Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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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 2007/017
JOB/PROJECT MANAGER Mark Willis
JOB/PROJECT NUMBER E200690/P202167
Document History and Status
Revision Prepared
by
Reviewed
by
Approved
by
Date
approved
Revision
type
1.0 J. Bennett Dr Fiona
Ling
C. Smythe July 2007 Final
1.1 M. Willis Dr Fiona
Ling
C. Smythe July 2008 Final
Current Document Approval
PREPARED BY James Bennett
Water Resources Mngt Sign Date
REVIEWED BY Fiona Ling
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.
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EXECUTIVE SUMMARY
This report is one of a series of reports that present the methods and results from the
development 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 Sisters Creek catchment
A model was developed for the Sisters Creek 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:
• Hydrological Disturbance Index
• Index of Mean Annual Flow
• Index of Flow Duration Curve Difference
• Index of Seasonal Amplitude
• Index of Seasonal Periodicity
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. It 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 allocation 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).
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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 9
3.6 Irrigation and water usage 9
3.7 Estimation of unlicensed dams 13
3.8 Environmental flows 14
4. MODEL DEVELOPMENT 16
4.1 Subarea delineation 16
4.2 Hydstra Model 16
4.2.1 Lake Llewellyn 18
4.3 AWBM Model 19
4.3.1 Channel Routing 21
4.4 Model Calibration 22
4.4.1 Model Accuracy – Fit Statistics and Visual Assessments 26
4.4.2 Model Accuracy throughout the catchment 27
4.4.3 Model Accuracy: Conclusions 33
4.5 Model results 34
4.5.1 Indices of hydrological disturbance 34
4.6 Flood frequency analysis 36
5. REFERENCES 37
5.1 Personal Communications 38
6. GLOSSARY 39
APPENDIX A 41
APPENDIX B 44
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LIST OF FIGURES
Figure 2-1 Subcatchment boundaries 3
Figure 3-1 Climate Drill Site Locations 6
Figure 3-2 Rainfall and Data Drill Comparisons 8
Figure 3-3 WIMS (Dec 2006) Water Allocations 12
Figure 4-1 Hydstra Model Schematic 17
Figure 4-2 Two Tap Australian Water Balance Model Schematic 21
Figure 4-3 Monthly Variation of CapAve Parameter (adapted from Flowerdale Model
(Willis 2007a)) 24
Figure 4-4 Long term average monthly, seasonal and annual comparison plot –
Flowerdale River (from Flowerdale DPIW Surface Water Model (Willis 2007a))
25
Figure 4-5 Long term average monthly, seasonal and annual comparison plot for
Sisters Creek (Modelled from 01/01/1968 – 01/01/2006) 25
Figure 4-6 Time Series of Monthly Volumes- SC4 flows plotted against Area- scaled
Flowerdale Observed flows 29
Figure 4-7 Time Series of Monthly Volumes- SC4 flows plotted against Area – and
Rainfall-Scaled Flowerdale Observed flows 29
Figure 4-8 Time Series of Monthly Volumes- SC3 flows plotted against Area- and
Rainfall-Scaled Flowerdale Observed flows 30
Figure 4-9 Time Series of Monthly Volumes- SC1 flows plotted against Area- and
Rainfall-Scaled Flowerdale Observed flows 31
Figure 4-10 Time Series of Daily Volumes- SC6 modelled flows plotted against Sisters
Creek flows Observed during 1991 33
Figure 4-11 Daily Duration Curve 34
Figure B-1 Forth catchment – monthly volumes at secondary site. 46
Figure B-2 George catchment – monthly volumes at secondary site. 46
Figure B-3 Leven catchment – monthly volumes at secondary site. 47
Figure B-4 Swan catchment – monthly volumes at secondary site. 47
Figure B-5 Montagu catchment – monthly volumes at secondary site. 48
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LIST OF TABLES
Table 3-1 Data Drill Site Locations 7
Table 3-2 Assumed Surety of Unassigned Records 9
Table 3-3 Sub Catchment High and Low Priority Entitlements 11
Table 3-4 Average capacity for dams less than 20 ML by Neal et al (2002) 14
Table 3-5 Environmental Flows 15
Table 4-1 Boughton & Chiew, AWBM surface storage parameters 19
Table 4-2 Hydstra/TSM Modelling Parameter Bounds 22
Table 4-3 Sisters Creek Model Parameters (adopted from Flowerdale Model (Willis
2007a)) 23
Table 4-4 Comparison of Flowerdale Model Parameters used Sisters Creek and model
parameters of other nearby catchments (Adapted from Willis 2007a, Peterson &
Willis 2007, Willis 2007b) 24
Table 4-5 Long term average monthly, seasonal and annual comparisons for Sisters
Creek 26
Table 4-6 Model Fit Statistics – Flowerdale River (adapted from Willis 2007a) 27
Table 4-7 Hydrological Disturbance Indices at the mouth of Sisters Creek 35
Table B-1 Model performance at secondary sites 49
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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 of the hydrological model (Australian Water Balance Model, AWBM) for the Sisters Creek catchment. No data were available to calibrate the model. The model parameters used for Sisters Creek have been taken directly from the DPIW surface water model developed for the adjoining Flowerdale 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 methods adopted, assumptions made, results of calibration and validation and description relating to the use of the developed hydrologic model and associated software.
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2. CATCHMENT CHARACTERISTICS
Sisters Creek is fed by a small catchment in north-western Tasmania. It flows northward
to Bass Strait where it discharges at the township of Sisters Beach, the only town within
the catchment. The 32.8 km2 Sisters Creek catchment is largely flat with some
topographical undulation in the North West. Elevation change is slight, varying from 300
m ASL in the south of the catchment to sea level at the Creek’s mouth.
