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DPIW – SURFACE WATER MODELS
CURRIES RIVER CATCHMENT
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
i
DOCUMENT INFORMATION
JOB/PROJECT TITLE Tascatch Variation 2 -Surface Water Models
CLIENT ORGANISATION Department of Primary Industries and Water
CLIENT CONTACT Bryce Graham
DOCUMENT ID NUMBER CONSULT- 20091, (WR 2008/014)
JOB/PROJECT MANAGER Mark Willis
JOB/PROJECT NUMBER E202869/P205357
Document History and Status
Revision Prepared
by
Reviewed
by
Approved
by
Date
approved
Revision
type
1.0 M. Willis J. Peterson C. Smythe May 2008 Final
1.1 M. Willis J. Peterson C. Smythe July 2008 Final
Current Document Approval
PREPARED BY M. Willis
Water Resources Mngt Sign Date
REVIEWED BY J. Peterson
Water Resources Mngt Sign Date
APPROVED FOR
SUBMISSION
Crispin Smythe
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.
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
ii
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 25
catchments (Tascatch – Variation 2) under both current and natural flow conditions. This
report describes the results of the hydrological model developed for the Curries
catchment.
A model was developed for the Curries 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).
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
iii
There is no observed flow record within the Curries catchment. In the absence of this
information the calibration parameters developed for the neighbouring Pipers River
catchment model (refer to Willis 2008) have been adopted. However these two
catchments have significant differences in area and topography, which may impact the
suitability of the Pipers calibration parameters for the Curries model. The installation of
a gauging site would allow a model calibration to be undertaken and it is recommended
this be considered.
The Curries catchment contains a large reservoir (Curries Reservoir) and the
information available on the operation of this storage is limited. The reservoir is
accounted for within the model using only a simple volume balance rule. An estimated
average monthly extraction profile has been included to approximate operational
conditions experienced in this reservoir. These reservoir modelling limitations and the
effect on model outputs on catchments affected by Curries Reservoir should be
considered when utilising this model.
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
iv
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 8
3.6.1 Estimation of unlicensed (small) farm dams 14
3.7 Environmental flows 15
4. MODEL DEVELOPMENT 17
4.1 Sub-catchment delineation 17
4.2 Hydstra Model 17
4.2.1 Curries Reservoir 18
4.3 AWBM Model 20
4.3.1 Channel Routing 22
4.4 Model Calibration 23
4.4.1 Factors affecting the reliability of the model calibration. 28
4.4.2 Model Accuracy - Model Fit Statistics 29
4.4.3 Model accuracy across the catchment 30
5. MODEL RESULTS 34
5.1.1 Indices of hydrological disturbance 35
6. FLOOD FREQUENCY ANALYSIS 37
7. REFERENCES 38
7.1 Personal Communications 38
8. GLOSSARY 39
APPENDIX A 41
APPENDIX B 47
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
v
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 WIMS Water Allocations 13
Figure 4-1 Hydstra Model Schematic 18
Figure 4-2 Two Tap Australian Water Balance Model Schematic 22
Figure 4-3 Curries Monthly Variation of CapAve Parameter (adopted from Pipers
Model) 24
Figure 4-4 Long term average monthly, seasonal and annual comparison plot 25
Figure 4-5 Daily time series plot (ML/d) – low flow year 27
Figure 4-6 Daily time series plot (ML/d) – mid flow year 27
Figure 4-7 Daily time series plot (ML/d) – high flow year 28
Figure 4-8 Time Series of Monthly Volumes- SC9_c 31
Figure 4-9 Time Series of Monthly Volumes- SC3_b 32
Figure 4-10 Time Series of Monthly Volumes- SC4_a 33
Figure 5-1 Daily Duration Curve 34
Figure A-1 Forth catchment – monthly volumes at secondary site. 43
Figure A-2 George catchment – monthly volumes at secondary site. 43
Figure A-3 Leven catchment – monthly volumes at secondary site. 44
Figure A-4 Swan catchment – monthly volumes at secondary site. 44
Figure A-5 Montagu catchment – monthly volumes at secondary site. 45
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
vi
LIST OF TABLES
Table 3.1 Data Drill Site Locations 7
Table 3.2 Assumed Surety of Unassigned Records 9
Table 3.3 Curries Reservoir – derived extraction profile 10
Table 3.4 Sub Catchment High and Low Priority Entitlements 11
Table 3.5 Average capacity for dams less than 20 ML by Neal et al (2002) 15
Table 3.6 Environmental Flows 16
Table 4.1 Boughton & Chiew, AWBM surface storage parameters 21
Table 4.2 Hydstra/TSM Modelling Parameter Bounds 23
Table 4.3 Curries Model Calibration Parameters (adopted from Pipers Model) 24
Table 4.4 Long term average monthly, seasonal and annual comparisons 26
Table 4.5 Model Fit Statistics achieved at neighbouring Pipers catchment. 30
Table 5.1 Hydrological Disturbance Indices 35
Table A-1 Model performance at secondary sites 46
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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 25 regional catchments
(Tascatch – Variation 2).
The main objectives for the individual catchments are:
• To compile relevant data required for the development and of the hydrological model (Australian Water Balance Model, AWBM) for the Curries River catchment. No calibration site exists for the Curries River, so the model parameters for Pipers River model have been used (Willis 2008);
• To source over 100 years of daily time-step rainfall and streamflow data for input to the hydrologic model;
• To develop and calibrate each hydrologic model, to allow running of the model under varying catchment demand scenarios;
• To develop a User Interface for running the model under these various 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.
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
2
2. CATCHMENT CHARACTERISTICS
The Curries catchment is located in Northern Tasmania, has a total catchment area of
113 km2 and discharges into Bass Strait east of Low Head. The catchment consists of
the Curries River with a catchment area of 83.3 km2 and 5 separate streams discharging
directly into the Bass Strait. These separate streams include the Curries Rivulet and four
un-named creeks. This total modelled area is referred to within this report as the Curries
catchment.
