… avoiding future floods & droughts …

About the author

Lisa Farnsworth is a Director of Stormsaver Ltd, and a member of the UK Rainwater Management Association.

Changing weather-patterns …

This year’s spring floods have served as a timely reminder of the social, economic and environmental damage and misery they cause, rightly placing flood-avoidance high on the domestic political agenda.

Less publicised, but rated as an even bigger threat to the UK by the respected International Panel on Climate Change, is the converse drought-risk posed by stresses on future water supplies in most parts of England south of the Humber estuary.

These twin rainfall-related threats are caused in part by man-made factors, such as population-growth and the development of new homes and jobs.  More people and jobs increases water demand, whilst development potentially increases flood-risks.  Further exacerbating the problem, changing weather patterns are causing increasingly frequent long dry spells, broken by short periods of intense rain which is hard to manage from both the perspectives of flood-avoidance, and of water-capture for subsequent use.

sustainable drainage systems (SuDS) …

The flood avoidance side of the equation is already well-reflected in national policies, with Building Regulations requiring all new developments to meet sustainable drainage criteria; this means simply that the overall development design must include arrangements for ensuring that it does not increase down-stream flood-risks under predicted future weather conditions.

Enlightened Welsh Government polices have evolved beyond this single-issue requirement to embrace the notion that one way of avoiding rainfall causing downstream flood risks, is to collect it instead for non-potable re-use for services such as toilet-flushing, clothes-washing, vehicle washing and irrigation.  At a stroke, this policy helps to tackle both sides of the surface water management equation, by also reducing the demand for mains-water.

taking a cost-effective approach …

Inevitably, particularly on domestic applications, the storage tanks used to harvest rainwater for re-use would occasionally be prone to overflowing given prolonged rainfall. The most sensible destination for this overflow, on a housing development for example, would be communal harvesting systems serving smaller/higher density properties that do not otherwise collect sufficient water from their own roofs to satisfy occupants’ demand for non-potable water.

In extreme weather conditions these communal tanks might also need to overflow, the best destination then being surface features such as water-gardens, swales or a balancing pond.  Taking this approach is also cost-effective on a life-cycle basis, when environmental and amenity benefits are taken into account, together with installation and ongoing maintenance costs.

Simplicity of maintenance, in particular, is a key cost consideration, bearing in mind the need for the SuDS reliably to perform its lifetime flood-avoidance role.