OTOP Regional Water Resource Assessment

OTOP Regional Water Assessment Environment Canterbury 21-Apr-2017

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

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21-Apr-2017

Job No.: 42197880

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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

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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

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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.

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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. OTOP south is shown to be short of water with respect to the desired supply reliability and potential new irrigated area. ‘Small water’ concepts (e.g., filling Lake Opuha to its design maximum lake level and lining Levels Plain distribution) to alleviate some of the demand on Lake Opuha were shown to yield a net gain back to the existing system (particularly in dry seasons), but these gains were not sufficient to supply additional future irrigated area without reliability reductions to existing shareholders. Changes to the Lake Opuha management rules (irrigation restrictions and river minimum flows) yielded small gains back to the system in particularly dry years, though minimal differences were shown in average years. To provide supply to further areas additional water needs to be conveyed to the area from beyond the OTOP South boundary and, depending on the infrastructure concept, additional centralised storage may also be required. Reliabilities of the irrigated areas within OTOP were found to be affected by the volume of available water within on-farm storage, and the ability of the modelled schemes to provide water to the on-farm storage. Reliabilities were improved where additional storage is available and conveyances are high enough to provide water at the required rates. Critical to this are the large storage reservoirs in the system and their ability to convey water to the on-farm storage. In the model, where this was able to be achieved, reliabilities showed improvements. The model includes additional on-farm storage to the volume required to provide 10 days of demand from the irrigation areas. Reliabilities improved with additional stored volume. Whereas the experiments described above considered the OTOP Zone in two separate areas, a final integrated infrastructure experiment was run to test how the north and south areas could be 3 considered together. A theoretical high demand scenario utilised 100 Mm of water storage and a 3 conveyance system with 7m /s capacity across the OTOP North area. Future studies will utilise this model with specific demand surveys and potential future planning constraints on irrigation area to refine these capacities and provide the basis for water supply cost estimations. It is a recommendation of this work that these further experiments be undertaken. The model has a number of limitations and aspects that need to be taken into consideration when assessing the outcomes of this work. Some assumptions were made regarding the reliability of existing groundwater and surface water takes which affect the available water to the irrigated areas and subsequently the additional water required to meet the required demand. These assumptions have been made broadly across the entire OTOP zone and in places where there is a small amount of irrigated land they can have a large effect on the modelled reliabilities. It was also assumed that if a consent for a surface water or groundwater take falls within an irrigated area, then the water allocated is used entirely within that irrigated area. This may not be the case in reality and some consented abstractions may cover land across multiple irrigation areas.

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The modelled flow at Saleyards Bridge will also require caution in its use. The south OTOP version of the model is complex in the way it calculates demand on the system and the way water is removed for abstractions. As Saleyards Bridge is at the bottom end of these calculations, the culmination of multiple assumptions upstream, results in an imperfect representation of flow conditions at Saleyards Bridge. The modelled reliabilities of irrigated areas in the south OTOP model that are not explicitly connected to any irrigation scheme (primarily irrigation areas south of the Opihi River) should also be considered with caution. As the model does not explicitly supply additional water to these areas, modelled reliabilities are primarily dependent on the amount of available on-farm storage and the rate at which that water could be removed from the on-farm storage ponds. Improving reliabilities in these areas will require some consideration of proposed infrastructure routes and the likelihood of these routes to go ahead. The model is able to determine the additional water that will be available to the zone, and the additional irrigated area that could be supplied. Future studies should investigate more fully the proposed route of additional infrastructure. In doing so, a more realistic interpretation of the likely outcomes will be achieved, as the model is highly dependent on where these routes and reservoirs will be placed. A more detailed investigation into the actual water that is abstracted from existing consents will be necessary as this will add further accuracy to the calculation of additional water that will be required. In addition, a further refinement of the soil-moisture demand modelling would be appropriate, with a revision to assumptions on future land use. It would be preferable to undertake this along with a further refinement of likely uptake of ‘new water’ from those that expressed an interest during this current work. Future studies should also include the period post-2011 as this contains a number of important droughts, the consideration of which would help define the most resilient and efficient scheme design.

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1.0 Introduction 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 inform the members of the OTOP Zone Committee as to 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. This work has been run in parallel with the detailed sub-regional planning being undertaken by Environment Canterbury technical staff. This report is intended to provide information to potential developers and the Zone Committee which can be used as they work through the sub-regional process in the coming years.

1.1 Use of Outcomes This work relies on water resource modelling and irrigation demand modelling undertaken at a high- level to meet the needs of this pre-feasibility study. Given the high-level nature of this project it was not possible to investigate each facet of the experiments in detail; nor are there the necessary detailed assessments of other key areas of the zone to support an in-depth study. This study investigates the broad issues associated with implementing the scenarios laid out, and suggests the merits or otherwise of pursuing such experiments. Subsequent investigations would be necessary to develop the depth of information and understanding required to take experiments towards the implementation stage. The outcomes should not be used in isolation, but rather the full range of information and experience available to decision makers should be considered along with this study’s outcomes, such that the best course for the zone can be pursued.

1.2 Document Layout This document is set out as below: Section 2 provides the project objectives, study area and model setting. Section 3 provides an overview of the model experiments. Section 4 provides the model experiments and results of the north OTOP Zone. Section 5 provides the model experiments and results of the south OTOP Zone. Section 6 presents the model experiments and results of the integrated OTOP model. Section 7 presents the overall conclusions and recommendations. Section 8 References. Section 9 Statement of Limitations Appendix A contains background information on the hydrology of the zone. Appendix B contains maps of the modelled zones Appendix C contains schematics of the north OTOP experiments Appendix D contains schematics of the south OTOP experiments

1.3 Acknowledgements The Ministry of Primary Industries, through the Irrigation Acceleration Fund, (Project C13-017) and Environment Canterbury have funded this work. Environment Canterbury also provided hydrological data sets and supporting technical reports.

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This work draws on previous work undertaken for Project Rata, which was funded through the Community Irrigation Fund (Project 11/02) and by Environment Canterbury, and for Water Quality Assessments funded through the Irrigation Acceleration Fund (Project C13-017) and by Environment Canterbury.

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2.0 Objectives, Study Area and Environmental Setting

2.1 Overview The aim of this study is to explore options for the development of infrastructure capable of allowing the efficient, integrated use of water within the OTOP Zone. Primarily this focuses on an assessment of potential water sources, storages, conveyances and demands. The study objectives are to: 1. Quantify the available resource 2. Identify demand locations and profiles 3. Determine logical infrastructure layout 4. Determine the sizing (volume) of storage required 5. Determine the sizing (flow rate) of conveyance required It is the intent of this work to inform future, more detailed, stages of infrastructure planning to allow the most efficient and integrated use of water in the zone.

2.2 Study Area The study area for this work is the OTOP Zone excluding the Pareora catchment. The area extends from the Rangitata River in the north to the Tengawai River in the south and as far west as the Ashwick flats surrounding Lake Opuha. Infrastructure operated or proposed by Rangitata Diversion Race Ltd on the north bank of the Rangitata River has also been included in this work, as it is used as a potential source of water for the OTOP Zone. To allow infrastructure development to be properly investigated the study area has been divided into north and south areas. This is explained in more detail below, however allows for the simplification of analysis.

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Figure 1 Study Area

21-Apr-2017 Prepared for – Environment Canterbury – Co No.: N/A !I 12/01/2017 2:11:15 p.m. T:\Jobs\42197880\GIS\Reports and GIS maps\Figures for report\20170112_OOP_WB_BaseMap_A4_Portrait_Map1.mxd

Sourced from the LINZ Data Service and licensed for re-use under the Creative Commons Attribution 3.0 New Zealand licence.

Printed 12 Jan 2017 14:11 Project: OTOP Water Resources Assessment Scale: Approved MM Date Scale: 1:500,000 (A4 size) Title: Designed SP Drawn SP OTOP Zone Extent Status: Rev. Map No. Checked MM Checked MM Primary Map No. 1 Final 1 1 © Copyright AECOM, 2015. This map is confidential and shall only be used for the purposes of this project. © Copyright AECOM New Zealand Limited 2015. This map is confidential and shall only be used for the purpose of this project. The information contained or referred to in this drawing-report was developed for use in the project. AECOM New Zealand Limited does not Legend accept any responsibility for the use of the information by any other parties and state expressly that they do not warrant the accuracy of the information. Any use of the information by other parties is at their own risk. The signing of this title block confirms the design and drafting of this project have been prepared and checked in accordance with the AECOM Quality Assurance system certified to AS/NZS ISO 9001:2000. No part of this drawing/report may be copied or used without the prior written consent of AECOM New Zealand Limited.

OTOP Zone Boundary Map features depicted in terms of NZTM projection.

Data Sources: NZ Topographical Features - LINZ NZ National Topo Dataset 2014 Cadastral Boundaries - LINZ NZ Cadastral Dataset 2014 Rev. By App. Description Date AECOM OTOP Regional Water Resource Assessment 13

2.3 Environmental Setting The environment of the OTOP Zone, in a water resources context, has been detailed in a previous report (Orari Opihi Pareora Zone Pre-Feasibility Studies, URS 2014). In the interests of brevity only the key details have been repeated below along with details about how this information is used in the subsequent modelling.

2.3.1 Rainfall and evapotranspiration Rainfall and evapotranspiration data are used to drive the water demand estimates for irrigated areas. There is no linkage between rainfall/evapotranspiration and river flows as the flow data was obtained directly from river flow monitors. Data for rainfall and evaporation was taken from NIWA’s Virtual Climate Station Network (VCSN), a country-wide interpolated grid set of climate records. The period of 1981-2011 was used.

2.3.2 Climate change The effects of a changing climate have not been covered in this project. However, such effects should be considered at a later stage of development, should the recommendations presented here be progressed. The important areas of consideration would be: 1. The change in water resource provided by the Rangitata River 2. The change in water resource provided by in-zone surface watercourses 3. The change in in-zone land surface recharge 4. The change in demand from users It is important to consider not only changes to the magnitude of these factors, but also any changes in the temporal distribution of the resource/demand.

2.3.3 Surface water hydrology The study considers the water resources of three river catchments (and their associated sub- catchments): the Orari, Opihi and Rangitata Rivers (Table 1).

Table 1 Catchment summary (WRENZ)

2 Mean flow Mean Annual 1% AEP Flow Catchment Area (km ) 3 3 3 (m /s) Flood (m /s) (m /s) Orari 715 11 414 2,020 Opihi 2,369 28 1,120 5,614 Rangitata 1,810 115 1,209 3,529

The Orari and Opihi Rivers are similar in that they rise in the front ranges directly behind the Canterbury Plains. These catchments receive much of their water from cold fronts and depressions from the south which move up the east coast of the South Island, and from slow moving depressions centred to the east, within the Canterbury Bight (de Joux, 1980). Significant storm events on the West Coast may push rain into these catchments; however, this would not be their main source of water. Snow storage is significantly less than on the Main Divide; however, snow within the headwaters of the Opihi and Opuha Rivers contributes melt water in spring and summer.

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The Rangitata River drains from three alpine catchments (Clyde, Havelock and Lawrence Rivers) on the Main Divide of the South Island. As such the majority of flow in the river is derived from storm events moving up the West Coast which spill precipitation across the Main Divide. During spring and early summer snow melt is a significant component of the Rangitata River’s flow. Conversely, during winter much of the precipitation falling on the upper catchments of the river does so as snow, and is stored over winter until the warm temperatures in spring melt stored snow. Given the very different weather systems and hydrological process involved in these catchments their combined use presents a potentially robust and resilient water resource for the OTOP Zone.

2.3.4 Land use Agribase landuse information was supplied by Environment Canterbury and is summarised below (Table 2).

Table 2 Landuse in the OTOP Zone

Land Use Area (ha) Beef 11,755 Cropping/horticulture 26,731 Dairy 26,970 Dairy support 1,172 Forestry 7,300 Lifestyle 2,502 Other 17,351 Piggery 579 Sheep 41,865 Sheep and Beef 89,693 Total 225,918

The largest single land use in the zone is listed as being sheep and beef (89,693 ha), although this land use type is skewed towards the upland areas of the zone. The majority of dairy land use (26,970 ha) is concentrated in the area between the Rangitata River and the Hae Hae Te Moana River, with much of it driven by water from RSIS.

2.3.5 Soil Soil information was used to develop the soil water balance model which in turn generated the irrigation demand estimates. Soils in the OTOP Zone were classified based on the general Plant Available Water (PAW) division into soil types described in Lilburne et al. (2010) (Table 3, Figure 2).

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Table 3 Soil classification

Group Code PAW (mm) Extremely Light XL <50 Very Light VL 50-80 Light L 80-110 Medium M 110-150 Heavy H 150-200 Deep D >200

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Figure 2 Soil map

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Legend

OTOP Zone Boundary PAW Soil Depth

T:\Jobs\42197880\GIS\Reports and GIS maps\20170327_OOP_WB_BaseMap_A4_Portrait.mxd Soil Description Deep Heavy Medium Light Very Light Extra Light Sourced from the LINZ Data Service and licensed for re-use under the Creative Commons Attribution 3.0 New Zealand licence.

Printed 12 Apr 2017 10:37 Project: OTOP Water Resources Assessment Scale: Approved MM Date Scale: 1:500,000 (A4 size) Title: Designed SP Drawn SP OTOP Zone Soils Status: Rev. Map No. Checked MM Checked MM Primary Map No. 2 Final 1 2 © Copyright AECOM, 2015. This map is confidential and shall only be used for the purposes of this project. © Copyright AECOM New Zealand Limited 2015. This map is confidential and shall only be used for the purpose of this project. The information contained or referred to in this drawing-report was developed for use in the project. AECOM New Zealand Limited does not accept any responsibility for the use of the information by any other parties and state expressly that they do not warrant the accuracy of the information. Any use of the information by other parties is at their own risk. The signing of this title block confirms the design and drafting of this project have been prepared and checked in accordance with the AECOM Quality Assurance system certified to AS/NZS ISO 9001:2000. No part of this drawing/report may be copied or used without the prior written consent of AECOM New Zealand Limited.

Map features depicted in terms of NZTM projection.

2.3.6 Existing water infrastructure The OTOP zone already has some large irrigation schemes operating. These being: x Rangitata South Irrigation Scheme (RSIS) x Kakahu x Opuha Water Limited (and associated schemes) x Levels Plain x Plus other minor schemes such as Waitohi, Totara Valley, Cascade. The Rangitata Diversion Race (RDR) is not a part of the OTOP zone, but may be useful in the delivery of water to OTOP.

2.3.7 Water demand Demand was calculated across the OTOP zone using AECOM’s IrriOptimiser tool to determine soil moisture deficit. Inputs to IrriOptimiser include climate data (obtained from the Virtual Climate Station Network (VCSN)) to provide estimates of rainfall and evapotranspiration across the zone, soils (categorised from Environment Canterbury data as either Extra Light, Very Light, Light, Medium or Heavy) and land use was also taken into account. Land uses were given a crop factor of 1 apart from forestry. A demand for irrigation is triggered in the model when the soil moisture deficit reaches a defined minimum for that particular soil type. Irrigation that is applied is capped at 4.5 mm/ha/day. Demand on the farm drives demand from on farm storages, or where there is no current on farm storage, directly from the rivers/groundwater. In turn, this demand drives the request for water from larger storages within the zone (Lake Opuha, RSIS ponds, Klondyke). Where there is on farm storage, this buffers the demand requested from Lake Opuha or the rivers. The model aims to keep the on farm storage as full as possible, but in times where there is not enough water to supply to the on-farm storage, the on-farm storage meets the demand to the farm gate (up to 10 days of storage at the 90th percentile). Demand was broken into specific irrigation areas (Refer to map in Appendix B). Areas were defined generally based on local knowledge of groups of water users or by elevation contours. For the south OTOP model, Aoraki Water Trust (AWT) shareholders were identified as possible areas of new irrigation demand. Current irrigated areas were defined through GIS using Aqualinc’s irrigation demand mapping layer. The layer used several different methods to determine areas currently being irrigated, the primary method being inspection of the infrared spectrum. AECOM further refined this layer according to current aerial images and correlation with resource consents. A key aspect of the project is to provide higher reliability water to those users who currently abstract from unreliable surface water and groundwater. In the north part of the zone, these users are concentrated along the margins of the rivers, with IA3 consisting solely of groundwater users. Determining infrastructure requirements for these users is particularly important as plan changes (e.g. Orari environmental flow and allocation regime, and potentially Schedule 9 in Canterbury’s Land and Water Regional Plan) come into effect further decreasing the reliability of these existing supplies.

