DPIW – SURFACE WATER MODELS MERSEY RIVER CATCHMENT Mersey River Surface Water Model Hydro Tasmania Version No: 1.1 DOCUMENT INFORMATION JOB/PROJECT TITLE Surface Water Hydrological Models for DPIW CLIENT ORGANISATION Department of Primary Industries and Water CLIENT CONTACT Bryce Graham DOCUMENT ID NUMBER WR 2007/027 JOB/PROJECT MANAGER Mark Willis JOB/PROJECT NUMBER E200690/P202167 Document History and Status Revision Prepared Reviewed Approved Date Revision by by by approved type 1.0 J. Bennett Dr Fiona C. Smythe July 2007 Final Ling 1.1 J. Bennett Dr Fiona C. Smythe July 2008 Final Ling Current Document Approval PREPARED BY James Bennett Water Resources Mngt Sign Date REVIEWED BY Dr Fiona Ling Water Resources Mngt Sign Date APPROVED FOR Crispin Smythe SUBMISSION Water Resources Mngt Sign Date Current Document Distribution List Organisation Date Issued To DPIW July 2008 Bryce Graham The concepts and information contained in this document are the property of Hydro Tasmania. This document may only be used for the purposes of assessing our offer of services and for inclusion in documentation for the engagement of Hydro Tasmania. Use or copying of this document in whole or in part for any other purpose without the written permission of Hydro Tasmania constitutes an infringement of copyright. i Mersey River Surface Water Model Hydro Tasmania Version No: 1.1 EXECUTIVE SUMMARY This report describes the results of the hydrological model developed for the Mersey River catchment in central-north Tasmania. This report is one of a series of reports that present the methods and results from the development and calibration of surface water hydrological models for 26 Tasmanian catchments under both current and natural flow conditions. A catchment flow model was developed for the Mersey River, and run under 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 of these model runs allowed the calculation of indices of hydrological disturbance. These indices were: • 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 formulas developed for the Natural Resource Management (NRM) Monitoring and Evaluation Framework developed by SKM for the Murray-Darling Basin (MDBC 08/04). A user interface is provided that allows the model to be run under varying scenarios. For information on the use of the user interface refer to the Operating Manual for the NAP Region Hydrological Models (Hydro Tasmania 2004a). This allows the user to see what effect additional extractions can have on the availability of water in the Mersey catchment. The interface provides summaries of flow statistics, duration curves, hydrological indices and water entitlements data for each subarea of the catchment. For information on the use of the user interface refer to the Operating Manual for the NAP Region Hydrological Models (Hydro Tasmania 2004b). ii Mersey River Surface Water Model Hydro Tasmania Version No: 1.1 CONTENTS EXECUTIVE SUMMARY ii 1. INTRODUCTION 1 2. CATCHMENT CHARACTERISTICS 2 3. DATA COMPILATION 4 3.1 Climate data (Rainfall & Evaporation) 4 3.2 Advantages of using climate DRILL data 4 3.3 Transposition of climate DRILL data to local catchment 5 3.4 Comparison of Data Drill rainfall and site gauges 7 3.5 Streamflow data 9 3.6 Irrigation and water use 9 3.7 Estimation of unlicensed dams 17 3.8 Environmental flows 19 4. MODEL DEVELOPMENT 22 4.1 Catchment Subarea Delineation 22 4.2 Hydstra Model 22 4.2.1 Accounting for Mersey Hydro Electric Scheme 23 4.3 AWBM Model 26 4.3.1 Channel Routing 29 4.4 Model Calibration 29 4.4.1 Accounting for flow diversions on the Mersey River 29 4.4.2 Calibration Method 30 4.4.3 Adopted Model Parameters 31 4.4.4 Model accuracy: Qualitative description 33 4.4.5 Factors affecting the reliability of the model calibration 37 4.4.6 Model Accuracy – Model fit statistics 39 4.4.7 Model Accuracy throughout the Mersey catchment 44 4.5 Model results 45 4.5.1 Indices of hydrological disturbance 46 4.6 Flood frequency analysis 49 5. REFERENCES 50 5.1 Personal Communications 51 6. GLOSSARY 52 iii Mersey River Surface Water Model Hydro Tasmania Version No: 1.1 LIST OF FIGURES Figure 2-1 Mersey catchment subarea 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 in the Mersey Catchment 16 Figure 4-1 Hydstra Model Schematic 25 Figure 4-2 Two-tap Australian Water Balance Model Schematic 28 Figure 4-3 Monthly Variation of CapAve Parameter 33 Figure 4-4 Daily time series - typical year (ML/d). Good fit 34 Figure 4-5 Daily time series – low inflow year (ML/d). Good fit. 34 Figure 4-6 Daily time series