The Living Murray
Foundation Report on the significant ecological assets targeted in the First Step Decision

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4 Information base for the Hattah Lakes

4.1 Introduction

The Hattah Lakes system is a large floodplain wetland system consisting of 18 (17 in some studies where Lake Waterap is excluded) shallow lakes, streams and temporary swamps and bordered by riverine forest. They are located approximately 15 km from the Murray River and most are fed by Chalka Creek, which is connected to the River Murray (Figure 4.1). Thus, flood flows from the River Murray are fundamentally important to the environmental condition of the Hattah Lakes. The system is downstream of Euston Weir and upstream of Mildura Weir, (1,110 km from the Murray Mouth) (Figure 1.1), between Ouyen and Mildura.

 

The Hattah Lakes system lies within two adjacent National Parks, the Hattah-Kulkyne National Park and the Murray-Kulkyne National Park (Figure 4.2). The Parks have a combined area of 49,500 ha, although the Hattah-Kulkyne National Park, with an area of approximately 48,000 ha, is by far the larger of the two. Twelve of the 18 lakes are Ramsar listed, and these have a surface area of 955 ha (DSE, 1999). The combined surface area of all the lakes in the Hattah Lakes system is at least 1,120 ha.

The main hydro-ecological feature of the Hattah Lakes is the large variation in permanency of the aquatic habitats ranging from episodically flooded lakes to almost permanent lakes that receive regular inflows (DSE, 2003). Hattah Lakes provide important breeding and foraging habitat for a range of waterbirds (Environment Australia, 2000; DSE, 2003). Wetland vegetation is predominantly lake-bed herbs and sedges, including Spiny mudgrass grassland, while the lakes are surrounded by River red gum woodland, Black box woodland and Lignum shrubland (DSE, 2003).

In November 2003, the Ministerial Council listed the Hattah Lakes as a significant ecological asset (SEA) in The Living Murray (TLM). Hattah Lakes is a particularly important site due to the size of the system of permanent and semi-permanent wetlands, carrying capacity for fauna, the diversity of vegetation species it supports and its important role in the lifecycles of waterbirds. These values have been threatened by river regulation, particularly through a decrease in floods in spring.

Under natural conditions, the majority of lakes in the Hattah Lakes complex would have been permanent (SKM, 2003a). As a result of river regulation, the lakes now receive reduced inflows and are wet for shorter periods than occurred under pre-regulation conditions (SKM, 2003a). This has the potential to impact on vegetation communities and water bird breeding (SKM, 2003a).

The First Step Decision Interim Ecological Objective for the Hattah Lakes is to restore healthy examples of all original wetland and floodplain communities (Table 1.2). The expected outcomes are: restore the aquatic vegetation zone in and around at least 50% of the lakes to increase fish and bird breeding and survival; increase successful breeding events of threatened colonial water birds to at least two in ten years (spoonbills, Little, Intermediate and Great egrets, Night herons and bitterns); and increase the population size of and breeding events of the endangered Murray hardyhead, Australian smelt, gudgeons and other wetland fish (Table 1.2). These outcomes will be achieved through various management opportunities, described later in this chapter. The following sections describe the characteristics of the Hattah Lakes, exploring the links between the biophysical condition of the forest and hydrological and other factors.

4.2 Value and condition of Hattah Lakes

4.2.1 Conservation significance

The Hattah-Kulkyne National Park, within which the Hattah Lakes Significant Ecological Asset is located, is a part of the network of international Biosphere Reserves coordinated by the UNESCO Man and the Biosphere Program (DNRE, 1997; DSE, 2003; Department of the Environment and Heritage, 2004a). The park is classed as Category II (National Parks) in the International Union for the Conservation of Nature (IUCN) List of National Parks and Protected Areas. IUCN Category II areas are managed primarily for ecosystem conservation and appropriate recreation (DNRE, 1996). Parks Victoria manages the park.

The Hattah Lakes system supports a range of productive habitat types and biota, although it is most noted for its 18 lakes (Figure 4.3). Some reports on the Hattah Lakes exclude Lake Waterap, but it is included as part of the Hattah Lakes in this report.

Twelve of the 18 lakes in the system are included in the Hattah-Kulkyne Lakes Ramsar Site, listed in December 1982 (DSE, 1999; Wetlands International, 2004) (Figure 4.3). The 12 lakes are: Arawak (40 ha); Bitterang (73 ha); Brockie (28 ha); Bulla (40 ha); Cantala (101 ha); Hattah (61 ha); Konardin (121 ha); Kramen (161 ha); Lockie (141 ha); Mournpall (243 ha); Yelwell (81 ha) and Yerang (65 ha) (DSE, 2003).

The Hattah Lakes comprise a wetland system consisting of lakes linked by interconnecting anabranch creeks to the River Murray. The Hattah-Kulkyne Lakes Ramsar site includes areas of two wetland types under the Victorian wetlands classification system: Deep Freshwater Meadow and Permanent Open Freshwater (DSE, 2003). Chalka Creek connects all but one of the lakes to the River Murray (Figure 4.2). Lake Cantala is the exception. This lake obtains inflows exclusively from Cantala Creek, a distributary of the River Murray, located downstream of Chalka Creek (Figure 4.2). Figure 4.4 shows an aerial view of the Hattah Lakes landscape.

Hattah-Kulkyne Lakes is of special value for maintaining the genetic and ecological diversity of the region (Wetlands International, 2004). Globally threatened bird species that occur in the site include the Grey falcon, Mallee emu-wren, Painted honeyeater and Australian bittern. Other threatened fauna include mammals (Common dunnart and Greater long-eared bat), and fish (Silver perch, Murray hardyhead and Murray jollytail) (Wetlands International, 2004). The large floodplain complex Hattah-Kulkyne Lakes supports a large variety and number of waterbirds, and includes breeding habitat for many species such as Australian pelican and Great crested grebe (Wetlands International, 2004). Hattah-Kulkyne Lakes regularly supports more than 1% of the Victorian population of Freckled duck (Wetlands International, 2004).

More than 100 species of indigenous flora have been recorded at the Hattah-Kulkyne Lakes Ramsar site. Six flora species considered to be threatened in Victoria have been recorded in the Ramsar site. One of the species recorded is listed under the Flora and Fauna Guarantee Act 1988 (Vic.) (DSE, 2003). Of considerable significance at a Victorian level are remnant stands of Slender cypress pine, Belah, and Buloke (DSE, 2003). A full list of all noteworthy flora and their conservation status can be found in DSE (1999), DSE (2003) and Wetlands International (2004).

More than 120 species of indigenous fauna have been recorded at the Hattah-Kulkyne Lakes Ramsar site. Of these, two fauna species are considered to be nationally threatened under the Commonwealth's Environment Protection and Biodiversity Conservation Act 1999 (DSE, 2003). A total of 39 fauna species considered to be threatened in Victoria have been recorded (DSE, 2003). Twenty-seven of the species recorded are listed under the Flora and Fauna Guarantee Act 1988, four of these as part of the Lowland Riverine Fish Community of the Southern Murray-Darling Basin (DSE, 2003). A full list of all noteworthy fauna and their conservation status can be found in DSE (1999), DSE (2003) and Wetlands International (2004).