2.4 Regulatory Setting The plan change experiment modelled the effects of new minimum flows in the Orari River combined with the effects of groundwater abstractions being assessed on 150 day stream depletion flows (Schedule 9). The result of these changes will be less water availability through existing methods of abstractions (surface and stream depleting groundwater), and therefore an alternative source of water is required. When applying this change to the model, deep groundwater takes (i.e. takes that are not hydraulically connected to surface water) are unaffected and remain as a source of water for that irrigation area.

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It was found that the consented volumes of water within the zone far exceeded the amount of water required by the zone. However, the consented volumes cannot take into account times where the water is not available due to minimum flow restrictions or from landowner’s choice of the amount of water to apply and when. As such, a reduction factor of 78% was applied to the consented volumes to bring the amount of water being applied in the model to those volumes reported in the Environment Canterbury Water Use Report – 2013/2014 Water Year.

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3.0 Model Experiments – Overview

3.1 General The OTOP zone covers a large area of South Canterbury. For this reason, it was practical to split the zone into north and south areas. This enabled AECOM to model the north and south separately and better determine the factors affecting each of the zones separately. There is a natural junction point in the model – the northern end of the existing Kakahu scheme. Water for this scheme is currently supplied via Lake Opuha through a limited capacity abstraction out of the Opuha River. Initial conceptualisation of the model provided an allowance for the users at the northern end of this scheme to be supplied with water from the north via a new conveyance canal. The north part of the model 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 proposed Klondyke pond and includes the area north of Geraldine. The south part of the model extends inland as far as the Ashwick Flats and Fairlie, and comes down to the coast including irrigated areas around the Opihi River and the Tengawai River. The outputs of the experiments are to initially determine a baseline demand for the zones, assess the existing sources of water to the irrigated areas, and to ultimately determine how much additional water is required to satisfy a 95% irrigation demand. Additional infrastructure will be required, and in this model some preliminary sizing of this infrastructure is another key output. The final experiment in this project will be to combine the north and the south model into one complete system, with water from the north being able to supply irrigation areas potentially as far south as Levels Plain. This will require some discussion and analysis on the infrastructure required with further discussion to be had on the specific route that any canals and pipes may need to take as well as the balance between northern (Klondyke and ‘swapped’ Lake Coleridge) storage and other in scheme storage.

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4.0 Model Experiments – North OTOP

4.1 General The north OTOP area extends from the Rangitata River south as far as the northern tributaries of the Opihi River (Waihi River, Hae Hae Te Moana River, Kakahu River). The north currently faces an overall reduction of available in-zone water resource due to increases in minimum flows associated with surface water abstractions and changes to assessment methodology for stream-depleting groundwater takes (Schedule 9, Land and Water Regional Plan). There is also a demonstrated interest in a small amount of irrigation expansion, and for existing irrigators to improve their reliabilities, as recorded in Environment Canterbury’s Farm Survey 2016. While additional irrigable area may well be constrained by nutrient planning rules and limits which are under development, this potential future constraint is not included in the current scenarios. Existing infrastructure in this zone includes the RSIS scheme in the north, and at the southern end of the area, the existing Kakahu Irrigation Limited (KIL) scheme which is supplied with water from Lake Opuha. The basis for investigations in this area is the supply of already consented Rangitata Diversion Race water from the Rangitata River. This is new water for the OTOP area and is in addition to that already abstracted by RSIS. It is considered to be supplied via the proposed Klondyke Storage on the north bank of the Rangitata River. The purpose of this work was to determine what volume of storage would be required at Klondyke (and/or via swap from Lake Coleridge) for the purposes of the OTOP north area. Modelled new infrastructure included a new main canal (Canal B) which is supplied with water from the Rangitata River. A new high volume storage pond at Klondyke was included, which is filled via the Rangitata River and subsequently into Canal B. It was assumed that other local distribution races or pipes would convey the water into on farm storage ponds. On farm storage forms an important part of the solutions provided in Experiment 1. On farm storage volumes have been set at 10 days of required demand. In some experiment model runs, the A block and the B block water that the RSIS scheme is consented to use was separated. Under certain conditions, there may be a benefit to storing the A block water separately and using this to augment the available stored water to the modelled areas between the Rangitata River and the Orari River. To facilitate the modelling, the zone has been split into ‘irrigation areas’. These areas are generally defined by some combination of natural boundaries (e.g. rivers), height above sea level, existing irrigation schemes and identified community interest areas. A map showing the irrigation areas is presented in Appendix B.

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Figure 3 OTOP north area

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Sourced from the LINZ Data Service and licensed for re-use under the Creative Commons Attribution 3.0 New Zealand licence., Environment Canterbury Regional Council; Hurunui District Council; Waimakariri District Council; Timaru District Council; Waimate District Council; Mackenzie District Council; Waitaki District Council

Printed 20 Jan 2017 15:31 Project: OTOP Water Resources Assessment Scale: Approved MM Date Scale: 1:300,000 (A4 size) Title: Designed SP Drawn SP North OTOP Irrigation Areas Status: Rev. Map No. Checked MM Checked MM Primary Map No. 2 Final 1 2 © Copyright AECOM, 2015. This map is confidential and shall only be used for the purposes of this project. © Copyright AECOM New Zealand Limited 2015. This map is confidential and shall only be used for the purpose of this project. The information contained or referred to in this drawing-report was developed for use in the project. AECOM New Zealand Limited does not Legend accept any responsibility for the use of the information by any other parties and state expressly that they do not warrant the accuracy of the information. Any use of the information by other parties is at their own risk. The signing of this title block confirms the design and drafting of this project have been prepared and checked in accordance with the AECOM Quality Assurance system certified to AS/NZS ISO 9001:2000. No part of this drawing/report may be copied or used without the prior written consent of AECOM New Zealand Limited.

North OTOP Irrigation Areas Map features depicted in terms of NZTM projection.

4.2 Model Variables and Conditions A number of variables affect the outcomes required in the area. Some of these variables have been fixed across all experiments whilst others have been varied to assess their effects. Provided below are the variables used.

4.2.1 Kakahu Irrigation Scheme The Kakahu scheme has two broad areas, one above the Kakahu gorge and one below. The supply of water to areas below the gorge via the existing distribution network has been found to be a constraint on the availability of water to this area. The Kakahu scheme receives water from Lake Opuha. This water is abstracted from the Opuha River near Skipton Bridge. The water is conveyed via a 9 km pipeline and is discharged into the Kakahu River at a site known as Mulvihills. The ordered water is then abstracted from the Kakahu River downstream of the gorge. The distribution race has a capacity of 0.9 m3/s (Section A), and then reduces to a capacity of 0.6 m3/s (Section B) and then further reduces to 0.4 m3/s (Section C) (Figure 4 – Taken from Pers. Comm. Stephen Pagan). Modelling of the OTOP north area assumes that the area south of the abstraction from the Kakahu River is supplied via the proposed Canal B, rather than Lake Opuha therefore removing any capacity constraints.

Figure 4 Kakahu conveyance infrastructure

4.2.2 Rangitata South Irrigation Scheme The RSIS operates with large storage ponds adjacent to the Rangitata River with a total capacity of 3 16.5 Mm . The consent held by the operators of the scheme (Rangitata Water Ltd) allows abstraction 3 of 0.4 m3/s of 'A' block water and 19.6 m /s of ‘B’ block water from the Rangitata River. An additional water sharing arrangement with RDRML is not modelled in this project. Due to a lack of information, a number of assumptions have been made for the purposes of modelling the operation of the RSIS scheme.

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It is known that there are significant losses to ground from the storage basins and the water races, though losses have reduced since construction. For the purposes of this exercise losses out of the storage basins were assumed to be 10 mm/day and out of water races to be 30% of conveyed flow. On farm storage volume has been calculated using aerial images, assuming a nominal 2 m depth of the ponds. A total on-farm storage volume for the scheme of 4.3 Mm3 was estimated.

4.2.3 Existing groundwater and surface water Based on consents from the Environment Canterbury database, an assessment was made of the existing water resources currently being used in the modelled area (Table 4). The results of this assessment are shown below. These are the average rates of take (Consented volume/consecutive days).

Table 4 Existing in-zone use Irrigation Stream-depleting groundwater takes Deep groundwater takes (average Area (average of consent [L/s]) of consent [L/s]) 1 255 3,362 2 563 2,744 1a 177 176 3 239 536 4 352 300 5 288.2 25.7 6 610 3.3 7 380 109 8 1,181 922 9 55 206 10 139 463 11 183 524 14 84 22 16 100 0

In the model, the average supply reliability is estimated for each irrigation area (IA) from reliability combinations multiplied by the percentage of time this volume of water is likely to actually be used. Percentage reliabilities under current conditions were set at 55% for A permits, 27% for B permits and a 50% reliability for all other shallow and deep groundwater or surface water takes. Based on the 2013/2014 Canterbury Region Water Use Report (Environment Canterbury), a percent time used value of 78% was applied to reflect the difference between the consented volumes and the volumes actually abstracted. This allows the model to replicate the measured use rates for consented water in the Zone, as detailed in the Water Use Report, of 38% for 2013-2014. Under the potential plan change restrictions experiment (Experiment F), ‘A’ permit reliabilities for stream-depleting consents were reduced to 46% and ‘B’ permit reliabilities were reduced to 0%. Under the full replacement experiment (Experiment G), all stream-depleting takes were removed and only deep groundwater takes were included. The model was run between 1981 and 2011.

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4.2.4 Potential new infrastructure In addition to the existing infrastructure a number of new conveyances and storages were modelled in the model (Figure 5). The model has utilised the storage at the proposed Klondyke site, though some of this storage could potentially be 'swapped' with Lake Coleridge supply. This storage reservoir volume was adjusted in order to meet the required irrigation demands from the downstream components of the modelled system. The reservoir is modelled on a ‘winter fill’ scenario, in that is always full at the beginning of the irrigation season. It was proposed that this storage pond be connected via a pipeline across the Rangitata River and into a new headrace canal named Canal B in the model. Canal B forms the main conveyance structure in the north model. Maximum capacities of this canal vary through each of the experiments depending on the demand, with the aim being to maintain 95 % reliability of water supply to the farm gate. The route the canal follows is non-specific, however generally it takes a path across the top of the irrigation areas, crossing the Orari, Hae Hae Te Moana and Kakahu Rivers and terminates at the end of the existing Kakahu Irrigation Scheme. Feeder pipelines off Canal B feed into bulk on farm storage ponds. Many of the irrigation areas already have some built on farm storage capacity and where this is the case, the volumes were summed to give a total storage capacity to that entire irrigation area. Generally, these currently built volumes were not sufficient to supply the irrigation areas with the required 95% reliable water, and so additional volume was added to each of these reservoirs to accommodate demand. It should be noted that the model does not consider individual farms in this respect. In many cases, the storage currently built in each irrigation area may only belong to one or two landowners. The model assumes a total volume of storage that will be available to all irrigated land parcels within the irrigation areas. Canal B terminates at the end of the existing Kakahu Irrigation Scheme. In recognition of the supply constraints in the Kakahu scheme, additional water is able to be supplied via Canal B into the water starved areas at the downstream end of the Kakahu network and also acts as a replacement water source to those users who will be affected by the proposed plan change rules related to stream depletion assessments and maintaining higher minimum flows in the rivers. All new infrastructure is modelled as being fully lined with no losses outside of the system.

4.2.5 Irrigation season The model uses an irrigation season of 1 September through to 30 April each year.

4.2.6 Additional irrigated areas Environment Canterbury commissioned a community survey to be carried out to gauge landowners’ estimates of land that could be further irrigated if water was available and affordable. The survey responses indicated that there could be as much as 1,315 ha of additional land requiring water (plus another 400 potential hectares subsequently identified out of the original survey area). Additional irrigated area is spread across the northern part of the OTOP zone.

4.2.7 Use of RSIS water In all scenarios, the RSIS consented ‘B Block’ water is diverted to the Arundel storage ponds. The B block water has a maximum rate of abstraction of 19.6 m3/s depending on the flow of the Rangitata River. In one of the experiments, the RSIS consented A Block water is diverted into a separate storage pond. This water is then directed down to IA3 (groundwater users) to replace their water requirements from groundwater. The A block water in this consent is highly reliable, and the Rangitata River is generally 3 always able to meet the consented flow of 0.392 m /s. Occasionally during certain experiments in the model, the demand is not sufficient to require this full amount and the storage pond becomes full. In these cases, the model automatically diverts the A block water back to the Arundel ponds, or in any case where those ponds are also full, returns the water back to the river.

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Figure 5 Modelled infrastructure – OTOP North

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Legend

T:\Jobs\42197880\GIS\Reports andmaps\20170327_OOP_WB_BaseMap_A4_Portrait.mxd GIS OTOP Zone Boundary Storage Reservoirs

OTOP Canal Network Status Status Existing Modelled Environment Canterbury Regional Council; Hurunui District Council; Waimakariri District Council; Timaru District Council; Waimate District Council; Mackenzie District Council; Waitaki District Council

Printed 21 Apr 2017 13:50 Project: OTOP Water Resources Assessment Scale: Approved MM Date Scale: 1:400,000 (A4 size) Title: Designed SP Drawn SP OTOP Zone Modelled Infrastructure Status: Rev. Map No. Checked MM Checked MM Primary Map No. 5 Final 1 5 © Copyright AECOM, 2015. This map is confidential and shall only be used for the purposes of this project. © Copyright AECOM New Zealand Limited 2015. This map is confidential and shall only be used for the purpose of this project. The information contained or referred to in this drawing-report was developed for use in the project. AECOM New Zealand Limited does not accept any responsibility for the use of the information by any other parties and state expressly that they do not warrant the accuracy of the information. Any use of the information by other parties is at their own risk. The signing of this title block confirms the design and drafting of this project have been prepared and checked in accordance with the AECOM Quality Assurance system certified to AS/NZS ISO 9001:2000. No part of this drawing/report may be copied or used without the prior written consent of AECOM New Zealand Limited.

Map features depicted in terms of NZTM projection.

4.3 Experiments and Outputs A range of experiments have been undertaken to demonstrate the effects of the variables defined above. Experiment 1A This experiment is intended to demonstrate the ability of the model to represent existing conditions. There is limited information around the current performance of RSIS given that this is a privately run scheme which is not required to declare its performance or operational regime. Similarly there is limited understanding of the current performance of existing groundwater, surface water and small scheme users. Anecdotal evidence, supported by aggregated performance statistics for the wider area, has been used to estimate current performance which can then be used to assess model performance. Experiment 1B Top-up reliability/new irrigable area (Variation 1). Supply of top-up water to existing users and full-supply water to new areas from the demand study (RSIS ‘A’ block stored mid-plains and supplied to IA1a and IA3 & topped up by RSIS ‘B’ block water, all other Irrigated Area - IAs [including IA16] supplied from Klondyke). This is the only experiment which uses RSIS ‘B’ block water in a wider scheme. For all other experiments, RSIS ‘B’ block water is left as a standalone scheme supplying the existing areas (IA 1 and IA 2). Experiment 1C Top-up reliability/new irrigable area (Variation 2). Supply of top-up water to existing users and full-supply water to new areas from the demand study (RSIS ‘A’ block stored mid-plains and supplied to IA1a and IA3 & topped up by Klondyke, all other IAs [including IA16] supplied from Klondyke). Experiment 1D Top-up reliability/new irrigable area (Variation 3). Supply of top-up water to existing users and full-supply water to new areas from the demand study (All IAs (except IA1 and IA2) supplied from Klondyke, with RSIS ‘A’ block supply stored at Klondyke). Experiment 1E High A Block Storage. RSIS ‘A’ block water stored at the top of the plains (topped up by Klondyke if required) and supplying IA16, IA1a and IA3. All other areas supplied by Klondyke. A separate iteration of this experiment was conducted to assess the effects of not topping up the A block storage pond with Klondyke water. These results are discussed later in this memorandum. Experiment 1F Top-up for those affected by plan changes/new irrigable area. Supply of plan related top-up water to all existing stream-depleting users and full-supply water to new areas from the demand study (RSIS ‘A’ block stored mid-plains supplied to IA1a and IA3 & topped up by Klondyke, all other IAs [including IA16] supplied from Klondyke). Experiment 1G Full replacement for those affected by plan changes/new irrigable area. Full supply of 95% reliability water to all existing stream-depleting consents and new areas from the demand study (with RSIS ‘A’ block stored mid-plains and supplied to IA1a and IA3 & topped up by Klondyke; all other IAs [including IA16] supplied from Klondyke). Using the infrastructure model developed, the following outputs are presented: 1. Irrigable area - IA (hectares) 2. Klondyke storage volume (active & constructed [for OTOP purposes only]) – Mm3 3. On-farm storage volume (as required to balance headrace capacity) – Mm3 4. Headrace capacity – m3/s 5. Reliability (Generally will be 95 % unless the combination of variables cannot achieve this and reporting the lower reliability is an important part of the narrative) In addition to the experiments listed above, parallel versions of Experiment 1F and 1G were carried out based on information collected from a demand survey conducted by Environment Canterbury. This consent survey version of the model focussed solely on understanding the demand and infrastructure requirements from survey respondents. This report details the results from three additional demand survey experiments based on the infrastructure layouts in Experiments 1F and 1G above. A variation to Experiment 1F was carried out which excluded the newly identified irrigated area in irrigation area IA4. Schematics showing the infrastructure layout of the experiments is given in Appendix C.

