Surface Water Hydrology of the Macquarie River Catchment

Water Assessment Hydrology Report

Series

Surface Water Hydrology of the

Macquarie River Catchment

December 2008 ISSN: 1835-9531 (Report No. WA 08/46)

W at er A s s essment Branch Water Resources Division Department Of Primary Industries and Water

Material contained in the report provided is subject to Australian copyright law. Other than in accordance with the Copyright Act 1968 of the Commonwealth Parliament, no part of this report may, in any form or by any means, be reproduced, transmitted or used. This report cannot be redistributed for any commercial purpose whatsoever, or distributed to a third party for such purpose, without prior written permission being sought from the Department of Primary Industries and Water, on behalf of the Crown in Right of the State of Tasmania.

Disclaimer:

Whilst DPIW has made every attempt to ensure the accuracy and reliability of the information and data provided, it is the responsibility of the data user to make their own decisions about the accuracy, currency, reliability and correctness of information provided. The Department of Primary Industries and Water, its employees and agents, and the Crown in the Right of the State of Tasmania do not accept any liability for any damage caused by, or economic loss arising from, reliance on this information.

Prepared by:

Suzanne Witteveen, Hydrologist

Preferred Citation:

DPIW (2008). Surface Water Hydrology of the Macquarie River Catchment. Water Assessment Hydrology Report Series, Report No. WA 08/46 Water Resources Division. Department of Primary Industries and Water, Hobart, Tasmania.

Contact Details:

Department of Primary Industries and Water Water Assessment 13 St Johns Avenue, New Town. Phone: 03 6233 6833 Web: www.dpiw.tas.gov.au Email: [email protected]

Cover Page Image:

The Macquarie River at Morningside (photo C.Bobbi)

The Department of Primary Industries and Water The Department of Primary Industries and Water provides leadership in the sustainable management and development of Tasmania’s resources. The Mission of the Department is to advance Tasmania’s prosperity through the sustainable development of our natural resources and the conservation of our natural and cultural heritage for the future. The Water Resources Division provides a focus for water management and water development in Tasmania through a diverse range of functions including the design of policy and regulatory frameworks to ensure sustainable use of the surface water and groundwater resources; monitoring, assessment and reporting on the condition of the State’s freshwater resources; facilitation of infrastructure development projects to ensure the efficient and sustainable supply of water; and implementation of the Water Management Act 1999, related legislation and the State Water Development Plan.

Executive Summary This report provides relevant hydrological information supporting the development of a water management plan for the Macquarie River catchment. Water management plans provide a framework for managing catchment water resources in accordance with objectives of the Water Management Act 1999, and the State Policy on Water Quality Management 1997.

The Macquarie River catchment described in this report lies upstream of Lake River in the Midlands region of Tasmania and covers an area of approximately 2,697 km2. Major tributaries of the Macquarie River include the Elizabeth, Tooms, Blackman and Isis rivers. Lake Leake, Tooms Lake and the Blackman Dam are the major man-made storages in the catchment.

The Macquarie catchment experiences medium to dry climatic conditions influenced by the prominent tiers in west and east of the catchment. The average annual rainfall varies from 500 mm in low lying areas to 1,200 mm in the highlands. The catchment- wide average rainfall is around 580 mm. The annual average evaporation in the catchment is around 1,000 mm.

Average floods (1 in 2 year) in the lower Macquarie River downstream of Elizabeth River peak at around 80 m3s-1. Large floods (magnitude greater than 1,200 m3s-1) observed in the lower Macquarie River have an average recurrence interval of more than 1 in 100 years. Peak discharges after a major flood event in the lower Macquarie River take approximately 10 days to recede to base flow level. Low flows in the Macquarie River and its major tributaries are common throughout the year. In the lower Macquarie the likelihood of occurrence of flows less than 35 ML/day over a five day consecutive period in a given year is around 80%.

Modelled annual water yields in the five Water Management Regions (WMRs) are 132,203 ML in the Upper Macquarie; 75,388 ML in the Elizabeth; 48,030 ML in the Lower Macquarie; 30,835 ML in the Blackman; and 32,663 ML in the Isis. The estimated total annual yield in the catchment is approximately 319 GL compared to 1,500 GL input from direct rainfall and runoff. This indicates that around 80% of gross water input is lost into the system through surface and subsurface interactions.

The current total annual water allocation in the Macquarie River catchment is around 77,660 ML and makes up about 24 % of the total annual yield. The bulk of the allocation (75,511 ML) is for irrigation purposes, while the remainder comprise of stock and domestic, town water supply, and recreational usage.

3 Macquarie Aquatic Environment Assessment

Hydrology and Water Use 2008

EXECUTIVE SUMMARY ...... 3

1. INTRODUCTION ...... 5

2. CATCHMENT DESCRIPTION ...... 6

2.1 DRAINAGE ...... 7 2.2 LAND USE ...... 8 2.3 WATER USE ...... 8

3. CATCHMENT HYDROLOGY ...... 10

3.1 RAINFALL AND EVAPORATION ...... 10 3.2 RIVER FLOW MONITORING ...... 12 3.3 GAUGED FLOW CHARACTERISTICS ...... 14 3.4 SPECIFIC YIELD ...... 17 3.5 FLOODS ...... 18 3.5 FLOW RECESSION ...... 19 3.6 LOW FLOWS ...... 20 3.7 WET AND DRY YEAR COMPARISONS ...... 22

4. CATCHMENT WATER BALANCE MODELS ...... 23

4.1 OVERVIEW ...... 23 4.2 NATURAL AND CURRENT FLOW ESTIMATIONS ...... 23

5. CATCHMENT AND SUBREGION WATER BUDGET ...... 25

5.1 WATER MANAGEMENT REGIONS ...... 25 5.2 CATCHMENT WATER ALLOCATIONS ...... 25 5.3 CATCHMENT WATER YIELD ...... 32 5.3 YIELD SUMMARY ...... 34

REFERENCES ...... 35

APPENDIX A. DESCRIPTION AND OPERATION OF MACQUARIE RIVER CATCHMENT LAKES ...... 36

APPENDIX B. POTENTIAL LIMITATIONS TO THE MACQUARIE RIVER CATCHMENT SURFACE WATER MODEL ...... 41

1. Introduction

This report provides relevant hydrological information supporting the development of a water management plan for the Macquarie River catchment. Water management plans provide a framework for managing catchment water resources in accordance with objectives of the Water Management Act 1999, and the State Policy on Water Quality Management 1997. This report presents analyses of rain, evaporation, and streamflow data from various locations around the catchment. Also presented are outputs from a catchment hydrological model. These analyses provide hydrological information for calculation of a catchment water budget, indicating the gross and net amounts of water in the catchment. Macquarie River streamflows have been analysed to show general variation in gauged flows, as well as potential flood frequencies, low flows, and flow recessions. Modelled flow data and catchment water allocations were analysed to provide water yield balances for the Macquarie River catchment as a whole, and for five proposed water management regions (WMRs): the Upper Macquarie, Elizabeth, Lower Macquarie, Blackman, and Isis (see Section 5).