A total of six bird species listed under the Japan-Australia Migratory Birds Agreement (JAMBA) (Department of Foreign Affairs, 1995a) and 11 species under the China-Australia Migratory Birds Agreement (CAMBA) (Department of Foreign Affairs, 1995a; ANCA, 1997) have been recorded at the Ramsar site (DSE, 2003). Ten species listed under the Convention on Migratory Species (CMS) (formerly known as the Bonn Convention) have also been recorded at the Ramsar site (DSE, 2003).

4.2.2 Hydrology of Hattah Lakes

Critical flow paths and flow timing

Flow paths through the Hattah Lakes system were defined in the Mallee Catchment Management Authority Draft Integrated Water Management Plan as primary and secondary flows (SKM, 2003a). Primary flows are flows to lakes that occur as an offtake from the Chalka and Cantala distributaries. Approximately 12 of the 18 lakes receive primary flows. Secondary flows are those that occur as a result of `spillover' from other lakes or tributaries within the system onto the floodplain of the wetland system. However, one of these lakes (Lake Kramen) receives primary flows from the River Murray and Chalka Creek and secondary flows from Lake Nip Nip and Lake Tullamook (through sheet flooding as a result of exceptional flood events). Figure 4.5 depicts flooding as a result of a `1 in 100 year' flood event, which generates filling by sheet flooding and distributary flows.

The overall sequence of events during floods is complex, with the filling and emptying of each lake depending on its position in the system, its area, and its depth (DSE, 2003). The sequence of primary and secondary flows from regional flooding results in a predefined order for infill of the lakes system for a given flood event. Chalka Creek bifurcates into a northern and a southern distributary (Figure 4.2). The first lake to receive floodwaters, several days after they first enter Chalka Creek, is Lake Lockie. All the southern lakes are then filled from Lake Lockie, typically taking another three weeks for water to reach the furthest lakes. After Lake Lockie, water flows into lakes Hattah and Little Hattah, followed by Lake Bulla, and then, in order, Lake Arawak, Lake Marramook, Lake Brockie, Lake Boich, Lake Tullamook, Lake Nip Nip and finally, Lake Kramen. Lake Lockie is believed to deliver flow to Lake Roonki (SKM, 2003a).

The northern part of the system, Lakes Mournpall, Yerang, Yelwell and Konardin, receives water both directly from Chalka Creek, and via Lake Lockie. Lake Bitterang is the last of the lakes to fill, with floodwaters only reaching it over a month after the beginning of flooding, and then only if the flood level is sufficiently high (DSE, 2003). When the lakes are full, floodwaters also spread over surrounding floodplains, including an area of Black box flats to the west and south-west of Lake Lockie (DSE, 2003). Lake Kramen fills by overland flow from the Murray in a very high river. Lake Cantala is fed by a minor anabranch of the Murray River (DSE, 2003).

The lakes only fill during high flow events in the River Murray, with a flood of at least 152,000 ML/d required for all of the lakes to fill. Water retained in lake basins after floodwaters recede is gradually lost through evaporation. Most lakes are shallow, and dry up within two years if not refilled, but Lake Hattah may retain water for three years, and Lake Mournpall for up to seven years (DSE, 2003).

Flow thresholds and flow capacity

Commence to flow discharges

Critical flow corresponds to the flow in the River Murray when the lakes commence to flow. Puckridge et al. (1997) defined critical flows with respect to flow at Euston. The critical flows for lake inundation are identified in Table 4.1. Minimum flows at Euston Weir correspond to an elevation of 42.7 m AHD at Euston Weir, and water must rise an additional 4 m before flow enters Chalka Creek. The bed of Chalka Creek has some high points, and even higher flows are required to ensure flooding of all lakes filled by this primary route.

Chalka Creek currently has a channel capacity of 91 ML/day due to construction of a regulator at Messengers Crossing. The estimated capacity for each of the lakes in the Hattah system is given in Table 4.2. Lake Mournpall has the largest capacity of 2,220 ML, while Lake Hattah and Lake Konardin are also large, both having estimated capacities of 1,476 ML.

 

Critical flows from the River Murray required to flood the lakes are shown in Figure 4.6. A regulated low flow of approximately 8,000 ML/day does not result in high flow down Chalka Creek (and therefore the lakes do not receive inflow). The 1998 flood of 19,300 ML/day was also too small to result in any flooding. However, the larger flood events in 1993, 1995 and 2000 resulted in the filling of Chalka Creek and subsequent lake flooding. The 1998 flood, with a peak flow of 37,900 ML/day, resulted in the flooding of Chalka Creek and Lake Lockie, Lake Mournpall, Lake Hattah and Lake Little Hattah, as well as the smaller southern lakes of Lake Bulla, Lake Arawak, Lake Brockie and Lake Murramook. In between large events, the lakes will often completely dry out, depending on time between events. This analysis of critical flows provides information on the extent of lake inundation after a flood event (Figure 4.6), but it falls short of providing information on the extent of floodplain inundation.

The extent of lake and floodplain inundation in response to floods of various magnitudes is shown in Figure 4.7 and Figure 4.8. However, it should be noted that the mapping was done before and after a flood event only. Antecedent conditions (time since the last flood) of the Hattah Lakes system will also determine the extent of inundation for a given flood event, that is, if the lakes are already wet, a smaller flood will be sufficient to fill the lakes (given the limited capacity of Chalka Creek under various flood volumes). Information on antecedent conditions was not available for Figures 4.7 and 4.8, so these maps should be interpreted as indicative only. Additional analysis is required in order to more accurately and comprehensively model the way in which the Hattah Lakes system responds to flooding.

Figure 4.7 shows the extent of inundation for two flood events that occurred between 1988 and 1993. Mapping of the lakes before the 1998 flood event showed that some of the larger capacity or deeper lakes (e.g., Mournpall) still contained water from the previous flood, while the others had dried out. Conditions after the 1988 flood showed that all of the lakes had been inundated, with the exception of Lake Kramen. This event corresponded to a flow peak of 37,900 ML/d, which is just above the minimum threshold of Chalka Creek for flooding (Table 4.1). Before the 1993 flood, most of the lakes were inundated except for Lake Kramen. The 1993 flood had a peak of 170,100 ML/day that resulted in extensive sheet flooding and the filling of Lake Kramen.

The 1995 flood, which corresponded to a peak Murray flow of 73,500 ML/d, was mapped for the northern area of Hattah Lakes only (Figure 4.8). This flood event resulted in an increase in connectivity between the lakes, and an increase in the surface area containing water (as shown by Lake Cantala). Prior to the 2000 flood event the Hattah Lakes were likely to have had dry antecedent conditions (Figure 4.8). In this case, a flood event corresponding to a River Murray flow of 51,340 ML/d resulted in flooding of some of the southern Lakes (Lake Lockie, Lake Hattah and Lake Little Hattah), although the flood peak did not result in flooding of any of the northern lakes or Lake Kramen. The analysis of these flood events shows that large flood events (>70,000 ML/d) are required to inundate all of the lakes in the Hattah Lakes system.