Rocky Cape National Park covers about one-tenth of the catchment in the catchment’s
north, and this protected area is covered by native forest. Forested areas in the
catchment are not restricted to the national park, and in sum about a third of the
catchment is covered by native forest (chiefly medium density Eucalypt forest with a
dense understorey). The remainder of the catchment is largely devoted to agriculture. A
small amount of land near the mouth of Sisters Creek is urban (Sisters Beach Township).
Rocky Cape National Park contains a significant water storage: Lake Llewellyn. Lake
Llewellyn was commissioned in 1968 for use in recreation, and is managed by Tasmania
Parks and Wildlife Service. It stores up to 340 ML.
Annual rainfall does not vary significantly across the catchment owing to the catchment’s
small size, varying from 1400 mm in the south to 1200 mm in the catchment’s north.
There are 61 registered (current) entitlements for water extraction. These entitlements
are spread across all subareas except the two nearest the mouth of Sisters Creek
(subareas 1 and 11). Most of the extractions are for agriculture, although the largest
single entitlement is for Llewellyn Dam (340 ML), which is used as a public recreational
facility.
For modelling purposes, the Sisters Creek catchment was divided into 11 sub areas.
The delineation of these areas is shown in Figure 2-1.
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Figure 2-1 Subcatchment boundaries
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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).
QDNRM provides interpolated evaporation and rainfall data (called ‘climate DRILL data’)
at intervals of 0.05 o latitude and 0.05 o longitude (i.e., grid points on a grid of squares
approximately 5 by 5 km in size). This interpolated rainfall and evaporation data are
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
These data have a number of benefits over other sources of rainfall data including:
• Continuous data back to 1889. (However, for earlier dates there are fewer 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 from
1957 onward distribution is considered “good” but before 1957 site availability
may need to be checked in the study area);
• Evaporation data (along with a number of other climatic variables) are also
included and 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
CLIMARC project data, is available from 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 Sisters Creek catchment the evaporation data were examined and it was found
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that before 1970 the evaporation information is based on the long term daily averages of
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 coverage of the Sisters Creek
catchment. Because the Sisters catchment is small, and data DRILL sites are separated
by at least 5 km, eight of the DRILL sites were located outside (but near to) the
catchment. Three sites used were also used (and originally extracted for) the
Inglis/Flowerdale DPIW surface water model.
See Figure 3-1 below for a map of the climate Data Drill sites and Table 3-1 for the
location information.
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Figure 3-1 Climate Drill site locations
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Table 3-1 Data Drill site locations
Site Latitude Longitude
SISTERS_01 -40°54’00” 145°30’00”
SISTERS_02 -40°57’00” 145°30’00”
SISTERS_03 -40°57’00” 145°33’00”
SISTERS_04 -40°57’00” 145°36’00”
SISTERS_05 -41°00’00” 145°30”00”
SISTERS_06 -41°00’00” 145°33’00”
SISTERS_07 -41°57’00” 145°30’00”
INGFLOW_02 -41°00’00” 145°36’00”
INGFLOW_04 -41°03’00” 145°30’00”
INGFLOW_05 -41°03’00” 145°36’00”
3.4 Comparison of Data Drill rainfall and site gauges
As rainfall data are critical inputs to the model it is important to have confidence that the
Data Drill long term generated time series reflect what is being observed within the
catchment. Rainfall sites in close proximity to the Data Drill locations were sourced and
compared. The annual rainfall totals of selected Data Drill sites and neighbouring sites
for coincident periods are plotted Figure 3-2. The visual comparison and the R2 value
indicate that there appears to be good correlation for two sites which is to be expected as
the Data Drill information is derived from site data. However at a third site (TSM site
1543.1), the correlation with the nearest data drill site is poor, particularly for the earlier
part of the record. It is notable that this poor correlation exists for a record that ends in
the 1950s – it is expected that better correlation occurs in more recent years of record
(as it does at the two other sites shown).
Sis
ters
Cre
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urf
ace W
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Hydro
Tasm
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V
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Figure 3-2 Rainfall and Data Drill comparisons
R2 =
0.8
6
R2 =
0.5
8
R2 =
0.9
7
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3.5 Streamflow data
No streamflow data were available to calibrate the Sisters Creek catchment model.
Model parameters were adopted from the DPIW surface water model for the adjoining
Flowerdale catchment, and this is discussed in section 4.4.
3.6 Irrigation and water usage
Information on the current water entitlement allocations in the catchment was obtained
from DPIW from the Water Information Management System (WIMS Dec 2006). The
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 significant
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:
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
In total there were 741.7 ML unassigned entitlements (surety = 0) identified for inclusion
in the surface water model, of which 97 ML were assigned surety 1 and 644.7 ML
assigned surety 6.
DPIW staff also advised that the water extraction information provided should be filtered
to remove the following records:
• 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
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available for Low Priority entitlements after environmental flow requirements have been
met.
DPIW estimated direct extractions in excess of water licenses to be 718 ML per year.
This volume was apportioned to subareas according to the proportions of licensed direct
extractions in each subarea (in lieu of more detailed information to the contrary).
Allowances for unlicensed dam extractions are covered in Section 3.7.
A summary table of monthly entitlement volumes by subarea is provided below in Table
3-3 and in the Catchment User Interface. A map of the water allocations in the
catchment is shown in Figure 3-3.
