IN THE MATTER of the Resource Management Act 1991
AND
IN THE MATTER of a Board of Inquiry appointed under s149J of the Resource Management Act 1991 to determine an application for resource consents sought by Watercare Services Limited for its Waikato River Take and Discharge Proposal.
STATEMENT OF EVIDENCE OF TOM BASSETT ON BEHALF OF WATERCARE SERVICES LIMITED
River Hydrology
1. Introduction, Qualifications and Experience
1.1 My name is Tom Bassett.
1.2 I am a Chartered Engineer (CEng) with a Bachelor of Engineering (Hons) and a Master of Engineering from the University of Auckland, and a Master of Business Administration from the University of Otago.
1.3 I have nearly 40 years’ post-graduate experience, principally in the water resources disciplines of hydrology, catchment management and water resources engineering. I am a member of the British Institution of Civil Engineers and the New Zealand Hydrological Society.
1.4 Since 1994, I have been employed by Tonkin & Taylor Ltd (T+T). I was, for two years, the Resource Group Manager of the Water Resources Group, and subsequently for two years, the Discipline Manager of the Water Engineering sub-Discipline.
1.5 I am a Principal of T+T, and am presently employed as an Advanced Water Engineering Specialist. I have wide experience in water resources engineering including hydrological analysis, computational modelling, catchment management investigations and reporting.
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1.6 Examples of specific projects I have been involved in relating to catchment management and river engineering include:
(a) Numerous investigations and studies for Watercare relating to the operation of its bulk water supply system, including:
(b) Hydrological analysis, hydraulic modelling on the Tongariro and Tauranga-Taupō Rivers;
(c) Integrated Catchment Studies for Metrowater and Auckland City Council investigating stormwater flows and water quality;
(d) Probable Maximum Precipitation and flood modelling for various New Zealand catchments; and
(e) Project Manager for Environmental Impact reporting for the Sarawak River barrage, which included modelling of impacts of proposed works on river water levels and water quality.
1.7 This evidence is provided in support of Watercare’s application for all necessary consents to enable the taking of up to 150,000 cubic metres (net) of water per day (m3/day) from the Waikato River for municipal water supply purposes (Project).
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1.8 In terms of my involvement in the Project, I provided specialist technical input into the applications for resource consent that were lodged with the Waikato Regional Council (WRC) in December 2013. Since 2013, I have held the role of Project Manager and Principal Hydrologist for the investigation and assessment of effects of the proposed take on the hydrology and river regime of the Waikato River. In that role, I have been involved in all other applications for resource consent by Watercare to take water from the Waikato River since 2013, and in the preparation of the hydrological assessment submitted in support of Watercare’s updated application lodged with the Environmental Protection Authority (EPA) on 11 December 2020.
2. Code of Conduct
2.1 My qualifications as an expert are set out above. I confirm that I have read the Expert Witness Code of Conduct set out in the Environment Court's Practice Note 2014. I have complied with the Code of Conduct in preparing this evidence. Except where I state that I am relying on the evidence of another person, this evidence is within my area of expertise. I have not omitted to consider material facts known to me that might alter or detract from the opinions expressed in this evidence.
3. Executive Summary
3.1 This evidence presents my assessment of the effects of Watercare’s proposed take of up to 150,000 m3 per day (net) of water from the Waikato River for municipal water supply purposes on the allocation status and hydrology of the Waikato River, as well as the effects on hydrology from the coffer dam that will be used during construction of the proposed new intake structure.
3.2 My evidence is based on:
(a) With respect to allocation: information provided by WRC regarding existing authorisations to take water from the River, and applications lodged with the WRC but yet to be decided (i.e. in the queue), as at 4 May 2021; and
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(b) With respect to hydrology effects: the analysis and modelling of the hydraulic regime of the River, as presented in the River Hydrology Assessment report submitted to the EPA on 11 December 2020 in support of the updated application. However, my evidence also includes some new and updated information based on supplementary modelling since the application was lodged.
3.3 I have a high degree of confidence in the assessment of the effects of the proposed water take on the hydraulic regime of the River set out in my evidence, as the assessment is based on analysis and modelling of the hydraulic regime for various flow conditions, and using various analytical tools. The analyses have modelled the effects on the flow in the River reach at the intake, and further downstream through the wetlands downstream of Tuakau. The results of the various analyses are consistent, and in my opinion provide a high degree of confidence for the results and the assessment of the effects of the proposed water take in terms of changes in water level and flow velocities in the River.
3.4 If Watercare’s application and all other applications in the queue were granted, the River would not be fully allocated. For the Coastal Marine Area catchment approximately 25,800 m3/day would still be available in peak months for future applications, and 192,000 m3/day in the winter months.
3.5 I consider that the impact of the proposed take on water levels in the intake reach of the river during both low flows and in flood conditions will be minimal. This is because of:
(a) the take’s small reduction in water levels (up to 46 mm during low flows), and water depth at the intake being at least 6 m during low flows; and
(b) the twice daily tidal fluctuation at the intake site during low flows, which varies from a minimum of approximately 500 mm increasing to approximately 1 m during Spring tidal cycles.
