RIVER BASIN REPORT PORTLAND BASIN 13 November 2000 Flood Data Transfer Project Department of Natural Resources and Environment This project has been supported Prepared by: by the 390 St.Kilda Rd. Natural Heritage Melbourne 3004 Ph: (03) 9272-6666 Trust Fax: (03) 9272-6611 DEPARTMENT OF NATURAL RESOURCES AND ENVIRONMENT River Basin Report - Portland Basin DISTRIBUTION RECORD Copy Company/Position Name No. 1 Department of Natural Resources and Environment Ian Gauntlett 2 Project File VV8159.001 3Library VV8159.090 VV8159.090.Rev0 (i) DEPARTMENT OF NATURAL RESOURCES AND ENVIRONMENT River Basin Report - Portland Basin REVISION LIST Revision Revision Description of Approved Date Number Date Revision By Revision Effected A 21/6/2000 Issued for Client Comments D B Sheehan 21/6/2000 0 13/11/00 Issued for General Distribution D B Sheehan 13/11/00 VV8159.090 VV8159.090.Rev0 (ii) DEPARTMENT OF NATURAL RESOURCES AND ENVIRONMENT River Basin Report - Portland Basin DEPARTMENT OF NATURAL RESOURCES AND ENVIRONMENT RIVER BASIN REPORT - PORTLAND BASIN TABLE OF CONTENTS PAGE NO. 1 INTRODUCTION 1 1.1 Objectives, Scope of Works and Deliverables 1 1.2 Areas of Responsibility 2 1.3 Report Contents 4 2 FLOODING CHARACTERISTICS 5 2.1 Available Information 5 2.2 Drainage Characteristics 5 2.3 Extent and Characteristics of Flooding 7 2.4 Impact of Levees and Structures 8 3 CATALOGUING AND MAPPING METHODOLOGY 9 3.1 Overview 9 3.2 GIS Content 9 4 INTERPRETIVE MAPPING 11 4.1 Coverage 11 4.2 Scope and Objectives of the Interpretive Mapping 11 4.3 Information Used 12 4.4 Criteria for Delineation of Floodways and 1% AEP Flood Extents 13 4.5 Basis of Floodway and 1% AEP Flood Extent Delineation 16 5 MAPPING OUTPUT 20 5.1 Hard Copy Mapping 20 5.2 Digital Mapping 21 6 ASSESSMENT OF DATA AND CONCLUSIONS 26 VV8159.090 VV8159.090.Rev0 (iii) DEPARTMENT OF NATURAL RESOURCES AND ENVIRONMENT River Basin Report - Portland Basin 6.1 Assessment of Data and Interpreted Extents 26 6.2 Conclusions 27 7 BIBLIOGRAPHY 29 APPENDIX A MAPPING METHODOLOGY APPENDIX B LIST OF CONTACTS MADE VV8159.090 VV8159.090.Rev0 (iv) DEPARTMENT OF NATURAL RESOURCES AND ENVIRONMENT River Basin Report - Portland Basin 1 INTRODUCTION 1.1 Objectives, Scope of Works and Deliverables The objectives of the digital data transfer project as stated in the Project Brief were: • To produce and deliver high quality, consistent and comprehensive GIS layer and hardcopy map products showing a range of flood data for urban and rural flood plains in Victoria. • To deliver, in hardcopy and digital form, a series of flood information reports based on Municipal and river basin boundaries. • As part of the above, to reorganise the storage of existing flood and related information within FPM (Floodplain Management Group of NRE). There are four major elements of the project: a) Collection and transfer of NRE and other authorities flood information - a data review and management process. b) Recording and analysing the flood information in a Geographical Information System (GIS). c) Reorganisation of the source flood data under a new cataloguing system for re- storing at NRE. d) Preparation of reports and mapping to record a), b) and c). A key output of the flood data transfer project is the formulation of Flood Data Maps which detail all captured data and Flood Planning Maps which provide 1% AEP1 Flood Extent and Floodway delineation. Both the 1% AEP Flood Extent and Floodway mapping are critical input to the flood management and land use control processes being developed by the CMA’s and Local Government. Dialogue with municipalities was a key element of the project. This included soliciting information from them and seeking advice regarding towns to be mapped in detail and the accuracy and presentation of reports and mapping. The Floodway and 1% AEP Flood Extent mapping has only been carried out for locations where information was available and of sufficient quality to justify delineation. Hence, the extent of Floodway and 1% AEP Flood Extent mapping is not a comprehensive coverage of all flood plains or all flooding problem areas. The Flood Data maps provide a record of available past mapping and as such known problem areas. Ã$QQXDOÃ([FHHGDQFHÃ3UREDELOLW\ VV8159.090 VV8159.090.Rev0 1 DEPARTMENT OF NATURAL RESOURCES AND ENVIRONMENT River Basin Report - Portland Basin The project requires delivery of three levels of reporting, namely: • Flood Mapping Reports - are, as stated in the Brief, to provide an easy to use reference source for flood information at the municipal scale in support of planning and other related activities; • River Basin Reports - are, as stated in the Brief, to provide an easy to use reference source for flood information at the river basin scale. The river basin reports will be a major source document on flooding for CMA’s in the delivery of floodplain management services. • A Glenelg Hopkins Catchment Management Report - an aggregate report covering those parts of the three river basin reports within the Glenelg Hopkins CMA operating area. Digital maps in GIS format facilitate access to flood information that can be readily, reviewed, analysed and amended. This Basin Report is for the Portland Basin. 