OTOP Regional Water Assessment Environment Canterbury 21-Apr-2017 OTOP Regional Water Resource Assessment Infrastructure Modelling Report 21-Apr-2017 Prepared for – Environment Canterbury – Co No.: N/A AECOM OTOP Regional Water Resource Assessment OTOP Regional Water Resource Assessment Infrastructure Modelling Report Client: Environment Canterbury Co No.: N/A Prepared by AECOM Consulting Services (NZ) Ltd Level 2, 2 Hazeldean Road, Addington, Christchurch 8024, P.O. Box 710, Christchurch MC, Christchurch 8140, New Zealand T +64 3 966 6000 F +64 3 966 6001 www.aecom.com 21-Apr-2017 Job No.: 42197880 AECOM in Australia and New Zealand is certified to ISO9001, ISO14001 AS/NZS4801 and OHSAS18001. © AECOM Consulting Services (NZ) Limited. All rights reserved. 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Storage of this electronic information should at a minimum comply with the requirements of the Electronic Transactions Act 2002. 21-Apr-2017 Prepared for – Environment Canterbury – Co No.: N/A AECOM OTOP Regional Water Resource Assessment Table of Contents Executive Summary 6 1.0 Introduction 9 1.1 Use of Outcomes 9 1.2 Document Layout 9 1.3 Acknowledgements 9 2.0 Objectives, Study Area and Environmental Setting 11 2.1 Overview 11 2.2 Study Area 11 2.3 Environmental Setting 13 2.3.1 Rainfall and evapotranspiration 13 2.3.2 Climate change 13 2.3.3 Surface water hydrology 13 2.3.4 Land use 14 2.3.5 Soil 14 2.3.6 Existing water infrastructure 17 2.3.7 Water demand 17 2.4 Regulatory Setting 17 3.0 Model Experiments – Overview 19 3.1 General 19 4.0 Model Experiments – North OTOP 20 4.1 General 20 4.2 Model Variables and Conditions 22 4.2.1 Kakahu Irrigation Scheme 22 4.2.2 Rangitata South Irrigation Scheme 22 4.2.3 Existing groundwater and surface water 23 4.2.4 Potential new infrastructure 24 4.2.5 Irrigation season 24 4.2.6 Additional irrigated areas 24 4.2.7 Use of RSIS water 24 4.3 Experiments and Outputs 26 4.4 Experiment Results 27 4.4.1 Experiment 1A 27 4.4.2 Experiment 1B 29 4.4.3 Experiment 1C 31 4.4.4 Experiment 1D 32 4.4.5 Experiment 1E 33 4.4.6 Experiment 1F 34 4.4.7 Experiment 1F (Demand Survey Experiment) 35 4.4.8 Experiment 1F Variation (Demand Survey Experiment) 36 4.4.9 Experiment 1G 38 4.4.10 Experiment 1G (Demand Survey Experiment) 39 4.5 Summary of Infrastructure Outcomes 40 4.6 Summary of Environmental Outcomes 43 5.0 Model Experiments – South OTOP 44 5.1 General 44 5.2 Model Variables and Conditions 44 5.2.1 Lake Opuha 46 5.2.2 Kakahu Irrigation Scheme 46 5.2.3 Other Irrigation Schemes 46 5.2.4 Potential New Infrastructure 46 5.2.5 Irrigation Season 47 5.2.6 Increased Lake Opuha Operating Level 47 5.2.7 Additional Irrigated Areas 47 5.2.8 Plan Change Outcomes 47 5.2.9 General Uptake of Surface Water and Groundwater 47 21-Apr-2017 Prepared for – Environment Canterbury – Co No.: N/A AECOM OTOP Regional Water Resource Assessment 5.3 Experiments and Outputs 48 5.4 Experiment Results 49 5.4.1 Experiment 2A 49 5.4.2 Experiment 2B 51 5.4.3 Experiment 2C (a, b, c) 54 5.4.4 Experiment 2C (a, b, c) Variation 58 5.4.5 Experiment 2D 61 5.4.6 Experiment 2D (Variation) 63 5.4.7 Experiment 2E 65 5.4.8 Experiment 2F 68 5.4.9 Experiment 2F (Variation) 70 5.5 Summary of Infrastructure Outcomes 71 6.0 Summary of Combined Experiments 72 6.1 Experiment Details 72 6.2 Results 72 6.2.1 Klondyke Ponds 73 6.2.2 Canal B 74 6.2.3 Large Reservoir 74 7.0 Concluding Summary 77 7.1 North OTOP Zone 77 7.2 South OTOP Zone 77 7.3 Combined Model 78 8.0 References 79 9.0 Standard Limitation 80 Appendix A Surface hydrology summary A Appendix B Irrigation Areas B Appendix C North OTOP Model Schematics C Appendix D South OTOP Model Schematics D 21-Apr-2017 Prepared for – Environment Canterbury – Co No.: N/A AECOM OTOP Regional Water Resource Assessment 6 Executive Summary Environment Canterbury has commissioned this work under the Canterbury Water Management Strategy (CWMS) to contribute to the understanding of potential future water use within the Orari Temuka Opihi Pareora (OTOP) CWMS Zone. The intent of the work is to assess the capacity for water resource development within the Zone. Specifically, it considers options for the availability, collection and utilisation of the water resource within and around the zone. Key current water resource pressures on the zone are the effect of groundwater abstraction