2. Catchment description

The Macquarie River catchment is located in the Midlands region of eastern Tasmania and makes up part of the Tamar River Basin. The catchment extends from Tooms Lake in the south to Longford in the north and has a total catchment area of 4,241 km2.

The Macquarie River catchment described in this report lies upstream of Lake River1 and covers an area of approximately 2,697 km2. The catchment has an oblong shape 84 km long and 64 km wide at its longest axis lengths. The upper reaches of the catchment consist of rugged terrain dominated by dolerites and related rocks while the low lying areas contain mainly quaternary sediments with common outcrops of basaltic rocks. The dominant vegetation types in the highland areas of the catchment are dry Eucalypt forests and woodlands. Vegetation and landscape in the low lying areas are extensively modified by agricultural activities.

Major tributaries of the Macquarie River include the Elizabeth, Tooms, Blackman and Isis rivers. Lake Leake, Tooms Lake and the Blackman Dam are the major man-made storages in the catchment. Campbell Town and Ross are the main population centres in the catchment and both discharge treated wastewater to the local rivers.

1 The Macquarie River downstream of the Lake River confluence lies outside of the proposed area of the water management plan and water management for this reach are covered by the Water Management Review process undertaken by Hydro Tasmania.

Figure 2.1 The Macquarie River catchment.

2.1 Drainage

The Macquarie River originates in the southeast of the catchment from Mount Morriston and Hobgoblin (Parramores Tier), at an elevation of around 800 m AHD (Figure 2.2). The headwaters drain a number of swamps south of Badger Hill. The river runs south then north, picking up flows from the Blackman, Elizabeth, and Isis rivers before joining with the Lake River at Woolmoor. The elevation at the bottom of the catchment is around 140 m.

Catchment drainage follows a dendritic pattern largely controlled by the dolorite country rocks. Stream sizes range from first to seventh order with a total drainage density of 1.7 km/km2. Over 80% of the smaller order streams are ephemeral while the larger order streams in the low-lying areas contain several broadwaters along the reaches. The total length of the Macquarie River is approximately 180 km with an average gradient of 3.6 m/km2.

Figure 2.2 Distribution of drainage of the Macquarie catchment

2.2 Land Use Landuse is extensively agricultural downstream of the Macquarie-Tooms River confluence. This lower part of the catchment is largely developed for grazing, with the majority of the catchment being cleared for pasture. Some intensive cropping for potatoes occurs along the Macquarie’s banks. Approximately one third of the catchment is forest or woodland, mostly in the catchment’s upper east and west highlands, and around 10% of the catchment is dedicated to plantation forestry2. Trout fishing is the principal recreational activity in the riverine environments of this region.

2.3 Water Use Water in the catchment is used primarily for irrigation, with town water supply being a much smaller yet vital use. The Macquarie River and its tributaries are the source

2 Estimated from theLIST (© State of Tasmania) base data.

8 of water for the towns of Campbell Town, Ross and Cressy. The Department of Primary Industries and Water (DPIW) manages the licensing of off-stream storages in the region (i.e. farm dams), direct takes from tributaries of the Macquarie River and the high flow water in the region. The Macquarie River is a highly regulated system. Two large storages exist at the top of the catchment, and river flows are regulated through the manipulation of these. Tooms Lake (full supply capacity 22,000 ML) is managed by the Elizabeth Macquarie Irrigation Trust and provides supplementary summer flows during the irrigation season to the upper Macquarie between Mt Morrison and the Elizabeth River. Lake Leake (full supply capacity 22,076 ML) is also managed by the Elizabeth Macquarie Irrigation Trust and provides supplementary flows for the Elizabeth River and the Macquarie below Elizabeth during the irrigation season (see Appendix A for a more detailed description of the lakes and their operation). Blackman Dam was built in 2005. It has a full supply capacity of 7,324 ML and an annual water licence allocation of 3,000 ML. The Blackman Water Pty Ltd is currently being established to manage water in the main stem of the Blackman River between the Blackman Dam and the confluence of the Blackman and Macquarie Rivers, including water stored in the Blackman Dam. There are numerous other storages located within the Macquarie River catchment ranging from 1 to 4,500 ML. There are also several large storages in the upper catchment that are currently under proposal.

3. Catchment Hydrology

3.1 Rainfall and evaporation The Macquarie River catchment is one of the driest areas in the state, lying in a rain shadow between the Western Tiers and highlands in the catchment’s east. Annual average rainfall throughout much of the Macquarie River catchment is between 500- 600 mm, increasing to around 1,200 mm in the eastern and western highland areas (Figure 3.1). Most of the rainfall occurring in the highland areas is reliant on easterly coastal weather patterns.

Figure 3.1 Distribution of mean annual rainfall in the Macquarie River catchment.

Analysis of the rainfall records in the catchment show that over the period 1970 to 2007 there was a recurring pattern of wet years followed by a dry period of at least one year (Figure 3.2). The overall average annual rainfall in this period was 580 mm. During the last ten years (1997–2007), the overall average annual rainfall was 520 mm, indicating a possible trend towards a drier climate in the catchment.

A 5-year moving average of annual rainfall data indicates that there has been a general decline in rainfall since the early 1970s (Figure 3.2). The years 1994, 2006, and 2007 were the driest years during the period, with mean annual rainfall not

10 exceeding 380 mm. Evaporation data shows a rising trend, particularly since the 1990s, in contrast to the overall declining trend in rainfall. Evaporation has tended to exceed rainfall in each year since 1970. Average annual evaporation is 1,000 mm.

1400 mean mean annual annual rainfall rainfall mean annualmean evaporationannual evaporation mean rainfall 1970-2007 mean rainfall 1997-2007 mean rainfall 1970-2007 mean rainfall 1997-2007 5 per. Mov. Avg. (mean annual rainfall) 1200 5 year moving average rainfall (mean annual rainfall)

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0 1970 1975 1980 1985 1990 1995 2000 2005

Figure 3.2 Variation in Macquarie River catchment annual rainfall and evaporation (1970- 2007) superimposed with rainfall’s 5-year moving average, and overall mean annual rainfalls for 1970-2007 and 1997-2007. Analysis of monthly rain and evaporation data (Figure 3.3) indicates August to be the wettest month (closely followed by December), and February the driest. It also shows that evaporation exceeds rainfall for eight months of the year, and that distinctive seasonal patterns (winter highs and summer lows) do not exist for the catchment; aside from a summer low in February, rainfall is fairly similar across the seasons. Rainfall is similar in summer and winter due to the general climate of the catchment, lying in a rain shadow created by highlands to both the east and west. Evaporation, however, does display seasonal variation, showing a distinctive low in winter and high in summer.

