Floodplain Risk Management Planning
- What is floodplain
- How are floodplains managed in NSW?
- Floodplain Risk Management Process
- What is a flood study
- What is a Floodplain Risk Management Study
- What is a Floodplain Risk Management Plan
- What is a Floodplain Risk Management Committee
- List of current Floodplain Risk Management Studies & Plans
As has occurred with many coastal cities and towns around Australia, many suburbs of Gosford have been built successively within local floodplains. This has been evidenced in the recent flood events in Gosford during the mid to late1980's, early 1990 and June 2007. Development within the floodplains has occurred naturally since the 1830’s as more and more people relocated to the region seeking good farm land, building materials, maritime and aquatic resources and finally coastal holiday and retirement destinations.
A floodplain is an area of land that has been formed by flooding over time and is still subject to periodic inundation. Floodplains are also referred to as flood prone land
Floodplains or flood prone land is all land affected by flooding up to and including the Probable Maximum Flood (PMF) event (or the highest conceivable flood that nature can produce). Only land that is above these levels is truly flood free.
Probable Maximum Flood
The Probable Maximum Flood (PMF) is the largest flood that could conceivably occur within a particular catchment, and is a very rare and unlikely event. However, when undertaking a Floodplain Risk Management Study, Council looks at all storm events up to and including the PMF.
1% or 1 in 100 year flood
A 1:100 year Average Recurrence Interval is the result of statistical data which estimates the probability that a particular rainfall event (or intensity) will be equalled or exceeded at a particular place within a certain period of time i.e. 100 years.
This is also referred to as the 1% Annual Exceedance Probability flood which is a flood that has a 1% chance of reaching or exceeding a particular magnitude in any one year.
It should be noted that if a 1% or 1 in 100 year flood is experienced in a certain year, that does not mean that there will not be another 1 in 100 year flood occurring in the same year or during the next 99 years
Local Government is primarily responsible for control of development on flood prone land in NSW. However, the NSW State Government, through the Office of Environment & Heritage, the State Emergency Service (SES) and the Bureau of Meteorology(BoM) also have a major role to play in managing the flood risk.
The NSW Government’s Flood Prone Land Policy is directed at providing solutions to existing flooding problems in developed areas and ensuring that future developments will not create flooding problems in other areas. The State Government provides specialist technical advice and financial support to assist local councils to develop Floodplain Risk Management Plans which consist of the following stages:
Floodplain Risk Management Study
Floodplain Risk Management Plan
Implementation of the Plan
For more detailed information regarding the Floodplain Risk Management Process, please refer to theNSW Floodplain Development Manual 2005
A Flood Study is a comprehensive technical investigation of flood behaviour in a particular catchment. The Flood Study provides detailed information on the nature of the flood risk including the distribution, extent, levels and velocity of floodwaters across the floodplain for various flood events including the 1 in 100 Year Flood and Probable Maximum Flood.
The purpose of a Floodplain Risk Management Study is to identify, assess and compare various risk management options and consider opportunities for environmental enhancements as part of mitigation works.
The management study draws together the results of the flood study and data collection exercises. It provides information and tools to allow strategic assessment of the impacts of management options for existing, future and continuing flood risk on flood behaviour and hazard. It also allows for a robust assessment of the social, economic, environmental and cultural issues and costs and benefits of all options.
The purpose of a Floodplain Risk Management Plan is to provide a strategic management plan which best balances social, economic, environmental and cultural interests in the floodplain; optimises the use of community infrastructure; minimises the risk to people, property and emergency response personnel; formalises and prioritises mitigation works; and forms the basis for development controls that will be used to assess future development in the floodplain.
Council has been carrying out studies into flood risks in the Local Government Area (LGA) since the early 1990’s. This has resulted in the creation of Floodplain Risk Management Studies & Plans which have been conducted under the Commonwealth Government’s Natural Disaster Mitigation Programme and the NSW State Government’s Floodplain Management Program in accordance with the NSW Floodplain Development Manual.
To date, Council has investigated the major creeks and waterways in the Local Government Area for flood liability. Identified properties have been encoded with a message on the S149 (2) planning certificate which is for development control. The management studies and plans involve the identification of significant flooding issues and evaluate a range of potential flood mitigation options and strategies to reduce the flood risk. Flood mitigation options may include emergency response measures, land modification, property acquisition, structural works, and planning and development controls.
Studies which were previously undertaken by Council are now being updated to plan for a future sea level rise projection of 0.9m and also for increased rainfall intensities both as a result from Climate Change. This is in line with the State Government’s Climate Change policies and direction that has been based on IPCC and CSIRO projections. Council is responsible for planning for future development in Gosford, and decisions made now may still be on the ground in 50 to 100 years time. This places a duty of care for Council to plan for the future based on the best available information.
In due course, Council will investigate the remaining minor creeks, hazard areas along the coastline and overland flowpaths throughout the Gosford LGA and encode any additional properties identified as being at risk to flooding on their 149 planning certificate.
The formation of a FRM Committee is the first step in undertaking the FRM process. The committee generally includes members drawn from the community who have indicated their interest in the study & plan being undertaken and generally who are associated with local community groups. This is to facilitate a more inclusive collection of data and conveyance of information to the public in their area. The committee also has representatives from social and business groups, Councillors, Council staff, State Government representatives and specialist consultants.
The committee has the enormous task of finding solutions to minimise the full range of flood risks to people and public and private property using the most cost effective measures. Those measures should also adequately address, where possible, issues of local communities being overly reliant on emergency services for flood evacuation.
The committee achieves this by steering the work that needs to be undertaken to produce the Management Plan using the risk management approach outlined in the NSW Floodplain Development Manual 2005.
Download a copy of the Glossary of Terms - Floodplain Risk Management Committee
Note: Some reports have not been published as they contain personal/copyright information however they are available upon request by contacting Customer Services on (02) 4325 8222
Council publishes open access, or mandatory release, information on its website unless there is an overriding public interest against disclosure or to do so would impose an unreasonable additional cost on Council. In respect of the latter, the Council makes the information freely available on its website or in its libraries. However, the study or plan may also be available at cost in either a hard copy or CD at the Council Administration Office.
GIPA Regulation requires that certain documents held by council be made publicly available for inspection, free of charge. The public is entitled to inspect these documents either on Council's Access to Information website or by visiting Gosford City Council, 49 Mann Street Gosford, during Monday to Friday 8:45 am to 5:00 pm. Any current and previous public document may be inspected free of charge. Printed copies can also be obtained, fee and charges will apply.
Copies of documents provided are given for information purposes only and are provided by Council to meet its requirements under relevant legislation. Copyright laws still apply to each document. The copyright-owner’s consent is required if any part of the document is used for any other purpose.
To obtain a printed copy of any document appearing in the List of current Floodplain Risk Management Studies & Plans please contact Council's Customer Service Centre on (02) 4325 8222 to request the information.
A fee will be applied for photocopies of documents. The relevant fees are listed in Council’s adopted Fees and Charges under the heading Flooding and Drainage.