Surface Water Models Forth River Catchment

DPIW – SURFACE WATER MODELS FORTH RIVER CATCHMENT

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

DOCUMENT INFORMATION

JOB/PROJECT TITLE Surface Water Hydrological Models for DPIW CLIENT ORGANISATION Department of Primary Industries and Water CLIENT CONTACT Bryce Graham

DOCUMENT ID NUMBER WR 2007/019 JOB/PROJECT MANAGER Mark Willis JOB/PROJECT NUMBER E200690/P202167 Document History and Status Revision Prepared Reviewed Approved Date Revision by by by approved type 1.0 Mark Willis Fiona Ling C. Smythe July 2007 Final

1.1 Mark Willis Fiona Ling C. Smythe July 2008 Final

Current Document Approval PREPARED BY Mark Willis

Water Resources Mngt Sign Date

REVIEWED BY Dr Fiona Ling

Water Resources Mngt Sign Date

APPROVED FOR Crispin Smythe SUBMISSION Water Resources Mngt Sign Date Current Document Distribution List Organisation Date Issued To DPIW July 2008 Bryce Graham

The concepts and information contained in this document are the property of Hydro Tasmania. This document may only be used for the purposes of assessing our offer of services and for inclusion in documentation for the engagement of Hydro Tasmania. Use or copying of this document in whole or in part for any other purpose without the written permission of Hydro Tasmania constitutes an infringement of copyright.

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

EXECUTIVE SUMMARY

This report is part of a series of reports which present the methodologies and results from the development and calibration of surface water hydrological models for 26 catchments under both current and natural flow conditions. This report describes the results of the hydrological model developed for the Forth River catchment.

A model was developed for the Forth River catchment that facilitates the modelling of flow data for three scenarios:

• Scenario 1 – No entitlements (Natural Flow);

• Scenario 2 – with Entitlements (with water entitlements extracted);

• Scenario 3 - Environmental Flows and Entitlements (Water entitlements extracted, however low priority entitlements are limited by an environmental flow threshold).

The results from the scenario modelling allow the calculation of indices of hydrological disturbance. These indices include:

• Index of Mean Annual Flow

• Index of Flow Duration Curve Difference

• Index of Seasonal Amplitude

• Index of Seasonal Periodicity

• Hydrological Disturbance Index

The indices were calculated using the formulas stated in the Natural Resource Management (NRM) Monitoring and Evaluation Framework developed by SKM for the Murray-Darling Basin (MDBC 08/04).

A user interface is also provided that allows the user to run the model under varying catchment demand scenarios. This allows the user to add further extractions to catchments and see what effect these additional extractions have on the available water in the catchment of concern. The interface provides sub-catchment summary of flow statistics, duration curves, hydrological indices and water entitlements data. For information on the use of the user interface refer to the Operating Manual for the NAP Region Hydrological Models (Hydro Tasmania 2004).

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

CONTENTS

EXECUTIVE SUMMARY ii 1. INTRODUCTION 1 2. CATCHMENT CHARACTERISTICS 2 3. DATA COMPILATION 4 3.1 Climate data (Rainfall & Evaporation) 4 3.2 Advantages of using climate DRILL data 4 3.3 Transposition of climate DRILL data to local catchment 5 3.4 Comparison of Data Drill rainfall and site gauges 7 3.5 Streamflow data 8 3.6 Irrigation and water usage 9 3.7 Estimation of unlicensed dams 15 3.8 Environmental flows 16 4. MODEL DEVELOPMENT 18 4.1 Sub-catchment delination 18 4.2 Hydstra Model 18 4.2.1 Hydro Tasmania Lakes 20 4.2.2 Lemonthyme Power Station and Wilmot Power Stations 21 4.3 AWBM Model 22 4.3.1 Channel Routing 25 4.4 Model Calibration 25 4.4.1 Factors affecting the reliability of the model calibration. 32 4.4.2 Model Accuracy - Model Fit Statistics 33 4.4.3 Model accuracy across the catchment 36 4.5 Model results 38 4.5.1 Indices of hydrological disturbance 39 4.6 Flood frequency analysis 40 5. REFERENCES 41 5.1 Personal Communications 41 6. GLOSSARY 42 APPENDIX A 44

iii

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

LIST OF FIGURES

Figure 2-1 Sub-catchment boundaries 3

Figure 3-1 Climate Drill Site Locations 6

Figure 3-2 Rainfall and Data Drill Comparisons 8

Figure 3-3 Water Allocations 14

Figure 4-1 Hydstra Model Schematic 19

Figure 4-2 Australian Water Balance Model Schematic 24

Figure 4-3 Monthly Variation of CapAve Parameter 28

Figure 4-4 Daily time series (ML/d) – Forth River - Good fit. 29

Figure 4-5 Daily time series comparison (ML/d) – Forth River – Good fit. 29

Figure 4-6 Daily time series comparison (ML/d) – Forth River – Good fit. 30

Figure 4-7 Monthly time series comparison – volume (ML) 30

Figure 4-8 Long term average monthly, seasonal and annual comparison plot 31

Figure 4-9 Duration Curve – Daily flow percentage difference 35

Figure 4-10 Duration Curve – Monthly volume percentage difference 35

Figure 4-11 Time Series of Monthly Volumes- Site 450 37

Figure 4-12 Time Series of Monthly Volumes- Site 815 37

Figure 4-13 Daily Duration Curve 38

Figure A-1 Forth catchment – monthly volumes at secondary site. 46

Figure A-2 George catchment – monthly volumes at secondary site. 46

Figure A-3 Leven catchment – monthly volumes at secondary site. 47

Figure A-4 Swan catchment – monthly volumes at secondary site. 47

Figure A-5 Montagu catchment – monthly volumes at secondary site. 48

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

LIST OF TABLES

Table 3.1 Data Drill Site Locations 7

Table 3.2 Potential calibration sites 9

Table 3.3 Assumed Surety of Unassigned Records 10

Table 3.4 Unlicensed extractions 11

Table 3.5 Sub Catchment High and Low Priority Entitlements 11

Table 3.6 Average capacity for dams less than 20 ML by Neal et al (2002) 16

Table 3.7 Environmental Flows 17

Table 4.1 Hydro Tasmania Lakes - assumed downstream flow 21

Table 4.2 Power Station inter-catchment transfer 22

Table 4.3 Adopted Calibration Parameters 27

Table 4.4 Long term average monthly, seasonal and annual comparisons 31

Table 4.5 Model Fit Statistics 33

Table 4.6 R 2 Fit Description 34

Table 4.7 Hydrological Disturbance Indices 39

Table A-1 Model performance at secondary sites 49

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

1. INTRODUCTION

This report forms part of a larger project commissioned by the Department of Primary Industries and Water (DPIW) to provide hydrological models for 26 regional catchments.

The main objectives for the individual catchments are:

• To compile relevant data required for the development and calibration of the hydrological model (Australian Water Balance Model, AWBM) for the Forth River catchment;

• To source over 100 years of daily time-step rainfall and streamflow data for input to the hydrologic model;

• To develop and calibrate the hydrologic model under both natural and current catchment conditions;

• To develop a User Interface for running the model under varying catchment demand scenarios;

• Prepare a report summarising the methodology adopted, assumptions made, results of calibration and validation and description relating to the use of the developed hydrologic model and associated software.

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

2. CATCHMENT CHARACTERISTICS

The Forth River catchment is located in North West Tasmania. It has a catchment area of 1119.8 km 2 and discharges into Bass Strait at Turner’s Beach.

The headwaters of the catchment start in the Cradle Mountain and Lake St Clair National Park are fed by runoff from Tasmania’s highest peaks such Mt Ossa (1617m AHD) and Mt Pelion West (1560m AHD). This portion of the catchment is virtually unpopulated except for the tourist settlement at Cradle Valley and the landscape is typical alpine and eucalypt vegetation.

The middle parts of the catchment are highly modified due to the control of the flow for hydro-electric generation activities. Infrastructure owned and operated by Hydro Tasmania within this catchment include; Lemonthyme Power Station, Lake Cethana, Cethana Power Station, Lake Barrington, Devils Gate Power Station, Lake Gairdner, Wilmot Power Station, Lake Paloona and Paloona Power Station. Flow through the Lemonthyme Power Station is via an inter-catchment water transfer from the Mersey River. The vegetation in the middle catchments is dominated by Eucalypt forests.

The lower part of the catchment consists of a mixture of agriculture and smaller (life style) residential allotments, including the township of Forth.

Variability in the annual rainfall total across this catchment is significant, mainly due to the changes in elevation and the varied exposure to the dominant westerly weather pattern. The lower catchment around Forth receives a typical annual rainfall of around 1000mm and the upper catchment around Cradle Valley around 2800mm.

There are 283 registered (current) entitlements for water extraction registered on the Water Information Management System (WIMS Dec 2006). Most of these extractions are concentrated in the lower sub-catchments and mainly relate to agriculture. The largest extraction entitlement is 4845 ML associated with the Cradle Coast water supply. As expected most of the upper sub-catchments have few or no registered WIMS entitlements as this is unpopulated and utilised either for electricity generation or contained within a national park.

For modelling purposes, the Forth River catchment was divided into 33 sub areas. The delineation of these areas and the assumed stream routing network is shown in Figure 2-1.

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

395000 400000 405000 410000 415000 420000 425000 430000 435000 440000 445000 450000 5445000 5445000

5440000 15 5440000 14 13 1 Forth at Paloona Bridge 5435000 Gauging Site 25 5435000 XY XY33 5430000 32 5430000 6 5 5425000 5425000 29 7

5420000 12 5420000 27 26 8 5415000 2 5415000 5410000 5410000

22 4 9 11 5405000 28 5405000 23 XY 24

5400000 30 3 5400000

Inter-catchment water transfer Lemonthyme Power Station 5395000 5395000 20 XY 31 21 5390000 5390000

5385000 18 5385000 5380000 5380000 10 5375000 Legend - 5375000 XY Gauging Sites 5370000 19 5370000 Stream Routing Network Sub-catchment boundary 5365000 5365000 02 4 8 12 16 Kilometers

395000 400000 405000 410000 415000 420000 425000 430000 435000 440000 445000 450000 Figure 2-1 Sub-catchment boundaries

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

3. DATA COMPILATION

3.1 Climate data (Rainfall & Evaporation) Daily time-step climate data was obtained from the Queensland Department of Natural Resources & Mines (QDNRM).