11 180 rain evaporation 160

140

120

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mean rainfall and evaporation (mm) andevaporation meanrainfall 20

0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Figure 3.3 Mean monthly rainfall and evaporation in the Macquarie River catchment (1970- 2007).

3.2 River flow monitoring

There are 17 stream gauging sites in the Macquarie River catchment with historical and current records of river height data (Table 3.1). Of these, six are currently operating, and eleven are closed. Only data from current sites has been used for analysis in this report, and all have good continuity of record without major gaps. Site 18211 is an exception, with unverified data between 1996 and 2007. Two of the current gauging stations, 18309 (Macquarie River at Coburg) and 18313 (Macquarie River at Fosterville) have been installed for water management purposes in the past several years but these have not been used for analysis due to the brevity of records. Other current sites have between 18 and 34 years of river height data. Sites 18217 (Macquarie River at Trefusis) and 18312 (Macquarie River at Morningside) have been primarily used for analysis due to their locations along the main river stem.

All current sites and their locations are highlighted in Table 3.1 and shown in Figure 3.4.

12 Table 3.1 Streamflow monitoring sites located within the Macquarie River catchment (above Lake River).

Catchment Site Location Period of Record area (km2) 8 Elizabeth River at Campbell Town 352.0 01/01/1922 – 30/09/1930 9 Elizabeth River at Lake Leake 64.8 01/08/1993 – 25/03/1997 20 Macquarie River at Ross 1497.0 02/10/1990 – 19/11/1993 83 Blackman River at Tunbridge 233.0 01/07/1925 – 31/08/1930 91 Isis River at Barton 241.0 26/05/1937 – 31/01/1947 259 Macquarie River at Morriston 387.0 23/04/1991 – 19/11/1993 18205 Birralee Creek u/s Kittys Rivulet 33.0 13/05/1971 - 29/08/1986 18206 Tooms River d/s Tooms Lake 60.2 03/07/1973 – current 18210 Macquarie River d/s Longmarsh Dam 89.7 22/05/1975 - 05/10/1990 18211 Elizabeth River d/s Lake Leake 69.7 06/09/1976 – current 18217 Macquarie River at Trefusis 365.0 11/07/1979 – current 18228 Back Run Creek 16.0 02/07/1985 – 16/06/1994 18304 Macquarie River at Coburg 2683.0 09/01/1990 – 05/07/1994 18309 Macquarie River u/s Lake River (‘Coburg’) 2694.0 06/06/2007 – current 18310 Elizabeth River u/s Macquarie 399.95 01/01/1988 – 05/09/1995 Macquarie River d/s Elizabeth River Junction 18312 1953.0 24/01/1989 - current (‘Morningside’) Macquarie River u/s Elizabeth River junction 18313 1525 26/07/2004 – current (‘Fosterville’)

Figure 3.4 Locations of current streamflow monitoring sites in the Macquarie River catchment.

3.3 Gauged flow characteristics Streamflow in the Macquarie River is highly variable and affected by persistent low flow conditions. Flow plots for the two major streamgauge sites (18217 and 18312) are presented below (Figures 3.5-6). Duration curves are also presented for the two sites, indicating the percent of time that a particular flow is equalled or exceeded (see Section 5 for a more detailed explanation). The Macquarie at Trefusis flow plot shows high variability in flows with no distinct seasonal patterns. The largest high flow events occurred in winter 1986, summer 1993-94, and early spring of 2003. The duration curve shows that high flows of 100 ML/day or above occurred 0 - 20% of the time. Fairly sustained, regular flows (10 - 100 ML/day) occurred around 20 - 95% of the time. Low flows of below 10 ML/day occurred 95 - 100% of the time. The Macquarie at Morningside flow plot also displays high variability in flows. High flow events occurred in summer 1993-94, spring 2003, and late in 2005. There are no distinct seasonal patterns to flows. The duration curve shows that high flows of 100 ML/day and above occurred up to 35% of the time. Low flows of 10 ML/day and below occurred 99 – 100% of the time.

14 18217.1/100.00/1: MACQUARIE RIVER [AT TREFUSIS] (PTo(140.02,0)) - Flw Ml/day

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1 0 10 20 30 40 50 60 70 80 90 100 % of time flow is equal to or exceeded

Fig. 3.5 Flow variation and flow duration at Macquarie River at Trefusis (18217) over streamgauge record period 1979-2008.

15 18312.1/100.00/1: MACQUARIE RIVER [D/S ELIZABETH] (PTo(140.02,0);Aggregate(Daily)) - Flw Ml/day

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1 0 10 20 30 40 50 60 70 80 90 100 % of time flow is equal to or exceeded

Fig 3.6 Flow variation and duration curve at Macquarie River at Morningside (18312) over streamgauge record period 1989-2008.

Monthly summary statistics for current streamflow monitoring sites are presented in Table 3.3. Mean monthly flows in the Macquarie River at Morningside varied between a minimum of 14.4 ML/day in Jun and a maximum of 2,903.4 ML/day in Dec, while flows in the Macquarie at Trefusis ranged between 8.7 ML/day in Jun to 1,731 ML/day in Dec. Flows in the Tooms River below Tooms Lake varied between 0.2 ML/day in Aug and 478.6 ML/day in Dec, and in the Elizabeth River below Lake Leake, from 2.1 ML/day in Sep to 507.4 ML/day in Jun.

Table 3.3. Summary statistics of average monthly streamflow (ML/day) at current Macquarie River catchment gauging sites.

Tooms River d/s Tooms Lake (18206) (1/1/1974 – 31/12/2007) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual mean 37.2 32.3 27.9 26.1 20.0 33.3 55.4 48.6 42.4 39.3 37.9 49.4 37.7 standard deviation 41.9 17.9 6.8 24.8 36.4 89.0 84.9 71.6 63.7 59.0 46.2 87.0 25.1 maximum 245.5 127.8 38.2 157.1 217.5 394.4 314.2 231.8 266.8 297.3 204.9 478.6 93.0 minimum 12.2 14.4 11.6 0.5 0.3 0.4 0.3 0.2 0.5 0.5 1.6 12.6 8.8

Elizabeth River d/s Lake Leake (18211) (1/1/1977 – 31/12/2007) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual mean 89.9 81.1 78.4 75.4 78.0 98.9 100.2 108.1 110.0 83.8 86.4 103.0 90.9 standard deviation 79.5 74.1 73.3 78.1 81.0 118.1 89.4 96.1 98.2 80.0 83.5 104.7 68.2 maximum 281.7 279.5 277.4 275.2 273.0 507.4 290.3 315.5 415.9 288.3 286.1 366.8 269.6 minimum 18.8 16.7 14.8 10.6 4.3 3.6 4.0 3.7 2.1 7.9 13.9 20.4 19.7