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4.4 Experiment Results 4.4.1 Experiment 1A This experiment aims to reflect the current conditions within the zone. Although not a calibration, the intent of the experiment is to ensure the model replicates reality as closely as possible, and where it does not, that the differences are understood. The results of the experiment are presented in Table 5 (below).

Table 5 Experiment 1A Results On-Farm Storage Volume Reliability Irrigated Area (ha) 3 (m )

no new Irrigation Area (IA) Current (modelled) – scheme water Under Plan Change Rules Existing Additional Total Existing Additional Total

1 98% 97% 10,740 — 10,740 — 4,305,132 4,305,132 2 81% 80% 7015 — 7015 — 1a 59% 56% 763 — 763 — — — 3 72% 65% 848 — 848 — — — 4 65% 63% 1,328 — 1,328 — 5 59% 56% 1,227 — 1,227 — 8 63% 60% 2,498 — 2,498 — 120,684 120,684 9 53% 53% 435 — 435 — 10 56% 55% 831 — 831 — 11 62% 60% 752 — 752 — 6 69% 54% 1,355 — 1,355 — 7 69% 54% 948 — 948 137,728 — 137,728 14 69% 47% 1,426 — 1,426 — 16 60% 58% 1,551 — 1,551 100,000 — 100,000 TOTAL — — 31,717 — 31,717 4,663,544 — 4,663,544

4.4.1.1 Discussion Experiment 1A is a representation of current conditions. All existing on-farm storage is included, as is the existing scheme storage at RSIS. Existing deep groundwater takes, surface water takes, stream- depleting groundwater takes and a contribution from Lake Opuha via Kakahu Irrigation Scheme are included and are the sole source of water outside of the RSIS. All existing infrastructure capacities are maintained. Irrigated areas are taken from Aqualinc (2016). The resulting reliabilities were circulated amongst a number of water users and were deemed an appropriate representation of the current conditions (pers comm, Brett Painter). To assist in the understanding of future experiments this experiment was also run using the potential plan change rules (grey text). The intention of this was to determine what the reliabilities could be if potential plan change reduction in reliabilities was enforced but with no additional water being supplied beyond the existing groundwater and surface water takes. The table above shows that reliabilities would drop by up to 22 % depending on the amount of A and B permit water that currently exists in the

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irrigation area. It should be noted that this is an average over large areas, used to consider bulk water supply and storage options. It does not reflect the actual reliability reductions which would apply to individual irrigators.

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4.4.2 Experiment 1B This experiment builds on Experiment 1A by including the supply of top-up water to existing users and full-supply water (95 % reliability) to new areas identified by the demand study. In general the supply of new water was taken from the proposed Klondyke storage. IA1a and IA3 were supplied using a potential storage area midway down the plains which was filled using the small RSIS A block allocation. RSIS B block allocation continues to supply IA1 and IA2. The results of Experiment 1B are presented in Table 6 (below).

Table 6 Experiment 1B Results

Irrigated Area (ha) On-Farm Storage Volume (m3)

Irrigation Area (IA) Reliability (modelled) Existing Additional Total Existing Additional Total

1a 96% 763 600 1,363 — 375,000 375,000 1 98% 10,740 — 10,740 — 4,305,132 4,305,132 2 81% 7015 — 7015 — 3 95% 848 — 848 — 26,000 26,000 4 98% 1,328 450 1,778 — 5 98% 1,227 — 1,227 — 8 95% 2,498 — 2,498 120,684 320,684 9 95% 435 — 435 200,000 10 95% 831 80 911 11 95% 752 — 752 6 96% 1,355 330 1,685 7 96% 948 — 948 137,728 402,000 539,728 14 96% 1,426 — 1,426 16 99% 1,551 287 1,838 100,000 — 100,000 TOTAL — 31,717 1,747 33,464 4,663,544 1,003,000 5,666,544

4.4.2.1 Discussion Experiment 1B introduces the proposed Klondyke storage as a source of water for the OTOP north area. Klondyke is modelled on a winter filling regime such that it is always at peak capacity on the 1st September and receives no top-up during the irrigation season. All irrigation areas from Experiment 1A are included and are supplied with water from Klondyke to top- up their reliability to the target 95 % level. Additional irrigable areas have also been included, as per the Environment Canterbury demand survey which Klondyke supplies fully.

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RSIS ‘A’ block water allocation is used in this experiment and stored in a separate storage above Irrigation Area 3 (IA3). This storage supplies IA1a and IA3. It is noted that the available ‘A’ block water is significantly in excess of the demand from these irrigation areas as an instantaneous flow rate (see later in report for discussion on ‘A’ block storage sizing). At the time of running these scenarios, it was not clear whether legal right to take this water was connected with or separate from the RSIS ‘B’ block water feeding the RSIS Arundel storage and shareholders. The experimental assumption that the ‘A’ block water could potentially be stored and used separately may not be correct. Under this experiment this excess RSIS ‘A’ block water is left unused in the river. Where ‘RSIS ‘A’ block water is unavailable then supply is topped-up via RSIS storage. It is noted however that when RSIS ‘A’ block water is unavailable it is often as a result of a prolonged dry period and this coincides with the ‘RSIS storage also being low or empty. This occurs from the middle / end of summer where river flows reduce. Relying on RSIS storage as a top-up for RSIS ‘A’ block water is therefore problematic.

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4.4.3 Experiment 1C Experiment 1C is as per 1B, however, rather than irrigation areas IA1a and IA3 being supplemented by RSIS B block when RSIS A block water is not available in the mid-plain storage, the supplementary water comes from the proposed Klondyke storage. This increases the demand on Klondyke over Experiment 1B. RSIS B block continues to supply IA1 and IA2. The results for Experiment 1C are presented in Table 7 (below).

Table 7 Experiment 1C Results

Irrigated Area (ha) On-Farm Storage Volume (m3)

Irrigation Area (IA) Reliability (modelled) Existing Additional Total Existing Additional Total

4.4.3.1 Discussion Experiment 1C is the same as 1B, however Klondyke is used to top-up the RSIS ‘A’ block water supply, rather than relying on water stored at RSIS. This has no effect on the overall areas supplied, only the infrastructure layout, and the volume of stored water at Klondyke for use in OTOP north.

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4.4.4 Experiment 1D Experiment 1D supplies top-up water to existing users and full-supply water to new areas exclusively from the proposed Klondyke storage. To account for water sources, the RSIS ‘A’ block water allocation is fed into the proposed Klondyke storage. This reduces the allocation of additional water from the Rangitata River into the proposed Klondyke storage to supply the OTOP north area. RSIS ‘B’ block water continues to supply IA1 and IA2. The results for Experiment 1D are presented in Table 8 (below).

Table 8 Experiment 1D Results

Irrigated Area (ha) On-Farm Storage Volume (m3)

Irrigation Area (IA) Reliability (modelled) Existing Additional Total Existing Additional Total 1a 96% 763 600 1,363 — 375,000 375,000 1 98% 10,740 — 10,740 — 4,305,132 4,305,132 2 81% 7015 — 7015 — 3 95% 848 — 848 — 26,000 26,000 4 96% 1,328 450 1,778 — 5 95% 1,227 — 1,227 — 8 96% 2,498 — 2,498 120,684 320,684 9 96% 435 — 435 200,000 10 96% 831 80 911 11 96% 752 — 752 6 97% 1,355 330 1,685 7 97% 948 — 948 137,728 402,000 539,728 14 97% 1,426 — 1,426 16 98% 1,551 287 1,838 100,000 — 100,000 TOTAL — 31,717 1,747 33,464 4,663,544 1,003,000 5,666,544

4.4.4.1 Discussion Experiment 1D considered storing the RSIS ‘A’ block allocation in the proposed Klondyke storage, rather than a separate storage much further down the plains. The concept behind this is to make the stored water available to a greater irrigation area without the need to pump or double up on infrastructure. The effect of this is that water abstracted by RDR for storage at Klondyke can be reduced by the volume available under the RSIS ‘A’ block allocation. Notwithstanding this, storage capacity is still required in the proposed Klondyke storage.

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4.4.5 Experiment 1E In Experiment 1E consideration is given to fully supplying all existing stream-depleting users (i.e. relinquishing the stream-depleting consent) as well as any new areas from the demand study. For irrigation areas IA16, IA1a and IA3 water is supplied via a potential storage at the top of the plains which is filled using the RSIS ‘A’ block allocation with all other areas being supplied via the proposed Klondyke storage. As with all experiments irrigation areas IA1 and IA2 are supplied by RSIS ‘B’ block water. The results of Experiment 1E are presented in Table 9 (below).

Table 9 Experiment 1E Results

Reliability Irrigated Area (ha) On-Farm Storage Volume (m3)

-Up

Solely A Block water (modelled Scenario 1E(a)) A Block with Klondyke Top (modelled) Irrigation Area (IA) Existing Additional Total Existing Additional Total 1a 86% 97% 763 600 1,363 — 375,000 375,000 1 98% 98% 10,740 — 10,740 — 4,305,132 4,305,132 2 81% 81% 7015 — 7015 — 3 94% 96% 848 — 848 — 26,000 26,000 4 96% 96% 1,328 450 1,778 — 5 95% 95% 1,227 — 1,227 — 8 98% 98% 2,498 — 2,498 120,684 320,684 9 98% 98% 435 — 435 200,000 10 98% 98% 831 80 911 11 98% 98% 752 — 752 6 95% 95% 1,355 330 1,685 7 95% 95% 948 — 948 137,728 402,000 539,728 14 95% 95% 1,426 — 1,426 16 85% 98% 1,551 287 1,838 100,000 — 100,000 TOTAL — — 31,717 1,747 33,464 4,663,544 1,003,000 5,666,544

4.4.5.1 Discussion Experiment 1E considered storing RSIS ‘A’ block water in a storage higher up the OTOP plains in order to serve IA16 in addition to IA1a and IA3. The intention of this experiment was to determine if the RSIS ‘A’ block water would be sufficient to serve a larger area (with IA16 included). Two iterations of this were run; one solely supplying the upper plains storage pond with RSIS ‘A’ block water [1E(a)], and the other using Klondyke to top up the storage pond [1]. From the table above, IA1a and IA16 would both fall short of the 95 % reliability target if only RSIS ‘A’ block water was supplied. The addition of Klondyke top-up water enabled both of these irrigation areas to meet the desired reliability targets.

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4.4.6 Experiment 1F This experiment extends Experiment 1C. Top-up water is supplied to existing users and full-supply water (95 % reliability) to new areas identified by the demand study. In general the supply of new water was taken from the proposed Klondyke storage. IA1a and IA3 were supplied using a potential storage area midway down the plains which was filled using the RSIS ‘A’ block allocation. When this storage was unable to meet the demand additional water was provided from the proposed Klondyke storage. RSIS ‘B’ block continues to supply IA1 and IA2. The additional variable considered here in Experiment 1F is the implementation of higher minimum flows and 150 day stream-depleting rule which required a larger degree of top-up.to keep stream- depleters at 95 % reliability. The results of Experiment 1F are presented in Table 10 (below).

Table 10 Experiment 1F Results

Irrigated Area (ha) On-Farm Storage Volume (m3)

Irrigation Area (IA) Reliability (modelled) Existing Additional Total Existing Additional Total 1a 94% 763 600 1,363 — 375,000 375,000 1 97% 10,740 — 10,740 — 4,305,132 4,305,132 2 81% 7015 — 7015 — 3 96% 848 — 848 — 26,000 26,000 4 99% 1,328 450 1,778 — 5 99% 1,227 — 1,227 — 8 98% 2,498 — 2,498 120,684 320,684 9 98% 435 — 435 200,000 10 98% 831 80 911 11 98% 752 — 752 6 96% 1,355 330 1,685 7 96% 948 — 948 137,728 402,000 539,728 14 96% 1,426 — 1,426 16 99% 1,551 287 1,838 100,000 — 100,000 TOTAL — 31,717 1,747 33,464 4,663,544 1,003,000 5,666,544

4.4.6.1 Discussion This experiment replicates the infrastructure layout of Experiment 1C. The important difference here is that planning rules have been implemented which reduce the reliability of surface water and stream- depleting groundwater takes to 46 % and 0 % for ‘A’ block and ‘B’ block abstractions respectively. This created a greater burden on the main supply infrastructure at Klondyke storage and the main headrace system. The result of this was a larger storage volume at Klondyke was required and a higher capacity head race.

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4.4.7 Experiment 1F (Demand Survey Experiment) Experiment 1F (Demand Survey) provided top-up water to all users and fully supply water to new areas identified in the demand survey and through additional conversations regarding IA16. In this experiment, RSIS ‘A’ block water is stored mid-plains and supplies irrigation areas IA1a and IA3 (with top-up water supplied by Klondyke). All other irrigation areas are supplied with Klondyke water via Canal B. The results for Experiment 1F (Demand Survey Experiment) are presented in Table 11 (below).

Table 11 Experiment 1F (Demand Survey Experiment) Results ) ) 3 3

Farm Farm

) 3 Irrigation Area (IA) Reliability (modelled) Existing Irrigated Area (ha) Deep Groundwater Area Removed (ha) Additional Irrigated Area (ha) Total Irrigated Area (ha) Existing On- Storage Farm Volume (m Additional On- Storage Farm Volume (m Total On Storage Volume (m 1 — 0 — 30 30 — 4,305,132 4,305,132 2 — 171 — — 171 — 1a 95% 863 148 400 1,115 — 113,000 113,000 3 96% 1,180.5 622.5 — 558 — 26,000 26,000 4 99% 788 160 400 1,028 — 5 99% 610 — 200 810 — 8 99% 1,762 1095 — 667 120,684 320,684 9 — 105 105 — — 200,000 10 99% 535 — — 535 11 99% 381 266 68 183 6 95% 1,755 — 330 2,085 7 — — — — — 137,728 208,000 345,728 14 — 600 600 — — 16 95% 763 282 287 768 100,000 — 100,000 TOTAL — 9,513.5 3833.5 1,715 7395 4,663,544 547,000 5,210,544

4.4.7.1 Discussion The infrastructure layout for experiment 1F (demand survey) comprises RSIS ‘A’ block water supplying a mid-plains storage pond which supplies IA1a and IA3. If required, Klondyke provides top-up to this pond. For all other areas (including IA16), Klondyke supplies scheme water via Canal B and offtakes to bulk on farm storage ponds. Additional bulk on farm storage has been modelled to provide extra demand storage for the irrigation areas. Existing KIL scheme water is also applied to this set of experiments.

Deep groundwater allocations and associated irrigated areas have been excluded from the model parameters for this experiment. Plan related reductions in existing reliabilities have been applied to remaining consents in the zone.

Additional irrigated area that was identified in the demand survey has been applied including an additional 400 ha in IA4.

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4.4.8 Experiment 1F Variation (Demand Survey Experiment) Experiment 1F Variation (Demand Survey) differs from the Experiment 1F (demand survey) above in that this variation excludes the newly identified irrigable area in IA4. The experiment provides top-up water to all users and fully supply water to new areas identified in the demand survey and through additional conversations regarding IA16. In this experiment, RSIS ‘A’ block water is stored mid- plains and supplies irrigation areas IA1a and IA3 (with top-up water supplied by Klondyke). All other irrigation areas are supplied with Klondyke water via Canal B. The results of Experiment 1F Variation (Demand Survey Experiment) are presented in Table 12 (below).

