Draft Flood Risk Management Study and Plan for Cootamundra
Council is working through the NSW Government Floodplain Risk Management Process, which will ultimately help us consider the consequences of living on flood prone land.
The first stage, the Cootamundra Flood Study was finalised and adopted by Council in January 2021. This study identified flood risk to people, property, infrastructure and assets across the study area, resulting from localised overland flow and large rainfall events over the broader catchment.
With assistance from the NSW Government, we have prepared the Draft Cootamundra Floodplain Risk Management Study and Plan. This project is the next step in increasing our community’s resilience to flooding. The Draft Plan identifies measures and strategies aimed at reducing the impacts of flood risk to residents and businesses in the study area.
The Draft Study and Plan has been developed under the guidance of Council’s Floodplain Risk Management Committee, which includes elected members of Council (Councillors), Council staff and community representatives.
Council engaged WMAwater to assist in the preparation of the Draft Floodplain Risk Management Study and Plan. The draft has been prepared in accordance with the NSW Government’s Flood Prone Land Policy, as outlined in the NSW Floodplain Development Manual 2005.
- Learn more about the NSW floodplain management process on the NSW Department of Planning and Environment’s website.
How has the plan been prepared?
The project commenced with Council and WMAwater meeting with the community, prior to starting their work; with residents taking the opportunity to provide very valuable historic information on flood experiences, feedback on what flood risks the community are most concerned about and how they would like to see these flooding problems managed. Your responses help us to understand the local flooding problems and are an invaluable source of data.
Computer-based flood models established as part of the Flood Study, were then updated to reflect any changes to the catchment that had occurred since the flood study was completed. These changes mainly included residential development in the Boundary Road subdivision.
Assessment then focused on testing scenarios with different management measures and strategies in place. The aim of these measures and strategies is to reduce the risk from living or running a business on flood-prone land. The assessment considers the change in flood behaviour, in addition to other financial, social and environmental impacts of implementing these measures and strategies.
The types of measures and strategies assessed include those which physically alter the flood behaviour, including detention basins, levees, drainage upgrades, channel works, for example. Other measures and strategies aim to alter the response during a flood event, by increasing understanding of possible flood risks and measures and strategies aimed at reducing flood risk as redevelopment occurs.
How is this project different from the flood study?
Unlike the Flood Study, which is simply a technical project that identifies flood behaviour, the Floodplain Risk Management Study and Plan has investigated and prioritised actions to manage and reduce the risk from flooding.
The Floodplain Risk Management Study and Plan aims to reduce the losses to our community from flooding. These losses can include financial and property losses but most importantly, floods can, and have, resulted in the loss of lives.
The Floodplain Risk Management Study and Plan aims to identify what actions Council, NSW SES and the community can undertake to improve and manage flood risk. The final steps of the process are to implement the actions identified in the plan. The floodplain risk management process is constantly reviewed and monitored for improvement. For example, the performance of management actions will be observed and reviewed following flooding events to determine if there is any scope for improvement.
How can you get involved?
Community participation is critical to the plan’s success, particularly when it comes to understanding the communities’ experiences in past flood events. The Cootamundra Floodplain Risk Management Committee has provided a forum for discussion of these experiences and for feedback on assessed measures and strategies.
We are now asking for the community to provide feedback on the draft Floodplain Risk Management Study and Plan. The draft plan will be placed on public exhibition in April 2023, with feedback submissions closing 1st May 2023. During this time the public will be invited to view the draft document on Council’s website and attend community sessions to ask questions of the project team and provide feedback on the recommendations of the draft plan.
Council is holding a drop-in information session for the community at the Alby Schultz Meeting Centre in Wallendoon Street Cootamundra on Thursday 27th April 2023 from 3pm – 6pm. The community can drop in at any time between these hours to meet with Council staff and WMAwater.
A further information session will be held at a venue to be confirmed, on Tuesday 9th May 2023 at 7pm. This session will include a more formal presentation of the draft recommendations, as well as an overview of the themes coming from the exhibition period. Following this session any additional submissions/feedback will be accepted until 16th May 2023.
Submissions/feedback should be forwarded to the General Manager CGRC by post to Cootamundra-Gundagai Regional Council, PO Box 420, Cootamundra NSW 2590, delivered to Council’s offices at Cootamundra or Gundagai or by email to email@example.com
Submissions/feedback can also be submitted through the online survey at https://www.surveymonkey.com/r/CootaFRMS
The online survey allows for both general feedback and specific feedback on each of the draft recommendations to be provided.
The Draft Floodplain Risk Management Study and Plan documents can be found on Council’s website: DOCUMENTS ON PUBLIC EXHIBITION | Cootamundra Gundagai Regional Council (nsw.gov.au)
Frequently Asked Questions
What is the 1% AEP (1 in 100) flood?
A 1% AEP (1 in 100) flood is a flood event that has the probability of occurring on average once every 100 years, i.e. there is a 1% chance of a flood of this size or larger occurring at a particular location in any given year and subsequently some parts of Australia have experienced more than one ‘1 in 100’ flood within a few years of each other. Within the Floodplain Risk Management Study and Plan the ‘1 in 100’ flood is referred to as the 1% AEP flood event. Floods of other sizes are also considered including, smaller, more frequent events, such as the 5% AEP (1 in 20) and larger, less frequent events, such as the 0.2% AEP (1 in 500).
