RIVER BASIN REPORT GLENELG 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 - Glenelg Basin DISTRIBUTION RECORD Copy Company/Position Name No. 1 Department of Natural Resources and Environment Ian Gauntlett 2 Project File VV8159.001 3Library VV8159.087 VV8159.087.Rev0 (i) DEPARTMENT OF NATURAL RESOURCES AND ENVIRONMENT River Basin Report - Glenelg Basin REVISION LIST Revision Revision Description of Approved Date Number Date Revision By Revision Effected A 21/6/2000 Issued for Comment D B Sheehan 21/6/2000 0 13/11/00 Issued for General Distribution D B Sheehan 13/11/00 VV8159.087 VV8159.087.Rev0 (ii) DEPARTMENT OF NATURAL RESOURCES AND ENVIRONMENT River Basin Report - Glenelg Basin DEPARTMENT OF NATURAL RESOURCES AND ENVIRONMENT RIVER BASIN REPORT - GLENELG 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 Flood Frequency 7 2.4 Extent and Characteristics of Flooding 8 2.5 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 23 VV8159.087 VV8159.087.Rev0 (iii) DEPARTMENT OF NATURAL RESOURCES AND ENVIRONMENT River Basin Report - Glenelg Basin 6 ASSESSMENT OF DATA AND CONCLUSIONS 24 6.1 Assessment of Data and Interpreted Extents 24 6.2 Conclusions 25 7 BIBLIOGRAPHY 27 APPENDIX A MAPPING METHODOLOGY APPENDIX B LIST OF CONTACTS MADE APPENDIX C FLOOD FREQUENCY INFORMATION VV8159.087 VV8159.087.Rev0 (iv) DEPARTMENT OF NATURAL RESOURCES AND ENVIRONMENT River Basin Report - Glenelg 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 CMAs 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\ VV8159.087 VV8159.087.Rev0 1 DEPARTMENT OF NATURAL RESOURCES AND ENVIRONMENT River Basin Report - Glenelg 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 CMAs 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 River Basin Report is for the Glenelg Basin. 1.2 Areas of Responsibility The area covered by this report is the Glenelg Basin as shown in Figure 1.1, Locality Plan. Figure 1.1 highlights the following: • Glenelg Hopkins Catchment Management Authority has jurisdiction over almost all of the Glenelg Basin including that within the project area. • part or all of the municipalities of Glenelg, Southern Grampians, Ararat, Northern Grampians, Horsham and West Wimmera are within the Glenelg Basin. The particular areas of responsibility are summarised in Table 1.1. The river systems covered are the Glenelg River, the Wannon River, Bryan’s Creek and Grange Burn. VV8159.087 VV8159.087.Rev0 2 DEPARTMENT OF NATURAL RESOURCES AND ENVIRONMENT River Basin Report - Glenelg Basin WW II MM MM EE RR AA WIMMERAWIMMERA CMACMA RURALRURAL CITYCITY BB AA SS II NN MM II LL LL II CC EE NN TT OFOF HORSHAMHORSHAM SHIRESHIRE OFOF MM II LL LL II CC EE NN TT EDENHOPEEDENHOPE SHIRESHIRE OFOF CC OO AA SS TT NORTHERNNORTHERN GRAMPIANSGRAMPIANS BB AA SS II NN GRAMPIANSGRAMPIANS HALLSHALLS GAPGAP SHIRESHIRE OFOF BALMORALBALMORAL WESTWEST WIMMERAWIMMERA BALMORALBALMORAL GLENELGGLENELG HOPKINSHOPKINS CMACMA GG LL EE NN EE LL GG BB AA SS II NN RURALRURAL CITYCITY SHIRESHIRE OFOF OFOF ARARATARARAT CASTERTONCASTERTON CASTERTONCASTERTON SOUTHERNSOUTHERN GRAMPIANSGRAMPIANS COLERAINECOLERAINE SOUTHERNSOUTHERN GRAMPIANSGRAMPIANS DUNKELDDUNKELD HAMILTONHAMILTON SHIRESHIRE OFOF GLENELGGLENELG PENSHURSTPENSHURST HH OO PP KK II NN SS BB AA SS II NN SHIRESHIRE OFOF MOYNEMOYNE NELSONNELSON L E G E N D River Basin Boundaries Glenelg % PP OO RR TT LL AA NN DD Municipal Boundaries BB AA SS II NN CMA Boundaries 0 10 20 Study Area Boundary Basin Kilometres Figure 1.1 – Glenelg Basin Locality Plan VV8159.087 VV8159.087.Rev0 3 DEPARTMENT OF NATURAL RESOURCES AND ENVIRONMENT River Basin Report - Glenelg Basin Table 1.1 - Glenelg Basin Responsibilities Municipality Extent of Responsibility for River and Creeks Glenelg - Lower reaches of the Glenelg and Wannon Rivers Southern - southern bank of the Glenelg River bordering the Grampians municipalities of West Wimmera, Horsham and Northern Grampians - upper reaches of the Wannon River - Bryan’s Creek - Grange Burn West Wimmera - upper reaches of the Glenelg River and tributaries Horsham - northern bank of the Glenelg River immediately downstream of Rocklands Reservoir Northern - northern bank of the Glenelg River within the Grampians Grampians National Park Ararat - uppermost reaches of the Wannon Rivers 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. VV8159.087 VV8159.087.Rev0 4 DEPARTMENT OF NATURAL RESOURCES AND ENVIRONMENT River Basin Report - Glenelg Basin 2 FLOODING CHARACTERISTICS 2.1 Available Information The available information on flooding is in the following categories: • Aerial photos of the August 1981 floods of the Glenelg and Wannon Rivers. • Non-flood aerial photography. • Old and new format planning schemes. • Designated and historic flood levels for the Glenelg River at Casterton. • Old Shire of Glenelg Rural Land Mapping. • Topographic and Geological Mapping. • Sketched 1946 extent of flooding for the Bryan’s Creek at Coleraine • One report which has relevance to this project is: − Lake Hamilton Spillway / Grange Burn Flooding Investigation Second Report City of Hamilton, October 1992 – this investigation determined 1% AEP flood levels for the Grange Burn through the City of Hamilton. 2.2 Drainage Characteristics The Glenelg Basin as shown on Figure 2.1 consists of the Glenelg River and its tributaries, the main one being the Wannon River. Most of the tributaries and the upper section of the Glenelg River run in a WSW direction before joining the Glenelg River which flows south through a gorge section to the ocean. 2.2.1 Glenelg River The Glenelg River starts in the Grampians National Park, passes through the Rockland Reservoir and continues in a westerly direction forming the boundary between the Shire of West Wimmera and the Shire of Southern Grampians until Chetwynd East. From here it starts to flow in a more southerly direction forming the boundary of the Shire of West Wimmera and the Shire of Glenelg briefly near Dergholm.