BEFORE THE CANTERBURY REGIONAL COUNCIL. Act 1991 AND. of Plan Change 3 to the Waitaki Catchment Water Allocation Regional Plan

Transcription

1 BEFORE THE CANTERBURY REGIONAL COUNCIL IN THE MATTER of the Resource Management Act 1991 AND IN THE MATTER of Change 3 to the Waitaki Catchment Water Allocation Regional STATEMENT OF EVIDENCE OF DAVID WILLIAM STEWART ON BEHALF OF TE RŪNANGA O AROWHENUA TRUST, TE RŪNANGA O WAIHAO INC, TE RŪNANGA O MOERAKI AND TE RŪNANGA O NGĀI TAHU HYDROLOGIST 1 MAY

2 1. INTRODUCTION 1.1 My name is David William Stewart. I am a hydrological consultant and a director of Raineffects Limited. 1.2 I have a BSc in Physical Geography, Climatology and Mathematics from the University of Otago and 41 years' experience in natural resource investigations and hydrology. Between 1974 and 1996 I was employed in various hydrology positions with the Otago Catchment Board and the Otago Regional Council. From 1992 to 1996 I was the Otago Regional Council s Manager of Hydrology. Since 1996 I have worked as an independent hydrological consultant. 1.3 Since leaving the Council, I have undertaken many water resource assessments and hydrological investigations including impacts of resource development, analysed water plans (Otago Regional Council, Environment Canterbury, draft Waitaki Catchment Water Allocation Regional ), analysed major project plans for water use, (Project Aqua, Dunedin City Council water supply, Oceana Gold Taieri River water take) and undertaken many water abstraction permit applications with the largest being the North Otago Irrigation Company/Lower Waitaki Irrigation Company applications to take 10 cumecs from the Waitaki River for irrigation which were subsequently granted. In 2008/2009/2010 I was Environment Canterbury s hydrologist and S42A report writer for the more than thirty applications to take water in the Upper Waitaki catchment. 1.4 I confirm that I have read the Code of Conduct for Expert Witnesses contained in the Environment Court Practice Note 2014 and that I agree to comply with it. I confirm that I have considered all the material facts that I am aware of that might alter or detract from the opinions that I express, and that this evidence is within my area of expertise, except where I state that I am relying on the evidence of another person. 1.5 Data and information used throughout this evidence has been provided by Environment Canterbury, Ngāi Tahu and Meridian Energy Limited 2

3 2. EXECUTIVE SUMMARY 2.1 This evidence is mainly concerned with identifying the reliability for the reserved water (mahinga kai 10 cumecs and Wainono lagoon flushing 1 cumec) and the post 2006 abstraction consents. 2.2 This evidence considers the three scenarios being the Waitaki Catchment Water Allocation Regional (the ), Change 3 and the Ngāi Tahu/Meridian Energy scenarios. Each was tested against the daily flow records from 1 July 1979 to 3 March 2014 (ie over 34 seasons). Based on my analysis, in my view, the Ngāi Tahu/Meridian scenario is the best option for least disruption to post 2006 abstractors. Compared to the other scenarios, there is no restriction to pre 2006 abstractors and to the mahinga kai/wainono water and no restriction possible to post 2006 abstractors in the key months October to March. There is also very little likelihood of restriction in the shoulder months of September and April 2.3 The analyses showed that: (a) (b) (c) the scenario, had it been fully implemented, is likely to have resulted in significant restriction to reserved water and post 2006 abstraction consents. The analysis showed, that over the 34 seasons, there could have been a total of 683 days when restrictions were likely to have occurred. This is calculated to be an average of 20 days per season (over the 34 seasons recorded) and a range from 0 to 57 days in a season. Change 3 is likely to result in some restriction to both reserved water and post 2006 consents but significantly less than the scenario. The analysis showed, that over the 34 seasons, there could have been a total of 189 days when restrictions were likely to have occurred. This calculated to be an average of 5.5 days per season (over the 34 seasons recorded) and a range from 0 to 23 days in a season. The Ngāi Tahu/Meridian scenario is likely to result in 100% reliability for reserved water and a close to 100% reliability for post 2006 abstractions. The analysis showed, that over the 32 seasons, there could have been a total of 15 days when restrictions were likely to have occurred. This calculated to be an average of 0.4 days per 3

