Management of risk of tree and shrub root intrusion into sewers

- The study concerned root intrusion into sewers.
- Root intrusion frequency and root sizes were determined from CCTV surveys.
- The analysis took account of sewer defects and factors not related to sewers.
- Risks of environmental failure were established.
- Categories of probability of root intrusion into sewers were proposed.

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 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 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 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 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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