Representative Rivers of Victoria – Discussion Paper Representative rivers of Victoria: Selection of regions – A Discussion Paper Report prepared for the Department of Natural Resources and Environment By Tim Doeg August 2001 Introduction As part of the River Health Strategy, it has been decided to select a series of rivers across the state of Victoria that “represent” typical examples of the different landform, flow regime and biology of rivers that occur in the State. To select the set of representative rivers, a regionalisation of the major characteristics of rivers and streams is required. Then, a particular river can be selected within each region that best typifies the region. In its special investigation into rivers and streams, the LCC (1991) suggested representative rivers for 16 different river type catchments, based on geomorphic units and hydrological regions. In that study, a representative river "typifies its river catchment type, and forms part of a set characterising the geomorphic units in catchments and hydrological regions of rivers across Victoria.” (p. 107). One condition placed on the selection of representative rivers was that “… wherever possible the one selected should be in a relatively natural condition, and the least degraded or altered of its type.” (p. 107). However, not all rivers in the state were included as candidates for representative river status, with restrictions based on length of hydrological record (ungauged catchments were not included). The LCC study did not include biological information in the selection of the regions. As “River Health” is ultimately tied to biological health, it is preferable that biological information be included in the selection of representative rivers. While it is assumed that the geomorphic and hydrological characteristics of a river has an important influence on the biology of the system, this is not always the correct conclusion (e.g. there is a fundamental north-south division in fish fauna that has nothing to do with hydrologic characteristics, or local geology). This report discusses a broad regionalisation of Victorian rivers based on including biological data into the usual geomorphic and hydrological data. From there, representative rivers can be selected that have biological meaning as well. Method Data were obtained for 6 different potential characteristics that influence or are the product of riverine aquatic habitats in Victoria (sources of data are described in the next section). These were: • Landform; • Climate (using rainfall as a surrogate); • Geology; • Hydrology; • Macroinvertebrate community composition; and • Fish community composition. Maps outlining previously derived regionalisations were obtained or produced. While some classifications produce complicated landscape patterns, these were generally smoothed by eye. A number of different unique biophysical regions were identified where each of the regionalisation areas intersected. 1 Representative Rivers of Victoria – Discussion Paper Results Landform/climate/geology Nathan and Weinmeann (1993) present a map, based on the 1982 Victorian Atlas, dividing the state into 14 landforms, 8 climatic zones and 11 geological types (Table 1). Of the 1232 possible combinations of conditions, only 59 combinations actually occur in Victoria. Table 1 Different landform, climate and geological categories used by Nathan and Weinmeann (1993) Landform Climatic Zone Geology Alluvial plains Arid to semi-arid (200-300 mm) Quaternary alluvium Dunes and sandplains Semi-arid (300-400 mm) Quaternary evaporites Aeolian loam and clay plains Semi-arid to sub-humid (400- Quaternary aeolian (sand) with loamy dunes 500 mm) Evaporative basin plains Sub-humid (500-600 mm) Quaternary and Tertiary basalt Volcanic plains Sub-humid to humid (600-700 Quaternary aeolian (clay) mm) Sandplains Humid (>700 mm) Paleozoic acid igneous Loam and clay plains Montane (>700 mm, usually Paleozoic sedimentary over 1000 mm, mean annual (sandstone) temp <12) Hilly land with gentle slopes Sub-alpine (>700 mm, usually Paleozoic sedimentary over 1250 mm, mean annual (mudstone) temp <12) Hilly land with moderate slopes Tertiary marine Plateaux lower than 1200m Tertiary alluvium elevation Plateaux higher than 1200m Mesozoic sedimentary elevation Mountains lower than 500 m elevation Mountains higher than 500 m elevation Thackway and Cresswell (1995) present an Interim Biogeographic Regionalisation of Australia (IBRA). This was based on the nominal attributes of climate, Lithology/Geology, Landform, Vegetation, Flora and Fauna and Land Use. In reality, the Victorian component was based on land system and geographic units produced by the LCC, and some vegetation information (Thackway and Cresswell 1995, p. 26). Eleven regions were