on nearby stream flows and the effect of low rainfall periods on supply reliability. The zone was divided into two areas; north and south, which are initially modelled separately. The north area extends from south of the Rangitata River to as far as the northern end of the existing Kakahu scheme. It extends inland as far as the base of the foothills and includes the area north of Geraldine. The south area extends inland as far as Ashwick Flats and Fairlie, and comes down to the coast including irrigated areas around the Opihi River and the Tengawai River. The Pareora River catchment is excluded from this work. The methodology for the modelling was to define irrigation areas and determine specific demand for these areas based on soil moisture demand modelling. Demand for the areas was met in the model through a combination of existing groundwater and surface water takes, and water supplied via the modelled infrastructure (both proposed and existing). Matching supply with soil moisture demand is different from most current practice, where supply is based on consented flow or the Opuha Water Ltd shareholder agreement. Soil moisture demand based supply however, has advantages in terms of improved water use efficiency and improved nutrient management potential. Key variables in the model include a large storage reservoir at Klondyke (although this can include Rangitata River water ‘swapped’ with Lake Coleridge water), a new headrace canal (Canal B), new connection from the north into the existing Kakahu scheme, a new large central zone reservoir, and potential new supply infrastructure for Lake Opuha. Existing infrastructure in the model includes the RSIS ponds and races, the existing Kakahu irrigation scheme, Lake Opuha and the Opuha Water Limited scheme network. Environment Canterbury commissioned a survey of users in the OTOP North area. Respondents were informed about an assessment of their current reliabilities and potential planning changes that could affect their future reliability. They were asked to comment on their interest in additional alpine water for improving future reliability on their existing irrigated land and / or through irrigated land expansion. A model experiment was undertaken to determine infrastructure sizing based solely on the information from the demand survey. This experiment resulted in Klondyke annual storage of 15.5 Mm3 and a main headrace capacity of 1.4 m3/s. If Klondyke were instead to deliver full-supply water to survey respondents it would need to have a constructed volume of approximately 30 Mm3 with water being conveyed through a headrace with a capacity of approximately 2.6 m3/s. Additional on-farm storage would be required to achieve 95 % supply reliability for both experiments. Under the highest modelled demand scenario (full replacement of all potentially stream depleting consents), and to meet 95 % reliability, a large storage (modelled as being located at Klondyke) would need to have a constructed volume of approximately 55 Mm3 with water being conveyed through a main headrace with a capacity of approximately 5.2 m3/s. Such a scheme would also rely on additional on-farm storage being built. 21-Apr-2017 Prepared for – Environment Canterbury – Co No.: N/A AECOM OTOP Regional Water Resource Assessment 7 Regulatory changes with regard to minimum flows in the streams and rivers of the OTOP zone were an important part of this modelling. Additional demand resulting from regulatory changes to minimum flows and stream depletion rules has been provided for. Generally, the results show that increases to minimum flows can be accommodated with no effect on users provided a new source of water is available. The existing Kakahu Irrigation scheme was modelled in several ways. In the north OTOP model, the northern end of the Kakahu scheme was modelled as being able to receive either top up supply from Klondyke, or a complete replacement to the northern end of the existing scheme. It was found that a complete replacement to the water currently being delivered by Lake Opuha was achievable provided that appropriately designed and sized infrastructure is in place. This was the scenario modelled in the 3 combined version of the model and returned approximately 3.3 Mm per season back to Lake Opuha with a gain in irrigated area of approximately 300 ha for OTOP south.