4 season and a range from 0 to 3 days in a season. Under this scenario, the restrictions would occur only in the shoulder months of September and April while the main irrigation months of October to March would have 100% reliability for post 2006 abstraction consents. 3. SCOPE OF EVIDENCE 3.1 I have been asked to give evidence on behalf of Te Rūnanga o Ngāi Tahu, Te Rūnanga o Arowhenua, Te Rūnanga o Waihao and Te Rūnanga o Moeraki (collectively Ngāi Tahu). This evidence assesses the reliability of allocated water in the Lower Waitaki Catchment from the Lower Waitaki River. There are three separate scenarios which will be reviewed including: (a) Scenario A: The Waitaki Catchment Water Allocation Regional (the ) scenario which sets: (i) an allocation limit of 90 cumecs; (ii) a minimum flow of 150 cumecs; and (iii) a required series of releases of water from the Waitaki Dam by Meridian Energy Limited ranging between 10 cumecs in the winter months to 80 cumecs in the summer irrigation months. (b) Scenario B: Change 3 (PC3) scenario which sets: (i) an allocation limit of 90 cumecs; (ii) a series of minimum flows ranging from 144 cumecs in wintertime to 102 cumecs in summertime for consents existing prior to the becoming operative (pre 2006 abstractors) and 152 cumecs for all new allocation since the plan became operative (post abstractors); (iii) and a series of releases of water from the Waitaki Dam by Meridian Energy Limited ranging between 4 cumecs in the winter months to 32 cumecs in the summer irrigation months. 4

5 (c) Scenario C: The Meridian/ Ngāi Tahu scenario which: (i) accepts an allocation limit of 90 cumecs, 10 cumecs of which is reserved for mahinga kai and 1 cumec for augmentation of the Wainono Lagoon (reserved water); (ii) sets a series of minimum flows ranging from 132 cumecs in the wintertime to 100 cumecs in summertime, to which, if the reserved water flows are added if they are not used out of stream, results in a series of minimum flows ranging from 142 cumecs in wintertime to 110 cumecs in summertime; and (iii) includes a series of releases from the Waitaki Dam by Meridian Energy Limited ranging between 4 cumecs in wintertime and 40 cumecs in summertime. There are other aspects of this Ngāi Tahu/Meridian Energy Limited flow regime which will be documented later. 3.2 In order to undertake this comparison it was assumed: (a) (b) That in all three scenarios, the flow throughout the month would be no less than the monthly Waitaki Dam discharges as listed in Rule 7 Table 6 for each of the three scenarios. In other words, this means that for the, the minimum flow from October to March at the base of the Waitaki Dam will be 230 cumecs, for Change 3 it will be 182 cumecs and for the Ngāi Tahu/Meridian Energy scenario, it will be 190 cumecs. Similarly in the months of September and April, the minimum flows at the base of the Waitaki Dam will be 200 cumecs, 170 cumecs and 168 cumecs respectively. That there were no periods when inflows to the Waitaki Dam were such that Meridian could reduce the discharges due to these low inflows. 3.3 In preparing my evidence I have considered: (a) (b) (c) the Waitaki Catchment Water Allocation Regional ; the provisions in Change 3; and the submission of Ngāi Tahu. 5