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Table 3-3 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 0.0 0.0 0.0 0.0 0.9 0.8 0.9 0.9 0.8 0.0 0.0 0.0 4.2
SC2 16.7 15.1 16.7 16.1 8.3 8.0 8.3 8.3 8.0 16.7 16.1 16.7 154.9
SC3 0.0 0.0 0.0 0.0 0.3 0.3 0.3 0.3 0.3 0.0 0.0 0.0 1.4
SC4 19.1 17.2 19.1 18.5 1.7 1.6 1.7 1.7 1.6 19.1 18.5 19.1 138.9
SC5 10.7 9.6 10.7 10.3 1.7 1.6 1.7 1.7 1.6 10.7 10.3 10.7 81.3
SC6 57.3 51.7 57.3 55.4 2.6 2.5 2.6 2.6 2.5 57.3 55.4 57.3 404.2
SC7 0.0 0.0 0.0 0.0 1.1 1.1 1.1 1.1 1.1 0.0 0.0 0.0 5.6
SC8 0.0 0.0 0.0 0.0 0.3 0.3 0.3 0.3 0.3 0.0 0.0 0.0 1.4
SC9 0.0 0.0 0.0 0.0 0.6 0.5 0.6 0.6 0.5 0.0 0.0 0.0 2.8
SC10 9.5 8.6 9.5 9.2 0.9 0.8 0.9 0.9 0.8 9.5 9.2 9.5 69.5
SC11 0.0 0.0 0.0 0.0 1.1 1.1 1.1 1.1 1.1 0.0 0.0 0.0 5.6
Total 113.2 102.3 113.2 109.6 19.3 18.7 19.3 19.3 18.7 113.2 109.6 113.2 869.8
Low Priority
Entitlements
SC1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
SC2 5.5 5.0 5.5 5.4 45.9 44.4 45.9 45.9 44.4 45.9 44.4 5.5 344.0
SC3 0.0 0.0 0.0 0.0 2.9 2.8 2.9 2.9 2.8 2.9 2.8 0.0 20.0
SC4 8.3 7.5 8.3 8.0 27.1 26.2 27.1 27.1 26.2 27.1 18.8 8.3 219.9
SC5 4.3 3.9 4.3 4.2 24.0 23.3 24.0 24.0 23.3 24.0 23.3 4.3 187.0
SC6 45.5 41.1 42.4 35.8 28.9 27.9 28.9 28.9 27.9 28.9 27.9 45.2 409.2
SC7 0.0 0.0 0.0 0.0 16.2 15.6 16.2 16.2 15.6 16.2 15.6 0.0 111.5
SC8 28.9 26.1 28.9 27.9 28.9 27.9 28.9 28.9 27.9 28.9 27.9 28.9 340.0
SC9 0.0 0.0 0.0 0.0 1.4 1.3 1.4 1.4 1.3 1.4 1.3 0.0 9.5
SC10 6.5 5.8 6.5 6.3 19.3 18.7 19.3 19.3 18.7 19.3 10.1 6.5 156.0
SC11 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Total 99.1 89.5 96.0 87.6 194.4 188.2 194.4 194.4 188.2 194.4 172.3 98.7 1797.1
All
Entitlements
SC1 0.0 0.0 0.0 0.0 0.9 0.8 0.9 0.9 0.8 0.0 0.0 0.0 4.2
SC2 22.2 20.1 22.2 21.5 54.2 52.4 54.2 54.2 52.4 62.6 60.6 22.2 498.9
SC3 0.0 0.0 0.0 0.0 3.2 3.1 3.2 3.2 3.1 2.9 2.8 0.0 21.4
SC4 27.4 24.8 27.4 26.5 28.8 27.8 28.8 28.8 27.8 46.1 37.3 27.4 358.8
SC5 15.0 13.5 15.0 14.5 25.7 24.9 25.7 25.7 24.9 34.7 33.6 15.0 268.3
SC6 102.8 92.8 99.7 91.2 31.4 30.4 31.4 31.4 30.4 86.1 83.3 102.4 813.4
SC7 0.0 0.0 0.0 0.0 17.3 16.7 17.3 17.3 16.7 16.2 15.6 0.0 117.1
SC8 28.9 26.1 28.9 27.9 29.2 28.2 29.2 29.2 28.2 28.9 27.9 28.9 341.4
SC9 0.0 0.0 0.0 0.0 1.9 1.9 1.9 1.9 1.9 1.4 1.3 0.0 12.3
SC10 16.0 14.5 16.0 15.5 20.1 19.5 20.1 20.1 19.5 28.8 19.3 16.0 225.5
SC11 0.0 0.0 0.0 0.0 1.1 1.1 1.1 1.1 1.1 0.0 0.0 0.0 5.6
Total 212.3 191.8 209.2 197.2 213.8 206.9 213.8 213.8 206.9 307.7 281.9 212.0 2666.9
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Figure 3-3 WIMS (Dec 2006) Water allocations
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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 is 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
the following method:
• Aerial photographs (dates unknown) supplied by DPIW were analysed.
These photographs did not cover the entire area of the catchment: only 6 of
11 subareas were completely covered. Farm dams were detected by eye
and counted for every subarea that was totally covered by the photographs.
The number of dams of any size was counted in each of the 6 visible
subareas. The number of unlicensed dams could be determined by
subtracting the licensed dams information: 17 unlicensed storages were
identified in 6 subareas.
• Using this information a ratio of unlicensed to licensed dams was
determined. For the 6 subareas that were counted the ratio of unlicensed :
licensed dams was 0.78. It was assumed that this ratio would be the same
across the catchment. This assumption is validated by the similar
unlicensed:licensed dam ratio of 1.1 calculated for the adjoining
Inglis/Flowerdale catchment, indicating that this ratio is reasonably
consistent across catchments in this region. The Sisters Creek
unlicensed:licensed dam ratio was then used to estimate the number of
unlicensed dams in uncounted sub-catchments: the catchment has a total
of 50 licensed storages, and thus an estimated 39 unlicensed dams (50 *
0.78 = 39).
• Difficulties in detecting farm dams from aerial photography by eye are
compounded when photography is not of suitably high resolution.
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, it was assumed that the number of false
detections is countered by the number of missed detections, and in the
absence of another suitably rapid method the approach was considered
acceptable.
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• 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.
• 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 also
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 3-4).