The Department provides time series climate drill data from 0.05 o x 0.05 o (about 5 km x 5 km) interpolated gridded rainfall and evaporation data based on over 6000 rainfall and evaporation stations in Australia (see www.nrm.qld.gov.au/silo ) for further details of climate drill data.

3.2 Advantages of using climate DRILL data This data has a number of benefits over other sources of rainfall data including:

• Continuous data back to 1889 (however, further back there are less input sites available and therefore quality is reduced. The makers of the data set state that gauge numbers have been somewhat static since 1957, therefore back to 1957 distribution is considered “good” but prior to 1957 site availability may need to be checked in the study area);

• Evaporation data (along with a number of other climatic variables) is also included which can be used for the AWBM model. According to the QNRM web site, all Data Drill evaporation information combines a mixture of the following data.

1. Observed data from the Commonwealth Bureau of Meteorology (BoM).

2. Interpolated daily climate surfaces from the on-line NR&M climate archive.

3. Observed pre-1957 climate data from the CLIMARC project (LWRRDC QPI- 43). NR&M was a major research collaborator on the CLIMARC project, and these data have been integrated into the on-line NR&M climate archive.

4. Interpolated pre-1957 climate surfaces. This data set, derived mainly from the CLIMARC project data, is available in the on-line NR&M climate archive.

5. Incorporation of Automatic Weather Station (AWS) data records. Typically, an AWS is placed at a user's site to provide accurate local weather measurements.

For the Forth River catchment the evaporation data was examined and it was found that

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

prior to 1970 the evaporation information is based on the long term daily averages of the post 1970 data. In the absence of any reliable long term site data this is considered to be the best available evaporation data set for this catchment.

3.3 Transposition of climate DRILL data to local catchment Ten climate Data Drill sites were selected to give good coverage of the Forth River catchment. Two of these sites correspond to the same location as Data Drill information sourced for the Clayton River catchment model.

See Figure 3-1 below for a map of the climate Data Drill sites and Table 3.1 for the location information.

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

400000 405000 410000 415000 420000 425000 430000 435000 440000 445000 450000 5445000 5445000 14 00 Clayton_03 5440000 ^_ 5440000 5435000 5435000

5430000 Clayton_09 5430000 ^_

5425000 Forth_01 Forth_02 5425000 ^_ ^_ 5420000 5420000 5415000 5415000 Forth_03 ^_ 5410000 5410000

5405000 0 5405000 0 4 Forth_04 Forth_05 1

5400000 ^_ ^_ 5400000 5395000 5395000

Forth_06 5390000 1 5390000 0 ^_ 6 0 0 180 4 0 0 Forth_07 2 5385000 ^_ 5385000 5380000 5380000

5375000 Forth_08 Legend 1200 - 5375000 ^_ Rainfall Isoheytal

5370000 ^_ Rainfall & Evaporation sites 5370000 2 Sub-catchment boundary 2

5365000 0 5365000 0 02 4 8 12 16 Kilometers 400000 405000 410000 415000 420000 425000 430000 435000 440000 445000 450000 Figure 3-1 Climate Drill site locations

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

Table 3.1 Data Drill site locations

Site Longitude Latitude Clayton_03 146:15:00 -41:12:00 Clayton_09 146:12:00 -41:18:00 Forth_01 146:06:00 -41:21:00 Forth_02 146:15:00 -41:21:00 Forth_03 146:06:00 -41:27:00 Forth_04 145:57:00 -41:33:00 Forth_05 146:09:00 -41:33:00 Forth_06 145:57:00 -41:39:00 Forth_07 146:06:00 -41:42:00 Forth_08 146:00:00 -41:48:00

3.4 Comparison of Data Drill rainfall and site gauges As rainfall data is a critical input to the modelling process it is important to have confidence that the Data Drill long term generated time series does in fact reflect what is being observed within the catchment. Rainfall sites in closest proximity to the Data Drill locations were sourced and compared. The visual comparison and the R 2 value indicate that there appears to be good correlation between the two, which is to be expected as the Data Drill information is derived from site data. The annual rainfall totals of selected Data Drill sites and neighbouring sites for coincident periods are plotted in Figure 3-2.

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

2500 Data Drill - Forth_03 Erriba - Site 1608 R2 = 0.99

2000

1500

1000

Annaul Annaul Rainfall (mm) 500

6 6 0 6 0 960 964 96 970 974 97 98 984 98 99 1958 1 1962 1 1 1968 1 1972 1 1 1978 1 1982 1 1 1988 1

4500 Data Drill - Forth_06 Cradle Mt - Site 887 R2 = 0.96

4000

3500

3000

2500 2000 1500 AnnaulRainfall (mm) 1000

500

2 4 3 2 4 6 19 31 40 61 73 85 94 925 928 937 949 958 967 970 979 982 991 19 192 1 1 19 193 1 19 194 1946 1 195 1955 1 19 196 1 1 19 197 1 1 19 1988 1 19

1800 Data Drill - Forth_02 Barrington - Site 1637 R2 = 0.97

1600

1400

1200

1000 800 600 AnnaulRainfall (mm) 400

200

5 2 3 9 0 2 6 9 0 69 70 76 77 83 84 87 91 966 967 971 974 978 981 988 196 1 1 1968 19 19 1 197 197 1 1975 19 19 1 197 198 1 198 19 19 1985 198 19 1 198 199 19

Figure 3-2 Rainfall and Data Drill comparisons

3.5 Streamflow data Selecting a site suitable for model calibration was difficult for this catchment. Although there were a significant number of Hydro Tasmania sites within this catchment there were few with significant periods of record, complete flow ratings and at a representative

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

location in the catchment. Forth River at Paloona Bridge (site 386) was the site identified that best met these criteria as it has sufficient flow record available prior to the dam construction period and it is situated low the catchment. The sites investigated as potential calibration potential sites are given in the following table.

Table 3.2 Potential calibration sites

Site Name Site Period of Record Easting Northing Comments No. Forth River above 450 12/12/1962 to present 427450 5392900 High in Lemonthyme Power catchment Station Iris River at Middlesex 815 21/04/1994 to present 416500 5401500 High in Plains catchment Wilmot River a/b Forth 524 13/07/1966 to present 435500 5430350 Low in catchment but Wilmot River only. Forth River below 665 04/09/1972 to present 437318 5430641 Post dam Wilmot River construction Forth River at Paloona 386 03/06/1961 to 437598 5431149 9 years record Bridge 23/01/1975 pre-dams. (uncontrolled flow).

Investigations of the rating histories and qualities at Forth River at Paloona Bridge, indicate that the record appears to be based on a natural control with 8 ratings covering the whole period of record and the data appears to be reliable during the period of interest, which is prior to the flow modification due to hydro generation commencing in May 1969.

3.6 Irrigation and water usage Information on the current water entitlement allocations in the catchment was obtained from DPIW and is sourced from the Water Information Management System (WIMS Dec 2006). The WIMS extractions or licenses in the catchment are of a given Surety (from 1 to 8), with Surety 1-3 representing high priority extractions for modelling purposes and Surety 4-8 representing the lowest priority. The data provided by DPIW contained a number of sites which had a Surety of 0. DPIW staff advised that in these cases the surety should be determined by the extraction “Purpose” and assigned as follows:

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

Table 3.3 Assumed Surety of unassigned records

Purpose Surety Aesthetic 6 Aquaculture 6 Commercial 6 Domestic 1 Industrial 6 Irrigation 6 Storage 6 Other 6 Power Generation 6 Recreation 6 Stock and Domestic S & D 1 Stock 1 Water Supply 1 Fire Fighting 1 Dust Proof 6

In total there were 554.25 ML unassigned entitlements (surety = 0) identified for inclusion in the surface water model, 290.15 of which were assigned surety 1 and 264.1 were assigned surety 6.

DPIW staff also advised that the water extraction information provided should be filtered to remove the following records:

• Extractions relating to fish farms should be omitted as this water is returned to the stream. These are identified by a Purpose name called “ fish farm ” or “ Acquacult”. There were no fish farms identified in this catchment. There were none identified for this model;

• The extraction data set includes a “WE_status” field where only “ current” and “existing” should be used for extractions. All other records, for example deleted, deferred, transferred, suspended and proposed, should be omitted;

• Six extractions relating to Cradle Coast Water shown as “ current” but with an expiry date of 31-Dec-01 were removed, as DPIW advised these related to temporary licenses.

In this catchment there was also an extraction identified for power generation for the Lemonthyme Lodge. This was excluded at it was assumed the water would be returned to the stream.

When modelling Scenario 3 (Environmental flows and Entitlements), water will only be available for Low Priority entitlements after environmental flow requirements have been

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

met.

There were multiple communications with DPIW staff, on allowances for extractions not yet included in the WIMS (Dec 2006) water licence database. A summary of the annual additional unlicensed extractions adopted for the model are given in the following table.

Table 3.4 Unlicensed extractions

Region or Assigned Period Assumed Assumed Assumed Licence Sub- Amount (ML) Start End Surety Number catchment 6198 SC1 102.3 01/05 30/11 6 4984 SC1 102.0 01/05 30/11 6 Cradle Coast SC1 3116.0 30/10 30/04 1 Water 5294 SC13 66.0 01/05 30/11 6 Hoggs Creek SC6 107.17 30/10 30/04 1 Kindred Creek SC25 532.21 30/10 30/04 1 Jones Creek SC16 64.0 30/10 30/04 1

Additional allowances for unlicensed dam extractions are covered in Section 3.7.