6 4. THE PLAN 4.1 Scenario (a) the was set up to provide 100% reliability to pre 2006 abstractors and consents for town and community water supplies, industrial and commercial activities, tourism and recreational activities and others. For post 2006 abstractors it provided up to 95% of the peak rate of taking. The words up to 95% indicates that a range of reliabilities less than or equivalent to 95% reliability was envisaged for new consents. 4.2 The also recognised that the shoulder months of September and April are usually periods of lower demand and provided only 50 cumecs extra instead of the 80 cumecs provided in the months of October to March inclusive. 4.3 It is to be noted that although 90 cumecs is the total allowable abstraction with a minimum flow of 150 cumecs, only 80 cumecs is added during the peak months and not 90 cumecs which could be allocated. This means that Meridian Energy only have to top up the lower Waitaki River whenever flows in the river fall below 230 cumecs which is 10 cumecs less than what could be abstracted. 4.4 I understand the anticipates that consents which were granted before 2006 are to retain their existing level of reliability of supply upon their renewal which is 100% reliability of supply. Assuming that this level of reliability of supply was maintained, when flows in the river are 230 cumecs and all abstractions would want to be at their peak, then the pre 2006 consents would be abstracting 52 cumecs at 100% reliability and the post 2006 consents would have access to 28 cumecs (ie making up the 80 cumecs referred to above). Since there is the ability to allocate 38 cumecs to post 2006 abstractors, then if the flow was at 230 cumecs, it means there is a short fall of 10 cumecs. With 10 cumecs less, this equates to about a 23% reduction in peak rate of take for post 2006 consents. Therefore some restrictions would apply to post 2006 abstractors when flows were below 240 cumecs. 4.5 Attached to my evidence is Table 1 which is the flow duration table for the Waitaki River based on daily flows between the period 1 July 1979 and 1 March The daily record is that provided by Environment Canterbury on 7 May There were gaps within the flow record which I have filled using 6

7 Meridian Energy Limited records at the Waitaki Dam. A record of these gaps is shown at Annexure A to my evidence. 4.6 The flow duration table shows the percentage of time flows were equalled or exceeded for the duration of the record. For example, for 100% of time, flows exceeded 131 cumecs and for 90% of time flows were equal to or greater than 238 cumecs. 4.7 Attached to my evidence is Table 2 which is a compilation of the lower ends of the flow duration tables for the irrigation months (September to April) from 80% through to 100% of exceedance flows. The flows with less than 80% exceedance are not provided since they are much higher flows and are not relevant to this discussion. Table 2 has the current flow duration values in the left column for each month while the highlighted columns are what these values may look like as a result of fully complying with the minimum flows and required flow releases. The blue highlighted cells are where, if abstraction was at its peak, restrictions would begin for the post 2006 abstractors. Note that this same exercise has been carried out for Scenario B (PC3) and Scenario C (Ngāi Tahu / Meridian) below. Therefore, Tables 2, 3, and 4 can all be compared against one another for an understanding of how the provisions work in practice. 4.8 In undertaking my analysis I have made a number of assumptions. Firstly during the September and April months under the scenario, I have assumed that all abstraction uses only up to 63% of the peak abstraction rate which is 57 cumecs out of total allowable 90 cumecs. This is based on the required supplementary discharge by Meridian of 50 cumecs, instead of 80 cumecs (as in the peak months). 50 cumecs is about 63% of 80 cumecs. Note that in Change 3 and the Ngāi Tahu/Meridian scenarios, abstractors are restricted to 63% and 65% respectively of their total allocation for these shoulder months. 4.9 During these months the anticipates 50 cumecs above the minimum flow of 150 cumecs to be released into the Lower Waitaki River. This in part ensures that the pre 2006 abstractors maintain their 100% reliability and are not affected by restrictions. However, post 2006 consent holders may be affected especially when flows are less than 207 cumecs (150 cumecs minimum flow plus 57 cumecs (see the previous paragraph). Table 2 shows 7

