The Characteristics of Waste Water Flow in a Danish Combined Sewer

Sustained measurements of dry and wet weather flow in sewer systems are difficult to obtain. Since autumn 1997, a Danish research station has been in continuously operation in a relatively small combined sewer system serving a population of about 2,000. The dry weather flow measurements of 1999 have been analysed in order to extract some of their characteristics. Furthermore it is emphasised that the presence of a self-cleansing capacity of a combined sewer system is of vital importance in order to reduce the impact of combined sewer overflows on receiving waters. Whether or not the pipelines of an existing sewer system are self-cleansing is mainly a question of the flow level during dry weather. It is discussed how the dry weather flow value, on which the self-cleansing capacity analysis is based, could be determined.