Stormwater

Council’s Role in Managing Stormwater

Council is responsible for the care and maintenance of the public stormwater drainage network within the Sorell Municipality. This includes public stormwater mains, manholes, pits and Council maintained roadside table drains.  Council also maintains the stormwater mains owned by Council but situated on private property.

As part of meeting its obligations, Council:

• undertakes assessments of the urban area of the Council’s municipal area;
• documents the stormwater assets under its control;
• conducts frequency-based inspections of its stormwater assets  with allocation of resources reflective of various risk factors; and
• completes required work on stormwater assets identified during the inspections.

One of the objectives of the Urban Drainage Act 2013 is to ensure stormwater services, infrastructure and planning are provided to minimise the risk of urban flooding due to stormwater flows.  To help meet the objective of providing stormwater systems as may be necessary to effectively drain the urban area of the Council’s municipal area, Council engaged a consultant to carry out a 1 in 100 year storm event catchment analysis.  This models overland flows and stormwater infrastructure capacity performance of Sorell’s urban areas during a significant storm event.

One of the outcomes of the catchment analysis was a set of recommended options.  Council is considering the practicality and financial sustainability of those recommended options.

Types of Stormwater Flow and Responsibilities of Property Owners

Natural Overland Flow

Property owners should also ensure that water in a concentrated form is directed to Council’s stormwater drainage system or another legal point of discharge, such as the street or on-site stormwater absorption trench.

Property owners should always seek professional advice before starting work that may change the drainage and water flow of their property.

Concentrated Overland Flow

Water that flows from hard stand areas e.g. driveways, paths, paved areas, landscaped areas, roofs, drains from roofs, open drains and cut-off drains.  A property owner must ensure that stormwater is not discharged from a private stormwater system so that it causes a nuisance to a neighbouring property or its residents.

Seepage (Ground) Water

Water that does not drain into a formed channel or stormwater system.  Seepage may be caused be a number of factors, including

• surface run-off from a neighbouring property;
• faulty internal plumbing;
• faults within Council’s stormwater mains or TasWater’s sewer or water mains;
• natural groundwater.

Individual property owners should ensure they control and minimise the risk of seepage to their properties by taking steps such as the installation of subsoil drains.

Where sloping blocks have been excavated to obtain a flat yard or building site, subsoil drains should be constructed to redirect water to a stormwater drainage system. Property owners should seek the advice of suitably qualified and/or experienced professionals in the design and installation of such drains.

Drains and pipes on private property

Property owners are responsible for management of stormwater drainage and surface water within their property.  This can be achieved by maintaining roof gutters, downpipes, rainwater tanks, surface channels and other components to minimise the possibility of stormwater entering theirs or their neighbour’s property.

Property owners must accept natural overland flow from adjoining properties or public land and must not divert or redirect the flow from its natural path onto neighbouring properties.

A downstream property owner should not erect any type of barrier that interferes with the path of stormwater unless provision is made for the flow to discharge to an approved drainage system.

When constructing hardstand areas such as driveways, concrete and paved areas, or landscaping that have associated drainage, property owners must control the stormwater in order to prevent concentrated water impacting onto adjacent properties.

Property owners generally need to ensure that roof water and hardstand areas are drained to a lawful point of discharge such as:

– Kerb and channel;

– Roadside table drain;

– An inter-allotment stormwater drainage pipe system; and

– Subject to Council approval, a Council controlled drainage easement or drainage reserve.

Council is responsible for regulating private drainage.  Council may direct a property owner to connect to Council’s stormwater drainage system or other legal point of discharge.

Property owners need to be aware that fences and landscaping can change the topography of a property and the way it disperses water.

It is the property owner’s responsibility to maintain private stormwater infrastructure. If there is a stormwater issue caused by the failure of your own internal plumbing, contact your plumber.

Reporting a stormwater drain issue

Council receives a number of complaints each year regarding stormwater runoff and overland flow from private property causing an issue to an adjoining or downstream private property. In such instances Council’s intervention powers are very limited and it is likely to be a private civil matter between the adjoining property owners.  Stormwater issues regarding runoff and overland flow between private properties should be resolved between those property owners.

You can report any Council related stormwater issue to us on 03 6269 0000. This number can also be used to report urgent after hour’s stormwater issues.

Where private property appears to have been impacted by stormwater from Council’s drainage network, Council will assess the site and determine any further action (if any) to be taken by the Council and the works required to rectify the issue.

Neighbouring properties impacted by sub-surface

If an owner excavates into the land and groundwater seeps out of the cut, it is the owner’s responsibility to manage this water. Similarly, if the land has a ‘spring’ or high water table.

Flooding

For further information on land prone to inundation please go to flooding – Understanding Flood Risk in Sorell

Private Nuisances – Disputes between neighbouring properties

Council or other government agencies do not have the power to deal with all drainage issues, land owners should seek their own legal advice to determine how these matters can be resolved.

