GEURIE FLOOD STUDY

The information below is a summary of the New/Updated Geurie Flood Study. The study is a joint undertaking by Dubbo Regional Council, HydroSpatial Pty Ltd and Department of Planning, Industry, and Environment

Council at its Ordinary Meeting on Monday 9 December 2019 considered a report on the Geurie Flood Study and endorsed the draft study for public exhibition. The study provides the information, and analysis of the existing flood risks. Flood modelling tools were developed that can be used by Council for decision-making about land-use planning, and future studies to access the effectiveness of potential measures to reduce flood risk.

Council is seeking feedback from the community to further inform flood risks within Geurie. 

Where to get a copy of the Plan

The Study is available to view and download on the link below:

DOWNLOAD VOLUME 1 (PDF 9.1MB)

DOWNLOAD VOLUME 2 (PDF 60.1MB)

Hard copies to view are also available at Dubbo and Wellington Civic Administration Buildings.

Have Your Say

Council invites you to have your say on the Geurie Flood Study, which is on public exhibition from Monday, January 13, 2020 until Friday, March 13, 2020.

Community Drop in Sessions will be held on Thursday 5 March, from 8.30am to 5pm, at Geurie General Store (47 Buckenbah Street, Geurie).

Submissions

Please submit your comments in writing by 5pm, Friday March 13, 2020. Submissions should be addressed to the Chief Executive Officer and titled “Geurie Flood Study – Public Exhibition Comment.”

You can lodge submissions by:

Email: council@dubbo.nsw.gov.au

Mail:  Dubbo Regional Council, PO Box 81, Dubbo NSW 2830

In person: Dubbo Civic Administration Building or Wellington Civic Administration Building

What happens next?

Feedback on the Geurie Flood Study Draft Report will be reported and appropriately incorporated into the final draft submitted to Council for endorsement. Once endorsed, development of the Floodplain Risk Management Study and Plan will commence.

Further information

Please contact Council’s Manager Infrastructure Strategy and Design, Stephen Howlett via email in.admin@dubbo.nsw.gov.au if you have any questions or require further information.


Background

The NSW State Government, through the Department of Planning, Industry, and Environment (DPIE), oversee the Floodplain Management Program. The program provides support to local councils in the implementation of the NSW Government’s Flood Prone Land Policy as outlined in the NSW Government’s Floodplain Development Manual.  The primary objective of the policy and manual is to reduce the impacts of flooding and flood liability on individual owners and occupiers.

As part of this program, Dubbo Regional Council, with the support of the NSW OEH, has commissioned HydroSpatial Pty Ltd to prepare the following Geurie Flood Study.

Dubbo Regional Council has a history of undertaking investigations and publishing mainstream flood data. These prior studies were undertaken in accordance with the then current best practice.

Flood Planning Process

The Flood Plain Risk Management Process as prescribed by the NSW Government is shown below.

Flood risk management process by NSW Governmement

More information about each stage can be found in the NSW Floodplain Development Manual, available here - https://www.environment.nsw.gov.au/-/media/OEH/Corporate-Site/Documents/Water/Floodplains/floodplain-development-manual.pdf

The Flood Study

This Flood Study consists of a data collection phase, hydrologic model development, hydraulic model development, historical flood simulations and design flood simulations. A data collection process was carried out to gather flood-related information that is used to inform the model development process. The hydrologic model development was carried out to calculate the runoff hydrographs as a function of the catchment conditions and the rainfall hyetographs.

The hydrologic model developed for this study used the Watershed Bounded Network Model (WBNM) software. The hydraulic model development was undertaken to estimate the flood levels, depths, velocities and extents generated from the catchment conditions and the runoff hydrographs. The hydraulic model developed for this study used the TUFLOW software.

Due to the scarcity of data, the 1999 historical event was modelled to verify the models and an extensive sensitivity analysis was undertaken. Following this, the design flood simulations were carried out to determine the flood behaviour across the study area through a range of statistically based rainfall events. These events ranged from the 20% AEP event to the 0.2% AEP event and the PMF event.

Key Results

Historic Flood Simulations

Due  to  the  scarcity  of  data,  a  full  model  calibration  and  validation  process  could  not  be undertaken for the study area. To compensate for this, a model verification process and extensive sensitivity analysis was undertaken.

The model verification process involved hydrologic and hydraulic modelling of the October

1999 event,  based  upon  the  community  consultation  process  undertaken  in  the previous flood study that described 1999 as the last  period of known flooding.

The  peak  flood  depth  was  found  to  be  less  than  0.15 m  across  the  majority  of  the  Geurie township  area, which was  considered  to  approximately  verify  the  hydraulic model.

Design Flood Simulations

Refer to Volume 2 of the report for detailed results.

Last Edited: 12 Feb 2020

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