8 that average reliability is about 97.5% for post 2006 abstractors in September and about 94.8% for April I have also undertaken a similar analysis for the months October to March. For this analysis I have assumed that all abstractors use 100% of the total allocable 90 cumecs. During these months the anticipates that up to 80 cumecs above the minimum flow of 150 cumecs will be released into the Lower Waitaki River. As with the above analysis, the pre 2006 abstractors would maintain their 100% reliability. However, post 2006 consents would be affected especially at flows below 240 cumecs. Table 2 shows that flows at and above 240 cumecs have a reliability of 82.6% for October, 89.5% for November, 82.6% for December, 92.2% for January, 96.1% for February and 95.3% for March. These reliabilities are what the post 2006 abstractors would have for full abstraction. At flows lower than 240 cumecs, there would be restrictions on their takes. In addition I have also undertaken an analysis of the number of days when post 2006 abstraction may have been affected due to flows not being sufficient to provide the full 90 cumecs allocation without breaching the minimum flow of 150 cumecs. Results and discussion of this is contained the section tiled in "Table 5". 5. PLAN CHANGE Scenario (b) PC3 as notified, once again assumes that pre 2006 abstractors will retain their 100% reliability. In addition, PC3 recognises the shoulder months of September and April as times of lesser irrigation demand and it places a restriction on all irrigation abstraction of 63% of peak demand (57 cumecs out of total 90 cumecs allocated). As part of the post 2006 abstraction, the reserved water allocations also appear to be subject to the same restrictions (ie only 63% of the take is available in the September and April months). Note that firstly of the total 90 cumecs to be allocated, 52 cumecs are considered to be pre 2006 consents and the remaining 38 cumecs is for post 2006 and reserved water. The reserved water accounts for 11 cumecs out of 38 cumecs in this post 2006 allocation group. In these two months only 24 cumecs is allowed for this group if the water is available. 5.2 Attached to my evidence is Table 3 which is a compilation of the lower ends of the flow duration tables for the irrigation months (September to April) from the 80% through to 100% of exceedance flows. Table 3 applies the relevant 8

9 Scenario B (PC3) provisions and is subject to the comments outlined in paragraph 4.7 above. 5.3 In the September and April months, all abstraction is restricted to 63% of the peak abstraction rate (57 cumecs out of total 90 cumecs allocated). PC3 anticipates that Meridian will release an extra 20 cumecs above the minimum flow of 150 cumecs that it must maintain for these two months into the Lower Waitaki River immediately below the Waitaki Dam, which equates to a flow of 170 cumecs. 5.4 PC3 proposes one minimum flow regime for pre 2006 abstractors and another minimum flow regime for post 2006 abstractors (which includes the 11 cumecs of reserved water). For the pre 2006 abstractors a minimum flow of 120 cumecs is proposed for these two months. For the post 2006 abstractors a minimum flow of 152 cumecs is proposed. 5.5 Therefore there is a total of 50 cumecs available for all abstraction and reserved water (170 cumecs less the minimum flow of 120 cumecs) The pre 2006 abstractors take 33 cumecs being 63% of their peak abstraction rate of 52 cumecs. This leaves 17 cumecs available to meet the total demand of 24 cumecs for the post 2006 abstractors and reserved water (24 cumecs is 63% of the 38 cumecs for this group). Once again this results in a shortfall of 7 cumecs for the post 2006 consents and reserved water. Therefore during September and April, restrictions will begin on the post 2006 abstractors and the reserved water at 177 cumecs. 5.6 PC3 anticipates that for the months of October to March inclusive, the minimum flow for all pre 2006 abstractors and the reserved water is 102 cumecs while that for the post 2006 abstractors remains at 152 cumecs. PC3 anticipates that Meridian will release 32 cumecs above the minimum flow of 150 cumecs it must maintain for these months into the Lower Waitaki River (results in a flow of 182 cumecs in the Lower Waitaki River immediately downstream of the Waitaki Dam). Therefore there is 80 cumecs available (182 cumecs less 102 cumecs minimum flow equals 80 cumecs) for abstraction. The pre 2006 abstractors can take 52 cumecs being their peak rate of abstraction. This leaves 28 cumecs available to meet the total demand of 38 cumecs for the post 2006 abstractors and reserved water, a shortfall of 10 cumecs. Therefore in October to March, restrictions will begin on the post 9