Macquarie River at Trefusis (18217) (1/1/1980 – 31/12/2007) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual mean 119.6 53.2 35.8 94.0 98.3 133.2 244.4 275.0 213.6 145.0 110.6 219.2 147.0 standard deviation 213.7 77.8 18.8 172.4 218.2 321.3 277.4 315.2 291.1 133.9 155.9 444.8 104.0 maximum 1005.4 415.0 110.7 809.7 1127.9 1699.3 971.8 1052.4 1284.5 494.9 648.9 1731.0 406.1 minimum 20.9 16.0 12.4 9.2 13.2 8.7 17.8 11.7 10.6 11.7 9.8 12.7 26.9

Macquarie River ‘Morningside’ d/s Elizabeth River Junction (18312) (1/1/1990 – 31/12/2007) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual mean 244.9 158.1 54.9 165.3 74.4 150.5 469.8 690.6 594.1 415.9 278.9 354.9 299.8 standard deviation 396.9 262.2 23.9 406.7 78.0 227.0 560.6 712.3 690.2 546.2 454.0 734.2 238.0 maximum 1609.3 1090.4 126.0 1757.8 306.5 843.8 1718.8 2273.6 2276.4 2102.4 1955.5 2903.4 879.6 minimum 23.0 17.1 20.4 14.5 18.3 14.4 29.6 47.1 27.6 31.0 29.6 37.2 54.9

3.4 Specific yield

The specific yield is the efficiency of a catchment to yield flow. Flows in the Macquarie River are modified, making accurate calculations of specific yield in the catchment impracticable. However calculations have been made based on measured flows in the catchment in order to give some indication of specific yields. It must be remembered that these are representative of the modified flow regimes, and not the natural flows.

Specific yield equates to a flow volume (ML) per unit pickup area (km2). A summary of specific yields from the gauged flows is presented in Table 3.4. The table shows Elizabeth River downstream of Lake Leake to be the most productive, with the Tooms Lake area the next most productive. These two values reflect the upper

17 catchment conditions of high rainfall from the eastern highlands. Specific yields decrease down the catchment, with the Macquarie at Morningside displaying the lowest specific yield, representative of the low rainfall and low gradient in the lower catchment.

Table 3.4 Specific yields of current streamflow monitoring site catchments.

area average flow specific yield site (km2) (ML/d) (ML/d/km2) Tooms River d/s Tooms Lake 60.2 37.7 0.6 Elizabeth River d/s Lake Leake 69.7 90.9 1.3 Macquarie River at Trefusis 365.0 147.0 0.4 Macquarie River at Morningside 1,953.0 299.8 0.2

3.5 Floods

3.5.1 Historical floods Flood events in the Macquarie River catchment are noted in the South Esk River and Macquarie River Flood Data Book (DPIWE, 2000). Historically, the Macquarie River seems to have been prone to flooding during high rain events in winter to spring, as noted in Steane (1968). At least fifteen confirmed floodings occurred in the catchment between 1828 (the first Tasmanian flood record) and the mid-1970s, often resulting in the bridge at Ross being covered by water, and sometimes in the evacuation of residents. Streamgauge records indicate there has been approximately one 1:20 year flood event and two 1:10 year events at Trefusis since 1980 (upper catchment), and one 1:10 year event at Morningside (lower catchment) since 1990.

3.5.2 Flood frequency Regulation of flows in the catchment means true flood frequency estimates cannot be performed. However flood frequency analysis was carried out on flows from streamgauge sites 18312 (Macquarie River at Morningside) and 18217 (Macquarie River at Trefusis) to give an indication of range and magnitude of events under the regulated system. The results of the analysis are given in Table 3.5. The average flood (1:2 years) is estimated at 82 cumecs in the upper catchment (Trefusis), and 81 cumecs in the lower reaches (Morningside, downstream of Elizabeth River). The similarities for the 1:2 ARI may result from several possibilities: irrigation releases from lake storages; minimal pickup between Mornington and Trefusis; and/or losses between the two sites from evaporation and groundwater recharge.

18 Table 3.5 Average recurrence interval (ARI, years) of floods (cumecs) at streamgauge sites 18217 and 18312 in the Macquarie River catchment.

18217 Macquarie at 18312 Macquarie at ARI Trefusis Morningside 1 2 2 2 82 81 5 212 238 10 320 400 25 471 670 50 587 919 100 703 1206

3.5 Flow recession

A recession curve is a specific part of the flood hydrograph after the flood peak, when streamflow diminishes. The recession segment shows how the water storage in the river decreases over time following a significant rain event. The recession curve basically reflects the baseflow component of the river flow and how groundwater storage influences and sustains flows in rivers. Each recession segment of the flood hydrograph is described by an exponential decay function of the form:

-αt Qt = Qo e where Qt is the streamflow at time t; Qo is the initial streamflow at start of the recession; e is the natural logarithm; and α is cut-off frequency constant.

The recession equation for the Macquarie River at Morningside (18312) is of the form:

Flow = 90.2 * e-0.0002*Time (Minutes) The recession curve for 18312 (Figure 3.7) shows that it takes approximately 10 days (14,400 minutes) for the peak flow at Macquarie at Morningside to recede from around 90 m3s-1 to 10 m3s-1, a recession rate of around 8 m3s-1 per day. The recession curve for flows at Macquarie River at Trefusis (18217) is of the form:

Flow = 69.3 * e-0.0002*Time (Minutes) The recession curve for 18217 (Figure 3.7) indicates that it takes approximately 10 days (14,400 minutes) for flows to recede from around 70 m3s-1 to 4 m3s-1, a recession rate of 6.6 m3s-1 per day.

19 100 90 Expon. (mean 18217 recession) 80 Expon. (mean 18312 recession)

70 )

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40 Flow(m 30 20 10 0 0 5000 10000 15000 20000 25000 Recession time (minutes)

Figure 3.7 Peak flow recession curves for site 18312 (Macquarie River at Morningside) and 18217 (Macquarie River at Trefusis).

3.6 Low flows Low rainfall and frequent drought has resulted in persistent low stream flow conditions in the Macquarie River catchment. Low flows for the Macquarie River at Morningside and Trefusis have been presented graphically on low-flow frequency curves (Figure 3.8). These show the proportion of time that flows will be less than or equal to a given flow over a particular time period (5, 30, 60, or 90 days) in a given year. For a 5-day period at the Macquarie River at Morningside, there is an 80% probability that low flows will average around 35 ML/day in a given year. For the same probability over a longer period such as 90 days, average low flows of 70 ML/day are likely to occur. By comparison at the Macquarie River at Trefusis, for a 5-day period there is an 80% probability that an average low flow of around 17 ML/day will occur. Over a 90-day period this increases to 50 ML/day. The prolonged period of low flow in the catchment has implications for environmental water provisions, water quality impacts and for the assessment of risk in supply of water from the river for purposes such as irrigation and domestic use.

20 Macquarie at Morningside 100

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Figure 3.8 Frequency curves of low flows at streamflow monitoring sites 18312 and 18217 in the Macquarie River catchment.

