Blocked drains – The intrusion of tree roots into sewers is probably the most destructive single element that faces those maintaining an aging wastewater collection system – Sanitary Sewer.
Blocked drains – There are almost thirty thousand kilometers of privately owned sewer pipes in the Sydney area and most of all these collection systems are made up of pipe with a diameter of 150mm or smaller that has already reach or exceeded it’s service life.
The potential for root intrusion to produce blocked drains and to damage valuable pipe is enormous. Roots normally do not grow underwater and seldom cause problems where ground water covers the pipe. But in most areas, this is not the case.
It is very unusual for tree roots to physically break drains and associated pipe work. However, tree roots are opportunistic by nature and if an old pipe with poor joints is leaking into the surrounding soil this will stimulate the tree roots that may then exploit the existing weakness. Then, when repairs are required, a proliferation of tree roots often leads to the blame being placed with a nearby tree. In a properly constructed and sound drainage system tree roots should not be able to get in. Tree root ingress should always be taken as indicating existing defect(s).
One Cell at a Time
When a seed germinates, it adds one cell at a time toward the best environment from which it might extract nutrients and moisture. The growing point of the root, the meristem, moves best through loosely cultivated soil. The most common practice to lay sewer pipe is by open trench. The back-filled soil offers a good growing medium for roots.
The flow in sanitary sewer lines is at a higher temperature than the surrounding soil; this causes condensation to appear on the crown of the pipe. The crown of the pipe is the top outside surface of the pipe. This process begins from the very first day the sewer line is used.
As the warm moisture from the sewer pipe evaporates up through the soil, the vapors offer an excellent trail for the root to follow. If even a tiny vapor leak exists in the pipe, the root concentrates its efforts at that point. Since some pipe joint compounds are of nutrient materials themselves, the root may entirely girdle the joint before entering the pipe.
Once inside the sewer pipe, the root takes on the appearance of either a “veil” or a “tail” type structure. If flows in the pipe are fairly constant, the root mass hangs down like a veil to the normal flow level where they accumulate deposits of grease, slime, toilet paper and other debris.
Conventional methods if removing roots by cutting or tearing with mechanical or high pressure water jet machines tend to INCREASE REGROWTH similar to pruning a hedge. Removing roots inside the pipe solves the immediate problem of stoppages, but does nothing to retard the growth or kill the root outside the pipe where the more serious and costly structural damage may take place.
It is important to understand that once a sewer line has been compromised by tree root intrusions the affected pipe work is doomed and there is really only two actions that can be taken to deal with the problem –
1) regular maintenance and inspection or
2) total rehabilitation or renewal.
Regular maintenance and inspection is not a long term solution and should only ever be considered as a temporary fix at best. Long term drain cleaning year after year is false economy and to be honest, bashing away at old, damaged and deteriorated pipe work time after time only encourages more root growth and helps to accelerate the eventual demise of the sewer system.
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