Flood Behaviour

Water level and rainfall stations can provide early warning of a flood risk, allowing action such as road closures, flood proofing or even evacuation to be taken, thus reducing the risk to life and property.


Flash Flooding

When flash flooding is likely, leave low-lying homes and businesses well before any flooding begins. Evacuation is the best action to take, but only if it is safe to do so.

If you are trapped by rising floodwater, seek refuge in the highest part of a sturdy building. Stay there and call '000' (triple zero) if you need rescue.

Look out for severe thunderstorms and heavy rainfall - ie 70mm of rain in 3 hours. That's more than 20mm in 1 hour. Keep an eye on your local rainfall conditions for this.


Flooding

It is important to understand the conditions which can cause flooding and act accordingly.

Flooding in and around Lake Macquarie waterways can occur due to an elevated ocean level. This may occur as a result of an ocean storm surge, wave setup at the entrance, a high astronomic tide or a combination of these.

East coast lows can also cause flooding because they can produce significant rainfall over the lake and its tributaries. There are a number of tributary catchments which discharge into Lake Macquarie including Dora Creek, Stony Creek and Cockle and Winding Creek catchments. Each of these catchments has specific characteristics which can influence how floods develop within the catchment or where it flows into the lake and in the surrounding area.

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  • Dora Creek, June 2007

  • Flooding at Swansea, 4 February 1990

  • Marks Point, 4 February 1990

  • Stony Creek at Toronto,7 February 1981

  • Winding Creek, April 1988


For a summary of current rainfall and water level conditions click here


Dora Creek

Dora Creek Catchment is located on the western side of Lake Macquarie and is the largest catchment flowing into Lake Macquarie. Flooding within the Dora Creek and Cooranbong townships occurs following heavy rainfall when flows exceed the creek's capacity. Within the lower reaches of Dora Creek, flooding may also be influenced by high water levels in Lake Macquarie. The largest flows are likely to occur after several days of heavy rain.

During the design 1% AEP, flood levels of approximately 3 m AHD are predicted to occur along Kalang Road with velocities up to 1.2 m/s between houses.

The Dora Creek Floodplain Risk Management Study and Plan (June 2015) suggests there are approximately 600 properties at risk of inundation in a 1% AEP flood event with 154 of these expected to experience above floor level flooding. Please refer to the NSW SES / LMCC Dora Creek FloodSafe brochure and the Dora Creek Community Safety Plan for more information.

Stony Creek

Stony Creek catchment is located on the western side of Lake Macquarie and drains to Lake Macquarie through Edmunds Bay Historic records of Stony Creek flood events indicate damage to property and high hazard flooding for residents living close to creeks, with the flood in 1981 causing widespread damage. Lower parts of the catchment, near Fennell Crescent and the area to the north of Awaba Road along Stony Creek, are severely affected in major flood events. The number of creek crossings in the area can exacerbate flooding and the potential for damage to surrounding properties. The largest flows are likely to occur after several days of heavy rain, but can also occur after several hours of extremely heavy rains. Key areas affected by flooding include Toronto, Blackalls Park and the Stony-Mudd Creek confluence.

The majority of land near the Toronto water level gauge is above 0.9 m AHD. Based on local topography and design flood events at Stony Creek, there is no predicted damage below a 1 in 5 year design flood event (peak approx.1.63 m AHD). The water level at this gauge reached 0.89 m AHD on 6/1/2016. Refer to the Stony Creek Floodplain Risk Management Study and Plan (December, 2011) for more information.





Lake Macquarie catchment area showing major tributary catchments

Cockle and Winding Creeks

Cockle and Winding Creek catchment is located on the northern side of Lake Macquarie and drains to Lake Macquarie at Boolaroo. Within the catchment, there have been several major floods in recent history which have caused significant damage and posed high safety risks for residents in this area. The most significant recent major floods occurred in February 1990 and June 2007. The most damaging of these was the June 2007 flood which was caused by an intense east coast low weather system and resulted in the worst natural disaster on record for the LMCC area. During this storm on-shore cyclonic winds averaging 93 km/hr (maximum recorded gust 135 km/h) were accompanied by heavy rainfall (340mm of rainfall recorded in 24 hours). Bridges in Cardiff, Glendale, and Wakefield were extensively damaged by the storm. Worst affected suburbs for urban stormwater flooding included Cardiff, Glendale, Warners Bay, Barnsley, Belmont, Windale and Gateshead. Cardiff Central Business District was the worst affected area with $2 million damage and losses to businesses (source: "Newcastle & Lake Macquarie Star" newspaper, 25 October 2007). The February 1981 event was also a large event for Cockle Creek but less so on Winding Creek. During that flood approximately 35 residential properties in the catchment were damaged by flood waters.

The suburbs of Barnsley, Edgeworth, Argenton, Glendale and Cardiff encroach on the floodplain. Historical records indicate that flooding has previously occurred in these areas, and at least 150 properties with houses are prone to flooding in the 100-year ARI event. Urbanised areas which exhibit high hazard flooding during the 1% AEP event include Cliffbrook Street in Barnsley, Roase Avenue in Glendale and Laurel Avenue and Patterson Avenue in Edgeworth.



Rainfall

Several factors contribute to flash flooding within the Lake Macquarie catchment. The two key elements are rainfall intensity and duration. Intensity is the rate of rainfall, and duration is how long the rain lasts.

Rainfall amounts provide an indication of the likelihood of flooding. These are basic trigger levels that may vary from place to place across the Lake Macquarie catchment. It is important to note that if the rainfall exceeds these levels then the degree of flooding could be much worse. These are not maximum levels of rainfall but simply an indication of how much rain will cause flooding.


Water Levels

MHL maintains a network of automatic water level recorders across the Lake Macquarie catchment. Data is typically recorded at 15 minute intervals, stored on-site and uploaded in near real time to the internet. This time series water level data is used for a number of purposes :

  • monitoring water quantity
  • informing decisions on day-to-day management
  • understanding the effects of storm events in our local area
The network also provides real time information to assist with flood forecasting and to prepare for and manage potential flood inundation.

Data from automatic water level recorders installed at Dora Creek (Kalang Road), Stony Creek (Toronto), and Lake Macquarie (Marmong Point and Belmont) provide flood classifications (nominated flood levels) on plots, in addition to the latest available data. Latest water level observations are compared with these flood levels on the Current Conditions page.




Rainfall Gauge at Eleebana Reservoir

In the case of the Dora Creek (Kalang Road) Level 1, the level was defined by the NSW Public Works and Lake Macquarie City Council in 2001. The Stony Creek (Toronto) Level 1, Level 2 and Level 3 flood classifications have recently been defined by Lake Macquarie City Council and Manly Hydraulics Laboratory. These levels have not yet been defined by SES/BOM, and do not directly correspond to Lake Macquarie flood levels, but have been identified to inform operational flood risk management.

In the case of Lake Macquarie flood classifications (Marmong Point and Belmont) the Minor, Moderate and Major levels have been defined by the Bureau of Meteorology's Service Level Specification for Flood Forecasting and Warning Services for New South Wales and the Australian Capital Territory - Version 3.0 (available online: http://www.bom.gov.au/nsw/NSW_SLS_Current.pdf).

The Bureau of Meteorology defines these classifications as follows:

The classification of minor, moderate and major flood levels at key river height stations is based upon the effect of flooding for some distance upstream and downstream of that station. These levels are determined using the following descriptive categories of flooding, historical data or relevant local information.

  • Minor flooding- Causes inconvenience. Low-lying areas next to watercourses are inundated. Minor roads may be closed and low-level bridges submerged. In urban areas inundation may affect some backyards and buildings below the floor level as well as bicycle and pedestrian paths. In rural areas removal of stock and equipment may be required.

  • Moderate flooding - In addition to the above, the area of inundation is more substantial. Main traffic routes may be affected. Some buildings may be affected above the floor level. Evacuation of flood affected areas may be required. In rural areas removal of stock is required.

  • Major flooding- In addition to the above, extensive rural areas and/or urban areas are inundated. Many buildings may be affected above the floor level. Properties and towns are likely to be isolated and major rail and traffic routes closed. Evacuation of flood affected areas may be required. Utility services may be impacted.


Lake Flooding

Lake Macquarie can fill up like a bath tub when it rains. If it continues to rain, the lake will overflow and cause flooding to surrounding land.

The lake and the ocean are connected via Swansea Channel. The size (width and depth) of the channel will influence the rate at which lake levels change. The duration of an ocean surge event will strongly influence the on lake water levels.

In very large storm events, flooding of properties is possible and you should work through your home or business FloodSafe Plan. The following links can help you to prepare your plan.

»» Home Emergency Plan

»» Emergency Business Continuity Plan