EUMUNGERIE FLOOD STUDY

The information below is a summary of the Eumungerie Flood Study. The study is a joint undertaking by Dubbo Regional Council, WRM Water & Environment, and Department of Planning, Industry, and Environment

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 Eumungerie. 

Where to get a copy of the Plan

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

DOWNLOAD REPORT (PDF 8.6MB)

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 Eumungerie Flood Study, which is on public exhibition from Monday, January 13, 2020 until Friday, March 13, 2020.

Community Drop in Sessions will be held in Eumungerie (date TBC). Further information will be sent out when these have been organised.

Submissions

Please submit your comments in writing by 5pm, Friday March 13, 2020. Submissions should be addressed to the Chief Executive Officer and titled “Eumungerie 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 Eumungerie 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 WRM Water Pty Ltd to prepare the Eumungerie Flood Study.

The primary objectives of this phase of the study are to:

  • Determine the flood behaviour including design flood levels over the full range of flood events up to and including the Probable Maximum Flood (PMF) from Drillwarrina and Coolbaggie creeks and the local stormwater catchments;
  • Provide hydrological and hydraulic models that can establish the effects on flood behaviour of future development;
  • Assess the sensitivity of flood behaviour to potential climate change effects such as increases in rainfall intensities; and
  • Assess the provisional hydraulic categories for future flood planning.

Subsequent phases of the study will investigate potential structural and non-structural (planning measures) options to mitigate the existing, continuing, and future flood risks.

The overall aim of the study is to improve the flood resilience of the Eumungerie community

Flood Planning Process

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

Flood risk management process

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.

The hydrologic model developed for this study used XP-RAFTS software to estimate design flood discharges in the study area. The hydraulic model development used TUFLOW software to simulate the movement of floodwaters across the floodplain.

Historical water level and rainfall data at Eumungerie to calibrate the computer models is limited to anecdotal data available for the January 1993 event. Data from this event was obtained from a community questionnaire and from a previous flood investigation of Eumungerie by PPK Consultants (1995).

The 1993 flood occurred because of a severe 60-minute storm that inundated many of the homes in Eumungerie, and is the largest known flood. Additional data obtained from a stream gauge located on Coolbaggie Creek (GS421055 - Rawsonville) about 25 km downstream of Eumungerie was used to validate the flood models.

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

XP-Rafts predicted a peak discharge of 236 m3/s and a time to peak of approximately 3 hours was predicted, which is consistent with the Eumungerie Flood Study (PPK, 1995).

The XP-RAFTS predicted hydrograph to the recorded discharge hydrograph at Coolbaggie Creek gauge at Rawsonville achieved a relatively good agreement for the time to peak. However, the predicted peak discharge is substantially higher than the recorded value.  Notwithstanding, the model adequately represented the behaviour of the 1993 event at Eumungerie and represents the timing of the flood peak at the gauge.

The TUFLOW model was able to predict peak water levels at each surveyed flood mark within ±0.2 m. With respect to the additional anecdotal information collected in the study, the model was able to adequately represent the anecdotal flood behaviour of the January 1993 event in Eumungerie.

Design Flood Simulations

Predicted flood extents, depths and flood contours for the eight design events are shown in Appendix B.

Last Edited: 07 Jan 2020

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