3.6 I consider that the impact of the installation of the coffer dam during construction on water levels in the intake reach of the river during flood conditions will be
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minimal, i.e. a small increase in water levels (up to 0.02 m) with a coincident water depth at the intake of at least 9 m during flood events.
3.7 Modelling indicates that the changes in the hydraulic regime in the wetland reaches downstream of Tuakau resulting from the proposed additional 150,000 m3/day take will be:
(a) Water levels reduced by 1 mm to 2 mm, with coincident water depths of 4 m or more and tidal fluctuations up to 1.8 m; and (b) Changes in mean velocity up to 0.006 m/s (on the flood tide) compared to a mean flood velocity in the river of between 0.23 m/s and 0.50 m/s for Neap and Spring cycles.
3.8 Overall, in practical terms, I consider that the changes in water levels and flow velocities in the intake reaches and further downstream will not be noticeable.
3.9 I consider that the effects on river hydrological values from the construction and operation of the proposed intake structure and abstraction of the water from the Waikato River will be ‘Very Low’.
3.10 Thus, I do not consider that any further mitigation measures are required beyond those identified in the evidence of others and included as part of the Project, specifically related to Ecological effects.
3.11 I have read all submissions lodged with the EPA raising matters relating to allocation of the River and the effects of the Watercare’s take on the hydrology of the River. I acknowledge the concerns raised by submitters, however, as outlined in my evidence the effects of Watercare’s take on the hydrology and hydraulic regime of the River will be ‘Very Low’, including for those matters of concern raised by submitters. Having considered those matters raised by submitters, my conclusions regarding the effects of the Project remain unchanged.
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4. Scope of Evidence
4.1 My evidence addresses the following matters:
(a) The existing hydrological environment of the Waikato River in the intake reaches and downstream; (b) The allocable flow in the Waikato River under the Operative Waikato Regional Plan (WRP); (c) The impact of the proposed take on the hydraulic regime of the river; (d) The impact of the proposed take on other water users in the catchment; (e) The impact of the proposed coffer dam on the flood regime of the river during construction of the intake; and (f) Response to matters raised in relation to river hydrology by submitters.
4.2 My evidence is based on investigations and technical assessments for Watercare in relation to the proposed take as described in the T+T report Waikato River Water Take and Discharge Proposal - Board of Inquiry: River Hydrology Assessment, ref 1014753.100, dated December 2020, and subsequent modelling to clarify and supplement earlier analyses outlined in that report. The report was prepared under my management and direction, and is included in full with the updated application.
5. The existing hydrological environment of the Waikato River
5.1 The Waikato River drains a significant portion of the central North Island, with two principal sub catchments being the main stem Waikato with headwaters in the Taupō area, and the Waipa River. The catchment is shown in Figure 1, which also indicates the catchment of the Tongariro Power Scheme in the upper reaches, and the locations of existing hydro dams along the main stem of the river.
5.2 The proposed abstraction will be located at the site of Watercare’s existing intake, upstream of Tuakau (also indicated in Figure 1). This is approximately 36 km from the Waikato River mouth and 23 km upstream of the extent of saline intrusion from the sea into the lower river reaches.
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Figure 1: Waikato River catchment
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5.3 The length of the main stem of the Waikato River from Lake Taupō downstream to the intake is approximately 389 km. The catchment area upstream of the intake is approximately 14,063 km2. The total catchment area of the Waikato River to the Coastal Marine Area (CMA) is approximately 14,411 km2, and to the river mouth 14,456 km2.
5.4 Flows from the Waikato sub-catchment upstream of Hamilton include water diverted from the headwaters of the Whanganui and Rangitikei Rivers by the Tongariro Power Scheme (refer to Figure 1). Downstream of Lake Taupō, River flows are regulated by dams and hydraulic structures constructed to generate hydroelectric power. The Karapiro Dam is the structure furthest downstream.
5.5 The operation of the schemes along the cascade of hydrolakes significantly affects flows downstream of Karapiro. The flows in the lower Waikato River are thus determined to a significant extent by conditions of consent for Mercury NZ Limited at Karapiro requiring the release of residual flow discharges, which may vary. The operation of the dams is also governed by requirements of WRC flood management rules during higher flows.
5.6 Water levels in the Waikato River are tidally influenced as far upstream as at least Mercer (approximately 42 km from the river mouth). Daily fluctuations in water level have also been observed as far upstream as Rangiriri (approximately 66 km from the river mouth), perhaps influenced by the hydroelectric power station releases upstream.
5.7 Reporting by WRC (Jones and Hamilton, 2014) indicates that the extent of saline intrusion into the river is up to 13 km from the river mouth.
5.8 There are a number of hydrological recording sites on the Waikato River, with those most relevant to the assessment of this application being the recording sites at:
(a) Rangiriri (upstream), recording water level and flow (records from 1965); (b) Mercer (upstream), recording water level and flow (records from 1963); (c) Tuakau (downstream), recording water level only (records from 1965); and
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(d) Hood’s Landing (downstream), recording water level only (records from 1962).