1.2 Areas of Responsibility The area covered by this report is the Portland Basin as shown in Figure 1.1, Locality Plan. Figure 1.1 highlights the following: • Glenelg Hopkins Catchment Management Authority has jurisdiction over the Eumeralla, Moyne and Fitzroy River systems. • part of the Shires of Glenelg, Moyne and Southern Grampians within the Portland Basin. The particular areas of responsibility are summarised in Table 1.1. The river systems covered are all of the Eumeralla, Moyne and Fitzroy River systems, and part of the original Merri River which was diverted through the Merri River Cutting to Lady Bay in Warrnambool. VV8159.090 VV8159.090.Rev0 2 DEPARTMENT OF NATURAL RESOURCES AND ENVIRONMENT River Basin Report - Portland Basin % HAMILTONHAMILTON SHIRESHIRE OFOF SOUTHERNSOUTHERN GRAMPIANSGRAMPIANS 0 10 20 PENSHURSTPENSHURST Kilometres PENSHURSTPENSHURST GG LL EE NN EE LL GG BB AA SS II NN HH OO PP KK II NN SS GLENELGGLENELG HOPKINSHOPKINS CMACMA GLENELGGLENELG HOPKINSHOPKINS CMACMA BB AA SS II NN MACARTHURMACARTHUR PP OO RR TT LL AA NN DD BB AA SS II NN HAWKESDALEHAWKESDALE HEYWOODHEYWOOD SHIRESHIRE OFOF MOYNEMOYNE SHIRESHIRE OFOF GLENELGGLENELG WOOLSTHORPEWOOLSTHORPE PORTLANDPORTLAND PORTPORT FAIRYFAIRY WARRNAMBOOLWARRNAMBOOL L E G E N D CITYCITY OFOF WARRNAMBOOLWARRNAMBOOL River Basin Boundaries Portland Municipal Boundaries CMA Boundaries Basin Study Area Boundary Figure 1.1 – Portland Basin Locality Plan VV8159.090 VV8159.090.Rev0 3 DEPARTMENT OF NATURAL RESOURCES AND ENVIRONMENT River Basin Report - Portland Basin Table 1.1 - Portland Basin Responsibilities Municipality Extent of Responsibility for River and Creeks - Fitzroy River and tributaries Glenelg - Wattle Hill Creek and tributaries - Surrey River and tributaries - Upper reaches of the tributaries of the Eumeralla River Southern Grampians - Upper reaches of the Fitzroy River tributaries (Darlot Creek, etc) - Eumeralla River and tributaries including the Shaw River - Part of the original Merri River which was diverted through Moyne the Merri River Cutting to Lady Bay in Warrnambool. - Moyne River and Tributaries 1.3 Report Contents The following sections of the report cover: Section 2. Flooding Characteristics - based on available information about flooding mechanisms and the effect of works on flooding. Section 3. Mapping Methodology - the data collection and assessment and flood mapping and GIS recording processes are outlined. Section 4. Interpretive Mapping - the basis of floodway and land subject to inundation delineation is presented. Section 5. Mapping Output - a summary of mapping output is presented. Section 6. Assessment and Recommendations - a brief summary of the quality of the mapping is provided and recommendations for extension and improvement of the data coverage. VV8159.090 VV8159.090.Rev0 4 DEPARTMENT OF NATURAL RESOURCES AND ENVIRONMENT River Basin Report - Portland Basin 2 FLOODING CHARACTERISTICS 2.1 Available Information The available information on flooding is in the following categories: • interpretive mapping of 1946 floods on part of the Moyne River in Port Fairy. This mapping was undertaken by the State Rivers and Water Supply Commission using historical flood levels and natural surface contours. • Non-flood aerial photography. • Hydraulic modelling to produce 1% AEP flood long-sections along the Moyne River downstream of Griffith Street Bridge. This work was undertaken by the Rural Water Commission. • A number of reports which have varying degrees of relevance to this project are: − Portland Floodplain Management Study, Rural Water Commission of Victoria and City of Portland, 1988 – this investigation determined 1% AEP flood levels for Fawthrop Lagoon and the extent of flooding along Finn Street Creek and Wattle Hill Creek. It also recommended appropriate strategies for existing and future development of the area. 2.2 Drainage Characteristics The Portland Basin as shown on Figure 2.1 consists of several separate river systems generally flowing in a southerly direction for up to 50km before reaching the coast. Within the basin the major river systems include the Eumeralla, Fitzroy and Moyne River Systems. 2.2.1 Eumeralla River The Eumeralla River rises in the Southern Grampians in the vicinity of Penshurst and flows approximately south west to Codrington. At Codrington the Eumeralla has a catchment