Stormwater Guidelines

Trees and the natural environment

Trees are a vital part of our natural environment. They produce oxygen, remove air pollution and absorb carbon dioxide. They also provide essential habitat and food for wildlife, help prevent soil erosion, and improve water quality by filtering rainwater and reducing runoff.

Trees and the built environment

Trees and the built environment are closely connected. Trees can lower energy costs, reduce urban temperatures, reduce noise, improve air quality, and even encourage people to be more active outdoors. When planted strategically, they also enhance biodiversity, act as green infrastructure and help manage stormwater.

Trees and underground infrastructure

Tree roots naturally seek out water and nutrients, which can sometimes cause problems for underground infrastructure. This can lead to blockages, leaks or damage to essential services, resulting in costly repairs, service disruptions and, in some cases, building subsidence. These impacts can be reduced through careful tree selection, planting larger trees away from utilities, using specialised root barriers and creating healthy growing conditions for urban trees.

How do tree roots damage pipes?

Tree roots anchor and support trees, but they also search for and absorb the moisture and nutrients needed for growth. In most cases, roots extend to around one and a half times the length of a tree’s branches. During dry periods, roots will actively seek out any available moisture, including the water found in stormwater pipes and trenches.

Tree roots are both persistent and surprisingly strong. They will take advantage of any small opening to enter stormwater pipes. This often occurs through tiny cracks, fractures, joints, or damaged sections of pipe, particularly in areas with high groundwater or geotechnical movement.

Many people don’t realise how aggressive some tree and shrub species can be when searching for water. Roots begin as fine, fibrous strands that can spread long distances inside a pipe. Over time, these strands thicken, slowing the flow of water and eventually causing complete blockages. In more severe cases, soil from the surrounding ground can enter the stormwater system, creating even greater obstructions.

The level of risk and potential damage depends on several factors: the tree species, how close it is to stormwater pipes, and the type of pipes in place (such as clay, concrete or HDPE/HDPP).

Where are my stormwater pipes located?

Stormwater lines are the most common pipes affected by root intrusion. This issue impacts both Kingborough Council and private property owners, often causing inconvenience, damage and costly repairs for both.

Many residents are unaware that Council stormwater pipes can run through residential and other private properties, where they connect to the privately owned stormwater pipes installed by homeowners.

Because these pipes are underground, their exact location can be difficult to identify without a plan. Kingborough Council can provide a plan showing any known public stormwater pipes on your property. Council may also be able to supply a plan of your private stormwater system, if it was lodged with Council by the installing plumber.

To request a public stormwater plan or a private stormwater plan if available, please contact our Customer Service Centre on 03 6211 8200. You can also email kc@kingborough.tas.gov.au, or visit us in person at 15 Channel Highway, Kingston (open 8.30am to 4.30pm, Monday to Friday).

Please note, private stormwater plans can only be issued to the:

• Property Owner/s;
• Licensed Plumber acting for the property owner(s) with the owner’s written authorisation; or
• Solicitor as part of a property settlement.

If you wish to obtain a stormwater plan and you do not meet the above criteria, you must obtain written consent from the property owner.

What can I plant near stormwater pipes?

Council generally recommends not planting vegetation, especially species that grow taller than 1 metre, over stormwater pipes or within drainage easements. Avoiding planting in these areas helps minimise maintenance costs, reduces the risk of blockages, ensures access to infrastructure when needed, and allows stormwater systems to reach their full life expectancy (typically around 100 years).

Most public stormwater pipes are relatively shallow, often with less than one metre of soil covering them. The backfill material around these pipes is usually more permeable than the surrounding soil, making stormwater trenches an attractive source of moisture and nutrients. As a result, tree roots are naturally drawn to these areas.

The following categories are intended as a general guide only, as appropriate planting distances can vary depending on the type and condition of your soil, as well as the materials used for your stormwater pipes. When in doubt, it’s always safer to plant further away, rather than too close.

If you have concerns about planting a particular species, please contact Council’s Natural Areas and Biodiversity Unit for advice.
**  Provided the root mass and spread are shallow (less than 0.5m)

What about trees causing problems now?