5.9 The locations of these monitoring sites are indicated in Figure 6 later in my evidence.
5.10 Table 1 below summarises the key flow statistics for the Waikato River taken from the hydrological recording sites noted above between Rangiriri and the river mouth. The flow statistics immediately upstream of Watercare’s intake have been calculated using catchment area scaling. It is noted that all the data are modified by existing takes, therefore the statistics are not representative of naturalised flows.
Table 1 Summary of relevant average and 7-day low flow statistics for the Waikato River
6 3 Site name Median Mean MALF q5 (m /s) flow flow (m3/s) (m3/s) (m3/s) Waikato River at Rangiriri 1 330.02 360.3 197.4 181.7 Waikato River at Mercer 1 359.8 407.9 203.8 185.3 Waikato River immediately upstream of Waikato intake (i.e. before Watercare 368.2 412.8 204.3 185.9 abstraction) 4 Waikato River at Tuakau 3 - - 204.6 186.0 Waikato River at Hood’s Landing 3 - - 205.2 186.5 Waikato River at Coastal Marine Area - - 205.24 187.95
1 Calculated by WRC from flow records, provided 23 March 2020 2 Calculated by WRC from flow records, provided 30 October 2020 3 Calculated by WRC as Mercer flow plus inflow estimates, provided 23 March 2020 4 Calculated by interpolation based on catchment area 5 Calculated by WRC, obtained from Surface Water Allocation Levels webpage (accessed 12 November 2020) 6 Mean Annual Low Flow (MALF)
5.11 The lowest 7-day average flow at Rangiriri in the 55-year record is 130 m3/s for a period, recorded in April 1973. There are 14 years in the record when the
annual low flow was less than the (presently) estimated q5.
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5.12 Figures 2, 3 and 3a illustrate the monthly variation of flows for the river as
determined from the WRC flow record at Rangiriri. The q5, median flow and allocable flow thresholds are also indicated. The figures show that:
(a) 96 % of flows in the river exceed q5, with seasonal exceedance rates of 99 % and 96 % for the May to September and October to April periods respectively; and
(b) The lowest flows are generally recorded from January to May, corresponding to the late summer and autumn seasons.
Figure 2: Flow duration curve for 7-day average flow record at Rangiriri
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Figure 3: Minimum, average and maximum 7-day flow rates by month, based on full record at Rangiriri
Figure 3a: Minimum and average 7-day flow rates by month, based on full record at Rangiriri
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5.13 Cross section information for the Waikato River channel in the vicinity of the Watercare intake is available from WRC survey data, as shown in Figure 4 below.
5.14 The cross section 44a transect (some 75 m downstream of the intake) is at a localised narrowing of the river, with the width (120 m) approximately 40 % narrower than upstream and downstream sections (cross sections 45 and 43). Apart from two reaches in the vicinity of Tuakau Bridge 5 km downstream, the river channel width generally increases towards the river mouth. At Port Waikato the width of the channel is greater than 500 m.
5.15 In normal flow conditions, the river depth in the intake reach varies between 6 m and 8 m depending on tide and upstream flow variations.
Figure 4: Lower Waikato River cross sections in vicinity of Watercare intake
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5.16 Further downstream, in the lower reaches of the river upstream of the river mouth, the river flows through braided reaches formed by wetland islands as shown in Figure 5, which also indicates the location of the Hoods Landing river gauge. The effects of the proposed water take on river hydraulics have also been assessed at cross section 6, which is considered to be representative of the lower river reaches through the wetlands.
Figure 5: Lower Waikato River cross sections in the wetland reaches
6. Allocable flow in the Waikato River catchment
6.1 For the purposes of assessing available water allocation in Waikato River as provided for in its Regional Plan, the WRC has divided the overall catchment into a number of sub-catchments – referred to as water allocation calculator (WAC) catchments. Those catchments most relevant to the Watercare application are:
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(a) The Rangiriri WAC catchment, at which point flows are monitored to inform consent condition thresholds; (b) The Mercer WAC catchment, the next catchment upstream of the Watercare intake; and (c) The CMA WAC catchment, used in the assessment of allocable flow for this application.
These are shown in Figure 6, which also shows the catchment to the river mouth.
Figure 6: Map of lower Waikato River WAC catchments
6.2 The proposed intake site is located within the CMA WAC catchment. The downstream boundary of the CMA catchment is 27 km downstream of the intake site, with the upstream boundary of the catchment 6 km upstream of the intake site, at Mercer. WRC has advised that the CMA catchment should be used for the assessment of the proposed water take of up to 150,000 m3/day net (or
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150 MLD). The CMA catchment is also applicable in assessing the existing Watercare take as it is located at the same location along the river.