• Assuming this dam size distribution is similar to the distribution of the study
catchment in South Australia, the total volume of unlicensed dams can be
estimated as 54.6 ML (39 * 1.4ML). This equates to 1.66 ML of unlicensed
dams/km2. The total volume of existing permitted extractions for storages
in the study catchment is 1567.3 ML. Therefore the 54.6 ML of unlicensed
dams equates to 3.4% of the total dam extractions from the catchment.
Table 3-4 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
3.8 Environmental flows
Scenario 3 was to account for environmental flows within the catchment. DPIW advised
that for Sisters Creek 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 scenario 1 and the environmental flow would be
assumed to be:
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• 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).
Modelled – No entitlements (Natural) scenario was run from 01/01/1900 to 01/01/2006.
A summary table of the environmental flows on a monthly breakdown by sub-catchment
is provided below in Table 3-3 and in the Catchment User Interface.
Table 3-5 Environmental Flows
Catch-ment area (km
2)
Environmental Flow (ML/d) Per Month at each subcatchment
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Average
SC1 1.5 3.5 2.9 3.1 5.9 7.4 18.2 34.9 43.8 31.1 15.1 13.6 7.4 15.6
SC2 4.9 0.6 0.5 0.6 1.2 1.4 3.3 5.9 7.6 5.5 2.6 2.4 1.5 2.8
SC3 1.0 1.9 1.6 1.7 3.2 4.1 10.7 20.3 25.6 18.5 8.8 7.8 4.2 9.0
SC4 7.3 0.7 0.6 0.6 1.2 1.6 4.5 8.3 10.1 7.5 3.3 3.2 1.7 3.6
SC5 3.0 0.4 0.3 0.3 0.7 0.7 1.9 3.4 4.4 3.1 1.5 1.4 0.8 1.6
SC6 5.1 1.4 1.2 1.3 2.3 3.1 8.5 16.0 20.1 14.2 6.8 5.9 3.3 7.0
SC7 2.5 0.2 0.2 0.2 0.4 0.5 1.5 2.8 3.4 2.4 1.1 0.9 0.5 1.2
SC8 0.6 3.3 2.7 3.0 5.6 7.0 17.4 33.4 41.7 29.7 14.4 13.0 7.0 14.9
SC9 1.8 2.8 2.3 2.5 4.8 5.9 15.1 28.0 35.2 25.8 12.3 11.2 6.0 12.6
SC10 5.2 0.4 0.4 0.4 0.7 1.0 2.2 4.7 5.6 3.7 2.0 1.6 0.9 2.0
SC11 1.1 0.1 0.1 0.1 0.2 0.2 0.5 1.0 1.2 0.8 0.4 0.4 0.2 0.4
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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4. MODEL DEVELOPMENT
4.1 Subarea delineation
Subarea 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 subarea boundaries,
generalises geophysical parameters and provides in-depth analysis tools to examine and
compare the hydrologic properties of subareas. 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 subarea networks.
For the purpose of this project, CatchmentSIM was used to delineate the catchment
area, break it up into numerous subareas, determine their sizes 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 Sisters
Creek subareas, 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 subarea, through the catchment via a channel routing
function.
The rainfall and evaporation are calculated for each subarea 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 subarea. 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 was used to calculate the runoff for each
subarea separately. This was chosen over the usual method of a single AWBM model
for the whole catchment as it more accurately distributes the runoff and base flow
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
17
spatially over the catchment.
The flow is routed between each subarea through the catchment via a channel routing
function.
Figure 4-1 Hydstra Model schematic
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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4.2.1 Lake Llewellyn
A significant storage - Lake Llewellyn - was identified during the creation of the Sisters
Creek catchment model in subarea SC8. Lake Llewellyn is managed by Tasmania
Parks and Wildlife and only has an influence on the flow regime of Sisters Creek of one
downstream subarea (SC1). No information relating to historic lake discharges was
identified. Discussions with DPIW staff on the appropriate way to model this lake
resulted in the following decisions:
• Scenario 1 will model the catchment with no dam or lake present for all of record.
• Both Scenarios 2 and 3 will model the catchment with:
o No dam or lake present in the model prior to and during its construction in
1967.
o From 1968 onwards, the lake will be modelled using a basic volume
balance rule assuming the following:
� Lake volume will be 340 ML (from DPIW dams database) and at
full supply level at start of model;
� Water entitlements falling within the Lake Llewellyn subarea (SC8)
will be extracted from the lake volume;
� Inflows in excess of the lake volume will be discharged
downstream as spill;
� If Scenario 3 is selected then a flow will be released downstream
equal to the environmental flow specified in the user interface for
the Lake Llewellyn subarea (SC8). However when the modelled
inflow to SC8 is less than the specified environmental flow, the
downstream release will be reduced to equal SC8 inflow. This
has been done to stop excessive draw down of the lake in periods
of low inflow.
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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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
& Chiew, 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 given in Table 4-1.
Table 4-1 Boughton & Chiew, AWBM surface storage parameters
Partial area of smallest store A1=0.134
Partial area of smallest store A2=0.433
Partial area of smallest store A3=0.433
Capacity of smallest store C1=(0.01*Ave/A1)=0.075*Ave
Capacity of smallest store C2=(0.33*Ave/ A2)=0.762*Ave
Capacity of smallest store C3=(0.66*Ave/ A3)=1.524*Ave
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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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 subarea. 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.
Although the AWBM accounts for base-flow, it is not intended that the AWBM be used to
predict base-flow contribution within catchments. Base-flow in the AWBM routine is used
as a fit parameter to obtain a good recession of surface water hydrographs. The AWBM
does not specifically account for attributes that affect baseflow such as geology and inter-
catchment groundwater transfers.
The AWBM processes are shown below in Figure 4-2. Further information on the 2 tap
variant of the AWBM model is provided in Parkyn & Wilson (1997).
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
21
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
Sisters Creek Surface Water Model Hydro Tasmania Version No: 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. e.g. αfl where fl is a length factor.
Parameters required by Hydstra/TSM Modelling and their legal bounds are given in
Table 4-2.
