Warracknabeal and Beulah Flood Study Study Report Report No. J404/R03 Final 1 March 2007 Michael Cawood and Associates Pty Ltd Planning and Environmental Design Price Merrett Consulting AAM Hatch Warracknabeal and Beulah Flood Study Study Report Report No. J404/R03 Final 1 March 2007 ISO 9001:2000 QEC22878 ACN No. 093 377 283 ABN No. 60 093 377 283 Warrackneabeal & Beulah Flood Study DOCUMENT STATUS Issue Revision Date Issued Prepared Reviewed Approved To By By By WCMA – Draft A 8/11/06 Clare Mintern SJD/CMB/SHM SHM SHM (via email as PDF) WCMA – Draft B 28/2/07 Clare Mintern SJD/CMB/SHM SHM SHM (via email as PDF) QFORM-AD-18 REV 5 It is the responsibility of the reader to verify the currency of revision of this report. Copyright Water Technology Pty Ltd has produced this document in accordance with instructions from Wimmera Catchment Management Authority for their use only. The concepts and information contained in this document are the copyright of Wimmera Catchment Management Authority. Use or copying of this document in whole or in part without written permission of Wimmera Catchment Management Authority constitutes an infringement of copyright. Water Technology Pty Ltd does not warrant this document is definitive nor free from error and does not accept liability for any loss caused, or arising from, reliance upon the information provided herein. J404/R03, March 2007, Final 1 Page i Warracknabeal and Beulah Flood Study EXECUTIVE SUMMARY This report details the input data, approach and outcomes for the Warracknabeal and Beulah Flood Study. The Warracknabeal and Beulah Flood Study has been initiated by the Wimmera Catchment Management Catchment Authority (WCMA) in conjunction with the Mallee Catchment Management Catchment Authority (MCMA) and Yarriambiack Shire Council (YSC). The study provides information on flood levels and flood risks within the townships of Warracknabeal and Beulah. The study was funded under the Natural Disaster Risk Management Studies Programme by the Australian and Victorian Governments with a contribution from the Yarriambiack Shire. The study team was lead by Water Technology with sub-consultants, Michael Cawood and Associates, Price Merrett Consulting, MPMedia Solutions, Planning and Environmental Design and AAMHatch. Both townships lie on Yarriambiack Creek, a distributary of the Wimmera River. The creek extends from an offtake from the Wimmera River near Longerenong and flows north for approximately 135 km, terminating at Lake Corrong, near Hopetoun. The townships have been subject to flooding on a number of occasions including 1909, 1923, 1955, 1956, 1960, 1964, 1974, 1975, 1981, and 1983. A hydrologic analysis of Yarriambiack Creek determined design flood hydrographs for the 10, 20, 50, 100 and 200 year flood events at both Warracknabeal and Beulah. Considerable uncertainty surrounds the design flood estimates developed by this study. Rigorous calibration and/or validation of the approach was restricted by the absence of streamflow data. The absolute reliability of design estimates is unknown, however, the relativity of design estimates is considered reasonable. Table 1 displays the design peak flows at both Warracknabeal and Beulah. Table - 1 Design peak flows at Warracknabeal and Beulah Design peak flow (m3/s) Location 1 in 5 1 in 10 1 in 20 1 in 50 1 in 100 1 in 200 year year year year year year Yarriambiack Creek at 13.3 14.6 20.7 31.3 41.4 43.7 Warracknabeal Yarriambiack Creek at 9.2 10.1 13.7 21.9 29.8 31.9 Beulah Digital terrain models were developed from field and aerial survey. Using the digital terrain models, hydraulic models were established to simulate flood behaviour within the study areas. Flood behaviour was assessed for flooding originating from Yarriambiack Creek and local stormwater runoff. The hydraulic models revealed that the weir structures in both Warracknabeal and Beulah (upstream and downstream) have a key influence on flood behaviour. For Yarriambiack Creek floods, the flood extents are generally limited to creek corridor in Warracknabeal. A significant breakaway from Yarriambiack Creek, occurs for a 20 year flood event and greater, to the south of Beulah across the Henty Highway and under the Hopetoun Railway. This breakaway results in extensive inundation of agricultural land to J404/R03, March 2007, Final 1 Page ii Warracknabeal and Beulah Flood Study the east of the Henty Highway. Limited Yarriambiack Creek flooding occurs in the township of Beulah. Local stormwater runoff in Warracknabeal leads to considerable ponding adjacent to the Warracknebeal Railway Station. Some minor stormwater ponding occurs in Beulah for the area bounded Bell, Phillips, Gladstone and Dingwell Streets. Average annual flood damages for Warracknabeal and Beulah were estimated