6.3 As set out in Table 3-5 of the WRP, the allocable flow for the Waikato River downstream of the Huntly Power Station mixing zone has been set at 10 % of
the one in five year 7-day low flow in the river (q5). For the two WAC catchments of relevance to this study, Mercer and CMA, the allocable flows are 18.53 m3/s
3 and 18.79 m /s respectively, being 10% of the q5 flow at these sites. Table 2 summarises the allocable flow for some of the river sites listed in Table 1.
Table 2 Allocable flow for the Waikato River
3 Site name q5 (m /s) Allocable flow m3/s m3/day
Waikato River at Rangiriri 181.7 18.2 1,572,480
Waikato River at Mercer 185.3 18.5 1,598,400
Waikato River immediately upstream of Waikato intake (i.e. before Watercare 185.9 18.6 1,607,040 abstraction)
Waikato River at Coastal Marine Area 187.9 18.8 1,624,320
6.4 Based on information obtained from the WRC website and from data provided directly by WRC, I have been able to analyse the water that is presently allocated in the River, and also the water that would be allocated based on applications that have already been received by WRC from Watercare and others if those applications are granted.
6.5 I note that commonly the water sought by users, and the allocation authorised by WRC, varies during the year, based on the seasonal requirements of applicants.
6.6 My analysis shows that as at 4 May 2021, of the 18.79 m3/s of water available for allocation in the CMA catchment, between 11.05 m3/s (in July) and 15.56 m3/s (in February and March) has already been allocated (refer Figure 7). Thus depending on the time of the year, between 3.24 m3/s and 7.74 m3/s remains available for allocation, i.e. between 279,000 m3/day and
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670,000 m3/day (279 MLD and 670 MLD), or 17 % and 41 % of the allocable flow.
Figure 7: Seasonal allocation summary for the Waikato River at CMA catchment (data from the WRC ‘Allocated Water Take (IRIS) GIS layer - accessed 4 May 2021)
6.7 I understand from information obtained from the WRC’s website on 11 May 2021 that, as of that date, 511 applications to take surface water and groundwater have been lodged with WRC, accepted as complete under s 88 of the RMA, and are awaiting determination. Of these:
(a) 377 are “in the Waikato River queue”, i.e. located within the Waikato River surface water catchment; and (b) Of those 377 applications, 93 are dated on or before 20 December 2013 (the lodgment date of the original Watercare application to WRC).
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6.8 I have also analysed a future seasonal allocation scenario, assuming Watercare’s application and all applications in the queue lodged with the WRC prior to the lodgement of Watercare’s application in December 2013 were granted and included alongside presently authorised allocations. This would result in:
(a) From November to April (inclusive), 6 % to 7 % of the allocable flow within the CMA catchment remaining available – that is more than 93,000 m3/day (93 MLD); (b) Over the remaining months (May through October), up to 30 % of the allocable flow with the CMA catchment remaining available, i.e. up to 480,000 m3/day (480 MLD); and (c) These correspond to between 37 and 193 Olympic-sized swimming pools depending on the season.
6.9 Furthermore, if Watercare’s application and all other applications in the queue lodged both before and after Watercare’s application in December 2013 were granted, the allocation status within the CMA catchment would range from 1.6 % to 2.6 % available for allocation in November through April to 12 % to 26 % available for allocation in May through October. That is, all the applications presently in the queue can be granted in full and remain within the CMA allocable flow limit. For clarity, 1.6 % of the allocable flow equates to approximately 25,800 m3/day being available in peak months for future applications, and 12 % equates to 192,000 m3/day in the winter months (as shown in Figure 8).
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Figure 8: Future seasonal allocation summary for the Waikato River at CMA catchment with 150 MLD Watercare application (data current as of 4 May 2021)
7. The impact of the proposed Watercare take on the hydraulic regime of the river
7.1 The potential effects of the proposed additional water take, in terms of changes to water level and mean flow velocity and the impact on the extent of the saline intrusion to the lower river, were assessed at two locations on the River: at the intake and in the wetland reaches downstream.
7.2 I note that although the application is for a take of up to 150,000 m3/day net, the intake will draw water at a peak rate of 3.2 m3/s. At this peak flow, the daily volume could be drawn from the river in approximately 15 hours. This provides flexibility regarding plant operations and maintenance requirements. Depending on daily operations, there may be up to 9 hours with no water drawn from the river if the intake has been drawing at maximum capacity for the other 15 hours. It is this peak rate through the intake which has been used for the assessment of effects, but which will not be persistent throughout a day.
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7.3 The proposed additional net take of 150,000 m3/day represents less than 1 %
of the total q5 low flow daily volume in the river at the intake, being approximately 16,062,000 m3 (approximately 16 billion litres). The proposed peak rate (3.2
3 3 m /s) is approximately 1.72 % of the q5 flow (185.9 m /s) at the intake.
7.4 The changes in flow of the proposed take were assessed assuming coincident
q5 conditions at the intake. Implicitly this assumes that other allocations upstream have already been abstracted, consistent with WRC advice that all recorded data are modified by takes, i.e. not naturalised. Thus, our assessment of the effects is conservative in the sense that it may overstate the level of
change at any time, e.g. when river flows are higher than q5, and if users upstream are not fully exercising their authorised takes.
