River modelling for Tasmania Volume 2: the Mersey-Forth region · River modelling for Tasmania...

Ling FLN, Gupta V, Willis M, Bennett JC, Robinson KA, Paudel K, Post DA and Marvanek S

A report to the Australian Government from the CSIRO Tasmania Sustainable Yields Project

December 2009

River modelling for Tasmania Volume 2: the Mersey-Forth region

Contributors

Tasmania Sustainable Yields Project acknowledgments

Prepared by CSIRO for the Australian Government under the Water for the Future Plan of the Australian Government Department of the Environment, Water, Heritage and the Arts. Important aspects of the work were undertaken by the Tasmanian Department of Primary Industries, Parks, Water and Environment; Hydro Tasmania Consulting; Sinclair Knight Merz; and Aquaterra Consulting.

Project guidance was provided by the Steering Committee: Australian Government Department of the Environment, Water, Heritage and the Arts; Tasmanian Department of Primary Industries, Parks, Water and Environment; CSIRO Water for a Healthy Country Flagship; and the Bureau of Meteorology.

Scientific rigour for this report was ensured by external reviewers, Tony Jakeman, Murray Peel and Peter Davies.

Valuable input was provided by the Sustainable Yields Technical Reference Panel: CSIRO Land and Water; Australian Government Department of the Environment, Water, Heritage and the Arts; Tasmanian Department of Primary Industries, Parks, Water, and Environment; Western Australian Department of Water; and the National Water Commission.

We acknowledge the Tasmanian Department of Primary Industries, Parks, Water, and Environment for providing the original TasCatch models for use in the current project, and for assistance in providing cease-to-take rules, operating rules for storages, and environmental flows.

We acknowledge input from the following individuals: Richard McLoughlin, Alan Harradine, Louise Minty, Ian Prosser, Patricia Please, Martin Read, Rod Oliver, Dugald Black, Ian Loh, Albert Van Dijk, Geoff Podger, Scott Keyworth, Helen Beringen, Mary Mulcahy, Paul Jupp, Amanda Sutton, Josie Grayson, Melanie Jose, Ali Wood, Peter Fitch, Wenju Cai, Ken Currie, Eric Lam, Imogen Fullagar, Nathan Bindoff, Stuart Corney, Mike Pook and Richard Davis.

Tasmania Sustainable Yields Project disclaimers

Derived from or contains data and/or software provided by the Organisations. The Organisations give no warranty in relation to the data and/or software they provided (including accuracy, reliability, completeness, currency or suitability) and accept no liability (including without limitation, liability in negligence) for any loss, damage or costs (including consequential damage) relating to any use or reliance on the data or software including any material derived from that data or software. Data must not be used for direct marketing or be used in breach of the privacy laws. Organisations include: the Tasmanian Department of Primary Industries, Parks, Water, and Environment; Hydro Tasmania Consulting; Sinclair Knight Merz; Aquaterra Consulting; Antarctic Climate and Ecosystems CRC; Tasmanian Irrigation Development Board; Private Forests Tasmania; and the Queensland Department of Environment and Resource Management.

Data on proposed irrigation developments were supplied by the Tasmanian Irrigation Development Board in June 2009. Data on projected increases in commercial forest plantations were provided by Private Forests Tasmania in February 2009.

CSIRO advises that the information contained in this publication comprises general statements based on scientific research. The reader is advised and needs to be aware that such information may be incomplete or unable to be used in any specific situation. No reliance or actions must therefore be made on that information without seeking prior expert professional, scientific and technical advice. To the extent permitted by law, CSIRO (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using this publication (in part or in whole) and any information or material contained in it. Data are assumed to be correct as received from the Organisations.

Citation

Ling FLN, Gupta V, Willis M, Bennett JC, Robinson KA, Paudel K, Post DA and Marvanek S (2009) River modelling for Tasmania. Volume 2: the Mersey-Forth region. A report to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

Publication Details

Published by CSIRO © 2009 all rights reserved. This work is copyright. Apart from any use as permitted under the Copyright Act 1968, no part may be reproduced by any process without prior written permission from CSIRO.

ISSN 1835-095X

Photo on cover: Forth River below Lake Paloona (CSIRO)

Project Management: David Post, Tom Hatton, Mac Kirby, Therese McGillion and Linda Merrin

Report Production: Frances Marston, Susan Cuddy, Maryam Ahmad, William Francis, Becky Schmidt, Siobhan Duffy, Heinz Buettikofer, Alex Dyce, Simon Gallant, Chris Maguire and Ben Wurcker

Project Team: CSIRO: Francis Chiew, Neil Viney, Glenn Harrington, Jin Teng, Ang Yang, Glen Walker, Jack Katzfey, John McGregor, Kim Nguyen, Russell Crosbie, Steve Marvanek, Dewi Kirono, Ian Smith, James McCallum, Mick Hartcher, Freddie Mpelasoka, Jai Vaze, Andrew Freebairn, Janice Bathols, Randal Donohue, Li Lingtao, Tim McVicar and David Kent

Tasmanian Department of Primary Industries, Parks, Water and Environment:

Bryce Graham, Ludovic Schmidt, John Gooderham, Shivaraj Gurung, Miladin Latinovic, Chris Bobbi, Scott Hardie, Tom Krasnicki, Danielle Hardie and Don Rockliff

Hydro Tasmania Consulting: Fiona Ling, Mark Willis, James Bennett, Vila Gupta, Kim Robinson, Kiran Paudel and Keiran Jacka

Sinclair Knight Merz: Stuart Richardson, Dougal Currie, Louise Anders and Vic Waclavik

Aquaterra Consulting: Hugh Middlemis, Joel Georgiou and Katharine Bond

Director’s foreword

Following the November 2006 Summit on the southern Murray-Darling Basin (MDB), the then Prime Minister and MDB

state Premiers commissioned CSIRO to undertake an assessment of sustainable yields of surface and groundwater

systems within the MDB. The project set an international benchmark for rigorous and detailed basin-scale assessment of

the anticipated impacts of climate change, catchment development and increasing groundwater extraction on the

availability and use of water resources.

On 26 March 2008, the Council of Australian Governments (COAG) agreed to expand the CSIRO assessments of

sustainable yield so that, for the first time, Australia would have a comprehensive scientific assessment of water yield in

all major water systems across the country. This would allow a consistent analytical framework for water policy decisions

across the nation. The Tasmania Sustainable Yields Project, together with allied projects for northern Australia and

south-west Western Australia, will provide a nation-wide expansion of the assessments.

The CSIRO Tasmania Sustainable Yields Project is providing critical information on current and likely future water

availability. This information will help governments, industry and communities consider the environmental, social and

economic aspects of the sustainable use and management of the precious water assets of Tasmania.

The projects are the first rigorous attempt for the regions to estimate the impacts of catchment development, changing

groundwater extraction, climate variability and anticipated climate change, on water resources at a whole-of-region-scale,

explicitly considering the connectivity of surface and groundwater systems. To do this, we are undertaking the most

comprehensive hydrological modelling ever attempted for the region, using rainfall-runoff models, groundwater recharge

models, river system models and groundwater models, and considering all upstream-downstream and surface-

subsurface connections.

To deliver on the projects CSIRO is drawing on the scientific leadership and technical expertise of national and state

government agencies in Queensland, Tasmania, the Northern Territory and Western Australia, as well as Australia’s

leading industry consultants. The projects are dependent on the cooperative participation of over 50 government and

private sector organisations. The projects have established a comprehensive but efficient process of internal and

external quality assurance on all the work performed and all the results delivered, including advice from senior academic,

industry and government experts.

The projects are led by the Water for a Healthy Country Flagship, a CSIRO-led research initiative established to deliver

the science required for sustainable management of water resources in Australia. By building the capacity and capability

required to deliver on this ambitious goal, the Flagship is ideally positioned to accept the challenge presented by this

complex integrative project.

CSIRO has given the Sustainable Yields Projects its highest priority. It is in that context that I am very pleased and proud

to commend this report to the Australian Government.

Dr Tom Hatton

Director, Water for a Healthy Country

National Research Flagships

CSIRO

© CSIRO 2009 River modelling for Tasmania. Volume 2: the Mersey-Forth region ▪ i

Executive summary

This report describes the river system modelling undertaken for the Mersey-Forth region as part of the CSIRO Tasmania

Sustainable Yields Project. The objective of the river system modelling is to estimate flows in river systems across

Tasmania using a consistent Tasmania-wide modelling approach for four scenarios involving a range of climate

conditions and catchment development levels. The four scenarios are:

Scenario A – historical climate (1 January 1924 to 31 December 2007) and current development

Scenario B – recent climate (data from 1 January 1997 to 31 December 2007 were concatenated to make an

84-year sequence) and current development

Scenario C – future climate (84-year sequence scaled for ~2030 conditions) and current development

Scenario D – future climate (84-year sequence scaled for ~2030 conditions) and future development.

In this project, current development is defined as the development at the end of 2007. Future development is defined to

include future projected levels of commercial forestry plantations, irrigation development and groundwater extraction.

This report only considers changes in future development associated with commercial forestry plantations and irrigation

development as these are the only factors which are likely to affect surface water availability in this region.

River system models were developed for each catchment to describe current infrastructure, water demands and water

management rules. These models were used to assess the implications of changed inflows for water availability and the

reliability of water supply to users. The models are node-link network models developed in Hydstra and they include

water allocations and extractions, streamflow routing and environmental flows. Gridded runoff, rainfall and areal potential

evapotranspiration were inputs to the models. The models were run on a daily time step and the runoff from each

subcatchment was routed through the river network to the next subcatchment downstream.

The Mersey and Forth-Wilmot catchments include areas covered by Tasmania’s hydro-electric system. Catchments with

river systems downstream of hydro-electric storages include inputs to the river models from Hydro Tasmania’s system

model, TEMSim. These inputs include flows through power stations and spills from storages. The hydro-electric system

is modelled separately as it is operated as an integrated system taking into consideration the National Electricity Market

and demand.

Over the historical period (1924 to 2007), the Mersey-Forth region had a mean annual flow of 3881 GL/year, and a

relatively low level of extraction with a mean annual extraction of 81 GL/year (2.0 percent of total water in the region).

The level of extraction varies between catchments up to a maximum of 7 percent in the Rubicon catchment. The volume

of allocated water varies each year in many catchments, due to restriction rules which limit extractions during periods of

low flow.

The volume of water extracted in the region is not expected to reduce significantly under the future climate (Scenario C)

relative to the historical climate (Scenario A). The largest impact is in the driest years, with a projected decrease of up to

11.9 percent in extracted water in the Mersey catchment for the driest one-year period under the dry extreme future

climate (Scenario Cdry) relative to the historical climate. Future climate is projected to have a greater impact on total

end-of-system flows for the region, ranging from a decrease of 1 percent (under the wet extreme future climate

(Scenario Cwet)) to a decrease of 10 percent (under the dry extreme future climate) with a median reduction of 6 percent

(under the median future climate (Scenario Cmid)).

Under the recent climate (Scenario B), the monthly mean discharge is lower than the long-term mean in all catchments in

summer, autumn and early winter. The flow duration curves show that flows under the recent climate are generally lower

than the long-term mean over the full range of flows. The volume of extracted water decreases by a mean of 4.3 GL/year

(5 percent) under the recent climate relative to the historical climate. The volume of non-extracted water decreases by a

mean of 525 GL/year (14 percent).

Future development in the Mersey-Forth region includes a projected increase of 248 km2 in commercial forestry

plantations, which will increase total forest cover from 25 percent of the region to 29 percent of the region by 2030. This

increase is entirely in the northern two-thirds of the region. Catchment runoff is projected to decrease by a maximum of

4.7 percent in the Tamar Estuary catchment due to the expansion of forestry plantations under future development

(Scenario D).

ii ▪ River modelling for Tasmania. Volume 2: the Mersey-Forth region © CSIRO 2009

Four irrigation developments are proposed in the region: the Sheffield-Barrington, Kindred-North Motton, Forthside-Don

and Sassafras-Wesley Vale schemes. These schemes rely on storage and flows from the Mersey-Forth hydro-electric

scheme. The Sheffield-Barrington and Sassafras-Wesley Vale schemes were modelled as extractions from hydro-electric

storages in TEMSim and the results showed that the hydro-electric system could be run to supply this demand in all

years under future development. The Kindred-North Motton and Forthside-Don schemes had a projected reliability of

97 percent or greater under future development.

