Submission No.51 Received 21 December
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PAT CONDINA & ASSOCIATES Consultants in waterway, wetland and lake management, Water quality monitoring and assessment, Community consultation and education Overview of Flood Drainage Capacity of the Dalmore Road Drain with reference to Drains in the Koo Wee Rup Longwarry Flood Protection District Report prepared for Landowners in the Dalmore locality August 2012 Aspromonte Enviro Pty Ltd (ABN 31 074 579 936), Trading as Pat Condina & Associates Director - Pat Condina, M. Env. Sc., Grad. Dip. Water Sc., Dip. App. Chem. 17 Olive Rd., Devon Meadows, Victoria 3977 Telephone & Fax. 03 5998 2034 Email: [email protected] Drainage Capacity of Dalmore Road Drain and KLFPD Drains TABLE OF CONTENTS Executive Summary ........................................................................................................................ 3 1. Introduction and Scope of Study .............................................................................................. 6 2. The Catchment and KLFPD Background ................................................................................... 7 2.1 The Westernport Catchment .................................................................................................. 7 2.2 The Koo Wee Rup District and the Great Swamp ................................................................. 8 2.3 Drainage in the Koo Wee Rup District ................................................................................ 10 2.3.1 Brief History of Drainage .............................................................................................. 10 2.3.2 Significant Flow Events in the District.......................................................................... 12 2.3.3 Flood Risk and Flood Protection ................................................................................... 16 2.3.4 Carrier Drains, Precept Drains and District Drainage Charges ..................................... 17 2.3.5 Maintenance of Carrier Drains and Precept Drains ....................................................... 19 2.3.6 Drainage impact of Upstream Development ................................................................. 20 3 The Dalmore Road Drain Catchment ......................................................................................... 22 3.1 Drainage area and land uses ................................................................................................. 22 4. Capacity and Condition of Dalmore Road Drain ...................................................................... 24 4.1 Factors Effecting Theoretical Flow Capacity ...................................................................... 24 4.2 Dalmore Road Drain Surveys .............................................................................................. 25 4.3 The Floodgates on Dalmore Road Drain ............................................................................. 28 4.4 Possible Sources of Drain Sediment .................................................................................... 29 5. Observation Following June 2012 Storm Event ....................................................................... 31 5.1 Dalmore Road Drain Condition and Levels ......................................................................... 32 5.2 The Diversion to Cardinia Catch Drain ............................................................................... 34 6 Potential Strategies to Improve Drainage ................................................................................... 38 6.1 Drainage Improvements by Landowners. ......................................................................... 38 6.2 Drainage Improvements by Councils. .............................................................................. 38 6.3 Drainage Improvements by Melbourne Water .................................................................. 38 6.3.1 Improve Drainage Capacity of Dalmore Road Drain and other Precept Drains ........... 38 6.3.2 Prepare 5 year plans for Carrier Drain and Precept Drain Maintenance ....................... 39 6.4 Clarification of Regulatory Restrictions .............................................................................. 39 6.5 Summary of Problems and Potential Responses .................................................................. 41 REFERENCES .............................................................................................................................. 43 APPENDICES ............................................................................................................................... 44 Appendix 1 Monthly Rainfalls ................................................................................................... 44 Appendix 2 Melbourne Water Community Newsletter ............................................................ 47 Pat Condina & Associates August 2012 2 Drainage Capacity of Dalmore Road Drain and KLFPD Drains Executive Summary Scope of Study This Report was commissioned by Landowners in the Dalmore Road Drain catchment who were adversely affected in the February 2011 and June 2012 floods, and by earlier flood events. The Landowners have contended for many years that, if proper maintenance and infrastructure is in place, the Dalmore Road Drain would service its catchment. This Report supports the Landowner’s contention with reference to data and the author’s physical observations. While partly technical, the Report aims to increase Landowner understanding of the drainage system in their locality, measures to improve that system, the risk of flooding, and how such risk could be managed. It also aims to: • Document observations of flow and condition in the Dalmore Road Drain during the June 2012 flood; • Identify potential mitigation measures for Melbourne Water’s consideration and assessment, to improve the drainage characteristics of the Dalmore Road Drain and other drains, and • Provide an overview of drainage in the Kooweerup Longwarry Flood Protection District (“KLFPD”) with reference to level of protection, flood drainage capacity and other challenges in both “Carrier” drains and “special Precept” drains. The Westernport Catchment and District Background The KLFPD covers an area of approximately 420 km2, and is totally within the wider 2980 km2 catchment draining to Westernport Bay. It is one of the most important food production areas in the state. The 40,000 hectare Kooweerup Swamp was drained in the late 1800’s to early 1900’s, by construction of over 500 km of major and minor channels to convey stream flows from the upstream catchment, and local runoff through the Swamp, to Westernport Bay. The draining and clearing of the Kooweerup Swamp was the largest swamp reclamation scheme undertaken in Victoria and resulted in major hydrological changes, accompanied by equally significant changes in the generation, transport and export of stormwater pollutants to Western Port Bay. The extraordinary flood of 30 November/1 December 1934 resulted in flows never seen before or since with great loss of property and stock. The subsequent Royal Commission noted the deficiencies in the drainage system and recommended that substantial improvements be made. The completion of the spillway at Cora Lynn in 1962 to divert floodwater into the Yallock outfall and so protect the township of Koo Wee Rup was the last major work to take place in the KLFPD until the Main Drain rehabilitation works in 2001. Pat Condina & Associates August 2012 3 Drainage Capacity of Dalmore Road Drain and KLFPD Drains The key issue for the continuing sustainability of the KLFPD is the level of flood protection provided, and the level of drain maintenance to achieve required protection. While residents and farmers may be accepting of losses from major flood events every 30, 50 or 100 years they will not be accepting of losses every 10 or 15 years. Loss of crops is not just related to size of the flood, it is probably even more dependent on duration of high levels in drains for long periods after rainfall ceases, as this prevents effective drainage of surrounding land. In recent years District landowners have expressed concern over perceived lack of adequate maintenance on Carrier and Precept drains and the consequent increased risk of overtopping, longer periods of land inundation, and crop losses. Landowners in the KLFPD pay a special “Precept” rate rather than the normal Metropolitan waterways and drainage rate. The Precept rate is to cover flood mitigation and maintenance services carried out by Melbourne Water on the extensive network of drains and channels within the District. In 2009/10, $980,907 was collected from 3544 properties within the District boundaries. The District is subject to external influences which may impact on the overall flood risk. This includes sea level rise and increased stormwater flows from the expansion of the urban growth areas to the north in the Shire of Pakenham and the City of Casey. The Dalmore Road Drain in the June 2012 flood event The Dalmore Drain catchment comprises a drainage area of 1075 hectares from Cardinia Road north of Cardinia to the outlet at Westernport Bay. By reference to site observations and past surveys this Report concludes that drain flow capacity has been diminished by sedimentation and the growth of bed and bank vegetation. The recent 21/22 June 2012 storm event highlighted the inability of the Dalmore Road Drain to effectively drain its contributing catchment within a reasonable period of time to ensure that pastures