Tukituki Catchment Model

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Tukituki Catchment Model

FINAL

11 October 2013

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Tukituki Catchment Model

11 October 2013

Sinclair Knight Merz Carlaw Park

12-16 Nicholls Lane, Parnell Auckland 1010, New Zealand T +64 9 928 5500

F +64 9 928 5501 www.globalskm.com

COPYRIGHT: The concepts and information contained in this document are the property of Sinclair Knight Merz Limited (SKM). Use or copying of this document in whole or in part without the written permission of SKM constitutes an infringement of copyright.

LIMITATION: This report has been prepared on behalf of and for the exclusive use of SKM’s client, and is subject to and issued in connection with the provisions of the agreement between SKM and its client. SKM accepts no liability or responsibility whatsoever for or in respect of any use of or reliance upon this report by any third party.

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Technical Report Title

Glossary of Terms 1

1. Executive Summary 3

2. Introduction 5

2.1. Purpose and Scope of Report 5

2.2. Assumptions and Exclusions in this Assessment 5

3. Tukituki Physical Setting 7

3.1. Surface Water Catchments 7

3.2. Geology 7

3.3. Hydrogeology 9

4. Plan Change 6 12

5. Methodology 13

5.1. Overview 13

5.2. SOURCE Model 13

6. Source Model Calibration and Verification 18

6.1. Calibration to HBRC gauges and naturalised flows 18

7. Model Scenarios 1

8. Water Quantity Results 1

8.1. Scenario 1a 1

8.2. Scenario 1d/e 1

8.3. Scenario 1f/1g 3

8.4. Scenario 2a/2b 4

9. Results Discussion 6

9.1. Impacts on water availability 6

9.2. Future modelling and model enhancements 6

10. Review of Limits and Allocation 8

10.1. Nitrate limits and targets. 8

10.2. Nitrate allocation 13

10.3. Surface water and groundwater allocation 13

10.4. Minimum flows 14

11. Conclusions and Recommendations 15

11.1. Nitrate limits and allocation 15

11.2. Lower Tukituki Surface water and groundwater allocation 16

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11.3. Minimum flows 16

12. References 18

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Document history and status

Revision Date issued Reviewed by Approved by Date approved Revision type

1 7/10/13 IWiseman/P

Jordan

M Sands 7/10/13 FINAL

Jordan

Distribution of copies

Revision Copy no Quantity Issued to

1 1 1 HortNZ

2 1 1 HortNZ

3 1 1 HortNZ

Printed: 11 October 2013

Last saved: 11 October 2013 01:12 PM

File name: Tukituki Catchment Source Model Technical Report Author: Lydia Cetin / Michelle Sands

Project manager: Nic Conland

Name of organisation: Hawke's Bay Regional Council Name of project: Tukituki Plan Change 6

Name of document: Tukituki Catchment Source Model Technical Report Document version: Draft

Project number: AE04485

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Glossary of Terms

Term Definition

Aquiclude A geologic formation, group of formations, or part of a formation through which virtually no water moves.

Aquifer A formation, group of formations, or part of a formations that contains sufficient saturated permeable material to yield economical quantities of water to wells and springs.

Aquitard

A saturated, but poorly permable bed, formation, or group of formations that does not yield water freely to a well or spring.

However, an aquitard may transmit appreciable water to or from adjacent aquifers.

Artesian A well deriving its water from a confined aquifer in which the water level stands above the ground surface; synonymous with flowing artesian.

Confined

A formation in which the groundwater is isolated from the atmosphere at the point of dischagre by impermeable geologic formations; confined groundwater is generally subject to pressure greater than atmosphere.

Connectivity The degree of the hydraulic connection between a stream and the groundwater source for a well.

Hydraulic gradient The rate of change in total head per unit of distance of flow in a given direction.

Leakage The transmission of water between aquifers separated by a low permeability layer or aquitard.

Piezometric contours An imaginery surface representing the total head of groundwater in a confined aquifer that is defined by the level to which water will rise in a well.

Semi-confined An aquifer that is partly confined by layers of

low permeability material through which recharge and discharge may occur.