 

Regional bankfull discharge

The bankfull flow level is when water just starts to spill onto the floodplain. On a stage-rating curve, this corresponds to the point where the rate of depth increase with volume starts to decline. According to rating tables records, River Murray Water, the bankfull discharge at Euston corresponds to approximately 48,000 ML/d, corresponding to a stage height of 40.7 m. This value is similar to the discharge that previously resulted in inflows to Lake Lockie, and hence other lakes, before the Chalka Creek channel entrance was lowered and the channel expanded in 1972-73 (i.e., 48,900 ML/d - Table 4.1).

Groundwater

The Hattah Lakes area is underlain by highly saline aquifers (salinity 40,000-60,000 EC) that could potentially affect the environment of the lakes under conditions of rising groundwater tables. SKM (2003a) summarised the results from recent assessment of the long-term regional watertable trends within the Hattah-Kulkyne National Park as indicating the following trends:

• water table levels are generally static to the north and south east of the National Park, where irrigation activity is occurring;

• there has been a long term decline in groundwater levels in the low-lying areas and lakes, to the west of the National Park; and

• since 1993-94, there has been a general decline in water level in the regional Parilla Sand aquifer in the vicinity of the National Park.

Previous studies and groundwater monitoring within the Hattah Lakes region have been effective in identifying the broad spatial extent of the groundwater mound, which occurs beneath the Nangiloc-Colignan irrigation area (SKM, 2003a). Monitoring has not conclusively shown any long-term rise in groundwater levels. However, this monitoring network is limited in its spatial coverage, and the potential for groundwater inflow to the National Park from the inland disposal of irrigation drainage water to the north of the National Park requires further assessment (SKM, 2003a). One issue of concern is the fact that over the past 10 years, when most of the groundwater data have been collected, conditions have been dry, and a return to wetter conditions could see a significant change in groundwater trend (SKM, 2003a).

A recent study by Lamontagne et al. (2002) found that regional groundwater discharge tends to occur in the floodplain rather than the river itself in the Hattah-Kulkyne area. While considerable work has been done on the role of groundwater processes in mobilising salts to the river, this study investigated the role of groundwater in nutrient cycles. It was found that riparian groundwater tends to be enriched in nutrients, and these nutrients can be released to the river by hyporheic processes during baseflow, or by bank discharge following floods.

Lamontagne et al. (2002) concluded that the `surface flow-based flood-pulse' concept, which implies severing of the hydrological link between river and floodplain at times of low flow, was overly simplistic for the case of Hattah-Kulkyne. Here the river remained connected to the floodplain in non-flood times through groundwater.

4.2.3 Vegetation distribution and hydrological regime

Vegetation classification schemes

Vegetation within the Hattah-Kulkyne and Murray-Kulkyne parks is currently grouped into three broad vegetation types (BVTs): riverine grassy woodland; mallee; and Boinka-Raak. Vegetation is also grouped into 11 ecological vegetation classes (EVCs) (SKM, 2003a). Of these EVCs, those most commonly associated with the Lakes and Chalka Creek are: drainage line grassy woodland; pine-buloke woodland; riverine grassy forest; and savannah woodland/savannah mallee/grassland mosaic. Details of the plant species generally associated with each EVC are not readily available floristic summaries are available for a range of relevant vegetation classes including: Floodplain woodlands and forests; Black box-Chenopod woodland; River red gum forest; Black box woodland; grasslands; and grassy woodlands (SKM, 2003a).

For MFAT modelling of Zone D (Wakool Junction to Lock 11), Treadwell (2003) described wetland vegetation in terms of Cumbungi, Phragmites, Spiny mudgrass grassland, Giant rush rushland and Ribbonweed herblands components. These components were also used by REG C (2003) for Gunbower and Barmah-Millewa forests, but they do not necessarily correspond to the same hydrologically classified elements in each of these areas. Treadwell (2003) described floodplain vegetation in terms of River red gum forest, River red gum woodland, Black box woodland, lignum shrubland, and Rats tail couch grassland components. Lignum shrubland and Rats tail couch grassland components did not appear in the REG C (2003) Gunbower and Barmah-Millewa forests classifications. The Hattah Lakes system is located in a different (drier and sandier) physiographic zone to Barmah-Millewa and Gunbower, Koondrook-Perricoota, and support mallee species that are not found further to the east. The River red gum and Black box tree classifications used at Hattah Lakes are the same as those used elsewhere in the River Murray system, but the composition of understorey communites varies from region to region.

Major vegetation types

Hattah-Kulkyne National Park supports a lake system in relatively natural condition with predominantly River red gum open woodlands in the lake margins and Black box in the more elevated areas (ID&A, 2001c; DSE, 2003). The shrub layer is composed primarily of chenopod shrubs such as Ruby saltbush, copper burrs and Bluebushes (DSE, 2003). Tangled lignum forms shrubby stands around three metres height around some lakes (DSE, 2003; Wetlands International, 2004). River red gum forests are generally confined to areas closer to the Murray River and are not widespread over the Hattah Lakes region (ID&A, 2001c). Rats tail couch grasslands are also a significant vegetation community at Hattah Lakes (Treadwell, 2003). A large part of the Hattah-Kulkyne National Park comprises sandy, semi-arid landscapes supporting mallee eucalypt species (Cumming & Lloyd, 1993).

Given that mean annual rainfall is low, climatic conditions tend to favour ephemeral plant species, although a number of perennial species do exist. Vegetation of the Hattah Lakes systems consist of mostly aquatic species and floodplain species. Within the Ramsar site (i.e., the lakes) the vegetation is dominated by lake-bed herbfield species such as Southern liquorice, Sneezeweed and Lesser joyweed (DSE, 2003).

The distribution of vegetation classes across the Hattah-Kulkyne Lakes system is shown in Figure 4.9 (an alternative vegetation distribution map based on Parks Victoria classifications is reproduced in SKM (2003a)). Black box and chenopod woodland are located in all areas of the Hattah-Kulkyne National Park, although River red gum is largely in the zones around the lakes, owing to its greater water requirements than Black box. Sampling of vegetation around the lakes by Souter (1996) indicated that most of the lakes in the drier parts of the Hattah Lakes system (i.e., away from the lakes and floodplains) supported mallee eucalyptus, with less coverage of River red gums with a native grass and sedge understorey (Figure 4.9).

SKM (2003a) identified five major groups of aquatic and floodplain plants within the Hattah Lakes system:

• trees and shrubs (e.g., Red gum, Black box and Tangled lignum);

• sedges and rushes;

• grasses;

• wetland herbs; and

• floodplain herbs.

 

Water requirements of major vegetation types

Specific information regarding the distributions and water requirements of both flora and fauna within the Hattah Lakes complex is extremely limited (SKM, 2003a), but some of the information derived from other parts of the River Murray system is also relevant to Hattah Lakes. The major community types identified in Hattah Lakes vary in water requirements. For flood dependent species, flood depth, flood duration, and flooding frequency are important.

The season and timing of flooding has a significant impact on the floristic composition of wetland communities in the River Murray system, given that germination and subsequent growth respond to climatic variables in the season. Roberts and Marston (2000) demonstrated the general principle that if flooding changes from winter to spring/summer, a change might occur in species to favour those that grow in summer. Similarly, in the absence of any seasonal flooding, some species will find it difficult to replenish seed stocks. Thus, flood timing and frequency is just as important as the volume of water required for wetland inundation.

