Inner West Council

Where is Ashfield Council up to in terms of Floodplain Management of Hawthorne and Dobroyd Canal Catchments?

Under the NSW Government Flood Prone Land Policy, Councils are required to identify and manage flood prone areas within their local government area. A Flood Study using computer models that estimate design flood levels was completed in 2014 for both Hawthorne and Dobroyd Canal Catchments.

The Flood Study constitutes the second stage of the Floodplain Risk Management process for the catchment and has been prepared for Ashfield Council, with the financial assistance of the Office of Environment and Heritage, to define flood behaviour under current conditions.

The purpose of the study was to define flood behaviour on both these catchments in terms of water levels, flows and velocities for a range of floods including the 1 in 100 year event.

The Floodplain Risk Management Study and Plan are the next stages in Floodplain Management process to ensure that future development of flood affected areas is carried out using procedures which recognise the nature of flooding and ascertain that the risk to present and future residents and consequent flood damages to properties are not increased.

As such, The Floodplain Risk Management Study will use the data from the Flood Study to determine the magnitude of flood risk issues in the catchment and the building floor levels that may be affected by flooding and examining the ways to reduce the flood damages.

What is the Floodplain Risk Management process:

The management process for implementing the Government’s Flood Policy involves four sequential stages.

These stages are:

I. Data Collection

- Gathering of historical flood data

- Resident flood survey

II. Preparation of a Flood Study

- Determines the nature and extent of the flooding problem.

- Provides data defining peak water levels, velocities and discharges for floods of varying severity.

- Establish a flood planning level

- Involves the inclusion of flood related planning controls within local  environmental plans and development control plans to ensure new development is compatible with the flood hazard.

III. Preparation of a Floodplain Risk Management Study

- Evaluates management strategies for the floodplain in terms of both existing and proposed development.

- Establishes and recommends an emergency response protocols.

IV. Development of a Floodplain Risk Management Plan

- Involves formal adoption by Council of a plan of flood risk management for the floodplain.

 V. Implementation of the Plan

- Involves identification of funding needs and preparation of a potential construction program.

- Involves construction of measures to reduce flood damages and protect existing development.

- Involves the review of existing flood related planning controls within local  environmental plans and development control plans to ensure new development is compatible with the flood hazard.

- Use of the Plan to identify and assess potential development areas.


Why Floodplain Risk Management?

Substantial parts of the Inner West, including the Ashfield Local Government Area, were originally developed prior to modern day drainage engineering practices or flood estimating capabilities. During the past few decades, trends towards continued urbanisation have caused increased impervious areas. This has in turn caused the increase in the volume and velocity of overland flow resulting in flooding downstream of the catchment areas in larger storms. Moreover, climate change also plays a role in flooding considerations and has to be recognised in the community and in design considerations.

The NSW Government has tried to address this problem by releasing a Flood Prone Land Policy, aimed at reducing the impact of flooding and flood liability on individual owners and occupiers of flood prone properties and to reduce private and public losses resulting from floods. The Policy is also directed at ensuring that future development is compatible with the flood hazard and does not create flooding problems in other areas. It highlights that primary responsibility for Floodplain Risk Management rests with Councils.

Accordingly, Council engaged consultants to complete flood studies on two trunk drainage systems located in Council’s Local Government Area; the Hawthorne Canal and Dobroyd Canal trunk drainage systems. These studies were undertaken on a catchment wide basis to assist Council to identify any flood hazards within these catchment areas.

Council adopted the final flood study reports in May 2015, so the next stage in the Floodplain Risk Management Process will be the preparation of a Floodplain Risk Management Study and Plan. The Floodplain Risk Management Study and Plan will identify and recommend flood mitigation options to manage flood risk including a review of the interim flood related development controls. This stage is expected to take approximately two to three years to complete.


Related Documents

To see the Dobroyd Canal Flood Study Final Draft Report click here

To see the Hawthorne Canal Flood Study Final Draft Report click here

To see Frequently asked questions concerning the flood studies click  here

(a) a flood storage area, (flood hydraulic categories map)

(b) a floodway area, (flood hydraulic categories map)

(c) a flow path, (flood extents map)

(d) a high hazard area, (provisional flood hazard categories map)

(e) a high risk area. (provisional flood hazard categories map)