The headwaters of the catchment start at Tippogoree Hills (350m AHD) and the
catchment can be generalised as flat, coastal land. Vegetation across the catchment
varies from eucalypt forest through to low coastal vegetation. Areas associated with
agriculture are limited and a large portion of the northern catchment is a restricted area
known as the Stony Head Artillery Range.
The population in this catchment is sparse, with the catchment containing only the small
settlements of Lefroy and Beechford.
The upper catchment contains a relatively large water supply (12000ML) known as
Curries River Reservoir used as a water supply for Georgetown.
Variability in the annual rainfall total across this catchment is not significant due to the
lack of significant topographic features and the small catchment size. The lower
catchment near Beechford receives a typical annual rainfall of around 800mm and the
upper catchment near Lefroy around 850mm.
There were only 2 registered (current) entitlements for water extraction on the Water
Information Management System (WIMS July 2007) identified for inclusion in this model.
The largest single extraction entitlement is associated with the Curries Reservoir water
supply in SC1_b.
For modelling purposes, the Curries catchment was divided into 21 sub areas. The
delineation of these areas and the assumed stream routing network is shown in Figure
2-1.
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
3
3-b
3-a
1-f
9-b
1-a
1-c
8-a
1-b
1-d 4-a
1-e5-a
10-a
2-a
12-a
9-a
7-a
11-a
6-a
9-c
13-a
495000
495000
500000
500000
5445000
5445000
5450000
5450000
5455000
5455000
5460000
5460000
Legend
Steam routing network
Sub-catchment boundary
0 1 2 3 40.5
Kilometers
Figure 2-1 Sub-catchment boundaries
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
4
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 0.05o x 0.05o (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, are 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 Curries catchment the evaporation data was examined and it was found that prior
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
5
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 Curries
catchment. One of these sites corresponds to the same location as Data Drill
information sourced for the Pipers River catchment model.
See the following Figure 3-1 for a map of the climate Data Drill sites and Table 3.1 for the
location information.
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
6
PIPERS_01
CURRIES_09CURRIES_08
CURRIES_07CURRIES_06CURRIES_05
CURRIES_04CURRIES_03CURRIES_02
CURRIES_01
490000
490000
495000
495000
500000
500000
505000
505000
5440000
5440000
5445000
5445000
5450000
5450000
5455000
5455000
5460000
5460000
5465000
5465000
Legend
Pipers_curries_datadrill Events
Sub-catchment boundary
Rainfall Isoheytal
0 2 4 6 81
Kilometers
700
800
900
Figure 3-1 Climate Drill site locations
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
7
Table 3.1 Data Drill site locations
Site Latitude Longitude
CURRIES_01 -41:00:00 147:00:00
CURRIES_02 -41:03:00 146:54:00
CURRIES_03 -41:03:00 146:57:00
CURRIES_04 -41:03:00 147:00:00
CURRIES_05 -41:06:00 146:57:00
CURRIES_06 -41:06:00 147:00:00
CURRIES_07 -41:06:00 147:03:00
CURRIES_08 -41:09:00 146:57:00
CURRIES_09 -41:09:00 147:00:00
PIPERS_01 -41:03:00 147:03:00
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, however the number of sites identified for
comparison was limited, so some comparisons sites are a significant distance apart. The
visual comparison and the R2 value indicate that there appears to be reasonable
correlation between the selected sites, which is to be expected as the Data Drill
information is derived from site data. The annual rainfall totals of the selected Data Drill
sites and neighbouring sites for coincident periods are plotted in Figure 3-2.
The second graph in Figure 3-2 shows a comparison between Georgetown (site 1674)
and Data Drill site Curries_05. The R2 value indicates a good relationship however the
magnitude of Curries_05 is always greater by approximately 100mm per annum. In this
case the sites are a significant distance apart (around 10km) and therefore rainfall
magnitude differences of this amount are not considered unusual.
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
8
0
200
400
600
800
1000
1200
1400
1914
1917
1920
1923
1926
1929
1932
1935
1938
1941
1944
1947
1950
1953
1956
1959
1962
1965
1968
1971
1974
Annaul Rainfall (mm)
Data Drill - Curries_06 Lefroy - Site 1547 R2 = 0.95
0
200
400
600
800
1000
1200
1400
1969 1970 1971 1972 1973 1974
Annaul Rainfall (mm)
Data Drill - Curries_05 Georgetown - Site 1674 R2 = 0.93
Figure 3-2 Rainfall and Data Drill comparisons
3.5 Streamflow data
There are no observed gauging sites within this catchment. The closest gauging site is
within the neighbouring Pipers River catchment. This site is Pipers River downstream of
Yarrow Creek (site 19204). In the absence of a suitable calibration site the model
calibration parameters adopted for the Pipers River catchment have been adopted for
this model (refer Willis 2008).
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 July
2007). 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 site
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
9
which had a Surety of 0. DPIW staff advised that in this case the Surety should be
determined by the extraction “Purpose” and assigned as follows:
Table 3.2 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 was 12000 ML of unassigned entitlements (Surety = 0) identified for
inclusion in the surface water model, relating to the Curries Reservoir water supply. This
single entitlement was assigned Surety 1.
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;
• 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.
When modelling Scenario 3 (Environmental flows and Entitlements), water will only be
available for Low Priority entitlements after environmental flow requirements have been
met.
There were multiple communications with DPIW staff, on allowances for extractions not
yet included in the WIMS (July 2007) water licence database. DPIW advised that the
unlicensed extractions estimate should be three times the current Surety 5, direct
extractions. However for the Curries catchment there were no direct Surety 5 extractions
(current) in the WIMS database and accordingly an estimate of zero unlicensed
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
10
extractions was used.
There was some doubt in the suitability of the WIMS information to accurately reflect the
water extraction information associated with the Curries Reservoir. Although there is a
license for 12000ML per annum it is unlikely that this is reflective of the amount
extracted, because modelling suggests the reservoir catchment cannot sustain this yield.