Table 12 Experiment 1F Variation (Demand Survey Experiment) Results ) ) 3 3

Farm Farm

) 3 Irrigation Area (IA) Reliability (modelled) Existing Irrigated Area (ha) Deep Groundwater Area Removed (ha) Additional Irrigated Area (ha) Total Irrigated Area (ha) Existing On- Storage Farm Volume (m Additional On- Storage Farm Volume (m Total On Storage Volume (m 1 — 0 — 30 30 — 4,305,132 4,305,132 2 — 171 — — 171 — 1a 95% 863 148 400 1,115 — 113,000 113,000 3 96% 1,180.5 622.5 — 558 — 26,000 26,000 4 99% 788 160 — 628 — 5 99% 610 — 200 810 — 8 99% 1,762 1095 — 667 120,684 320,684 9 — 105 105 — — 200,000 10 99% 535 — — 535 11 99% 381 266 68 183 6 96% 1,755 — 330 2,085 7 — — — — — 137,728 208,000 345,728 14 — 600 600 — — 16 99% 763 282 287 768 100,000 — 100,000 TOTAL — 9,513.5 3,833.5 1,315 6,995 4,663,544 547,000 5,210,544

4.4.8.1 Discussion The infrastructure layout for experiment 1F Variation (demand survey) comprises RSIS ‘A’ block water supplying a mid-plains storage pond which supplies IA1a and IA3. If required, Klondyke provides top-up to this pond. For all other areas (including IA16), Klondyke supplies scheme water via Canal B and offtakes to bulk on farm storage ponds. Additional bulk on farm storage has been modelled to provide extra demand storage for the irrigation areas. Existing KIL scheme water is also applied to this set of experiments.

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There is no material change to the reliabilities under this experiment compared with Experiment 1F (demand survey).

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4.4.9 Experiment 1G Experiment 1G represents the greatest demand placed on the proposed storage at Klondyke. Under this experiment the proposed Klondyke storage provides full-supply of water to all existing stream- depleting consents and new areas from the demand study (i.e. all stream depleting consents are retired). Irrigation areas IA1a and IA3 are supplied via a small on-plains storage which is filled with the RSIS ‘A’ block allocation and topped up from Klondyke when the A block water is unavailable. Again, IA1 and IA2 continue to be supplied from RSIS ‘B’ block water. The results of Experiment 1G are presented in Table 13 (below).

Table 13 Experiment 1G Results

Irrigated Area (ha) On-Farm Storage Volume (m3)

Irrigation Area (IA) Reliability (modelled) Existing Additional Total Existing Additional Total 1a 96% 763 600 1,363 — 375,000 375,000 1 97% 10,740 — 10,740 — 4,305,132 4,305,132 2 79% 7015 — 7015 — 3 95% 848 — 848 — 32,000 32,000 4 96% 1,328 450 1,778 5,000 5 99% 1,227 — 1,227 8 100% 2,498 — 2,498 120,684 325,684 9 100% 435 — 435 200,000 10 100% 831 80 911 11 100% 752 — 752 6 95% 1,355 330 1,685 7 95% 948 — 948 137,728 402,000 539,728 14 95% 1,426 — 1,426 16 100% 1,551 287 1,838 100,000 — 100,000 TOTAL — 31,717 1,747 33,464 4,663,544 1,014,000 5,677,544

4.4.9.1 Discussion This experiment replicates the infrastructure layout of Experiment 1C. Rather than the minimum flow restrictions placed on stream-depleting consents in Experiment 1F this experiment replaces all existing surface water and stream-depleting groundwater takes. This requires the main supply infrastructure at the proposed Klondyke storage and the main headrace system to fully replace these lost supplies. Deep groundwater, unconnected to surface waters, remains unaffected. A substantially larger sized Klondyke pond and increased Canal B capacity is required for this experiment to meet the 95% reliability demand requirements. In this experiment, Klondyke was sized at 55 Mm3 and Canal B was sized at a capacity of 4.5 m3/s.

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4.4.10 Experiment 1G (Demand Survey Experiment) Experiment 1G (Demand Survey) provides full supply water to all existing stream depleting consents and new irrigated areas as identified in the demand survey. RSIS ‘A’ block water supplies irrigation areas IA1a and IA3 and is topped up by Klondyke. All other areas are supplied via Klondyke. The results of Experiment 1G (Demand Survey Experiment) are presented in Table 14 (below).

Table 14 Experiment 1G (Demand Survey Experiment) Results ) ) 3 3

Farm Farm

) 3 Irrigation Area (IA) Reliability (modelled) Existing Irrigated Area (ha) Deep Groundwater Area Removed (ha) Additional Irrigated Area (ha) Total Irrigated Area (ha) Existing On- Storage Farm Volume (m Additional On- Storage Farm Volume (m Total On Storage Volume (m 1 — — — 30 30 — 4,305,132 4,305,132 2 — 171 — — 171 — 1a 96% 863 148 400 1,115 — 113,000 113,000 3 96% 1,180.5 622.5 — 558 — 26,000 26,000 4 98% 788 160 400 1,028 — 5 98% 610 — 200 810 — 8 98% 1,762 1,095 — 667 120,684 320,684 9 — 105 105 — — 200,000 10 98% 535 — — 535 11 98% 381 266 68 183 6 97% 1,755 — 330 2,085 7 — — — — — 137,728 208,000 345,728 14 — 600 600 — — 16 99% 763 282 287 768 100,000 — 100,000 TOTAL — 9,513.5 3833.5 1,715 7,395 4,663,544 547,000 5,210,544

4.4.10.1 Discussion This experiment replicates the infrastructure layout of Experiment 1F (demand survey). Rather than the minimum flow restrictions placed on stream-depleting consents in Experiment 1F (demand survey) this experiment replaces all existing groundwater takes. This requires the main supply infrastructure at Klondyke storage and the main headrace system to fully replace these lost supplies.

There is no material change to the reliabilities under this experiment compared with Experiment 1F (demand survey).

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4.5 Summary of Infrastructure Outcomes The experiments detailed above were undertaken for the OTOP north area only; the outcomes for the key variables are summarised below (Table 15).

Table 15 Experiment 1 Infrastructure Outcomes (Modelled Constructed Volumes) th 100 Percentile th 80 Percentile Volume Volume ) ) ) ) 3

3 3 3 New on- farm volume (Mm3) /s) 3 Experiment Modelled Irrigated Area (ha) north OTOP capacityheadrace (m Klondyke Storage Volume (Mm RSIS ‘A’ Storage Block volume (Mm Klondyke Storage volume (Mm RSIS ‘A’ Storage Block volume (Mm

1A 31,717 — — — — — — 1B 33,464 3.2 25 1 22.3 1 1 1C 33,464 3.7 31 1 27.9 1 1 1D 33,464 4.3 37 — 33.6 — 1 1E 33,464 1.6 21 1 19.3 1 1 1E (a) 33,464 1.6 21 1 19.3 1 1 1F 33,464 4.3 45 1 41.2 1 1 1G 33,464 5.2 55 1 49.3 1 1 1F 7,395 1.9 19 1 17.2 1 0.5 (demand survey) 1F 6,995 1.4 15.5 1 13.9 1 0.5 Variation (demand survey) 1G 7,395 2.6 30 1 26.4 1 0.5 (demand survey)

The potential storage volumes presented for Klondyke and RSIS ‘A’ block water above relate to the th volume required to meet demand in all modelled years (100 percentile volume) and in 8 years out of 10 (80th percentile volume). These figures are useful in determining what size an economical and reliable storage may need to be; for reference the full percentile plots have been provided (Figure 6, Figure 7). The integration of the RSIS ‘A’ block water into a wider solution proves challenging. The allocation allows for a relatively small flow rate. Depending on the area of irrigation served with this water an independent scheme may be possible without connection to the wider OTOP north area. Alternatively, the water could be abstracted to either the proposed Klondyke storage or to RSIS storage (as currently). RDRML have applied for consent to construct the Klondyke storage at a maximum capacity of 53 3 3 Mm . The experiments presented for the OTOP north area would require 40 % (21 Mm ) - 104 % (55 Mm3) of this capacity to meet demand in all years. It has been noted previously in this report that RDRML run-or-river water can also potentially be supplied to OTOP via a water ‘swap’ where the equivalent volume of water is supplied from Lake Coleridge to shareholders at the northern end of the RDR scheme.

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The required head race capacity does not vary significantly in the experiments, except in Experiment 1G. The capacities required are well within the range for economic use of pipe conveyance.

Figure 6 Required volume at proposed Klondyke Storage (OTOP north only)

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Figure 7 Required storage volume for RSIS ‘A’ block water (OTOP north only)

The demand survey set of experiments presented different required storage volumes (see Figure 8) than the main set of series one experiments. It was noted that the Klondyke volumes are much smaller than the original experiment F (demand survey) and G (demand survey) model runs using the consented data. The modelled Klondyke volumes are approximately 40%–50% smaller than those model runs. This is mainly due to the smaller irrigated areas being modelled (as areas are only based on survey respondents) and subsequently less demand for water from Klondyke from the irrigated areas. When the raw demand of Experiment G was plotted together for each of the model variations, a similar (or greater) reduction in demand is also evident. There are a few occasions where demand under the demand survey version is higher than demand under the consented version of the model. It is thought that this could be as a result of a reduction in on farm storage sizes which was allowed for under the demand survey version. These on farm storages act as an additional layer of buffering demand from the farms and so where the on farm storages are not big enough to be able to buffer demand they will request more water from Klondyke to keep themselves topped up.

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Figure 8 Average active volume Klondyke (Demand Survey Experiments)

35,000,000

30,000,000 ) 3 25,000,000

20,000,000

15,000,000

10,000,000

5,000,000 Average Yearly Volume (m Volume Yearly Average

0 0.0 0.2 0.4 0.6 0.8 1.0 Percentile Scenario 1G Scenario 1F(a) Scenario 1F(b)

4.6 Summary of Environmental Outcomes A key benefit of a scheme as modelled is that the current stream depleting groundwater takes and users of surface water abstracted from sensitive river catchments can be replaced with an alpine source of water. In particular, groundwater users in the conjunctive use zone adjacent to the Orari River can be reliably supplied with water to supplement or replace their existing consents. The model considered two options for this water to reach these users: via a direct take from a new headrace, or via an additional storage reservoir holding RSIS ‘A’ block water (if this is legally possible and desired by the consent holder). Either of these experiments were able to supply the required water, however the success of such an extension to RSIS will rely on an increase in on farm storage. Increasing the on farm storage allows for smaller infrastructure upstream of the irrigated areas within IA3 and provides greater reliability for these users.

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5.0 Model Experiments – South OTOP

5.1 General The south of the OTOP Zone extends from the Opihi River catchment south, and to the west into the Ashwick Flats area. For the purposes of this study the OTOP south area excludes the Pareora River catchment. Experiment 2 is intended to demonstrate the opportunities for efficient water use in the southern part of the OTOP Zone, and what scale this infrastructure would need to be. Any connection to and from the OTOP north area is excluded from consideration. The south of the Zone benefits from the presence of Lake Opuha which stores water from the Opuha River and provides both irrigation and environmental flows to downstream users/values. As with the north of the Zone an overall reduction in available water resource may occur in relation to a review of the planning rules. There is also a desire to increase irrigable area and reliability in some areas, though additional irrigable area may well be constrained by nutrient planning rules and limits which are under development. In addition to this there is an interest in exploring options to change the way in which environmental flows from Lake Opuha are managed, such that greater environmental outcomes can be achieved. As with Experiment 1 in the OTOP north area, consideration of an out-of-zone source of water has been included. This allows an assessment of whether such water is useful in supporting outcomes for the area. Previous studies have considered the technical feasibility of supplying parts of OTOP north from the Waitaki system or from the Rangitata system (in particular, ‘swapping’ Lake Opuha supply to the lower catchment with Rangitata water so that Lake Opuha water can instead be supplied further up the catchment). The source of external water for these OTOP north experiments is not required to be specified, though it is assumed as a 100 % reliable source for the rates and volumes being considered. The basis for investigations in the OTOP south area are what effects changes to stream depletion rules may have on the need for water in the area, and what effects changes to operating regimes of existing infrastructure may have. Also considered are smaller scale new infrastructure, and the opportunity to develop a large-scale storage in the area.

Schematics for the South OTOP model are provided in Appendix D.

5.2 Model Variables and Conditions A number of variables were tested with Experiment 2 to identify what infrastructure would best fit with the outcomes required in the area. Within Experiment 2, a source of water external to the area has been included which can meet the demand challenges stated above.

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Figure 9 OTOP south area

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Environment Canterbury Regional Council; Hurunui District Council; Waimakariri District Council; Timaru District Council; Waimate District Council; Mackenzie District Council; Waitaki District Council, Land Information New Zealand & Eagle Technology Group Ltd

Printed 24 Jan 20 17 09:15 Pr oj e c t : OTOP Water Resources Assessment Sc ale: Approved MM Da te Scale: 1:300,000 (A 4 si ze ) De sig n ed SP Dr aw n SP Ti tl e : So uth OT OP Ir rig ation Ar eas St at u s : R ev . Ma p N o . Ch ec ke d MM Ch ec ke d MM

Primary Map N o. 5 Fin al 1 5

© C opyright A ECOM , 2015. This map is confidentiala nd shallonly be used for the purposes of this project. © C opyright A ECOM New Zealand Limited 2015. This map is confidential and shall only be used for the pur pose of this pr oject. The infor mation contained or referred to inth isdr awing-r eport w as developed for use in the project. A ECOM New Zea land Limited d oesn ot Legend accept any responsibility fo r the use of the infor mation by any other parties and state expressly that they do not warrant the accuracy of the information. A ny use of the information by other parties isat their own risk. The signing of this title block confirms the design and dr afting of thisp roject have been prepar ed and checked inaccorda ncewith the A ECOM Quality A ssur ance system cer tified to A S/NZS ISO 9001:200 0. No part of this drawing/ report may be copied or used w ithout the prior writte n consent of AE C OM N ew Zealand Limited.

South OTOP Irrigation Areas Map features depicted in terms of N ZTM projection.

Data S ources: NZ T opographical Feature s- LINZ NZ National Top o Dataset 2014 Cadastral B oundaries - LIN Z N Z C adastral D ataset 2014 Re v. By App. Desc ription Date AECOM OTOP Regional Water Assessment 46 OTOP Regional Water Resource Assessment

5.2.1 Lake Opuha Lake Opuha is an irrigation storage reservoir that was completed in 1998. The dam was formed through impounding the Opuha River downstream of the confluence of the North and South Opuha Rivers. The lake has a capacity (at current operating capacity of 391.2 mRL) of approximately 81 Mm3, and incorporates a small hydropower plant at the dam. The lake provides water supply for land owners who are shareholders in the Opuha Water Limited (OWL) irrigation scheme. Shareholders generally receive good reliability from the lake, however in recent years a lack of winter snowfall and dry summers have put pressure on the water supply. The OWL system uses the Opuha River as a conveyance mechanism with the lake releasing water down the Opuha River. Some irrigation water is directly abstracted at various points along the river, whilst other water is abstracted from a local source (e.g., upper Opihi catchment) which is 'swapped' with Lake Opuha supply. Environmental contributions released from the dam remain in the river. One of the experiments explores what effects a change in the lake management regime will have on stored volumes and irrigation reliabilities. The existing regime uses 2 bands. In the model the lake fills naturally (as opposed to an artificial winter fill scenario), according to inflows from the catchments of the North and South Opuha Rivers.

5.2.2 Kakahu Irrigation Scheme The supply of water to Kakahu Irrigation Scheme (below Kakahu Bush) via the existing distribution network has been found to be a constraint on the availability of water to this area. Based on information received from Environment Canterbury, the Kakahu scheme abstracts water from the Opuha River near Skipton Bridge. The water is conveyed via a 9km sealed pipeline and is discharged into the Kakahu River at a site known as Mulvihills. The ordered water is then abstracted from the Kakahu River downstream of the gorge. The distribution race has a capacity of 0.9 m3/s (Section A), and then reduces to a capacity of 0.6 m3/s (Section B) and then further reduces to 0.4 m3/s (Section C). The north part of the OTOP model handles the reliability and water supply of the users on this scheme. A demand is placed on the Opuha River in the south part of the model to represent the water that is abstracted for this scheme.

5.2.3 Other Irrigation Schemes Opuha Water Limited also supplies water via Lake Opuha to other irrigation schemes along the Opihi River. These schemes are the Totara Valley, Waitohi and Levels Plain schemes. The model represents these schemes as abstractions from the Opihi River which are then fed into bulk on farm storages to service the entire irrigation area. Losses from the Levels Plain scheme are well documented and are represented in the model with a loss rate of 50 %. This loss rate creates an additional demand on Lake Opuha. In some of the experiments, this loss rate is eliminated (assuming development of a fully lined refurbishment of the system), thereby returning water back to Lake Opuha for alternative use.

5.2.4 Potential New Infrastructure In addition to the existing infrastructure a number of new conveyances and storages are explored in the model. One experiment in the model considers a new canal between the Opihi River near Fairlie and Lake Opuha. The intention of this canal is to provide an additional source of water to Lake Opuha through flood harvesting of the Opihi River. This canal has a fixed modelled capacity of 10 m3/s.