Hattah Lakes water levels are highly variable from season to season. Ideal watering conditions occur in the form of a flood that inundates the lake for several months of the year before periodic drying of the lakes occurs (Figure 4.10).

 

River red gum, Black box and Tangled lignum communities

River red gum is particularly well adapted to the variability of water availability from season to season. Studies from the Barmah-Millewa Forest show that ideal watering conditions for River red gum are once every two years with complete drying of the soil in between events (Chesterfield, 1986). A key to survival between floods is access to groundwater (SKM, 2003a). Although River red gums are resilient to variable hydrological conditions, frequent seasonal flooding provides the best conditions for their germination and growth. Sheet flooding is not believed to be essential for maintenance of adult River red gum, but it is vital to seedling establishment (SKM, 2003a). In the Hattah Lakes system, sheet flooding is most common from the River Murray into Lake Kramen, although this only occurs for high flow events (Figure 4.5). This area of the Hattah Lakes corresponds to the occurrence of most of the River red gum and Black box communities in the National Parks. However, Thorburn et al. (2004) argued the general principle that groundwater, or the presence of a shallow aquifer, may be equally, if not more important, than surface water characteristics for the health of River red gum.

Studies from the Barmah-Millewa Forest show that winter-spring watering is ideal for River red gum, with the duration of flooding between four and seven months providing the best conditions for growth. Summer flooding, while providing adequate water for growth of small trees and maintenance of established trees, may alter the understorey community (Robertson et al., 2001).

Black box is normally located at a higher elevation in the landscape than River red gum, which is explained by its lower flood tolerance. The Black box community is healthiest when flooded for a period of between four and six months every four to five years. As for River red gum, the most successful periods of regeneration of Black Box occur after large-scale flooding. In western New South Wales and on the lower Darling River, germination is most successful if it occurs during the cooler months-May to October (SKM, 2003a). Black box seedlings do not have any specific adaptations for flood tolerance, and seedlings can tolerate flooding for about one month (SKM, 2003a).

Tangled lignum is extremely tolerant of waterlogging and moderately tolerant of salinity (Craig et al. 1991). It appears to grow most vigorously when soil moisture is high, and when pH and conductivity are relatively low (Craig et al., 1991). Maintenance of Tangled lignum populations requires flooding every three to ten years, with more frequent flooding required in saline areas (Craig et al., 1991). Although Tangled lignum is tolerant of waterlogging, it cannot survive in continuously wet conditions, requiring a phase of complete drying between floods (Roberts & Marston 2000). Natural flood duration is 3-5 months in southern areas of the Murray-Darling Basin, or 6-12 months in northern areas (Roberts & Marston 2000).

Grasslands

Spiny mudgrass, Water couch and Cane grass grasslands are present in Hattah-Kulkyne National Park. Although information on grassland water requirements is not as widely available as for River red gum and Black box, indicative studies from the River Murray system have shown that flooding every one to two years for a period of approximately six months is required for ideal germination and growing conditions. Roberts and Marston (2000) have shown that periods of inundation up to 18 months can result in a significant level of vegetation dieback.

Cane grass is drought and flood tolerant, but is relatively sensitive to alterations in its water regime (SKM, 2003a). Spiny mudgrass or Moira grass forms wet grasslands in open areas where flooding is frequent or nearly annual (Roberts & Marston, 2000). Research from Barmah Forest suggests that a minimum flood duration of 5-7 months, with a minimum depth of 0.5 m (and maximum of 2 m), is needed to maintain and enhance growth of Spiny mudgrass (SKM, 2003a). Flooding shorter than approximately two months is not sufficient to replenish the seed bank. Grass species that are more sensitive to changes in water regime include perennial species such as the Water couch-a summer-growing species that requires spring or summer flooding between four and eight weeks of greater than 10 cm in depth (Roberts and Marston, 2000). Annual flooding provides the best conditions for such species.

Sedges and rushes

Sedges in the Hattah Lakes system vary in their water requirements for optimum growth. In general, most species require flooding of between two and six months, with a minimum depth of 0.1 m (SKM, 2003a). Common spike sedge has an optimum flooding duration of eight months. Most species of sedge found in the Hattah Lakes area require flooding in winter-spring for optimum growth but can tolerate flooding later in the season (summer). Annual flooding provides ideal conditions for germination and growth. There is little information on the maximum duration between floods that sedges and rushes are able to tolerate without damage to the seed bank and future recruitment (SKM, 2003a).

Wetland herbs (submerged and emergent macrophytes) and floodplain herbs

The design of water management strategies to meet the water requirements of wetland herbs is vital for the maintenance of biodiversity within the Hattah Lakes (SKM, 2003a) because of their roles as a food source and nesting material for birds and food source and habitat for aquatic invertebrates and fish. Knowledge of the water requirements for species occurring in the Hattah Lakes complex is only available for species from the emergent and submerged growth form categories.

Maintenance of the submerged herb Ribbonweed requires a water depth of between about 1 to 2 m, where turbidity less than 80 NTU (Roberts et al. 2000). Emergent Cumbungi and Phragmites do not commonly occur in Hattah Lakes (SKM, 2003a) because they require more permanent, stable water levels (Roberts & Marston, 2000). Even though the lakes contain water for many years once filled, the levels are variable, which does not suit these species (Treadwell, 2003).

Health of vegetation

Since European settlement the structure and composition of the vegetation around the Hattah-Kulkyne Lakes Ramsar site has been severely modified by domestic stock and native animal grazing, logging and the introduction of exotic flora and fauna (DSE, 2003). The impacts of reduced flooding frequency include dieback and reduced vigour of riparian River red gum, as well as affecting tree distributions (DSE, 1999; Wetlands International, 2004). There is no evidence of widespread dieback of flood-dependent vegetation around the lakes, although pockets of dieback, possibly due to length of inundation, rising groundwater and water stress between floods, have been recorded (P. Murdoch pers. comm., reported in DSE, 2003). The distribution of flood-dependent woody vegetation may also be changing with evidence of regeneration of both River red gum and Black box (DNRE, 1996).

Grazing pressure has suppressed the regeneration of woody species and has resulted in reduced abundance of perennial taxa in the shrub and ground layers including the threatened Sand sida, Silky glycine, Upright adder's tongue, Hooked needlewood and the Prickly bottlebrush (DSE, 2003). Where grazing has been excluded, native perennial grasses are common and frequently form a large proportion of the understorey (Sluiter et al., 1997). The remaining proportion of the understorey (up to 10%) is comprised largely of exotic flora.

A kangaroo management program was initiated within Mournpall Block of Hattah-Kulkyne National Park in 1990 and outside Mournpall Block in 1996. Since that time, reduced grazing pressure has allowed some regeneration of woody species and a suite of perennial subshrubs, herbs and grasses, including some rare or threatened plants, have been recorded within and outside the Mournpall Block (Sluiter et al. 1992; P. Murdoch pers. comm., reported in DSE, 2003).

4.2.4 Birds

The National Park contains 65 bird species, many of which are considered rare, threatened or endangered at either the state or national level. The Regent parrot has been specifically listed under the Environmental Protection and Biodiversity Conservation Act 1999 (EPBC Act) (SKM, 2003a). The Regent parrot is known to be closely associated with River red gum forest. Therefore, the maintenance or restoration of River red gum should favour the establishment of the Regent parrot (Ian Sluiter pers. comm., as reported in SKM, 2003a).

