Urban Drainage and the Water Environment: a Sustainable Future?
FR/R0011
Revised April 2013
This review describes how drainage systems in urban areas developed in order to understand how we have got to where we are today and how systems can be developed to cope with increasing urban populations and changing weather in the future.
Originally urban areas were drained to remove surface water, though some waste, manure, etc. got washed into the drains adventitiously but that was not the intention and in many places it was an offence to foul the drains with wastes. In the mid-19th century all that changed. Piped water supplies enabled water closets and the old cesspools (never entirely satisfactory) became even more overloaded. The paradigm changed to diverting foul as well as surface water into the drains, which became sewers and continued draining to the rivers. A safe, reliable water supply and sewage free streets benefited public health greatly and made cities and towns pleasanter but the extra organic load killed the rivers. Interceptor sewers were built to move the discharges from the sewers further downstream, which solved the odour problem temporarily (or at least moved it) but before too long wastewater treatment was established at the ends of the interceptors. Sewage farming and then physico-chemico-biological wastewater treatment developed.
Progressively, with massive investment and better understanding of the science and engineering of wastewater treatment, the rivers have been restored. Fish and even otters have returned and riverside recreation and living is fashionable and desirable once again.
However this is in jeopardy because weather is becoming more “freaky”. Rainfall events that were categorised as extreme historically are occurring more frequently; climate modellers predict they will become even more frequent. Drought and high temperature events are also becoming more frequent. The proportion of urban and suburban areas given over to impervious surfaces (roads, roofs, parking, patios, etc.) from which surface water runs off rapidly has been increasing progressively. Heavy rainfall and rapid runoff mean that larger volumes of water hit the drains and sewers in short spaces of time. Somewhere in the network these large volumes are likely to exceed the capacity of the pipes resulting in flooding on the surface or an overflow to the river. There are two possible solutions, which could be used in combination or separately, larger pipes could be installed or the water could be held back on the surface so that less runs off and the time period over which water enters the system is extended.
This 60 page ROCK, with 17 illustrations, covers the issues concerned, including sustainability. If it all goes down the drain, it all has to be pumped and treated. Handled appropriately, surface water could be a less expensive alternative than opening new resources when weather stresses the existing ones.
Copies of the report are available from the Foundation for £15.00, less 20% for members.