Streamflow depletion A decrease in stream flow due to the effect of groundwater pumping.

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Transmissivity

The rate at which water is transmitted through a unit width of an aquifer under a unit hydraulic gradient. It is given in cubic meters per day through a vertical section of an aquifer one meter wide and extending the full saturated height of an aquifer under a hydraulic gradient of 1.

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1. Executive Summary

Sinclair Knight Merz (SKM) was engaged to assist Horticulture New Zealand, in understanding the effects of the proposed Plan Change 6 and the Ruataniwha Water Storage Scheme (RWSS), on water quality and water quantity in the Tukituki catchment.

To analyse the effects of Plan Change 6 and RWSS, SKM reviewed the methods used to develop the water quality and quantity limits and allocation provisions, and developed a SOURCE model to test the effects of the provisions, compared to the existing situation.

Tukituki catchment model

A hydrological model of the Tukituki catchment was constructed to represent runoff and nutrient generation from land and transport to surface water and ground waters. The model generates predictions for stream flow and in-stream nutrient concentrations. The catchment model was run at a daily time step in order to capture changes in the flow regime.

The model was constructed in the SOURCE modelling platform and was informed by previous modelling of the Tukituki catchment conducted by the National Institute of Water and Atmospheric Research and information from the Hawkes Bay Regional Council.

The surface water hydrology was modelled using the Soil Moisture Water Balance Model

developed by SKM. Spatial data grids of daily rainfall and evapotranspiration were used to capture historical trends and spatial variability in climate. Forty years of rainfall data was used spanning 1972 – 2012. The modelling did not include the 2013 drought.

Surface water and groundwater interactions were modelled using a simplified groundwater store model for the unconfined aquifers for the Ruataniwha Basin, Otane Basin and The Heretaunga aquifers underlying the Tukituki River. Surface water and groundwater abstractions were grouped into common allocation requirements, such as direct take, stream depleting, irrigation and potable use.

Nutrient generation from different landuses was represented as flow-weighted Event Mean Concentration for high flow and Dry Weather Concentration for baseflow generation rates. The Waipawa and Waipukarau Wastewater Treatment Plants are included as a daily discharge and nutrient concentrations into the Waipawa River and Tukituki River, respectively

Nitrate limits and allocation

The Hawkes Bay Regional Council’s nitrate risk management framework makes changes to the ANZECC guidelines framework, the outcome of which is to assign a lower level of ecological protection to Zones 2 and 3, than would more usually be applied.

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Under the proposed limits elevated nitrate concentrations will be discharged out of Zones 2 and 3 into Zone 1 and to groundwater. How the allocation process accounts for the effects on nitrate allocation in the downstream Zone 1 is uncertain.

We recommend further analysis is undertaken to explore options for the managing the nitrate allocation in an equitable manner across the Zones, which accounts for existing users and also meets water quality limits set to achieve objective TT1.

Surface water and groundwater allocation

The method used to calculate the Plan Change 6 surface water allocation in the lower Tukituki is unlikely to have accounted for all of the streamflow depletion effects in the Lower Tukituki

catchment because it only includes takes that are currently classified as ‘Stream Depleting’. There is not groundwater allocation in the lower Tukituki.

The method is not consistent with Policy B1 of the National Policy Statement for Freshwater Management, because it did not provide sufficient regard to “the connection between waterbodies”, as demonstrated in the Tukituki Streamflow Depletion Assessment (SKM 2013a).

We recommend further analysis is undertaken to calculate, with a greater degree of confidence, the lower Tukituki surface water allocation.

Minimum flows

We have tested a scenario (1f) that represents the proposed surface water allocation and minimum flows described in Plan Change 6. This scenario may understate effects in the lower Tukituki because the surface water allocation is unlikely to have accounted for all the streamflow depleting takes. Under this scenario the security of supply threshold described in TT8 as: “an irrigation ban of ten consecutive days occurring more frequently than one year in ten”, is achieved with the proposed 2018 limit, but is not achieved with the proposed 2023 limits, when 2 in 10 years are predicted to experience flow restrictions for 10 consecutive days or longer.