10 2006 abstractors and the reserved water at 192 cumecs. If flows are held at 182 cumecs and total demand is 192 cumecs, then restrictions will occur to the post 2006 abstractors and reserved water. 5.7 Table 3 shows that average reliability under the PC3 flow and allocation regime is about 98.8% for post 2006 abstractors and reserved water in September and April. 5.8 I have also undertaken a similar analysis for the months October to March. For this analysis I have assumed that all abstractions use 100% of the total allocable 90 cumecs. During these months PC3 anticipates that up to 32 cumecs above the minimum flow of 150 cumecs will be released into the Lower Waitaki River. As with the above analysis, the pre 2006 abstractors would maintain their 100% reliability. However, post 2006 consents would be affected especially as flows fall below 192 cumecs. Table 3 shows that at flows of 192 cumecs the post 2006 abstractors would have a reliability of 95% for October, 98.4% for November, 94.3% for December, 98.2% for January, 99.5% for February and 98.9% for March. 5.9 In addition I have also undertaken an analysis of the number of days when post 2006 abstraction may have been affected due to flows not being sufficient to provide the full 90 cumecs allocation without breaching the minimum flow of 150 cumecs. Results and discussion of this is contained in the section titled 'Table 5'. 6. NGĀI TAHU/MERIDIAN 6.1 Scenario (c) Ngāi Tahu/Meridian is set up to provide: (a) 100% reliability for pre 2006 abstractions; and (b) At least 95% reliability for both the reserved water and post 2006 abstractors. 6.2 Before I discuss my analysis, I would like to highlight a typo in the Ngāi Tahu submission. In the Ngāi Tahu submission Table 3A proposes a minimum flow of 110 cumecs in the months October to March whenever the mahinga kai allocation is not being abstracted. I note the mahinga kai allocation is in fact 11 cumecs and as such the minimum flow recorded here should be 111 cumecs 10

11 rather than the 110 cumecs. Similarly for April it should be 118 cumecs, May 135 cumecs, June and July 143 cumecs, August 135 cumecs and September 118 cumecs. 6.3 As with the PC3 scenario, this scenario assumes that during the shoulder months of September and April there is less demand for irrigation water and places a restriction on all irrigation abstraction of 65% of peak demand. In this case because the reserved water will be exempt from this restriction, it is 65% of 79 cumecs (90 cumecs-11 cumecs=79 cumecs) which is about 51 cumecs. Of this, the pre 2006 abstractors can abstract 34 cumecs, and the post 2006 abstractors can take 17 cumecs if it is available. 6.4 Table 4 is a compilation of the lower ends of the flow duration tables for the irrigation months (September to April) from the 80% through to 100% of exceedance flows. Again the flows with less than 80% exceedance are not provided since they are much higher and not relevant to this discussion. Table 4 applies the relevant Scenario C (Ngāi Tahu / Meridian) provisions and is subject to the comments outlined in paragraph 4.7 above. 6.5 This flow and allocation regime anticipates that during the September and April months, with the exclusion of the reserved water, all abstraction (79 cumecs) is restricted to 65% of the peak abstraction rate (51 cumecs out of total 79 cumecs able to be allocated). This scenario requires Meridian to discharge 18 cumecs on top of the Meridian minimum flow of 150 cumecs into the Lower Waitaki River during these months which brings the total flow up to 168 cumecs. The pre 2006 abstractors who can take a maximum of 34 cumecs in these two months, have a separate minimum flow of 107 cumecs (or 118 cumecs if the reserved water is left in the river). The reserved water has a minimum flow of 141 cumecs for these two months and can take 11 cumecs. The post 2006 abstractors have a minimum flow for these months of 152 cumecs and can take 17 cumecs. There is 61 cumecs available for abstraction ( = 61) of which 11 cumecs is allocated to reserved water with no restriction and 34 cumecs is allocated to pre 2006 abstractors. This leaves a total of 16 cumecs remaining available to meet the total demand of 17 cumecs for the post 2006 abstractors. This is a shortfall of 1 cumec for the post 2006 abstractors. Therefore in September and April, restrictions will begin at 169 cumecs for post 2006 abstractors. 11