© CSIRO 2009 River modelling for Tasmania. Volume 2: the Mersey-Forth region ▪ iii

Table of contents

1 Introduction ............................................................................................................................ 1

2 Methods .................................................................................................................................. 5 2.1 Allocations and extractions ..............................................................................................................................................5

2.1.1 Water entitlements.............................................................................................................................................5 2.1.2 Unlicensed storages ..........................................................................................................................................6 2.1.3 Unlicensed extractions ......................................................................................................................................7 2.1.4 Environmental flows and releases.....................................................................................................................7 2.1.5 Diversions, storages, and model customisation ................................................................................................7

2.2 Hydro-electric infrastructure .............................................................................................................................................9 2.3 Future development .......................................................................................................................................................11

2.3.1 Forestry............................................................................................................................................................11 2.3.2 Irrigation...........................................................................................................................................................12

3 Under historical climate (Scenario A) and future climate (Scenario C)......................... 15 3.1 Water balance and water availability..............................................................................................................................15 3.2 Storage behaviour..........................................................................................................................................................21 3.3 Consumptive water use..................................................................................................................................................21 3.4 End-of-system river flow.................................................................................................................................................29 3.5 Share of available resource ...........................................................................................................................................32

4 Under historical climate (Scenario A) and recent climate (Scenario B) ........................ 38

5 Under future development (Scenario D)............................................................................ 42 5.1 Reliability of proposed irrigation developments..............................................................................................................42 5.2 Hydrological impacts of future development ..................................................................................................................44

6 Conclusions .......................................................................................................................... 49

7 References............................................................................................................................ 50

Tables

Table 1. Catchments in the Mersey-Forth region.................................................................................................................................4 Table 2. Large storages in the Mersey-Forth region............................................................................................................................4 Table 3. Department of Primary Industries, Parks, Water and Environment surety descriptions (from DPIPWE, 2009) ....................6 Table 4. Extraction restriction rules......................................................................................................................................................8 Table 5. Irrigable area for proposed irrigation developments for Scenario D ....................................................................................14 Table 6. Mean annual water balance for each catchment under scenarios A and C ........................................................................16 Table 7. Storage behaviour under scenarios A and C.......................................................................................................................21 Table 8. Allocated and extracted mean annual flows for catchments under scenarios A and C .......................................................23 Table 9. Mean reliability of high and low priority allocations for catchments under scenarios A and C (annual) ..............................24 Table 10. Mean reliability of high and low priority allocations for catchments under scenarios A and C (summer – October to March inclusive) ............................................................................................................................................................................................24 Table 11. Mean reliability of high and low priority allocations for catchments under scenarios A and C (winter – April to September inclusive) ............................................................................................................................................................................................25 Table 12. Indicators of use during dry periods for catchments under Scenario A and change under Scenario C relative to Scenario A.........................................................................................................................................................................................................28 Table 13. Peak flows for catchments under scenarios P and A, and under Scenario C relative to Scenario A ................................31 Table 14. Percentage of time end-of-system flow is greater than 1 ML/day under scenarios P, A and C.........................................31 Table 15. End-of-system flow for catchments during dry periods under Scenario A and under Scenario C relative to Scenario A..32 Table 16. Extracted and non-extracted shares of water for Mersey-Forth region under scenarios A and C (annual).......................33 Table 17. Extracted and non-extracted shares of water for catchments under scenarios A and C (annual).....................................35 Table 18. Extracted and non-extracted shares of water for the Mersey-Forth region under scenarios A and C (summer – October to March inclusive) .............................................................................................................................................................................35 Table 19. Extracted and non-extracted shares of water for catchments under scenarios A and C (summer – October to March inclusive) ............................................................................................................................................................................................36 Table 20. Percentage of water extracted as a proportion of total end-of-system flow for catchments under scenarios A and C (annual)..............................................................................................................................................................................................37 Table 21. Percentage of water extracted as a proportion of total end-of-system flow for catchments under scenarios A and C (summer – October to March inclusive) .............................................................................................................................................37 Table 22. Percentage of water extracted as a proportion of total end-of-system flow for catchments under scenarios A and C (winter – April to September inclusive) ..............................................................................................................................................37

iv ▪ River modelling for Tasmania. Volume 2: the Mersey-Forth region © CSIRO 2009

Table 23. Mean annual extracted and non-extracted shares of water for Mersey-Forth region under scenarios A and B................39 Table 24. Extracted and non-extracted shares of water for Mersey-Forth region under scenarios A and B (summer – October to March inclusive) .................................................................................................................................................................................40 Table 25. Mean annual extracted and non-extracted shares of water for catchments under scenarios A and B..............................40 Table 26. Extracted and non-extracted shares of water for catchmentsunder scenarios A and B (summer – October to March inclusive) ............................................................................................................................................................................................41 Table 27. Comparison of allocated and extracted water under Scenario D schemes .......................................................................43 Table 28. Indicators of use during dry periods under Scenario D schemes ......................................................................................44 Table 29. Inflows from catchment runoff under Scenario D relative to Scenario C ...........................................................................44 Table 30. Inflows from downstream of hydro storages under Scenario D relative to Scenario C......................................................44 Table 31. Percent time end-of-system flow for catchments greater than 1 ML under Scenario D relative to Scenario C .................45 Table 32. Comparison of extractions for catchments under Scenario D relative to Scenario C ........................................................45 Table 33. Comparison of change in peak flows under Scenario D relative to Scenario C ................................................................48

Figures

Figure 1. Project extent and reporting regions.....................................................................................................................................1 Figure 2. Land cover, major rivers and towns in the Mersey-Forth region ..........................................................................................2 Figure 3. Modelled catchments, major storages and reporting locations in the Mersey-Forth region .................................................3 Figure 4. Subcatchment delineation and WIMS licence locations .......................................................................................................7 Figure 5. Hydro-electricity catchment areas included in TEMSim .....................................................................................................10 Figure 6. Proposed irrigation developments and increase in forest cover due to future commercial forest plantations in the Mersey-Forth region...........................................................................................................................................................................12 Figure 7. Mersey-Forth hydro-electric system ...................................................................................................................................13 Figure 8. River transects showing streamflow under scenarios P, A and C ......................................................................................19 Figure 9. End-of-system (EOS) streamflow in the Mersey-Forth region under (a) Scenario A, and difference from Scenario A under scenarios (b) Cwet, (c) Cmid and (d) Cdry ........................................................................................................................................20 Figure 10. Storage behaviour over representative ten-year period under scenarios A and C...........................................................21 Figure 11. Total annual extractions for Mersey-Forth region under (a) Scenario A, and difference from Scenario A under scenarios (b) Cwet, (c) Cmid and (d) Cdry.........................................................................................................................................................22 Figure 12. Allocation and extraction reliability for catchments under scenarios A and C (annual) ....................................................25 Figure 13. Allocation and extraction reliability for catchments under scenarios A and C (summer – October to March inclusive) ...27 Figure 14. Mean monthly end-of-system flow and daily flow duration curves under scenarios P, A and C ......................................29 Figure 15. Extracted and non-extracted shares of water for Mersey-Forth region under scenarios A and C (annual) .....................32 Figure 16. Extracted and non-extracted shares of water for catchments under scenarios A and C (annual) ...................................34 Figure 17. Mean end-of-system monthly flow and daily flow duration curves for catchments under scenarios A and B ..................38 Figure 18. Mean annual extracted and non-extracted shares of water for Mersey-Forth region under scenarios A and B ..............39 Figure 19. Allocation and extraction reliability under Scenario D schemes .......................................................................................43 Figure 20. Mean monthly end-of-system flow under scenarios P, A and C; and changes under Scenario D relative to Scenario C 47

© CSIRO 2009 River modelling for Tasmania. Volume 2: the Mersey-Forth region ▪ 1

1 Introduction

This report is one in a series of technical reports from the CSIRO Tasmania Sustainable Yields Project. The terms of

reference for the project require an assessment of the current and likely future extent and variability of surface and

groundwater resources in Tasmania. This information will help governments, industry and communities consider the

environmental, social and economic aspects of the sustainable use and management of the precious water assets of

Tasmania.

The purpose of this report is to describe in detail the river system modelling undertaken for the project. The main

objective of the river system modelling is to estimate flows in river systems across Tasmania for four scenarios using a

consistent Tasmania-wide modelling approach, recognising that the natural and managed behaviour of rivers means that

variability in runoff is not uniformly translated to variability in river flows and water uses. The four scenarios are:

Scenario A – historical climate (1 January 1924 to 31 December 2007) and current development

Scenario B – recent climate (data from 1 January 1997 to 31 December 2007 were concatenated to make an

84-year sequence) and current development

Scenario C – future climate (~2030) and current development (84-year sequence scaled for ~2030 conditions)

Scenario D – future climate (~2030) and future development (84-year sequence scaled for ~2030 conditions).

These were compared with a fifth scenario, Scenario P, which represents water availability modelled with historical

climate, current infrastructure and no extractions. This allows the impact of extractions to be explicitly considered.

The results of the climate and runoff modelling are key inputs to the river system modelling. The climate and runoff

modelling are described in separate reports by Post et al. (2009) and Viney et al. (2009) respectively.

This report describes the river system modelling and results for the Mersey-Forth region. The river system modelling

method is described in Section 2. The key modelling results for each scenario are presented in sections 3 to 5. This

report is part of a series of reports describing river system modelling for each of the five regions, namely the

Arthur-Inglis-Cam, Mersey-Forth, Pipers-Ringarooma, South Esk and Derwent-South East regions (Ling et al., 2009a–e).

The reporting regions are shown in Figure 1. The project provides only limited reporting on sustainable yields for parts of

the west coast and south-west and for the smaller offshore islands. Figure 2 illustrates the location of the major towns

and main land uses in the region. A map of the reporting locations in the Mersey-Forth region is shown in Figure 3. The

model catchment boundaries are also shown on this figure.

Figure 1. Project extent and reporting regions

2 ▪ River modelling for Tasmania. Volume 2: the Mersey-Forth region © CSIRO 2009

Figure 2. Land cover, major rivers and towns in the Mersey-Forth region


Figure 3. Modelled catchments, major storages and reporting locations in the Mersey-Forth region


Table 1. Catchments in the Mersey-Forth region

Number Catchment Area Mean annual rainfall

Mean annual runoff

Mean annual extraction

km2 mm/y GL/y

33 Leven 735 1624 607.3 16.4

34 Forth-Wilmot 1120 1922 102.2* 12.9

35 Mersey 1865 1435 526.3* 32.3

36 Rubicon 641 932 166.7 11.4

43 Tamar Estuary 1049 872 263.8 7.6

*As the Mersey and Forth-Wilmot catchments are partially modelled using TEMSim, these statistics are for the catchment area downstream of hydro-electric storages.

For modelling purposes, the Mersey-Forth region was divided into 5 catchments (see Table 1). Most of the

end-of-system flow comes from the Forth-Wilmot catchment, even though the Mersey catchment is larger (Figure 3). This

occurs because of the large hydro transfers of water from the Mersey and Forth-Wilmot into the Leven, which occurs

upstream of the catchment model areas and is reflected in the inflows from hydro schemes in Table 6. Rainfall varies

across the region from a mean of 872 mm/year over the Tamar Estuary catchment to 1922 mm/year over the

Forth-Wilmot catchment.

The Mersey-Forth region includes one large storage (Lake Isandula in the Leven catchment) which was modelled as part

of the river system. See Table 2 for details of this storage. The release represents controlled releases only and not spill

from the storage.

Table 2. Large storages in the Mersey-Forth region

Effective storage

Mean annual inflow

Mean annual

releases

Degree of regulation

GL GL/y

Major irrigation supply reservoirs

Isandula 0.63 19.41 3.19 0.16

Region total 0.63 19.41 3.19 0.16


2 Methods

This section is a summary of the generic approach used for river system modelling and a brief description of the

5 catchment models in the Mersey-Forth region.

River system models describing current infrastructure, water demands and water management rules were used to

assess the implications of changed inflows for water availability and the reliability of water supply to users. Most of the

river system models are based on the TasCatch models developed for Department of Primary Industries, Parks, Water

and Environment (DPIPWE) (Willis, 2008). These models were funded by the Australian Government Water Fund, for the

Water Smart Australia Project, Better Information for Better Outcomes Enhancing Water Planning in Tasmania and the

Tasmanian Government SMART Farming budget initiative. New models were developed for the catchments which were

not covered by existing DPIPWE models.

TasCatch models are node-link network models developed in Hydstra (Kisters, 2009) which include a water balance

model, streamflow routing, water allocations and extractions, and environmental flows. For the purposes of the CSIRO

Tasmania Sustainable Yields Project, the water balance and streamflow lag and attenuation were removed from the

models, as gridded runoff, rainfall and evaporation were provided as inputs to the models (Viney et al., 2009). The lag

and attenuation of streamflow was therefore removed as the calibration technique used to produce the input runoff grid

implicitly included routing. The models run on a daily time step and route the runoff through the river system. The runoff

in each subcatchment was calculated as the mean of the gridded runoff over the subcatchment. Runoff from each grid

cell was weighted in the averaging process depending on the proportion of the grid cell that fell within a subcatchment.

Subcatchment runoff was then routed through the river network to the next subcatchment downstream. In areas where a

number of catchment models flow into one another in series, the models were run in logical sequence so that the outflow

from the upstream model was an input to the downstream model. Running of the models was automated so that all

catchment models were run in logical order for each scenario.

Rainfall and evaporation grids were used to calculate the rainfall and evaporation occurring over the surface area of

storages within the models.

Many catchments include areas covered by Tasmania’s hydro-electric system. Catchments which include river systems

downstream of hydro-electric storages include inputs to the river models from Hydro Tasmania’s system model, TEMSim.

These inputs include flows through power stations and spills from storages. TEMSim is described in detail in Section 2.2.

Model subcatchment delineation and definition of the river network was initially performed using CatchmentSIM GIS

software (Catchment Simulation Solutions, 2009). Within a given catchment, subcatchments were defined to be of similar

size and to ensure that the routing length between catchment centroids was representative of the river length.

Subcatchments were broken upstream of river junctions. The outputs were visually checked to ensure accurate

representation of the catchment, and modifications were made manually as required. The subcatchment delineation is

shown in Figure 4.

2.1 Allocations and extractions

2.1.1 Water entitlements

Information on the current water entitlements as of December 2008 was obtained from DPIPWE’s Water Information

Management System (WIMS) database. WIMS includes an annual allocation and period for each licence. For example, a

licence may be for 200 ML from October to February. Each licence in the catchment is of a given surety (from 1 to 8),

with surety 1 to 4 representing high priority extractions for modelling purposes and surety 5 to 8 representing low priority.

Details of surety levels are given in Table 3 and the location of the WIMS licences are shown in Figure 4.


Table 3. Department of Primary Industries, Parks, Water and Environment surety descriptions (from DPIPWE, 2009)

Surety Description

High priority

1 Rights for the taking of water for domestic purposes, consumption by livestock or firefighting under Part 5 of the Water Management Act 1999 and rights of councils to take water under Part 6 of the Act. Surety 1 water is expected to be available at about 95 percent reliability.

2 The water provision allocated to supply the needs of ecosystems dependent on the water resource.

3 Rights of licensees granted a water licence as a replacement of the ‘prescriptive rights’ (‘pre-Hydro Tasmania rights’) granted under the previous Water Act 1957.

4 Rights of special licensees such as Hydro Tasmania.

Low priority

5 Rights issued for the taking of water otherwise than for the purposes described above under surety levels 1 to 4. This includes rights issued for the taking of water under Part 6 of the Act for direct extraction, and for winter storage in dams, for use for irrigation or other commercial purposes. Surety 5 water is expected to be available at about 80 percent reliability.

6 Rights at this surety level issued for the taking of water under Part 6 of the Act for direct extraction for use for irrigation and other commercial purposes and for winter storage in dams. Surety 6 water is expected to be available at less than 80 percent reliability.

7, 8 Water allocations available with a lower level of reliability than a surety 6 allocation.