21 3.7 Wet and dry year comparisons

A wet and dry year comparison has been made to indicate seasonal natural flow variation within the catchment. The regulation of water (storage during wet periods and release during dry periods) in the Macquarie River prevents an accurate comparison being made between the observed streamflow data for wet and dry years, so the comparison has been made between wet and dry years of natural modelled data. See Section 4 below for an explanation of natural modelled data. In terms of rainfall, the years 2001 and 2006 respectively represent years of wetter- than-average and drier-than-average conditions. Figure 3.9 provides a comparison of modelled natural flow hydrographs for these years at the catchment outlet. Also plotted are the median daily flows each month for the whole modelled period (1970- 2007), again at the catchment outlet. This has been included to demonstrate the degree of interannual variation that occurs in runoff from the catchment.

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Figure 3.9 Monthly variation of natural (modelled) flow at the Macquarie River outlet during a typical wet and dry year.

4. Catchment Water Balance Models

4.1 Overview

Under a project funded by the National Action Plan for Salinity and Water Quality (NAPSWQ), a rainfall and runoff water balance model was developed for the Macquarie River catchment (HEC, 2005). The model was revised to a Tascatch format in 2008. The model generates a daily time-series of natural flow3 and current flow4. The effect of water allocations on the hydrological system has been used to derive the hydrological disturbance indices, and these are described in Section 5.2.4 below.

In this analysis, yields have been generated for the five water management regions (WMRs - see Section 5 below) over the 37-year period 1970 to 2007.

4.2 Natural and current flow estimations

The model has been calibrated by matching modelled flow to observed flow records for the streamgauge sites Macquarie River at Morningside (18312) and Macquarie River at Trefusis (18217). The result of the calibrated data is shown in Figure 4.1a.

The time series (Figure 4.1a) of modelled and observed flow for a reasonably average rainfall year (1992) shows that the Macquarie River catchment model gives a poor representation of the natural flows in the Macquarie River catchment. The daily flow regression coefficient values (modelled flow vs observed flow) at the calibration sites were around 55% and 58% for Trefusis and Morningside respectively. The regression coefficient values for monthly flow were 77% and 68% at Trefusis and Morningside respectively. A general summary of regression coefficient values is presented in Table 4.1 for an indication of the model’s performance. Overall, there is a general tendency for the model to underestimate natural flows at the low flow end.

Table 4.1 Regression coefficient (R2) fit descriptions

Qualitative Fit Daily R2 Monthly R2 Poor R2 < 0.65 R2 < 0.8 Fair 0.65 ≥ R2 < 0.7 0.8 ≥ R2 < 0.85 Good R2 ≥ 0.7 R2 ≥ 0.85

3 Natural flow: Flow that is expected to occur in a river where there is no water extracted for consumptive use. This is generally produced from a catchment hydrologic model using rainfall and evaporation as the primary input data. It does not take into account any changes in land-use that may have occurred over the period of interest.

4 Current flow: Flow in a river where water has been extracted for consumptive use. For the purpose of this report this involved subtracting the licensed water use for 2008 from the entire ‘natural’ flow record produced by the hydrologic catchment model.

The duration curve indicates that the model performs reasonably well at high to medium flows (Figure 4.1b). The current flow is below the natural, and the natural corresponds with the observed, between around the 0-25% flow exceedance range. At the low flow end, natural falls below current, indicating an underestimation of natural flow in the low flow range. Limitations to the Macquarie River catchment model are presented in Appendix B. Further general limitations to the Tascatch models are listed in the NWI Tascatch surface water model reports (HEC, 2005).

observed flow Currentcurrent flow flow Observed flow Natural flow natural flow 16000

14000 (a) Time Series Analysis (2001) at Morningside

12000

10000

8000

6000

Flow (ML/day) 4000

2000

2001 2002 Period(01/01/2001 @ 00:00:00 to 01/01/2002 @ 00:00:00)

18312.1/100.00/1: MACQUARIE RIVER [D/S ELIZABETH] (PTo(140.02,0)) - Flw Ml/day (01/01/2001 to 01/01/2002) C:\CATCHMENT_MODELS\Macquarie_Model_Upgrade\Output\report_calibration\morningside_J17_current_2001.tsf (01/01/2001 to 01/01/2002) C:\CATCHMENT_MODELS\Macquarie_Model_Upgrade\Output\report_calibration\morningside_J17_natural_2001.tsf (01/01/2001 to 01/01/2002)

100000

(b) Duration Analysis (2001) at Morningside

10000

1000

100

Flow (ML/day)

1 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

Figure 4.1 a) Time series and b) flow duration analysis of the current, observed and natural flow data for Macquarie River at Morningside (streamgauge 18312).

24 5. Catchment and Subregion Water Budget

5.1 Water Management Regions After consultation with the Water Management and Water Policy and Planning Branches of DPIW, the Macquarie River catchment was divided into five Water Management Regions (WMRs) for management purposes. These regions were used in the hydrological modelling of the Macquarie River catchment. They were determined using a combination of the following: Existing water management areas (eg. irrigation districts and old water districts) Practical and logical management areas based on experiences of managing water resources in the catchment Confluence of streams (nodes), as these form the basis of water trading zones Areas with similar riverine geomorphology The five WMRs that will be referred to in this report are as follows (Figure 5.1): 1. Upper Macquarie River including Tooms Lake and all tributaries upstream of the confluence with the Elizabeth River, except the Blackman River and its tributaries. 2. Blackman River and its tributaries. 3. Isis River and its tributaries. 4. Lower Macquarie River, downstream of Elizabeth River and including all tributaries down to the confluence with Lake River. 5. Elizabeth River and its tributaries, including Lake Leake.

5.2 Catchment Water Allocations The distribution of current consumptive water allocations within the five WMRs is shown in Figure 5.1. Allocations are for surface water flows and do not include groundwater takes.

Figure 5.1 Distribution of water allocations in the water management plan regions of the Macquarie River catchment. Allocations based on WIMS data (2008)5. A WIMS database summary gives a total current annual water allocation in the Macquarie River catchment of approximately 77,660 ML. The majority of this is for irrigation. A summary of the water usage and distribution of allocation by WMRs is given in Table 5.1. The table shows that 60% of the volume of allocated water is used in the Upper Macquarie and Elizabeth WMRs, primarily for irrigation. A significant portion of this is held and allocated out by the Elizabeth Macquarie Irrigation Trust. These allocations are initially held as storage in Lake Leake and Tooms Lake, and

5 DPIW’s Water Management Branch (WMB) is responsible for upkeep and quality control of the Tasmanian water usage and licensing database (WIMS). All water allocations used in this Macquarie River catchment hydrology report are provided by WMB.

26 taken throughout the year for irrigation across the Elizabeth Macquarie Irrigation District (the Elizabeth and Macquarie River above Ross). The two storages have a bulk allocation and store water all year round, primarily for irrigation. These bulk storage allocations have been removed from the tables presented below as they are accounted for as direct extractions under individual licences.

Table 5.1 Summary of annual water usage (ML/year) for the Macquarie River catchment WMRs (WIMS, 2008).