12 6.6 In the summer months (October to March) the total abstraction (irrigation plus reserved water) is 90 cumecs. During this time Meridian Energy will discharge 40 cumecs above its minimum flow of 150 cumecs thereby maintaining a flow of 190 cumecs (150 cumecs + 40 cumecs = 190 cumecs) in the Lower Waitaki River. 6.7 The pre 2006 abstractors can take 52 cumecs, the reserved water take is 11 cumecs and the post 2006 abstractors can take 27 cumecs (52 cumecs+11 cumecs+27 cumecs=90 cumecs). The post 2006 abstractors will have 100% reliability of their allocation since the total abstraction is 90 cumecs and with the minimum flow set at 100 cumecs and the flows required to be at 190 cumecs throughout this 6 month period, 90 cumecs is available for all users so no restrictions should occur to any abstractor. 6.8 Table 4 shows that average reliability is about 99.2% for post abstractors and reserved water in September and similar for April. In the months October to March, flows never fall below 190 cumecs so all 90 cumecs allocated have 100% reliability through these months. 6.9 Table 5 shows the number of days per season when the Ngāi Tahu/Meridian scenario may not have been sufficient to provide the full monthly allocation without breaching the minimum flow for post consents. From the above discussion only the months of September and April may be marginally affected. In October to March, 100% reliability is provided to all users and abstractors. 7. TABLE Table 5 shows the number of days some form of restriction may have been required, had any of the scenarios been in place over the 34 irrigation seasons from 1979/80 to 2012/13. It does not show the degree of restriction but that could be calculated if required. 7.2 Under the scenario, there was an average of 20 days per year when the post 2006 consents/reserved water would have experienced a forced reduction in take. In only 3 of the 34 seasons there may have been no restrictions. 12

13 7.3 Under the PC3 scenario, there was an average of 5.5 days per season when the post 2006 consents/reserved water would have experienced a forced reduction in take. In 7 of the 34 seasons, there may have been no restrictions. 7.4 The scenario under the Ngāi Tahu/Meridian is significantly different and much better for the post 2006 abstractors than the previous 2 scenarios. Firstly like the previous 2 scenarios, all pre 2006 consents would have 100% reliability. Secondly unlike the previous 2 scenarios, the reserved water would have 100% reliability. And thirdly, the only restriction to post 2006 consents occurs in the shoulder months of September and April and there is no restriction in most years in these months. The table shows that there may have been a 0.4 days per season on average when the post 2006 consents would have experienced a forced reduction in take. In 26 of the 34 seasons, there may have been no restrictions, and some restrictions in the remaining 8 seasons but only in the shoulder months. No restrictions would have occurred in the main irrigation months of October to March inclusive. Mr David William Stewart 1 May

14 Annexure A Gaps in Environment Canterbury Flow Record Start of Gap End of Gap Number of Days

15 Table 1. Flow Duration Table-Irrigation Months-1 July March 2014 (cumecs) Percent Note: The numbers on the left hand column represent the percentage in tens. The numbers on the top row represent the percentage in ones. For example, to work out the flow duration of 46 percent, you would locate the number that aligns with "40" in the left hand column and "6" in the top row. This would give you the result of 370 cumecs from within the body of the table. 15

16 Table 2. Truncated Current and the dicted Flow Duration Tables for the Lower Waitaki River (cumecs) Percent September October November December January February March April

17 Table 3. Truncated Current and the PC3 dicted Flow Duration Tables for the Lower Waitaki River (cumecs) Percent September October November December January February March April

18 Table 4. Truncated Current and the Ngāi Tahu/Meridian Scenario dicted Flow Duration Tables for the Lower Waitaki River (cumecs) Percent September October November December January February March April

19 Table 5. Days of Restriction for Water Users Season The Change 3 Ngāi Tahu/Meridian 1979/ / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / /