by a clear understanding of the situation and the lucid demonstration of how the issues may be overcome. While it is important that the various calculations are derived correctly, our 'common sense' approach to the subject leads to the successful furtherance of projects to everyone's satisfaction and with the most economically and environmentally sound methods.