Following discussions with DPIW the WIMS entitlement was replaced with a derived
average monthly extraction profile. Information for determining this profile was limited
and the only useful information sourced was 14 years of lake level (volume) information
from 1980 to 1995. Using this information and modelled natural inflows an estimate of
the typical (average) monthly extraction profile from this reservoir was estimated. This
profile was included in the User Interface as 12 (monthly) water entitlements at SC1-b
and they are summarized in the following table. In summary the annual entitlement was
reduced from 12000ML to 2975ML.
Table 3.3 Curries Reservoir – derived extraction profile
Month Extraction (ML)
January 350
February 350
March 290
April 160
May 160
June 95
July 160
August 270
September 320
October 220
November 270
December 330
In addition to the extractions detailed above, an estimate was made for small farm dam
extractions currently not requiring a permit and hence not listed in the WIMS database.
These extractions are referred to in this report as unlicensed (small) farm dam
extractions and details of the extraction estimate are covered in Section 3.6.1.
A summary table of total entitlement volumes on a monthly basis by sub-catchment is
provided below in Table 3.4 and in the Catchment User Interface. These values include
the estimates of unlicensed extractions, unlicensed farm dams and WIMS database
extractions. A map of the WIMS (July 2007) water allocations in the catchment is shown
in Figure 3-3.
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
11
Table 3.4 Sub Catchment High and Low Priority Entitlements
Water Entitlements Summarised - Monthly Demand (ML) for each Subarea & Month
Subcatch Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total
High Priority Entitlements
SC1_a 0.00 0.00 0.00 0.00 2.84 2.75 2.84 2.84 2.75 0.00 0.00 0.00 14
SC1_b 350.00 350.00 290.00 160.00 160.28 95.27 160.28 270.28 320.27 220.00 270.00 330.0
0
2,976
SC1_c 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -
SC1_d 0.00 0.00 0.00 0.00 3.12 3.02 3.12 3.12 3.02 0.00 0.00 0.00 15
SC1_e 0.00 0.00 0.00 0.00 2.27 2.20 2.27 2.27 2.20 0.00 0.00 0.00 11
SC1_f 0.00 0.00 0.00 0.00 6.52 6.31 6.52 6.52 6.31 0.00 0.00 0.00 32
SC2_a 0.00 0.00 0.00 0.00 2.55 2.47 2.55 2.55 2.47 0.00 0.00 0.00 13
SC3_a 0.00 0.00 0.00 0.00 4.25 4.12 4.25 4.25 4.12 0.00 0.00 0.00 21
SC3_b 0.00 0.00 0.00 0.00 2.27 2.20 2.27 2.27 2.20 0.00 0.00 0.00 11
SC4_a 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_a 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -
SC6_a 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -
SC7_a 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -
SC8_a 0.00 0.00 0.00 0.00 1.99 1.92 1.99 1.99 1.92 0.00 0.00 0.00 10
SC9_a 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_b 0.00 0.00 0.00 0.00 0.85 0.82 0.85 0.85 0.82 0.00 0.00 0.00 4
SC9_c 0.00 0.00 0.00 0.00 0.28 0.27 0.28 0.28 0.27 0.00 0.00 0.00 1
SC10_a 0.00 0.00 0.00 0.00 1.99 1.92 1.99 1.99 1.92 0.00 0.00 0.00
10
SC11_a 0.00 0.00 0.00 0.00 0.57 0.55 0.57 0.57 0.55 0.00 0.00 0.00 3
SC12_a 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
-
SC13_a 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 350
350
290
160
190
124
190
300
349
220
270
330
3,122
Low Priority Entitlements
SC1_a 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -
SC1_b 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -
SC1_c 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -
SC1_d 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -
SC1_e 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -
SC1_f 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -
SC2_a 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -
SC3_a 0.00 0.00 0.00 0.00 1.68 1.63 1.68 1.68 1.63 1.68 0.00 0.00
10
SC3_b 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -
SC4_a 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
-
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
12
SC5_a 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -
SC6_a 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -
SC7_a 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -
SC8_a 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_a 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_b 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_c 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_a 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_a 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_a 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -
SC13_a 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 -
-
-
-
2
2
2
2
2
2
-
-
10
All Entitlements
SC1_a 0.00 0.00 0.00 0.00 2.84 2.75 2.84 2.84 2.75 0.00 0.00 0.00 14
SC1_b 350.00 350.00 290.00 160.00 160.28 95.27 160.28 270.28 320.27 220.00 270.00 330.0
0 2,976
SC1_c 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -
SC1_d 0.00 0.00 0.00 0.00 3.12 3.02 3.12 3.12 3.02 0.00 0.00 0.00 15
SC1_e 0.00 0.00 0.00 0.00 2.27 2.20 2.27 2.27 2.20 0.00 0.00 0.00 11
SC1_f 0.00 0.00 0.00 0.00 6.52 6.31 6.52 6.52 6.31 0.00 0.00 0.00 32
SC2_a 0.00 0.00 0.00 0.00 2.55 2.47 2.55 2.55 2.47 0.00 0.00 0.00
13
SC3_a 0.00 0.00 0.00 0.00 5.94 5.75 5.94 5.94 5.75 1.68 0.00 0.00 31
SC3_b 0.00 0.00 0.00 0.00 2.27 2.20 2.27 2.27 2.20 0.00 0.00 0.00
11
SC4_a 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_a 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
-
SC6_a 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -
SC7_a 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -
SC8_a 0.00 0.00 0.00 0.00 1.99 1.92 1.99 1.99 1.92 0.00 0.00 0.00 10
SC9_a 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_b 0.00 0.00 0.00 0.00 0.85 0.82 0.85 0.85 0.82 0.00 0.00 0.00
4
SC9_c 0.00 0.00 0.00 0.00 0.28 0.27 0.28 0.28 0.27 0.00 0.00 0.00 1
SC10_a 0.00 0.00 0.00 0.00 1.99 1.92 1.99 1.99 1.92 0.00 0.00 0.00
10
SC11_a 0.00 0.00 0.00 0.00 0.57 0.55 0.57 0.57 0.55 0.00 0.00 0.00 3
SC12_a 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
-
SC13_a 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 350
350
290
160
191
125
191
301
350
222
270
330
3,132
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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3-b
3-a
1-f
9-b
1-a
1-c
8-a
1-b
1-d 4-a
1-e5-a
10-a
2-a
12-a
9-a
7-a
11-a
6-a
9-c
13-a
490000
490000
495000
495000
500000
500000
5445000
5445000
5450000
5450000
5455000
5455000
5460000
5460000
Legend
WIMS water allocations
Sub-catchment boundary
0 1 2 3 40.5
Kilometers
Figure 3-3 WIMS water allocations
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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3.6.1 Estimation of unlicensed (small) farm 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 2003. The number of dams, of any size, in all
sub-catchments was counted by eye. Generally there were a low number
of unlicensed dams identified during the physical count.
• This count determined a total of 107 dams within the catchment. There are
only 2 licensed WIMS storages within this catchment and accordingly 105
of these counted dams are unlicensed.
• 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 3.5).
• 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.
• Assuming this dam size distribution is similar to the distribution of the study
catchment in South Australia, then the total volume of unlicensed dams can
be estimated as 147 ML (105 * 1.4ML). The total volume of existing
permitted dams extractions in the study catchment is 12010 ML. Therefore
the 147 ML of unlicensed dams equates to approximately 1.2% 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
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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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 3.5 Average capacity for dams less than 20 ML by Neal et al (2002)
Size Range (ML)
Average Volume (ML)
Number of Dams
Total Volume (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
3.7 Environmental flows
One of the modelling scenarios (Scenario 3) was to account for environmental flows
within the catchment. DPIW advised, that for the Curries 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:
• The 20th percentile for each sub-catchment during the winter period (01May to
31st Oct).
• The 30th percentile for each sub-catchment during the summer period (01 Nov –
30 April).
The Modelled – No entitlements (Natural) flow scenario was run from 01/01/1970 to
01/01/2008.
However following further discussion with DPIW, there were selected sub-catchments
affected by Curries Reservoir excluded from this methodology and no environmental flow
was defined. In these sub-catchments the flow is highly modified due to Curries
Reservoir and setting minimum environmental flows based on natural conditions would
have no relationship with currently observed flows.
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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A summary table of the environmental flows on a monthly breakdown by sub-catchment
is provided in the following table and in the Catchment User Interface.
Table 3.6 Environmental flows
Catchment Area (km2)
Environmental Flow (ML/d) Per Month at subcatchment
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Average
SC1_a 7.3 0.28 0.11 0.07 0.21 0.40 0.97 3.89 2.99 1.80 0.59 0.65 0.32 1.02
SC1_b 6.2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
SC1_c 6.4 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
SC1_d 5.8 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
SC1_e 5.2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
SC1_f 7.7 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
SC2_a 4.0 0.15 0.06 0.04 0.12 0.22 0.52 2.09 1.47 0.95 0.31 0.36 0.17 0.54
SC3_a 9.0 0.32 0.13 0.08 0.28 0.51 1.21 4.21 3.38 1.98 0.72 0.77 0.38 1.16
SC3_b 9.7 0.63 0.28 0.16 0.61 1.04 2.42 8.43 6.56 3.77 1.48 1.56 0.80 2.31
SC4_a 5.5 0.19 0.07 0.05 0.20 0.31 0.73 2.55 1.85 1.03 0.41 0.46 0.22 0.67
SC5_a 4.8 0.13 0.06 0.04 0.17 0.24 0.61 1.86 1.26 0.75 0.33 0.38 0.18 0.50
SC6_a 2.2 0.07 0.03 0.02 0.08 0.12 0.29 0.99 0.69 0.39 0.16 0.18 0.09 0.26
SC7_a 3.5 0.06 0.04 0.02 0.09 0.16 0.36 0.53 0.64 0.32 0.19 0.22 0.08 0.23
SC8_a 6.1 0.15 0.07 0.05 0.22 0.30 0.76 2.15 1.53 0.88 0.40 0.48 0.20 0.60
SC9_a 3.6 0.07 0.04 0.02 0.09 0.17 0.37 0.55 0.67 0.34 0.19 0.25 0.09 0.24
SC9_b 8.0 0.20 0.11 0.08 0.29 0.49 1.07 1.65 1.79 0.96 0.57 0.75 0.25 0.68
SC9_c 2.1 0.24 0.13 0.09 0.34 0.57 1.24 1.94 2.10 1.12 0.70 0.87 0.29 0.80
SC10_a 5.7 0.10 0.05 0.04 0.17 0.24 0.63 1.26 1.16 0.63 0.33 0.39 0.15 0.43
SC11_a 3.0 0.06 0.03 0.02 0.08 0.12 0.34 0.70 0.61 0.33 0.17 0.20 0.08 0.23
SC12_a 5.1 0.10 0.05 0.03 0.14 0.20 0.57 1.18 1.02 0.54 0.28 0.34 0.14 0.38
SC13_a 1.9 0.04 0.02 0.01 0.05 0.07 0.21 0.43 0.37 0.20 0.10 0.12 0.05 0.14
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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4. MODEL DEVELOPMENT
4.1 Sub-catchment delineation
Sub-catchment delineation was performed using CatchmentSIM GIS software.
CatchmentSIM is a 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. If any minor modifications were required these 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 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.