The conservation status of the Hattah Lakes (Ramsar listing and inclusion on international migratory bird agreements) indicates that the area historically supported large numbers of colonially nesting waterbirds. The site provides important feeding, resting and breeding habitat for more than 47 waterbird species (DSE, 2003). In terms of carrying capacity, up to 288 Hoaryheaded grebes, 101 Freckled duck, 1,960 Pacific black duck, 2,550 Grey teal, 1,280 Pink-eared duck, 128 Black-fronted dotterel and 1,000 Australian pelicans have been counted at the lakes (ANCA, 1996).

A total of 18 waterbird species have been recorded breeding at the Hattah-Kulkyne Lakes Ramsar site (DSE, 2003). Of these species 16 are threatened in Victoria, eight are listed under the Flora and Fauna Guarantee Act 1988, two under the Bonn Convention, and one under CAMBA (DSE, 2003).

4.2.5 Fish

The main fish groups present in the Hattah Lakes system are flood spawners, main channel specialists and generalists, wetland specialists and low-flow specialists (SKM, 2003a). While some species prefer fast turbulent flows, others prefer the slower and less turbulent flow of pools, billabongs or deflation basin lakes (SKM, 2003a). Fish are only present in the system when the lakes are wet, so the fish assemblage is temporary. Macquarie perch were once recorded in the region but are now considered extinct (Cadwallader, 1981). Freshwater catfish have also undergone a reduction in range (Clunie & Koehn, 2000). Flood spawners are a dominant component of the fish populations. Catfish are likely to be less influenced by a changed flow regime than by other factors such as sedimentation of spawning sites, habitat degradation, the effects of introduced species such as carp, and declines in water quality (Treadwell, 2003).

When full, the Hattah Lakes support nine native fish species as well as three exotic species (as reported in Mallee Catchment Management Authority Draft Integrated Water Management Plan, Dr Oliver Scholz, pers. comm., MDFRC Lower Basin Laboratory, Mildura). Conservation status of native fish present is listed in DSE (2003):

1 Murray cod - may occur here - endangered in Vic., FFG Act listed;

2 Flat-headed galaxis - insufficient data;

3 Freshwater catfish - endangered in Vic., FFG Act listed;

4 Murray hardyhead - critically endangered in Vic., vulnerable in Australia, FFG Act listed;

5 Big-headed gudgeon - not threatened;

6 Western carp-gudgeon - not threatened;

7 Australian smelt - not threatened;

8 Golden perch - vulnerable in Vic., FFG Act listed;

9 Silver perch - critically endangered in Vic., FFG Act listed.

The Murray hardyhead has been specifically listed under the EPBC Act (SKM, 2003a). Murray hardyhead do show a preference for habitats dominated by macrophytes (Ben Gawne, pers. comm., as cited in SKM, 2003a). Therefore, the restoration of these habitats in the Hattah Lakes complex is likely to be beneficial to the long-term maintenance of this fish species within the region (SKM, 2003a).

The most abundant and diverse fish fauna in Hattah Lakes have been found to be associated with more permanent lakes that are frequently flooded (Souter et al., 2000). Fish species richness and the ratio of exotic to native species abundance are correlated with the depth of lake inundation and the duration of the falling and rising limbs of present and past flood pulses (Puckridge et al., 1997).

The changed hydrological regime is likely to have altered faunal habitat leading to lower recruitment rates within some fish and macroinvertebrate populations dependent upon certain flooding regimes (Cumming & Lloyd, 1993).

4.2.6 Macroinvertebrates

A major study of macroinvertebrates in the Hattah Lakes system by Souter (1996), Ward et al. (2000) and Souter et al. (2000) found habitat diversity and structure to be the most important factors in determining community structure, abundance and diversity. The macroinvertebrate fauna of the Hattah Lakes was also strongly correlated with flood frequency and drying time. Lake Kramen was found to be highly productive and diverse compared to the other lakes surveyed (lakes Hattah, Arawak, Konardin, Bitterang and Mournpall). There was an overall pattern of declining species richness, but increasing productivity, the less frequently flooded the lake (Souter, 1996). In general, the project concluded that a diverse range of flooding frequencies throughout the Hattah Lakes will result in the greatest biological benefit, because lakes with different flooding frequencies support different biological communities and different ecological processes (Ward et al., 2000). The relative condition of macroinvertebrates in the Hattah Lakes has not been reported.

4.2.7 Frogs

While the links between frogs and flow regime are poorly understood. It is highly likely that frogs benefit from increased flows (SKM, 2003a). Large breeding events are associated with big summer storms and floods, and frogs have been known to appear in the thousands when the lakes are flooded (Phillip Murdoch, pers. comm.., as cited in SKM, 2003a). The relative condition of frogs in the Hattah Lakes has not been reported.

4.2.8 Water quality and algal blooms

DSE (2003) reported that water quality in the Hattah-Kulkyne Lakes Ramsar site, in terms of dissolved oxygen, pH and heavy metals (arsenic, cadmium, chromium, copper, lead, zinc), is generally good and complies with State Environment Protection Policy (SEPP) water quality objectives (EPA, 1985) and Australian and New Zealand Environment and Conservation Council water quality guidelines (ANZECC, 1992). Conversely, water quality in terms of nutrients (total nitrogen and total phosphorus) and chlorophyll-a is generally poor (Water ECOscience Pty Ltd, 1996 and Souter, 1996).

Nutrients are transported into the lakes during floods and other high streamflow events when the lakes are recharged with water from Chalka Creek. The increase in nutrient levels in the waters of the River Murray, primarily due to intensive land use within its catchment, has produced a nutrient enrichment in the Hattah Lakes system. As a result, the incidence and severity of algal blooms in the lakes have increased (DSE, 1999; Wetlands International, 2004).

The low-lying Hattah Lakes area is at risk of salinisation due to rising groundwater levels. The Mallee Dryland Draft Salinity Management Plan (MDCWG, 1993) predicts lakes Bitterang, Konardin, Yelwell and Hattah are all at risk of becoming salt-affected. Increases in salinity levels of the Hattah Lakes may threaten the habitat of fish and aquatic invertebrates, which in turn provide food for waterbirds. Raised salinity levels also favour certain blue-green algae, increasing the likelihood and severity of algal blooms (DSE, 2003).

4.2.9 Human use values

Commercial land use activities

Pastoralists first settled the Hattah Lakes area in 1838. Three pastoral groups began operation in 1847: Kidds Station; Gayfield; and Mournpall. Kidds Station occupied an area of 25,000 ha, while Gayfield or `Kulkyne' occupied 26,000 ha including 32 km of water frontage. The Mournpall pastoral group occupied 7,168 ha and, unlike the other two larger stations, relied upon lake water for stock and domestic water supply. Although banks and weirs were constructed to retain water, the Hattah area was not deemed suitable for larger scale irrigation development.

Timber resources in the Hattah area were used as a local source of wood for boats, houses and other construction needs. Although commercial forestry and timber production have never been established in the area, between 1924 and 1941 most of the mature trees in the region were harvested to supply fuel for a local pumping station. Harvesting of timber resources after this point was not significant enough to have an impact on forest area or forest composition (Bardwell, 1980).

