Abstract: The major objective of this study was to determine the frequency of root intrusion into sewers and the
sizes of the roots reported. The data were used to develop two methods one for determining environmental
risks related to root intrusions into sewers and sewage flow blockage and the other for establishing
the category of probability of root intrusion into sewers with structural defects.
The data on root intrusions into sewers and sewer defects allowing such intrusions were collected
through CCTV surveys conducted by the Kielce University of Technology for more than 29 km of concrete
and vitrified clay sewers. The frequency of root intrusions into sewers and the sizes of the roots were
determined for sewers in Polish cities. The root sizes were classified as one of the five categories of
probability of environmental failure sewage flow blockage, proposed on the basis of the ratio of the
cross-sectional area of the roots intruding into a sewer to the total cross-sectional area of the sewer.
The study involved proposing a method for determining the category of root intrusion consequences for
sewers with roots already growing inside and a method for determining the environmental sewage flow
blockage risks related to root intrusion. The latter method can be used to establish the category of root
intrusion probability on the basis of structural sewer defects allowing root intrusion as well as factors
not related to the sewer, e.g. tree species or the distance of the tree from the sewer.
From the investigations it is evident that root intrusions into sewers are serious problems environmental
hazards in Poland and in other countries. The methods proposed in this paper are important tools
to be used for proper management of sewer systems.
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