A summary table of total entitlement volumes on a monthly basis by sub-catchment is provided below in Table 3.5 and in the Catchment User Interface. A map of the water allocations in the catchment is shown in Figure 3-3.

Table 3.5 Sub Catchment High and Low Priority Entitlements

Table 3. Water Entitlements Summarized - Monthly Demand (ML) for each Subarea & Month Subc atch Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total High Priority Entitlements SC1 869.63 785.47 869.63 841.58 415.41 402.01 415.41 415.41 402.01 869.63 841.58 869.63 7,997 SC2 26.63 24.05 26.63 25.77 28.05 27.15 28.05 28.05 27.15 26.63 25.77 26.63 321 SC3 0.32 0.29 0.32 0.31 0.45 0.43 0.45 0.45 0.43 0.32 0.31 0.32 4 SC4 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC5 0.00 0.00 0.00 0.00 0.37 0.36 0.37 0.37 0.36 0.00 0.00 0.00 2 SC6 15.67 14.15 15.67 15.17 3.40 3.29 3.40 3.40 3.29 15.67 15.17 15.67 124 SC7 0.00 0.00 0.00 0.00 0.50 0.48 0.50 0.50 0.48 0.00 0.00 0.00 2 SC8 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC9 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC10 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC11 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC12 9.64 8.71 9.64 9.33 10.88 10.53 10.88 10.88 10.53 9.64 9.33 9.64 120 SC13 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC14 0.00 0.00 0.00 0.00 1.13 1.10 1.13 1.13 1.10 0.00 0.00 0.00 6 SC15 0.38 0.35 0.38 0.37 3.86 3.73 3.86 3.86 3.73 0.45 0.44 0.38 22 SC16 10.12 9.14 10.12 9.80 1.62 1.56 1.62 1.62 1.56 10.12 9.80 10.12 77 SC17 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

SC18 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC19 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC20 0.00 0.00 0.00 0.00 0.12 0.12 0.12 0.12 0.12 0.00 0.00 0.00 1 SC21 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC22 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC23 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC24 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC25 0.00 0.00 0.00 0.00 1.70 1.65 1.70 1.70 1.65 0.00 0.00 0.00 8 SC26 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC27 1.09 0.99 1.09 1.06 1.46 1.42 1.46 1.46 1.42 1.09 1.06 1.09 15 SC28 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC29 5.63 5.09 5.63 5.45 6.31 6.11 6.31 6.31 6.11 5.63 5.45 5.63 70 SC30 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC31 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC32 0.85 0.76 0.85 0.82 0.85 0.82 0.85 0.85 0.82 0.85 0.82 0.85 10 SC33 110.58 99.88 110.58 107.01 110.58 107.01 110.58 110.58 107.01 110.58 107.01 110.58 1,302 Total 1,051 949 1,051 1,017 587 568 587 587 568 1,051 1,017 1,051 10,080 Low Priority Entitlements SC1 217.99 201.41 222.99 197.26 46.91 45.40 46.91 46.91 49.12 50.76 47.81 216.62 1,390 SC2 8.65 7.82 8.65 8.38 22.14 21.43 22.14 22.14 21.43 22.14 21.43 8.65 195 SC3 0.09 0.08 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 0.09 1 SC4 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC5 0.00 0.00 0.00 0.00 10.92 10.57 10.92 10.92 10.57 10.92 10.57 0.00 75 SC6 1.85 1.67 1.85 1.79 47.97 46.43 47.97 47.97 46.43 47.97 37.46 1.85 331 SC7 5.54 5.01 5.54 5.36 15.79 15.28 15.79 15.79 15.28 15.79 15.28 5.54 136 SC8 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC9 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC10 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC11 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC12 23.83 23.03 25.50 23.44 15.04 14.55 15.04 15.04 14.55 15.04 14.55 20.96 221 SC13 0.00 0.00 0.00 0.00 12.24 11.85 12.24 12.24 11.85 12.24 11.85 0.00 85 SC14 2.31 2.09 2.31 2.24 11.80 11.42 11.80 11.80 11.42 11.80 11.42 2.31 93 SC15 23.84 21.54 13.95 13.19 2.90 2.80 2.90 2.90 6.52 6.74 7.48 23.84 129 SC16 4.25 3.84 4.25 4.11 12.59 12.19 12.59 12.59 12.19 12.59 11.86 4.25 107 SC17 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC18 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC19 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC20 2.72 2.45 2.72 2.63 3.22 3.12 3.22 3.22 3.12 3.22 3.12 2.72 36 SC21 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC22 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC23 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC24 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC25 154.72 139.75 154.72 125.89 66.37 64.23 66.37 66.37 64.23 66.37 88.07 154.72 1,212 SC26 4.62 4.17 4.62 4.47 0.00 0.00 0.00 0.00 0.00 0.00 0.00 4.62 23 SC27 1.85 1.67 1.85 1.79 2.33 2.26 2.33 2.33 2.26 2.33 2.26 1.85 25 SC28 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC29 5.54 5.01 5.54 5.36 14.41 13.94 14.41 14.41 13.94 14.41 11.99 5.54 125 SC30 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC31 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC32 6.47 5.84 6.47 6.26 13.12 12.70 13.12 13.12 12.70 13.12 12.70 6.47 122 SC33 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - Total 464 425 461 402 298 288 298 298 296 306 308 460 4,304

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

All Entitlements 1087.6 SC1 2 986.89 1092.62 1038.84 462.32 447.41 462.32 462.32 451.13 920.39 889.39 1086.25 9,388 SC2 35.28 31.87 35.28 34.14 50.19 48.58 50.19 50.19 48.58 48.77 47.19 35.28 516 SC3 0.42 0.38 0.42 0.40 0.54 0.52 0.54 0.54 0.52 0.42 0.40 0.42 6 SC4 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC5 0.00 0.00 0.00 0.00 11.29 10.93 11.29 11.29 10.93 10.92 10.57 0.00 77 SC6 17.52 15.82 17.52 16.95 51.38 49.72 51.38 51.38 49.72 63.64 52.62 17.52 455 SC7 5.54 5.01 5.54 5.36 16.29 15.76 16.29 16.29 15.76 15.79 15.28 5.54 138 SC8 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC9 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC10 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC11 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC12 33.47 31.74 35.14 32.77 25.92 25.09 25.92 25.92 25.09 24.68 23.88 30.60 340 SC13 0.00 0.00 0.00 0.00 12.24 11.85 12.24 12.24 11.85 12.24 11.85 0.00 85 SC14 2.31 2.09 2.31 2.24 12.93 12.52 12.93 12.93 12.52 11.80 11.42 2.31 98 SC15 24.23 21.88 14.34 13.56 6.75 6.54 6.75 6.75 10.26 7.19 7.92 24.23 150 SC16 14.37 12.98 14.37 13.91 14.21 13.75 14.21 14.21 13.75 22.71 21.66 14.37 185 SC17 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC18 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC19 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC20 2.72 2.45 2.72 2.63 3.35 3.24 3.35 3.35 3.24 3.22 3.12 2.72 36 SC21 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC22 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC23 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC24 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC25 154.72 139.75 154.72 125.89 68.07 65.88 68.07 68.07 65.88 66.37 88.07 154.72 1,220 SC26 4.62 4.17 4.62 4.47 0.00 0.00 0.00 0.00 0.00 0.00 0.00 4.62 23 SC27 2.94 2.65 2.94 2.84 3.80 3.67 3.80 3.80 3.67 3.42 3.31 2.94 40 SC28 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC29 11.17 10.09 11.17 10.81 20.72 20.05 20.72 20.72 20.05 20.04 17.44 11.17 194 SC30 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC31 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 - SC32 7.31 6.60 7.31 7.08 13.97 13.52 13.97 13.97 13.52 13.97 13.52 7.31 132 SC33 110.58 99.88 110.58 107.01 110.58 107.01 110.58 110.58 107.01 110.58 107.01 110.58 1,302 Total 1,515 1,374 1,512 1,419 885 856 885 885 863 1,356 1,325 1,511 14,384

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

400000 405000 410000 415000 420000 425000 430000 435000 440000 445000 450000

!( !( !(!(!( !( !(!(!(!( !( 16!(!(!( !(!( !( !( !( !( 5440000 15!( !( !(!(!( 5440000 !( !(!(!( !( 14 !( !( 13 !( !( !(!( !( !( !(!( !( !(!( !(!(!(!( !(!(!( !( !(!(!( !( !(1 !( !( !(!(!(!( !(!(!( !(!( !( !( 5435000 !(!(!( 5435000 !(!( !(!(!(25 !(!(!(!( !( !(!( !(!(!(!(!( !( !(!( !(!(!(!( !( !( !( !(!(!(!( !( !(!( !(!( 33 !(

5430000 !( 5430000 !( !( !( 32 !( !( !( !(!( !(!(6 !( !(!( !( 5 !( !(!( !(

5425000 !(!( 5425000 !( 29 !(!( !( !( !( !( !( !(!( !(!(!(!(!( 7 !( !( !(!( !( !( !( !( !( !( !( !( !(!( !( !( !( !( !( !( !(!(!( !( !( !( !(!(!( 5420000 !( !( !( !(!( 5420000 !( !( !(!(!( !( !(12 !(!(!( !( !( 27 !( !( !(!( !( !( !( !( !( !( 26 !( !( !( !( !( 8 !(!( 5415000 5415000 2 !( 5410000 5410000

22 4 9 11 5405000 28 5405000 23 !( 24 !( !( 5400000 5400000 30 3 !(

!( !( 5395000 5395000 20 31 21 5390000 5390000

5385000 18 5385000 5380000 5380000 10

5375000 Legend - 5375000 Sub-catchment boundary 5370000 5370000 19 !( Water Allocations

01.5 3 6 9 12 Kilometers 5365000 5365000 400000 405000 410000 415000 420000 425000 430000 435000 440000 445000 450000

Figure 3-3 Water allocations

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

3.7 Estimation of unlicensed dams Under current Tasmanian law, a dam permit is not required for a dam if it is not on a watercourse and holds less than 1ML of water storages (prior to 2000 it was 2.5 ML), and only used for stock and domestic purposes. Therefore there are no records for these storages. The storage volume attributed to unlicensed dams was estimated by analysis of aerial photographs and the methodology adopted follows:

• Aerial photographs were analysed. There was reasonable coverage of this catchment with high resolution photography. GoogleEarth had the best photographs, which covered the majority of areas of interest. The dates of these maps varied between 2002 and 2007. The number of dams, of any size, in eight selected sub-catchments was counted by eye and a ratio of unlicensed to licensed dams was calculated for each sub-catchment. Generally there were a low number of unlicensed dams identified during the physical count;

• Using this information, an average ratio of unlicensed to licensed dams was determined to be 0.2. Therefore it is estimated that on average, for every five licensed dam there is one unlicensed dam. This is in the lower range of what has been determined in other catchments along the North West coast, with the Duck ratio being 0.23, Leven & Gawler 0.49 and Panatana 0.41. The ratio of unlicensed to licensed dams was used as an estimation tool to determine the number of unlicensed dams in each uncounted sub- catchment. In total it is estimated that the catchment contains 59 unlicensed dams;

• It was assumed most of these dams would be legally unlicensed dams (less than 1 ML and not situated on a water course) however, it was assumed that there would be a proportion of illegal unlicensed dams up to 20ML in capacity. Some of these were visible on the aerial photographs;

• A frequency distribution of farm dam sizes presented by Neal et al (2002) for the Marne River Catchment in South Australia showed that the average dam capacity for dams less than 20 ML was 1.4 ML (Table 3.6);

• Following discussions with DPIW staff, the unlicensed dam demand was assumed to be 100%. The assumption is that all unlicensed dams will be empty at the start of May and will fill over the winter months, reaching 100% capacity by the end of September;

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

• Assuming this dam size distribution is similar to the distribution of the study catchment in South Australia, and then the total volume of unlicensed dams can be estimated as 82.6 ML (59 * 1.4ML). The total volume of existing permitted dams extractions in the study catchment is 2080.7 ML. Therefore the 82.6 ML of unlicensed dams equates to approximately 3.8% of the total dam extractions from the catchment.

There are some inherent difficulties in detecting farm dams from aerial photography by eye. Depending on the season and time of day that the aerial photograph is taken, farm dams can appear clearly or blend into the surrounding landscape. Vegetation can obscure the presence of a dam, and isolated stands of vegetation can appear as a farm dam when in fact no such dam exists. On balance, however, the number of false detections is countered by the number of missed detections and in the absence of another suitably rapid method the approach gives acceptable results.

Table 3.6 Average capacity for dams less than 20 ML by Neal et al (2002)

Average Total Size Range Volume Number of Volume (ML) (ML) Dams (ML) 0 - 0.5 0.25 126 31.5 0.5 - 2 1.25 79 98.75 2 - 5 3.5 13 45.5 5 - 10 7.5 7 52.5 10 - 20 15 6 90 27.5 231 318.25 Average Dam Volume: 1.4 ML

3.8 Environmental flows One of the modelling scenarios (Scenario 3) was to account for environmental flows within the catchment. DPIW advised, that for the Forth River catchment, they currently do not have environmental flow requirements defined. In the absence of this information it was agreed that the calibrated catchment model would be run in the Modelled – No entitlements (Natural) scenario and the environmental flow would be assumed to be:

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

• The 20 th percentile for each sub-catchment during the winter period (01May to 31 st Oct).

• The 30 th percentile for each sub-catchment during the summer period (01 Nov – 30 April).

The Modelled – No entitlements (Natural) flow scenario was run from 01/01/1900 to 01/01/2007.

A summary table of the environmental flows on a monthly breakdown by sub-catchment is provided below in Table 3.5 and in the Catchment User Interface.

Table 3.7 Environmental Flows

Sub - Catch Environmental Flow (ML/d) Per Month at each sub-Catchment ment Area (km2) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Average SC1 12.5 703.4 413.0 364.3 1179.8 2150.6 3124.0 3867.3 4422.8 3807.6 2198.1 1809.3 1431.3 2122.6 SC2 89.2 502.4 278.9 271.8 918.3 1495.6 2135.4 2669.1 2994.5 2590.6 1662.8 1253.9 969.3 1478.5 SC3 111.1 460.7 245.8 259.2 823.0 1347.2 1881.8 2239.1 2602.2 2280.9 1522.5 1168.5 898.8 1310.8 SC4 8.3 149.7 77.0 72.4 275.7 452.4 602.6 745.7 826.3 711.4 421.0 382.6 285.9 416.9 SC5 36.3 516.6 284.3 271.1 892.7 1525.2 2179.0 2685.5 3136.0 2697.5 1682.5 1280.3 1002.9 1512.8 SC6 7.4 0.8 0.6 0.5 1.0 1.7 5.9 11.5 14.5 10.0 3.2 2.1 1.9 4.5 SC7 21.3 9.3 6.8 5.4 13.9 35.1 70.7 97.7 124.9 82.4 40.9 27.2 25.0 44.9 SC8 42.3 165.5 90.0 80.5 301.5 492.6 714.8 900.8 976.2 847.0 482.5 424.5 323.0 483.2 SC9 47.5 65.9 31.2 31.6 121.7 198.8 248.7 307.2 337.5 298.7 190.8 162.4 118.0 176.0 SC10 96.2 137.8 74.1 73.7 277.0 407.9 560.7 630.9 755.4 661.4 478.8 356.8 279.8 391.2 SC11 10.8 2.1 1.5 1.1 2.8 6.8 19.1 28.6 33.5 22.4 10.1 6.7 5.0 11.6 SC12 16.0 6.7 4.7 3.8 9.1 24.5 51.8 78.2 98.5 62.2 29.7 19.5 17.5 33.8 SC13 1.1 0.1 0.1 0.1 0.1 0.2 0.5 1.2 1.6 1.1 0.4 0.2 0.2 0.5 SC14 2.7 0.3 0.2 0.2 0.3 0.4 1.2 2.9 3.9 2.6 1.0 0.6 0.6 1.2 SC15 3.3 0.3 0.3 0.2 0.4 0.5 1.6 3.7 4.9 3.2 1.2 0.8 0.7 1.5 SC16 2.2 0.2 0.2 0.1 0.3 0.3 1.1 2.5 3.3 2.2 0.8 0.5 0.5 1.0 SC17 60.2 40.6 21.9 21.9 75.1 137.7 191.6 230.7 260.5 228.9 155.6 114.3 88.4 130.6 SC18 80.8 168.4 92.9 93.1 320.3 498.7 742.6 862.0 1013.2 891.5 594.6 450.1 357.8 507.1 SC19 64.2 56.1 30.4 30.2 118.6 167.5 224.8 253.9 298.9 262.4 201.2 146.8 115.3 158.8 SC20 124.9 164.9 78.9 90.9 280.8 440.5 533.0 625.9 687.0 645.3 456.9 386.4 286.9 389.8 SC21 49.3 36.1 18.2 17.4 67.4 125.6 165.7 197.2 219.1 197.9 131.6 99.1 74.6 112.5 SC22 18.9 75.6 39.0 35.5 141.0 233.8 308.3 381.0 422.5 363.6 217.5 196.8 144.5 213.3 SC23 36.2 71.1 35.0 35.1 127.7 210.9 274.2 334.3 372.2 324.1 196.8 174.1 129.3 190.4 SC24 16.8 6.5 3.3 2.7 9.0 24.0 42.0 57.7 63.5 51.5 24.8 18.0 13.7 26.4 SC25 18.4 696.2 409.4 360.1 1176.7 2149.9 3106.0 3847.6 4399.9 3785.2 2192.6 1804.9 1415.9 2112.0 SC26 14.8 3.7 2.5 2.0 5.1 14.8 29.6 41.1 51.0 33.8 16.6 11.1 9.8 18.4 SC27 13.8 4.1 2.8 2.2 5.9 15.5 30.6 41.9 51.4 34.6 18.1 12.5 10.3 19.2 SC28 14.9 18.9 8.2 9.6 32.6 51.7 63.2 77.6 85.9 76.0 50.9 43.2 31.5 45.8 SC29 27.3 189.3 106.4 89.7 319.9 530.9 835.8 1089.2 1170.0 993.8 540.4 456.5 368.0 557.5 SC30 35.3 48.4 21.4 26.4 81.4 129.7 154.2 189.9 210.6 187.9 124.9 108.6 78.4 113.5 SC31 8.8 213.2 118.8 121.8 403.1 644.0 959.5 1104.9 1298.3 1135.8 755.2 578.8 452.0 648.8 SC32 23.0 192.7 110.5 92.9 319.3 531.9 873.9 1101.8 1228.6 1045.8 556.0 470.8 379.9 575.4 SC33 3.8 687.6 403.5 353.7 1188.3 2145.4 3071.9 3795.5 4344.4 3736.5 2181.2 1796.0 1388.8 2091.1

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

4. MODEL DEVELOPMENT

4.1 Sub-catchment delineation Sub-catchment delineation was performed using CatchmentSIM GIS software.

CatchmentSIM is a freely available 3D-GIS topographic parameterisation and hydrologic analysis model. The model automatically delineates watershed and sub-catchment boundaries, generalises geophysical parameters and provides in-depth analysis tools to examine and compare the hydrologic properties of sub-catchments. The model also includes a flexible result export macro language to allow users to fully couple CatchmentSIM with any hydrologic modelling package that is based on sub-catchment networks.

For the purpose of this project, CatchmentSIM was used to delineate the catchment, break it up into numerous sub-catchments, determine their areas and provide routing lengths between them.

These outputs were manually checked to ensure they accurately represented the catchment. Any minor modifications were made manually to the resulting model.

For more detailed information on CatchmentSIM see the CatchmentSIM Homepage www.toolkit.net.au/catchsim/

4.2 Hydstra Model A computer simulation model was developed using Hydstra Modelling. The sub- catchments, described in Figure 2-1, were represented by model “nodes” and connected together by “links”. A schematic of this model is displayed in Figure 4-1. The flow is routed between each sub-catchment, through the catchment via a channel routing function.

The rainfall and evaporation is calculated for each sub-catchment using inverse- distance gauge weighting. The gauge weights were automatically calculated at the start of each model run. The weighting is computed for the centroid of the sub- catchment. A quadrant system is drawn, centred on the centroid. A weight for the closest gauge in each quadrant is computed as the inverse, squared, distance between the gauge and centroid. For each time step and each node, the gauge weights are applied to the incoming rainfall and evaporation data.

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

The AWBM Two Tap rainfall/runoff model was used to calculate the runoff for each sub- catchment separately. This was chosen over the usual method of a single AWBM model for the whole catchment as it allows better simulation of base flow recessions.

The flow is routed between each sub-catchment, through the catchment via a channel routing function.

Figure 4-1 Hydstra Model schematic

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

4.2.1 Hydro Tasmania Lakes Several major lakes were identified during the creation of the Forth River catchment model. These dams are owned by Hydro Tasmania and have a major influence on the flow regime in the Forth River as water is released from the associated power stations for electricity generation or when the dam spills. The lakes and construction dates are as follows:

• Lake Gairdner, construction completed in 1970. Wilmot Power Station commenced Oct 1970; however this does not discharge directly downstream. Refer to Section 4.2.2;

• Lake Cethana, construction completed in 1971. Cethana Power Station commenced May 1971, which discharges directly downstream;

• Lake Barrington, construction completed in 1969. Devils Gate Power Station commenced Sept 1969, which discharges directly downstream;

• Lake Paloona, construction completed in 1971. Paloona Gate Power Station commenced Dec 1971, which discharges directly downstream.

Custom code was entered into the outflow node of the relevant sub-catchments. The basic rules associated with this code are:

• Scenario 1, “No Entitlements (Defines ‘Natural’ Flows)” will model the catchment with no dam or lake present for all of record.

• Both the Scenario 2 “ with Entitlements (extraction not limited by Env.Flows)” and Scenario 3, “ Environmental Flows & Entitlements (‘Low Priority Ents. Limited by Env Flows’)” scenarios will model the catchment with:

o No dam or lake present in the model prior to its construction completion date;

o All years following the completion date, flows downstream of the dam will be a total of the average long term monthly values which will include spill, power station discharge (if applicable) and any known environmental release.

Calculation of Lake Paloona, Lake Barrington & Lake Cethana long term discharge values was problematic due to the limited amount and accuracy of data. Initially it was intended to estimate discharge based on the power station generation data and an

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

average power to flow conversion factor. However, assessment of flow data derived from this data showed inconsistencies between lakes expected due to average mega- watt to flow relationships used to derive flow data from power station MW. The final discharge estimates were based on flow measured at the gauging sites, Forth below Wilmot (site 665) and Wilmot above Forth (site 524). Using this data the Paloona Dam discharge was derived. Lake Barrington and then Lake Cethana discharge was estimated by subtracting proportional amounts of natural inflow which was derived using the Forth catchment model. The adopted monthly values, based on the last 10 years (01/04/1997 to 01/04/2007), are shown in Table 4.1.

Table 4.1 Hydro Tasmania Lakes - assumed downstream flow

Lake Lake Lake Lake

Gairdner Cethana Barrington Paloona Discharge Disch arge Discharge Discharge Month (ML/day) (ML/day) (ML/day) (ML/day) January 19 1835 1915 1930 February 4 1780 1825 1835 March 3 1325 1370 1380 April 32 2670 2735 2745 May 82 4760 4900 4915 June 94 6670 7005 7070 July 185 7610 8045 8130 August 164 8390 8875 8980 September 202 8100 8565 8670 October 75 6630 6890 6945 November 6 4385 4575 4620 December 10 2720 2805 2825

4.2.2 Lemonthyme Power Station and Wilmot Power Stations Two Hydro Tasmania power stations were identified in this model that transfer water between catchments as a result of the associated power generation activities.

• Wilmot Power Station which transfers water from Lake Gairdner (Wilmot River) to Lake Cethana (Forth River). This station commenced operation in October 1970.

• Lemonthyme Power Station which transfers water from Lake Parangana (Mersey River) to Lake Cethana (Forth River). This station commenced operation in May 1969.

Custom code was entered into the model at the relevant sub-catchments to account for this water transfer. The basic rules associated with this code are:

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

• Scenario 1, “No Entitlements (Defines ‘Natural’ Flows)” will model the catchment with no power station present for all of record and accordingly no water transfer.

• Both Scenario 2 “ with Entitlements (extraction not limited by Env.Flows)” and Scenario 3, “ Environmental Flows & Entitlements (‘Low Priority Ents. Limited by Env Flows’)” will model the catchment with:

o No power station or diversion present in the model prior to its construction completion date.

o All years following the power station completion date, diverted flows will be the average long term monthly values given in Table 4.2. These values are based on record from the last 10 years (01/04/1997 to 01/04/2007).

Table 4.2 Power Station inter-catchment transfer

Wilmot Power Lemonthyme

Station Power Station Month Flow (ML/day) Flow (ML/day) January 171 892 February 147 872 March 113 544 April 279 914 May 655 1699 June 953 2637 July 931 3014 August 1034 3021 September 887 3116 October 691 2927 November 397 2275 December 237 1317

4.3 AWBM Model The AWBM Two Tap model is a relatively simple water balance model with the following characteristics:

• it has few parameters to fit,

• the model representation is easily understood in terms of the actual outflow hydrograph,

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• the parameters of the model can largely be determined by analysis of the outflow hydrograph,

• the model accounts for partial area rainfall-run-off effects,

• runoff volume is relatively insensitive to the model parameters.

For these reasons parameters can more easily be transferred to ungauged catchments.

The AWBM routine used in this study is the Boughton Revised AWBM model (Boughton, 2003), which reduces the three partial areas and three surface storage capacities to relationships based on an average surface storage capacity.

Boughton & Chiew (2003) have shown that when using the AWBM model, the total amount of runoff is mainly affected by the average surface storage capacity and much less by how that average is spread among the three surface capacities and their partial areas. Given an average surface storage capacity (Ave), the three partial areas and the three surface storage capacities are found by;

Partial area of S1 A1=0.134

Partial area of S2 A2=0.433

Partial area of S3 A3=0.433

Capacity of S1 C1=(0.01*Ave/A 1)=0.075*Ave

Capacity of S2 C2=(0.33*Ave/ A 2)=0.762*Ave

Capacity of S3 C3=(0.66*Ave/ A 3)=1.524*Ave

The AWBM routine produces two outputs; direct run-off and base-flow. Direct run-off is produced after the content of any of the soil stores is exceeded; it can be applied to the stream network directly or by catchment routing across each subcatchment. Base-flow is usually supplied unrouted directly to the stream network, at a rate proportional to the water depth in the ground water store. The ground water store is recharged from a proportion of excess rainfall from the three surface soil storages.

Whilst the AWBM methodology incorporates an account of base-flow, it is not intended that the baseflow prediction from the AWBM model be adopted as an accurate estimate

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of the baseflow contribution. The base flow in the AWBM routine is based on a simple model and does not specifically account for things such as geology and inter-catchment ground water transfers. During the model calibration the baseflow infiltration and recession parameters are used to ensure a reasonable fit with the observed surface water information.

The AWBM processes are shown below in Figure 4-2.

Figure 4-2 Australian Water Balance Model schematic

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4.3.1 Channel Routing A common method employed in nonlinear routing models is a power function storage relation.

S = K.Q n

K is a dimensional empirical coefficient, the reach lag (time). In the case of Hydstra/TSM Modelling:

and

Li = Channel length (km)

α = Channel Lag Parameter

n = Non-linearity Parameter

Q = Outflow from Channel Reach (ML/day)

α A reach length factor may be used in the declaration of to account for varying reach lag α for individual channel reaches. eg. .fl where fl is a length factor.

Parameters required by Hydstra/TSM Modelling and their legal bounds are:

α Channel Lag Parameter Between 0.0 and 5.0

L Channel Length (km) Greater than 0.0 (km)

n Non-linearity Parameter Between 0.0 and 1.0

4.4 Model Calibration Calibration was achieved by adjusting catchment parameters so that the modelled data best replicates the record at the site selected for calibration (for information on this site, refer to Section 3.5). The best fit of parameters was achieved by comparing the monthly, seasonal and annual volumes over the entire calibration period, using regression statistics and using practitioner judgment when observing daily and monthly time series comparisons. It should be noted that during the calibration process matching of average

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long term monthly volumes (flows) was given the highest priority and matching of peak flood events and daily flows was given lower priority. Further discussion of the model calibration fit is given in 4.4.2.

The calibration process can best be understood as attempting to match the modelled calibration flow (MCF) to the observed flow record. The MCF can be described as:

MCF = MNEM - (WE x TPRF)

Where: MCF = Modeled Calibration Flow MNEM = Modeled - No Entitlements (Modified). *

WE = Water Entitlements TPRF = Time Period Reduction Factor

* Refer to Glossary for additional explanation of these terms

In the Forth River catchment, data from the period 04/06/1961 to 01/03/1969 was selected at Forth River at Paloona Bridge (site 386) for calibration.