Commercial land use activities are limited in the National Park. However, the mallee area supports part of the apiculture industry. Growth in this activity has increased in recent years. Growth in the number of apiarists was capped in 1989 until environmental concerns over the growth of the industry were reviewed (LCC, 1989).

Commercial-scale mining has not been undertaken in the Hattah area, although the Mallee Parks Management Plan has identified that gravel and sand extraction takes place on limited occasions to support local road maintenance (DNRE, 1996).

Recreation

Land (16,800 ha) was set aside as State Forest for the purpose of hunting of game in 1941. The Hattah-Kulkyne National Park was declared in 1980 with the amalgamation of the State Forests and a larger area.

The Hattah-Kulkyne National Park supports mostly recreational activities, given that commercial activities have largely ceased since the area was gazetted as a National Park in 1980. For a full description of recreational and tourist activities in the Hattah area, see the Mallee Tourism and Recreation Strategy (DCNR, 1993). The park attracts over 70,000 visitors annually who partake in a wide range of activities centred around some of the lakes including bushwalking, camping, driving, fishing, canoeing, swimming and nature study (DSE, 2003). Game hunting is not permitted in the Ramsar site.

European cultural heritage

Three cultural heritage sites found in the Hattah-Kulkyne National Park are listed in Table 4.3.

Indigenous culture and management

The Hattah-Kulkyne Lakes Ramsar site has been a focus for traditional Aboriginal society for thousands of years. The Lakes provided reliable sources of water as well as a rich and diverse supply of plant and animal resources for food, medicines, shelter, clothing and tools (DSE, 2003). Long and Edmonds (1997) provided an overview of Indigenous cultural heritage values and archaeological sensitivity in the National Parks. The management plan also provides detailed recommendations for the protection of Indigenous cultural heritage in the National Parks. SKM (2003a) provide a comprehensive review of Indigenous cultural heritage values in the Hattah Lakes complex.

Hattah Lakes is on the border of two groups of traditional owners, the Latji Latji group and the Jari Jari group. According to Clark (1990) the Latji Latji group occupied the southern Murray valley and northern mallee between the Hattah area and Wentworth, while the Jari Jari group occupied the southern bank of the Murray immediately upstream of the Latji Latji.

The reliable food source is believed to be the main reason for the dense tribal population in the Hattah Lakes region (and the Murray corridor in general) (Edmonds, 1994). Crayfish, shellfish, waterfowl and eggs are believed to have been the main food staples. The natural flooding regimes of the Lakes and River Murray provided Indigenous people with a reliable source of River mussel, which has resulted in the prevalence of middens around the lakes and along the riverbanks within the Hattah-Kulkyne National Park.

European settlement of the area resulted in a decline in tribal numbers, with the last remaining tribe members in residence of the Hattah area up until 1914, although real population decline and the disruption to traditional life began in the 1860s. The last documented burial of a tribe member was in 1914 at Lake Mournpall.

A cultural heritage assessment of the Hattah region was last carried out in 1993 (Edmonds, 1993). Table 4.4 shows the frequency and type of significant sites in the Hattah-Kulkyne National Park. Other sites of particular importance include shell middens that have been dated to 13,000 years BP. Late Holocene burials have been dated between 25,000 to 14,000 years BP (Luebbers, 1995).

4.2.10 Summary of knowledge of the condition of Hattah Lakes

The high conservation value of the Hattah Lakes has long been recognised, with 12 of the 18 lakes Ramsar listed. The area also has significant cultural heritage and recreation values. The main hydro-ecological feature of the Hattah Lakes is the large variation in permanency of the aquatic habitats ranging from episodically flooded lakes to almost permanent lakes. Despite its high conservation values, surveys have demonstrated some environmental changes in the Hattah Lakes. There is no evidence of widespread dieback of flood-dependent vegetation around the lakes, although pockets of dieback, rising groundwater and water stress between floods, have been recorded. The distribution of flood-dependent woody vegetation may also be changing with evidence of regeneration of both River red gum and Black box.

The Hattah Lakes historically supported large numbers of waterbirds, and currently provides an important drought refuge for waterbirds, reflecting the presence of permanent water within the wetland system. Fish are only present in the system when the lakes are wet, so the fish assemblage is temporary. Macquarie perch were once recorded in the region but are now considered extinct. Freshwater catfish have also undergone a reduction in range due to the combined effects of habitat and water quality degradation and introduced species such as carp. Carp may have been favoured by the regulated flow regime.

Various factors have impacted the health of the Hattah Lakes, including the altered flooding regime due to river regulation and internal hydraulic modification of flow paths. Under natural conditions, the majority of lakes in the Hattah Lakes complex would have been permanent. As a result of river regulation, the lakes now receive reduced inflows and are wet for shorter periods than occurred under pre-regulation conditions.

The extent of lake and floodplain inundation in response to floods of various magnitudes has been investigated, but additional analysis is required in order to more accurately and comprehensively model the hydraulic behaviour of the Hattah Lakes system.

The knowledge base for Hattah Lakes is extensive, as described in a large body of literature, but there is scope to improve on this. The various data on the ecological components of the lakes system (i.e., birds, fish, mammals, amphibians, macroinvertebrates, algae, vegetation) have not yet been compiled into a single database and summarised in terms of relevant and consistent measures of diversity, extent, abundance, and long-term trends.

The current knowledge of biophysical processes in the Hattah Lakes (as synthesised in SKM, 2003a) is adequate to specify environmental flows and works and measures that have a reasonable likelihood of achieving, or partially achieving, their objectives. Uncertainty can be reduced through improved knowledge of ecological processes, which can be achieved through hypothesis-driven investigations that will likely have specific data collection requirements.

4.3 Factors causing loss in environmental values

4.3.1 Hydrology

Local and internal hydraulic modification of flow paths

The climate of the Hattah Lakes system is semi-arid with an annual average rainfall of approximately 250 mm-October is the wettest month on average. Significant local rainfall can briefly fill the lakes, and it is an important source of water that helps to maintain vegetation between flood inundation events. However, the overall wetting and drying cycle of the Hattah Lakes is largely dependent on the pattern of inflows due to river flooding. There have been substantial changes to the hydrological regime of the Hattah Lakes system due to the regulation and modification of flow in the Murray River and structural and earthworks in the Chalka Creek (Cumming and Lloyd, 1993).

The hydrology of the Hattah Lakes system has altered in response to the construction of locks and weirs along the River Murray, and the inlet channel, Chalka Creek, has undergone deepening and widening. A regulator on Chalka Creek at Messengers Crossing now delays flow recession from the lakes, which helps to increase the duration of inundation when floods do occur (DNRE, 1996) (Figure 4.11). Channels (with regulators) have been constructed between Lake Lockie and Lake Hattah and between Lake Hattah and Lake Little Hattah. Internal modifications first occurred in the early 1900s to ensure more reliable water supply to the Victorian Railways (Hattah railway station is just west of the Park). Subsequent alterations were also made to achieve a more permanent supply of water to the settlement of Hattah (SKM, 2003a). The history of internal modifications to the hydrology of the Hattah Lakes is provided in Box 4.1.

The most significant consequences of internal hydraulic modification of the Hattah Lakes system are:

• a reduction in the critical inflow for Lake Lockie from 48,900 ML/d to 36,700 ML/d (meaning that flow enters the system at a lower River Murray discharge, but also drains more quickly). Given that Lake Lockie provides inflow to a number of lakes during flood events, there is also a follow-on reduction in the critical flow to those lakes

• a reduction in the retention level of Lake Hattah (from 42.8 mAHD to 41.8 mAHD) which has allowed more water to drain out of the lake, and reduced the average depth of the lake (SKM, 2003a).

Degree of change to flows due to river regulation

The Hattah Lakes are upstream of the Darling River confluence with the River Murray, and downstream of:

• major headworks storages on the River Murray (Hume and Dartmouth dams);

• three of the largest point diversions from the River Murray (Mulwala Canal, Yarrawonga Main Channel and National Channel [Torrumbarry]);

• the confluence of the River Murray and the Goulburn River;

• the confluence of the River Murray and the Murrumbidgee River; and

• the Ovens and Kiewa unregulated rivers.

Flows in this section of the River Murray follow a seasonal pattern similar to that experienced prior to river regulation, with maximum flows in winter and spring and minimum flows in autumn (Maheshwari et al., 1995). However, River Murray headworks storage and diversions have resulted in an overall reduction of mean annual flow at Euston Weir to 50% of pre-regulation volumes. Flow regulation has also been associated with a reduction in the frequency and magnitude of small- to medium-sized floods to the lakes (Maheshwari et al., 1995).

A comparison of the natural and current median monthly flows in the river zone of the Hattah Lakes is shown in Figure 4.12. In this context, current condition refers to flow as at 2002 operating conditions. This includes the operation of all weirs and locks and irrigation diversions. Natural conditions are simulated flow without locks, weirs and diversions and are an estimate of flow conditions pre-regulation.

The flow pattern in the River Murray downstream of Euston Weir has changed as the flows in spring are considerably less than under natural conditions. Under pre-regulation median conditions the lakes were wet, whereas under current median conditions the lakes do not get wet despite the reduced commence to flow threshold. The Hattah Lakes system under current conditions presents a trade-off between the frequency of wetting and the duration of wetting. While the frequency of events may have increased, the reduced `commence to flow' threshold allows water to drain from the lakes faster than under natural conditions. The function of the regulator at Messengers Crossing on Chalka Creek is to reduce this problem.

A comparison of flood categories over the last 109 years under natural and current conditions at Euston Weir is provided in Figure 4.13. The contribution of flows to the system from the Murrumbidgee River at Balranald upstream of the junction with the River Murray is shown in Figure 4.14. Under natural conditions, the Lakes began to flood at a threshold of 48,900 ML/day and all of the lakes, with the exception of Lake Kramen, were flooded when the river reached 70,000 ML/d.

For flow gauged at Euston, under current conditions, the minimum threshold for inflow of water to the Lakes now occurs at 36,700 ML/d, which in principle would allow for more frequent flooding of the lakes. However, the frequency of flood events has been reduced by flow regulation, resulting in much less frequent inundation, with most flows failing to reach the inflow threshold (Figure 4.12). Also, the flood events that do occur are of reduced duration, and there has been an increase in the time between flood events. Flood events still occur over the July to December period, as they did prior to regulation. However, while under natural conditions August was a common start month for large flood events, lasting through to December, the larger floods now tend to begin in September or October (Figure 4.13).

The Murrumbidgee River is a potential source of water for filling the Hattah Lakes. Under regulated operation, discharge is typically maintained in the range 600 ML/d to 800 ML/day. In contrast, under natural conditions, flows at these low levels were rare (Figure 4.14). Under the regulated regime it is less likely that flows in the Murrumbidgee River will make a significant contribution to inundation of the Hattah Lakes.

Combined effects of river regulation and lowered Lake Lockie inflow threshold on overall hydrology of the Lake Hattah system

Under natural conditions, the majority of lakes in the Hattah Lakes complex would have been permanent, with modelling of a 100-year time series by SKM (2003a) indicating that many lakes would have contained water for 98% of the time. As a result of river regulation, the lakes now receive reduced inflows and are wet for shorter periods than occurred under pre-regulation conditions. This has the potential to impact on vegetation communities and water bird breeding (SKM, 2003a). Some summary statistics on the change of flow regime in the Hattah Lakes are presented in Box 4.2.

Changes in the frequency and duration of lake inflow events from the River Murray

An analysis of the change in flood frequency and duration for natural and current conditions was conducted using 109 years of modelled data. The results are indicative only, because the pattern of flooding has also been impacted by structures that control the movement of water within the Lakes system (Box 4.1), and it was not possible to account for these effects in the modelling. Table 4.5 provides results of the analysis of the percentage of time that flow thresholds are exceeded at Euston Weir, resulting in inflows into the Hattah Lakes system. Three flow thresholds were selected for analysis: 36,700 ML/d is the minimum discharge required for the lakes to begin filling under current conditions; 48,900 ML/d is the minimum discharge required for the same conditions to occur under natural conditions; and 70,000 ML/d was assumed to be a discharge which would result in the majority of the lakes filling (Table 4.1).

The duration of a flood event is important for ensuring the success of bird breeding and seedling recruitment. The literature on the hydrological requirements of waterbirds in the River Murray system indicates that inundation for two months once every two to three years will maintain habitat and provide an opportunity for bird breeding. An analysis indicates that the frequency of sustained floods at the commence to fill level have reduced in frequency, and the larger flood events (that fill most of the lakes at more than 70,000 ML/d) have more than halved in their frequency under current conditions (Table 4.6).

For flood events exceeding 70,000 ML/day for at least 14 consecutive days (assumed to be `large floods' in this analysis) the median interval between events was around one year (calculated value was 322 days) under natural conditions, compared to around two years (calculated value was 650 days) under current conditions. This means that the median time between major events that flood the entire Lake system has doubled under current conditions compared to natural. Similarly, the number of large flood events (greater than 70,000 ML/day) has been reduced from 77 in 109 years under natural conditions to 31 under current conditions.

When a flood event does occur (defined as a critical volume that results in onset of flow into one or more of the lakes), the duration of the event is significantly less under current conditions compared to natural conditions (Table 4.7). For events greater than 14 days duration, the median duration for the smaller flood events has been reduced from 82 to 62 days. The decrease in the duration for the larger events (more than 70,000 ML/day) has been less (11 days), but this represents a similar percentage reduction.

4.3.2 Other factors

A past history of livestock grazing before the National Park was declared as well as excessive grazing pressure by rabbits, goats, Western grey kangaroos and Red kangaroos have degraded native vegetation and hence faunal habitat around the Hattah-Kulkyne Lakes Ramsar site (DSE, 2003). Other threats include nutrients, algal blooms and salinity.

Pest plants are of concern, particularly environmental weeds, because they reduce opportunities for regeneration of indigenous flora through competitive growth and by changing soil conditions required for successful germination and development. Flora species at greatest risk from weed invasion include those of highest conservation significance including the Garland lily and the Sand sida (DSE, 2003).