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 streamflow records of Sisters Creek of sufficient duration were available to calibrate
the Model. Model parameters used to calibrate the Flowerdale River component of the
Inglis/Flowerdale DPIW surface water model were adopted for this model as the
Flowerdale River catchment adjoins Sisters Creek catchment.
Calibration of the Inglis/Flowerdale model was achieved by adjusting model parameters
by comparing the monthly, seasonal and annual volumes. A generalised calibration
method is presented in APPENDIX A. This process is detailed in the Inglis/Flowerdale
DPIW surface model report (Willis, 2007a). The adopted model parameters are shown in
Table 4-3.
In the absence of other data, the model parameters used for the Flowerdale catchment
model are assumed to be valid for the Sisters Catchment model. The geographical
proximity of the two catchments implies similar climatic and environmental regimes
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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(notably soil and vegetation types). A visual inspection of maps shows that the Sisters
Creek and Flowerdale catchments have similar topography. Land use in both
catchments is also similar: both catchments are dominated by agriculture and natural
forested areas, with only small proportions of both catchments dedicated to urban use.
Further, the calibration parameters for two other nearby surface water models, Leven &
Gawler and Claytons, are very similar to that of Flowerdale (Table 4-4). The
consistency of model parameters in models for Catchments surrounding Sisters Creek
further validates the assumption that adopting the Flowerdale model parameters for the
Sisters Creek model will result in a reasonable approximation of actual flows in Sisters
Creek. Thus the assumption that both catchments will share hydrological
characteristics (and hence model parameters) is justified.
Modelled flow volumes at the mouth of Sisters Creek (subarea SC1) under two
scenarios are shown in Table 4-5 and Figure 4-5: 1) flow volumes accounting for all
licensed and unlicensed water extractions but not for environmental flows (labelled
Modelled – with entitlements), and 2) flow volumes that do not account for any water
extractions or environmental flows (labelled Modelled – natural). There is considerable
discrepancy in monthly volumes between the two scenarios. This reflects the high
level of demand for water relative to flow volumes in Sisters Creek.
Table 4-3 Sisters Creek Model Parameters (adopted from Flowerdale Model
(Willis 2007a))
PARAMETER Flowerdale VALUE
INFBase 0.75
K1 0.96
K2 0.98
GWstoreSat 70
GWstoreMax 100
H_GW 90
EvapScale 1
Alpha 3
n 0.8
CapAve Variable
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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0
50
100
150
200
250
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month
CapAve
Figure 4-3 Monthly Variation of CapAve Parameter (adapted from Flowerdale
Model (Willis 2007a))
Table 4-4 Comparison of Flowerdale Model Parameters used Sisters Creek and
model parameters of other nearby catchments (Adapted from Willis 2007a,
Peterson & Willis 2007, Willis 2007b)
PARAMETER Flowerdale
value Claytons Value
Leven Value
Gawler Value
INFBase 0.75 0.8 0.75 0.75
K1 0.96 0.96 0.97 0.95
K2 0.98 0.995 0.98 0.98
GWstoreSat 70 160 70 70
GWstoreMax 100 200 100 100
H_GW 90 80 90 90
EvapScale 1 1 1 1
Alpha 3 3 3 3
n 0.8 0.8 0.8 0.8
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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0
100
200
300
400
500
600
700
Ja
n
Fe
b
Ma
r
Ap
r
Ma
y
Ju
n
Ju
l
Au
g
Se
p
Oct
No
v
De
c
WIN
TE
R
SU
MM
ER
AN
NU
AL
Average Flow (ML/Day)
Observed
Modelled Calibration Flow
Scenario 1 (Natural)
Demand
Figure 4-4 Long term average monthly, seasonal and annual comparison plot –
Flowerdale River (from Flowerdale DPIW Surface Water Model (Willis 2007a))
0
10
20
30
40
50
60
70
80
90
100
Ja
n
Fe
b
Ma
r
Ap
r
Ma
y
Ju
n
Ju
l
Au
g
Se
p
Oct
No
v
De
c
WIN
TE
R
SU
MM
ER
AN
NU
AL
Average Flow (ML/Day)
Modelled Calibration Flow
Scenario 1 (Natural)
Demand
Figure 4-5 Long term average monthly, seasonal and annual comparison plot for
Sisters Creek (Modelled from 01/01/1968 – 01/01/2006)
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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Table 4-5 Long term average monthly, seasonal and annual comparisons for
Sisters Creek
Long term Averages (ML/Day)
MONTH Modelled-Calibration
Flow (MCF)1
Scenario 1 “Modelled -- No Entitlements (Natural)” Demand
January 7.47 12.02 6.85
February 6.45 10.64 6.85
March 7.33 11.48 6.75
April 19.41 24.54 6.57
May 27.86 33.93 6.90
June 41.90 48.61 6.90
July 62.60 69.50 6.90
August 80.31 87.16 6.90
September 60.70 67.53 6.90
October 42.47 51.78 9.93
November 24.35 32.50 9.40
December 13.96 19.66 6.84
WINTER 52.64 59.75 7.40
SUMMER 13.16 18.47 7.21
ANNUAL 32.90 39.11 7.30
WINTER from May to Oct, SUMMER from Nov - Apr.
4.4.1 Model Accuracy – Fit Statistics and Visual Assessments
It is an assumption of the Sisters model that the calibration parameters of the adjacent
Inglis/Flowerdale catchment model are appropriate for the Sisters catchment. The
calibration for the Inglis/Flowerdale River catchment model resulted in good replication
of observed streamflows, as evidenced by high coefficients of determination (R2
values) (Table 4-6) and low proportional differences between observed and modelled
flows (Willis 2007a). Annual hydrographs were judged to have fair-to good replication
of observed flows, and modelled flow volumes showed excellent fidelity to observed
flow volumes (Figure 4-4). Calibration of the Inglis/Flowerdale catchment is discussed
in detail by Willis (2007a).
