Flooding and drainage FAQs

Because of major river systems and low lying topography the Port Stephens area is prone to flooding.

Flooding in Port Stephens is caused by:

  • river or creek banks over flowing;
  • estuary levels rising and covering foreshore areas; and
  • stormwater drainage that is unable to cope causing overland flows.

Council manages land affected by flooding by:

  • undertaking studies that identify flood risk and flood levels;
  • undertaking floodplain risk management studies and plans that provide provisions of the management of flood prone land; and
  • assessing the compatibility of new development (and major renovations) with flood risk thereby encouraging development that is appropriate to the flood risk of the area.

Common flood definitions:

The chance of a flood of a given or larger size occurring in any one year, usually expressed as a percentage. E.g. if a peak flood discharge of 500 m3/s has an AEP of 5% it means that there is a 5% chance (that is a one in 20 chance) of a 500m3/s or larger events occurring in any one year.

Freeboard is a safety margin of height on top of a modelled flood level height.

The purpose of freeboard is to allow reasonable margin for error after a flood height has been modelled. The Flood Planning Level (FPL) that applies to a site includes a standard freeboard of 0.5m to allow for anomalies/errors.

Land that is likely to be inundated by the probable maximum flood (PMF). It is this land area that defines the "floodplain" for that catchment.

The level of the 1% AEP (annual exceedance probability) flood event in the year 2100 plus 0.5 metre freeboard, except for overland flooding areas where a freeboard of 0.3 metre is applied.

The area of land below the FPL (flood planning level) which is subjected to flood related development controls.

The Probable Maximum Flood (PMF) is the largest flood that could occur.

Australian floods have reached the PMF and we know that that extreme flood events do happen in Australia.

A floodway area is land that is a pathway taken by major discharges of floodwaters. If there was a partial obstruction of this area it would cause a significant redistribution of floodwaters, or a significant increase in flood levels.

Floodways are often aligned with natural channels, are usually characterised by deep and relatively fast flowing water, and have major damage potential.

Flood storage areas are parts of the flood plain that are important for the temporary storage of flood waters.

The loss of these storage areas may increase the severity of flood impacts by increasing natural flood intensity.

The flood fringe area is the remaining area of flood prone land after the floodway area and flood storage area have been defined.

Areas of inundation by local runoff rather than inundation created by overbank flows discharging from a watercourse.

The area of a flood which poses a possible danger to personal safety. This can include:

  • Areas where the evacuation of trucks would be difficult;
  • Areas where able-bodied adults would have difficulty wading to safety; or
  • Areas where there is a potential for significant damage to buildings.

The area of a flood where, should it be necessary:

  • A truck could evacuate people and possessions; or
  • An able-bodied adult would have little difficulty wading to safety.

Flooding FAQs

Flooding can be:

  • high streamflow caused by an overflow from a stream, river, estuary, lake or dam,
  • major excess of drainage before entering a watercourse,
  • coastal inundation resulting from elevated sea levels and/or waves going over coastline defences.

In Port Stephens, there are three main types of flooding:

  1. Flash flooding - is the most common type of flooding in Port Stephens. It is caused by heavy rainfall that exceeds the capacity of the drainage network resulting in flooding that happens quickly and with little warning.
  2. River flooding - caused by heavy rainfall in rivers that causes high water levels to spill into nearby floodplains.
  3. Storm surge - caused by coastal storms that result in elevated water levels, severe winds and large waves.

The 1 in 100 year flood is better referred to as the 1% AEP flood event - a flood with a 1% AEP has a 1% chance, or 1 in 100 chance, of occurring in any given year.
There is a common misconception that the 1 in 100 year flood means that it can and will only occur every 100 years. As weather and flooding is variable, we know this is not the case.

Flood Studies identifies flood behaviour including the areas previously flooded, water depth, hazard and the likelihood of flooding within the area.

Floodplain Risk Management Studies and Plans identifies the ways to reduce the impact of flooding. This can include drainage upgrades, development controls, community awareness and emergency response arrangements.

es. Most home building and contents insurance policies will include flood cover as a standard inclusion. However, make sure you read your Product Disclosure Statement (PDS) to know exactly what you are covered for.

If your property is suddenly identified by Council as being in a flood prone area, the real flood risks on your property have not necessarily changed; rather, present information regarding risk estimates has become more available for Council to inform decision making.

Ultimately, the market determines property value. Owners should seek their own valuation advice if they are concerned flood risk estimation will influence their property value.

Stormwater FAQs

Rainwater becomes stormwater once it has runoff surfaces such as roofs, paved areas, gardens and other open spaces.

Natural overland flow is stormwater that has flowed from neighbouring lands due to the natural slope of the land.

If your property is on lower land you will need to accept and manage natural overland flow from higher ground, whether this is private property or public land.

If your property is affected by natural overland flow, you must not restrict, divert or redirect the flow to cause impact or nuisance to an adjoining property.

Local drainage refers to the pit and pipe network that drains urban areas to the nearest creek or open channel. This network is designed and intended to manage more frequent rainfall events than rare floods. Every now and then, it is normal for street drainage systems to overflow.

Local drainage problems can occur anywhere and are not included in Council’s floodplain management planning. However if the street drainage system is overflowing more regularly, there may be a problem that Council needs to have a look at, you should write to Council to describe the problem and Council will respond to your request.

Before Council can begin any storm water drainage investigation, you are required to complete the following:

  1. Read all information concerning stormwater drainage complaints as contained on Council's website.
  2. Attempted to resolve the situation by raising the issue with the owner of the property the water is coming from.

Problems with overland stormwater flow between neighbouring properties are generally a matter to be resolved between the respective owners. Landowners are encouraged to talk to their neighbours about the problem and seek a mutually satisfactory solution. If this is not possible advice and mediation support to resolve neighbourhood disputes can be sourced from the NSW Community Justice Centre at no cost.

The CJC may be contacted on:

  • Free call:  1800 990 777

1.  It may be necessary to seek independent legal advice through a private Solicitor or by consulting with a Chamber Magistrate at a Local Court.

2.  Record your complaint in writing outlining what action you have taken and the result.

When reporting a stormwater drainage issue on private property, a customer must provide the following information to assist Council in ensuring that proper action is taken if required and/or if legislatively possible:

  • Describe what is occurring;
  • When did it occur and on how many past occasions?
  • Have you made contact with Council about this issue previously?
  • What is the source on the neighbouring land that is causing the problem?
  • Describe how your land and/or building are being damaged (include a written report from a suitably qualified person stating the land or building is likely to or is being damaged);
  • Have you obtained professional advice as to the source of the stormwater issue?
  • Have you liaised with your neighbour to address this matter?
  • Have you sought advice or initiated mediation with your neighbour through the Community Justice Centre? and
  • Do you have photos of the stormwater problem as it is occurring?

Council will not commence any investigation until these actions have been completed.

A catchment is an area where water is collected by the natural landscape. In a catchment, rainwater and stormwater run-off will eventually flow to a creek, river, dam, lake, ocean, or into a groundwater system. Drinking water catchments deliver water to surface water and groundwater storages.

Drainage FAQs

When will Council take action?

Council will investigate and take action on stormwater drainage complaints on when it relates to the flow of surface water from one property to another, and where the following have been demonstrated:

  • evidence that water has caused, or is likely to case, significant soil erosion or physical damage to a building on the other land
  • surface water has been directed to and/or concentrated in a particular area by a man-made structure or drain
  • surface water is the result of defective roof drainage from a dwelling or outbuilding.

When Council will not take action?

Be aware that Council will not take action under the following circumstances:

  • the surface water is a natural runoff from a property due to topography and isn't redirected in any manner
  • surface water is flowing down existing hard surface areas such as driveways, concrete slabs or paved areas
  • the location of a dwelling or outbuilding impacts on surface runoff
  • surface water runoff occurs only in periods of exceptionally heavy rain
  • surface water is a result of overflows from stormwater absorption pits where contours of land and lack of access prevent direct connection of a buildings roof water to Council's stormwater drainage system
  • the runoff is from new development work that is the subject of a development consent and has been constructed in accordance with that consent
  • the drainage problem involves discharges from defective or blocked private inter-allotment drainage easement.

Private inter-allotment easements are the responsibility of the property owner who is burdened by and/or benefited by the easement.

Before Council will take action:

You must provide the following to Council before an investigation can commence:

  • a description of the issue/s including times and dates
  • describe how your land and/or building is being developed - if lives and property are at risk of being severely damaged, act immediately to impede or lessen the impact of the damage
  • provide any documentation if the issue has already been reported to Council
  • provide any written professional advice as to the source of the stormwater issue
  • provide any information you  have regarding conversations you may have had with your neighbour or any initiated mediation that has occurred
  • provide any photos/videos demonstrating the stormwater issues with dates and times.

Your submission can be provided to Council by:

Speak with your neighbours initially to address any issues. If possible, drainage easements can be created to direct water to a Council stormwater drainage system.

If you're land is on a sloping site, natural surface water runoff flows down the slope following the contours of the block.

Unless the cause of surface water runoff meets the requirements above, the landowner carries the responsibility to install surface water controls. Any diversion of surface water must be carried out in a way that does not have a detrimental impact on any other properties further down the slope.

Seepage water  is the responsibility of individual property owners. Where sloping blocks have been excavated to create a flat yard or building site, seepage drains should be constructed to redirect water to a stormwater drainage system

If you need information regarding a neighbouring development and/or drainage, this is applied for via the GIPA process.