The AWBM Two Tap rainfall/runoff model (Parkyn & Wilson 1997) was used to calculate
the runoff for each sub-catchment separately. This was chosen over the usual method of
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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a single-tap 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
4.2.1 Curries Reservoir
A significant lake known as Curries Reservoir was identified during the creation of this
model and is located in sub-catchment SC1-b. The lake is significant when compared to
the size of the catchment and accordingly it will have a major impact on the flow regime
downstream of this storage. Following discussions with DPIW staff on the appropriate
way to model this lake, the following model rules were adopted:
• Scenario 1, “No Entitlements (Defines ‘Natural’ Flows)” will model the catchment
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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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 of 1981. Although the dam
completion date is indicated as 1979 (from DPIW dams database), lake
level records indicate the lake wasn’t operational until 1981 and prior to
this it was simply filling. The model does not account for the 1979 to 1981
filling period so caution should be used when interpreting results over this
period.
o From 1981 onwards, the lake will be modelled using a basic volume
balance rule assuming the following:
� Maximum lake volume will be 12000 ML (from DPIW dams
database). Lake level record indicates the lake started operation
in 1981 when it had reached a capacity of around 8000ML, and
hence this is the starting capacity of the reservoir within the model;
� Water entitlements falling within the Curries Reservoir sub-
catchment (SC1-b) will be extracted from the lake volume. Refer
to section 3.6 regarding estimates of water extractions for the
Curries Reservoir;
� Flows in excess of the lake volume will be discharged downstream
as spill;
� If the Environmental Flows & Entitlements scenario is selected
then a flow will be released downstream equal to the
environmental flow specified in the user interface, for the Lake
sub-catchment (SC1-b). However when the modelled inflow to the
lake (inflow + pickup) is less than the specified environmental flow,
the downstream release will be reduced to equal this. This has
been done to stop excessive draw down of the lake due to
environmental release in periods of low inflow. The environmental
flow for Curries Reservoir is currently set to zero so this code
would only become relevant should the default environmental flow
be changed.
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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Due to its relative large size, a basic reservoir evaporation rule was also included in the
model for this sub-catchment. The approximate surface area of the lake was determined
from 1:25k TASMAP to be 1.96km2. Change in lake volume attributable to rainfall and
evaporation falling on this area was determined on a daily basis utilising the Data Drill
rainfall and evaporation inputs and added to the basic volume balance rule described
above.
4.3 AWBM Model
The AWBM Two Tap model (Parkyn & Wilson 1997) 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;
• 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 (A1 to A3) and three surface storage
capacities (Cap1 to Cap3) 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 (CapAve), the three partial areas and
the three surface storage capacities are found by;
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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Table 4.1 Boughton & Chiew, AWBM surface storage parameters
Partial area of S1 A1=0.134
Partial area of S2 A2=0.433
Partial area of S3 A3=0.433
Capacity of S1 Cap1=(0.01*CapAve/A1)=0.075*CapAve
Capacity of S2 Cap2=(0.33*CapAve/ A2)=0.762*CapAve
Capacity of S3 Cap3=(0.66*CapAve/ A3)=1.524*CapAve
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.
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 and it is applied to the
stream network directly. Base-flow is 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 baseflow, it is not intended
that the baseflow prediction from the AWBM model be adopted as an accurate estimate
of the baseflow contribution. The base flow in the AWBM routine is based on a simple
model and does not specifically account for attributes that affect baseflow 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 in the following Figure 4-2.
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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Figure 4-2 Two Tap Australian Water Balance Model schematic
4.3.1 Channel Routing
A common method employed in nonlinear routing models is a power function storage
relation.
S = K.Qn
K is a dimensional empirical coefficient, the reach lag (time). In the case of Hydstra/TSM
Modelling:
α
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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and
Li = Channel length (km)
α = Channel Lag Parameter
n = Non-linearity Parameter
Q = Outflow from Channel Reach (ML/day)
A reach length factor may be used in the declaration of α to account for varying reach lag
for individual channel reaches. eg. α.fl where fl is a length factor.
Parameters required by Hydstra/TSM Modelling and their recommended bounds are:
Table 4.2 Hydstra/TSM Modelling parameter bounds
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
No observed streamflow record was available within the Curries catchment for model
calibration. Model parameters used to calibrate the Pipers River catchment surface
water model were adopted for this model as the Pipers catchment adjoins the Curries
catchment.
Calibration of the Pipers model was achieved by adjusting model parameters by
comparing the monthly, seasonal and annual volumes. A generalised calibration method
is presented in APPENDIX B. This process is also detailed in the Pipers catchment
model report (Willis, 2008). The adopted model parameters are shown in Table 4.3.
In the absence of other data, the model parameters used for the Pipers catchment
model are assumed to be valid for the Curries catchment model. The geographical
proximity of the two catchments implies similar climatic and environmental regimes
(notably soil and vegetation types). A visual inspection of maps indicated that the
Curries and lower Pipers catchments share similar topography and land use. However,
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
24
the Pipers catchment is larger (4 times larger) and the topography of the upper Pipers
catchment is significantly different, which may impact the suitability of the Pipers
calibration parameters for the Curries catchment. In the absence of a calibration site or
other nearby catchment models for comparison the Pipers calibration parameters were
deemed the best available option.
Table 4.3 Curries Model Calibration Parameters (adopted from Pipers Model)
PARAMETER VALUE PARAMETER VALUE
INFBase 0.42 CapAve Jan 80
K1 0.955 CapAve Feb 100
K2 0.83 CapAve Mar 109
GWstoreSat 70 CapAve Apr 118
GWstoreMax 150 CapAve May 120
H_GW 24 CapAve Jun 120
RainScaleF 1 CapAve July 120
EvapScaleF 1 CapAve Aug 120
Alpha 3.0 CapAve Sept 110
n 0.8 CapAve Oct 100
CapAve Nov 78
CapAve Dec 57
0
20
40
60
80
100
120
140
1 2 3 4 5 6 7 8 9 10 11 12MONTH
CapAve
CapeAve
Figure 4-3 Curries Monthly Variation of CapAve Parameter (adopted from Pipers
Model)
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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The monthly, seasonal and annual volume balances for the last 20 years of record
(01/03/1988 to 01/03/2008) record are presented in Figure 4-4 and Table 4.4 for
Curries River at sub-catchment SC1_f. The demand values shown represent the total
water entitlements upstream of the SC1_f. The demand has been included to provide
a general indication of the relative amount of water being extracted from Curries River.