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A new centrally located large reservoir is included in the south OTOP model. This reservoir has varying capacity depending on the irrigation requirements. Its role in the model is to provide water to irrigation areas downstream of Totara Valley, allowing Lake Opuha to meet more demand from existing and new irrigated areas elsewhere. In this set of experiments, the reservoir is modelled under a winter fill scenario with the source of that water not specified, but assumed to be from outside the OTOP Zone. In the integrated experiment (Section 6) the large reservoir is connected to the north OTOP model via Canal B to allow winter filling. Depending on its placement, this could require pumping from the canal up into the reservoir. All new infrastructure is modelled as being fully lined with no losses outside of the system.

5.2.5 Irrigation Season The model uses an irrigation season of 1 September through to 30 April each year.

5.2.6 Increased Lake Opuha Operating Level One variable that is explored in the scenarios is that of raising the operating level of Lake Opuha. The current operating level of 391.2 mRL can hold a volume of approximately 81 Mm3 of water. Raising 3 the operating level to 391.7 mRL will result in approximately an additional 6 Mm of storage capacity but importantly would not require any physical works at the dam. The additional water could then be used to meet higher demand during the irrigation season and / or to supply environmental flows.

5.2.7 Additional Irrigated Areas Additional areas for irrigation in the south OTOP area were identified as being those who are shareholders of the Aoraki Water Trust (AWT). The AWT scheme proposes transferring water from Lake Tekapo, over Burkes Pass, and into the Fairlie Basin. While the AWT scheme is not modelled here, the areas of currently unirrigated land specific under the AWT scheme were used as an indication of likely new demand for water. In Section 5.1 it is noted that these areas could feasibly be supplied from the Waitaki system or from the Rangitata system via a water ‘swap'.

5.2.8 Plan Change Outcomes The plan change experiment modelled the effects of new minimum flows in the Opihi River system combined with the effects of groundwater abstractions being assessed on 150 day stream depletion volumes. The result of these changes will be less water availability through existing methods of abstractions (surface and groundwater), and therefore an alternative source of water is required to maintain reliability. When applying this change, deep groundwater takes (i.e. takes that are not hydraulically connected to surface water) are unaffected and remain as a source of water for those irrigation areas.

5.2.9 General Uptake of Surface Water and Groundwater It was found that the consented volumes of water within the zone far exceeded the amount of water required by the zone. However, the consented volumes cannot take into account times where the water is not available due to minimum flow restrictions, or from landowners' choice of the amount of water yto a appl nd when. As such, a reduction factor of 78 % was applied to the consented volumes to bring the amount of water being applied in the model to those volumes reported in the Environment Canterbury Water Use Report – 2013 / 2014 Water Year.

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5.3 Experiments and Outputs A range of experiments were undertaken in the south OTOP zone to demonstrate the effects of the variables defined above: 1. Experiment 2A This experiment is intended to demonstrate the ability of the model to represent current conditions and water supply. For the most part, the model’s performance has been compared against the measured Lake Opuha water levels. It is important to note that Lake Opuha has been in service since 1998, whereas the model operates from 1981. The extended model period is useful as it enables a wider variety of climatic situations to be considered. 2. Experiment 2B This experiment is intended to model current irrigated areas and supply capacities, but with potential plan changes imposed. The ‘plan changes’ are: - Imposition of higher minimums flows in the rivers which will reduce the number of days on which water can be taken - Classification of stream depleters by the Schedule 9 150 day rule, rather than just 7 or 30 days. This will increase the number of abstractors classified as stream depleting and therefore falling under restrictions. 3. Experiment 2C This experiment investigates potential plan change rules as well as new ‘small new water’ solutions. Using Experiment 2B as a base, a new Ashwick canal was modelled, new Lake Opuha maximum operating level, new lake management regime, and piping/lining Levels Plain. These small water solutions were assessed individually and in combination. 4. Experiment 2C (Variation) As in experiment 2C above, but this experiment explored the effect of removing lower Kakahu (supplied instead from the Rangitata). 5. Experiment 2D This experiment modelled the potential plan change rules and new small water solutions (as per Experiment 2C), but also included newly identified areas that could be irrigated. 6. Experiment 2D (Variation) As above (Experiment 2D), but with the removal of lower Kakahu. 7. Experiment 2E This experiment considered applying the small water solutions as above as well as a new central storage reservoir. Irrigation areas downstream of the new reservoir were supplied via the new central storage and gains in water to the system were calculated. 8. Experiment 2F This experiment includes a new central storage reservoir, but also includes newly identified irrigated areas. It considers how much additional land could be irrigated from Lake Opuha if a central storage is in place and the infrastructure exists to convey the water where it is needed. 9. Experiment 2F (Variation) This experiment is the same as Experiment 2F above, but with the removal of lower Kakahu from the scheme.

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5.4 Experiment Results 5.4.1 Experiment 2A This experiment determined how well the current model infrastructure reproduced the known conditions. Irrigated areas were considered to be those areas identified by aerial photography and remote sensing (as identified by Aqualinc, 2016). Demand for these areas was determined through soil moisture demand modelling based on AECOM’s in-house Irrioptimiser model. All existing rules for maintaining minimum flows at current monitoring sites were retained and water abstractions from surface and groundwater were determined through consents data. The model’s performance was assessed using actual lake levels of Lake Opuha (Figure 10).

Table 16 Experiment 2A Results ) ) ) 3 3 3

- -farm Irrigation Area (IA) Reliability (modelled) Existing Irrigated Area (ha) Additional Irrigated Area (ha) Total Irrigated Area (ha) Existing on- farm storage volume (m Additional on storage volume (m Total on farm storage volume (m

17 75% 1,161 — 1,161 11,194 — 11,194 18 65% 4,707 — 4,707 39,496 — 39,496 19 50% 616 — 616 — — — 20 49% 291 — 291 31,172 — 31,172 21 100% 1,918 — 1,918 69,868 — 69,868 22 100% 14 — 14 — — — 23 88% 87 — 87 — — — 24 23% 417 — 417 88,830 — 88,830 25 93% 875 — 875 114,554 — 114,554 26 100% 311 — 311 — — — 27 78% 179 — 179 39,878 — 39,878 28 62% 123 — 123 — — — 29 55% 221 — 221 — — — 30 82% 1,680 — 1,680 220,000 — 220,000 31 100% 2,016 — 2,016 220,000 — 220,000 32 100% 1,447 — 1,447 260,000 — 260,000 33 N/A 0 — — — — — TOTAL — 16,063 — 16,063 1,094,992 — 1,094,992

5.4.1.1 Discussion This base case model experiment was calibrated against the actual Lake Opuha water level data provided by Opuha Water Limited. This dataset began at the time of lake filling in 1998. A graph comparing the actual lake stage height with the modelled stage height is included in Figure 10 below.

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Figure 10 Lake Opuha model outcome

The graph shown above shows that under the current conditions the model reproduces the measured Lake Opuha stage heights reasonably well. Given the large number of assumptions and simplifications of the system being modelled, this result represents an appropriate level of calibration to the existing system. Reliabilities of the current scenario are modelled and given in the table above. Generally, the high reliability areas are in areas where there is also a high amount of existing on farm storage (relative to the irrigated area) or where there is a small amount of irrigated land which is able to be fully met by existing groundwater and surface water takes. From the assumptions made in the model, it is uncertain if these high reliabilities reflect actual conditions; it is possible they are a result of mis-allocation of consents to irrigated areas.

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5.4.2 Experiment 2B This experiment uses the current areas and water supply and implements the modified minimum flows in the rivers and classifies stream depleting takes by the Schedule 9 150 day rule. Classifying stream depleters in this way creates additional demand which is supplied by Lake Opuha for this experiment. The adjustment of minimum flows at Saleyards Bridge comprises: x Imposition of higher minimums flows in the rivers which will reduce the number of days on which water can be taken x Classification of stream depleters by the 150 day rule, rather than 7 or 30 days. This will increase the number of abstractors classified as stream depleting and therefore falling under restrictions.

Table 17 Experiment 2B Results ) ) ) 3 3 3 farm farm

- ge

Irrigation Area (IA) Reliability (modelled) Existing Irrigated Area (ha) Additional Irrigated Area (ha) Total Irrigated Area (ha) Existing on- farm storage volume (m Additional on- farm storage volume (m Total on stora volume (m 17 75% 1,161 — 1161 11,194 — 11,194 18 64% 4,707 — 4707 39,496 — 39,496 19 50% 616 — 616 — — — 20 48% 291 — 291 31,172 — 31,172 21 100% 1,918 — 1918 69,868 — 69,868 22 100% 14 — 14 — — — 23 88% 87 — 87 — — — 24 23% 417 — 417 88,830 — 88,830 25 93% 875 — 875 114,554 — 114,554 26 100% 311 — 311 — — — 27 77% 179 — 179 39,878 — 39,878 28 62% 123 — 123 — — — 29 54% 221 — 221 — — — 30 81% 1,680 — 1680 220,000 — 220,000 31 100% 2,016 — 2016 220,000 — 220,000 32 100% 1,447 — 1447 260,000 — 260,000 33 N/A — — — — — — TOTAL — 16,063 — 16,063 1,094,992 — 1,094,992

5.4.2.1 Discussion Three minimum Saleyards Bridge flow regimes were modelled: 1. Current minimum flows using two lake level bandings (ORRP regime) 2. Current minimum flows using three lake level bandings (OEFRAG regime) 3. Revised minimum flows using three lake level bandings (Possible revision) (results shown in the table above).

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Table 18 Lake Opuha Operating Rules – Saleyards Bridge Minimum Flows

Saleyards Bridge Minimum Flows (m3/s) Month Current Regime OEFRAG Regime Possible Revision (ORRP) Opuha Lake 385 m – 380 m – 385 m – 380 m – >374 m <374 m >385 m >385 m Level 380 m 370 m 380 m 370 m January 3.5 3.35 3.5 3.4 3.35 4.45 3.4 3.0 February 3.5 3.35 3.5 3.4 3.35 4.45 3.4 3.0 March 7.5 5.35 7.5 6.4 5.35 7.5 6.0 5.0 April 8.0 5.6 8.0 8.0 5.6 6.5 5.0 4.5 May 4.5 3.85 4.5 4.5 3.85 4.5 4.5 3.5 June 4.0 3.6 4.0 4.0 3.6 4.0 3.5 3.5 July 4.0 3.6 4.0 4.0 3.6 4.0 3.5 3.5 August 4.5 3.85 4.5 4.5 3.85 4.5 4.0 3.85 September 6.0 4.6 6.0 5.3 4.6 6.0 5.0 4.6 October 8.5 5.85 8.5 7.2 5.85 8.0 7.0 5.5 November 7.0 5.1 7.0 6.1 5.1 7.0 6.0 5.1 December 6.0 4.6 6.0 5.3 4.6 6.0 5.0 4.6 Average 5.58 4.39 5.58 5.18 4.39 5.58 4.69 4.14

Average reliabilities in the irrigation areas do not differ markedly from the base case scenario under each of the plan change scenarios. This is due to Lake Opuha meeting the extra demand (where occurring) under a potential plan change to the minimum flow regime at Saleyards Bridge. To understand the differences between these scenarios, results of the Lake Opuha active volumes and volume of outflows each irrigation season were assessed. Figure 11 and Figure 12 shows the lowest lake levels (during dry seasons) and highest outflow volumes (during wet seasons) under the current minimum flows using the two lake level banding. Irrigation outflow remains unchanged, and therefore the higher outflow volumes would contribute to environmental flows. In seasons that are not extremely wet or dry, the differences between the lake management regimes are small.

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Figure 11 Stored Volume Lake Opuha

Figure 12 Lake Opuha Outflows (Irrigation Season) under different flow regimes

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5.4.3 Experiment 2C (a, b, c) Using Exp2B as a base (revised flow regime with three lake level bands), the model included the Ashwick canal (a), new Lake Opuha maximum level (b), and piping/lining Levels Plain (c). No new irrigated areas were considered at this point. This is referred to as the ‘small new water’ solution. The goal was to assess each of these changes individually to determine what benefits they may be able to deliver the system individually. The changes can then be aggregated to determine a total volume of ‘additional’ water that may be available.

5.4.3.1 Experiment 2C(a) This experiment sought to understand the effect of a potential Ashwick canal on the lake levels in Lake Opuha. The source of this water was modelled to come from the Opihi River near Cloudy Peaks and move across the Ashwick Flats to flow into Lake Opuha. The aim was to understand how much water may be available for abstraction from the Opihi River near Cloudy Peaks. A canal was modelled with a 10 m3/s capacity to abstract water from the Opihi when it was at sufficiently high flow. The take was modelled as a BA consent and was limited by minimum flow requirements at the downstream Rockwood site. The graph below (Figure 13) shows the percentile distribution of flow that could be abstracted under the modelled rules.

Figure 13 Flow Duration Curve – Potential Ashwick Canal.

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3 The model predicts less than 2 m /s is available 90 % of the time, indicating very low reliability of supply through this canal. The gains seen in Lake Opuha are similarly small, and did not change the downstream reliabilities of the irrigation areas.

5.4.3.2 Experiment (2C b) Experiment 2C(b) explored what a higher maximum operating level (design maximum) in Lake Opuha could achieve. The maximum level was raised to 391.7m asl (as suggested by OWL, pers. comm.) with a relative increase in total available storage volume of approximately 6 Mm3. When this experiment is compared to Experiment 2B (under the current flow regime), Figure 14 shows increased stored volume in all but the driest 15% of modelled years.

Figure 14 Stored Volume (Irrigation Season) Lake Opuha

5.4.3.3 Experiment 2C(c) This experiment sought to understand the effect of removing the losses through the existing Levels Plain system. Piping (or lining) Levels Plain potentially benefits Lake Opuha as the lake no longer needs to also meet the distribution losses through the existing distribution network. Losses in this network were estimated to be in the order of 50 % and modelled as such. In removing these losses, the demand on Lake Opuha was reduced by approximately 220 l/s during the irrigation season.

5.4.3.4 Combined Results The ‘small water’ experiments presented above were run collectively to determine the resulting effect on irrigation reliabilities. These results are presented below.

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Table 19 Experiment 2C (combined) Results ) ) ) 3 3 3

- -farm -farm Irrigation Area (IA) Reliability (modelled) Existing Irrigated Area (ha) Additional Irrigated Area (ha) Total Irrigated Area (ha) Existing on- farm storage volume (m Additional on storage volume (m Total on farm storage volume (m

17 75 1,161 — 1,161 11,194 — 11,194 18 72 4,707 — 4,707 39,496 — 39,496 19 50 616 — 616 — — — 20 48 291 — 291 31,172 — 31,172 21 100 1,918 — 1,918 69,868 — 69,868 22 100 14 — 14 — — — 23 88 87 — 87 — — — 24 23 417 — 417 88,830 — 88,830 25 92 875 — 875 114,554 — 114,554 26 100 311 — 311 — — — 27 76 179 — 179 39,878 — 39,878 28 62 123 — 123 — — — 29 54 221 — 221 — — — 30 81 1,680 — 1,680 220,000 — 220,000 31 100 2,016 — 2,016 220,000 — 220,000 32 100 1,447 — 1,447 260,000 — 260,000 33 N/A — — — — — — TOTAL — 16,063 — 16,063 1,094,992 — 1,094,992

5.4.3.5 Discussion Average reliabilities under these small water solution experiments are largely unchanged from Experiment 2B as Lake Opuha is able to supply high reliability water to its current shareholders in all but the driest of seasons. The model relies on Lake Opuha having water available in it to supply water to the irrigation areas. The only scenario where Lake Opuha would fail to meet its obligations in the model is if the lake level drops below the minimum lake level. In the modelled years, this occurs on few occasions. In reality, the lake may be operated differently, with water held back in the lake despite water being requested. The model does not currently reflect these operational discretions. A graph of Lake Opuha outflow volumes and stored volumes is provided in Figure 15 below. Table 20 outlines the gains and losses to Lake Opuha under each of these scenarios when compared with Experiment 2B.

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Figure 15 Stored Volume Lake Opuha (small water solutions)

Table 20 Lake Opuha Stored Volumes (small water solutions)

Lake Opuha Stored Volumes Over Irrigation Season (September to April) Only Percentile Base Case Opuha Volume Opuha New Lake Height Piping Levels Plain Volume (m3) Difference (m3) Difference (m3) 0.05 19,126,000 2,362,000 4,168,000 0.1 32,854,000 2,556,000 3,390,000 0.5 77,170,000 3,450,000 850,000

While these small water solutions do not offer an improvement in average supply reliability over all modelled years for the irrigation areas, Table 20 shows that the proportional benefits are greatest in the driest years. In the driest 5 % of modelled years the proportional benefit of additional lake height was 12 % compared with 4 % for an average year. In the driest 5 % of modelled years the proportional benefit of piping/lining Levels Plain was 22 % compared with 1% for an average year. It needs to be noted that piping/lining Levels Plain is likely to have secondary effects on the groundwater quality, as it is thought that presently this lost water from the irrigation system assists with diluting nitrogen concentrations in the groundwater. Removing this water will likely have negative water quality implications that would need to be managed in a different way.