Upper Lower Whole subregion Elizabeth Blackman Isis Macquarie Macquarie catchment area (km2) 966.71 399.95 558.97 327.09 444.99 2,697.71 Water use

Irrigation 25,972 19,493 7,563 4,124 18,359 75,511 Stock & domestic 17 - 180 - 11 208 Water supply 182 - 353 - - 535 Recreation 500 900 - - - 1,400 Other - - - - 8 8 ML/year 26,671 20,393 8,096 4,124 18,378 77,662 Direct Take 21,582 16,275 5,322 1,882 9,204 54,265 Storage 5,089 4,118 2,774 2,242 9,174 23,397 ML/year 26,671 20,393 8,096 4,124 18,378 77,662 Year long 525 900 642 - 105 2,172 Summer 12,373 1,724 1,900 442 9,198 25,637 Winter 13,773 17,769 5,554 3,682 9,075 49,853 ML/year 26,671 20,393 8,096 4,124 18,378 77,662

% of Total Allocation 34 26 11 5 24 100%

5.2 Subregion flow characteristics

5.2.2 Natural and current flow characteristics A summary of modelled natural and current flow characteristics for the five WMRs are presented in Table 5.2. The table shows that the Upper Macquarie has the most flow and that natural monthly mean flows exceed current flows in the Upper Macquarie, Blackman, and Isis WMRs. Current means exceed natural in the Elizabeth and Lower Macquarie, which may reflect losses to the hydrological system (such as groundwater recharge) and/or over-allocation of water.

27 Table 5.2. Modelled long-term monthly average flow (ML) characteristics under natural and current flow conditions. Model flow data analysed for the five Macquarie catchment WMRs over the period 1970-2007.

Upper Macquarie Elizabeth Blackman Isis Lower Macquarie Natural Current Natural Current Natural Current Natural Current Natural Current Mean 11,055 10,622 6,298 6,496 2,566 2,240 2,720 2,485 4,552 10,740 Median 3,756 3,765 2,137 3,196 834 555 777 587 1,435 5,355 CV 2 2 3 1 2 2 2 2 2 1 monthly Min 369 2 159 199 173 18 118 0 16 21 monthly Max 119,410 112,865 59,036 49,134 38,232 37,554 30,945 30,717 47,389 81,081 10th%ile 3,803 2,993 2,109 2,570 974 865 711 560 903 701 30th%ile 7,688 6,832 3,639 4,268 2,209 1,893 1,825 1,593 2,637 2,890 90th%ile 18,012 17,938 10,985 10,936 3,832 3,380 5,065 4,671 8,195 11,937

5.2.3 Flow duration analysis A flow duration curve (FDC) gives a discharge plotted against percent of time that a particular discharge is equalled or exceeded. A series of FDCs have been generated for the five Macquarie River catchment WMRs (Figure 5.2). These duration curves compare daily flow characteristics of modelled natural and current flows. Table 5.3 gives the probability of exceedance of natural flows for all the WMRs.

Table 5.3 Probability of exceedance (POE) of natural flows (ML/day) in the five Macquarie River catchment WMRs (1970 – 2007).

POE % Upper Macquarie Elizabeth Blackman Isis Lower Macquarie 5 1590 944 322 405 593 10 829 493 151 178 271 20 352 209 60 75 117 30 183 110 28 38 60 40 102 61 14 19 31 50 58 34 9 10 15 60 34 18 8 6 9 70 21 10 8 5 7 80 15 6 8 5 7 90 14 6 8 5 6 95 14 6 7 5 6 99 13 6 6 4 6 The shape of an FDC at its extremities is particularly significant in evaluating the stream and basin characteristics. The shape of the curve in the high-flow region indicates the type of flood regime the basin is likely to have, whereas the shape of the low-flow region characterizes the ability of the basin to sustain low flows during dry seasons. A very steep curve (high flows for short periods) would be expected for rain-driven floods on small watersheds. In the low-flow region, an intermittent stream would exhibit periods of no flow, whereas a very flat curve indicates that moderate flows are sustained throughout the year due to natural or artificial streamflow regulation, or due to a large groundwater capacity which sustains the base flow in the stream.

28 Water abstractions and various landuse practices in the catchment can be reflected in an FDC. Figure 5.2 shows the various impacts of water abstraction and irrigation releases on natural flows. In the Isis and Blackman, the natural curve (in blue) remains well above the current curve (orange), but there are no current low flows (75% of flows and above in the Blackman and 60% of flows and above in the Isis). In the Lower Macquarie, current flows remain just below natural flows, indicating minimal impact to natural flows by abstractions. Comparison between current and natural flows is complicated within the remaining Macquarie WMRs by the man- made storages of Tooms and Lake Leake. Impacts of the lakes on flows can be seen in the Elizabeth curve. Current flows are above natural in the low flow end of the Elizabeth FDC, reflecting losses to the hydrological system and/or over-allocation in low flow periods. A similar effect is seen in the Upper Macquarie during medium flows (20 – 80% flows). The reasonably flat current curve for the Elizabeth WMR also indicates flow sustained through the year by regulated releases for irrigation. Current flow has been derived using water allocation data that has been evenly distributed through the license period, and does not take into account periodic restrictions to water use. This may, as a result, magnify the impact of water usage on the low flow end of the duration curve (there are no restrictions within the Blackman and Isis WMRs, however). Cease-to-flow events are predicted to occur under modelled current flow. However in reality water use restrictions during dry periods usually prevent this from occurring along the Elizabeth and Macquarie Rivers (Appendix A outlines system regulation and the irrigation restriction thresholds).

29 Flow duration curve - Upper Macquarie 1970-2007 Flow duration curve - Elizabeth 1970-2007

100000 100000 natural natural current current 10000 10000

1000 1000

100 100

Discharge (ML/d) Discharge Discharge (ML/d) Discharge 10 10

1 1 0 20 40 60 80 100 0 20 40 60 80 100 % of time discharge equalled or exceeded % of time discharge equalled or exceeded

Flow duration curve - Blackman 1970-2007 Flow duration curve - Isis 1970-2007

100000 10000 natural natural current current 10000 1000

1000

100

Discharge (ML/d) Discharge (ML/d) Discharge 10 10

1 1 0 20 40 60 80 100 0 20 40 60 80 100 % of time discharge equalled or exceeded % of time discharge equalled or exceeded

Flow duration curve - Lower Macquarie 1970-2007

10000 natural current

1000

100 Discharge (ML/d) Discharge 10

1 0 20 40 60 80 100

% of time discharge equalled or exceeded

Figure 5.2 Flow duration curves for the Macquarie River catchment WMRs. Curves indicate stand-alone flows for each WMR (ie. without upstream WMR flows).

5.2.4 Hydrological disturbance indices

Hydrological disturbance indices for the Macquarie River catchment were derived from a comparison of the natural and current flows estimated from the Macquarie catchment model (Table 5.4). The indices were derived using the formulas detailed in the Natural Resource Management (NRM) Monitoring and Evaluation Framework developed by SKM for the Murray-Darling Basin (SKM, 2003).