Water entitlements were included in the calibration model and adjusted to the time period of calibration by applying a Time Period Reduction Factor (TPRF). The TPRF was calculated by a method developed in the Tasmanian State of the Environment report (1996). This states that water demand has increased by an average of 6% annually over the last 4 decades. However, following discussions with DPIW the TPRF was capped at 50% of the current extractions if the mid year of the calibration period was earlier than 1994. In the Forth River catchment, data from the period 04/06/1961 to 01/03/1969 was selected at Forth River at Paloona Bridge (site 386) for calibration. Accordingly a TPRF of 50% was applied to all extractions as the mid year of the calibration period was deemed to be 1965 which is prior to the 50% capped date of 1994. In the case of the Forth River the water entitlement extractions at the calibration site are insignificant in relation to the observed flow (approx 0.1%), and accordingly the model calibration would be unchanged regardless of the TPRF applied.

The model was calibrated to the observed flow as stated in the formula MCF = MNEM - (WE x TPRF). Other options of calibration were considered, including adding the water entitlements to the observed flow. However, the chosen method is considered to be the better option as it preserves the observed flow and unknown quantities are not added to the observed record. The chosen method also preserves the low flow end of the calibration, as it does not assume that all water entitlements can be met at any time.

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The model assumes that water entitlements are extracted at a constant daily flow for each month. For each daily time step of the model if water entitlements cannot be met, the modelled outflows are restricted to a minimum value of zero and the remaining water required to meet the entitlement is lost. Therefore the MCF takes account of very low flow periods where the water entitlements demand can not be met by the flow in the catchment. Table 4.4 shows the monthly water entitlements (demand) used in the model calibration upstream of the calibration site.

The adopted calibrated model parameters are shown in Table 4.3. These calibration parameters are adopted for all three scenarios in the user interface. Although it is acknowledged that some catchment characteristics such as land use and vegetation will have changed over time, it is assumed that the rainfall run-off response defined by these calibration parameters has not changed significantly over time and therefore it is appropriate to apply these parameters to all three scenarios.

To achieve a better fit of seasonal volumes, the normally constant store parameter CapAve has been made variable and assigned a seasonal profile. In order to avoid rapid changes in catchment characteristics between months, CapAves of consecutive months were smoothed. A CapAve of a given month was assumed to occur on the middle day of that month. It was assumed that daily CapAves occurring between consecutive monthly CapAves would fit to a straight line, and a CapAve for each day was calculated on this basis. The annual profile of CapAves for the catchment is shown in Figure 4-3.

Table 4.3 Adopted Calibration Parameters

PARAMETER VALUE INFBase 0.4 K1 0.96 K2 0.95 GWstoreSat 70 GWstoreMax 100 H_GW 90 EvapScaleF 1 Alpha 2.2 n 0.8 CapAve Variable

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80 70 CapeAve 60 50 40

CapAve 30 20 10 0 1 2 3 4 5 6 7 8 9101112 MONTH

Figure 4-3 Monthly Variation of CapAve Parameter

Results of the calibration are shown in the plots and tables that follow in this section. In all comparisons the “Modelled Calibration Flow” (refer to previous description) has been compared against the observed flow at the calibration location.

Daily time series plots of three discrete calendar years (Figure 4-4 to Figure 4-6) have been displayed for the calibration location, showing a range of relatively low to high inflow years and a range of calibration fits. The general fit for each annual plot is described in the caption text. This indication is a visual judgement of the relative model performance for that given year compared to the entire observed record. There is also a goodness of fit statistic (R2) shown on each plot to assist in the judgement of the model performance.

The catchment average precipitation as input to the model is also displayed to provide a representation of the relative size of precipitation events through the year. Note that the precipitation trace is plotted on an offset, secondary scale.

The monthly time series, over the whole period of observed record, are plotted in Figure 4-7 and overall shows a good comparison between Modelled Calibration Flow and observed totals at the calibration location.

The monthly, seasonal and annual volume balances for the whole period of calibration record are presented in Figure 4-8 and Table 4.4. The demand values shown represent the adopted total water entitlements upstream of the calibration location, which in this case is small and accordingly have been multiplied by 100 for plotting

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purposes. The demand has been included to provide a general indication of the relative amount of water being extracted from the river.

Precipitation Modelled Calibration Flow Observed 50000 70.0 R 2 = 0.88 45000 50.0 40000 30.0 35000 10.0 30000

25000 -10.0

20000 -30.0 15000 -50.0 10000 -70.0 5000

0 -90.0 01/1962 04/1962 07/1962 10/1962 01/1963

Figure 4-4 Daily time series (ML/d) – Forth River - Good fit.

Precipitation Modelled Calibration Flow Observed 45000 50.0 R 2 = 0.87 40000 30.0

35000 10.0 30000

25000 -10.0

20000 -30.0

15000 -50.0 10000 -70.0 5000

0 -90.0 01/1964 04/1964 07/1964 10/1964 01/1965

Figure 4-5 Daily time series comparison (ML/d) – Forth River – Good fit.

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Precipitation Modelled Calibration Flow Observed 30000 50.0 R 2 = 0.89 30.0 25000

10.0 20000

-10.0 15000 -30.0

10000 -50.0

5000 -70.0

0 -90.0 01/1966 04/1966 07/1966 10/1966 01/1967

Figure 4-6 Daily time series comparison (ML/d) – Forth River – Good fit.

450000 Observed - Forth Rv - Site 386 Modelled Calibration Flow R 2 = 0.87 400000

350000

300000

250000

200000

150000 MonthlyVolume (ML) 100000

50000

0 1961 1962 1963 1964 1965 1966 1967 1968 1969

Figure 4-7 Monthly time series comparison – volume (ML)

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8000 Observed

Modelled Calibration Flow 7000 Modelled - No Entitlements (Natural) 6000 Demand x 100

5000

4000

3000 Average Flow (ML/Day) Flow Average 2000

1000

0 Jul Jan Jun Apr Oct Nov Feb Mar Sep Dec Aug May WINTER ANNUAL SUMMER Figure 4-8 Long term average monthly, seasonal and annual comparison plot

Modelled- Scenario 1 MONTH Observed Calibration “Modelled -- Demand 2 1 No Entitlements Flow (MCF) (Natural)” January 894.33 976.25 979.64 3.74 February 1157.94 1181.45 1184.93 3.76 March 995.02 991.76 995.25 3.76 April 2117.38 2138.12 2141.57 3.74 May 4198.86 4228.35 4232.48 4.97 June 5453.76 5287.52 5279.19 4.97 July 6248.40 6340.89 6340.77 4.97 August 7285.85 7311.60 7314.72 4.97 September 5792.77 5820.06 5823.92 4.97 October 3751.63 3580.45 3584.43 5.09 November 3089.51 3067.90 3071.94 4.91 December 1752.21 1754.33 1757.73 3.69 WINTER 5455.21 5428.15 5429.25 4.99 SUMMER 1667.73 1684.97 1688.51 3.93 ANNUAL 3561.47 3556.56 3558.88 4.46 WINTER from May to Oct, SUMMER from Nov - Apr. Table 4.4 Long term average monthly, seasonal and annual comparisons

1 Refer to page 25 for explanation of this modelling scenario. 2 The demand value includes all extractions upstream of calibration site with a 50% time period reduction factor applied.

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4.4.1 Factors affecting the reliability of the model calibration.

Regardless of the effort undertaken to prepare and calibrate a model, there are always factors which will limit the accuracy of the output. In preparation of the Forth River model the most significant limitations identified, that will affect the calibration accuracy are:

• The assumption that water entitlements are taken as a constant rate for each month. Historically the actual extraction from the river would be much more variable than this and possess too many levels of complexity to be accurately represented in a model;

• The current quantity of water extracted from the catchment is unknown. Although DPIW have provided water licence information (WIMS Dec 2006) and estimates of extractions in excess of these licences, these may not represent the true quantity of water extracted. No comprehensive continuous water use data is currently available;

• The quality of the observed flow data (ratings and water level readings) used in the calibration may not be reliable for all periods. Even for sites where reliable data and ratings has been established the actual flow may still be significantly different to the observed (recorded) data, due to the inherent difficulties in recording accurate height data and rating it to flow. These errors typically increase in periods of low and high flows;

• Misrepresentation of the catchment precipitation. This is due to insufficient rainfall gauge information in and around the catchment. Despite the Data DRILL’s good coverage of grid locations, the development of this grid information would still rely considerably on the availability of measured rainfall information in the region. This would also be the case with the evaporation data, which will have a smaller impact on the calibration;

• Catchment freezing and snowmelt in the upper catchment, during the winter months, may affect the flow regime and this has not been specifically handled within this model;

• The daily average timestep of the model may smooth out rainfall temporal patterns and have an effect on the peak flows. For example, intense rainfall events falling in a few hours will be represented as a daily average rainfall, accordingly reducing the peak flow;

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• The model does not explicitly account for changes in vegetation and terrain within individual sub-cathments. Effects due to vegetation and terrain are accounted for on catchment average basis, using the global AWBM fit parameters. Therefore individual sub-catchment run-off may not be accurately represented by the model’s global fit parameters. To account for this a much more detailed and complex model would be required.

4.4.2 Model Accuracy - Model Fit Statistics The following section is an additional assessment of how reliably the model predicts flow at the calibration site.

One of the most common measures of comparison between two sets of data is the coefficient of determination (R 2). If two data sets are defined as x and y, R 2 is the variance in y attributable to the variance in x. A high R 2 value indicates that x and y vary together – that is, the two data sets have a good correlation. In this case x and y are observed flow and modelled calibration flow. So for the catchment model, R 2 indicates how much the modelled calibration flow changes as observed flow changes. Table 4.5 shows the R 2 values between observed and modelled daily and monthly flows, as well as the proportional difference (%) between long-term (8 years) observed and modelled calibration flow.

Table 4.5 Model Fit Statistics

Measure of Fit Forth River at Paloona Bridge (Site 386) Daily coefficient of determination (R 2 Value) 0.86 Monthly coefficient of determination (R 2 Value) 0.97 Difference in observed and estimated long term -0.1% annual average flow

As previously mentioned the focus of the calibration process was to obtain a good correlation between monthly long term volumes (and flows) and lesser priority was given to daily correlations. However without a good simulation of daily flows, a good simulation of monthly flows would be difficult to achieve. A target R2 of 0.70 (or greater) was set for the daily flows and a target of R 2 of 0.85 (or greater) was set for monthly flows. It was deemed that these were acceptable targets considering the model limitations and potentials sources of error (refer to 4.4.1). A summary of

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comparative qualitative and statistical fit descriptions are provided in the following Table.