There is no record of actual extraction amounts over the year because extractions are currently not metered. In the

absence of any information on the monthly profile of irrigation extractions, allocation was assumed to be evenly extracted

over the allocation period, resulting in a constant daily allocation over the allocation period. Allocations were accumulated

in each subcatchment, and daily extraction of the allocated amount was attempted, based on surety priority. Where

sufficient water is not available for the full allocation, the extracted amount equalled the amount available.

2.1.2 Unlicensed storages

In Tasmania, a water licence is not required for storages of less than 1 ML. Numbers of unlicensed storages were

estimated by visually identifying small dams not included in the WIMS database as extractions in selected catchments.

These results were then extrapolated to other similar catchments. Where unlicensed storages had been estimated for a

catchment in the TasCatch modelling process, these figures were used (Willis, 2008). For the remaining areas, a

combination of dam counting and extrapolation of unlicensed storages in neighbouring catchments was used. Dams

were manually counted in all calibration catchment areas (details of calibration catchments can be found in Viney et al.

(2009)).


Figure 4. Subcatchment delineation and WIMS licence locations

2.1.3 Unlicensed extractions

It is assumed that there will be some unlicensed extractions. The volume of unlicensed extractions for each catchment

was estimated based on local advice provided by DPIPWE.

2.1.4 Environmental flows and releases

An environmental release of 2 m3/second is mandated from Lake Parangana on the Mersey River (see Figure 7 for

location). The exception to this rule is that when the inflow to Lake Parangana is less than 2 m3/second the

environmental release must be equal to the inflow. Environmental flow studies have also been completed in the Leven

and Rubicon catchments, however, rules are not yet formalised in a water management plan.

2.1.5 Diversions, storages, and model customisation

A number of catchments include water diversion infrastructure or specific rules which control extractions. This includes

rivers where a ‘cease-to-take’ flow rule is in place, meaning that extractions from the river must be ceased when flow in

the river at a specified location falls below a set minimum (or threshold). Flow rules are set in stages, with stage 1 as the

first rule to be enforced, followed by stage 2. In catchments where a flow rule is in place, the models required custom

coding to account for associated operating rules, and these were treated as a reduction in allocation. Restriction rules for

catchments in the Mersey-Forth region are shown in Table 4.


Table 4. Extraction restriction rules

River Location Catchment Month Threshold Stage Restriction rule

ML/d

Gawler Preston Road Gauge board

Leven All year 3.45 1 Ban on direct takes

Gawler Preston Road Gauge board

Leven All year 2.76 2 Ban on direct takes

Dec–May 195 1 Ban on surety 4 to surety 7 allocations from all streams in plan area

June 370 1 Ban on surety 4 to surety 7 allocations from all streams in plan area

July 570 1 Ban on surety 4 to surety 7 allocations from all streams in plan area

Aug–Sep 680 1 Ban on surety 4 to surety 7 allocations from all streams in plan area

Oct 370 1 Ban on surety 4 to surety 7 allocations from all streams in plan area

Mersey Latrobe Mersey

Nov 260 1 Ban on surety 4 to surety 7 allocations from all streams in plan area

Rubicon Tidal limit Rubicon All year 2 1 Ban on surety 6 direct takes on reaching 1st stage trigger

Rubicon Tidal limit Rubicon All year 2 2 Ban on surety 5 direct takes on reaching 2nd stage trigger

Generic model functions representing storage and restriction rules were coded for use in the models. The values specific

to the catchment conditions were passed to these functions during the running of the model. Customisations of

catchment models within the Mersey-Forth region are briefly described below. A more detailed description of the models

can be found in Willis et al. (2009).

Mersey Model

The upper Mersey River is heavily regulated by the Mersey Forth Power Development, including a large inter-basin

transfer from the Mersey River to the Forth River. The integrated operation of the hydro-electric infrastructure within the

Mersey catchment was modelled using TEMSim. Lake Parangana is the lowest hydro-electricity generation asset on the

Mersey River and the TEMSim model outflow from this location was utilised as an input to the Mersey catchment model

which models the river system downstream of Lake Parangana. The outflows from Lake Parangana include spill flows

and the environmental release into the Mersey River (see Figure 7).

DPIPWE extraction restriction rules for the Mersey catchment stipulate restriction rules measured at Mersey River at

Latrobe, as detailed in Table 4.

Industrial Extractions

Part of the lower Mersey River is diverted for industrial use. In the absence of any other information, the volume of the

diversion has been set at 30 ML/day on the basis of a 2001 DPIW report (Green, 2001). The extraction has been

assigned the same priority as surety 5 direct extractions, and is included as a surety 5 direct extraction for reporting

purposes.

Forth-Wilmot Model

The upper Forth River is heavily regulated by the Mersey-Forth Power Development, including a large inter-basin

transfer from the Mersey River to the Forth River. The Wilmot River, the major tributary of the Forth, is also affected by

the hydro-electric scheme. The integrated operation of the hydro-electric infrastructure within the Forth and Wilmot

catchments was modelled using TEMSim. Lake Gairdner is the lowest hydro-electricity generation asset on the Wilmot

River and the TEMSim model outflow from this location was utilised as an input to the Wilmot River in the Forth-Wilmot

catchment model which models the river system downstream of hydro-electricity generation assets. The outflows from

Lake Gairdner include spill flows into the Wilmot River. Lake Paloona is the lowest hydro-electricity generation asset on

the Forth River and the TEMSim model outflow from this location was utilised as an input to the Forth River in the

Forth-Wilmot catchment model. The outflows from Lake Paloona include spill flows and power station flows into the Forth

River (see Figure 7).


Leven River Model

Lake Isandula is the major storage in this catchment (see Figure 3). Ulverstone Township and an industrial user are the

major users of water from this lake. The mean daily extraction rates from Lake Isandula for winter and summer are

7.71 ML/day and 10.57 ML/day respectively. Environmental or other downstream releases from this lake have not been

specified. The full supply volume for Lake Isandula is 700 ML. Minimum operating volume is 75 ML. This gives an

effective storage of 625 ML.

DPIPWE extraction restriction rules for the Leven catchment stipulate restriction rules measured at Gawler River at

Preston Road Gaugeboard, as detailed in Table 4.

Rubicon Model

DPIPWE extraction restriction rules for the Rubicon catchment stipulate restriction rules measured at Rubicon River at

tidal limit, as detailed in Table 4.

2.2 Hydro-electric infrastructure

Tasmania’s hydro-electric system covers a large proportion of the western and central areas of the state. The

system is optimally operated in an integrated manner to meet demand for electricity and to maximise opportunities for

trading in the National Electricity Market (NEM). The catchments and storages that are used for hydro-electricity

generation must therefore be modelled as a total system rather than individual catchments for the purposes of this

project. Hydro-electricity catchment areas are shown in Figure 5.


Figure 5. Hydro-electricity catchment areas included in TEMSim

For the purposes of operational planning and trading, Hydro Tasmania developed the Tasmanian Electricity Market

Simulation Model (TEMSim). TEMSim was used in this project to simulate the operation of Tasmania’s hydro-electric

system including operation of storages, spills and flows through power stations. TEMSim simulates the operation of the

Hydro generating system assuming that Hydro Tasmania is operating within the National Electricity Market (NEM), and

the current infrastructure is in place. The model simulates the interactive operation of 26 power stations and 46 storages.

Generation is offered according to current NEM rules and dispatch simulates NEM dispatch. The model produces daily

estimates of generation, revenue, spills from storages, and flow through power stations.

TEMSim uses estimates of daily inflows to each of the storages as input. There are 47 inflow series to TEMSim

representing natural inflows to storages, canals and diversions at key points in the system. These daily inflow estimates


were created prior to running TEMSim. The inflows were calculated retrospectively based on a variety of methods,

depending on available data. These methods include regression analysis with available data and water balances based

on the storage volume and known outflows. TEMSim is restricted to run with data from 1924 onwards due to lack of

availability of data to estimate inflows to storages prior to this date.

Outflows from TEMSim were input to the individual catchment models at any point in the river system where there are

outflows from power stations, riparian or environmental releases, or spills from hydro storages. TEMSim was therefore

run for each scenario before running the river system models.

TEMSim has a maximum run length of 20 years. To construct the 84-year series needed for this project, TEMSim was

run five times with subsets of the historical inflows, and the outputs were concatenated. For example, the first run used

inflows from 1924 to 1943 and the second run used inflows from 1944 to 1963. At the end of each 20-year run the

finishing lake storage positions were input as the starting position for the next run to preserve volume balances over the

84 years. Historical inflows to TEMSim were consistent with the definition of Scenario A (i.e. historical inflows and current

infrastructure). Inflows to TEMSim were modified for scenarios B, C and D using the process described below.

The TEMSim Scenario B model utilised the last 11 years (1997 to 2007) of the inflow series from Scenario A. The

11 years were concatenated to form an 84-year series for each inflow, and TEMSim was run as described above.

Outflows from TEMSim were required as inputs to river models for scenarios B, C and D. TEMSim inflow series were

created in order to run TEMSim for these scenarios. TEMSim inflow series for scenarios C and D were derived by scaling

each of the 47 Scenario A inflow series (one per catchment) by differences in the duration curves of flows. The

methodology used is described below:

The TEMSim catchment area was divided into 15 broad catchments. Each of the 47 inflow series were assigned

to one of these 15 catchments. The selection of the 15 broad catchments was based on areas which were

hydrologically similar. The 47 inflow series were not investigated individually as initial investigations found that

there was little difference in the scaling at this level of detail, and that this was not warranted within the

constraints of the project.

For each of the 15 catchments a daily time series of total catchment runoff was calculated from the Scenario A,

Scenario C and Scenario D runoff grids.

Duration percentiles were generated for each of the 15 catchment runoff series and each of the 47 Scenario A

inflow series. These percentiles (duration curves) were calculated in 0.5 percent increments.

For each of the 15 catchments, Scenario C and Scenario D runoff duration curves were compared against

Scenario A, and scaling factors were calculated for each of the 0.5 percent increments.

A Hydstra model was created to scale the 47 Scenario A TEMSim inflow series for each scenario based on the

duration curve scaling factors.

2.3 Future development

2.3.1 Forestry


plantations which will increase total forest cover from 25 to 29 percent of the region by 2030. This projected increase is

entirely in the northern two-thirds of the region (Figure 6) and the derivation of these projections described in Viney et al.

(2009).


Figure 6. Proposed irrigation developments and increase in forest cover due to future commercial forest plantations

in the Mersey-Forth region

2.3.2 Irrigation

A number of irrigation developments are proposed in the Mersey-Forth region. The total mean annual demand for all the

proposed developments is 29,010 ML/year.

Sheffield-Barrington irrigation scheme

An irrigation development is proposed on the Forth River where it is proposed to extract an annual mean of

10,200 ML/year of water from Lake Barrington via a pipeline. Information on the proposed development was provided by

Tasmanian Irrigation Development Board (TIDB) (P Ellery (TIDB), 2009, pers. comm.). This extraction is from the

hydro-electric system and was therefore modelled in TEMSim and not explicitly coded within the Forth River model. Lake

Barrington is part of the Mersey-Forth hydro-electric system, which is a complex integrated system of canals, pipelines,

pumping stations, storages and rivers (see Figure 7).


Figure 7. Mersey-Forth hydro-electric system

The effects of the proposed development will be reflected in the Forth-Wilmot River model by changes in the outflow from

the Hydro Tasmania infrastructure at Lake Paloona, which is the lowest downstream storage in the Forth system. It is

assumed that all the water from the scheme will be extracted directly for irrigation. There are no details on the locations

of these irrigation extractions, therefore it was assumed that water extracted would be fully utilised on-farm for irrigation.

IQQM software was used to derive a crop demand which projected a daily extraction profile (ML/day). This was then

used in the relevant catchment model as a consumptive extraction taken directly from the proposed dam. The daily

demand was determined using the SILO gridded rainfall and evaporation over the irrigation area, an adopted soil

moisture parameter and summer grasses as the crop type. The model was run over the 84-year period, and the irrigable

area was adjusted until the annual mean demand was equal to the proposed annual mean extraction of 10,200 ML. For

each year, the irrigation volume required to water this irrigable area was then determined. This varied year to year

depending on the rainfall and evaporation. This process produced a daily extraction series which maintained the mean

annual demand whilst varying the required amount year to year to reflect actual demand. This extraction series was used

as the Scenario D extraction taken directly from the proposed dam.

Forthside-Don irrigation scheme

A direct extraction of 2590 ML/year from the Forth River downstream of Lake Paloona is proposed (see Figure 7), which

is reliant on operation of Paloona power station. All information on the proposed development was provided by

Tasmanian Irrigation Development Board (TIDB) (P Ellery (TIDB), 2009, pers. comm.). The extraction from the river is

constrained by the following issues:

The extraction is opportunistic, primarily relying on flows out of Hydro Tasmania’s Lake Paloona.


The extraction is taken after existing WIMS allocations. The WIMS includes existing allocations associated with

this irrigation scheme including a 900 ML approved allocation and an 1100 ML pending allocation.

The assumed maximum pump capacity of the extraction is 25 ML/day and the annual demand is attempted to

be taken at this rate over 150 days of summer (1 December to 30 April).

During periods when the Paloona Power station is not operating, Hydro Tasmania releases a riparian flow of

0.71 m3/second downstream for town water supply purposes (Cradle Coast Water). Extractions from the river

are ceased if flow in the river drops to 0.71 m3/second.

There are other proposed upstream extractions included in this model. These will impact the results obtained at

this extraction point. The reliability of this extraction should be reassessed if there are changes to the proposed

upstream schemes.

Kindred-North Motton irrigation scheme

A direct extraction of 8,660 ML/year from the Forth River downstream of Lake Paloona is proposed (see Figure 7), which

is reliant on operation of Paloona power station. All information on the proposed development was provided by

Tasmanian Irrigation Development Board (P Ellery (TIDB), 2009, pers. comm.). The extraction from the river is

constrained by the following issues:

The extraction is opportunistic, primarily relying on flows out of Hydro Tasmania’s Lake Paloona.

The extraction is taken after existing WIMS allocations.

The assumed maximum pump capacity of the extraction is 70 ML/day and the annual demand is attempted to

be taken at this rate over 150 days of summer (1 December to 30 April).