The two cases (Scenario1 & Scenario 2) show very different monthly values and this is
due to the major impact Curries Reservoir has on the flow regime within this
catchment. In this model the summer demand significantly exceeds the catchment
yield and this is because this demand is supported by the storage in Curries Reservoir.
0
10
20
30
40
50
60
70
80
90
100
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
WINTER
SUMMER
ANNUAL
Average Flow (ML/Day)
Scenario 2 - Modelled
Entitlements Extracted
Scenario 1 - Modelled No
Entitlements (Natural)
Demand x1
Figure 4-4 Long term average monthly, seasonal and annual comparison plot
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
26
Table 4.4 Long term average monthly, seasonal and annual comparisons
MONTH
Scenario 2 - Modelled
Entitlements Extracted
Scenario 1 - Modelled No Entitlements (Natural) Demand
1
Jan 6.57 8.34 11.29
Feb 3.73 4.95 12.50
Mar 2.18 2.80 9.35
Apr 9.80 12.64 5.33
May 12.65 17.40 6.06
Jun 31.54 42.51 4.06
Jul 56.30 74.57 6.06
Aug 66.80 87.62 9.61
Sep 55.67 70.99 11.56
Oct 29.44 36.64 7.15
Nov 9.63 12.62 9.00
Dec 6.00 7.76 10.65
WINTER 42.07 54.95 7.42
SUMMER 6.32 8.19 9.69
ANNUAL 24.19 31.57 8.55
WINTER from May to Oct, SUMMER from Nov - Apr
Daily time series plots of three discrete calendar years (Figure 4-5 to Figure 4-7) have
been displayed for the sub-catchment SC1_f, showing a range of relatively low to high
inflow years, running the model using Scenario 2.
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.
1 The demand value includes all extraction potential upstream of sub-catchment SC1_f.
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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0
10
20
30
40
50
60
70
80
01/06 02/06 03/06 04/06 05/06 06/06 07/06 08/06 09/06 10/06 11/06 12/06 01/07
-90
-70
-50
-30
-10
10
30Precipitation Scenario 2- Modelled with Entitlements Extracted
Figure 4-5 Daily time series plot (ML/d) – low flow year
0
100
200
300
400
500
600
700
01/89 02/89 03/89 04/89 05/89 06/89 07/89 08/89 09/89 10/89 11/89 12/89 01/90
-90
-70
-50
-30
-10
10
30
50
70Precipitation Scenario 2- Modelled with Entitlements Extracted
Figure 4-6 Daily time series plot (ML/d) – mid flow year
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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0
200
400
600
800
1000
1200
1400
1600
01/03 02/03 03/03 04/03 05/03 06/03 07/03 08/03 09/03 10/03 11/03 12/03 01/04
-90
-70
-50
-30
-10
10
30
50Precipitation Scenario 2- Modelled with Entitlements Extracted
Figure 4-7 Daily time series plot (ML/d) – high flow year
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 this model the most
significant limitations identified that will affect the calibration accuracy are:
1. The assumption that water entitlements are taken at 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;
2. The current quantity of water extracted from the catchment is unknown. Although
DPIW have provided water licence information (WIMS July 2007) 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;
3. 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;
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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4. 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;
5. 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;
6. 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;
7. The simple operating rules and assumptions used to model the Curries Reservoir
cannot capture the complexities of operation that occur in reality;
8. The catchment contains coastal areas containing flat terrain. It is likely that the flow
in these sub-catchments will experience the effects of backwater, especially in
periods of high flow and near estuaries. The adopted model does not account for
this effect and therefore stream routing between catchments is likely to be
misrepresented, especially within modelled daily outputs. To accurately account for
backwater effects a hydraulic model that utilises the Saint Venant equations for
natural rivers would be required and this has not been undertaken as part of this
project.
4.4.2 Model Accuracy - Model Fit Statistics
It is an assumption of the Curries model that the calibration parameters of the adjacent
Pipers catchment model are appropriate for the Curries catchment. The calibration for
the Pipers catchment model resulted in good replication of observed streamflows, as
evidenced by high coefficients of determination (R2 values) (Table 4.5) and low
proportional differences between observed and modelled flows (Willis 2008). Annual
hydrographs were judged to have good replication of observed flows, and modelled
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
30
flow volumes showed excellent fidelity to observed flow volumes. Calibration of this
catchment is discussed in the Pipers catchment model report detail (Willis 2008).
However, good performance of the Pipers surface water model does not give a
guarantee of good performance of the Curries model. With no observed flow record in
this catchment, it is difficult to make this judgment. However in the absence of other
information it is deemed the best option.
Table 4.5 Model Fit Statistics achieved at neighbouring Pipers catchment.
Measure of Fit Pipers River d/s Yarrow
Creek (Site 19204)
Daily coefficient of determination (R2 Value) 0.77
Monthly coefficient of determination (R2 Value) 0.92
Difference in observed and estimated long term annual average flow
+0.1%
4.4.3 Model accuracy across the catchment
The Curries model uses the Pipers catchment calibration fit and this model was
calibrated to provide a good simulation of monthly and seasonal flow volumes at the
calibration site. It is difficult to assess how reliably a model performs throughout the
catchment, although it is assumed that a model operates satisfactorily at other sites in
the catchments. The ability of five other DPIW Surface Water models (developed by
the same method as the Curries Model) to simulate flows throughout these catchments
was assessed. These analyses suggest that on average the models predict volumes
well throughout their catchments (see Appendix A). The Pipers model performed
consistently throughout the catchment (Willis 2008). A detailed description of the
Pipers surface flow model’s performance throughout its catchment is available (Willis
2008).
As there is no observed flow record available for Curries catchment, the reliability of the
model throughout the catchment could not be tested directly. As the Curries model
adopted the parameters of the Pipers model, the record used to calibrate the Pipers
(Pipers River, site 19204) was used to derive a proxy ‘observed’ record with which to
test the Curries model.