Large numbers of carp enter the Hattah-Kulkyne Lakes Ramsar site from the Murray River via Chalka Creek (DSE, 2003). The feeding strategy of carp can result in increased water turbidity and the destruction of submerged aquatic vegetation that provide food and shelter for native fishes and habitat for waterbirds (Barnham, 1998). Muddying the water makes the environment unsuitable for many of the aquatic biota that naturally thrive in the lakes (DSE, 2003).

Feral pigs cause localised soil disturbance, spread weeds and disturb understorey vegetation. Pigs also forage for tortoise and waterfowl eggs that have been laid around the perimeter of the lakes (DSE, 2003).

Some recreational activities also pose a threat to some of the values of the Hattah-Kulkyne Lakes Ramsar site (DSE, 2003). High visitation has led to problems associated with fire, damage to native vegetation, firewood collection, soil erosion and compaction. Firewood collection causes significant environmental damage through the destruction of habitat of many small, ground-dwelling animals (DSE, 2003). Disturbance by visitors during bird breeding season may pose a potential threat to the survival of threatened species such as the Freckled duck, Blue-billed duck, Spotted bowerbird and Whitebellied sea-eagle (DSE, 2003).

Hattah Lakes are located in northern Victoria where high fire danger conditions occur throughout summer. Wildfires, inappropriate fuel reduction burning and fire suppression operations have the potential to reduce the site's values (DSE, 2003). Changes to natural fire regimes can adversely affect the diversity of flora and its dependent fauna. Fire frequency, intensity and season can have a major influence on the floristic composition of grassy woodland communities and grassland communities, which are the predominant vegetation types surrounding the Hattah-Kulkyne Lakes Ramsar site (DSE, 2003).

Based on current understanding, DSE (2003) rated altered water regimes, pest plants, pest animals and grazing the most serious threat to the Hattah-Kulkyne Lakes Ramsar site's environmental values and ecological character (Table 4.8).

n n n Higher priority risk - risks that currently or may potentially result in significant loss of the site's environmental values and ecological character.

n n Medium priority risk - risks that currently or may potentially result in moderate loss of the site's environmental values and ecological character.

n Lower priority risk - risks that currently or may potentially result in minor loss of the site's environmental values and ecological character.

These various threats to the health of the Hattah Lakes have been recognised for some time. Management plans have been developed at various levels, and a number of site management strategies have been developed in response to the analysis of risks to the values (DSE, 2003). The following section examines opportunities to address flow-related threats.

4.4 Opportunities to meet objectives for this site

4.4.1 Introduction

The Hattah Lakes is located downstream of significant water management headworks and diversions and it is also affected by regulation within the lakes system itself. The area has also been affected by grazing and introduced species. Hydrological options for improving the ecological condition of the lakes fall into two categories: increasing the frequency and duration of flooding through allocating additional water; and structural works that more efficiently capture and retain water. The ecological condition of the lakes could also be improved through control of grazing by rabbits and kangaroos.

4.4.2 Use of environmental water

Environmental water allocation would provide an opportunity to increase the frequency of watering, and reduce the length of dry spells at the Hattah Lakes. Additional water could be used to increase the number of lakes that fill by increasing the magnitude of existing flood peaks in the river. This could be facilitated by releases from Euston Weir. Gippel (2003) reported on an attempt to manipulate Euston Weir during the October 2000 flood to fill the Hattah Lakes. For example the December 2000 flood enabled the weir pool operation and the natural flood to be used to inundate the lakes. Another possibility for increasing the frequency of flow to the Lakes system could be to source water from the Murrumbidgee or Goulburn rivers.

In considering any future watering options for the Hattah Lakes, it should be noted that only very large floods result in complete inundation of all of the lakes. Smaller floods that have a recurrence interval of every several years are of the magnitude that floods from 30% to 50% of the Lakes. Utilising these smaller flood events that occur relatively frequently will be just as important as managing the less frequent larger flood.

4.4.3 Structural and operational measures

There is potential for improving the health of the Hattah Lakes system through structural and operational measures that make better use of existing inflows into the lakes. Water could be retained for longer in the lakes to improve conditions for recruitment and growth of flood dependent plants and for bird-breeding events.

A detailed study of potential water management options, including the locations for regulators to manipulate the water regime and increase duration of inundation at lakes, has recently been conducted by SKM (2003a). Twelve potential options for water management were evaluated. The favoured option comprised the construction and operation of four regulators within the lakes complex. Two regulators could be positioned in the southern arm of the lake chain (between lakes Little Hattah and Hattah, and lakes Bulla and Arawak). The remaining two regulators could be positioned in the northern arm of the lake chain (between lakes Yerang and Mournpall, and lakes Mournpall and Konardin).

The regulators could be kept open until the lakes are filled by a flood event, whereupon they could be closed. The regulators could remain closed until the next flood event, and opened if the level of the flood exceeds the water level in the lake (David Sheehan, Sinclair Knight Merz, pers. comm., 2003). Potential adverse impacts of the regulators might include increased groundwater levels, and trapping of biocides and pollutants, and these should be monitored (SKM, 2003a). These factors would need to be considered in operating rules if such structures are built.

There have been suggestions for deepening Chalka Creek in order to provide flows to the Hattah Lakes at lower river discharges. However, recent analysis has indicated that this option is unlikely to achieve significant environmental benefits (SKM, 2003a). Installing a pump station at Chalka Creek to pump water into Chalka Creek and the Hattah Lakes is also an option. It would allow an increase in flood frequency as well as duration and magnitude, (SKM, 2003a).

The structural and operational works and measures already considered or identified to improve flow management within the Hattah Lakes include (MDBMC, 2004):

• identification of ecological objectives and their water requirements;

• identification of options for water management which will provide a range of water regimes representing pre-regulation conditions and will meet the ecological objectives;

• upgrade the regulating structure between lakes Hattah and Little Hattah;

• feasibility studies into all priority options, including construction of regulators between lakes Bulla and Arawak, Yerang and Mournpall, Mournpall and Konardin;

• investigation into feasibility of pumping water into the lakes system to address the ecological objectives.

4.4.4 Links between ecological objectives and management opportunities

The proposed opportunities for managing flows in the forest aim to reverse or partially reverse the effects of River Murray flow regulation and internal hydraulic modifications by providing a range of water regimes representing pre-regulation conditions. This will help meet the objective of restoring healthy examples of all original wetland and floodplain communities. Large floods exceeding 70,000 ML/d are required to inundate all of the lakes and such floods are too large to be significantly modified by management actions. So the expected outcomes of the actions under the First Step Decision are with respect to smaller floods that have a recurrence interval of every several years and have a magnitude that can flood around 50% of the Lakes. Floods of this magnitude (which have decreased in frequency and duration under regulation) are the major target of flood enhancement efforts. Thus, the expected outcome is restoration of the aquatic vegetation zone in and around at least 50% of the lakes.

The structural and operational works will enable water that floods into the lakes (through natural and/or enhanced natural floods) to be retained for longer to improve conditions for recruitment and growth of flood dependent plants. The likelihood of successful bird-breeding events (for colonial waterbirds, some of which are threatened) will increase through longer-lasting inundation events.

The most abundant and diverse fish faunas have been found to be associated with more permanent lakes that are frequently flooded. So, frequent and longer-lasting flooding will provide opportunities to enable increased population size and frequency of successful breeding events of the fish species present, some of which are listed as endangered.

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