LANDSCAPE & GROUNDS MAINTENANCE THE ROOT OF THE ISSUE
With the onset of climate change, better understanding of the risks that trees pose for buried water utility assets is vital to asset maintenance, says UKDN Waterflow (LG) Ltd Director Richard Leigh.
Trees are a much-loved part of our landscape both in the countryside and in towns and cities. However, there is often concern about the presence of trees, especially in urban landscapes.
They are regularly blamed for causing damage to a range of assets, including buildings, walls, footpaths, roads, and underground utilities, especially drainage pipes.
In Sheffield, South Yorkshire, some of these issues have fuelled a major dispute about long-term management of trees, though public safety also appears to be of significant concern there. However, there is still misunderstanding of what tree roots can and cannot do to built structures and underground pipes.
There is also a need for facilities managers, especially in the south of England, to take account of climate change in their approach to tree management and asset maintenance.
Tree roots do cause problems in drain and sewer systems. Drainage engineers from UKDN Waterflow (LG) are continuously responding to blockages caused by root ingress into underground pipes.
However, research shows that trees roots do not cause initial damage to drains and sewers. Instead, they take advantage of cracks and gaps in pipe joints to get into pipes in their search for water.
Because tree roots of all trees grow close to the surface – most do not go down more than 600mm into the soil – they will only have an impact on relatively shallow pipes.
Only roots less than two metres from the tree truck grow large enough to cause direct damage. This means that poor installation and maintenance of drainage pipes is
more likely to be the primary cause of tree root ingress.
Tree roots – impact on drainage systems Once tree roots have gained entry into pipes they can have a significant impact on its water carrying efficiency.
They can build up significant density in long lengths of pipe, then during heavy rain water backs up and causes flooding. Roots also combine with other materials, such as fats, oils, and grease, sanitary products, and wet wipes to make blockages worse.
Around 4% of all drainage investigation and repair jobs UKDN Waterflow (LG) is called out to involved tree root infestation of pipes. Clay pipes as particularly prone to root ingress, due to gaps in the joints between each section of pipe.
However, modern plastic pipe systems are also affected, and there is research that indicates rubber seals that connect plastic piping are prone to failure under pressure from tree roots.
Pitch fibre pipes, installed extensively between the 1940s and 1970s, have also proved to be at higher risk of root ingress. Made from wood pulp and coal tar, and favoured for their cheapness and lightness, they deform and crack easily, so prove an easy target for probing root systems.
Measuring the value of trees There is now greater urgency to establishing best practice in the management of trees in towns and cities to establish sustainable drainage systems (SuDS) and obtain maximum value from their presence.
New thinking on this work is contained in a report, Trees In Hard Landscape – A Guide For Delivery, from the Trees And Design Action Group (TDAG).
24 | TOMORROW’S FM
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