The indices indicate that the natural flow regime is the most disturbed in the Blackman and Isis, with all WMRs displaying some degree of hydrological disturbance.

Table 5.4 Hydrological disturbance indices for the Macquarie River catchment.

Hydrological Disturbance Indices Upper Macquarie Elizabeth Blackman Isis Lower Macquarie

Mean Annual Flow Index1 0.92 0.97 0.87 0.91 0.91 Flow Duration Curve Difference Index2 0.67 0.50 0.41 0.40 0.72 Seasonal Amplitude Index3 0.86 0.84 0.83 0.84 0.87 Season Period Index4 1.00 0.92 0.83 0.83 1.00 Hydrological Disturbance Index5 0.82 0.73 0.67 0.68 0.84

1Mean Annual Flow Index: This provides a measure of the difference in total flow volume between current and natural conditions. It is calculated as the ratio of the current and natural mean annual flow volumes and assumes that increases and reductions in mean annual flow have equivalent impacts on habitat condition.

2Flow Duration Curve Difference Index: The difference from 1 of the proportional flow deviation, averaged over p monthly flow percentile point. A measure of the overall difference between current and natural monthly flow duration curves. All flow diverted would give a score of 0.

3Seasonal Amplitude Index: The change in amplitude of the seasonal pattern of monthly flows. It is defined as the average of two current: natural ratios, firstly, that of the highest monthly flows, and secondly, that of the lowest monthly flows based on calendar month means.

4Seasonal Period Index: The change in seasonal timing of flows. It is defined as the difference from 1 of one twelfth of the sum of the absolute values of the differences between current and natural of first, the numerical values of the months with the highest mean monthly flows, and second, the numerical values of the months with the lowest mean monthly flows.

5Hydrological Disturbance Index: This provides an indication of the hydrological disturbance to the river’s natural flow regime. A value of 1 represents no hydrological disturbance, while a value approaching 0 represents extreme hydrological disturbance.

5.3 Catchment Water Yield

5.3.1 Natural monthly yields The estimated annual natural flow yield of the Macquarie River at the outlet (above Lake River) is 319,119 ML, with an average daily discharge of 874 ML/day. Table 5.5 presents a summary of natural flow yields from the WMRs and the catchment outlet of the Macquarie River above Lake River. About 47% of the total natural flow yield at the outlet is contributed by winter flows from the upper reaches of the catchment (Upper Macquarie and Elizabeth WMRs). Natural monthly yields are highest during July for the Upper Macquarie, Elizabeth and Blackman, and September for the Isis and Lower Macquarie. Monthly yields are lowest during February or March in all WMRs.

Table 5.5 Average monthly, seasonal, and annual natural yields (ML) in the WMRs of the Macquarie River catchment. Annual allocations (ML) within each WMR are also given.

Upper Lower Yield (ML) Macquarie Elizabeth Blackman Isis Macquarie outlet Jan 7,050 3,244 2,414 1,597 2,658 16,963 Feb 3,087 1,330 947 554 1,581 7,500 Mar 3,793 2,100 945 675 766 8,280 Apr 3,892 2,184 1,212 1,039 828 9,155 May 11,254 6,815 2,396 2,771 3,708 26,944 Jun 16,669 9,832 2,680 2,962 4,786 36,929 Jul 20,176 11,288 4,071 5,092 8,382 49,009 Aug 18,161 11,045 3,846 4,829 6,507 44,388 Sep 16,348 10,446 3,340 5,109 8,903 44,148 Oct 11,393 6,558 2,130 2,654 4,392 27,126 Nov 9,178 4,562 3,145 2,357 2,628 21,870 Dec 11,201 5,984 3,708 3,024 2,890 26,807 Winter 94,002 55,984 18,463 23,417 36,678 228,544 Summer 38,201 19,404 12,372 9,246 11,352 90,574 Annual 132,203 75,388 30,835 32,663 48,030 319,119

Annual allocation 26,671 20,393 8,096 4,124 18,378 77,662

5.3.2 Specific yields Seasonal and annual specific yields of the WMRs are displayed in Figure 5.3, and indicate the yield per km2. Specific yields are greater in the upper catchment WMRs where a greater proportion of high rainfall areas lie.

200

180 Annual Winter Summer 160

140 2 120

100

80 ML/day/km 60

0 Upper Macquarie Elizabeth Blackman Isis Lower Macquarie Outlet (total catchment)

Figure 5.3 Specific yields (natural flow) for the Macquarie River catchment WMRs. The ability of a catchment to convert runoff to river flow is best shown by looking at the monthly specific yields (Table 5.6). The Elizabeth is the most productive WMR, yielding 4,288 ML/km2 in winter, and 1,477 ML/km2 in summer.

Table 5.6 Monthly specific yields in the WMRs.

specific yield (ML/km2) Upper Lower Macquarie Elizabeth Blackman Isis Macquarie outlet Jan 226 251 134 151 185 195 Feb 89 93 47 47 99 78 Mar 122 163 52 64 53 95 Apr 121 164 65 95 56 102 May 361 528 133 263 258 310 Jun 518 737 144 272 323 411 Jul 647 875 226 483 584 563 Aug 583 856 213 458 453 510 Sep 508 783 179 469 600 491 Oct 366 508 118 252 306 312 Nov 285 342 169 216 177 243 Dec 359 464 206 287 201 308 Winter 2,982 4,288 1,013 2,195 2,524 2,597 Summer 1,203 1,477 673 861 772 1021 Annual 4,185 5,765 1,686 3,056 3,297 3,618

5.3 Yield Summary

The overall water budget for the Macquarie River catchment is given in Table 5.7. The average annual yield for the entire catchment up to the outlet (above Lake River) is around 319,120 ML, with a current annual water allocation of 77,662 ML (about 24 %). Allocations are mostly consumptive, being used mainly for irrigation, water supply, and recreation (non-consumptive). Approximately 240,000 ML of the catchment yield remains available for environmental purposes and potential further resource allocation.

Table 5.7 Distribution of average annual yield (ML) in the WMRs.

Annual yield (ML) Annual allocation (ML) Available yield (ML) Upper Macquarie 132,203 26,671 105,532 Elizabeth 75,388 20,393 54,995 Blackman 30,835 8,096 22,739 Isis 32,663 4,124 28,539 Lower Macquarie 48,030 18,378 29,652 Whole catchment 319,119 77,662 241,457

Based on the catchment size and rainfall, gross water input to the catchment is estimated at 1,564 GL/year. The total annual yield at the catchment outlet is around 20% of this (319 GL/yr). A simple water budget indicates, therefore, that 80% of water input into the catchment is lost through evaporation, transpiration, recharge to groundwater, or consumption.

34 References

DPIWE (2000) South Esk River and Macquarie River Flood Data Book. Land and Water Management Branch, Report Series WRA 00/03.

