Ingress of Roots
Next to deposits, the ingress of roots (Image 184.108.40.206-1) (Image 220.127.116.11-2) into sewer systems presents a further common form of flow obstacles, although root resistance of all piping materials, sealing media and gasket rings, as well as of the complete pipe joints, has been a requirement of all the effective standards since the 50's of the 20th Century.
The problem of root ingress occurs almost exclusively in those sewers, which constantly or partly lie above the groundwater level or in soil with a very limited amount of water, because in other cases the water requirements of the trees and bushes in the line of the pipe is covered by the groundwater.
The sewage exfiltrated due to leakage and diffusing moisture stimulates the outer ends of the roots, the so-called hydrotropism, causing them to form new cells in order to grow towards the source of the stimulation. As these cells are extremely small, they can enter through the finest cracks, pores, holes, leaks of the sewers [Sulli77]. There, the roots grow further until the complete closing of the cross section whereby root lengths of several metres are no exceptions. Complete destruction of the corresponding region of the pipe can occur in the area of the entry of the roots.
Further possible damage can be positional deviation (Abschnitt 2.4.1) and partial destruction of pipes.
As already mentioned, the ingress of roots can be prevented, by the use of root-proof pipe materials, sealers and gasket rings, by the prevention of all leaks, but also by either adhering to a minimum distance from vegetation or by means of special constructive measures such as the laying of sewers in a protective pipe or with a protective cover [Hofma85] [Schmi81] [DVGWGW125] (Abschnitt 1.12).