at $41,000 and $9,600 respectively. For the I in 100 year Yarriambiack Creek flood event, the following buildings were affected: o Warracknabeal : 79 above floor and 279 below floors (Total 358) o Beulah : 2 above floor and 50 below floor (Total 52) Two structural mitigation options, consisting of improvements to the weir capacity, were assessed in Warracknebeal. For Beulah, four structural mitigation options were assessed. Three of the mitigation options for Beulah considered increases in the flow capacity of the upstream and downstream weirs, with the fourth option closing the railway culvert to south of the township. The above structural mitigation options investigated were considered by the study team not to warranted further investigation. This is due to the limited reduction in flood levels and extents achieved, and the adverse flood related impacts due to flow re-direction. Impacts due to stormwater related flooding in Beulah could be mitigated by improvements to drainage under Bell Street. For Warracknabeal, stormwater drainage improvements adjacent to the Warracknabeal Railway Station could less the stormwater related flooding impacts . A draft planning scheme amendment has been prepared to reflect the study outcomes. The study team recommends that the Yarriambiack Shire Council adopt all aspects of the draft planning scheme amendment. Further, the study team recommends that Wimmera CMA provide the appropriate assistance to Yarriambiack Shire to enable the timely adoption of the planning scheme amendment. The Wimmera Catchment Management Authority, in conjunction with local authorities in the Wimmera River Catchment, including Yarriambiack Shire, is undertaking a project to enhance the total flood warning system for the Wimmera Catchment. The study team recommends that the Yarriambiack Shire Council and the Wimmera Catchment Management Authority continue to actively pursue the completion of the current flood warning related project. A Flood Sub-plan draft planning scheme amendment has been prepared to reflect the study outcomes. The study team recommends that the Yarriambiack Shire Council adopt all aspects of the revised Flood Sub-plan as an integral part of the Yarriambiack MEMP. This includes measures aimed at ‘keeping the Plan alive’ and relevant to the community. For both Warracknabeal and Beulah, the operation of the weirs has a significant influence on local flood behaviour. The study team recommends that the Yarriambiack Shire and the Wimmera CMA develop formal operating procedures for the Warracknabeal Weir and the Beulah Upstream and downstream Weirs. The adopted operating procedures be incorporated into Flood Sub-plan as an integral part of the Yarriambiack MEMP. J404/R03, March 2007, Final 1 Page iii Warracknabeal and Beulah Flood Study TABLE OF CONTENTS Executive Summary...................................................................................................... ii 1 Introduction ........................................................................................................... 1 2 Study background.................................................................................................. 3 3 Available information............................................................................................ 4 3.1 Previous studies.........................................................................................................................4 3.1.1 Wimmera River Basin URBS Model (BoM 2004)..........................................................4 3.1.2 Assessment of the impact of priority structures on natural flow regimes and flooding in Yarriambiack Creek (Parts 1 and 2) (SMEC 2002) ................................................4 3.1.3 Yarriambiack Creek Flood Investigation Study (WBM 2003) ....................................6 3.1.4 Yarriambiack Creek Management Plan (KBR 2004).....................................................7 3.1.5 River Basin Report - Wimmera River - DNRE Flood Data Transfer Project (SKM 2000)..........................................................................................................................................7 3.1.6 Ecological Associates and Fluvial Systems – Environmental Water Requirements of Lake Corrong and Lake Lascelles for Mallee CMA (2006)..................................................7 3.2 Hydrologic data .........................................................................................................................8 3.2.1 Streamflow data....................................................................................................................8 3.2.2 Rainfall data............................................................................................................................9