However, the accuracy of the Inglis/Flowerdale surface water model does not
necessarily give an indication of the performance of the Sisters Creek model. While
Sisters Creek lies in close proximity to the Flowerdale River, differences in catchment
characteristics (not least the considerable discrepancy in size) mean that the use of
Flowerdale model parameters in the Sisters Creek model may not be appropriate.
Without the verification of a lengthy, reliable flow record, it is simply not possible to
make this judgment.
1 Refer to page 41 for explanation of this modelling scenario.
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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Table 4-6 Model Fit Statistics – Flowerdale River (adapted from Willis 2007a)
Measure of Fit Flowerdale River at
Moorleah
Daily coefficient of determination (R2 value) 0.74
Monthly coefficient of determination (R2 value) 0.91
Difference in observed and estimated long term
annual average flows +0.45%
4.4.2 Model Accuracy throughout the catchment
The Sisters Creek model uses the Flowerdale calibration fit and this model was
calibrated to provide a good simulation of monthly and seasonal flow volumes at the
calibration site. Calibration sites were low in the Flowerdale catchment to encompass
as much of the catchment as possible. It is difficult to assess how reliably the model
performs throughout the catchment, although it is assumed that the 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 Sisters Creek Model) to simulate
flows throughout these catchments was assessed. These assessments are detailed in
Appendix B. These analyses suggest that on average the models predict volumes well
throughout their catchments (see Appendix B). The Inglis and Flowerdale model
performed consistently throughout the catchment (Willis 2007a). A detailed description
of the Inglis and Flowerdale surface flow model’s performance throughout its
catchment is available in Willis (2007a).
As there was only a very limited observed flow record available for Sisters Creek, the
reliability of the model throughout the catchment could not be tested directly. As the
Sisters Creek model adopted the parameters of the Inglis and Flowerdale model, the
record used to calibrate the Flowerdale Catchment (Flowerdale at Moorleah, TSM site
14215) was used to derive a proxy ‘observed’ record with which to test the Sisters
model. The Flowerdale calibration record scaled by a factor of 0.8 to account for
differences in rainfall between the two catchments, calculated from the ratio of the
catchment centroid mean annual rainfall obtained from a mean annual rainfall isohyetal
map. The Flowerdale calibration record was also scaled by area to approximate
‘observed records at 3 subcatchments in the Sisters catchment. These proxy records
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
28
were compared to modelled calibration flows (MCFs)2 for three subcatchments, SC4,
SC2, and SC1, located high, mid and low in the Sisters catchment, respectively.
Comparison of Flowerdale scaled observed record and subcatchment 4
The area ratio of SC4 to the observed data was calculated to be 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 Figure
4-6. Considering the uncertainties and difficulty in generating a scaled observed trace,
the results appear reasonable, although the MCF is noticeably lower than the scaled
observed flow. This is unsurprising, as Sisters Creek catchment is not exposed to the
high rainfalls of Tasmania’s northern highlands that feed the Flowerdale catchment. To
account for differences in rainfall between the Flowerdale and Sisters catchments a
rainfall scaling factor of 0.8 was calculated from the ratio of the catchment centroid
mean annual rainfall obtained from a mean annual rainfall isohyetal map. When the
observed data are scaled for area and rainfall, the traces appear noticeably closer
(Figure 4-7), and the comparison is more useful (the remaining plots show only proxy
records that have been scaled for area and rainfall). However, the MCF trace is still
lower than the scaled observed trace. This difference may be attributable to the fact
that water extractions in the Sisters Creek catchment are proportionally much higher
than those of the Flowerdale catchment. These proportionally higher extractions will
not be present in the scaled Flowerdale observed record.
2 A time period reduction factor (TPRF) of 0.5 was applied to water entitlements to generate the
MCF - see Glossary, and 0 for an explanations of MCF and TPRF
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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0
500
1000
1500
2000
2500
1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989
Monthly Volume (ML)
Area-scaled Observed
SC4 MCF (TPRF = 0.5)
R2 = 0.59
Figure 4-6 Time Series of Monthly Volumes- SC4 flows plotted against Area-
scaled Flowerdale Observed flows
0
200
400
600
800
1000
1200
1400
1600
1800
2000
1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989
Monthly Volume (ML)
Area- and rain-scaled Observed
SC4 MCF (TPRF = 0.5)
R2 = 0.59
Figure 4-7 Time Series of Monthly Volumes- SC4 flows plotted against Area –
and Rainfall-Scaled Flowerdale Observed flows
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
30
Comparison of Flowerdale scaled observed record and subcatchment 3
The area ratio of SC3 to the observed data was calculated to be 16 %. The observed
monthly volumes at the calibration site were multiplied by this ratio and the rainfall
scaling factor of 0.8 in order to calculate a proxy ‘observed’ record at the catchment
outflow. The results are shown in Figure 4-8. Again, the Sisters Creek MCF is lower
than the scaled Flowerdale flow, which is attributable to the higher water extractions in
the Sisters catchment.
This 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, as well as accounting for water
extractions for each catchment, thus the modelled flow prediction will not be
disadvantaged by rainfall spatial variation.
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989
Monthly Volume (ML)
Area- and rain-scaled Observed
SC3 MCF (TPRF = 0.5)
R2 = 0.61
Figure 4-8 Time Series of Monthly Volumes- SC3 flows plotted against Area- and
Rainfall-Scaled Flowerdale Observed flows
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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Comparison of Flowerdale scaled observed record and subcatchment 1
The area ratio of SC1 to the observed data was calculated to be 22 %. The observed
monthly volumes at the calibration site were multiplied by this ratio and the rainfall
scaling factor of 0.8 in order to calculate a proxy ‘observed’ record at the catchment
outflow. The results are shown in Figure 4-9. Again, the Sisters Creek MCF is lower
than the scaled Flowerdale flow, which is attributable to higher water extractions in the
Sisters catchment.