During periods when the Paloona Power station is not operating, Hydro Tasmania releases a riparian flow of

0.71 m3/second downstream for town water supply purposes (Cradle Coast Water). Extractions from the river

are ceased if flow in the river drops to 0.71 m3/second.

There are other proposed upstream extractions included in this model. These will impact the results obtained at

this extraction point. The reliability of this extraction should be reassessed if there are changes to the proposed

upstream schemes.

Irrigable area for the Sheffield-Barrington, Forthside-Don and Kindred-North Motton irrigation developments are shown in

Table 5.

Table 5. Irrigable area for proposed irrigation developments for Scenario D

Scheme Irrigable area

Dwet Dmid Ddry

ha

Sheffield-Barrington 3756 3546 3590

Forthside-Don 1574 1489 1507

Kindred-North Motton 6372 6003 6081

Sassafras-Wesley Vale irrigation scheme

An irrigation extraction of 7200 ML/year is proposed from the Mersey River downstream of Lake Parangana (G Bullock

(TIDB), 2009, pers. comm.) The extraction amount was based on the responses to an expression of interest issued by

TIDB. The primary source of this water is from Lake Parangana, which is part of the Mersey-Forth hydro-electric system.

This extraction is from the hydro-electric system and was therefore modelled in TEMSim and not explicitly coded within

the Mersey River model. Lake Parangana is part of the Mersey-Forth hydro-electric system, which is a complex

integrated system of canals, pipelines, pumping stations, storages and rivers (see Figure 7).

The extraction was assumed to be released from Lake Parangana at a constant rate of 35 ML/day from November to

April inclusive. The effects of this extraction will be primarily reflected in the Forth River model due to changes in the

outflow from Hydro Tasmania’s infrastructure at Lake Paloona. The effect of this development on the Mersey River

downstream of Lake Parangana will be minimal as the majority of the Lake Parangana run-off is diverted into the Forth

River.


3 Under historical climate (Scenario A) and future

climate (Scenario C)

This section reports on hydrology under Scenario A and on hydrology under Scenario C relative to Scenario A. Three

scenarios are presented for Scenario C: wet extreme (Scenario Cwet), median (Scenario Cmid) and dry extreme

(Scenario Cdry). The selection of these scenarios was based on projected changes in mean annual runoff from the

14 km resolution pattern-scaled projections of the 15 global climate models (GCMs). The selection of climate scenarios is

described in detail by Viney et al. (2009). In summary, the wettest of the three global warming projections from the

second wettest GCM (MIROC) was chosen as Scenario Cwet. The projection representing 1.0 degree global warming

from the eighth wettest GCM (MIUB) was chosen as Scenario Cmid. The driest of the three global warming projections

from the second driest GCM (INMCM) was chosen as Scenario Cdry. This selection of scenarios Cwet, Cmid and Cdry

was performed separately for each reporting region. As the selection of these scenarios was based on mean annual

runoff over the region, they can vary in order on the basis of season and catchment. In many catchments in the

Mersey-Forth region, this results in a lower flow during summer under Scenario Cmid relative to Scenario Cdry. A higher

winter flow is also observed under Scenario Cdry relative to Scenario Cmid.

Statistics reported for ‘summer’ or ‘winter’ refer to October to March and April to September respectively.

3.1 Water balance and water availability

The mass balance table (Table 6a–e) shows the net fluxes for each catchment in the Mersey-Forth region. Fluxes under

Scenario A are presented as GL/year, while fluxes under all other Scenarios are presented as a percentage change

relative to Scenario A.

The storage volumes refer to Lake Isandula only. The inflows are separated into flows from catchment runoff, and flows

from hydro-electric schemes. The catchment losses include any water transfers (diversions) into or out of the catchment,

and evaporation from major storages. Extractions are shown based on surety level. The catchment losses are positive

for a net loss for the catchment and negative for a net gain (for example the loss will be negative if rainfall over a storage

surface exceeds evaporation, or water is transferred into a catchment). The net catchment transfer in the Leven

catchment represents direct extractions from Lake Isandula.

Table 6 shows that mean annual catchment runoff increases under Scenario Cwet relative to Scenario A in the Rubicon

and Tamar Estuary catchments, and decreases in the Leven, Forth-Wilmot and Mersey catchments. Mean annual

catchment runoff decreases under Scenario Cdry relative to Scenario A in all catchments, by a maximum of 12 percent in

the Forth-Wilmot catchment. Under Scenario Cmid relative to Scenario A, catchment runoff decreases in all catchments

except for Tamar Estuary. The Forth-Wilmot and Mersey catchments include significant inflows from hydro-electric

storages. In the case of the Forth-Wilmot, the flows through Paloona Power Station and spills from Paloona storage

represent more than 95 percent of inflows under Scenario A. Spills and riparian releases from Lake Parangana represent

23 percent of inflows to the Mersey catchment. In the Forth-Wilmot catchment, the inflows from hydro-electric storages

decrease by up to 10 percent under Scenario Cdry relative to Scenario A. In the Mersey catchment, the flows from

hydro-electric storages increase under Scenario Cwet, and decrease by 10 percent under Scenario Cdry relative to

Scenario A. These changes reflect changes in the operation of the system as a response to changing inflows.

The mean annual extraction amounts decrease slightly or remain the same under Scenario Cwet relative to Scenario A

in all catchments except the Leven where the surety 6 extraction increases. Mean annual extractions remain the same or

decrease under scenarios Cmid and Cdry relative to Scenario A by up to 4 percent in the Mersey and Rubicon

catchments. These changes are reasonably consistent over all sureties.

End-of-system (EOS) flows decrease or remain the same in the Leven, Forth-Wilmot and Mersey catchments, and

increase in the Rubicon and Tamar Estuary catchments under Scenario Cwet relative to Scenario A. EOS flows

decrease in all catchment under Scenario Cdry relative to Scenario A. The decrease under Scenario Cdry is up to

11 percent in the Leven and Mersey catchments.


Table 6. Mean annual water balance for each catchment under scenarios A and C

(a) 33_Leven

A Cwet Cmid Cdry

GL/y percent change relative to Scenario A

Storage volume

Mean annual change in volume 0.0 0% 0% 0%

Inflows

From catchment runoff 607.3 -4% -7% -11%

From flows downstream of hydro schemes 0.0 na na na

Total (inflows) 607.3 -4% -7% -11%

Outflows

Net catchment transfers/losses (including storages if any)

3.2 0% -2% -2%

Net evaporation (evaporation – rainfall) from storages – Isandula

0.0 31% 61% 88%

Sub-total (net transfer and net evaporation) 3.2 0% -2% -2%

Extractions

Surety 1 0.5 0% 0% 0%

Surety 2 0.0 na na na



Surety 5 8.6 0% -1% -1%

Surety 6 0.5 4% -13% -10%



Unlicensed 6.8 0% -4% -4%

Sub-total (extractions) 16.4 0% -3% -2%

End-of-system (EOS) streamflow 587.7 -4% -7% -11%

Total (outflows) 607.3 -4% -7% -11%na – not applicable

(b) 34_Forth-Wilmot

A Cwet Cmid Cdry


Storage volume

Mean annual change in volume na na na na

Inflows


From flows downstream of hydro schemes 2056.6 -1% -7% -10%

Total (inflows) 2158.8 -1% -7% -10%

Outflows


na na na na

Net evaporation (evaporation – rainfall) from storages na na na na

Sub-total (net transfer and net evaporation) na na na na

Extractions

Surety 1 6.2 0% 0% 0%




Surety 5 3.2 0% 0% 0%

Surety 6 0.2 0% 0% 0%



Unlicensed 3.3 0% 0% 0%

Sub-total (extractions) 12.9 0% 0% 0%

End-of-system (EOS) streamflow 2145.8 -1% -7% -10%

Total (outflows) 2158.8 -1% -7% -10%na – not applicable


Table 6. Mean annual water balance for each catchment under scenarios A and C (continued)

(c) 35_Mersey

A Cwet Cmid Cdry


Storage volume


Inflows


From flows downstream of hydro schemes 157.8 8% 0% -10%

Total (inflows) 684.2 0% -4% -11%

Outflows


na na na na



Extractions

Surety 1 0.7 0% 0% 0%




Surety 5 21.7 -1% -3% -4%

Surety 6 2.2 -1% -5% -5%




Sub-total (extractions) 32.3 -1% -4% -4%

End-of-system (EOS) streamflow 651.9 0% -4% -11%

Total (outflows) 684.2 0% -4% -11%

na – not applicable

(d) 36_Rubicon

A Cwet Cmid Cdry


Storage volume


Inflows

From catchment runoff 166.7 2% -1% -8%

From flows downstream of hydro schemes na na na na

Total (inflows) 166.7 2% -1% -8%

Outflows


na na na na



Extractions

Surety 1 0.4 0% -2% -2%




Surety 5 8.5 -1% -3% -4%

Surety 6 1.0 -2% -6% -7%




Sub-total (extractions) 11.4 -1% -3% -4%

End-of-system (EOS) streamflow 155.2 2% 0% -8%

Total (outflows) 166.7 2% -1% -8%



Table 6. Mean annual water balance for each catchment under scenarios A and C (continued)

(e) 43_Tamar Estuary

A Cwet Cmid Cdry


Storage volume


Inflows

From catchment runoff 263.8 5% 3% -5%

From flows downstream of hydro schemes na na na na

Total (inflows) 263.8 5% 3% -5%

Outflows


na na na na



Extractions

Surety 1 0.5 0% -1% -1%


Surety 3 0.0 0% 0% 0%


Surety 5 4.0 0% -1% -1%

Surety 6 0.0 0% 0% 0%




Sub-total (extractions) 7.6 0% -1% -1%

End-of-system (EOS) streamflow 256.2 5% 3% -5%

Total (outflows) 263.8 5% 3% -5%


Figure 8 shows the mean annual total streamflow for the major river reaches in each catchment under scenarios P, A

and C where C range is defined by the upper and lower bounds of Scenario C streamflow. Generally this is defined by

streamflow under scenarios Cwet and Cdry, but due to the way that the C scenarios are derived, occasionally

Scenario Cmid may be used. All of the major rivers in the region are gaining reaches (where the flow in the river

increases moving downstream). Up to a maximum of eight reporting locations were included for each major river reach.

The number of reporting locations on a river is related to the number of modelled subcatchments on the river. In some

catchments, there are less than eight reporting locations, as the largest river reach in the catchment is modelled by less

than eight subcatchments. EOS represents the total flow at the end of the catchment. In catchments where there is a

major river and a number of smaller rivers, the EOS flow is the summation of the end-of-river flow for all rivers within the

catchment.

The reporting locations are shown in Figure 3. The Forth-Wilmot and Mersey catchments are reported only downstream

of hydro-electric storages, as the catchments upstream are entirely controlled by the hydro-electric system. In many

cases, the flows for Scenario P are indistinguishable from Scenario A as there are relatively small extractions from the

river.

On all the major rivers, river flows decrease or remain the same under Scenario C relative to Scenario A.


(a) 33_Leven (Leven River)

0

100

200

300

400

500

600

700

1 2 3 4 5 6 7 8 EOSReporting location

Mea

n an

nual

flow

.(G

L).

C range

Cmid

A

P

(b) 34_Forth-Wilmot (Forth River)

0

500

1000

1500

2000

2500

1 2 3 4 EOSReporting location

Mea

n an

nual

flow

.(G

L).

C range

Cmid

A

P

(c) 35_Mersey (Mersey River)

0

100

200

300

400

500

600

700

800


Mea

n an

nual

flow

.(G

L).

C range

Cmid

A

P

(d) 36_Rubicon (Rubicon River)

020406080

100120140160180


Mea

n an

nual

flow

.(G

L).

C range

Cmid

A

P

Figure 8. River transects showing streamflow under scenarios P, A and C


(e) 43_Tamar Estuary (Supply River)

0

50

100

150

200

250

300

1 2 EOSReporting location

Mea

n an

nual

flow

.(G

L).

C range

Cmid

A

P

Figure 8. River transects showing streamflow under scenarios P, A and C (continued)

A time series of annual water availability for the whole Mersey-Forth region, represented as total EOS flow under

Scenario A is shown in Figure 9a. There is a high level of variability in water availability between years, ranging from

1811 to 6694 GL/year, with a mean of 3797 GL/year. Figure 9b–d shows the difference in annual total surface water

availability under Scenario C relative to Scenario A. The annual water availability decreases in most years under

Scenario Cwet compared to Scenario A, by up to 81 GL/year, with a mean of 25 GL/year. The decrease in annual water

availability under Scenario Cmid ranges from 125 to 325 GL/year, with a mean of 217 GL/year. Under Scenario Cdry the

decrease in water availability ranges from 227 to 539 GL/year with a mean of 382 GL/year. The regional EOS flow is

dominated by the Forth-Wilmot catchment which accounts for over 50 percent of the regional EOS flow.

(a) Scenario A (b) Scenario Cwet

0

1000

2000

3000

4000

5000

6000

7000

0 20 40 60 80

Year

Ann

ual E

OS

vol

ume

(GL)

.

-600

-500

-400

-300

-200

-100

0

100

0 20 40 60 80Year

Ann

ual d

iffer

ence

(G

L)

(c) Scenario Cmid (d) Scenario Cdry

-600

-500

-400

-300

-200

-100

0

100

0 20 40 60 80

Year

Ann

ual d

iffer

ence

(G

L) .

-600

-500

-400

-300

-200

-100

0

100

0 20 40 60 80

Year

Ann

ual d

iffer

ence

(G

L)

Figure 9. End-of-system (EOS) streamflow in the Mersey-Forth region under (a) Scenario A, and difference from Scenario A under

scenarios (b) Cwet, (c) Cmid and (d) Cdry


3.2 Storage behaviour

The modelled behaviour of storages gives an indication of the level of regulation of a system, as well as how reliable the

storage is during extended periods of low inflows. Table 7 details the behaviour of Lake Isandula under scenarios A and

C for the full 84-year run. The mean and maximum days between spills increase under scenarios Cmid and Cdry relative

to Scenario A. Time series of storage volume for a representative ten years are shown in Figure 10. These time series

represent the modelled storage behaviour which included 2007 operating rules. The storage behaviour therefore is not

necessarily representative of historical storage levels. The storage is generally drawn down to lower volumes under

Scenario C relative to Scenario A, however, these differences are minor. Lake Isandula is regularly drawn down to

minimum volume during the 84 years under all scenarios.