What is the probable maximum flood?
The probable maximum flood (PMF) is the largest flood that could possibly occur and is an extremely rare flood. The PMF defines the extent of flood prone land.
What determines the size of a flood?
The size of a flood depends on several factors. These include the intensity and duration of rainfall, the area of catchment that rain falls over and the catchment conditions prior to the event, i.e. what level of infiltration occurs. Large floods happen less frequently than small floods. The size of the area flooded is also affected by the shape and fall of the catchment. For example, a large flat area at the bottom of a catchment is more likely to have a larger flooded area.
How significant was the flooding on 31 October 2022 and 13 March 2023?
Cootamundra has experienced two significant flood events over the last few months. In particular, the 31 October 2022 event has been analysed in the Study and was shown to be comparable to a 5% AEP (1 in 20) flood. The 13 March 2023 flood was a smaller flood than this, with flood levels reported to be up to 0.5m lower than the October event. If a 1% AEP (1 in 100) event were to occur, it would be significantly higher (up to 0.45m higher than October 2022 at Wallendoon Street, for example) than any known floods in Cootamundra.
What types of flooding are considered in the study?
Mainstream flooding occurs following heavy rainfall across the broader Muttama Creek catchment, resulting in rising water levels in the creeks. Water levels may overtop the creek banks and inundate surrounding, usually dry, land.
Overland flow flooding is caused by intense local rainfall events, which results in flowpaths forming from the runoff that is not captured by the stormwater drainage system. Overland flow flooding is typically shallow depths and short duration (less than a few hours). Water follows the natural topography to the lowest point, generally ending up in a creek or a drain. Overland flow paths are the routes taken by rainfall runoff and are not always obvious until they flood.
Why is Council undertaking this project?
Councils are responsible for identifying and managing flood prone land in NSW and are supported in this responsibility by the NSW Department of Planning and Environment, through technical and financial support. The Floodplain Risk Management Process is outlined in the NSW Floodplain Development Manual 2005 which encompasses the NSW Government’s Flood Prone Land Policy. Learn more about the NSW floodplain management process on the Department of Planning and Environment’s Website: www.environment.nsw.gov.au/topics/water/floodplains/floodplain-management-program
This information will help assist the Council to make informed decisions about managing flood risks and providing greater data to residents to inform development and the risk of flooding at their property. The Floodplain Risk Management Study and Plan also provides essential information to the NSW State Emergency Service (NSW SES), Council and residents to deal with flood emergencies.
What is the difference between a Flood Study, a Flood Risk Management Study, and a Flood Risk Management Plan?
- The Cootamundra Flood Study (2021) is a technical project that identifies flood behaviour such as depth, velocity and extent across the floodplain. The study is undertaken using current techniques and industry guidance. The study outputs provide a representation of the expected flood behaviour for a range of past and future flood events.
- A Floodplain Risk Management Study (Current Study) draws on the results of the flood study to examine the options available to potentially manage flood risk. Options are aimed at reducing the social, environmental and economic losses of flooding.
- A Floodplain Risk Management Plan (Current Study) presents specific mitigation options which are recommended for further consideration and provides a strategic plan for implementation.
How are flood risks managed?
Flood risk mitigation options fall into three broad categories:
- Response Modification – changes to the community’s response to flooding, such as flood awareness and education, flood warning, response planning.
- Property Modification – changes to properties including management of future development, such as development controls, voluntary house raising or purchase.
- Flood Modification – changes to the flood behaviour through constructed works, such as drainage upgrades, detention basins, levees
Why can’t flooding be prevented?
Flooding is a natural process that will always occur. Floods of different sizes can occur, both small and large. Problems with flooding arise when development has been undertaken in floodplains without fully taking account of existing flooding. It is almost impossible to retrofit solutions to completely mitigate against the full range of flooding. Additionally, the scale of works required to mitigate against the full range of flooding often have significant constraints in developed catchments. While it is rarely viable to completely prevent flooding, flood risk to life and property can be managed.
What can I do to prepare for a flood event?
Visit the NSW State Emergency Service www.floodsafe.com.au to get advice on simple things you can do to prepare for a flood. For assistance during an event please contact the NSW State Emergency Service (SES) on 132 500 or visit their website at www.ses.nsw.gov.au.
What are the risks associated with flooding?
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.
What if I want to sell my property which has been identified as flood affected?
Prospective buyers are able to find out if a property is flood affected because Council has a duty to disclose this information. When selling property, the prospective purchaser will request a Section 10.7 certificate from Council. This will inform the purchaser if there are any Council policies (including policies relating to flooding) applying to the property which restricts the use or development of the land or places obligations on the owner.
Will I be able to get insurance if my property is flood affected?
The methods and information used by insurance companies to set their policies varies between individual companies. Individual insurance companies typically identify Flood Prone Land and assess risk through their own flood studies, analysis and flood mapping exercises, irrespective of whether Council has undertaken a flood study. You will need to speak to your insurer to find out how your premium is calculated.
What does this mean for property owners?
For most people, there is nothing to do in response to this Draft Plan. However, property owners who are planning redevelopment of their property may need to appropriately consider the impacts of flood risk during the development process. This could include the requirement to have the floor levels of the development set at or above the Flood Planning Level. This ensures that the impacts of flooding are reduced.