Health of the Catchment Report 2002

Health of the Catchment Report 2002 CONTENTS SECTION 1 INTRODUCTION 4 SECTION 2 REGIONAL GEOMORPHOLOGY 4 SECTION 3 CLIMATE OF THE GLENELG HOPKINS BASIN 5 SECTION 4 SOILS 9 4.1 Soils of the Glenelg Hopkins Region 9 4.2 Land Use in the Glenelg Hopkins Region 9 4.3 Land Capability 9 4.4 Land Degradation 16 4.5 Water Erosion 16 4.6 Gully and Tunnel Erosion 16 4.7 Sheet and Rill Erosion 16 4.8 Mass Movement 17 4.9 Streambank Erosion 17 4.10 Wind Erosion 18 4.11 Soil Structure Decline 18 4.12 Coastal Erosion 18 4.13 Soil Acidity 18 SECTION 5 WATERWAYS WITHIN THE HOPKINS DRAINAGE BASIN 25 5.1 Hopkins River and its Tributaries 26 5.2 Condition of the Hopkins River and its Tributaries 26 5.3 Merri River and its Tributaries 27 5.4 Condition of the Merri River and its Tributaries 27 SECTION 6 WATERWAYS WITHIN THE GLENELG DRAINAGE BASIN 27 6.1 Glenelg River and its tributaries 27 6.2 Condition of the Glenelg River and its tributaries 28 SECTION 7 WATERWAYS WITHIN THE PORTLAND DRAINAGE BASIN 29 7.1 Condition of the Portland Coast Basin Rivers 29 SECTION 8 RIPARIAN VEGETATION CONDITION IN THE GLENELG HOPKINS REGION 30 SECTION 9 GROUNDWATER AND SALINITY 31 SECTION 10 WETLANDS WITHIN THE GLENELG HOPKINS CATCHMENT 37 10.1 Descriptions of Wetlands and Lakes in the Glenelg Hopkins Region 37 10.2 Lake Linlithgow Wetlands 37 10.3 Lake Bookaar 38 10.4 Glenelg Estuary 39 10.5 Long Swamp 39 10.6 Lindsay-Werrikoo Wetlands 39 10.7 Mundi-Selkirk Wetlands 40 10.8 Lower Merri River Wetlands 41 10.9 Tower Hill 41 10.10 Yambuk Wetlands 42 10.11 Lake Muirhead 42 10.12 Mount William Swamp 42 10.13 Lake Bolac 43 10.14 Lake Burrumbeet 43 10.15 Bryan’s Swamp 43 10.16 Myuna Lane Swamp 43 10.17 Chinaman’s Swamp 43 10.18 Lake Buninjon 44 10.19 Nerrin Nerrin Swamp 44 SECTION 11 SURFACE WATER SALINITY EFFECTS IN THE GLENELG HOPKINS BASIN 44 SECTION 12 NUTRIENT ENRICHMENT IN THE GLENELG HOPKINS BASIN 46 SECTION 13 CONDITION OF THE BIODIVERSITY IN THE GLENELG HOPKINS REGION 47 13.1 Biodiversity Condition of the Major Bioregions within the Glenelg Hopkins Catchment 49 13.2 Glenelg Plain Bioregion 49 13.3 Victorian Volcanic Plain Bioregion 50 13.4 Dundas Tablelands Bioregion 51 13.5 Greater Grampians Bioregion 51 13.6 Warrnambool Plain Bioregion 52 SECTION 14 CONDITION OF PARKS WITHIN THE GLENELG HOPKINS CATCHMENT 53 14.1 Bay of Islands Coastal Park 53 14.2 Cape Nelson State Park 53 14.3 Dergholm State Park 53 14.4 Discovery Bay Coastal Park 54 14.5 Grampians National Park 54 14.6 Lower Glenelg National Park 55 14.7 Mount Eccles National Park 56 14.8 Mount Napier State Park 56 14.9 Mount Richmond National Park 57 14.10 Crawford River Regional Park 57 14.11 Tower Hill State Game Reserve 57 SECTION 15 PEST PLANTS IN THE GLENELG HOPKINS REGION 59 SECTION 16 PEST ANIMALS IN THE GLENELG HOPKINS REGION 64 References 66 2 Figure 1 The Glenelg Hopkins Region SECTION 1 INTRODUCTION The Glenelg Hopkins region lies to the south of the Great Dividing Range in south-west Victoria and covers 2,660,780 hectares (ha). The boundaries of Glenelg Hopkins Catchment Management Authority (GHCMA) extend from Ballarat in the east, to the South Australian border in the west, and from the southern coast of Victoria to the townships of Edenhope and Ararat in the north1. The region includes the cities and townships of Hamilton, Warrnambool, Ararat, Ballarat, Casterton, Coleraine, Port Fairy, Beaufort and Portland. Figure 1 shows the area covered by the GHCMA. SECTION 2 REGIONAL GEOMORPHOLOGY In broad physiographic terms the Glenelg Hopkins region lies at the foot of the Great Diving Range of Eastern Australia. Compared to the highlands further east, the local range has diminished to a low subdued watershed, punctuated only by several remnant-striking landforms such as the Grampians Ranges2. The divide finally culminates as the low undulating upland of the Dundas Tablelands, west of which the landscape flattens into extensive aeolian and alluvial deposits3. Otherwise the Glenelg Hopkins region is dominated by generally flat volcanic plains that extend to the coast. Significant upland relief is provided by the north-south strike ridges of the Grampians Ranges, steep sided granitic monoliths of Mt Cole, Mt Buangor and Mt Langhi Ghiran, and the weathered sedimentary slopes of the divide north of Beaufort4. Moderate relief is provided by the gentle and steeply dissected plateaux of the Dundas and Merino tablelands. The Dundas Tablelands marked the shores of the Murray inland sea in the Late Tertiary period5. Two identifiable periods of vulcanism have occurred. During these periods extensive volcanic deposits were laid down over much of western Victoria. Extensive olivine basalt flows (referred to as ‘newer volcanics’) erupted from volcanos (some 400 existed at various times), fissures and vents6. Flows from Mt. Rouse