We have developed an alternative scenario (2a). This scenario accounts for additional surface water allocation to account for streamflow depletion effects. Under this scenario the security of supply threshold described in TT8 as: “an irrigation ban of ten consecutive days occurring more frequently than one year in ten”, is not achieved in 2018 with 1.25 in 10 years predicted to experience flow restrictions for ten consecutive days or longer. With the 2023 limit, this increases to 4 in 10 years predicted to experience flow restrictions for ten consecutive days or longer.

We recommend further analysis to assess options for mitigating the effects of the proposed minimum flow on existing users security of supply.

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2. Introduction

2.1. Purpose and Scope of Report

Sinclair Knight Merz (SKM) was engaged to assist Horticulture New Zealand, in understanding the effects of the proposed Plan Change 6.

The scope of this technical report is to:

Present the results of modelling work that has been undertaken to test the effect of the proposed provisions in Plan Change 6 and the RWWS on water flows and volumes, and Review the proposed water quality and quantity limits and the allocation regime in Plan Change 6.

The modelling work presented in this technical report has been informed by the Tukituki

Streamflow Depletion Assessment (SKM 2013a). The model results have been used in the Tukituki Rhyhabsim Assessment (SKMb 2013).

The modelling presented in this report will be used to inform the economic evidence presented by Stuart Ford and the planning evidence presented by Hamish Peacock.

2.2. Assumptions and Exclusions in this Assessment

The SOURCE model relies on data supplied by third parties (eg, HBRC, NIWA) often preconfigured for other models or studies. Inconsistencies between some datasets negated simplification of some aspects of the model, such as raw consent allocation data and post-processed seasonal allocation data prepared for Plan Change 6. This could be improved in the SOURCE model by representing each consent explicitly and by using a crop model to determine the pro rata seasonal allocation during runtime

The SOURCE model has built on other models eg, TRIM, HBRC MODFLOW. No formal review of those models was undertaken as part of this analysis.

The modelling has focused on a limited number of scenarios in this report. The model could be used to test other potential scenarios.

Assumptions used for scenarios includes simplifications: use of TRIM catchment data do define subcatchment boundaries, grouping of consents by abstraction type or water use, and ground water allocation has been grouped by allocation zone and water use.

Many individual consents have different minimum flow limits than the current minimum flow limits specified in Plan Change 6 and supporting documentation. Where possible the SOURCE model retains these minimum flow limits as specified in the original consent data Actual water use data was insufficient to use in the model as the data was sparse and only annual volumes spanning a five year record was available for some years and/or some

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consents. Therefore, the “basecase” model represents a fully allocated scenario. The model performance was verification against HBRC estimated timerseries of naturalised flows, which provided a “fully unallocated (no take)” scenario in term of calibration to low flows.

The same set of rainfall-runoff model parameters were applied to the whole catchment, based upon calibration to flows at the three flow gauges with long term records. There may be some areas within the catchment with higher or lower rates of runoff generation than would be represented by the model.

Consistent sets of generation rates were applied for nutrients across each landuse type within the catchment. The annual generation rates for nutrients were consistent with annual estimates from OVERSEER and modelled concentrations of nutrients in-stream are

consistent with monitoring data. However, there may be some individual land parcel where the actual rates of generation for nutrients are higher or lower than the rates estimated by the model for the relevant landuse as a whole.

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3. Tukituki Physical Setting

This section describes the natural environment in the vicinity of the lower Tukituki river including surface water, geology and hydrogeology.

3.1. Surface Water Catchments

The Tukituki river catchment is located in the southern part of the Hawke’s Bay region. The largest tributary of the Tukituki river is the Waipawa river. It joins the Tukituki river east of the Ruataniwha Plains and the Waipawa and Waipukurau townships, about half way down the catchment.

Other significant tributaries that cross the Ruataniwha plains include the Mangaonuku stream, Tukipo river and Makaretu stream, Porangahau and the Maharakeke streams.

Beneath the Ruataniwha plains, a complex aquifer system of gravels, silts and clays contain water from rainfall and rivers. Water discharges the Ruataniwha basin through springs, joining the Tukituki and Waipawa rivers through their river beds.

Apart from some areas of exotic forestry, and the native vegetation in the Ruahine Forest Park, the catchment is largely deforested. Land use in the hill country is predominantly dry stock farming with more intensive farming on the plains, predominately horticulture.

The lower Tukituki river is part of the iconic landscape of Te Mata Peak and the Kahuranaki range.

The river is appreciated for its aesthetic, recreational and cultural values and with the aquifer, is valued for the water it provides for household, stock and public supply, commercial and irrigation users.

3.2. Geology

The Heretaunga plains were formed during the last 250,000 years by river sediments deposited by the Tutaekuri, Ngaruroro and Tukituki rivers and coastal lagoon, estuarine and embayment

deposits. The fluvial deposits that accumulated as gravel river channels during and immediately after the glacial periods form permeable high yielding aquifers. The aquifers are interbedded with interglacial silt, clay, peat and shelly sand and clay down to explored depths of 250 m. There is a general layered structure with coarse permeable gravel beds alternating with fine impermeable beds (as shown on Figures 1, 2 and 3). The fine grained sediments separating gravel aquifers form aquicludes and aquitards, which can impede vertical groundwater flow (Dravid & Brown, 1997).

The permeable gravel beds form aquifers that reflect their formation as meandering river channels.

The Mohaka, Tukituki, Ngaruroro, Esk, and Tutaekuri rivers have undergone course adjustment in response to tectonic deformation. The tectonic influence has been a major influence on the hydrology of the Hawke’s Bay Rivers and the deposition of the aquifer/aquiclude sequence of the Heretaunga depression (Dravid & Brown, 1997).

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Figure 1. Topographical map of the Lower Tukituki catchment showing the locations of the geological cross-sections.

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3.3. Hydrogeology

The Heretaunga basin has an area of 330 km² and has a maximum thickness of 400 m. It is made up of 7 primary aquifers including the Tukituki aquifer (Brooks, 2006). Where the Tukituki river intersects the Heretaunga plains, it contributes water to a shallow semi-confined to confined aquifer system underlying its floodplain. The lower Tukituki groundwater resource is represented by a localised gravel aquifer deposited by the Tukituki river and is a semi confined aquifer with leaky conditions and high transmissivities in the range of 10,000 – 15,000 m²/day and a storativity of 0.015 (Dravid & Brown,1997). The average thickness of the Tukituki aquifer system is about 20 metres.

Groundwater data such as groundwater levels and aquifer tests suggest the lower Tukituki and Heretaunga plains aquifer systems are hydraulically connected (Harper, 2013). The Tukituki aquifer is interbedded with, and overlies the main Heretaunga plains aquifer system between Thompson Road and Karamu stream. The western extent of the aquifer system is marked by the terrace east of Mangateretere – Havelock North Road. Along the coast, the beach gravel deposits from south Haumoana to Te Awanga merge with the Tukituki aquifer system (Figure 2) (Dravid &

Brown,1997).

During summer increased groundwater abstraction for irrigation may cause piezometric pressures in the main aquifer system to decline below the level of the overlying Tukituki aquifer system. This reversal of the hydraulic gradient would produce a downward flow of groundwater from the Tukituki River aquifer system to recharge the underlying Heretaunga plains aquifer system (Dravid &

Brown, 1997).

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Figure 2. Aerial extent of the aquifer systems on the Heretaunga Plains (from Dravid &

Brown (1997)).

Groundwater flows from the western Heretaunga Plains to the sea with a gradient of about 0.008 (Brooks, 2006). The piezometric contours measured across the Heretaunga Plains shows the Ngaruroro River as the major source of groundwater that flows eastwards towards Flaxmere and Hastings and the Tukituki River, then northeastwards toward Taradale and Napier, rather than directly to the coast. Piezometric surveys indicate a sudden drop in groundwater pressure from 10 to 9 m above sea level just north of Havelock North. This was hypothesised to have resulted from significant water loss from the aquifer through abstractions, leakage between aquifers or loss to surface water (Dravid & Brown, 1997).

