Frequently Asked Questions

Flooding occurs when there are large volumes of rainfall. Some rain soaks into the ground at first (known as infiltration), but when the soil is saturated, rainfall runoff flows across the ground surface towards water courses In major river systems it may take several hours or even days for flood water to rise and break its banks. Along creeks or overland flow paths, which have relatively small catchments, this happens more quickly and is often referred to as flash flooding.

Other factors that can affect flood behaviour include the topography of an area, soil conditions and impervious ground cover (e.g. concrete).

Being located on the banks of Stonequarry Creek, Picton is exposed to flooding when heavy rainfall occurs in the catchment.

Flooding can cause significant damage to property and risk to life. It may also result in the loss of valuables and disruption to essential services. Flood waters can become dangerous at relatively low depths, and it is very dangerous to enter floodwaters (either on foot or in a vehicle). Floodwaters can contain hidden debris or snags, become electrified if powerlines are down, and contain sewage and bugs that can cause illness.

Floods are independent events and randomly distributed over time. Being located on the banks of Stonequarry Creek, Picton is exposed to flooding when heavy rainfall occurs in the catchment.

The flood in June 2016 was the largest in the history of Picton and as such was an extraordinary event. The June 2016 flood occurred as a result of an extreme amount of rainfall across the whole Stonequarry Creek catchment (including the upper Stonequarry Creek and Racecourse Creek catchments), brought by an intense East Coast Low that also resulted in devastation across the NSW coastline, particularly in Sydney’s northern beaches, Tweed Heads, Coffs Harbour, and Eden on the far south coast. Reaching 8.8 m at the Stonequarry Creek gauge, this event is estimated to be between a 200-500 year ARI event at Picton.

The February 2020 event was also a notable event, however differed from the June 2016 event in 2 key ways. Firstly, the heaviest rainfall in 2020 was localised to Picton itself, with less intense rain occurring in the upper Stonequarry Creek and Racecourse Creek catchments. Secondly, the rain fell more gradually over a longer period, resulting in lower peak flood levels in Stonequarry Creek, which peaked at 6.28m, some 2.5m lower than in June 2016. The February 2020 event is estimated to be between a 20-50 year ARI event, making it the second largest event in the gauged record, which covers the last 30 years. The observed flood behaviour is similar to the mapped results produced in the Flood Study Update for events of this size. There have been other floods larger than February 2020 prior to the gauge record, including one in 1969 with 1m of water over the Argyle St Bridge. 

Flood risk mitigation options fall into three broad categories:

·  Response Modification - changes to the flood response

·  Property Modification - changes to properties including management of future development

·  Flood Modification - changes to the flood behaviour through constructed works.

·  Council’s Local Emergency Management Committee involves and coordinates a range of agencies in Picton.

·  A flood warning system based on three gauges in the catchment area sends automated SMS warning messages to council and agencies.

·  Management of vegetation in Stonequarry Creek which includes vegetation thinning, vegetation debris removal, weed control and crown lifting.

·  Management of development to ensure new buildings are located and constructed in a way that is compatible with their flood risk.

·  Support during and recovery after flood events.

No. There is no way to stop flooding in Picton. Aggressive removal of vegetation in Stonequarry Creek would cause much greater erosion of the banks, which could lead to bank slump and significant reduction of the channel capacity. Currently there is a vegetation management program in place which aims to achieve a balance between vegetation removal to promote better drainage, whilst retaining enough vegetation to ensure the integrity and stability of the creek banks is not compromised.

·  The Updated Draft Stonequarry Creek Flood Study contains updated flood modelling, following new rainfall information and changes to industry guidelines. The flood modelling provides a representation of the expected flood behaviour for a range of design flood events.

·  The draft Stonequarry Creek Floodplain Risk Management Study examines the options available to potentially mitigate flood risk.

·  The draft Stonequarry Creek Floodplain Risk Management Planpresents specific mitigation options which are recommended for further consideration.

High priority actions are related to planning and preparing for flooding, and major changes to the creek are not recommended.

Recommendations include:

Response Modification Recommendations

• Investigation and improvement of existing Flood Warning System
• Improve Emergency Response Coordination
• Implement an ongoing and collaborative community education program to maintain and improve flood awareness in Picton

Property Modification Recommendations

• Amend Wollondilly Local Environment Plan (LEP) 2011 to:

             -  Revise the definition of the Flood Planning Area (FPA) and Flood Planning Level (FPL) based on outcomes of this study

             -  Requirement for development consent for critical facilities between the FPA and Probable Maximum Flood (PMF)

• Amend Wollondilly Development Control Plan (DCP) 2016 to:

            -  Utilise mapped outputs and modelling tools from this study

            -  Consider advice regarding controls relating to basement carparks and community facilities

• Provide information to Residents via S10.7 Planning Certificates
• Explore flood proofing measures for commercial properties

Flood Modification Recommendations (identified for further investigation, not necessarily direct implementation)

• Feasibility Study for a detention basin on Stonequarry Creek upstream of Picton
• Argyle Street Stormwater Pipe Upgrade
• South Picton Diversion Bank
• Menangle Street Culvert Upgrade
• Feasibility Study to Investigate Voluntary Purchase in Picton in the floodway
• Current vegetation management program to be continued and reviewed periodically

The currently adopted flood information/management plan was completed in 1996 and covered Stonequarry Creek from the railway viaduct up to near the junction with Racecourse Creek (Davies Pl / Magnolia Dr).

A new flood study began in 2006 and went through a number of revisions. One draft was publicly exhibited in 2012 before the final draft flood study was completed in 2017 by Advisian. The Advisian final draft flood study included a review of the 2016 flood event. It also extended flood information further upstream in Stonequarry Creek (Barkers Lodge Rd) and into Racecourse Creek (Yallambi St)

The Advisian final draft flood study was publicly exhibited in 2018 to start a new floodplain risk management study (FRMS). During the FRMS, it was decided to revise the flood modelling to ensure longevity of the data. The update utilised the latest industry guidelines, as well as recorded flood information collected in the June 2016 flood event. A draft flood study update was prepared, and became the basis for the FRMS. The mapping produced in this study is consistent with observed flooding in Picton, and allows Council to better plan for future flood events.

The draft flood study update has also studied overland flooding (runoff from local rain that travels towards the creek) and further extended the coverage for Racecourse Creek. This means there are new properties identified as subject to flooding particularly from overland flow sources.

Visit the State Emergency Service www.floodsafe.com.au to get advice on simple things you can do to prepare for a flood.

Council is not in a position to advise you on this matter. The methods and information used by insurance companies to set their policies varies between individual companies. You will need to speak to your insurer to find out how this will affect your premium. General information is available here: https://www.floods.org.au/client_images/1787680.pdf

Council is not in a position to advise you on this matter. Information provided in these studies assists property owners in making informed decisions regarding ongoing management of their properties.