Lake Isandula

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

15 16 17 18 19 20 21 22 23 24Year

Vol

ume

(GL)

.

C range A Cmid

Figure 10. Storage behaviour over representative ten-year period under scenarios A and C

Table 7. Storage behaviour under scenarios A and C

Lake Isandula

A Cwet Cmid Cdry

Minimum storage volume (GL) 0 0 0 0

Mean days between spills 36 36 45 43

Maximum days between spills 224 226 230 230

3.3 Consumptive water use

Consumptive water use includes both the licensed and unlicensed extractions from the river system. The modelling of

extractions is described in Section 2.1.1. Time series of annual extractions under Scenario A are shown in Figure 11a.

Total annual extractions for the region vary from a minimum of 57 to a maximum of 96 GL/year over the 84 years. The

differences in annual extractions under Scenario C are shown in Figure 11b–d. Extractions are reduced in most years

under Scenario Cwet relative to Scenario A. Extractions are lower in every year under scenarios Cmid and Cdry relative

to Scenario A. The mean annual decrease in extractions under scenario Cwet, Cmid and Cdry relative to Scenario A are

0.3, 2.1 and 2.3 GL/year respectively. These reductions are relatively small in comparison to the mean annual extraction

of 81 GL/year under Scenario A. The changes in extraction volumes are spread over a range of sureties, representing a

reduction in both summer and winter extractions.


(a) Scenario A (b) Scenario Cwet

0

20

40

60

80

100

120

0 20 40 60 80Year

Ann

ual e

xtra

ctio

n vo

lum

e .

(GL)

.

-4

-3

-2

-1

0

1

0 20 40 60 80Year

Ann

ual d

iffer

ence

(G

L) .

(c) Scenario Cmid (d) Scenario Cdry

-4

-3

-2

-1

0

1

0 20 40 60 80

Year

Ann

ual d

iffer

ence

(G

L) .

-4

-3

-2

-1

0

1

0 20 40 60 80

Year

Ann

ual d

iffer

ence

(G

L) .

Figure 11. Total annual extractions for Mersey-Forth region under (a) Scenario A, and difference from Scenario A under

scenarios (b) Cwet, (c) Cmid and (d) Cdry

Table 8 shows the mean annual volume of allocated and extracted water in each catchment in the region under

scenarios A and C. The mean annual extracted volumes are less than the mean annual allocation in all catchments

under all scenarios. The mean annual extracted volume does not decrease significantly under Scenario C relative to

Scenario A. The most significant difference between the mean annual extracted and allocated volumes is in the Rubicon

catchment where under Scenario A, the allocated volume is 17.5 GL/year, whilst the extracted volume is 11.4 GL/year.

Based on these annual means from the river modelling, the river system is unable to supply the full allocation for

extraction. In the absence of any information on actual extractions from rivers, the river models assume that each water

licence’s full allocation is divided evenly over the applicable months. In reality, irrigators may have off-stream storages

that can be used to store water when there is less water in the river system, and thus will extract water from the river

when it is available. The methods used in the river modelling may therefore result in a lower volume of water being

extracted in the model relative to the actual situation. It was noted that in some catchments the low flow volumes are

lower than those modelled in TasCatch due to the differences in the runoff modelling. This will also impact on the

estimated reliability of extractions.


Table 8. Allocated and extracted mean annual flows for catchments under scenarios A and C

A Cwet Cmid Cdry

GL/y

33_Leven

Allocated water 18.3 18.3 18.1 18.1

Extraction 16.4 16.4 15.9 16.0

Difference 1.9 1.9 2.1 2.1

34_Forth-Wilmot


Extraction 12.9 12.9 12.9 12.9

Difference 0.1 0.1 0.1 0.1

35_Mersey


Extraction 32.3 32.1 31.0 31.0

Difference 1.5 1.5 1.6 1.6

36_Rubicon


Extraction 11.4 11.3 11.1 10.9

Difference 6.1 6.1 6.3 6.4

43_Tamar Estuary


Extraction 7.6 7.6 7.6 7.5

Difference 1.4 1.4 1.4 1.5

The mean annual reliability of high and low priority extractions is shown in Table 9 for each catchment as fraction

extracted per unit of water allocated. The reliabilities of extractions over summer and winter are shown in Table 10 and

Table 11 respectively. The annual reliability of high priority extractions under Scenario A ranges from 80 percent in the

Rubicon catchment to 100 percent in the Forth-Wilmot. In summer, the reliability of both high and low priority extractions

in the Rubicon catchment is slightly lower than the reliability of annual extractions, reflecting the lower water availability in

this catchment in summer. The reliability of low priority extractions in summer in the Tamar Estuary is also lower than the

reliability of annual extractions.

The reliability of annual extractions changes by less than 2 percent in all catchments for both high and low priority

extractions under Scenario C relative to Scenario A on an annual and seasonal basis.


Table 9. Mean reliability of high and low priority allocations for catchments under scenarios A and C (annual)

A Cwet Cmid Cdry

fraction extracted per unit allocated

33_Leven

High priority (surety 1 to 4) 0.99 0.99 0.99 0.99

Low priority (surety 5 to 8 & unlicensed) 0.89 0.89 0.88 0.88

34_Forth-Wilmot



35_Mersey



36_Rubicon



43_Tamar Estuary



Table 10. Mean reliability of high and low priority allocations for catchments under scenarios A and C

(summer – October to March inclusive)

A Cwet Cmid Cdry


33_Leven



34_Forth-Wilmot



35_Mersey



36_Rubicon



43_Tamar Estuary




Table 11. Mean reliability of high and low priority allocations for catchments under scenarios A and C

(winter – April to September inclusive)

A Cwet Cmid Cdry


33_Leven



34_Forth-Wilmot



35_Mersey



36_Rubicon



43_Tamar Estuary



Figure 12 shows the allocation and extraction reliability as percentage of years for exceedance of a given volume. The

allocation volume is not constant each year in some catchments due to regulations which restrict allocations under low

flow conditions (see Table 4). Allocation restrictions result in a significant reduction in allocations in many years in the

Mersey catchment. Extraction volumes vary significantly over the 84 years, particularly in the Rubicon catchment, where

the extraction volume drops to less than 40 percent per unit allocated. There is a slight reduction in extractions under

Scenario C relative to Scenario A in most catchments. Figure 13 shows the same figures for summer only. Summer

extractions generally show more variation over the 84-year sequence than on an annual basis.

(a-1) 33_Leven – allocated water (a-2) 33_Leven – extracted per allocated

02468

10121416182022

0% 20% 40% 60% 80% 100%Percent of years exceeded

Ann

ual v

olum

e (G

L) .

C rangeCmidA

0.00.10.20.30.40.50.60.70.80.91.0


Ext

ract

ed v

olum

e pe

r

unit

allo

cate

d .

C range

Cmid

A

Figure 12. Allocation and extraction reliability for catchments under scenarios A and C (annual)


(b-1) 34_Forth-Wilmot – allocated water (b-2) 34_Forth-Wilmot – extracted per allocated

02468

10121416182022


Ann

ual v

olum

e (G

L) .

C rangeCmidA

0.00.10.20.30.40.50.60.70.80.91.0


Ext

ract

ed v

olum

e pe

r

unit

allo

cate

d .

C range

Cmid

A

(c-1) 35_Mersey – allocated water (c-2) 35_Mersey – extracted per allocated

0

5

10

15

20

25

30

35

40

45


Ann

ual v

olum

e (G

L) .

C rangeCmidA

0.00.10.20.30.40.50.60.70.80.91.0


Ext

ract

ed v

olum

e pe

r

unit

allo

cate

d .

C range

Cmid

A

(d-1) 36_Rubicon – allocated water (d-2) 36_Rubicon – extracted per allocated

02468

101214161820


Ann

ual v

olum

e (G

L) .

C rangeCmidA

0.00.10.20.30.40.50.60.70.80.91.0


Ext

ract

ed v

olum

e pe

r

unit

allo

cate

d .

C range

Cmid

A

(e-1) 43_Tamar Estuary – allocated water (e-2) 43_Tamar Estuary – extracted per allocated

0

1

2

3

4

5

6

7

8

9


Ann

ual v

olum

e (G

L) .

C rangeCmidA

0.00.10.20.30.40.50.60.70.80.91.0


Ext

ract

ed v

olum

e pe

r

unit

allo

cate

d .

C range

Cmid

A

Figure 12. Allocation and extraction reliability for catchments under scenarios A and C (annual) (continued)


(a-1) 33_Leven – allocated water (a-2) 33_Leven – extracted per allocated

02468

10121416182022

0% 20% 40% 60% 80% 100%

Percent of years exceeded

Sum

mer

vol

ume

(GL)

.

C rangeCmidA

0.00.10.20.30.40.50.60.70.80.91.0


Ext

ract

ed v

olum

e pe

r

unit

allo

cate

d .

C range

Cmid

A

(b-1) 34_Forth-Wilmot – allocated water (b-2) 34_Forth-Wilmot – extracted per allocated

02468

10121416182022

0% 20% 40% 60% 80% 100%


Sum

mer

vol

ume

(GL)

. C rangeCmidA

0.00.10.20.30.40.50.60.70.80.91.0


Ext

ract

ed v

olum

e pe

r

unit

allo

cate

d .

C range

Cmid

A

(c-1) 35_Mersey – allocated water (c-2) 35_Mersey – extracted per allocated

0

5

10

15

20

25

30

35

40

45

0% 20% 40% 60% 80% 100%


Sum

mer

vol

ume

(GL)

. C rangeCmidA

0.00.10.20.30.40.50.60.70.80.91.0


Ext

ract

ed v

olum

e pe

r

unit

allo

cate

d .

C range

Cmid

A

(d-1) 36_Rubicon – allocated water (d-2) 36_Rubicon – extracted per allocated

02468

101214161820

0% 20% 40% 60% 80% 100%


Sum

mer

vol

ume

(GL)

. C rangeCmidA

0.00.10.20.30.40.50.60.70.80.91.0


Ext

ract

ed v

olum

e pe

r

unit

allo

cate

d .

C range

Cmid

A

Figure 13. Allocation and extraction reliability for catchments under scenarios A and C (summer – October to March inclusive)


(e-1) 43_Tamar Estuary – allocated water (e-2) 43_Tamar Estuary – extracted per allocated

0

1

2

3

4

5

6

7

8

9

0% 20% 40% 60% 80% 100%


Sum

mer

vol

ume

(GL)

. C rangeCmidA

0.00.10.20.30.40.50.60.70.80.91.0


Ext

ract

ed v

olum

e pe

r

unit

allo

cate

d .

C range

Cmid

A

Figure 13. Allocation and extraction reliability for catchments under scenarios A and C (summer – October to March inclusive)

(continued)

The mean annual volume of extracted water for the lowest one-, three-, and five-year periods under Scenario A, and the

percentage change under Scenario C relative to Scenario A are shown in Table 12. These figures indicate the impact on

water use during dry periods. Extraction volumes generally decrease during dry periods under Scenario Cwet relative to

Scenario A, except in the Tamar Estuary catchment. Extraction volumes decrease during dry periods under

scenarios Cmid and Cdry relative to Scenario A, by up to 11.9 percent for the lowest one-year period of extraction in the

Mersey catchment under Scenario Cdry. Extraction volumes show a greater reduction during dry periods under

Scenario C relative to Scenario A when compared to changes in the long-term mean extractions, indicating that the

ability to extract water would be reduced in drier periods under this scenario.

Table 12. Indicators of use during dry periods for catchments under Scenario A and change under Scenario C relative to Scenario A

A Cwet Cmid Cdry


33_Leven

Lowest 1-year period of extraction 13.8 -1.7% -5.5% -5.3%



Mean annual extraction for 84 years 16.4 -0.1% -2.8% -2.5%

34_Forth-Wilmot



Lowest 5-year period of extraction 12.9 0.0% -0.1% -0.1%

Mean annual extraction for 84 years 12.9 0.0% -0.1% -0.1%

35_Mersey





36_Rubicon





43_Tamar Estuary




Mean annual extraction for 84 years 7.6 0.3% -0.8% -1.1%


3.4 End-of-system river flow

The EOS monthly streamflow and daily flow duration curves for each catchment under scenarios P, A and C are shown

in Figure 14. Scenario P represents current infrastructure with no extractions under historical climate. In all catchments,

the shape of the flow duration curve is consistent under Scenario C compared to Scenario A. The impact of extractions

on low flows is evident under Scenario A relative to Scenario P in the Leven, Rubicon and Tamar Estuary catchments.

The monthly plots show a strong seasonal distribution of flows, with highest flows occurring in winter months. In the

Rubicon and Tamar Estuary catchments, mean monthly flows under Scenario A are generally within the range of flows

under Scenario C. In the Leven, Forth-Wilmot and Mersey catchments, mean monthly flows are reduced over spring and

early summer under Scenario C relative to Scenario A.

(a-1) 33_Leven – monthly flow (a-2) 33_Leven – daily flow duration

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

J F M A M J J A S O N DMonth

EO

S m

onth

ly fl

ow (

GL)

. C rangeCmidAP

1

10

100

1000

10000

100000

0 20 40 60 80 100Percent time volume is exceeded

EO

S d

aily

flow

(M

L) .

C rangeCmidAP

(b-1) 34_Forth-Wilmot – monthly flow (b-2) 34_Forth-Wilmot – daily flow duration

0

2

4

6

8

10

12


EO

S m

onth

ly fl

ow (

GL)

. C rangeCmidAP

1

10

100

1000

10000

100000


EO

S d

aily

flow

(M

L) .

C rangeCmidAP

(c-1) 35_Mersey – monthly flow (c-2) 35_Mersey – daily flow duration

0

1

2

3

4

5


EO

S m

onth

ly fl

ow (

GL)

. C rangeCmidAP

1

10

100

1000

10000

100000


EO

S d

aily

flow

(M

L) .