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5.4.4 Experiment 2C (a, b, c) Variation This experiment was run to determine what effect removing the lower Kakahu demand (0.4 m3/s) from Lake Opuha would be. As demonstrated in the North OTOP model, the existing lower Kakahu irrigated areas can have their demand met by a new main canal headrace being supplied with water from the Rangitata River, thereby removing the demand on Lake Opuha. This experiment was run to determine what additional reliability could be gained in OTOP South by doing so. Additionally, by removing the demand from KIL on Lake Opuha, supply reliability improvements and / or additional demand from new irrigated area may be able to be met from Lake Opuha in areas where the extent of the northern supply cannot easily reach. In this experiment, the model was run with all three of the small water solutions applied.

Table 21 Experiment 2C Variation Results ) ) ) 3 3 3 -farm Irrigation Area (IA) Reliability (modelled) Existing Irrigated Area (ha) Additional Irrigated Area (ha) Total Irrigated Area (ha) Existing on- farm storage volume (m Additional on storage volume (m Total on- farm storage volume (m

17 75% 1,161 — 1,161 11,194 — 11,194 18 72% 4,707 — 4,707 39,496 — 39,496 19 50% 616 — 616 — — — 20 48% 291 — 291 31,172 — 31,172 21 100% 1,918 — 1,918 69,868 — 69,868 22 100% 14 — 14 — — — 23 88% 87 — 87 — — — 24 23% 417 — 417 88,830 — 88,830 25 92% 875 — 875 114,554 — 114,554 26 100% 311 — 311 — — — 27 76% 179 — 179 39,878 — 39,878 28 62% 123 — 123 — — — 29 54% 221 — 221 — — — 30 82% 1,680 — 1,680 220,000 — 220,000 31 100% 2,016 — 2,016 220,000 — 220,000 32 100% 1,447 — 1,447 260,000 — 260,000 33 N/A — — — — — — TOTAL — 16,063 — 16,063 1,094,992 — 1,094,992

5.4.4.1 Discussion Figure 16 and Figure 17 provide a comparison of the stored volume in Lake Opuha (Figure 16) and volume outflows per irrigation season (Figure 17) between the combined ‘small water’ experiments and 3 the combined ‘small water experiments’ with KIL demand removed. Removing the 0.4 m /s of demand from the bottom section of the KIL scheme yields benefits to Lake Opuha for the driest 50 % of modelled years (increasing to approximately 5 Mm3 per year for the driest 10 % of modelled years).

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Figure 16 Stored Volume in Lake Opuha

Figure 17 Outflow volumes Lake Opuha

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Experiment 2C (Variation) represents the maximum gains to the current system without adding a separate large storage. Modelled average reliabilities showed little change in this experiment. This is due in part to limitations on the model sensitivity, as well as the lack of on farm storage constraining the reliabilities, as any direct surface water and groundwater takes are not able to be stored. Later experiments will explore what the effects are once additional irrigated areas are included and the subsequent change in required storage. Table 22 and Figure 18 below show the volumetric change in the stored volume in Lake Opuha between the base case scenario and Experiment 2C (Variation). The benefits from a higher maximum lake level dominate in wetter seasons, while the benefits from removing lower KIL and lining Levels Plain can be seen in the driest modelled seasons.

Figure 18 Stored volume at Lake Opuha

+ Expt 2C (Var)

Table 22 Lake Opuha Stored Volumes Comparison

Lake Opuha Stored Volumes Over Irrigation Season (September to April) Only Experiment 2C (Variation) Lake Opuha Percentile Base Case Opuha Volume Stored Volume Volume (m3) Difference (m3) 0.05 31,854,000 2,902,000 0.1 46,368,000 1,250,000 0.5 78,930,000 3,320,000 0.8 81,580,000 3,500,000

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5.4.5 Experiment 2D

Small new water benefits are likely to be prioritised for improving supply reliability for current Opuha Water shareholders followed by irrigators affected by potential plan changes. This experiment sought to go one step further, assessing the supply and reliability shortfalls should the small new water solutions be implemented alongside the implementation of a large area (16,001 ha) of new irrigation.

Table 23 Experiment 2D Results ) ) ) 3 3 3

17 75% 1,161 — 1,161 11,194 — 11,194 18 69% 4,707 37 4,744 39,496 — 39,496 19 45% 616 1,002 1,618 — — — 20 38% 291 589 880 31,172 — 31,172 21 100% 1,918 139 2,057 69,868 — 69,868 22 54% 14 2,710 2,724 — — — 23 54% 87 3,776 3,863 — — — 24 23% 417 1,108 1,525 88,830 — 88,830 25 65% 875 2,528 3,403 114,554 — 114,554 26 100% 311 — 311 — — — 27 76% 179 — 179 39,878 — 39,878 28 62% 123 — 123 — — — 29 53% 221 637 858 — — — 30 66% 1,680 2,403 4,083 220,000 — 220,000 31 99% 2,016 478 2,494 220,000 — 220,000 32 87% 1,447 339 1,786 260,000 — 260,000 33 69% — 255 255 — — — TOTAL — 16,063 16,001 32,064 1,094,992 — 1,094,992

5.4.5.1 Discussion Table 23 shows that average reliabilities decreased in areas where additional irrigated area has been introduced. This will result in significant reliability reductions in drier seasons. New irrigated area was determined based on the AWT shareholders and apportioned to the same irrigation area boundaries. Where no new irrigated area has been included, reliabilities have remained the same as the previous Experiment 2C. Figure 19 below shows the difference in modelled Lake Opuha outflows when compared with the plan change scenario. It can be seen that overall, the additional demand placed on Lake Opuha is much higher with the additional irrigated areas included in the model. The difference is approximately 30 M m3 in an average season, increasing to approximately 75 M m3 in wetter seasons. Without external supply into the Opuha system, the supply reliability reductions resulting from spreading the available volume over a wider irrigated area will most likely be unacceptable to Opuha Water Ltd and its shareholders.

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Figure 19 Lake Opuha Outflow Volumes

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5.4.6 Experiment 2D (Variation) This experiment is based on Experiment 2D, but includes the added provision of removing the demand from the existing lower Kakahu scheme (0.4 m3/s) from Lake Opuha and instead supplying the required water for this scheme from the north (Rangitata River).

Table 24 Experiment 2D (Variation) Results ) ) ) 3 3 3

17 75% 1,161 — 1,161 11,194 — 11,194 18 69% 4,707 37 4,744 39,496 — 39,496 19 45% 616 1,002 1,618 — — — 20 38% 291 589 880 31,172 — 31,172 21 100% 1,918 139 2,057 69,868 — 69,868 22 54% 14 2,710 2,724 — — — 23 54% 87 3,776 3,863 — — — 24 23% 417 1,108 1,525 88,830 — 88,830 25 65% 875 2,528 3,403 114,554 — 114,554 26 100% 311 — 311 — — — 27 76% 179 — 179 39,878 — 39,878 28 62% 123 — 123 — — — 29 53% 221 637 858 — — — 30 66% 1,680 2,403 4,083 220,000 — 220,000 31 99% 2,016 478 2,494 220,000 — 220,000 32 88% 1,447 339 1,786 260,000 — 260,000 33 69% — 255 255 — — — TOTAL — 16,063 16,001 32,064 1,094,992 — 1,094,992

5.4.6.1 Discussion Figure 20 below shows a comparison between Experiment 2D and the variation to 2D. Removing KIL demand from Experiment 2D (16,001 ha new irrigation) has had a net benefit to the stored volumes held in the lake, but has no effect on the modelled average reliabilities when the new irrigated areas are included. This is because the demand from the large new irrigated area far exceeds the gains from removing lower KIL demand. Proportional improvements in drier years of 20 - 25 % are shown, but the low average supply reliability is still well below acceptable levels.

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Figure 20 Stored Volume Lake Opuha

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5.4.7 Experiment 2E This experiment introduces a new large water reservoir. The new reservoir is filled artificially under a winter fill scenario, whereby the reservoir is always at maximum capacity at the start of the irrigation season. The large reservoir is set up to supply water to irrigation areas IA17, IA18, IA21, IA27, and IA33. By including this large reservoir, demand is taken off Lake Opuha, freeing up additional water to support irrigation demand in new irrigated areas. Additionally, on farm storage volumes are also increased to meet 10 days of demand (at the 80th percentile). Previous experiments have not included additional on farm storage. The results are presented below in Table 25.

Table 25 Experiment 2E Results ) ) ) 3 3 3 -farm Irrigation Area (IA) Reliability (modelled) Existing Irrigated Area (ha) Additional Irrigated Area (ha) Total Irrigated Area (ha) Existing on- farm storage volume (m Additional on storage volume (m Total on- farm storage volume (m

17 100% 1,161 — 1,161 11,194 247,117 258,311 18 100% 4,707 — 4,707 39,496 1,082,060* 1,121,556* 19 50% 616 — 616 — 178,009 209,181 20 64% 291 — 291 31,172 21 100% 1,918 — 1,918 69,868 369,342 439,210 22 100% 14 — 14 — — — 23 99% 87 — 87 — — — 24 99% 417 — 417 88,830 — 88,830 25 99% 875 — 875 114,554 41,135 155,689 26 100% 311 — 311 — 75,178** 75,178** 27 100% 179 — 179 39,878 — 39,878 28 85% 123 — 123 — 75,178** 75,178** 29 55% 221 — 221 — 40,945 40,495 30 82% 1,680 — 1,680 220,000 86,398 306,398 31 100% 2,016 — 2,016 220,000 76,754 296,754 32 100% 1,447 — 1,447 260,000 — 260,000 33 100% — — — — 1,082,060* 1,082,060* TOTAL — 16,063 — 16,063 1,094,992 2,196,938 3,291,930 * Modelled on farm storage is shared between IA18 and IA33 ** Modelled on farm storage is shared between IA26 and IA28

5.4.7.1 Discussion This experiment introduces a new large reservoir in the model for the first time. The intention of this reservoir is to remove some of the demand from Lake Opuha by supplying downstream areas with an alternative supply source. The large reservoir is sized at 40 Mm3, and is filled artificially under a winter-fill scenario. Figure 21 below shows a time series of the large reservoir over the modelled time.

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Figure 21 Large Reservoir Volume Time Series

The large reservoir was sized to meet demand in the majority of years. This experiment also includes additional on farm storage. Sizes for the additional storage have been calculated based on 10 days of demand (at the 80th percentile), based on existing irrigated areas only. The combination of a new large storage and additional on farm storage makes a considerable improvement to the average modelled reliabilities. Areas that still experience low reliability are those irrigation areas where the existing Opuha Water scheme does not reach, and these users rely on direct groundwater and surface water takes. Figure 22 below shows a comparison in Lake Opuha stored volumes between the plan change scenario and Experiment 2E. It shows a net benefit to Lake Opuha stored volumes for all modelled seasons through the addition of the large central storage.

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Figure 22 Lake Opuha Stored Volume

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5.4.8 Experiment 2F This experiment models the effect of the new storage reservoir with the addition of the identified new irrigation areas. The large storage reservoir is supplying water to the same irrigation areas as in 2E above (IA17, IA18, IA21, IA27, and IA33). Newly identified areas for irrigation place a higher demand on Lake Opuha and to a lesser extent the large reservoir (the majority of the new irrigated areas are within the reach of any water coming out of Lake Opuha).

Table 26 Experiment 2F(a) Results ) ) ) 3 3 3

(ha) -farm Irrigation Area (IA) Reliability (modelled) Existing Irrigated Area (ha) Additional Irrigated Area Total Irrigated Area (ha) Existing on- farm storage volume (m Additional on storage volume (m Total on- farm storage volume (m

17 100% 1,161 0 1,161 11,194 247,117 258,311 18 100% 4,707 37 4,744 39,496 1,159,790** 1,199,286 19 45% 616 1,002 1,618 0 505,895 537,067 20 45% 291 589 880 31,172 21 100% 1,918 139 2,057 69,868 395,184 465,052 22 56% 14 2,710 2,724 0 23 56% 87 3,776 3,863 0 914,110 1,002,940 24 56% 417 1,108 1,525 88,830 25 68% 875 2,528 3,403 114,554 445,942 560,496 26 100% 311 0 311 0 75,178* 75,178* 27 100% 179 0 179 39,878 - 39,878 28 85% 123 0 123 0 75,178* 75,178* 29 53% 221 637 858 0 147,693 147,693 30 66% 1,680 2403 4,083 220,000 496,403 716,403 31 100% 2,016 478 2,494 220,000 138,577 358,577 32 88% 1447 339 1,786 260,000 - 260,000 33 100% 0 255 255 0 1,159,790** 1,159,790** TOTAL — 16,063 16,001 32,064 1,094,992 4,498,889 5,593,881 * Modelled on farm storage is shared between IA18 and IA33 ** Modelled on farm storage is shared between IA26 and IA28

5.4.8.1 Discussion Demand for water for those areas connected to the new large reservoir is fully met under this scenario. However, most of the newly identified irrigated areas are located upstream of the large reservoir and are not modelled as being connected to it. The majority of the new irrigated areas are in locations that could be served by Lake Opuha (provided a method of connection exists). In particular, this would involve getting water to the areas south of the Opihi River and above the Tengawai River.

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Excluding the areas that are connected to the large reservoir, the new irrigated areas create an additional demand in the zone of 112,262,021 m3 per year (95th percentile demand). Including the large reservoir removes approximately 56,000,000 m3 of demand from Lake Opuha per year. There is still a significant shortfall in water supply to the identified new areas, and including a large central reservoir does not free up enough water in Lake Opuha to meet the demand used in this experiment. If new irrigators were provided the same supply rights as existing irrigators, supply reliability to existing irrigators would reduce significantly.

The location of the new central storage is important in this experiment. The model placed the storage in such a location as to reach existing areas of IA17, IA18, IA21, IA27, and IA33. It could be supplied from the Opuha and / or from the Rangitata without significant pumping requirements. If the storage was located higher, or if infrastructure is in place, additional areas may be able to be serviced, with corresponding increases in storage sizes required.

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5.4.9 Experiment 2F (Variation) This experiment models the effect of the new storage reservoir with the addition of the identified new irrigation areas and excludes supplying water from Lake Opuha to the lower Kakahu Irrigation scheme. The large storage reservoir is supplying water to the same irrigation areas as in 2E and 2F above (IA17, IA18, IA21, IA27, and IA33). Newly identified areas for irrigation place a higher demand on Lake Opuha and to a lesser extent the large reservoir (the majority of the new irrigated areas are within the reach of any water coming out of Lake Opuha).

Table 27 Experiment 2F (Variation) Results ) ) ) 3 3 3 -farm -farm Irrigation Area (IA) Reliability (modelled) Existing Irrigated Area (ha) Additional Irrigated Area (ha) Total Irrigated Area (ha) Existing on- farm storage volume (m Additional on storage volume (m Total on- farm storage volume (m

17 100% 1,161 0 1,161 11,194 247,117 258,311 18 100% 4,707 37 4,744 39,496 1,159,790** 1,199,286 19 45% 616 1,002 1,618 0 505,895 537,067 20 44% 291 589 880 31,172 21 100% 1,918 139 2,057 69,868 395,184 465,052 22 56% 14 2,710 2,724 0 23 56% 87 3,776 3,863 0 914,110 1,002,940 24 56% 417 1,108 1,525 88,830 25 68% 875 2,528 3,403 114,554 445,942 560,496 26 100% 311 0 311 0 75,178* 75,178* 27 100% 179 0 179 39,878 — 39,878 28 85% 123 0 123 0 75,178* 75,178* 29 53% 221 637 858 0 147,693 147,693 30 67% 1,680 2,403 4,083 220,000 496,403 716,403 31 100% 2,016 478 2,494 220,000 138,577 358,577 32 88% 1,447 339 1,786 260,000 — 260,000 33 100% 0 255 255 0 1,159,790** 1,159,790** TOTAL — 16,063 16,001 32,064 1,094,992 4,498,889 5,593,881 * Modelled on farm storage is shared between IA18 and IA33 ** Modelled on farm storage is shared between IA26 and IA28 5.4.9.1 Discussion As in Experiment 2F above, water demand of the irrigation areas connected to the large reservoir is fully met. This experiment sought to understand what the effect on Lake Opuha is from the removal of the lower Kakahu scheme. As has been shown in Experiments 2D, the effect is not great as the modelled new irrigation area is significantly greater than the portion of the Kakahu scheme that can feasibly swapped with Rangitata supply.