7.5 Representative water levels have been determined from WRC water level records when a spring tide coincided with a low flow period (28 February 2013 to 1 March 2013). The observed Waikato River mouth tidal range during this period was 1.55 m. Steady-state hydraulic analysis of cross-sections, assuming a constant hydraulic gradient, was used to determine the expected effect of the additional take.
7.6 The hydraulic analysis indicates that the proposed additional 150,000 m3/day (net) take will result in a very small change to flow velocities in the river, based on comparison to the baseline 150,000 m3/day net take scenario. Mean velocity
change (reduction) at the q5 threshold due to the proposed additional take is no greater than 0.003 m/s (3 mm/s), compared to a mean river velocity of up to 0.53 m/s. Cumulatively, together with the already authorised Watercare take, there will be a reduction in velocity of 0.006 m/s (6 mm/s) at maximum. The
impacts will be less when river flow is greater than q5, and if not all upstream users are fully using their entitlements meaning there is more water in the River.
7.7 With regards to water levels at the intake reach, the greatest water level change occurs when low flow events coincide with a Spring high tide. Considering the existing and proposed takes, cumulatively, the water level at the intake site (i.e. at cross section 44a) will be lower by a maximum of up to approximately 82 mm
at the q5 threshold compared to a river depth of 6.4 m (6,400 mm). The incremental change of the additional take of 150 MLD is up to approximately 46 mm. For smaller tides (i.e. less than Springs) the changes will be less.
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7.8 However, at the wider cross section 43 downstream with a similar depth (i.e. 6 m in Spring high tide conditions), the changes to water levels and velocities are reduced. Here, the cumulative impact of the existing and proposed takes is
approximately 58 mm at q5, with the incremental change of the additional take being approximately 34 mm. The incremental and cumulative changes in mean
velocity at the q5 threshold reduce to 0.002 m/s (2 mm/s) and 0.005 m/s (5 mm/s) respectively at this cross section.
7.9 I note that in earlier reporting for the application lodged by Watercare in 2013, the incremental impact on water levels in the intake reach for 200,000 m3/day sought in that application was reported to be up to 22 mm, i.e. for a greater net flow, a smaller impact on levels. However, I note that the 2013 assessment was based on the mean daily flow (2.3 m3/s), and not the peak intake flow (3.2 m3/s) which is the basis for the present application. This explains an apparent anomaly in effects between the two assessments.
7.10 I have also assessed the effect on water levels during flood conditions of the proposed coffer dam to be installed in the river during construction of the intake. The proposed coffer dam is described in detail in the evidence of Mr André Bresler. Essentially this coffer dam will be approximately 21 m long and extend approximately 10 m from the riverbank. The Waikato River channel in this reach is approximately 120 m wide.
7.11 I have modelled the hydraulic regime of the River during flood for the mean annual 10 year and 100 year return period flows (i.e. up to 1,600 m3/s). For all these events the water depth in the river will be over 9 m. The effect of the coffer dam in the River cross section will be to increase the flood level by up to 0.02 m. In my opinion this will not cause any adverse effects for other users of the River, especially given the relatively limited period of time that the coffer dam, a temporary structure, will be present in the river (i.e. for a construction period estimated at up to approximately 21 months).
7.12 I consider that the impact on water levels in the intake reach of the river during both low flows and in flood conditions will be minimal. This is because of:
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(a) the take’s small impact on water levels, being up to 46 mm reduction at the intake location during low flows, and coincident water depth of least 6 m; (b) the twice daily tidal fluctuation at the intake site varies from a minimum of approximately 500 mm increasing to approximately 1 m during Spring tidal cycles; and (c) An increase in flood level of only approximately 0.02 m due to the coffer dam in the river during construction, with a coincident depth of over 9 m during flood events.
7.13 Overall, in practical terms, I consider that the changes in water levels will not be noticeable.
7.14 Since the lodgement of the updated application with the EPA on 11 December 2020, a computational hydraulic model of the lower estuary has been developed to investigate in more detail the scale of any effects on the hydraulic regime in the wetland reaches. In these reaches, the hydraulic regime was modelled through Spring and Neap tide cycles. The model results indicate that the changes in the wetland reaches resulting from the proposed additional 150,000 m3/day take will be:
(a) The maximum water levels reduced by 1 mm to 2 mm incrementally, with a cumulative reduction of 2 mm to 3 mm;
(b) Changes in mean velocity changes at the q5 threshold due to the existing and proposed additional takes of:
7.15 I consider that the effects of the proposed take on water levels in the lower river are minimal (and virtually impossible to discern) given the water depth of at least 4 m and given that the daily tidal fluctuation in the wetland reaches is approximately 1 m at Neap tides, increasing to approximately 1.8 m during
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Spring cycles. I also consider that the changes in velocity are also minimal compared to the mean velocities in the river which fluctuate daily due to the tidal influence.
7.16 I note that no provision has been made in the assessment for any off- specification water) flows returned to the river at the time that the intake is operating. These discharges, contributing water back to the river, would reduce to some extent the already minimal changes in water levels and velocities outlined above.
7.17 WRC reports, with which I agree, note that the extent of saline intrusion is strongly influenced by tidal variation and river flow.
7.18 Our analysis indicated salinity intrusion to extend from 1.05 km upstream from the river mouth, during mean flow and mean sea level conditions, to approximately 10 km upstream, during low flows and high tide. This is comparable to the WRC sampling over a full range of flow and tidal cycles, which indicated the intrusion at the surface extending from the river mouth to at least 13 km upstream (in the vicinity of cross section 6, refer Figure 5 above).
7.19 Whereas our previous analysis indicated changes in extent of salinity intrusion resulting from the increased abstraction 150,000 m3/day (net) of up to approximately 150 m, the results of the more detailed modelling analysis show a negligible impact on the saline intrusion extent for both Neap and Spring tide
cycles (refer Figure 9 below). This is based on sustained q5 flows. Higher river flows will reduce the extent of saline intrusion from the river mouth: generally,
flows in the river are significantly greater than q5.
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Figure 9: Modelled extent of saline intrusion at q5 for existing conditions and if proposed 150,000 m3/day application is granted
8. Effects on other abstractions
8.1 Due to the geographical location of the intake, the distribution of downstream users is limited to an approximately 36 km section of the lower Waikato River. There are 102 consent holders with takes located in the catchment downstream of Watercare’s treatment plant, with 140 authorisations across 147 sites. Of these, 15 of the 102 consents holders have authorisations to take surface water, and another seven have authorisations to take both surface and groundwater.
8.2 Effects on downstream users are expected to be negligible due to the proposed take only causing a very small reduction in water levels, as noted above.
8.3 Downstream users with consented water takes, or users anywhere in the CMA sub-catchment who have applications to take water that were lodged with WRC before Watercare’s application was lodged in December 2013, will not have their actual or potential allocations impacted by the granting of Watercare’s proposed take, which is within the allocable flow available in the river.
8.4 Further, as all applications in the queue can now be granted within the allocable flow limit, applicants whose applications were lodged after Watercare’s application in December 2013 will not be adversely impacted by the granting of Watercare’s proposed take.
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9. Response to Submissions
9.1 I have read all the submissions which have raised issues regarding the possible effects of Watercare’s proposed new take on the hydrology of the river and implications for allocation of water. I comment on specific submissions as identified in the following paragraphs.
Ngati Tahu-Ngati Whaoa Runanga Trust
9.2 The Ngati Tahu-Ngati Whaoa Runanga Trust (submission no. 22) has raised issues about “potential ramifications on the availability of future water allocation”.
9.3 I note that the impact that the grant of Watercare’s application may have on future applications that have not yet been made will be addressed in planning evidence and legal submissions. However, from an allocation perspective, the granting of Watercare’s application will not result in the current allocation limit being exceeded. As set out in my evidence, Watercare’s application, and all other applications currently before the WRC, can be granted within the allocation limit.
Waikato Conservation Board
9.4 The Waikato Conservation Board (submission no. 43) identifies a particular concern regarding the increased saline intrusion into the Waikato awa as a result of the application. Earlier analysis of the effects of the proposed application indicated that the extent of saline intrusion could move further upstream by 150 m. However, more detailed computational modelling of the hydraulic regime of the river in the wetland reaches indicates a negligible impact on the saline intrusion extent for both Neap and Spring tide cycles, as outlined in paragraph 7.19 of my evidence.
Waipa District Council and Hamilton City Council
9.5 The Waipa District Council (submission no. 45) and Hamilton City Council (submission no. 46) have both lodged submissions raising concerns regarding over-allocation of water from the Waikato River, as a result of the granting of
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consent to Watercare. In particular, Waipa District Council and Hamilton City Council have expressed concerns that the granting of consent to Watercare will hinder their ability to obtain renewed consents with an increased quantity of water when their existing consents expire (in 2049 and 2046 respectively).
9.6 The granting of Watercare’s application will not result in the current allocation limit in the WRP being exceeded. As outlined earlier in my evidence, there is sufficient allocation available to enable Watercare’s application and all other applications currently “in the queue” before the WRC (lodged both before and after Watercare’s application) to be granted within the current allocation limit. I cannot speculate on the extent to which allocable flow will be available when the Waipa District Council and Hamilton City Council consents expire in 2049 and 2046, and whether there may, at that time, be allocation available to allow for increased takes by Waipa District Council and Hamilton City Council.
Te Kotahitanga o Ngāti Tuwharetoa
9.7 Te Kotahitanga o Ngāti Tuwharetoa (submission no. 49) has submitted that “the physical and metaphysical connection between Waikato River and Lake Taupō is important to mana whenua hapu”. The submission also raises concerns regarding the effects of Watercare’s proposed take on ecosystems and habitats upstream of the intake site.