Council commissioned a number of flood studies for the Municipality, including:

• Urban areas of Sorell, Midway Point and the Southern Beaches 1% AEP flood mapping: broad scale flood modelling used to approximate flood extents through the Municipality’s overland flow paths at a whole of catchment scale.

They show the drainage lines and natural flood ways where flood water is predicted to travel through during a 1% AEP event.

The modelling has been done at a catchment wide level and provides an indication of potential hazards but may not be accurate at a property level. Seek independent advice for your site-specific flood risk.

The modelling identifies major flow paths during extreme events. It does not pick up localised nuisance flooding associated with undersized pits or pipes or localised road camber. It also does not pick up un-concentrated sheet flow, such as what occurs at the bush-urban interface. Just because your property is not within the mapped hazard extent does not mean you won’t be affected in a flood.

Sorell Council Flood Modelling 1 in 100 Year Event

Like most of Tasmania’s East Coast, the Sorell Municipality, on average, receives a lower than average annual rainfall when compared with the rest of the State.  However, the Municipality on occasions, is subject to rainfall events that are high in intensity and short in duration.  These events can occur at any time during the year.  Depending on the amount of rain and where it falls determines the extent of local flooding issues.  Flash floods are a result of fast rising water and fast receding water. Flood events are often shallow waters, but fast moving.

Flooding also occurs when the Municipality has received regular rainfall over an extended period of time and the ground becomes so saturated that it cannot absorb any further rainfall.   In coastal areas when a high tide occurs in the same period as an extreme rainfall event, flooding can be even worse.

Most residents are aware of the rivers, streams and rivulets that run through the region.  There are also a number of constructed drains (e.g. the one that runs along Montagu Street) and naturally occurring overland drainage pathways that generally remain dry for most of the year.  It is important that all these overland drainage paths are well maintained and kept free from obstructions including fencing and other structures.

Your property maybe at risk of flood damage if:

• You are near a waterway, including naturally occurring ephemeral waterways that are usually dry.
• Your property is in a natural depression, including behind a coastal dune strip.
• Your property slopes up into surrounding farmland or natural bushland.
• Your property is in a low-lying area near the coast or a waterway.
• Your property is located at the bottom of a hill with adjoining developed properties above.

Flood maps are available for the urban areas to see if your property maybe subject to flooding.

Flood Maps

Council commissioned a number of flood studies for the Municipality, including:

• Urban areas of Sorell, Midway Point and the Southern Beaches 1% AEP flood mapping: broad scale flood modelling used to approximate flood extents through the Municipality’s overland flow paths at a whole of catchment scale.

They show the drainage lines and natural flood ways where flood water is predicted to travel through during a 1% AEP event.

The modelling has been done at a catchment wide level and provides an indication of potential hazards but may not be accurate at a property level. Seek independent advice for your site-specific flood risk.

The modelling identifies major flow paths during extreme events. It does not pick up localised nuisance flooding associated with undersized pits or pipes or localised road camber. It also does not pick up un-concentrated sheet flow, such as what occurs at the bush-urban interface. Just because your property is not within the mapped hazard extent does not mean you won’t be affected in a flood.

Sorell Council Flood Modelling 1 in 100 Year Event

Council’s Role in Mitigating Flood Risk

Before a flood:

• Model and map flood risk.
• Statutory planning in flood risk areas.
• Undertake stormwater pit and grate inspections prior to a major rainfall event.

During a flood:

• Keep the pipe system clear of blockages.
• Ensure the main natural drains are kept free of debris as much as possible.
• Respond to customer requests about blockages with the existing infrastructure.

After a flood:

• Clear debris from waterways, roadways, and parks.
• Repair damaged assets.

Whilst Council does all it can within available resources to ensure the drainage/stormwater infrastructure for which Council is responsible is efficiently and effectively maintained and continuously improved, it should be noted that it is not unusual for drainage and storm water infrastructure to reach capacity very quickly during significant rain events.

Property Owner’s Role in Mitigating Flood Risk

We encourage you to monitor local flood levels and seek appropriate weather warnings via the Bureau of Meteorology’s Flood Knowledge Centre – Flood Knowledge Centre (bom.gov.au)

Property owners should do everything practicable to ensure drainage and stormwater infrastructure within their properties is kept clear of debris.

It is important for property owners in flood prone areas to have an emergency/flood plan in place to prepare for such an event, including ensuring the safety of animals and stock where practicable.

Before a flood:

• Know and understand the likely flood risk at your property.
• Ensure that you have adequate insurance, including coverage for all parts of your property likely to be affected (such as fences and outbuildings).
• Prepare a flood response plan.

During a flood:

• Move valuable and hazardous possessions to higher levels.
• Follow your flood response plan.
• If evacuating, do not return home until you have been advised it is safe to do so.
• Call the SES on 132 500 if you are in immediate danger.

After a flood:

• Contact your insurance company if there has been damage to your property.
• Check in with your neighbours.

To learn more about what you can do before, during and after floods, please visit the Tasmania State Emergency Service website.