Table 4.6 R2 Fit Description

Qualitative Fit Description Daily R 2 Monthly R 2

Poor R2 < 0.65 R2 < 0.8

Fair 0.65 ≥ R 2 > 0.70 0.8 ≥ R 2 > 0.85

Good R2 ≥ 0.70 R2 ≥ 0.85

It should be noted that although the R2 value is a good indicator of correlation fit it was only used as a tool, to assist in visually fitting the hydrographs. One of the major limitations is that minor differences in the timing of hydrograph events can significantly affect the R2 value, although in practice a good calibration has been achieved.

Another indicator on the reliability of the calibration fit is the proportional difference between observed data and modelled data, measured by percent (%). The proportional difference for the daily flows and monthly volumes were calculated and are presented in Figure 4-9 and Figure 4-10 in the form of a duration curve. These graphs show the percentage of time that a value is less than a specified bound. For example in Figure 4-9, 40% of the time the difference between modelled and observed flow is less than 20%. Similarly in Figure 4-10, for the All of Record trace, 50% of the time the difference between modelled monthly volume and observed volume is less than 10%.

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All record Winter Summer 200 180 160 140 120 100 80

(%) - Observed vs Modelled vs (%) - Observed 60 40

Difference 20 0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percentage of time Difference is less than

Figure 4-9 Duration Curve – Daily flow percentage difference

100 All record Winter Summer 90 80 70 60 50 40

(%) - Observed vs Modelled vs Observed - (%) 30 20 10 Difference 0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percentage of time Difference is less than

Figure 4-10 Duration Curve – Monthly volume percentage difference

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Although these duration curves are an indicator of the reliability of the modelled data, they also have their limitations and should be used in conjunction with a visual assessment of the hydrograph fit in determining calibration reliability. One of the major limitations is that in periods of low flow, the percentage difference between observed and modelled can be large although the value is not significant. For example, a 1ML/day difference would show as a 200% difference if the observed flow was 0.5 ML/day. The duration curve graphs show three traces, the Summer 3, the Winter 4 and All of Record . The higher values, caused by the larger proportion of low flows, can be clearly seen in the Summer trace.

4.4.3 Model accuracy across the catchment The model has been calibrated to provide a good simulation for monthly and seasonal volumes at the calibration site. Calibration sites are typically selected low in the catchment to represent as much of the catchment as possible. How the reliability of this calibration translates to other specific locations within the catchment is difficult to accurately assess, however on average it would be expected that the model calibration would translate well to other locations within the catchment. The accuracy of the model in predicting monthly volumes at other locations has been analysed for five river catchments modelled as part of this project. The results of this assessment are summarised in Appendix A. These analyses suggest that on average the models predict volumes well across the catchment.

The fit of the hydrograph shape (daily flows) is expected to be more site specific and therefore it is predicted that the calibration fit of these will deteriorate as the catchment area decreases.

In the Forth catchment there are two gauging sites which can be used to assess the calibration fit at alternative locations. Plots of the monthly times series volumes and the corresponding R2 values are shown in Figure 4-11 and Figure 4-12. The results show that the correlation between modelled and observed volumes at these two sites compares favourably with that of the calibration site.

3 Summer period = Nov to April. 4 Winter period = May to Oct.

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Observed - Forth a/b Lemonthyme Site 450 Modelled with entitlements (extracted) 200000 R2 = 0.90 180000

160000

140000

120000

100000

80000

Monthly Volume (ML) Volume Monthly 60000

40000

20000

0 1963 1965 1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004

Figure 4-11 Time Series of Monthly Volumes- Site 450

18000 Observed - Iris River Site 815 R2 = 0.93 16000 Modelled - with entitlements (extracted)

14000

12000

10000

8000

6000 Monthly Volume (ML) 4000

2000

0 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

Figure 4-12 Time Series of Monthly Volumes- Site 815

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4.5 Model results The completed model and user interface allows data for three catchment demand scenarios to be generated;

• Scenario 1 – No entitlements (Natural Flow)

• Scenario 2 – with Entitlements (with water entitlements extracted)

• Scenario 3 - Environmental Flows and Entitlements (Water entitlements extracted, however low priority entitlements are limited by an environmental flow threshold).

For each of the three scenarios, daily flow sequence, daily flow duration curves, and indices of hydrological disturbance can be produced at any sub-catchment location.

For information on the use of the user interface refer to the Operating Manual for the NAP Region Hydrological Models (Hydro Tasmania 2004).

Outputs of daily flow duration curves and indices of hydrological disturbance at the model calibration sites are presented below and in the following section. The outputs are a comparison of scenario 1 (No entitlements - Natural) and scenario 3 (environmental flows and entitlements) for period 01/01/1900 to 01/01/2007. Results have been produced at the calibrations site, Forth River at Paloona Bridge, site 386. It should be noted that for this catchment the hydro generation activities influence these results as the flow regime changes significantly between scenarios 1 & 3, overwhelming any affects that extracting entitlements may have.

100000.00 Natural 10000.00 Entitlements Extracted

1000.00

100.00

Flow (ML/d) 10.00

1.00

0.10 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Percent Of Time Exceeded

Figure 4-13 Daily Duration Curve

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4.5.1 Indices of hydrological disturbance The calculation of the estimates of natural flows and current flows (farm dams and irrigation) were used to calculate indices of hydrological disturbance. These indices include:

• Index of Mean Annual Flow

• Index of Flow Duration Curve Difference

• Index of Seasonal Amplitude

• Index of Seasonal Periodicity

• Hydrological Disturbance Index

The indices were calculated using the formulas stated in the Natural Resource Management (NRM) Monitoring and Evaluation Framework developed by SKM for the Murray-Darling Basin (MDBC 08/04).

The following table shows the Hydrological Disturbance Indices at 3 locations within the catchment, comparing scenario 1 (No entitlements - Natural) and scenario 3 (environmental flows and entitlements) for period 01/01/1900 to 01/01/2007. Two sites in addition to the calibration site have been selected to give an indication of the variability of the indices of hydrological disturbance across the catchment.

Table 4.7 Hydrological Disturbance Indices

SubC 33 undisturbed SubC 1 SubC 30 Disturbance Indices (natural Forth River (Low in (High in flow) at Paloona catchment) catchment) Bridge Index of Mean Annual Flow, A 1.00 0.83 0.84 1.0 Index of Flow Duration Curve Difference, M 1.00 0.71 0.72 1.0 Index of Seasonal Amplitude, SA 1.00 0.84 0.86 1.0 Index of Seasonal Periodicity, SP 1.00 0.92 0.92 1.0 Hydrological Disturbance Index, HDI 1.0 0 0.81 0.82 1.0

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

Index of Mean Annual Flow: This provides a measure of the difference in total flow

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volume between current and natural conditions. It is calculated as the ratio of the current and natural mean annual flow volumes and assumes that increases and reductions in mean annual flow have equivalent impacts on habitat condition.

Index of Flow Duration Curve Difference: The difference from 1 of the proportional flow deviation. Annual flow duration curves are derived from monthly data, with the index being calculated over 100 percentile points. A measure of the overall difference between current and natural monthly flow duration curves. All flow diverted would give a score of 0.

Index of Seasonal Amplitude: This index compares the difference in magnitude between the yearly high and low flow events under current and natural conditions. It is defined as the average of two current to natural ratios. Firstly, that of the highest monthly flows, and secondly, that of the lowest monthly flows based on calendar month means.

Index of Seasonal Periodicity: This is a measure of the shift in the maximum flow month and the minimum flow month between natural and current conditions. The numerical value of the month with the highest mean monthly flow and the numerical value of the month with the lowest mean monthly flow are calculated for both current and natural conditions. Then the absolute difference between the maximum flow months and the minimum flow months are calculated. The sum of these two values is then divided by the number of months in a year to get a percentage of a year. This percentage is then subtracted from 1 to give a value range between 0 and 1. For example a shift of 12 months would have an index of zero, a shift of 6 months would have an index of 0.5 and no shift would have an index of 1.

4.6 Flood frequency analysis No flood frequency plot has been developed for this model as the river is highly regulated by the hydro – generation activities at the calibration site and in the lower catchment where the majority of water entitlements are located.

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5. REFERENCES

CatchmentSIM Homepage www.toolkit.net.au/catchsim/ , December 2006

QNRM Silo (Drill Data) Homepage www.nrm.qld.gov.au/silo , January 2005

SKM (2003) Estimating Available Water in Catchments in Catchments Using Sustainable Diversion Limits. Farm Dam Surface Area and Volume relationship, report to DSE, Draft B October 2003

Hydrology Theme Summary of Pilot Audit Technical Report – Sustainable Rivers Audit. MDBC Publication 08/04.

National Land and Water Resources Audit (NLWRA) www.audit.ea.gov.au/anra/water/ ; January 2005.

Hydro Tasmania internal report, (2004) South Esk River Catchment Above Macquarie River, Impact of Water Entitlements on Water and Hydro Power Yield.

Hydro Tasmania, (2005), NAP Region Hydrological Model, North Esk Catchment.

Neal B, Nathan RJ, Schreider S, & Jakeman AJ. 2002, Identifying the separate impact of farm dams and land use changes on catchment yield. Aust J of Water Resources, IEAust,; 5(2):165-176.

State of the Environment Report, Tasmania, Volume 1 Conditions & Trends 1996. State of Environment Unit, Lands Information Services, DELM.

SKM (2005) Development and Application of a Flow Stress Ranking Procedure, report to Department of Sustainability and Environment, Victoria.

Hydro Tasmania (2004). Operating Manual for the NAP region Hydrological Models. Hydro Report 118783 – Report -015, 17 September 2004.

