One of the aims of my employer, the Environment Agency, is to promote sustainable systems. Drainage systems such as those described by Aidan Millerick in The drain brain (NCE last week), formed an element of that promotion.
However, it has become increasingly apparent that the benefits do not necessarily stand up to the rigorous test of mother nature.
The techniques of underground storage and attenuation require a storage capacity to work. If you dig a hole and it fills with water it is of no further use. But we now have virtual artesian ground conditions in the winter months filling storage units before the rain gets to them. Those in clay strata never empty because of the lack of percolation.
The position improves every summer when the trees come into leaf, but in the winter - the time when we need the system to work - there are no leaves or evapotranspiration. Road drainage then becomes more of a substitute water distribution system than a disposal system.
Laudable as the aims of sustainable drainage are, they can never replace adequate and efficient pipework. The need in this country is for adequate provision of highway drainage and surface water systems which are adequately financed.
There should no longer be the attitude that because it is underground it can be forgotten. There is no return for investment in new pavements and surfacing if this is installed on sub-bases which are saturated with water from blocked or failed road drains.
Martin Luker, improvements engineer, EA Thames-West martin. luker@environmentagency. gov. uk