9.8 In my opinion the magnitude of the incremental changes in water level at the intake (up to 46 mm) will have a negligible effect on water levels in the river upstream of the intake.
9.9 I also note that hydraulic regime of Lake Taupo and its headwaters are separated from the regime of the lower river by the existing dams and hydraulic structures of the hydrolakes cascade.
9.10 From a hydrological point of view, Watercare’s proposed take at Tuakau will not have any effects on the levels of Lake Taupō and its headwaters.
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Raukawa Settlement Trust and Raukawa Charitable Trust
9.11 The Raukawa Settlement Trust and Raukawa Charitable Trust (submission no. 57) have submitted that limited consideration has been given to the Waikato region or the implications on iwi and communities upstream from the resulting loss of water.
9.12 From a hydrological point of view, Watercare’s proposed take at Tuakau will have a negligible to nil effect on water levels in the Waikato River and its tributaries upstream of the intake.
9.13 In terms of permanent water loss, the proposed take will extract water that is flowing past the intake location, which ultimately flows out to sea a relatively short distance downstream1. From a scientific point of view, the proposed take will not result in any “permanent water loss”. The flow of the Waikato River is part of a natural water cycle sustained by runoff from rainfall in the wider catchment, with the water in the River then flowing to the sea. This will not be affected by Watercare’s proposed take.
Te Whakakitenga o Waikato Incorporated
9.14 Te Whakakitenga o Waikato Incorporated (submission no. 62) opposes the application as a matter of fundamental principle having regard to, among other matters, uncertainty and concerns regarding the environmental effects of the Watercare application if granted, and the long-term and permanent loss of water from the Waikato River.
9.15 As outlined in my evidence, the impact of Watercare’s take on the hydrology of the river in terms of water levels and flow velocities will, in my opinion, be negligible.
9.16 In terms of permanent water loss, as outlined above the proposed take will extract water that is flowing past the intake location, which ultimately flows out to sea. The proposed take will not result in any “permanent water loss”.
1 As explained in my evidence, the proposed point of intake is 389 km from the start of the River at Lake Taupo, and 36 km from the River Mouth.
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Federated Farmers of New Zealand (Waikato Province) Incorporated and Federated Farmers of New Zealand (Auckland Province) Incorporated
9.17 Federated Farmers of New Zealand (Waikato Province) Incorporated and Federated Farmers of New Zealand (Auckland Province) Incorporated (submission no. 63) have submitted that the Application has potentially significant flow-on effects for members within the Waikato River catchment. Specifically, their submission expresses a concern that if all the applications currently in the Waikato River queue were to be granted, there would only be approximately 6,000 m3/day of water still available for allocation.
9.18 As noted above, the impact that the grant of Watercare’s application may have on future applications will be addressed in planning evidence and legal submissions. In terms of the amount of water remaining in the River and available for allocation, as set out in Paragraph 6.9 of my evidence, the granting of Watercare’s application and all other applications presently in the queue would result in between 25,800 m3/day in peak months and 192,000 m3/day in the winter months being available for future applications.
The Director General of Conservation
9.19 The Director General of Conservation (submission no. 64) notes that the river is of high ecological significance, particularly as a habitat for aquatic species and supporting nationally significant freshwater ecosystems. The effects of Watercare’s proposal on Ecology have been assessed in the evidence of Mr Dean Miller, who concludes the effects of Watercare’s proposed take on the ecological values of the Waikato River and wetlands will be between Low and Very Low.
9.20 The Director General’s concerns specific to freshwater matters related to Hydrology are:
(a) The effects during very low flows on the river and wetland levels; (b) The projected impacts of climate change; and (c) The adverse effects of saline intrusion on ecosystems including īnanga spawning sites.
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9.21 As outlined in my evidence, I have considered the effects of the proposed take
on the Hydrology of the Waikato River during q5 flow conditions, i.e. the low flow expected on average once in every five years. In my experience, low flows at this frequency are commonly used to assess the effects of proposed takes on very low flows in a stream or river. As stated in my evidence, an assessment
of effects based on q5 flow conditions is conservative in the sense that it may overstate the magnitude of change at most times, e.g. when river flows are
higher than the q5 flow.
9.22 With respect to the effects of the proposed take q5 flows, the maximum change in water levels due to the proposed additional take will be 46 mm in the intake
reach. This is compared to a water depth of over 6 m during q5 flows, and with daily fluctuations due to tide of up to 1,000 mm at the intake site. In the wetland reaches some 20 km downstream of the intake the effect on water levels will be 3 mm or less.
9.23 With respect to flow velocity in the river the changes in mean velocity at the q5 threshold:
(a) In the wetland reaches due to the existing and proposed additional takes will be:
(b) In the intake reach, incremental and cumulative mean velocity changes
at the q5 threshold due to the proposed additional take up to 0.006 m/s, compared to a mean velocity in the river of approximately 0.53 m/s.
9.24 In terms of river hydraulics, I consider that the water level and mean velocity changes are minimal, and will, in practicable terms, not be discernible to river users.
