The Sewage and Drainage Problem
The Victorian attitude to drainage was to get rid of unwanted water as quickly as possible, hidden away in underground pipes and culverts. For many years this continued to be the strategy, with a single pipe, called a "combined sewer" used to carry both foul water and surface water drainage. Most of our drainage is still through combined sewers. The problem with this system of course is that when there is a heavy rainstorm the combined sewer pipes cannot take the volume of water and they overflow, leading to sewage contaminated flooding and backup through toilets and baths into houses.

Sewage contaminated flooding is particularly unpleasant and costly, with potentially serious health risks. Sewage backup claims are commonly insured, even in countries like Australia and Canada where private flood insurance is unavailable. This is because insurers are prepared to accept that such claims can happen anywhere, not just in floodplains.

As more land is covered with buildings, and as climate change increases the threat of severe rainfall events, sewage backup and drainage surcharge floods are becoming increasingly common in Britain . If someone suffers from such events on a regular basis, insurers will be bound to consider that such claims are becoming inevitable and uninsurable. Alternatively they may seek recovery from the responsible water company or authority.

In England there was a recent successful lawsuit against Thames Water (Peter Marcic v Thames Water Utilities). The court determined that Thames Water had potentially violated human rights as a result of allowing a sewer to flood Mr Marcic's garden many times over a period of nine years. Thames Water has estimated that it would cost £1bn to rectify all such problems. The case went to an Appeal to the House of Lords in October 2003. The Lords reversed the decision of the Court of Appeal, so the water company was held to be not liable. Otherwise, there could have a string of similar cases from the insurance industry. A consequence of this decision seems to be that water companies and Scottish Water are no longer turning out to clean up sewage flooding in gardens (as they had started to do after the Court of Appeal decision). This has serious implications for the risk of disease, especially for families with children and pets.

The EA report on the autumn 2000 floods indicated that 14% of the properties flooded were flooded by drainage surcharge or sewage overflows. Insurance claims data suggests that the figure could be much higher. For example, it is estimated that 30 to 50% of flood insurance claims after the autumn 2000 floods related to properties outside any floodplain. In the Boxing Day storm in Scotland in 1999, only 40 out of 240 claims were within the indicative floodplain map area. In the April 2000 floods in Edinburgh , it was alleged that less than 600 out of nearly 2,400 claims were in the indicative floodplain map area, and while that figure is probably incorrect, there was no doubt a significant number of such cases.

Robust data is hard to obtain, because many events are unreported to the water companies, but the Construction Industry Research and Information Association (CIRIA) estimated in 1998 that 32,500 properties have a one in ten or one in 20 chance of sewage flooding each year . At an estimated cost of £50,000 per house, it would cost £1,625m to cure the problem just in this relatively small number of properties.

The problem is not just lack of money; there is also a lack of skilled water engineers. Nick Reeves, executive director of the Chartered Institute of Water and Environmental Managers was recently quoted in the Guardian as saying: "At a time when we are having to manage the effects of climate change and flooding, it is critical that we have the innovative engineers and environmental managers in place to deal with these important issues. We have a good track record in this country, but now we have a skills shortage."

The Office of Water Services (Ofwat) Annual Report for 2001-2002 states: "Flooding caused by blocked or overloaded sewers is one of the worst failures of companies' activities that customers experience." They published a consultation paper on the subject in March 2002 , to which the customer representative bodies, known as "Water Voice" groups, have now responded. The response from "Water Voice Thames" (WVT) is particularly interesting. Thames Water has over half the properties at risk of sewer flooding in England and Wales , and WVT say they are convinced that "a continuation of the established approach to correcting the deficiencies in the system will not succeed." They call for the avoidance of sewer flooding to be given the highest priority over the next five years.

In March 2001, The Ofwat National Customer Council (ONCC) called for the planning process to take into account sewer flood risk.

The ONCC which formulates the views of water customers in England and Wales expressed its support for the Government's proposals for reducing flood risk through the planning process. However they have called for water and sewerage companies to become statutory consultees in the planning process and for planning permission for new developments not to be granted unless the design and capacity of the existing local sewer system has been checked and approved.

A relatively new development is the current practice of constructing new pipelines along the coast beside coastal cities to divert sewage outfalls which previously went into the sea towards new water treatment works. While this is excellent for reducing marine and beach pollution, there are signs that such diversions are resulting in a more frequent incidence of sewage backup into the cities during major rainfall events. In one case, a pipe only 1.5m in diameter is now capturing the outfalls of 37 combined sewage and surface water pipes, serving a population equivalent of 270,000. Three months after opening the pipe became blocked, resulting in localised flooding.

One of the main causes of sewer flooding is the excessive load on sewers from surface water draining into inadequate combined sewer systems. A solution that is strongly supported by the EA and the Scottish Environment Protection Agency (SEPA) is "Sustainable Urban Drainage Systems", or "SUDS". This initiative is also called "Sustainable Drainage Systems" to reflect the fact that it is not limited to urban applications. (Following this, the abbreviation was changed to SuDS in England and Wales , but has now changed back to SUDS). SUDS is a method of source control to reduce the overloading of sewers and improve the quality of rainfall run off. At the same time, it improves the environment and the amenity of new housing and commercial developments, increasing property values. It is therefore being strongly supported by developers.

In the last five years, SUDS have become an increasingly common solution to the problems of drainage in new developments. It is important that the insurance industry should learn about SUDS and lend its support to SUDS schemes, because of their potential for reducing flooding and pollution problems. The panel contains a brief summary of SUDS, how it works, and the benefits for society and the environment. The author would strongly recommend that all planners, developers, and property insurance underwriters obtain or borrow a copy of a video produced in 2002, called "Designs that hold water". This short video should be available from any regional office of the EA or SEPA, and it gives an excellent introduction to the benefits of SUDS. It also illustrates how it works, using some of the best examples of SUDS systems in the country. For those who wish to have more details of SUDS, there are a number of technical manuals and guidance notes available. There is also an excellent introductory booklet produced in March 1999 by EA and SEPA entitled "Sustainable Urban Drainage - An Introduction".

20 to 50% of poor river quality is due to urban run off, and 50% of oil in the sea comes from urban drainage. SUDS can prevent diffuse pollution reaching watercourses, while at the same time creating attractive amenities for the community and providing habitat for wildlife. It therefore has a very positive impact on property values.

SUDS is about sustainable development, water quality, and environmental issues. It is not primarily a flood control system, or a substitute for a flood alleviation scheme for developments in flood hazard areas. Indeed SUDS will not work properly in areas prone to regular flooding. Nevertheless, it can prevent flooding upstream or downstream, provided it is well designed and maintained. SUDS is relatively new in the UK (although elements of SUDS have been used in Canada for over 100 years) and developers and planners still have much to learn about how to use the techniques properly.

«back to top«