5.1 Personal Communications Graham, B. Section Head, Ecohydrology, Water Assessment, DPIW. April-May 2007.

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6. GLOSSARY

Coefficient of determination (R 2): One of the most common measures of comparison between two sets of data is the coefficient of determination (R2). If two data sets are defined as x and y, R 2 is the variance in y attributable to the variance in x. A high R 2 value indicates that x and y vary together – that is, the two data sets have a good correlation

High priority entitlements: Water entitlements with an assigned Surety 1 to 3.

Low priority entitlements: Water entitlements with an assigned Surety 4 to 8.

Modelled – No entitlements (Natural) : The TimeStudio surface water model run in a natural state. That is, all references to water entitlements have been set to zero. Additionally any man made structures such as dams, power stations and diversions have been omitted and the modelled flow is routed, uncontrolled through the catchment. This is also referred to as Scenario 1.

Modelled – No entitlements (Modified) : The TimeStudio surface water model run with no water entitlements extracted. That is, all references to water entitlements have been set to zero. Where human structures are identified that significantly affect the flow regime, such as large dams, power stations and diversions, the TimeStudio model contains custom code to estimate the flow effect on the downstream subareas. This custom code takes effect from the completion date of the structure. Where there are no significant human structures in the catchment or the model is run before the completion of these structures this model will produce the same output as “Modelled – No entitlements (Natural)”. This option is not available within the user interface and is one of several inputs used to derive a modelled flow specifically for calibration purposes. It is also referred to as MNEM in Section 4.4.

Modelled – with entitlements (extracted): The TimeStudio surface water model with water entitlements removed from the catchment flow. Where human structures are identified within a catchment that significantly affect the flow regime, such as large dams, power stations and diversions, the TimeStudio model contains custom code to estimate the flow effect on the downstream sub-catchments. This custom code takes effect from the completion date of the structure. This is also referred to as Scenario 2.

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Modelled – environmental flows and entitlements (extracted ): The TimeStudiosurface water model with water entitlements removed. However, low priority entitlements are only removed when sub-catchment flow exceeds a specified environmental threshold. Where man made structures are identified within a catchment, such as dams, power stations and diversions the TimeStudio model contains code to estimate the flow effect on the downstream subcatchments, commencing on the completion date of the structure. This is also referred to as Scenario 3.

Time Period Reduction Factor (TPRF): A reduction factor applied to current levels of water extracted from a catchment. The TPRF was applied to satisfy the assumption that the amount of water extracted from Tasmanian catchments (e.g. for agriculture) has increased over time. The TPRF was calculated by a method developed in the Tasmanian State of the Environment report. This states that water demand has increased by an average of 6% annually over the last 4 decades. This factor is applied to current water entitlements to provide a simple estimate of water entitlements historically. However, following discussions with DPIW the TPRF was capped at 50% of the current extractions if the mid year of the calibration period was earlier than 1994.

Water entitlements: This refers generally to the potential water extraction from the catchment. Included are licensed extractions documented in WIMS (Dec 2006), estimates of additional unlicensed extractions and estimates of unlicensed farm dams. Unless specified otherwise, Hydro Tasmania dams and diversions are not included.

WIMS (Dec 2006): The Department Primary Industries and Water, Water Information Management System, updated to December 2006.

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

APPENDIX A

This appendix investigates the reliability of the catchment models at predicting river flow throughout the catchment. One of the difficulties in assessing model reliability is the lack of observed data, as there is often only one reliable gauging site within the catchment. Five catchments that do have more than one gauging site and concurrent periods of record were selected and investigated with the results presented in Table A-1. The analysis undertaken is outlined below.

• The relationship between catchment area of the calibration site (primary site) and the secondary site was determined. Good variability is represented within this selection, with the secondary site catchment area ranging between 6.6% and 41.5% of the calibration site.

• The catchment area relationship was used to derive a time series at the secondary site based on scaled observed data from the calibration site. This was used in subsequent analysis to assess the suggestion that an area scaled time series, derived from a primary site was a good representation of sub- catchment flow in the absence of a secondary gauging site.

• For concurrent periods, estimated monthly volumes (ML) were extracted at both the calibration site and the secondary site.

• R2 values were calculated on the following data sets for concurrent periods:

o Correlation A: The correlation between the calibration site observed data and calibration site modelled data . This provides a baseline value at the calibration site for comparison against the other correlations.

o Correlation B: The correlation between the calibration site observed data (which has been reduced by area) and secondary site observed data . This shows the relationship of area scaled estimates as a predictor of sub-catchment flows, in this case by comparison with a secondary gauge.

o Correlation C: The correlation between the calibration site observed data (which has been reduced by area) and secondary site modelled data . This compares modelled data with an area scaled data set derived from observed data. This has been done because in the absence of a gauging site, observed data from another site is often

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

assumed as a good indication of flow within the sub-catchment (Correlation B addresses this assumption). Where this assumption is applied, this correlation provides a statistical comparison of the models ability to predict comparable volumes to that of an area scaled estimate.

o Correlation D: The correlation between the secondary site observed data and secondary site modelled data . This has been done to assess how well the calibration undertaken at the primary site directly translates to other sub-catchments within the model.

The catchment model has been calibrated to provide good calibration for monthly and seasonal volumes at the calibration site. Calibration sites are typically selected low in the catchment to represent as much of the catchment as possible. Therefore the calibration fit parameters on average are expected to translate well to other sub-catchments. However, where individual sub-catchments vary significantly in terrain or vegetation or rainfall compared to the catchment average, errors are expected to be greater. The analysis undertaken in this section appears to that the confirm models perform acceptably and the conclusions of this analysis are summarised below:

1. Four of the five catchments studied showed reasonable to good R2 values between observed and modelled data at the secondary site. (Correlation D).

2. The George secondary site was the worst performing in the study. It is expected that this is due to localised changes in terrain, vegetation and/or rainfall. This is a known limitation of the model and is therefore expected in some cases.

3. Scaling the calibration site observed data by area to derive a data set at another location is not recommended. Area scaled data does not consistently out perform the model at predicting flow/volumes within catchment. It is demonstrated that the model does (in the majority of cases) a good job of directly predicting the flow/volumes within catchment.

Time Series plots of the monthly volumes in megalitres for the five catchments studied in this section are shown in Figure A-1 to Figure A-5. These plots show that generally the calibration fit at the primary site translates well as a direct model output at other locations within the catchment, when modelling monthly volumes.

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

Observed - Forth a/b Lemonthyme Site 450 140000 Site 450 - Modelled - with entitlements Observed- Scaled Forth at Paloona Bdg - site 386 120000

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60000 Monthly Volume (ML) Volume Monthly 40000

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0 1963 1964 1964 1965 1966 1967 1968

Figure A-1 Forth catchment – monthly volumes at secondary site.

Observed - Ransom Rv Site 2217 5000 Site 2217 Modelled - with entitlements Observed - Scaled George at WS site 2205 4500

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Monthly Volume (ML) Volume Monthly 1500

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0 1983 1984 1987 1989

Figure A-2 George catchment – monthly volumes at secondary site.

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

Observed - Leven at Mayday Rd - Site 821 20000 Site 821 Modelled - with entitlements 18000 Observed- Scaled Leven at Bannons site 14207

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Monthly Volume (ML) Volume Monthly 6000

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0 1983 1984 1987 1989 1991 1993

Figure A-3 Leven catchment – monthly volumes at secondary site.

Observed - Swan u/s Hardings F - Site 2219 Site 2219 Modelled - with entitlements 16000 Observed - Scaled Swan at Grange site 2200

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6000 Monthly Volume (ML) Volume Monthly 4000

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0 1983 1984 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994

Figure A-4 Swan catchment – monthly volumes at secondary site.

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

Observed - Montagu at Togari - Site 14216 Site 14216 Modelled - with entitlements 20000 Observed- Scaled Monatgu at Montagu Rd Brg - Site 14200

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Monthly Volume (ML) Volume Monthly 6000

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0 1985 1986 1987 1988 1988 1989 1990

Figure A-5 Montagu catchment – monthly volumes at secondary site.

Forth River Surface Water Model Hydro Tasmania Version No: 1.1

Table A-1 Model performance at secondary sites

Catchme Calibration Site Secondary Site Correlation A Correlation B Correlation C Correlation D nt Primary Site

Name Site Name & Sub- Catchmen Concurren Site Name Sub- Catchment Catchment Monthly ML Monthly ML Monthly ML Monthly ML

No. Catchmen t Area t data & No. Catchment Area area factor 2 2 2 2 t Location periods Location (compared with R Value R Value R Value R Value Km2 Km2 used in calibration site) Calibration site Secondary site Calibration site Secondary this observed vs observed vs observed(scale site observed analysis Calibration site Calibration site d) vs Modelled vs Modelled modelled observed (scaled) Forth Forth at SC33 1079.6 01/01/1963 Forth River SC31 310.2 0.2873 0.97 0.95 0.95 0.97 Paloona to above Bridge – Site 01/03/1969 Lemonthyme 386 – site 450 George George River SC2 397.9 01/03/1983 Ransom Rv SC3 26.1 0.0656 0.91 0.96 0.86 0.83 at SH WS – to at Sweet Hill Site 2205 01/10/1990 – Site 2217 Leven Leven at SC4 496.4 01/04/1983 Leven at SC6 37.5 0.0755 0.93 0.87 0.88 0.92 Bannons to Mayday Rd Bridge – 01/09/1994 – site 821 Site14207 Swan Swan River SC20 465.9 01/07/1983 Swan River SC4 35.6 0.0764 0.92 0.95 0.82 0.85 at Grange – to u/s Hardings Site 2200 01/10/1996 Falls – site 2219 Montagu Montagu at SC3 325.9 01/01/1985 Montagu at SC2 135.4 0.4155 0.98 0.98 0.95 0.94 Montagu Rd to Togari – Site Brdge – Site 01/01/1990 14216 14200