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9.25 The submission by the Director General of Conservation also raises concerns regarding the adequacy of the assessment of hydrological effects, on the basis that projected impacts of climate change have not been taken into account.
9.26 I have not considered climate change effects for the hydrology of the Waikato River. I note, however, that WRC indicates on its website that the effects of projected climate change will mean that “our rainfall distribution is expected to be different from the current situation with more intense storms and longer periods of no rainfall that tend towards droughts in some areas” with implications for the availability of water and water quality. WRC also identifies a projected rise in sea level of 1 m by the end of the century, which may mean that suitable habitat for spawning is steadily pushed further upstream. These processes may be significant for the hydrology of Waikato River system, and will be so regardless of Watercare’s proposed take. A change in low flows may at some time in the future lead to a change in the allocable flow regime by WRC. In my opinion, the scale of the effects of sea level rise will clearly be more significant than the effects due to the proposed Watercare take.
9.27 In terms of saline intrusion, my analysis shows that Watercare’s proposed take will have negligible effects on the extent of this in the lower wetland reaches of the river. I cannot comment of the effects of on īnanga spawning sites, but Mr Miller addresses this in his evidence.
Ms Veronique Cornille
9.28 Ms Veronique Cornille (submission no. 66) has expressed a concern regarding the effects of the proposed take on tidal saline water and freshwater within the delta. As I have already outlined and discussed above, if granted, the proposed take would have a negligible effect on the extent of saline intrusion into the lower river reaches.
The Nga Muka Development Trust
9.29 The Nga Muka Development Trust (submission no. 77) expresses various concerns including:
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(a) Uncertainty regarding the environmental effects if the application is approved; (b) Permanent loss of water from the Waikato River catchment; and (c) Changes in hydrology of the Waikato River as a result of climate change.
9.30 With regard to the environmental effects, as I have already discussed earlier in my evidence, in my opinion the physical effects of the proposed take (as assessed for changes in water level and mean flow velocity, and the extent of saline intrusion) will be negligible. Mr Miller in his evidence assesses the effects of these hydrological changes on the Ecology of the river. Overall, he concludes the effects of the proposal on the ecological values of the Waikato River will range between Low and Very Low.
9.31 In terms of permanent water loss, as outlined earlier in my evidence, the proposed take will extract water that is flowing past the intake location, which ultimately flows out to sea. The proposed take will not result in any “permanent water loss”.
9.32 In terms of climate change, as set out above, the WRC indicates on its website that the effects of projected climate change will mean that “our rainfall distribution is expected to be different from the current situation with more intense storms and longer periods of no rainfall that tend towards droughts in some areas” with implications for the availability of water and water quality. WRC also identifies a projected rise in sea level of 1 m by the end of the century, which may mean that suitable habitat for spawning is steadily pushed further upstream. These processes may be significant for the hydrology of Waikato River system, and will be so regardless of Watercare’s proposed take.
The Ngati Naho Trust
9.33 The Ngati Naho Trust (submission no. 79) opposes the application on the grounds that (amongst other things) the application will detrimentally affect all the tributaries and waterways associated with the river, and in particular the Whangamarino Wetlands.2
2 Paragraph 7 of the submission.
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9.34 From a hydrological perspective I note that:
(a) The confluence of the Whangamarino River (a Waikato tributary) is upstream of Mercer, and approximately 8.5 km upstream of the Watercare intake site; (b) The Whangamarino River is the receiving watercourse for flow from the Whangamarino Wetlands; and (c) In my opinion, Watercare’s proposed take will have no effect on the hydraulic regime of either the Whangamarino River or the Whangamarino wetlands, due to the negligible effect on water levels at the intake site. Nor will Watercare’s proposed take affect any other tributary upstream of the intake site.
10. Conclusion
10.1 I have summarised my assessment in Table 3 below, drawn from the T+T River Hydrology Assessment report and updated as relevant for additional modelling since.
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Issue Change Implication of Mitigation Overall change measures level of effect 1 Flow and Reduction in flows Negligible – None Very Low water level in up to 1.7 % at the flows within required the Waikato intake site, allocable limits River maximum and change in incremental water water level not level change of up significant to 46 mm reducing compared to downstream, total water changes of mean depth, mean flow velocity of up to velocity in the 0.006 m/s. river and daily tidal fluctuations. Salinity in the Negligible shift in Negligible – None Very Low river estuary extent of saline compared to required and delta intrusion at Spring existing 10 km to and Neap tides 13 km extent and to regular tidal fluctuations. Other users Reduction in flows Negligible – None Very Low up to 1.7 % at the flows within required intake site, and allocable limits maximum and change in incremental water water level not level change of up significant to 46 mm reducing compared to downstream to 3 depth and daily mm or less. fluctuations. 1. Adapted from the Ecological Impact Assessment Guidelines (EcIAG) (Roper- Lindsay et al, 2018)
10.2 Overall, in my opinion, Watercare’s proposal will not result in adverse effects on the Hydrology of the Waikato River and other abstractions.
Tom Bassett 21 May 2021
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