Managing the chemical cocktail
While rainwater is comparatively clean when it falls, as soon as it comes into contact with the human environment it quickly becomes polluted. In addition to particles of paint and bleached metals from roofs and buildings, a major rainwater pollution source is roads and vehicles. Heavy metals and other toxins, plus litter and microplastics mainly in the form of rubber particles from tyres, are collected and transported by the surface run-off, resulting in a chemical cocktail that is then often transported directly into our waterways.
Increasingly sealed surfaces
Impermeable surfaces predictably have a high run-off coefficient, meaning that most of the precipitation falling onto man-made environments will become surface run-off. In turn, while these surfaces and the conventional systems designed to transport them can often handle large flows, a huge amount of water can be transported to key points in a very short time –resulting in flash floods. Additionally, these impermeable surfaces affect groundwater levels negatively as very little rain actually enters the ground.
Rough weather forecast
What’s more, studies show that both the intensity and frequency of heavy rain are set to increase substantially. Compared with rainfall averages between 1971-2000, rainfall may increase 7-8% by 2040 and by a total of 12-20% by the end of the century. Likewise, according to one Finnish study, heavy rain intensity in Finland is set to increase by 10-25%.
In the past, the practical response by municipalities and major landowners was to build a large enough pipe to carry any surface water away, with the objective of safely dispersing it – usually into waterways, or then into the ground via broad, shallow ditches.
The old ways just won’t cut it
This “big pipe out”, quantity-oriented solution was fine for its time. Water was “out of sight, out of mind”. Yet we now live in an increasingly crowded and polluted environment, and the “big pipe out” approach doesn’t resolve the current challenges we face. The old solution merely passes the problems downstream for treatment elsewhere – and at someone else’s expense.
New challenges demand new solutions
With rapidly increasing awareness of the consequences of our actions, system designers and local authorities – particularly those with heavy traffic and major commercial and industrial centres in their remit – are increasingly looking to deal with issues around local treatment of storm-water run-off in more practical and informed ways.
Local problems need local solutions
The unappealing alternative is for municipalities and businesses to deal with waste from neighbouring areas – waste which they can neither predict nor manage, and which will be commingled with other debris. Conversely, they may face additional statutory pressure mandating effective storm-water management policies from central government agencies. Either way, these are unpredictable and thus potentially expensive outcomes.
Instead, a localised solution which accounts for water quality as well as quantity in run-off can optimise the effectiveness and cost of water run-off management, in ways that are responsive to local circumstances. Dealing with oils and plastics nationally is painfully expensive and also yields a far lower return on recycling. On the other hand, locally managed attenuation and treatment systems allow for sediments, pollutants and debris to be contained and dealt with before they enter the network and are dispersed. They can also then be safely handled and, ideally, usefully recycled.