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989
Monthly Volume (ML)
Area- and rain-scaled Observed
SC1 MCF (TPRF = 0.5)
R2 = 0.64
Figure 4-9 Time Series of Monthly Volumes- SC1 flows plotted against Area- and
Rainfall-Scaled Flowerdale Observed flows
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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Comparison of Sisters observed record and subcatchment 6
A short term flow record is available for Sisters Creek (TSM site 14241) for the first 6
months of 1991. This record is neither long nor reliable enough for calibration
purposes, but serves to help assess the reliability of the model. The flow record was
recorded near at the outflow of SC6, and hence modelled flows from this subarea were
compared to the observed flow (Figure 4-10). There is poor agreement between
observed and the MCF (TPRF = 0.5) modelled under scenario 2 (with entitlements
extracted), where the MCF volumes are notably lower than observed flows. There is a
better match between observed flow volumes and MCF (TPRF = 0.5) under scenario 1
(natural flows), although even under this scenario MCF flow volumes are substantially
lower than observed volumes. Without a longer and more reliable flow record it is
impossible to confidently explain these discrepancies. However, these differences are
likely due to one or more of the following:
• Water extractions in Sisters catchment are a substantial proportion of total flow
(up to 50 % in some months). As noted, a number of assumptions were made
to calculate water entitlements. If any of these assumptions used to estimate
water extractions from the catchment are inaccurate (e.g. estimate of average
dam size, the temporal distribution of extractions), this will have a large impact
on the modelled flows of Sisters Creek;
• There is the possibility that the observed flows are higher than modelled
because they are being augmented by groundwater flows. The hydrograph
recession periods in the observed record indicate there is a steady baseflow in
Sisters Creek;
• The coarse nature of the rainfall spatial distribution information may lead to a
misrepresentation of the rainfall on the Sisters Creek catchment. The data
DRILL sites used as rainfall input into the model cover a much larger area than
the size of the catchment itself. Discrepancies due to temporal differences in
rainfall are evident in Figure 4-10, notably in the modelled peak flow in
February, which presents a significantly different temporal response in the
observed flow;
• Some of this disagreement may be due to inaccuracies in the flow record at site
14241. As previously stated there are serious doubts about both the reliability of
the observed data and the associated flow rating at site 14241;
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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• It is possible that the Flowerdale calibration parameters are not appropriate for
use on the Sisters Creek catchment. The Flowerdale catchment is much larger,
and is on average a slightly steeper catchment. This may lead to the model
yielding faster response times (i.e. being ‘peakier’) than may occur in reality.
0
5
10
15
20
25
30
35
40
45
Jan Feb Mar Apr May Jun
1991
Monthly Volume (ML)
Sisters Creek observed flow record (TSM site 14241)
SC6 Under Scenaro 1
SC6 Scenario 2 MCF (TPRF = 0.5)
Figure 4-10 Time Series of Daily Volumes- SC6 modelled flows plotted against
Sisters Creek flows observed during 1991
4.4.3 Model Accuracy: Conclusions
The inaccuracy of the model during the only period of record available indicates that
this model should be used with caution. Modelled flows are, in all cases, lower than
comparable observed or proxy records. The transfer of model parameters from the
Flowerdale model may not be suitable for the Sisters Catchment, but have been
applied as a necessity in the absence of better information. Further, in the Sisters
catchment water entitlements are a substantial proportion of flow (as much as 50 % for
some months). Possible inaccuracies in the calculation of water entitlements (e.g. the
assumption of 1.4 ML average dam size may not hold) can lead to large differences in
modelled flows. In the absence of a lengthy, reliable flow record, any conclusions
drawn about the suitability and accuracy of the model are necessarily uncertain. It is
recommended that DPIW consider the installation of a flow measurement site in the
Sisters Creek catchment in order to provide greater surety in the availability of water in
this catchment. This would be a prudent course of action in light of the substantial
water entitlements in the Sisters Creek catchments (as much as 50 % of available
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
34
volume in some months). Additionally, the collection of such information will allow the
Sisters Creek model to be more reliably calibrated.
4.5 Model results
The completed model and user interface allows data for three catchment demand
scenarios to be generated;
• Scenario 1 - Natural Flow
• Scenario 2 - Entitlements (river flows with water entitlements extracted)
• Scenario 3 - Entitlements and Environmental Flows (a scenario modelling
environmental flows with all extractions included)
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.
Outputs of daily flow duration curves and indices of hydrological disturbance at the mouth
of Sisters Creek (SC1) are presented below and in the following section. The outputs
are a comparison of scenario 1 (natural) and scenario 3 (environmental flows with all
extractions included) for period 01/01/1900 to 01/01/2006.
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 4-11 Daily Duration curve
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:
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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• Hydrological Disturbance Index;
• Index of Mean Annual Flow;
• Index of Flow Duration Curve Difference;
• Index of Seasonal Periodicity;
• Index of Seasonal Amplitude;
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 the mouth of Sister
Creek (subarea SC1), comparing scenario 1 (natural) and scenario 3 (environmental
flows with all extractions included) for period 01/01/1900 to 01/01/2006.
Table 4-7 Hydrological Disturbance Indices at the mouth of Sisters Creek
Disturbance Indices Values
undisturbed
(natural flow)
SC4 (High
in
Catchment)
SC3 (Mid
Catchment)
SC1
(Catchment
Outflow)
Index of Mean Annual Flow, A 1.00 0.92 0.88 0.88
Index of Flow Duration Curve
Difference, M 1.00 0.70 0.60 0.66
Index of Seasonal Amplitude, SA 1.00 0.86 0.77 0.81
Index of Seasonal Periodicity, SP 1.00 1.00 0.92 0.92
Hydrological Disturbance Index, HDI 1.00 0.83 0.76 0.79
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.