C rangeCmidAP

Figure 14. Mean monthly end-of-system flow and daily flow duration curves under scenarios P, A and C


(d-1) 36_Rubicon – monthly flow (d-2) 36_Rubicon – daily flow duration

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4


EO

S m

onth

ly fl

ow (

GL)

. C rangeCmidAP

1

10

100

1000

10000

100000


EO

S d

aily

flow

(M

L) .

C rangeCmidAP

(e-1) 43_Tamar Estuary – monthly flow (e-2) 43_Tamar Estuary – daily flow duration

0.0

0.5

1.0

1.5

2.0

2.5


EO

S m

onth

ly fl

ow (

GL)

. C rangeCmidAP

1

10

100

1000

10000

100000


EO

S d

aily

flow

(M

L) .

C rangeCmidAP

Figure 14. Mean monthly end-of-system flow and daily flow duration curves under scenarios P, A and C (continued)

EOS daily peak flows for return periods of two, five and ten years are shown in Table 13 under scenarios A and P with

changes under Scenario C relative to Scenario A. Peak flows were determined based on the procedure used in the

Murray-Darling Basin Sustainable Yields Project (CSIRO, 2008), using a partial series analysis and a plotting position

assigned based on rank. Peak flows increase for all return periods shown under Scenario Cwet relative to Scenario A in

the Rubicon and Tamar Estuary catchments, and decrease or remain the same in the Leven, Forth-Wilmot and Mersey

catchments. The maximum increase in peak flows is 12 percent for the two-year return period in the Tamar Estuary

catchment. Peak flows decrease in all catchments under Scenario Cdry relative to Scenario A for most return periods;

however, there is an increase in peak flows for the ten-year return periods in the Tamar Estuary catchment. The

maximum reduction in peak flows under Scenario Cdry relative to Scenario A is 14 percent for the two-year return period

flow in the Forth-Wilmot catchment. In some catchments, peak flows under Scenario Cmid are greater than those under

Scenario Cwet. The selection of Cwet, Cmid and Cdry scenarios was based on mean annual runoff and peak flows may

actually be higher in some years under Scenario Cmid relative to Scenario Cwet, or Scenario Cdry relative to Scenario

Cmid because different GCMs were used to define these scenarios and these GCMs may scale peak rainfalls by

different amounts.


Table 13. Peak flows for catchments under scenarios P and A, and under Scenario C relative to Scenario A

P A Cwet Cmid Cdry

ML/d percent change relative to Scenario A

33_Leven

2-year 11,784 11,750 -1% -2% -10%

5-year 14,840 14,806 1% 1% -7%

10-year 18,029 17,971 0% -2% -8%

34_Forth-Wilmot

2-year 22,952 22,928 -3% -7% -14%

5-year 32,765 32,740 -1% -1% -10%

10-year 36,556 36,532 0% 1% -6%

35_Mersey

2-year 19,330 19,239 0% -1% -9%

5-year 26,938 26,847 0% 2% -8%

10-year 31,858 31,767 -2% 1% -9%

36_Rubicon

2-year 7,241 7,156 2% 6% -7%

5-year 10,026 9,952 5% 7% -4%

10-year 12,219 12,145 2% 6% -4%

43_Tamar Estuary

2-year 9,861 9,820 12% 9% -3%

5-year 13,865 13,824 9% 8% -3%

10-year 16,794 16,754 4% 10% 4%

The percentage of time EOS flow is greater than 1 ML/day under scenarios P, A, and C is shown in Table 14. Flows less

than 1 ML/day are defined as ‘cease-to-flow’ for the purposes of this report. The rivers in all catchments are essentially

perennial under Scenario P, ceasing to flow for only a small percentage of time. The percentage of time that the river is

flowing decreases under Scenario A compared to Scenario P in the Rubicon and Tamar Estuary catchments, reflecting

the impact of extractions on low flows. There is a slight decrease in the percentage of time the river is flowing in the

Rubicon catchment and the Tamar Estuary under scenarios Cmid and Cdry compared to Scenario A.

Table 14. Percentage of time end-of-system flow is greater than 1 ML/day under scenarios P, A and C

P A Cwet Cmid Cdry

33_Leven 100% 100% 100% 100% 100%

34_Forth-Wilmot 100% 100% 100% 100% 100%

35_Mersey 100% 100% 100% 100% 100%

36_Rubicon 95% 89% 89% 87% 87%

43_Tamar Estuary 98% 95% 95% 94% 94%

The EOS flow during dry periods under Scenario A with relative changes under Scenario C is shown in Table 15. The

EOS flow for the lowest one-, three- and five-year periods reduces in all catchments under Scenario Cdry, with a

maximum reduction of 15.4 percent in the Leven catchment for the lowest one-year period. This indicates that under

Scenario Cdry, the river system is more stressed in periods of low flow. The flow increases for all reported periods under

Scenario Cwet relative to Scenario A in the Rubicon and Tamar catchments, indicating that there is more water available

during dry periods under this scenario in these catchments.


Table 15. End-of-system flow for catchments during dry periods under Scenario A and under Scenario C relative to Scenario A

A Cwet Cmid Cdry


33_Leven

Lowest 1-year period of EOS flow 293.5 -6.5% -11.0% -15.4%



Mean annual EOS flow for 84 years 587.7 -4.0% -7.3% -11.5%

34_Forth-Wilmot

Lowest 1-year period of EOS flow 1263.9 0.4% -10.8% -13.7%




35_Mersey





36_Rubicon




Mean annual EOS flow for 84 years 155.2 2.4% -0.3% -8.4%

43_Tamar Estuary


Lowest 3-year period of EOS flow 118.0 4.1% 0.3% -8.1%

Lowest 5-year period of EOS flow 176.1 6.2% 1.7% -5.7%

Mean annual EOS flow for 84 years 256.2 5.5% 2.7% -4.8%

3.5 Share of available resource

The mean annual volume of extracted and non-extracted shares of water for the Mersey-Forth region under scenarios A

and C are shown in Figure 15 and Table 16. The methods for modelling extractions and allocations are described in

Section 2.1.1. On an annual basis, there is a very low volume of extracted water relative to the total mean annual volume

of water in the region. The mean annual non-extracted water decreases by 25 GL/year under Scenario Cwet relative to

Scenario A, and extracted water decreases by 1 GL/year. The non-extracted water decreases by 382 GL/year under

Scenario Cdry relative to Scenario A, but extracted water only decreases by 3 GL/year.

0500

1000150020002500300035004000

A Cwet Cmid Cdry

Mea

n an

nual

vol

ume

(GL)

.

Non-extracted water Extracted water

Figure 15. Extracted and non-extracted shares of water for Mersey-Forth region under scenarios A and C (annual)


Table 16. Extracted and non-extracted shares of water for Mersey-Forth region under scenarios A and C (annual)

A Cwet Cmid Cdry

GL/y

Non-extracted water 3800 3775 3583 3418

Extracted water 81 80 79 78

Total 3881 3856 3662 3497

The mean annual extracted and non-extracted shares of water for each catchment are shown in Figure 16 and Table 17.

The volume of extracted water does not change significantly under Scenario C relative to Scenario A for any catchment.

For the Rubicon and Tamar Estuary catchments the volume of non-extracted water is higher under Scenario Cwet and

lower under Scenario Cdry relative to Scenario A. In the other catchments the volume of non-extracted water is lower

under scenarios Cwet, Cmid and Cdry. This implies that the reduction in the runoff under Scenario C would be borne

more in the non-extracted proportion of river flows due to the extraction rules. The implication of these changes for

environmental values is assessed in Graham et al. (2009).


(a) 33_Leven (b) 34_Forth-Wilmot

0

100

200

300

400

500

600

700

A Cwet Cmid Cdry

Mea

n an

nual

vol

ume

(GL)

.


0

500

1000

1500

2000

2500

A Cwet Cmid Cdry

Mea

n an

nual

vol

ume

(GL)

.


(c) 35_Mersey (d) 36_Rubicon

0

100

200

300

400

500

600

700

A Cwet Cmid Cdry

Mea

n an

nual

vol

ume

(GL)

.


020406080

100120140160180

A Cwet Cmid Cdry

Mea

n an

nual

vol

ume

(GL)

.


(e) 43_Tamar Estuary

0

50

100

150

200

250

300

A Cwet Cmid Cdry

Mea

n an

nual

vol

ume

(GL)

.


Figure 16. Extracted and non-extracted shares of water for catchments under scenarios A and C (annual)


Table 17. Extracted and non-extracted shares of water for catchments under scenarios A and C (annual)

A Cwet Cmid Cdry

GL/y

33_Leven

Non-extracted water 590.9 567.5 547.7 523.3

Extracted water 16.4 16.4 15.9 16.0

Total 607.3 583.9 563.6 539.3

34_Forth-Wilmot



Total 2158.8 2142.0 2006.2 1941.8

35_Mersey



Total 684.2 681.5 655.3 611.0

36_Rubicon



Total 166.7 170.3 165.8 153.1

43_Tamar Estuary



Total 263.8 277.9 270.6 251.4

The mean extracted and non-extracted shares of water for the Mersey-Forth region for summer only are shown in

Table 18. The mean summer extraction does not change significantly under Scenario C compared to Scenario A. The

extracted volume of water is small in summer compared to the total water available. The non-extracted water decreases

in summer under Scenario C compared to Scenario A.

Table 18. Extracted and non-extracted shares of water for the Mersey-Forth region under scenarios A and C (summer – October to

March inclusive)

A Cwet Cmid Cdry

GL/season

Non-extracted water 1074 1064 961 939

Extracted water 40 40 38 39

Total 1114 1104 999 977

The mean extracted and non-extracted shares of water for each catchment for summer only are shown in Table 19. The

mean summer extraction does not change significantly under Scenario C compared to Scenario A.


Table 19. Extracted and non-extracted shares of water for catchments under scenarios A and C (summer – October to March inclusive)

A Cwet Cmid Cdry

GL/season

33_Leven



Total 159.8 153.9 136.5 137.2

34_Forth-Wilmot



Total 705.6 699.3 638.0 619.6

35_Mersey



Total 168.5 167.2 151.6 148.2

36_Rubicon



Total 29.7 30.3 26.5 26.0

43_Tamar Estuary



Total 50.7 53.3 46.8 46.4

The mean percentage of water extracted as a proportion of total EOS flow under scenarios A and C annually and for

summer and winter are shown in Table 20, Table 21 and Table 22 respectively. On an annual basis, the percentage of

water extracted as a proportion of total flow is 7 percent or less in all catchments. The proportion of the total flow

extracted in summer is larger than the annual proportion of flow extracted in all catchments except for the Forth-Wilmot.

The largest proportion of water extracted is in the Rubicon catchment where the mean percentage of water extracted in

summer is 11 percent of total flow. There is little or no change in the percentage of extractions as a proportion of total

flow under Scenario C compared to Scenario A annually or seasonally.


Table 20. Percentage of water extracted as a proportion of total end-of-system flow for catchments

under scenarios A and C (annual)

A Cwet Cmid Cdry

33_Leven 3% 3% 3% 3%

34_Forth-Wilmot 1% 1% 1% 1%

35_Mersey 5% 5% 5% 5%

36_Rubicon 7% 7% 7% 7%

43_Tamar Estuary 3% 3% 3% 3%

Region mean 2% 2% 2% 2%


under scenarios A and C (summer – October to March inclusive)

A Cwet Cmid Cdry

33_Leven 7% 7% 8% 8%


35_Mersey 10% 10% 10% 10%

36_Rubicon 11% 11% 12% 12%




under scenarios A and C (winter – April to September inclusive)

A Cwet Cmid Cdry

33_Leven 1% 1% 1% 1%


35_Mersey 3% 3% 3% 3%

36_Rubicon 6% 6% 6% 6%




4 Under historical climate (Scenario A) and recent

climate (Scenario B)

This section compares recent hydrology (under Scenario B) with historical hydrology (under Scenario A). The mean

end-of-system (EOS) flow volume in GL/year, and daily EOS flow duration plots for each catchment are shown in

Figure 17. Summer, autumn and winter flows are lower in all catchments, and spring flows are higher over recent climate

relative to the long-term mean. The flow duration curves show that flows over recent climate have generally been lower

than the long-term mean over the full range of flows.

(a-1) 33_Leven – monthly flow (a-2) 33_Leven – daily flow duration

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0


EO

S m

onth

ly fl

ow (

GL)

. B

A

1

10

100

1000

10000

100000


EO

S d

aily

flow

(M

L) . B

A

(b-1) 34_Forth-Wilmot – monthly flow (b-2) 34_Forth-Wilmot – daily flow duration

0

2

4

6

8

10

12


EO

S m

onth

ly fl

ow (

GL)

. B

A

1

10

100

1000

10000

100000


EO

S d

aily

flow

(M

L) .

B

A

(c-1) 35_Mersey – monthly flow (c-2) 35_Mersey – daily flow duration

0

1

2

3

4

5


EO

S m

onth

ly fl

ow (

GL)

. B

A

1

10

100

1000

10000

100000


EO

S d

aily

flow

(M

L) . B

A

Figure 17. Mean end-of-system monthly flow and daily flow duration curves for catchments under scenarios A and B


(d-1) 36_Rubicon – monthly flow (d-2) 36_Rubicon – daily flow duration

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4


EO

S m

onth

ly fl

ow (

GL)

. B

A

1

10

100

1000

10000

100000


EO

S d

aily

flow

(M

L) . B

A

(e-1) 43_Tamar Estuary – monthly flow (e-2) 43_Tamar Estuary – daily flow duration

0.0

0.5

1.0

1.5

2.0


EO

S m

onth

ly fl

ow (

GL)

. B

A

1

10

100

1000

10000

100000


EO

S d

aily

flow

(M

L) . B

A

Figure 17. Mean end-of-system monthly flow and daily flow duration curves for catchments under scenarios A and B (continued)

The mean annual extracted and non-extracted shares of water for the Mersey-Forth region under scenarios A and B are

shown in Figure 18 and Table 23. The total water in the region is 530 GL/year lower under Scenario B; however, the

volume of extracted water reduces by a mean of only 4.3 GL/year, reflecting the low level of extraction on a regional

basis. The reduction in the total EOS flow under Scenario B relative to Scenario A is borne by the non-extracted water.

The implication of these changes for environmental values is assessed in Graham et al. (2009).

0

500

1000

1500

2000

2500

3000

3500

4000

A B

Mea

n an

nual

vol

ume

(GL)

.