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5.5 Summary of Infrastructure Outcomes These experiments sought to understand the effects on Lake Opuha through a variety of different scenarios. Initially, some small water solutions were explored to determine the volume of water that could be gained back to the lake if some small initiatives were implemented. One of these solutions – an additional abstraction from the Opihi River, has been deemed to hold too small a gain for the required investment in infrastructure. Piping/lining the existing Levels Plain irrigation scheme was also explored. This yielded some gains back to Lake Opuha (particularly in drier seasons), however the resulting loss of dilution of nitrates in groundwater will need to be considered also. If the gains are used to top up supply reliability for current Levels Plain groundwater users potentially affected by plan changes, then the groundwater left in the system may provide similar benefits. Alternatively the Levels Plain races could be left to recharge the groundwater system, but this could be paid for by groundwater users to counter their stream depletion effects. This requires further analysis. Of the three small water solutions, raising the maximum operating level of the lake yielded the most benefit to the lake (particularly in average to wetter seasons). Modelled average reliabilities showed little change throughout the modelled experiments. This is due to limitations in the model and the lack of on farm storage constrains the reliabilities, as any direct surface water and groundwater takes are not able to be stored.

Table 28 Gains to Lake Opuha represented as additional irrigated area

Base Case Lake 3 Additional volume (m Additional irrigated Experiment Opuha stored volume th 3 th at 50 percentile) area (ha) (m at 50 percentile) 2A 78,930,000 — — 2B 78,930,000 -330,000 -29 2C(combined) 78,930,000 2,950,000 262 Removing KIL 78,930,000 3,320,000 295 Adding Large 78,930,000 40,000,000 3,556 Reservoir

A more appropriate measure of the gains being made to the system through the improvements in Experiment 2 could be to look at the overall gains and convert the increased water to an irrigable area (based on 4.5 mm/ha/day). Table 28 details the gains made in each experiment and the associated additional land that could be irrigated based on these gains. The gains could also be spread more widely as reliability improvements. Experiment 2D introduced new irrigated areas to the zone. These areas were identified broadly as those land parcels which had registered as shareholders in the AWT scheme, and were considered to be indicative of land parcels that, should water and nutrient allocation be available, would otherwise be irrigated. In total, the amount of new irrigated land was approximately 16,000 ha, doubling that of the current irrigated area in OTOP South. This additional demand if connected to Lake Opuha, would place significant strain on the lake's ability to provide water. Regardless of the considerations of how to transport the water to the new areas (which for the most part were identified in parts of the zone not currently connected to the OWL scheme), there remains an issue of water resource – there is not enough water currently in the OTOP South area to meet this demand. In order to reduce the demand on Lake Opuha further, a new large central reservoir was modelled to supply water to those irrigation areas downstream of it. In total this reduced the demand on Lake Opuha by approximately 38,000,000 m3 per year (at the 50th percentile). The reservoir was sized at 40,000,000 m3 which was sufficient storage to supply the connected irrigation areas with their full th demand for water (at the 50 percentile). However, Table 28 shows that this reservoir only provided the ability to swap 3,556 ha of Opuha supply without reducing Opuha supply reliabilities. This is significantly less than the 16,000 ha identified as potential new irrigation.

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6.0 Summary of Combined Experiments For all experiments discussed in the previous sections the OTOP north and OTOP south have operated independently of each other. Experiment 3 presents an example of the integrated model where the demands and water supply routes work in conjunction with each other. These linkages are centred mainly through the existing KIL scheme and through a potential large central reservoir. Experiment 3 assesses supply reliabilities and irrigated areas through including a central storage reservoir. A selection of scenarios were selected from the north and south versions of the model, including the full 16,000 ha of AWT potential new irrigation in south OTOP (as a 'large' new water scenario).

6.1 Experiment Details The integrated model was run using a specific set of scenario options from the north and south versions of the OTOP experiments. From the north experiments, the following options were selected to run: x Utilising a large storage reservoir at Klondyke x Applied potential new irrigated areas to the demand for the zone x Applied potential plan changes x IA1 and IA2 continue to be supplied via existing RSIS scheme with associated losses x ‘A’ block water tied to the RSIS scheme is held separately in an additional storage pond and is used to supply IA3 (existing groundwater users on the north side of the Orari River) x Canal B is used to top up supply to existing and new areas to 95% reliability x On farm storage is used to buffer demand from the Klondyke storage pond x The existing lower portion of the Kakahu Irrigation scheme is supplied via Canal B From the south experiments, the following options were selected: x Utilising a large central zone storage reservoir x Using the large reservoir as supply to irrigation areas IA17, IA18, IA21 and IA33. x Applied potential new irrigated areas to the demand for the zone x Applied potential plan changes The model has been optimised to maintain the existing reliabilities that were achieved in the separate north and south experiments. The main difference in the combined experiment is that the large central reservoir is now being filled via a modelled demand on Klondyke ponds, which has necessitated an increase in stored volume at Klondyke and the capacity of Canal B.

6.2 Results In order to maintain the 95% supply reliabilities to areas that would be connected to this scheme, the following infrastructure parameters to the model are required:

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Table 29 Summary of infrastructure requirements (Combined Model)

Parameter Size 3 Klondyke Ponds (including Lake Coleridge swap) 100,000,000 m Canal B 7 m3/s Conveyance from Canal B to Large Reservoir 2 m3/s 3 Large Central Reservoir 40,000,000 m

6.2.1 Klondyke Ponds 3 In the north only experiment, Klondyke Pond was sized at a maximum required capacity of 55 Mm to supply the north areas with water (including new irrigation areas). To meet the additional demand of supplying water to the central reservoir in the south, and in order to maintain enough water to meet the 3 demands from the north side of the model, Klondyke was required to be sized at 100 Mm . This volume includes a water swap with Lake Coleridge. A timeseries of the held volume within Klondyke ponds is given below in Figure 23.

Figure 23 Klondyke Ponds Stored Volume Klondyke Ponds Stored Volume 1.20E+08

1.00E+08

8.00E+07

6.00E+07

4.00E+07 Stored Volume (m3)

2.00E+07

0.00E+00

Date

As Klondyke Pond is filled artificially under a winter fill scenario, the pond is modelled as being full at the start of the irrigation season. Demand to supply water to the central reservoir is year round (Klondyke supplies water to the large reservoir over winter), and so Klondyke continues to supply water to the Large Reservoir over the winter period. Capacities stated in the model experiments represent the upper bound of constructed sizes. If the scheme was implemented, it would be more efficient (both in canal sizing and to a lesser degree in the constructed size of Klondyke) to have a binary system of operation on the Klondyke reservoir. During the summer, Klondyke would be

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dedicated to refilling the central reservoir in preparation for the next irrigation season. Klondyke would still need to retain water over winter to supply the north OTOP irrigation season, but there may be efficiencies in the canal sizing under this operating regime. These considerations have not been explored in the model experiments, but should be considered in the next stage of the project.

6.2.2 Canal B The north experiments required a Canal B maximum capacity of 4.5 m3/s in order to maintain 95% reliabilities in that part of the zone. Supplying water via Canal B to fill the Large Reservoir has required an increase in that capacity to 7 m3/s. Figure 24 below shows the time series of the demand on Canal B over the model run. The oscillation in the demand for Canal B is caused by the Large Reservoir nearing capacity. The model is set to supply water at the minimum of either the pumping rate to the reservoir (set at 2 m3/s) or the flow required over the course of one day to top up the reservoir. As the Large Reservoir nears capacity, demand reduces so to avoid the Large Reservoir overflowing.

Figure 24 Canal B Demand

6.2.3 Large Reservoir The Large Reservoir was filled via a 2 m3/s pumped supply from the end of Canal B. This rate was found to be sufficient to maintain a volume of stored water in the Large Reservoir in order to maintain enough capacity to supply the irrigation areas connected to it at a required 95% reliability. Figure 25 below shows the stored volumes held in the Large Reservoir over the time of the model run.

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Figure 25 Large Reservoir Stored Volumes

There is a higher level of demand placed on the large reservoir during the early part of the model run. Figure 26 below shows the total demand per year on the Large Reservoir.

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Figure 26 Large Reservoir Demand

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7.0 Concluding Summary

7.1 North OTOP Zone The zone faces a shortage of water with respect to the desired on farm reliabilities, and to achieve environmental benefits through relieving pressure on the aquifers and streams in the zone. The solutions that have been presented in this report are hinged on a large storage reservoir (modelled as a reservoir at Klondyke) which is linked to a reliable source of alpine water. Should the necessary water be obtained from the Rangitata River, this will achieve one part of the solution. In conjunction with this reservoir, a suitably sized headrace canal and an appropriate route of this canal will be required to convey the stored water to the desired irrigated areas and in doing so will achieve the second part of the solution. Outside the RSIS there is limited use of on-farm storage. Additional on-farm storage provides a buffer to the demand on Klondyke pond, and in this work it has been sized for 10 days of storage to meet demand during dry periods. If the required on-farm storage is available, then this will achieve the third part of the solution for the zone. Provided that the three parts of the solution are achieved, the experiments presented here model reliabilities of at least 95% at the farm gate. Consideration was made to store currently consented RSIS ‘A’ Block water separately on the plains between the Rangitata River and the Orari River. It was found that a constructed storage volume of 1 Mm3 was required to supply water to groundwater users in IA3 along the north bank of the Orari River. Consideration was made of where the A block storage could be located. A higher location to serve a greater area requires top up water from Klondyke. If the RSIS 'A' Block water needs to stay with the current RSIS command area, IA3 can just as easily be supplied from Klondyke.

7.2 South OTOP Zone As with the north zone, there is a shortage of water available with respect to the desired reliablities, and potential increase in irrigated area. The modelling has shown that there is not enough water currently in the zone to achieve the desired outcomes. Small water solutions such as raising the operating level of Lake Opuha and reducing losses through the existing system will yield a net gain back to the system, but the corresponding increase in irrigated area through these methods is not enough to serve modelled future demand. Removing demand from the bottom part of the Kakahu scheme has also been modelled to show a net gain back to the system, however this is also not enough to achieve the desired results. A large central reservoir, modelled to provide irrigation water to irrigation areas IA17, IA18, IA21, IA27 and IA33 will provide for approximately 3,500 ha of additional irrigated land (at the specified application rate). A 'water swap' with Lake Opuha would mean that some of the desired new irrigated area could then be supplied. However, nutrient allocation limits to be set in the current planning process may also constrain new irrigation areas. A summary of the gains that can be achieved and the additional irrigated areas that could be supplied is provided below.

Base Case Lake 3 Additional volume (m Additional Experiment Opuha stored volume th 3 th at 50 percentile) irrigated area (ha) (m at 50 percentile) 2A 78,930,000 - - 2B 78,930,000 -330,000 -29 2C(combined) 78,930,000 2,950,000 262 Removing KIL 78,930,000 3,320,000 295 Adding Large 78,930,000 40,000,000 3,556 Reservoir

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7.3 Combined Model Combining the two halves of the model together provides an opportunity to assess integrated concepts for the entire OTOP zone. Stored water from Klondyke/Coleridge could then be conveyed along the same headrace used by the irrigation areas in the north OTOP zone and then delivered into a centrally located reservoir. This will enable reliable supply to south OTOP, which could service new irrigation areas in the upper catchment via a water swap with Lake Opuha. Planning and commercial constraints could both limit the amount and locality of new irrigation in the zone. A summary table of the maximum required infrastructure modelled is provided below. Further scenarios based on specific demand surveys are recommended to refine these capacities and provide the basis for water supply cost estimations. Note that the provision to include 100 Mm3 of storage at Klondyke for the integrated model will be significantly challenging, given the current consent conditions for the ponds.

Element Capacity North OTOP example only 3 Klondyke / Lake Coleridge 55 Mm Canal B 4.5 m3/s A Block reservoir 1 Mm3 South OTOP example only 3 Large Central Reservoir 40 Mm Integrated Example 3 Klondyke / Lake Coleridge 100 Mm Canal B 7 m3/s 3 Pump capacity (if required) to Large Reservoir 2 m /s 3 Large Central Reservoir 40 Mm

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8.0 References

Aqualinc (2015). Irrigated area mapping: Waimakairiri and Orari-Opihi-Pareora. Report No. C15043/1.

Burbery, L. (2012). Delineation of the Rangitata riparian zone. Environment Canterbury report No. R12/65. ISBN 978-1-927210-97-0. Environment Canterbury.

Burbery, L. (2012b): Interaction between the Orari and Waihi Groundwater Systems. Report No. 1050- 12-R1. Lincoln Ventures Limited.

Burbery, L. and Ritson, J. (2010). Integrated study of surface water and shallow groundwater resources of the Orari catchment. Environment Canterbury report R10/36. ISBN 978-1-877574-06-1. Environment Canterbury.

De Joux, R. T. (1980). The water resources of the Orari River. Publication No. 24, South Canterbury Catchment Board and Regional Water Board.

Lilburne, L., Webb, T., Ford, R., and Bidwell, V. (2010): Estimating nitrate-Nitrogen leaching rates under rural land uses in Canterbury. Report No. R10/127. Environment Canterbury. McEwan, G. (2002). The hydrogeology of the Orari River shallow aquifer system. Environment Canterbury report No. U02/02. Environment Canterbury. Pagen, S. (2015). Personal Communication. Kakahu Irrigation Scheme conveyance infrastructure. Painter, B. (2016). Personal Communication. Current reliabilities and RSIS scheme. Scarf, F. (2002). Low flows of the Opihi River and it’s tributaries. Environment Canterbury report No. U02/12. Environment Canterbury. URS (2014). Orari Opihi Pareora Zone Pre-Feasibility Studies. Ref: 42192460_R002_B. URS New Zealand Limited.

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9.0 Standard Limitation AECOM Consulting Services (NZ) Limited (AECOM) has prepared this report in accordance with the usual care and thoroughness of the consulting profession for the use of Environment Canterbury and only those third parties who have been authorised in writing by AECOM to rely on this Report. It is based on generally accepted practices and standards at the time it was prepared. No other warranty, expressed or implied, is made as to the professional advice included in this Report. It is prepared in accordance with the scope of work and for the purpose outlined in the contract dated 5 December 2014. Where this Report indicates that information has been provided to AECOM by third parties, AECOM has made no independent verification of this information except as expressly stated in the Report. AECOM assumes no liability for any inaccuracies in or omissions to that information. This Report was prepared between 5 December 2014 and 30 March 2017 and is based on the conditions encountered and information reviewed at the time of preparation. AECOM disclaims responsibility for any changes that may have occurred after this time. This Report should be read in full. No responsibility is accepted for use of any part of this report in any other context or for any other purpose or by third parties. This Report does not purport to give legal advice. Legal advice can only be given by qualified legal practitioners. Except as required by law, no third party may use or rely on this Report unless otherwise agreed by AECOM in writing. Where such agreement is provided, AECOM will provide a letter of reliance to the agreed third party in the form required by AECOM. To the extent permitted by law, AECOM expressly disclaims and excludes liability for any loss, damage, cost or expenses suffered by any third party relating to or resulting from the use of, or reliance on, any information contained in this Report. AECOM does not admit that any action, liability or claim may exist or be available to any third party. Except as specifically stated in this section, AECOM does not authorise the use of this Report by any third party. It is the responsibility of third parties to independently make inquiries or seek advice in relation to their particular requirements and proposed use of the site. Any estimates of potential costs which have been provided are presented as estimates only as at the date of the Report. Any cost estimates that have been provided may therefore vary from actual costs at the time of expenditure.

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Appendix A

Surface hydrology summary

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Appendix A Surface hydrology summary

Provided below is a summary of the flow information available to support this report. The main hydrological base data used in this project consists of flow data from flow gauges within the catchment (Figure 27, Figure 28). For hydrological modelling purposes, 30 year mean daily flow series from 1st September 1981 to 31st August 2011 were chosen as the base inputs. The base inputs were obtained via the following methods (in order of decreasing preference): 1. Recorded Flow Series. If there were continuous flow gauge data available for the specified period and the flow gauge location was less than 1 km from the modelling point of interest along the river (with no major flow gains), the flow gauge data was used as the base input. 2. Modified Flow Series. There were several scenarios in which an available flow series was modified (infilled or naturalised) to allow its use: a. Missing flow data within records were filled based on correlation with another flow gauge site nearby of similar catchment characteristics (such as rainfall and topography). or b. Missing flow data within records were filled by adjusting records from an upstream / downstream gauge based on catchment area and/or mean flow obtained from NIWA Water Resources Explorer, or c. If there are water abstractions or discharge due to human activities occurring within the catchment of interest, a naturalised flow series is created by removing the effects of human activities on the river flow, based on correlation with another flow gauge nearby of similar catchment characteristics. 3. Synthetic Flow Series. If there are no flow data available or flow data is only available for a short period (less than 10 years), then a synthetic flow series is created using correlations obtained from past studies on the river which allow the use of whole records from nearby rivers.