It was assumed that streamflow volume increased by the same proportion as
catchment area. Thus if a calibration site has a sub-catchment area A and a flow
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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volume of QA, and another site has a sub-catchment area B and a flow volume of QB,
then
QB = QA.(B/A)
This assumption is crude, as it ignores rainfall variability and variability in water
extractions within the catchment, and therefore it will not definitively demonstrate a
model’s performance throughout the catchment. However, after discussion with DPIW,
the method was included as a basic overview of the model’s ability to predict flow
volumes throughout the catchment.
Three sub-catchments were selected across the catchment. Due to the impact of the
Curries Reservoir on the main stream flows, catchments unaffected by this reservoir
were chosen
Comparison of scaled observed site and sub-catchment SC9_c
The area ratio of sub-catchment SC9_c to the observed data (site 19204) was
calculated to be 4.5%. The observed monthly volumes at the calibration site were
multiplied by this ratio in order to calculate a proxy ‘observed’ record at the catchment
outflow. The results are shown in the following plot and show a poor volume
relationship. This is not unexpected due to the difference in catchment area and
annual rainfall. This plot highlights the dangers of using scaled observed data as a
guide for determining flows at alternate locations or assessing model performance.
The model allows for the spatial variability of rainfall over the catchment, thus the
modelled flow prediction will not be disadvantaged by rainfall spatial variation.
0.0
500.0
1000.0
1500.0
2000.0
2500.0
01/88 01/89 01/90 01/91 01/92 01/93 01/94 01/95 01/96 01/97 01/98 01/99 01/00 01/01 01/02 01/03 01/04 01/05 01/06 01/07
Monthly Volume (ML)
Observed - Area Scaled - Pipers River - Site 19204Modelled with entitlements (extracted) - SC9_c
R2 = 0.73
Figure 4-8 Time Series of Monthly Volumes- SC9_c
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
32
Comparison of scaled observed site and sub-catchment SC3_b
The area ratio of sub-catchment SC3_b to the observed data (site 19204) was
calculated to be 6.2%. The observed monthly volumes at the calibration site were
multiplied by this ratio in order to calculate a proxy ‘observed’ record at the catchment
outflow. The results are shown in the following plot and show a poor to fair volume
relationship. This is not unexpected due to the difference in catchment area and
annual rainfall. This plot highlights the dangers of using scaled observed data as a
guide for determining flows at alternate locations or assessing model performance.
The model allows for the spatial variability of rainfall over the catchment, thus the
modelled flow prediction will not be disadvantaged by rainfall spatial variation.
0.0
500.0
1000.0
1500.0
2000.0
2500.0
3000.0
3500.0
01/88 01/89 01/90 01/91 01/92 01/93 01/94 01/95 01/96 01/97 01/98 01/99 01/00 01/01 01/02 01/03 01/04 01/05 01/06 01/07
Monthly Volume (ML)
Observed - Area Scaled - Pipers River - Site 19204Modelled with entitlements (extracted) - SC3_b
R2 = 0.81
Figure 4-9 Time Series of Monthly Volumes- SC3_b
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
33
Comparison of scaled observed site and sub-catchment SC4_a
The area ratio of sub-catchment SC4_a to the observed data (site 19204) was
calculated to be 1.8%. The observed monthly volumes at the calibration site were
multiplied by this ratio in order to calculate a proxy ‘observed’ record at the catchment
outflow. The results are shown in the following plot and show a poor to fair volume
relationship. This is not unexpected due to the difference in catchment area and
annual rainfall. This plot highlights the dangers of using scaled observed data as a
guide for determining flows at alternate locations or assessing model performance.
The model allows for the spatial variability of rainfall over the catchment, thus the
modelled flow prediction will not be disadvantaged by rainfall spatial variation.
0.0
100.0
200.0
300.0
400.0
500.0
600.0
700.0
800.0
900.0
1000.0
01/88 01/89 01/90 01/91 01/92 01/93 01/94 01/95 01/96 01/97 01/98 01/99 01/00 01/01 01/02 01/03 01/04 01/05 01/06 01/07
Monthly Volume (ML)
Observed - Area Scaled - Pipers River - Site 19204Modelled with entitlements (extracted) - SC4_a
R2 = 0.81
Figure 4-10 Time Series of Monthly Volumes- SC4_a
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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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 01/01/1981 to 01/01/2008, which corresponds to the
start of Curries Reservoir. Results have been produced low in the Curries River at sub-
catchment SC1_f.
0.10
1.00
10.00
100.00
1000.00
10000.00
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Percent Of Time Exceeded
Flow (ML/d)
Natural
Entitlements Extracted
Figure 5-1 Daily Duration Curve
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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5.1.1 Indices of hydrological disturbance
The calculation of the modeled flow estimates 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 01/01/1970 to 01/01/2008. Three sites
have been selected to give an indication of the variability of the indices of hydrological
disturbance across the catchment.
It can be seen that the highest hydrological disturbance occurs mid catchment due to the
effects of the Curries Reservoir extraction.
Table 5.1 Hydrological Disturbance Indices
Disturbance Indices undisturbed (natural flow)
SC1_f
Low in catchment)
SC1_d
(Mid catchment)
SC3_a
(High in catchment)
Index of Mean Annual Flow, A 1.00 0.76 0.63 0.98
Index of Flow Duration Curve Difference, M 1.00 0.69
0.58 0.91
Index of Seasonal Amplitude, SA 1.00 0.75 0.63 0.99
Index of Seasonal Periodicity, SP 1.00 1.00 1.00 1.00
Hydrological Disturbance Index, HDI 1.00 0.77 0.66 0.96
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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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
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.
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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6. FLOOD FREQUENCY ANALYSIS
No flood frequency plot has been developed for this model as the river is highly
regulated and there is no observed gauging site within this catchment.