Figure 18. Mean annual extracted and non-extracted shares of water for Mersey-Forth region under scenarios A and B

Table 23. Mean annual extracted and non-extracted shares of water for Mersey-Forth region under scenarios A and B

A B

GL/y

Non-extracted water 3800 3275

Extracted water 81 76

Total 3881 3351


The extracted and non-extracted shares of water under scenarios A and B for summer only are shown in Table 24. There

is a significant decrease in mean summer flows under Scenario B relative to Scenario A. This has only a minimal impact

on the mean summer extraction volume, reflecting the low level of water usage on a regional basis.

Table 24. Extracted and non-extracted shares of water for Mersey-Forth region

under scenarios A and B (summer – October to March inclusive)

A B

GL/season

Non-extracted water 1074 923

Extracted water 40 38

Total 1114 961

The mean annual extracted and non-extracted shares of water are shown in Table 25 for each catchment under

scenarios A and B. The mean annual volume of total water is reduced under Scenario B relative to Scenario A in all

catchments. The volume of water extracted is slightly less under Scenario B relative to Scenario A in all catchments

except the Forth-Wilmot where it is unchanged.

Table 25. Mean annual extracted and non-extracted shares of water for catchments under scenarios A and B

A B

GL/y

33_Leven

Non-extracted water 590.9 534.9

Extracted water 16.4 15.6

Total 607.3 550.5

34_Forth-Wilmot



Total 2158.8 1889.4

35_Mersey



Total 684.2 569.9

36_Rubicon



Total 166.7 134.6

43_Tamar Estuary



Total 263.8 206.4

The extracted and non-extracted shares of water for each catchment for summer only under scenarios A and B are

shown in Table 26. The mean summer volume of water extracted does not vary significantly under Scenario B compared

to Scenario A in the majority of catchments. The largest impact is in the Mersey catchment where the mean volume of

water extracted over summer is 14.8 GL/summer under Scenario B and 16.4 GL/summer under Scenario A.


Table 26. Extracted and non-extracted shares of water for catchments under scenarios A and B (summer – October to March inclusive)

A B

GL/season

33_Leven



Total 159.8 145.8

34_Forth-Wilmot



Total 705.6 594.7

35_Mersey



Total 168.5 150.8

36_Rubicon



Total 29.7 26.7

43_Tamar Estuary



Total 50.7 43.1


5 Under future development (Scenario D)

The impacts of future development under future climate are modelled in Scenario D. These developments include

proposed irrigation developments and projected future expansion in commercial forestry. The impacts of future

development are shown relative to Scenario C, which models future climate with current infrastructure.

5.1 Reliability of proposed irrigation developments

Sheffield-Barrington irrigation scheme

The proposed irrigation extraction of 10,200 ML/year was modelled as an extraction from Lake Barrington in TEMSim.

Lake Barrington is generally operated at full supply level for electricity generation, and as part of the Mersey-Forth

scheme, is supplied from a head storage, Lake Rowallan.

Modelled results show that with the additional extraction from Lake Barrington, the reservoir volume falls to minimum

operating level under Scenario D 13 times for periods of up to two days during the 84-year period. Lake Rowallan is

always operated above minimum operating level under Scenario D, indicating that water is always available in the head

storage to supply the irrigation extraction if necessary. This indicates that the irrigation extraction can be supplied at all

times under Scenario D with the appropriate commercial arrangement resulting in operation of the hydro-electric system

to supply this demand.

Sassafras-Wesley Vale irrigation scheme

The proposed irrigation extraction of 7200 ML/year was modelled as an extraction from Lake Parangana in TEMSim.

Lake Parangana is generally operated at full supply level for electricity generation, and as part of the Mersey-Forth

scheme, is supplied from a head storage, Lake Rowallan.

Modelled results show that with the additional extraction from Lake Parangana, the reservoir volume is drawn below

minimum operating level under Scenario D 18 times for periods of up to three days over the 84-year period. The

minimum operating level of Lake Parangana is set due to the level of the tunnel off-take. It would be possible to draw the

lake down to lower levels if the irrigation off-take was below the tunnel off-take. Lake Rowallan is always operated above

minimum operating level under Scenario D, indicating that water is always available in the head storage to supply the

irrigation extraction if necessary. This indicates that the irrigation extraction can be supplied at all times under Scenario D

with the appropriate construction and a commercial arrangement resulting in operation of the hydro-electric system to

supply this demand.

Forthside-Don and Kindred-North Motton irrigation schemes

The proposed Forthside-Don and Kindred-North Motton irrigation extractions of 2590 ML and 8660 ML respectively from

the Forth River downstream of Lake Paloona were modelled as direct extractions from the Forth River downstream of

Lake Paloona. These extractions are reliant on operation of Paloona power station. All proposed developments from the

Forth River were modelled together, which means that the performance of the downstream scheme may be affected by

the proposed upstream extractions.

The mean allocated water and extracted water for each scheme are shown in Table 27. As these are summer

extractions, statistics were calculated on a water-year basis from July to June. Both schemes have a high reliability of

extractions of 97 percent or greater under Scenario D.


Table 27. Comparison of allocated and extracted water under Scenario D schemes

Dwet Dmid Ddry

GL/y

Forthside-Don Scheme

Allocated water 2.6 2.6 2.6

Extraction 2.5 2.5 2.5

Percent extraction 98% 97% 98%

Kindred-North Motton Scheme

Allocated water 8.7 8.7 8.7

Extraction 8.5 8.4 8.4

Percent extraction 98% 97% 97%

The allocated and extracted water over the 83 water-years are shown in Figure 19. The allocated volume of water varies

year to year, depending on the modelled demand (Section 2.3.2). The mean allocated water reflects the mean annual

demand figures supplied by the Tasmanian Irrigation Development Board (Section 2.3.2, Table 5). The extracted volume

is 100 percent of the allocated volume for 80 percent of years on the Forthside-Don Scheme, and more than 70 percent

of years for the Kindred-North Motton Scheme.

(a-1) Forthside-Don Scheme – allocated water (a-2) Forthside-Don Scheme – extracted per allocated

0.0

0.5

1.0

1.5

2.0

2.5

3.0


Ann

ual v

olum

e (G

L) .

D range

Dmid

0.0

0.2

0.4

0.6

0.8

1.0

0% 20% 40% 60% 80% 100%


Ext

ract

ed v

olum

e pe

r .

unit

allo

cate

d .

D range

Dmid

(b-1) Kindred-North Motton Scheme – allocated water (b-2) Kindred-North Motton Scheme – extracted per allocated

0

2

4

6

8

10


Ann

ual v

olum

e (G

L) .

D range

Dmid

0.0

0.2

0.4

0.6

0.8

1.0

0% 20% 40% 60% 80% 100%


Ext

ract

ed v

olum

e pe

r .

unit

allo

cate

d .

D range

Dmid

Figure 19. Allocation and extraction reliability under Scenario D schemes

The volume of water extracted in dry periods is shown in Table 28. The volume of water extracted for the lowest periods

of extraction is lower than the mean annual extraction, indicating that the schemes will be less reliable during dry periods.


Table 28. Indicators of use during dry periods under Scenario D schemes

Dwet Dmid Ddry

GL/y

Forthside-Don Scheme

Lowest 1-year (water year) period of extraction 1.6 1.5 1.5



Mean water-year extraction for 84 years 2.5 2.5 2.5

Kindred-North Motton Scheme




Mean water-year extraction for 84 years 8.5 8.4 8.4

5.2 Hydrological impacts of future development

The projected changes in mean annual inflows from catchment runoff to each catchment are shown in Table 29 as the

percentage difference under Scenario D relative to Scenario C. Scenario D represents future expansion in commercial

forestry and irrigation under future climate. The largest projected changes in inflows due to increases in commercial

forestry are in the Mersey, Rubicon and Tamar Estuary catchments where inflows decrease by up to 4.7 percent under

Scenario D relative to Scenario C. This reflects the fact that the largest increases in future forestry are concentrated in

these catchments (Viney et al., 2009), as shown in Figure 6.

Table 29. Inflows from catchment runoff under Scenario D relative to Scenario C

Dwet Dmid Ddry

percent change relative to Cwet

percent change relative to Cmid

percent change relative to Cdry

33_Leven -1.7% -1.7% -1.7%

34_Forth-Wilmot -2.3% -2.4% -2.5%

35_Mersey -4.3% -4.4% -4.4%

36_Rubicon -4.2% -4.2% -4.2%

43_Tamar Estuary -4.7% -4.7% -4.7%

Region mean -3.3% -3.3% -3.3%

The projected changes in mean annual inflows from hydro storages to each catchment are shown in Table 30 as the

percentage change under Scenario D relative to Scenario C. The Forth-Wilmot and Mersey catchments are affected by

hydro flows. The operation of the hydro-electric system will change under Scenario D due to proposed extractions from

hydro storages for irrigation. The largest projected change in flows due to changes in hydro system operation is in the

Mersey catchment where there is an increase of 4.8 percent under Scenario Ddry relative to Scenario Cdry. These

increases in inflows downstream of hydro storages occurs because of hydro dams in this region releasing more water

under the future development scenario. This could occur because of lower diversions into the Leven catchment for

example.

Table 30. Inflows from downstream of hydro storages under Scenario D relative to Scenario C

Dwet Dmid Ddry

percent change relative to Cwet



33_Leven - - -

34_Forth-Wilmot -4.6% -1.2% -1.2%

35_Mersey -0.7% 4.3% 4.8%

36_Rubicon - - -

43_Tamar Estuary - - -

Region mean -4.3% -0.8% -0.8%


The projected changes in end-of-system (EOS) flows are shown in Table 31 as change in percentage of time EOS flows

are greater than 1 ML. There are only very minor changes under Scenario D relative to Scenario C in any catchment,

indicating that future development will not impact on the percentage of time rivers cease-to-flow in this region.

Table 31. Percent time end-of-system flow for catchments greater than 1 ML under Scenario D relative to Scenario C

Cwet Cmid Cdry Dwet Dmid Ddry

percentage of time EOS flow >1 ML

33_Leven 100% 100% 100% 100% 100% 100%

34_Forth-Wilmot 100% 100% 100% 100% 100% 100%

35_Mersey 100% 100% 100% 100% 100% 100%

36_Rubicon 89% 87% 87% 88% 86% 87%

43_Tamar Estuary 95% 94% 94% 93% 92% 93%

Extractions under Scenario C and relative changes under Scenario D are shown in Table 32. The change in extractions

under Scenario D relative to Scenario C is consistent with changes in runoff in most catchments. The change in

extractions under Scenario D relative to Scenario C is large in the Mersey catchment compared to the change in mean

annual runoff, indicating that the ability to extract water from the river would be affected by future development in this

catchment.

Table 32. Comparison of extractions for catchments under Scenario D relative to Scenario C


GL/y percent change relative to Cwet



33_Leven

Surety 1 0.5 0.5 0.5 -3.1% -3.1% -3.0%

Surety 2 0.0 0.0 0.0 - - -

Surety 3 0.0 0.0 0.0 - - -

Surety 4 0.0 0.0 0.0 - - -

Surety 5 8.6 8.5 8.5 -0.8% -0.8% -0.8%

Surety 6 0.5 0.4 0.4 -0.5% -0.7% -0.8%

Surety 7 0.0 0.0 0.0 - - -

Surety 8 0.0 0.0 0.0 - - -

Unlicensed 6.8 6.5 6.6 -2.3% -2.3% -2.2%

Total extractions 16.4 15.9 16.0 -1.5% -1.5% -1.5%

34_Forth-Wilmot

Surety 1 6.2 6.2 6.2 -21.2% -21.2% -21.2%

Surety 2 0.0 0.0 0.0 - - -

Surety 3 0.0 0.0 0.0 - - -

Surety 4 0.0 0.0 0.0 - - -

Surety 5 3.2 3.2 3.2 2.0% 2.0% 2.0%

Surety 6 0.2 0.2 0.2 0.0% 0.0% 0.0%

Surety 7 0.0 0.0 0.0 - - -

Surety 8 0.0 0.0 0.0 - - -

Unlicensed 3.3 3.3 3.3 -0.2% -0.3% -0.2%


35_Mersey

Surety 1 0.7 0.7 0.7 -6.7% -6.7% -6.7%

Surety 2 0.0 0.0 0.0 - - -

Surety 3 0.0 0.0 0.0 - - -

Surety 4 0.0 0.0 0.0 - - -

Surety 5 21.5 20.9 20.9 -10.2% -10.3% -10.3%

Surety 6 2.2 2.1 2.1 -16.6% -17.1% -17.3%

Surety 7 0.0 0.0 0.0 - - -

Surety 8 0.0 0.0 0.0 - - -

Unlicensed 7.7 7.3 7.4 -15.9% -16.3% -16.4%



Table 32. Comparison of extractions for catchments under Scenario D relative to Scenario C (continued)


GL/y percent change relative to Cwet



36_Rubicon

Surety 1 0.4 0.3 0.3 -4.5% -4.4% -4.4%

Surety 2 0.0 0.0 0.0 - - -

Surety 3 0.0 0.0 0.0 - - -

Surety 4 0.0 0.0 0.0 - - -

Surety 5 8.4 8.3 8.1 -3.0% -2.9% -3.0%

Surety 6 1.0 0.9 0.9 -4.0% -4.1% -4.0%

Surety 7 0.0 0.0 0.0 - - -

Surety 8 0.0 0.0 0.0 - - -

Unlicensed 1.6 1.5 1.5 -2.9% -2.8% -2.8%


43_Tamar Estuary

Surety 1 0.5 0.5 0.5 -5.0% -5.5% -5.5%

Surety 2 0.0 0.0 0.0 - - -

Surety 3 0.0 0.0 0.0 -5.6% -5.2% -5.2%

Surety 4 0.0 0.0 0.0 - - -

Surety 5 4.0 4.0 4.0 -2.5% -2.5% -2.5%

Surety 6 0.0 0.0 0.0 -0.3% -0.6% -0.3%

Surety 7 0.0 0.0 0.0 - - -

Surety 8 0.0 0.0 0.0 - - -

Unlicensed 3.0 3.0 3.0 -4.0% -3.8% -3.9%


Total

Surety 1 8.2 8.2 8.2 -17.3% -17.3% -17.3%

Surety 2 0.0 0.0 0.0 - - -

Surety 3 0.0 0.0 0.0 -5.6% -5.2% -5.2%

Surety 4 0.0 0.0 0.0 - - -

Surety 5 45.8 44.9 44.7 -5.6% -5.5% -5.6%

Surety 6 3.9 3.7 3.7 -10.3% -10.8% -10.9%

Surety 7 0.0 0.0 0.0 - - -

Surety 8 0.0 0.0 0.0 - - -

Unlicensed 22.5 21.7 21.8 -6.9% -6.9% -7.0%


The mean monthly percent change in EOS flow under Scenario D relative to Scenario C is shown in Figure 20. The

largest percentage change is observed in the drier summer months where reductions in EOS flows of up to 25 percent

can be seen in the Mersey catchment. However, flows at this time of the year are very low (see Figure 14), and thus,

volumetrically, these reductions are fairly small.


