Environmental Essay no.29 – Adapting to the Climate of the Future

Adapting to the Climate of the Future

Example 2 Sufficient sewerage

The summer of 2002 was one of the wettest ever seen in Denmark. Many people, in Aalborg for instance, were bothered by sewage retained in the sewer system. After this incident, in 2003, the Aalborg municipality and departments responsible for sewerage distributed an information leaflet advising residents in several hundred properties on how to avoid flooded basements. The leaflet was part of a major project in which the local authorities, in cooperation with the consulting firm NIRAS, the assistance and emergency company Falck, and the facility services company ISS, have recorded data on water-related emergency calls to these firms. Therefore, the municipal authorities had a good overview of incidents of flooded basements in Aalborg.

The aim of this unusual cooperation concept was, however, not only to assist private house owners. A second aim is to be able to incorporate the data in the planning and prioritisation of the redevelopment plans and the sewer renewal plans prepared by the municipality, and make sure that the new systems have sufficient capacity to discharge larger volumes of water than the old facilities.

Increasing precipitation
So far incidents of heavy rain like the one in Aalborg have not been seen very frequently in Denmark. In the last 25-30 years the intensity of precipitation incidents has not increased, but calculations of climate change do in fact foresee increasing intensities. Sewage retained in the sewerage installations, flooded basements, roads and fields may become a problem in the future – unless the individual municipalities take steps now to plan the capacity of sewers for the future, for instance in connection with sewage plans and specific renewal work.

Local authorities should take account not only of increased intensity and frequency of heavy rain, but also consider the possible effects of sea-level rise on the planning of sewer facilities.

The lifetime of sewer systems is typically about one hundred years. Sewers established today must thus, have sufficient capacity for the sea-level rise and the water volumes we expect to see within one hundred years.

Backlog of renewal work The municipalities are currently renewing the existing sewer systems – and therefore now is also the time to take the climate change of the future into account.

It is true that the pressure on the sewer systems has lightened in recent years, due to water savings in private households and in industry, and to some extent also because Danes are tending to move out of urban areas. But the important question is whether the sewer systems can handle the peak loads occurring during heavy rain.

The dimensions of pipes are calculated on the basis of experience with heavy rain during short periods of time (up to 30 minutes), while the requirements for retention basins are based on longer precipitation periods (more than 30 minutes). Work to Increase the capacity of retention basins in densely built-up areas is very expensive, and it would therefore be most appropriate to establish the capacity required in the future in connection with current repair work and with the construction of new plants.