Figure 27 Flow monitor data availability

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Figure 28 Flow monitor locations

1.1.1.1 Orari River The Orari River stretches 87 km from the Ben McLeod Range in the north-west to the mouth of the river, located about 8 km east of Temuka township. The river`s catchment is bounded to the north by the Rangitata River catchment and to the south by the Opihi River catchment. The catchment can be divided into two areas; (i) the upper Orari above the outlet to the Orari Gorge which consists of hill country between 1370 m and 1850 m elevation, and (ii) the lower Orari on the Canterbury plains below the gorge outlet which consists of alluvial fans sloping gently towards the coast.

1.1.1.2 Upper Orari The Orari catchment upstream of the Orari Gorge intake is predominantly steep hill-country made up of sandstone and siltstone rocks between 1370 m and 1850 m elevation (de Joux 1980), with some flat areas around Mowbray River.

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The Orari River Gorge flow gauge (Site no. 69505) is located at the western end of Orari River Road. The flow series used in the modelling of the Orari Gorge was derived by infilling gaps in the Orari at Gorge record. The median flow for the gorge site is 6.1 m3/s, with the mean flow approximately 9 m3/s (Table 30).

Table 30 Upper Orari Summary

Flow (m3/s) Orari Gorge Burdons Crossing Minimum Flow 1.6 1.2 7-Day Mean Annual Low Flow (7dMALF) 2.8I - Median Flow 6.1 5.5 Mean Flow 9 8.4 Maximum Flow 353 345

Source: IScarf (2003) 1.1.1.3 Lower Orari From the Orari Gorge to the river mouth, the lower Orari catchment is relatively flat with alluvial fans comprising of silt loams from the Brown and Psallic soil groups (Burbery and Ritson 2010). A strong groundwater and surface water interaction was found with relatively shallow groundwater in the lower reaches of the catchment (Burbery 2011). All the lower Orari tributaries originate from a major spring network, providing further evidence of a strong interaction between surface water and shallow groundwater (McEwan 2002). The Orari River, prior to 1852 flowed into the Waihi River above the Winchester settlement. Although the river has since changed its course, the groundwater still flows in this general direction, into the Waihi catchment (Burbery and Ritson 2010). Scarf (2003) and Burberry & Ritson (2010) both found that there were flow losses in the lower reaches of Orari River, particularly between Burdons Road and SH72, and flow gains downstream of SH1. During summer months the Orari is known to run dry between SH72 and SH1.

1.1.1.4 Opihi River The Opihi River has a catchment area of approximately 243,000 ha, of which the main tributaries are the Hae Hae Te Moana River, Kakahu River, Opuha River and Tengawai River. In this investigation a selected number of flow sites were used to determine flows throughout the catchment. The following provides a brief overview of the flow sites used.

1.1.1.5 Opihi River (Main Stem) The Opihi River catchment comprises an upland headwater which reaches over 2,300 m elevation at the catchment divide. The catchment does not extend into the Main Divide. From these upland areas the river and its tributaries flow across flats above Fairlie, with the Opuha River tributary being impounded by Lake Opuha. Below Fairlie the river`s main stem enters a gorge, joining the Opuha River at Raincliff. From here the river flows along a wider, flat bottomed valley issuing onto the Canterbury Plains above Pleasant Point. The Tengawai River joins immediately above Pleasant Point. The Opihi River then flows across the plains, discharging into the sea, south of Temuka. Around 4 km upstream from the river mouth water from the Hae Hae Te Moana, the Waihi, and Kakahu Rivers join the main stem, via the Temuka River. Flow statistics for the flow gauging sites used in this project are summarised in Table 31 below.

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Table 31 Flow statistics for gauging sites Parameter Cloudy Hanging 3 SH79 Rockwood Saleyards SH1 (m /s) Peaks Rock Minimum Flow 0.00 0.01 0.5 1.8 1.1 1.8 7-Day Mean 0.6 — 1.3 4 3.7 2.9 Annual Low Flow (7MALF) Median Flow 1.4 2.2 3.2 9.2 10.3 9.7 Mean Flow 2.2 3.7 5 13.5 16.6 15.6 Maximum Flow 117 397 485 871 1354 3568

The Opihi River at Saleyards Bridge (Site no. 69650) flow gauge is located just downstream of the confluence with Tengawai River at Pleasant Point, where there are statutory minimum flow requirements. Meeting these flow requirements requires Lake Opuha to discharge a range of flows, depending on its stored volume. Scarf (2002) investigated the low flows of the Opihi River and stated that the effect of snowmelt on the Opihi catchment is limited to Firewood Stream which is affected by snowmelt from Mount Dobson. Along the main stem of Opihi River, Scarf (2002) found that flow losses occur particularly along a 15 km river stretch from Cloudy Peaks to the Allandale Bridge at Fairlie, due to the underlying bed shingles or unconfined aquifers. Gains in surface flow were found to occur along a 6 km stretch between Fairlie and the entrance to the Opihi Gorge as the subsurface and groundwater flow emerge due to the impermeable greywacke rocks at the gorge. Scarf (2002) found that the low flows at Rockwood (the exit of the Opihi Gorge) are significantly affected by spring flow from four named spring systems i.e. Three Springs, Gillies Springs, Glenburn Springs and Woolwash Springs, and that flow losses to subsurface flow are often encountered at the confluence between tributary streams and the main Opihi river stem where the underlying soils consist of highly permeable alluvial outwash fans. Downstream of Hanging Rock, there appeared to be minimal flow losses along Opihi River up to Pleasant Point. Conversely, there appears to be no significant flow gains under mean flow conditions in this reach which would otherwise indicate a discharging groundwater system.

1.1.1.6 Hae Hae Te Moana River The Hae Hae Te Moana River (South Branch) meets the Hae Hae Te Moana River (North Branch) 3 km north of Pleasant Valley to form the Hae Hae Te Moana River which in turn joins the Kakahu and Waihi Rivers just north of Temuka township. From here it meets the Opihi River just south of Temuka. Scarf (2003) demonstrated that there are flow losses along the Hae Hae Te Moana River reach downstream from Glentohi site through to the Te Awa settlement. The modified mean daily flow series is based on catchment area with the Te Moana at Glentohi (Site no. 69644) flow gauge. This site was used as the upstream site for this project. The downstream flow site at SH1 for the Hae Hae Te Moana River is located on the Temuka River, downstream of the Waihi River confluence. Median flows in the SH1 indicate an increase in flows in the downstream end of the catchment, illustrating the incoming flow from the Kakahu River and the Waihi River, which flows in response to groundwater discharge associated with flow losses from the Orari River.

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3 Hae Hae Te Moana Sth Parameter (m /s) Hae Hae Te Moana SH1 Branch Minimum Flow 0.04 0.2 7-Day Mean Annual Low Flow (7MALF) 0.18 - Median Flow 0.55 3.3 Mean Flow 1.34 5.51 Maximum Flow 118.74 523.8

1.1.1.7 Opuha River The North Opuha River (29 km) and South Opuha River (35 km), drain from Sherwood Range and Two Thumb Range respectively and converge south of Ewarts Corner (site of present Lake Opuha) to form the Opuha River. The river then flows through a narrow gorge for approximately 14 km before emerging at Skipton where the Opuha at Skipton (Site no. 69614) flow gauge is located. The Opuha River flows for about 27 km before meeting the Opihi River downstream of Raincliff Bridge. Scarf (2002) noted that 28 % of the catchment area is above the 1200 m winter snowline and snowmelt between late September to late December is a significant contributing factor towards delaying the summer low flows until late February to April. The Ashwick Flat stockwater race abstracts flow from the South Opuha River just upstream of where it meets the North Opuha River. The effects of the stockwater race were removed from the main Opuha River flow analysis by Scarf (2002) and it was found that there were some natural losses between the confluence and Te Puni. However, as most of the flow seemed to be confined to subsurface flow within the immediate vicinity of the main channel, most of the flow were recovered before reaching Te Puni and Skipton. Hence, Scarf (2002) concluded that there seems to be minimal surface flow loss by the time the Opuha River meets the Opihi River. The Lake Opuha Dam was completed in 1998 and flows from the dam have been regulated by the Opihi River Regional Plan and consents granted to Opuha Dam company, based on minimum flow requirements at the Opihi River at Saleyards Bridge (Site no. 69650) flow gauge near Pleasant Point, approximately 16 km downstream from the confluence of Opuha and Opihi Rivers.

Parameter (m3/s) Skipton Raincliff Minimum Flow 1.3 1.3 7-Day Mean Annual Low Flow (7MALF) 2.6 - Median Flow 6 6.3 Mean Flow 8.5 9.6 Maximum Flow 457 645

1.1.1.8 Tengawai River Scarf (2002) states that flow in the Tengawai River is not influenced by seasonal snow storage as any snow in the mountain ranges tends to have a short lifespan. Some surface and subsurface flow interaction may occur in the river from Cricklewood Bridge (SH8) to the Cave Picnic Grounds due to the underlying gravel shingle bed, but as the river flows past Cave, the underlying tertiary mudstone is at the surface and this is likely to force all the river flow to occur as surface flow just downstream of the Cave. Scarf (2002) estimated the 7MALF flow at Cave Picnic Ground to be 0.652 m3/s. Scarf also estimates a flow loss of about 0.25 m3/s between Cave and Hammonds (approximately 2.5 km from Pleasant Point), and a flow gain of 0.1 m3/s between Hammonds and Pleasant Point. The flow gain was likely due to inflow from Totara Valley Stream and partial recovery of the river’s surface flow. By the time

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the river flows past Saleyards Bridge, surface flow loss to groundwater was estimated by Scarf (2002) to be 0.15 m3/s. The flow gauge at Tengawai downlands was used to generate a synthetic flow record for the upper catchment. The flow gauging site at the Picnic Grounds at Cave were used for the downstream gauging point.

Parameter (m3/s) Downlands Cave Minimum Flow 0.1 0.2 7-Day Mean Annual Low Flow (7MALF) — 0.7 Median Flow 1 1.8 Mean Flow 1.7 3.9 Maximum Flow 253 477

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Appendix B

Irrigation Areas

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Appendix B Irrigation Areas

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Primary Map N o. 5 Fin al 1 5

South OTOP Irrigation Areas Map features depicted in terms of N ZTM projection.

Data S ources: NZ T opographical Feature s- LINZ NZ National Top o Dataset 2014 Cadastral B oundaries - LIN Z N Z C adastral D ataset 2014 Re v. By App. Desc ription Date !I 20/01/2017 3:31:59 p.m.

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North OTOP Irrigation Areas Map features depicted in terms of NZTM projection.

Data Sources: NZ Topographical Features - LINZ NZ National Topo Dataset 2014 Cadastral Boundaries - LINZ NZ Cadastral Dataset 2014 Rev. By App. Description Date !I 26/01/2017 9:29:14 a.m.

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Printed 26 Jan 20 17 09:29 Pr oj e c t : OTOP Water Resources Assessment Sc ale: Approved MM Da te Scale: 1:300,000 (A 4 si ze ) De sig n ed SP Dr aw n SP Ti tl e : South OTOP Current Irrigation Areas St at u s : R ev . Ma p N o . Ch ec ke d MM Ch ec ke d MM

Primary Map N o. 6 Fin al 1 6

Data S ources: NZ T opographical Feature s- LINZ NZ National Top o Dataset 2014 South OTOP Irrigation Areas Cadastral B oundaries - LIN Z N Z C adastral D ataset 2014 Re v. By App. Desc ription Date !I 20/01/2017 3:25:20 p.m.

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Printed 20 Jan 2017 15:25 Project: OTOP Water Resources Assessment Scale: Approved MM Date Scale: 1:300,000 (A4 size) Title: Designed SP Drawn SP North OTOP Current Irrigated Areas Status: Rev. Map No. Checked MM Checked MM Primary Map No. 3 Final 1 3 © Copyright AECOM, 2015. This map is confidential and shall only be used for the purposes of this project. © Copyright AECOM New Zealand Limited 2015. This map is confidential and shall only be used for the purpose of this project. The information contained or referred to in this drawing-report was developed for use in the project. AECOM New Zealand Limited does not Legend accept any responsibility for the use of the information by any other parties and state expressly that they do not warrant the accuracy of the information. Any use of the information by other parties is at their own risk. The signing of this title block confirms the design and drafting of this project have been prepared and checked in accordance with the AECOM Quality Assurance system certified to AS/NZS ISO 9001:2000. No part of this drawing/report may be copied or used without the prior written consent of AECOM New Current Irrigated Areas (North OTOP) Zealand Limited. Map features depicted in terms of NZTM projection.

Data Sources: NZ Topographical Features - LINZ NZ National Topo Dataset 2014 North OTOP Irrigation Areas Cadastral Boundaries - LINZ NZ Cadastral Dataset 2014 Rev. By App. Description Date AECOM OTOP Regional Water Assessment OTOP Regional Water Resource Assessment

Appendix C

North OTOP Model Schematics

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Appendix C North OTOP Model Schematics

21-Apr-2017 Prepared for – Environment Canterbury – Co No.: N/A Kakahu River Hei Hei Te Orari River Rangitata Moana River River

LAKE OPUHA IA 16

‘B’ block IA 14 IA 5 RSIS IA 1a B IA 4

Scenario 1A IA 6 Current Conditions

Proposed storage IA 9 IA 1

Existing storage IA 8 IA 10 IA3 Irrigation area IA 2 Existing conveyance Proposed conveyance IA 11 River Kakahu River Hei Hei Te Orari River Rangitata Moana River River

RDR KLONDYKE

LAKE OPUHA IA 16 ‘A’ block ‘B’ block IA 14 IA 5 RSIS IA 1a B IA 4

Scenario 1B IA 6 RSIS Existing reliability top-up A

Proposed storage IA 9 IA 1

Existing storage IA 8 IA 10 IA3 Irrigation area IA 2 Existing conveyance Proposed conveyance IA 11 River Kakahu River Hei Hei Te Orari River Rangitata Moana River River

RDR KLONDYKE

LAKE OPUHA IA 16 ‘A’ block ‘B’ block IA 14 IA 5 RSIS IA 1a B IA 4

Scenario 1C/F/G IA 6 RSIS Various A

Proposed storage IA 9 IA 1

Existing storage IA 8 IA 10 IA3 Irrigation area IA 2 Existing conveyance Proposed conveyance IA 11 River Kakahu River Hei Hei Te Orari River Rangitata Moana River River

RDR KLONDYKE

LAKE OPUHA IA 16 ‘A’ block ‘B’ block IA 14 IA 5 RSIS IA 1a B IA 4

Scenario 1D IA 6 RSIS A block -> Klondyke

Proposed storage IA 9 IA 1

Existing storage IA 8 IA 10 IA3 Irrigation area IA 2 Existing conveyance Proposed conveyance IA 11 River AECOM OTOP Regional Water Assessment OTOP Regional Water Resource Assessment

Appendix D

South OTOP Model Schematics

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Appendix D South OTOP Model Schematics

21-Apr-2017 Prepared for – Environment Canterbury – Co No.: N/A Opuha River(s) IA IA 31 On LAKE On 32 farm On OPUHA farm IA farm 25 IA On farm 30 Opuha River IA On Tengawai On farm farm 26 River IA IA IA 29 28 27 IA On 22 farm IA IA 23 24 Opihi River On Scenario 2A/2B/2C/2D farm On farm IA Various IA 17 21 On Existing storage farm

On farm Irrigation area IA IA 20 18 On Existing conveyance IA IA farm 33 River 19 Opuha River(s) IA IA 31 On LAKE On 32 farm On OPUHA farm IA farm 25 IA On farm 30 Opuha River Tengawai IA IA On River IA On farm 26 27 29 IA farm IA On farm 28 22 Large IA IA Storage 23 24 Opihi River On Scenario 2E/2F farm On farm IA Various IA 17 21 On Existing storage farm

On farm Proposed storage IA IA 20 18 On IA farm Irrigation area IA 19 33 Existing conveyance Proposed conveyance River AECOM OTOP Regional Water Assessment OTOP Regional Water Resource Assessment

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