Floods and SuDs: Making Drainage Sustainable
It is, perhaps, one of the most irritating paradoxes of British weather that, having endured downpours and deluges throughout the winter, we'll often be met with hosepipe bans in the summer, as the water supply struggles to meet demand. Then, as if to rub salt into the wound, when the clouds do eventually burst, we are told that it's the "wrong sort of rain," and it won't replenish the reservoirs. With the UK set to see drier summers and wetter winters as our climate continues to change over the century - and with extreme flooding events predicted to become more frequent - it's all shaping up to be a bit of a ticking time-bomb for planners, builders and home-owners alike.
Tackling floodingThe massive flooding that has hit various parts of the country at different times over the last decade make it very clear that this is an issue that seriously needs to be addressed - and the good news is, it is. The Flood and Water Management Act (2010) in England and Wales, and the broadly equivalent Flood Risk Management (Scotland) and Water Environment and Water Services (Scotland), coupled with the European Water Framework Directive, have established a strong legislative framework for sorting out the problem.
So what is going wrong, how do you make drainage effective and sustainable - and just how ready are we in Britain to do it?
Current problemPart of the current problem lies in the arrangements that have been inherited in many urban areas, which worked perfectly well some years ago, but have become increasingly outmoded as times, demands and weather patterns have changed.
Typically, drainage systems fall into one of two general types:
- those which provide separate collection arrangements for sewage and surface water
- those in which both kinds of effluent are collected together, in what are known as 'combined sewers'
As towns have grown and additional areas been developed, especially in flood plains, ever bigger tracts of the surrounding ground have been covered over in concrete and tarmac, reducing the land's natural ability to soak up rainfall. As a result, in times of heavy rain, this additional storm water now runs off the surface and pours into the existing drains, often stretching - and sometimes exceeding - sewer capacity. It can be a particularly unpleasant problem for the sewage-rich mix in combined sewers, and may lead to public health concerns, but for local residents served by either drainage system, the outcome is seldom a comfortable one.
Towards a solutionFacing a future which, according to the Met Office predictions, will see the intensity of rain-storms grow, and the probability of sudden and un-seasonable downpours increase, it is a problem that is only going to get bigger.
One possible solution would be to upgrade the existing infrastructure to increase capacity, and build new, larger sewers to help meet the growing need - but this would be expensive, and in many cases simply shove the problem along to another town or village, further downstream.
A growing body of opinion, however, now believes that the real answer to this situation will be found by adopting an approach to managing rainfall and surface water flow that more closely resembles the way it occurs in nature.
Drainage goes sustainableRejoicing in the wonderfully appropriate acronym of 'SuDS', Sustainable Urban Drainage Systems provide a means of mitigating the worst effects of excess surface run, and reducing its high-peak demand for drain and sewer capacity.
They achieve this in three main ways:
- By decreasing the amount of surface run-off leaving the area, soaking up the rainfall, or collecting and containing it. Something as simple as planting trees, or including large areas of amenity grassland can achieve this.
- Reducing the speed of the flow, slowing its arrival at the drains, and spreading the extra volume needing to be accommodated over a longer period of time; creating artificial watercourses, culverts and mini streams in the landscape, for example.
- Diverting it to some form of beneficial use, such as irrigation or for wildlife ponds.
Intentionally designed to be a flexible drainage approach, dependent on local need and the lie of the land, SuDS schemes can include a wide range of elements, from straight-forward soak-aways, to large scale ponds or lakes, and make a significant contribution to both site amenity and biodiversity.
The state of the nationOne of the things that the Flood and Water Management Act (2010) establishes is county councils or unitary authorities as Lead Local Flood Authorities, with the responsibility, amongst other things, for developing and implementing a flood risk strategy, and managing the risk of surface water flooding. They are also set to become SuDS Approving Bodies (SABs) - and in an attempt to find out how prepared they felt to play their new forthcoming role, Hydro International commissioned "SuDs: The State of the Nation Survey".
Conducted in association with British Water, The Chartered Institution of Water and Environmental Management (CIWEM) and the Society of British Water and Wastewater Industries (SBWWI) and with the participation of 149 local authority officers, the results make for interesting reading.
Key findingsFor one thing, a staggering 68% of the respondents felt that the Government was not entirely committed to SuDS in the long-term - and some felt that Westminster was not committed at all! The provisions which relate to SuDS are contained in Schedule 3 of the Act - and there have been delays in bringing it into force; understandably it seems that this has evidently not helped boost confidence amongst local authorities.
Other key findings included:
- "Most did not feel ready to act as SABs, with 60% saying they felt under-prepared, while 75% said that they needed more training for the role.
- "Most felt that funding was an issue; only around a quarter felt that their local authority had access to adequate funds for the task.
- "Few felt that approval should depend on affordability; only just over a third of respondents thought that the affordability of SuDS for developers should be considered.
- "Nearly 80% of those who were familiar with the current draft National Standards felt they were clear enough.
In addition, views on retro-fitting SuDs to existing sites and encouraging SuDS as a means of bolstering water resources were distinctly mixed.
It seems there is still some work to be done, on a number of levels, before the 'state of the nation' in relation to SuDS can really be described as an entirely good one. Never-the-less, even now it offers some major benefits for sustainable building, and those seem certain to grow over the coming years.
Cost savingsOne of the reasons for that lies in the idea that it manages storm-water flows locally, as close as practically possible to the source, which inevitably helps scale back on the environmental disruption - and the financial cost - of excavating and installing conventional drainage infrastructure.
In fact, surprisingly, SuDS should generally cost no more than a comparable traditional drainage scheme. Indeed, although more research is needed on long-term costs, in terms of construction and operational expenditure, there is some evidence to suggest that SuDS can even be cheaper - 10% or more - especially when it forms part of the overall landscaping component of the development.
Wider benefitsBeyond the potential cost savings - and the obvious advantages of reduced flood risk, improved water quality and increased site amenity value - depending on the particular site and local conditions, wider benefits can include:
- Boosting local water resources by recharging groundwater, or via rainwater collection.
- Foster community spirit and pride in an attractive shared environment.
- Help overcome planning issues and relieve land pressures by reducing demand on existing infrastructure.
- Provide an educational and recreational resource, when incorporated into good public open space designs.
It is small wonder, then, that the virtues of SuDS which have been extolled by an increasing number of enthusiasts over the years are now gradually becoming accepted into the mainstream by the industry.