(a-1) 33_Leven – monthly flows (scenarios P, A and C)

(a-2) 33_Leven – monthly flows (Scenario D)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0


EO

S m

onth

ly fl

ow (

GL)

. C rangeCmidAP

-25

-20

-15

-10

-5

0


Per

cent

cha

nge

in E

OS

mon

thly

flow

rel

ativ

e .

to S

cena

rio

C .

D range

Dmid

(b-1) 34_Forth-Wilmot – monthly flows (scenarios P, A and C)

(b-2) 34_Forth-Wilmot – monthly flows (Scenario D)

0

2

4

6

8

10

12


EO

S m

onth

ly fl

ow (

GL)

. C rangeCmidAP

-25

-20

-15

-10

-5

0


Per

cent

cha

nge

in E

OS

mon

thly

flow

rel

ativ

e .

to S

cena

rio

C .

D range

Dmid

(c-1) 35_Mersey – monthly flows (scenarios P, A and C)

(c-2) 35_Mersey – monthly flows (Scenario D)

0

1

2

3

4

5


EO

S m

onth

ly fl

ow (

GL)

. C rangeCmidAP

-25

-20

-15

-10

-5

0


Per

cent

cha

nge

in E

OS

mon

thly

flow

rel

ativ

e .

to S

cena

rio

C .

D range

Dmid

(d-1) 36_Rubicon – monthly flows (scenarios P, A and C)

(d-2) 36_Rubicon – monthly flows (Scenario D)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4


EO

S m

onth

ly fl

ow (

GL)

. C rangeCmidAP

-25

-20

-15

-10

-5

0


Per

cent

cha

nge

in E

OS

mon

thly

flow

rel

ativ

e .

to S

cena

rio

C .

D range

Dmid

Figure 20. Mean monthly end-of-system flow under scenarios P, A and C; and changes under Scenario D relative to Scenario C


(e-1) 43_Tamar Estuary – monthly flows (scenarios P, A and C)

(e-2) Tamar Estuary – monthly flows (Scenario D)

0.0

0.5

1.0

1.5

2.0

2.5


EO

S m

onth

ly fl

ow (

GL)

. C rangeCmidAP

-25

-20

-15

-10

-5

0


Per

cent

cha

nge

in E

OS

mon

thly

flow

rel

ativ

e .

to S

cena

rio

C .

D range

Dmid

Figure 20. Mean monthly end-of-system flow under scenarios P, A and C; and changes under Scenario D relative to Scenario C

(continued)

The peak flows under Scenario C and changes under Scenario D are shown in Table 33. Peak flows are reduced for all

return periods in all catchments under Scenario D relative to Scenario C, showing that high flows are impacted by future

development. These impacts are outcomes of the FCFC modelling used to determine the effects of forestry on

streamflow (Viney et al., 2009). Compared to the impacts on low flows however (see Figure 20), the impacts on high

flows are relatively minor. Changes in hydro-operation as seen in Table 30 may also act to reduce peak flows in these

catchments.

Table 33. Comparison of change in peak flows under Scenario D relative to Scenario C


ML/d percent change

relative Cwet percent change relative to Cmid


33_Leven

2-year 11,583 11,501 10,597 -1.04% -1.17% -1.24%

5-year 15,023 14,889 13,768 -1.32% -1.16% -1.53%

10-year 17,882 17,557 16,525 -1.39% -1.56% -1.32%

34_Forth-Wilmot

2-year 22,254 21,404 19,625 -3.81% -0.28% -1.93%

5-year 32,570 32,534 29,368 -3.19% -1.12% -0.70%

10-year 36,523 36,916 34,516 -2.13% -0.59% -1.30%

35_Mersey

2-year 19,204 19,042 17,586 -1.98% -2.93% -3.20%

5-year 26,911 27,444 24,696 -3.40% -2.75% -3.00%

10-year 31,237 31,988 29,013 -3.11% -3.24% -2.09%

36_Rubicon

2-year 7,327 7,615 6,689 -4.05% -4.37% -4.37%

5-year 10,401 10,639 9,527 -3.95% -3.85% -4.16%

10-year 12,433 12,898 11,674 -4.05% -4.21% -4.43%

43_Tamar Estuary

2-year 10,971 10,702 9,570 -4.47% -3.48% -3.28%

5-year 15,059 14,902 13,476 -3.20% -3.09% -3.21%

10-year 17,499 18,352 17,407 -3.09% -3.49% -3.49%


6 Conclusions

The Mersey-Forth region has a mean annual flow of 3881 GL/year, and a relatively low level of extraction, with a mean

annual extraction of 81 GL/year (2.0 percent of total water in the region). The volume of allocated water varies each year

in many catchments, due to restriction rules which limit extractions during periods of low flow.

The volume of extracted water in the region is not expected to reduce significantly under future climate (Scenario C)

relative to historical climate (Scenario A). The largest impact is seen in the driest years. In comparison to extractions, it is

projected that future climate has a greater impact on total end-of-system (EOS) flows.

Peak flows were evaluated for return periods of two, five and ten years. They are projected to increase under

Scenario Cwet relative to Scenario A in the Rubicon and Tamar Estuary catchments, and decrease or remain the same

in the Leven, Forth-Wilmot and Mersey catchments. Peak flows are projected to decrease in all catchments under

Scenario Cdry relative to Scenario A for the majority of return periods.

Under the recent climate (Scenario B), the mean monthly flow is lower than the long-term mean in all catchments in

summer, autumn and early winter. The flow duration curves show that flows over recent climate have generally been

lower than the long-term mean over the full range of flows. The volume of water extracted decreases by a mean of

4.3 GL/year under Scenario B relative to Scenario A. The volume of non-extracted water decreases in all catchments

under Scenario B relative to Scenario A by a mean of 525 GL/year (14 percent) over the region as a whole.


plantations increasing total forest cover from 25 percent of the region to 29 percent of the region by 2030. This increase

is entirely in the northern two-thirds of the region. Catchment runoff is projected to decrease by a maximum of

4.7 percent in the Tamar Estuary catchment due to the expansion of forestry plantations.

Four irrigation developments are proposed in the region: the Sheffield-Barrington, Kindred-North Motton, Forthside-Don

and Sassafras-Wesley Vale schemes. The total mean annual demand for all the proposed developments is 29 GL/year.

These schemes rely on storage and flows from the Mersey-Forth hydro-electric scheme. The Sheffield-Barrington and

Sassafras-Wesley Vale schemes were modelled as extractions from hydro storages and the results showed that the

hydro-electric system could be run to supply this demand in all years under Scenario D. The Kindred-North Motton and

Forthside-Don schemes had a predicted reliability of 97 percent or greater under Scenario D.


7 References

Catchment Simulation Solutions (2009) Catchment-Sim. Viewed 10 September 2009, <http://www.csse.com.au/index.php?option=com_content&task=view&id=66&Itemid=127>.

CSIRO (2008) Water availability in the Murrumbidgee. A report to the Australian Government from the CSIRO Murray-Darling Basin Sustainable Yields Project. CSIRO, Australia.

Department of Primary Industries, Parks, Water and Environment (2009) Applying for a Water Licence. Department of Primary Industries, Parks, Water and Environment, Hobart. Viewed 6 August 2009, <http://www.dpiw.tas.gov.au/inter.nsf/WebPages/JMUY-4YA86N?open#SuretyLevels>.

Department of Primary Industries and Water, and Inland Fisheries Service Tasmania (2005) Lakes Sorell and Crescent Water Management Plan, Department of Primary Industries and Water, Tasmania.

Graham B, Hardie S, Gooderham J, Gurung S, Hardie D, Marvanek S, Bobbi C, Krasnicki T and Post DA (2009) Ecological impacts of water availability for Tasmania. A report to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

Green G (2001) North-west rivers environmental review: A review of Tasmanian environmental quality data to 2001. Supervising Scientist Report 167, Supervising Scientist, Darwin.

Hydro Tasmania (1997) Modelling the operation of Lake Sorell and Lake Crescent, Report No. 001-0587-CR-001, for Department of Primary Industries and Fisheries, Tasmania.

Kisters (2009) Hydstra/MO network modelling, Kisters Pioneering Technologies. Viewed 10 August 2009, <http://www.kisters.de/english/html/au/homepage.html>.

Ling FLN, Gupta V, Willis M, Bennett JC, Robinson KA, Paudel K, Post DA and Marvanek S (2009a) River modelling for Tasmania. Volume 1: the Arthur-Inglis-Cam region. A report to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

Ling FLN, Gupta V, Willis M, Bennett JC, Robinson KA, Paudel K, Post DA and Marvanek S (2009b) River modelling for Tasmania. Volume 2: the Mersey-Forth region. A report to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

Ling FLN, Gupta V, Willis M, Bennett JC, Robinson KA, Paudel K, Post DA and Marvanek S (2009c) River modelling for Tasmania. Volume 3: the Pipers-Ringarooma region. A report to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

Ling FLN, Gupta V, Willis M, Bennett JC, Robinson KA, Paudel K, Post DA and Marvanek S (2009d) River modelling for Tasmania. Volume 4: the South Esk region. A report to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

Ling FLN, Gupta V, Willis M, Bennett JC, Robinson KA, Paudel K, Post DA and Marvanek S (2009e) River modelling for Tasmania. Volume 5: the Derwent-South East region. A report to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

Post DA, Chiew FHS, Teng J, Vaze J, Yang A, Mpelasoka F, Smith I, Katzfey J, Marston F, Marvanek S, Kirono D, Nguyen K, Kent D, Donohue R, Li L and McVicar T (2009) Production of climate scenarios for Tasmania. A report to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

Viney NR, Post DA, Yang A, Willis M, Robinson KA, Bennett JC, Ling FLN and Marvanek S (2009) Rainfall-runoff modelling for Tasmania. A report to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

Willis M (2008) TasCatch Finalisation Report – Stage 1 & Stage 2. HTC Report Consult-20294, for Department of Primary Industries and Water. Hydro Tasmania Consulting, Hobart.

Willis M, Bennett J, Robinson K, Ling F, Gupta V (2009) Tasmania Sustainable Yields River Modelling Methods Report. Hydro Tasmania Consulting, Hobart. in prep.

Tasmania Sustainable Yields Project reports

Region reports

CSIRO (2009) Water availability for Tasmania. Report one of seven to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

CSIRO (2009) Climate change projections and impacts on runoff for Tasmania. Report two of seven to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

CSIRO (2009) Water availability for the Arthur-Inglis-Cam region. Report three of seven to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

CSIRO (2009) Water availability for the Mersey-Forth region. Report four of seven to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

CSIRO (2009) Water availability for the Pipers-Ringarooma region. Report five of seven to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

CSIRO (2009) Water availability for the South Esk region. Report six of seven to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

CSIRO (2009) Water availability for the Derwent-South East region. Report seven of seven to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

Technical reports

Graham B, Hardie S, Gooderham J, Gurung S, Hardie D, Marvanek S, Bobbi C, Krasnicki T and Post DA (2009) Ecological impacts of water availability for Tasmania. A report to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

Harrington GA, Crosbie R, Marvanek S, McCallum J, Currie D, Richardson S, Waclawik V, Anders L, Georgiou J, Middlemis H and Bond K (2009) Groundwater assessment and modelling for Tasmania. A report to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

Ling FLN, Gupta V, Willis M, Bennett JC, Robinson KA, Paudel K, Post DA and Marvanek S (2009) River modelling for Tasmania. Volume 1: the Arthur-Inglis-Cam region. A report to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

Ling FLN, Gupta V, Willis M, Bennett JC, Robinson KA, Paudel K, Post DA and Marvanek S (2009) River modelling for Tasmania. Volume 2: the Mersey-Forth region. A report to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

Ling FLN, Gupta V, Willis M, Bennett JC, Robinson KA, Paudel K, Post DA and Marvanek S (2009) River modelling for Tasmania. Volume 3: the Pipers-Ringarooma region. A report to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

Ling FLN, Gupta V, Willis M, Bennett JC, Robinson KA, Paudel K, Post DA and Marvanek S (2009) River modelling for Tasmania. Volume 4: the South Esk region. A report to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

Ling FLN, Gupta V, Willis M, Bennett JC, Robinson KA, Paudel K, Post DA and Marvanek S (2009) River modelling for Tasmania. Volume 5: the Derwent-South East region. A report to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

Post DA, Chiew FHS, Teng J, Vaze J, Yang A, Mpelasoka F, Smith I, Katzfey J, Marston F, Marvanek S, Kirono D, Nguyen K, Kent D, Donohue R, Li L and McVicar T (2009) Production of climate scenarios for Tasmania. A report to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

Viney NR, Post DA, Yang A, Willis M, Robinson KA, Bennett JC, Ling FLN and Marvanek S (2009) Rainfall-runoff modelling for Tasmania. A report to the Australian Government from the CSIRO Tasmania Sustainable Yields Project, CSIRO Water for a Healthy Country Flagship, Australia.

Enquiries

More information about the CSIRO Tasmania Sustainable Yields Project can be found at <www.csiro.au/partnerships/TasSY.html>. This information includes the full terms of reference for the project and all associated reporting products.

More information about the Water for the Future Plan of the Australian Government can be found at <www.environment.gov.au/water>.

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River modelling for Tasmania Volume 2: the Mersey-Forth region · River modelling for Tasmania...

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