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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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
As no observed data were available for Sisters Creek, a comparison plot of modelled
and observed flood frequencies was not possible.
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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5. 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.
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.
Parkyn R & Wilson D, (1997) Paper: Real-Time Modelling of the Tributary Inflows to
ECNZ's Waikato Storages. Published in 24th Hydrology & Water Resources
Symposium Proceedings Auckland NZ 1997.
Peterson, J and Willis, M (2007) DPIW – Surface Water Models: Claytons Catchment.
Report to DPIW. Hydro Tasmania Consulting Document Number WR 2007/003.
State of the Environment Report, Tasmania, Volume 1 Conditions & Trends 1996. State
of Environment Unit, Lands Information Services, DELM.
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
38
SKM (2005) Development and Application of a Flow Stress Ranking Procedure, report
to Department of Sustainability and Environment, Victoria.
Willis, M (2007a) DPIW – Surface Water Models: Inglis and Flowerdale Catchment.
Report to DPIW. Hydro Tasmania Consulting Document Number WR 2007/004.
Willis, M (2007b). DPIW – Surface Water Models: Leven and Gawler Catchment.
Report to DPIW. Hydro Tasmania Consulting Document Number WR 2007/008.
5.1 Personal Communications
Graham, B. Section Head, Ecohydrology, Water Assessment, DPIW. March-April 2007.
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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6. 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.
Sisters Creek Surface Water Model Hydro Tasmania Version No: 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 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.
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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APPENDIX A
Generalised Model Calibration Method
Calibration 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 = 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
No streamflow records of Sisters Creek of sufficient duration were available to calibrate
the Model. Model parameters used to calibrate the Flowerdale River component of the
Inglis/Flowerdale DPIW surface water model were adopted for this model as the
Flowerdale River catchment adjoins Sisters Creek catchment.
The Flowerdale catchment calibration used observed records from Flowerdale at
Moorleah (TSM site 14215) from 23/03/1966 to 28/01/2007. The Inglis catchment
calibration used observed records from Inglis above Flowerdale (TSM site 14210) from
08/06/1967 to 07/02/1989.
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
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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50% of the current extractions if the mid year of the calibration period was earlier than
1994. A TPRF of 50% was applied to both the Inglis River above Flowerdale and
Flowerdale River at Moorleah calibration sites as the mid years of the calibration periods
were 1978 and 1987, respectively.
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
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.
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.
Two sets of CapAve profiles were applied across the catchment to achieve an optimum
volume balance at each calibration location. The adopted name and extent of each
CapAve parameter is itemized below.
• CapAve: All of the Inglis River catchment and individual (separate) streams
to the east of the Inglis River.
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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• CapAve_F: All of the Flowerdale River catchment
To achieve a good fit at both the calibration locations, it was also necessary to vary some
of the other calibration parameters from one location to the next. The adopted name and
extent of each location specific parameter is itemized below.
• INFbase, K1, K2, GWstoreSat & GWstoreMax: All of the Inglis River catchment and
individual (separate) streams to the east of the Inglis River.
• INFbase_F, K1_F, K2_F, GWstoreSat_F & GWstoreMax_F: All of the Flowerdale
River catchment.
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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APPENDIX B
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
Table B -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
Sisters Creek Surface Water Model Hydro Tasmania Version No: 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 that the confirm
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 B-1 to Figure B-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.
Sisters Creek Surface Water Model Hydro Tasmania Version No: 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 B-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 B-2 George catchment – monthly volumes at secondary site.
Sisters Creek Surface Water Model Hydro Tasmania Version No: 1.1
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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 B-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 B-4 Swan catchment – monthly volumes at secondary site.
Sisters Creek Surface Water Model Hydro Tasmania Version No: 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 B-5 Montagu catchment – monthly volumes at secondary site.
Sis
ters
Cre
ek S
urf
ace W
ate
r M
od
el
Hydro
Tasm
ania
V
ers
ion N
o: 1.1
49
Table B -1 Model perform
ance at secondary sites
Catch-
ment
Calibration Site
Primary Site
Secondary Site
Correlation A
Correlation B
Correlation C
Correlation D
Name
Site Name
& No.
Sub-
Catchment
Location
Catchment
Area
Km
2
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
Fort
h
Fort
h a
t P
alo
ona
Bridge –
S
ite 3
86
SC
33
1079.6
01/0
1/1
963 t
o
01/0
3/1
969
Fort
h R
iver
above
Lem
onth
ym
e –
site 4
50
SC
31
310.2
0.2
873
0.9
7
0.9
5
0.9
5
0.9
7
Georg
e
Georg
e
Riv
er
at S
H
WS
– S
ite
2205
SC
2
397.9
01/0
3/1
983 t
o
01/1
0/1
990
Ransom
Rv
at S
weet
Hill
– S
ite
2217
SC
3
26.1
0.0
656
0.9
1
0.9
6
0.8
6
0.8
3
Leven
Leven a
t B
annons
Bridge –
S
ite14207
SC
4
496.4
01/0
4/1
983 t
o
01/0
9/1
994
Leven a
t M
ayday R
d
– s
ite 8
21
SC
6
37.5
0.0
755
0.9
3
0.8
7
0.8
8
0.9
2
Sw
an
Sw
an R
iver
at
Gra
nge –
S
ite 2
200
SC
20
465.9
01/0
7/1
983 t
o
01/1
0/1
996
Sw
an R
iver
u/s
H
ard
ings
Falls
– s
ite
2219
SC
4
35.6
0.0
764
0.9
2
0.9
5
0.8
2
0.8
5
Monta
gu
Monta
gu a
t M
onta
gu
Rd B
rdge –
S
ite 1
4200
SC
3
325.9
01/0
1/1
985 t
o
01/0
1/1
990
Monta
gu a
t T
ogari –
S
ite 1
4216
SC
2
135.4
0.4
155
0.9
8
0.9
8
0.9
5
0.9
4