Applying the Cumulative Hydrological Effects Simulator (CHES) for managing water allocation A demonstration of CHES in the Grey catchment, West Coast Prepared for West Coast Regional Council June 2016 Prepared by : Jo Hoyle Jan Diettrich Paul Franklin For any information regarding this report please contact: Dr Jan Diettrich Software developer Hydrology +64-3-343 8076 [email protected] National Institute of Water & Atmospheric Research Ltd PO Box 8602 Riccarton Christchurch 8011 Phone +64 3 348 8987 NIWA CLIENT REPORT No: CHC2016-074 Report date: June 2016 NIWA Project: WCRC5501 Quality Assurance Statement Reviewed by: Roddy Henderson Formatting checked by: Tracy Webster Approved for release by: Helen Rouse © All rights reserved. This publication may not be reproduced or copied in any form without the permission of the copyright owner(s). Such permission is only to be given in accordance with the terms of the client’s contract with NIWA. 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Contents Executive summary ............................................................................................................. 7 1 Introduction .............................................................................................................. 9 1.1 Background ............................................................................................................... 9 1.2 Purpose ..................................................................................................................... 9 1.3 Scope ......................................................................................................................... 9 2 Water allocation in the West Coast region ................................................................ 10 3 Methods .................................................................................................................. 12 3.1 The CHES model ...................................................................................................... 12 3.2 CHES set-up for the Grey River catchment ............................................................. 13 3.3 Data analyses .......................................................................................................... 15 3.4 Examining different abstraction scenarios ............................................................. 17 4 Results .................................................................................................................... 20 4.1 Understanding the catchment ................................................................................ 20 4.2 Reference scenario – current takes (Scenario 1) .................................................... 23 4.3 Applying Policy 7.3.1 and Policy 7.3.2 (Scenario 2) ................................................ 34 4.4 Proposed NES limits (Scenario 3) ............................................................................ 39 4.5 Adding water storage (Scenario 4) ......................................................................... 50 4.6 Adding a large new abstraction (Scenario 5) .......................................................... 53 4.7 Climate change (Scenario 6) ................................................................................... 58 5 Discussion ............................................................................................................... 68 5.1 Limitations, assumptions and uncertainty in results .............................................. 68 6 Conclusion ............................................................................................................... 71 7 Acknowledgements ................................................................................................. 72 8 Glossary of abbreviations and terms ........................................................................ 73 9 References ............................................................................................................... 74 Appendix A CHES model description .................................................................... 77 Appendix B TopNet calibration of the Grey River catchment ................................ 87 Applying the Cumulative Hydrological Effects Simulator (CHES) for managing water allocation Appendix C Abstraction database ....................................................................... 90 Tables Table 3-1: A summary of current consented consumptive takes in the Grey River catchment. 15 Table 4-1: Statistical properties of reliability R for Abstraction 1 and Abstraction 2 in the same reach. 25 Table 4-2: Statistical properties of the different methods of simulating habitat change for brown trout adult. 27 Table 4-3: Statistical properties of reliabilities R1 and R2 for Scenario 1 and Scenario 2. 36 Table 4-4: Statistical properties of reliabilities R1 and R2 for Scenario 3. 40 Table 4-5: Total water taken daily upstream of Grey at Dobson under Scenario 1, Scenario 2 and Scenario 3. 41 Table 4-6: Statistical properties of mean weekly abstraction upstream of Grey at Dobson under Scenario 1, Scenario 2 and Scenario 3. 42 Table 4-7: Statistical values of water supply over time for Scenario 1, Scenario 2, and Scenario 3. 42 Table 4-8: Statistical properties of the natural flow time series for reach 12019562. 42 Table 4-9: Statistical properties of reliability R for Scenario 1 and Scenario 2. 51 Table 4-10: Statistical properties of R1 and R2 of current abstraction in the Grey River catchment under the example climate change scenario. 61 Table 4-11: Statistical properties of change in R1 and R2 of current abstraction in the Grey River catchment under as a result of climate change. 62 Table A-1: Species for which generalised physical habitat models are available in New Zealand. 81 Table C-1: Grey River catchment abstraction database. 90 Figures Figure 3-1: The Grey River catchment. 13 Figure 4-1: Annual mean flows (Q) over approximately 42 years for Grey at Dobson. 21 Figure 4-2: Weekly ensemble mean flows (Q) over approximately 42 years for Grey at Dobson. 21 Figure 4-3: (a) Map showing variability in MALF in the Grey River catchment, (b) histogram quantifying the variability in MALF in the Grey River catchment. 22 Figure 4-4: Map of reaches affected (touched) by current water abstraction in the Grey River catchment. 23 Figure 4-5: Histogram of the reliability (R1 ) of current abstraction in the Grey River catchment. 24 Figure 4-6: An example where there are two abstractions on the same reach with the same ∆Q but with varying reliability. 25 Figure 4-7: Mean habitat change for adult brown trout as a result of current abstraction presented as (a) a map and (b) an histogram. 26 Applying the Cumulative Hydrological Effects Simulator (CHES) for managing water allocation Figure 4-8: Histograms of mean, median, minimum and maximum habitat change for adult brown trout under current abstraction (Scenario 2). 27 Figure 4-9: Mean habitat change for longfin eels as a result of current abstraction. 28 Figure 4-9: Percentage of time that adult brown trout habitat is reduced in the Grey River catchment due to current water abstraction. 29 Figure 4-11: Percentage of time that longfin eels habitat is reduced in the Grey River catchment due to current water abstraction. 30 Figure 4-12: Maximum consecutive duration that adult brown trout habitat is reduced in the Grey River catchment due to current water abstraction. 31 Figure 4-13: Maximum consecutive duration that longfin eels habitat is reduced in the Grey River catchment due to current water abstraction. 32 Figure 4-14: Reaches which exceed Policy 7.3.1 under current abstraction. 33 Figure 4-15: Reaches which exceed Policy 7.3.1 under Scenario 2. 35 Figure 4-16: (a) Reliability R1 for Scenario 1 (blue) and Scenario 2 (yellow), and (b) Reliability R2 for Scenario 1 (blue) and Scenario 2 (yellow). 36 Figure 4-17: Mean habitat change for adult brown trout under Scenario 2. 37 Figure 4-18: Mean habitat change for longfin eels under Scenario 2. 38 Figure 4-19: (a) Reliability R1 under proposed NES limits and (b) Reliability R2 under proposed NES limits. 40 Figure 4-20: Mean weekly abstraction hydrographs showing total water taken upstream of Grey at Dobson under Scenario 1 (red), Scenario 2 (green) and Scenario 3 (black). 41 Figure 4-21: Water supply (availability) over time for an example abstractor (#12019562) under Scenario 1 (a), Scenario 2 (b), and Scenario 3 (c). 43 Figure 4-22: Mean habitat change for adult brown trout under Scenario 3. 45 Figure 4-23: The difference in mean habitat change between Scenario 3 and Scenario 1 for adult brown trout. 46 Figure 4-24: The difference in mean habitat change between Scenario 3 and Scenario 1 for longfin eels. 47 Figure 4-25: The difference in the maximum consecutive duration of habitat loss for adult brown trout between Scenario 3 and Scenario 1. 48 Figure 4-26: The difference in the maximum consecutive duration of habitat loss for longfin eels between Scenario 3 and Scenario 1. 49 Figure 4-27: Natural flows in the example reach (NZREACH 12030747) used