east of Penshurst extended more than 60km. Eruptions mostly occurred two to four million years ago, although it is estimated that the youngest volcanic activity occurred at Mt. Napier south of Hamilton, some 7,000 years ago7. During volcanic periods, extensive lakes developed when lave flows blocked regional drainage and hundreds of lakes were formed by slumping lava crust. The plains resulting from volcanic activity are mostly flat, to gently undulating. However, major streams such as the Hopkins River and Mt. Emu Creek cut through the basalt rocks creating U-shaped valleys8. Deposits from later periods of vulcanism consist of scoria cones such as Mt. Napier and Mt. Eccles, maars (now crater lakes) and stony rise basalts9. Scoria cones were active in the southern areas due to interactions between shallow groundwater and magma10. The isolated scoria cones, such as Mt. Shadwell, arising from the second phase of volcanic activity are often steep-sided and reach elevations up to 200m above the surrounding plain11. There were about 40 maar type volcanoes between Colac and Port Fairy12. These volcanoes have very large craters of up to 2km across which are often filled with lakes as in the case of Tower Hill. They were formed as a result of explosive eruptions and resulted in deposition of volcanic ash and some limestone from underlying deposits for several hundred kilometers. The Dundas and Merino Tablelands are dominant features in the north-west of the region. These elevated plains are underlain by a variety of basement rocks13. The Dundas Tablelands are undulating to rolling hills dissected in places by deep V-shaped valleys. The eastern Dundas Tablelands are dissected by shallower U-shaped valleys. The Merino Tablelands are heavily dissected and little remains of the original plateau surface. In the far west of the region, plains comprising unconsolidated fine or coarse textured sediments have developed14. Dune complexes occur along the coast, often extending several kilometers inland. The southern half of the Grampians extends into the north of the Glenelg Hopkins region. Moderate to steep sedimentary hills occur along the north-eastern margin of the Glenelg region. Granite outcroppings occur among these hills, east and south of Ararat. Gentle to moderate sedimentary hills also occur in the central part of the region between Hamilton and Lake Bolac15. Most of the Glenelg Hopkins region is covered in basalt landforms. These landforms range from young stony rise flows and older weathered stony barriers, to Late Tertiary period lava plains with greater or lesser elevation and dissection depending upon age. Drainage across the basalt plains is mainly provided by the south flowing Hopkins River and Mt. Emu Creek. This is complimented by the Glenelg and Wannon river systems that receive tributary drainage and snake around either side of 4 the Dundas Tablelands and Grampians Ranges. Drainage is frequently poor and internal resulting in the formation of many lakes and wetlands. Poor and ill-defined drainage in landscapes of low relief which lead to terminal discharge into depressions is characteristic of parts of the basalt plains, northern alluvial districts (east of the Grampians), and in the dune swales of the far west. The most prominent of these lake or swamp systems are at Willaura, Woorndoo-Lake Bolac, east of Hamilton and south of Dorodong. During the Quaternary geological period extending from 1.6 million years ago to the present, a number of ice ages occurred which resulted in fluctuating sea level changes16. At the peaks of the ice ages, sea levels were significantly lower than present and rivers flowed across what is now the continental shelf to a coastline located south-west of the present one17. In interglacial periods the sea level rose to present day levels. During the most recent glacial period the icecap reached its maximum extent about 17,000 to 20,000 years ago18. During this time the sea level along the Victorian coast was some 120m below present day levels19. When sea levels retreated, carbonate rich sediments were exposed and provided the source material for calcareous coastal dunes. During the glacial period arid conditions prevailed and windblown silt and clay deposits were deposited in many areas20. A feature of the Glenelg Hopkins landscape is the remnants of lateritic type weathering that occurred in the Late Tertiary period. This occurred during a warmer climate that produced deep weathered profiles often with iron enrichment in the near surface21. Such profiles are observed extensively across the Dundas Tablelands and other exposed Palaeozoic surfaces such as the Merino Tablelands and Stavely Hills. Deep weathered profiles have also developed over the earliest of the Late Tertiary basalt extrusions22.

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