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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7. REFERENCES
Boughton, W.C. and Chiew, F.,(2003) Calibrations of the AWBM for use on Ungauged
Catchments
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 (2004). Operating Manual for the NAP region Hydrological Models.
Hydro Report 118783 – Report -015, 17 September 2004.
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.
Parkyn R & Wilson D, (1997): Real-Time Modelling of the Tributary Inflows to ECNZ's
Waikato Storages. 24th Hydrology & Water Resources Symposium Proceedings
IEAust, Auckland NZ 1997.
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.
Willis (2008). DPIW – Surface Water Models, Pipers River Catchment, May 2008.
7.1 Personal Communications
Graham, B. Section Head, Ecohydrology, Water Assessment, DPIW. April-May 2008.
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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8. GLOSSARY
Coefficient of determination (R2): 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, R2 is the variance in y attributable to the variance in x. A high R2
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.
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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Modelled – environmental flows and entitlements (extracted): The TimeStudio
surface 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 1995.
Water entitlements: This refers generally to the potential water extraction from the
catchment. Included are licensed extractions documented in WIMS (July 2007)
estimates of additional unlicensed extractions and estimates of unlicensed farm dams.
Unless specified otherwise, Hydro Tasmania dams and diversions are not included.
WIMS (July 2007): The Department Primary Industries and Water, Water Information
Management System, updated to July 2007.
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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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
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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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 a good fit 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 confirm that the
models perform acceptably and the conclusions of this analysis are summarised
below:
1. Four of the five catchments studied showed fair 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 with a fair
R2 value of 0.83. 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.
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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0
20000
40000
60000
80000
100000
120000
140000
1963 1964 1964 1965 1966 1967 1968
Monthly Volume (ML)
Observed - Forth a/b Lemonthyme Site 450
Site 450 - Modelled - with entitlements
Observed- Scaled Forth at Paloona Bdg - site 386
Figure A-1 Forth catchment – monthly volumes at secondary site.
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
1983 1984 1987 1989
Monthly Volume (ML)
Observed - Ransom Rv Site 2217
Site 2217 Modelled - with entitlements
Observed - Scaled George at WS site 2205
Figure A-2 George catchment – monthly volumes at secondary site.
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
44
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
1983 1984 1987 1989 1991 1993
Monthly Volume (ML)
Observed - Leven at Mayday Rd - Site 821
Site 821 Modelled - with entitlements
Observed- Scaled Leven at Bannons site 14207
Figure A-3 Leven catchment – monthly volumes at secondary site.
0
2000
4000
6000
8000
10000
12000
14000
16000
1983 1984 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994
Monthly Volume (ML)
Observed - Swan u/s Hardings F - Site 2219
Site 2219 Modelled - with entitlements
Observed - Scaled Swan at Grange site 2200
Figure A-4 Swan catchment – monthly volumes at secondary site.
Curries River Surface Water Model Hydro Tasmania Version No: Final 1.1
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0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
1985 1986 1987 1988 1988 1989 1990
Monthly Volume (ML)
Observed - Montagu at Togari - Site 14216
Site 14216 Modelled - with entitlements
Observed- Scaled Monatgu at Montagu Rd Brg - Site 14200
Figure A-5 Montagu catchment – monthly volumes at secondary site.
Curries River Surface Water Model Hydro Tasmania
Version No: Final 1.1
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Table A-1 Model perform
ance at secondary sites
Catchme
nt
Calibration Site
Primary Site
Secondary Site
Correlation A
Correlation B
Correlation C
Correlation D
Name
Site Name
& No.
Sub-
Catchment
Location
Catchment
Area
Km2
Concurrent
data
periods
used in
this
analysis
Site Name
& No.
Sub-
Catchment
Location
Catchment
Area
Km2
Catchment
area factor
(compared with
calibration site)
Monthly ML
R2 Value
Calibration site
observed vs
Calibration site
modelled
Monthly ML
R2 Value
Secondary site
observed vs
Calibration site
observed
(scaled)
Monthly ML
R2 Value
Calibration site
observed(scale
d) vs Modelled
Monthly ML
R2 Value
Secondary
site observed
vs Modelled
Forth
Forth at
Paloona
Bridge –
Site 386
SC33
1079.6
01/01/1963
to
01/03/1969
Forth River
above
Lemonthym
e – site 450
SC31
310.2
0.2873
0.97
0.95
0.95
0.97
George
George
River at SH
WS – Site
2205
SC2
397.9
01/03/1983
to
01/10/1990
Ransom Rv
at Sweet
Hill – Site
2217
SC3
26.1
0.0656
0.91
0.96
0.86
0.83
Leven
Leven at
Bannons
Bridge –
Site14207
SC4
496.4
01/04/1983
to
01/09/1994
Leven at
Mayday Rd
– site 821
SC6
37.5
0.0755
0.93
0.87
0.88
0.92
Swan
Swan River
at Grange –
Site 2200
SC20
465.9
01/07/1983
to
01/10/1996
Swan River
u/s
Hardings
Falls – site
2219
SC4
35.6
0.0764
0.92
0.95
0.82
0.85
Montagu Montagu at
Montagu
Rd Brdge –
Site 14200
SC3
325.9
01/01/1985
to
01/01/1990
Montagu at
Togari –
Site 14216
SC2
135.4
0.4155
0.98
0.98
0.95
0.94
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APPENDIX B
Generalised Model Calibration Method
Calibration for all DPIW surface water models was achieved by adjusting catchment
parameters so that the modelled data best replicates the record at the site selected for
calibration. 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 long term
monthly volumes (flows) was given the highest priority and matching of peak flood events
and daily flows was given lower priority.
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 = Modelled Calibration Flow
MNEM = Modelled - No Entitlements (Modified). *
WE = Water Entitlements
TPRF = Time Period Reduction Factor
* Refer to Glossary for additional explanation of these terms
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
1995.
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.
In the absence of information on daily patterns of extraction, the model assumes that
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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.
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.
Recommended