HEC (2005). NAP Region Hydrological Model for Macquarie River Catchment, Department of Primary Industries and Water, Hobart, Tasmania, Australia (in) Development of Hydrological Models for the NAP (National Action Plan) Region in Tasmania. Hydro Electric Corporation (HEC) Consulting Report No.118784-Report- 13: 25p. SKM (2003) Sustainable Rivers Audit Hydrology Theme – Ovens River Basin Hydrology Report, Murray-Darling Basin Commission. Sinclair Knight Mertz.

Steane, JD (1968) Tasmanian Water Resources Survey Report No 4: The Elizabeth and Macquarie Rivers above Baskerville, Rivers and Water Supply Commission, Tasmania.

Appendix A. Description and Operation of Macquarie River Catchment Lakes

36 Background The upper Macquarie River catchment is one of the driest areas in the state as it lies in the rain shadow of both westerly and easterly weather systems. Townships such as Campbell Town and Ross have historically experienced hardships in terms of the available supply of water and it is for this reason that man-made storages have been constructed. Lake Leake and Tooms Lake were created largely to meet township requirements for water as well as stock and domestic requirements downstream, but they also provide irrigation relief from the ephemeral (i.e. intermittent) nature of the streams in these areas. It is not unusual for there to be effectively zero flow in this region during summer months.

Lake Leake An artificial lake constructed at Kearneys Marsh in 1885, Lake Leake is an earth fill dam with a concrete spillway. It has a surface area of 6 km2, average depth of 5 metres, and storage volume of some 22,000 ML. The catchment area for the lake is around 70 km2 (Rivers & Water, 1968).

DPIW has various records of levels in Lake Leake (see table A.1). The most recent records, taken from the BOM website daily readings since 2003, indicate that the lake exceeded full supply level four times between June 2003 and December 2005. Levels fell below the draw down limit of 6,000 ML over the period December 2006 and June 2007, reaching around 4,000 ML for most of that time. See Figure A.1 for historical lake levels.

Operating criteria for the lake is not based solely on the allocation of water downstream. Water levels within the lake are also managed to maintain the lake as a popular fishing and recreational attraction.

Tooms Lake First formed as a dam in the 1830s from a lagoon at the Macquarie River headwater, Tooms Lake is also an earth dam with concrete spillway. It has an estimated surface area of 6 km2, and full supply capacity of around 22,000 ML. Its catchment size is approximately 57 km2.

Less level data is available for Tooms Lake than Lake Leake. Recorded lake levels are given in Figure A.2. In broad terms, the behaviour of Tooms Lake is not unlike that of Lake Leake.

Tooms Lake supplies drinking water for Ross township, as well as downstream irrigation and stock.

37 Table A.1 Level records for Tooms Lake and Lake Leake as available on DPIW Hydstra.

Data type Start End Tooms Lake (Hydstra site 687) Gauge board (Ross Council) 9/7/1938 27/11/1991 BOM disk 1/1/1990 30/9/1991 Manual readings 4/1/1974 29/1/1999 Lake Leake (Hydstra site 210) Continuous 16/1/1986 26/11/1990 BOM disk 1/2/1991 31/7/1997 Edited BOM disk 1/1/1993 31/7/1998 Manual readings 1/4/1928 27/3/1992 Edited manual readings 1/4/1928 31/12/1992 Other (not on Hydstra) Manual readings (BOM records) 1/7/2003 19/6/2008

System Regulation The Macquarie River is maintained as a regulated system, with summer irrigation releases from Lake Leake and Tooms Lake. Flow releases at all times allow for town water supply, environmental flows, and stock and domestic supplies.

There are no flow restriction protocols in place, but the following flows are required to be maintained for environmental purposes:

. 4.1 ML/day at Fosterville (streamgauge station 18313) . 6.1 ML/day at Morningside (streamgauge station 18312) 6 . 6.1 ML/day at Coburg (streamgauge station 18309)

A significant portion of allocations directly below the lakes (the Lake Leake/ Elizabeth/ Macquarie Rivers Irrigation District and the Tooms Lake/ Macquarie Rivers Irrigation District) are managed by the Elizabeth Macquarie Irrigation Trust. The main aims of the Trust are to maintain water supplies to Campbell Town and Ross; maintain environmental flows to the rivers; and manage surplus water for irrigation and stock.

As part of the main water licences on the lakes (managed by the Elizabeth Macquarie Irrigation Trust), flows for irrigation are also curbed when Lake Leake drops below 6,000 ML, and Tooms below 9,000 ML.

While Hydro Tasmania operations have an effect on flows in Lake River, there is no impact to the catchment as described in this study (above Lake River).

6 As of the 2006 water licences; actual streamgauges may change.

38 Appendix A Figure A.1 – Lake Leake levels as recorded for site 210.

5.5

4.5

3.5

3 metres

2.5

1.5 Lake Leake

1 continuous levels BOM disk edited BOM disk manual readings edited manual readings BOM manual data 0.5 draw dow n limit full supply

Jul-72 Jul-09

Jun-31 Oct-43 Jan-52 Jun-68 Oct-80 Jan-93

Feb-56 Mar-60 Mar-97 Apr-01

Sep-39 Nov-47 Nov-84 Dec-88

May-27 Aug-35 May-64 Aug-76 May-05

Appendix A Figure A.2 – Tooms Lake levels as recorded for site 687.

4.5

3.5

2.5 metres

1.5

1 Tooms Lake

0.5 gauge board BOM disk

0 Dec-36 Oct-43 Aug-50 Jun-57 May-64 Mar-71 Jan-78 Nov-84 Sep-91

Appendix B. Potential limitations to the Macquarie River catchment surface water model A number of factors should be borne in mind when viewing results from the Macquarie River catchment surface water model (HEC, 2007):

Current flow is derived by subtracting water usage data for 2008 from the entire period of the observed flow record. A 6% decrease is calculated on the allocations each year proceeding backwards from the present to account for incremental increases in allocations over time. The true allocations, however, have not been applied in each year. This could accentuate differences between both natural and current flow, and between current and observed flow.

The current quantity of water extracted from the catchment is unverified. Entitlements used in the model rely on water licence records for extraction information, however these may not always represent the true quantity of water being extracted.

The modelled current flow does not take into account periods of water restriction, which may result in observed flows during dry periods (exceedance greater than 90%) being closer to modelled natural flow.

Precise soil properties across the catchment are unknown. While the model uses an estimated homogenous soil saturation capacity (cap ave), in reality high soil variability is likely to exist.

The model does not account for the flat nature of land from below Morningside to the outlet, and that there is likely to be minimal pickup and runoff on such a landscape.

Due to the flat landscape and releases from lake storages, flows in the upper Macquarie sometimes outweigh those in the Lower Macquarie, particularly in current flows. This can result in net negative flows in the Lower Macquarie catchments, once Upper Macquarie flows are subtracted.