described for Victoria (Table 2). The IBRA shows a clear similarity to the Nathan and Weinmeann (1993) map, with some IBRA regions composed of combinations of similar landforms (e.g. the Victorian Midlands IBRA contain pretty well all of the two Hilly landform categories from Table 1). In the Biodiversity Strategy for Victoria, Crown (1997) delineate 21 management regions (Figure 1, Table 2). These mostly represent a splitting of the 11 IBRA regions based on natural resource data to accommodate the management scale requirements of a state based strategy. In addition, IBRA regions that were not a contiguous area were split into geographic units (e.g. the South East Coastal Plains IBRA are split to form three geographically distinct areas – the Warnambool, Otway and Gippsland Plains). These “bioregionalisations” were not based on aquatic biological data. There is some logical aquatic divisions of the regions in the Biodiversity Strategy classification (dividing the IBRA South East Highlands into northern and southern slopes could be based on a major fish division). But it is probably sufficient that either the IBRA and/or the Biodiversity Strategy regions are a good starting point for geomorphological or climatic representation. 2 Representative Rivers of Victoria – Discussion Paper Figure 1 Biodiversity Strategy regionalisation Table 2 IBRA and Biodiversity Strategy regionalisation IBRA Bioregion Biodiversity strategy region Murray Darling Depression Lowan Mallee Murray Mallee Wimmera Naracoorte Coastal Plain Glenelg Plain Victorian Volcanic Plain Victorian Volcanic Plain South East Coastal Plain Warrnambool Plain Otway Plain Gippsland Plain South Eastern Highlands Highlands – southern fall Highlands – northern fall Otway Ranges Australian Alps Victorian Alps Victorian Midlands Dundas Tablelands Greater Grampians Goldfields Central Victorian Uplands Riverina Victorian Riverina Furneaux Wilsons Promontory South East Corner East Gippsland Uplands East Gippsland Lowlands NSW South Western Slopes Northern Inland Slopes (some patches in Riverina as well) 3 Representative Rivers of Victoria – Discussion Paper River Hydrology Hughes and James (1989) described 5 different streamflow types across the state based on classification of 13 hydrological variables. The main variables responsible for the classification groups related to monthly constancy (Cvs of mean monthly flows and mean monthly maxima) and annual constancy (Cv of annual flows). The groups derived were not spatially distinct, with representatives of each group found in many areas of the State. A more recent attempt to regionalise streamflow characteristics under the Sustainable Diversion Limit Project (NRE/SKM, unpublished data) also found that there was no clear regionalisation of streamflow types across the State (Figure 2). Hence, hydrological classifications do not seem to be a basis for the selection of representative regional rivers. Rather, it may be desirable to ensure that the range of representative rivers chosen include all of the hydrological groups identified by either Hughes and James (1989) or the Sustainable Diversion Limit Project (NRE/SKM, unpublished data). 4 Representative Rivers of Victoria – Discussion Paper Variables considered: Cv(A)%Zero(A) Cv(mon) BFI(W) Cv(W) FDur_Slope(W) Cluster analysis of 6 N(0,1) variables Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Variables considered: Cv(A)%Zero(A) Cv(mon) BFI(W) Cv(W) FDur_Slope(W) Reduced to three factors that explain 88% of total variance Cluster analysis of 3 PCA scores Group 1 Group 2 Group 3 Group 4 Group 5 Figure 2 Regionalisation of Victorian stream gauge sites based on six hydrological variables (top) and PCA components (bottom). From the results of the Sustainable Diversion Limits Project (NRE/SKM, unpublished data). 5 Representative Rivers of Victoria – Discussion Paper Macroinvertebrates Information on macroinvertebrate regions in the state were obtained from the EPA, produced as part of the AUSRIVAS project, conducted under the River Health Initiative (RHI). This generated 5 distinct regional communities based on species level identification of macroinvertebrates from reference sites (Figure 3, Table 3). Figure 3 Aquatic macroinvertebrate regionalisation (from EPA data) Table 3 Aquatic macroinvertebrate regionalisation (from EPA data) RHI Region General locations Region B1 • Various alpine areas (actually 4-5 different alpine “islands”) Region B2 • East Gippsland (east of the Bemm inclusive) • Central highlands (upper Yarra, La Trobe, Bunyip, Big) • The far north-east (Kiewa, Mitta Mitta.) • Strezlecki Ranges • Wilsons Promontory • Grampians Region B3 • Southern slopes east of Mt Baw Baw (upper Thomson, Mitchell, Tambo, Snowy Rivers) • Northern slopes (upper Goulburn, Broken,