comparison – high inflow year (ML/d). Good fit. 35 Figure 4-7 Monthly Time Series comparison – Volume (ML) 35 Figure 4-8 Long term average monthly, seasonal and annual flows 36 Figure 4-9 Duration curve – MCF Daily flow proportional difference 41 Figure 4-10 Duration curve - MCF Monthly volume proportional difference 42 Figure 4-11 Duration curve – UIM Daily flow proportional difference 43 Figure 4-12 Duration curve – UIM Monthly volume proportional difference 44 Figure 4-13 Time series of Monthly Volumes – Arm above Mersey (TSM 624.1) (SC9) 45 Figure 4-14 Time series of Monthly Volumes – Don River upstream of Bass Highway (TSM 16200.1) (SC30) 45 Figure 4-15 Daily Duration Curve for Modelled flows 01/01/1900 – 01/01/2006 at the Calibration Site (SC6) 46 Figure B-1 Forth catchment – monthly volumes at secondary site. 59 Figure B-2 George catchment – monthly volumes at secondary site. 59 Figure B-3 Leven catchment – monthly volumes at secondary site. 60 Figure B-4 Swan catchment – monthly volumes at secondary site. 60 Figure B-5 Montagu catchment – monthly volumes at secondary site. 61 iv Mersey River Surface Water Model Hydro Tasmania Version No: 1.1 LIST OF TABLES Table 3-1 Data DRILL Site Locations 7 Table 3-2 Calibration Site 9 Table 3-3 Assumed Surety of Unassigned Records 10 Table 3-4 Estimated Unlicenced Direct Water Extractions from Mersey and Don River Catchments 11 Table 3-5 Monthly water extractions (ML) from Mersey River by subarea 12 Table 3-6 Average capacity for dams less than 20 ML from Neal et al. (2002) 18 Table 3-7 Environmental Flows 20 Table 4-1 Boughton & Chiew, AWBM surface storage parameters 26 Table 4-2 Hydstra/TSM Modelling Parameter Bounds 29 Table 4-3 Adopted Calibration Parameters 32 Table 4-4 Long term average monthly, seasonal and annual comparisons 37 Table 4-5 Model Fit Statistics – Mersey River 39 Table 4-6 Coefficient of Determination (R 2) Fit Categories 40 Table 4-7 Hydrological Disturbance Indices at the Catchment Outflow measuring disturbance between Scenario 1 and Scenario 3 at 3 sites in the Mersey Catchment 48 Table A-1 Hydro Tasmania Sites used for long term mean model inputs (ML/day)55 Table B-2 Tascatch Models’ performance at secondary sites 62 v Mersey River Surface Water Model Hydro Tasmania Version No: 1.1 1. INTRODUCTION This report forms part of a larger project commissioned by the Department of Primary Industries and Water (DPIW) to provide hydrological models for 26 regional catchments. The main objectives for the individual catchments are: • To compile relevant data needed to develop and calibrate an Australian Water Balance Model (AWBM) hydrological model for the Mersey River catchment; • To compile more than 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 scenarios; • To prepare a report that summarises the methods and assumptions used to develop the model. This report discusses the results of calibration and validation as well as material relating to the use of the hydrologic model (and associated software). 1 Mersey River Surface Water Model Hydro Tasmania Version No: 1.1 2. CATCHMENT CHARACTERISTICS The Mersey River is fed by a 1680 km 2 catchment in central-north Tasmania. It flows northward and discharges into Bass Strait at the city of Devonport. The south of the catchment is distinguished by the steep, mountainous terrain and alpine plateaus of the central highlands of Tasmania, and includes Tasmania’s tallest mountain, Mt Ossa, which stands at 1617 m ASL. Further north the catchment becomes less mountainous but remains undulating. Narrow alluvial plains form along the banks of the Mersey in the north of the catchment. Land-use in the Mersey catchment is divided between agricultural areas and large tracts of protected native forest and alpine tundra. The alluvial plains - about one tenth of the catchment area - are largely dedicated to agriculture. The hills in the catchment (the remaining catchment area) – particularly the mountains of the south - are covered in native forests. There are several towns in the Mersey catchment area, but the quantity of land covered by urban areas is negligible compared to forested and agricultural land. Annual rainfall varies significantly across the catchment owing to the catchment’s large size and diverse topography. Average annual rainfall ranges from 2000 mm in the southern mountains to 800 mm in the catchment’s north. This model also simulates flows for the adjoining Don River catchment, which is located to the west of the Mersey and also discharges into Bass Strait.