Planting the right tree at the right distance will ensure that the public stormwater pipes are protected and you don’t experience damage to your private stormwater pipes.  But what do you do about trees that may have begun to cause damage?  

Kingborough Council will remove tree roots that are obstructing public stormwater pipes. However, if the source of those roots is traced to a tree on private property, Council may require the property owner to remove the tree to prevent future damage. The cost of removing the offending tree or trees is the responsibility of the owner.

Council does not remove tree roots from private stormwater pipes. If you suspect a blockage on your property, you will need to engage a licensed plumber to investigate the problem and clear the pipes at your own cost.

Any material causing a blockage must be removed from the system and the site. It is not acceptable practice to clear a private blockage by pushing debris into the public stormwater system.

If your private stormwater pipes require repair or replacement, this is also the responsibility of the property owner, and a licensed plumber should be engaged to complete the work.

For further guidance, we recommend reviewing Council’s Stormwater Drain Blockages Guidelines using the following link: https://www.kingborough.tas.gov.au/wp-content/uploads/2018/11/Stormwater-Drain-Blockage-Guidelines-1.0.pdf

Protection of Public Stormwater Systems

Councils have an obligation under the Urban Drainage Act 2013 (urban areas only) to provide an adequate public stormwater system.  Where that system could be impeded or impacted by the inadvertent introduction of native flora, and this reduces or restricts the functional performance of that system, it is reasonable that Councils manage that system with reasonable levels of guidance and protection to achieve the expected performance and efficiency intended.

ARR November 2024 Updated Climate Change Factors

General Information

Stormwater design follows engineering standards to estimate how much water runs off an area after a storm. This can be done using formulas or computer models. As better methods become available, approaches to stormwater design change.

Climate change is complex, and our ability to predict its effects has improved over time. The latest report from the International Panel on Climate Change (IPCC) has updated how future rainfall patterns are predicted. These new methods provide better estimates of how rainfall may change and how to manage stronger storms. Predictions now extend up to the year 2100.

As rainfall increases, more water will run off into drainage systems. This affects the size of underground pipes needed to carry stormwater (called the minor drainage system) and how excess water flows overland (called the major drainage system).

Australia’s key stormwater and flood management guide, Australian Rainfall and Runoff (ARR), now includes the latest climate change data. In November 2024, the ARR Committee updated climate change factors that engineers must use when designing drainage systems.

With increased rainfall intensities, this results in:

• More catchment runoff
• Requiring larger underground drainage systems
• Increased surface water flow especially in urban areas
• Higher costs for councils, developers, and the community

To manage this, Kingborough Council is updating its stormwater design standards. Previously, underground systems were designed for a storm with a 5% chance of happening each year (5% AEP). Now, designs will be based on a 10% AEP storm, meaning a more frequent storm but with a lower intensity is used as the standard.

For all council and private development projects:

• Major drainage systems must handle a 1% AEP storm for the year 2100
• Minor drainage systems must handle a 10% AEP storm for the year 2100

For Frequently Asked Questions and Information on Climate Change factors refer to these websites.
🔗 Engineers Australia: Climate Change FAQs
🔗 ARR Data Hub: ARR Data Hub

For Engineers, Consultants, and Developers

Kingborough Council has reviewed the latest climate change factors in line with the latest IPCC reports and Australian Rainfall and Runoff (ARR) updates.

• Previously, the Council used a 22.5% increase in rainfall intensity for the year 2100.
• The new factors vary depending on the storm type, location, and climate model used.
• Kingborough Council has adopted an interim standard:
  • SSP3-7.0 for catchment analysis (major drainage)
  • SSP2-4.5 for underground drainage design (minor drainage)

Changes include:

• Underground systems were previously designed for a 5% AEP storm.
• This has been updated to a 10% AEP storm to reflect changes in rainfall predictions.

To find the latest climate change factors:

1. Visit the ARR Data Hub.
2. Select the location and check the climate change factors box.
3. Click submit.
   • Example: For Kingston, the SSP3-7.0 factor for a 2-hour storm in 2100 is 1.55.

Effective Date

These updates apply to all stormwater designs, catchment analyses, and flood studies from 1 February 2025.