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Brooks (2006) developed a steady-state numerical groundwater model for the Heretaunga

groundwater basin. The main objectives for this model were to predict pumping effects on the basin water levels, predict effects of pumping wells on surface water, and determine the basin water balance. The simulation suggested that water levels have declined about 2 metres across the Heretaunga groundwater basin since groundwater pumping began in the early 1900s.

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4. Plan Change 6

The Hawke’s Bay Regional Resource Management Plan (including the Regional Policy Statement) is a second generation statutory planning document, and became operative in August 2006. It identifies regionally significant issues facing the region, and sets out regional level policies and region-wide rules for addressing those issues. Within the regional plan policy provisions, there are some catchment specific water allocation limits and minimum flows and some catchment specific water quality guidelines.

Plan Change 6 is the first of a number of catchment specific plan changes for the Hawke’s Bay region which seek to implement the National Policy Statement for Freshwater Management, as well as address specific water allocation and water quality issues in the catchment.

The proposed water quality polices are outlined in provisions TT1 – TT6 of Plan Change 6. The proposed water quality target and limits are provided in Tables in 5.91a, 5.9.1b and 5.9.2.

The proposed water quantity policies are outlined in provisions TT1 – TT6 of Plan Change 6, with minimum flow limits and surface and ground allocation limits provided in Tables 5.9.3, 5.9.4 and 5.9.5.

Figure 3, Figure 4 and Figure 5 are maps are taken from Plan Change 6. These maps illustrate the water quality and water quantity management and allocation zones and flow sites.

Figure 3 Water Management Zones

Figure 4 Surface water allocation zones and proposed minimum flow sites Figure 5 Groundwater allocation zones

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Waipawa River at RDS/SH2

Tukituki River at Tapairu Rd

Tukituki River at Red Bridge

Tukipo River at Ashcott Road

Papanui Stream at Middle Road

Mangaonuku Stream U/S Waipawa

Tukipo River at State Highway 50

2 Waipawa

1 Lower Tukituki 3

Middle-upper Tukituki

DATA FROM: Farm information obtained from the Hawke's Bay Regional Council's Geographic Information Systems Database.

LIMITATIONS AND COPYRIGHT

This map may not be reproduced or transmitted to any other party, in any form or by any means, electronic, mechanical,

1:250,000

´

Minimum Flow Recording Sites Surface Water Allocation Zones

1, Lower Tukituki 2, Waipawa

3, Middle-upper Tukituki

Tukituki Plan Change 6 Surface Water Allocation Zones &

Minimum Flow Sites SCHEDULE XVI

Tukituki River at Black Bridge

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3

Ruataniwha Basin South Tukituki Catchment

2

Ruataniwha Basin North Waipawa Catchment

1 Otane Basin Papanui Catchment

DATA FROM: Farm information obtained from the Hawke's Bay Regional Council's Geographic Information Systems Database.

LIMITATIONS AND COPYRIGHT

This map may not be reproduced or transmitted to any other party, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the written permission of the copyright holder.

1:250,000

´

Tukituki Water Allocation Zones GW 1, Otane Basin, Papanui Catchment

2, Ruataniwha Basin North, Waipawa Catchment 3, Ruataniwha Basin South, Tukituki Catchment

Tukituki Plan Change 6 Groundwater Allocation Zones

SCHEDULE XVII

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5. Methodology

5.1. Overview

The focus of the analysis described in this report is on the proposed nitrate limits and allocation, and on the minimum flow and surface water allocation. There are two parts to the analysis.

The first part of this assessment is to test the proposed water quantity limits and allocation, and compare the proposed framework with the existing situation. A SOURCE model has been developed to undertake this analysis. The purpose of the SOURCE modelling is to provide, improved data for the assessment of economic and ecological effects of Plan Change 6. Detail on the SOURCE modelling method is provided in section 5.2 below.

The second part of the analysis is a review of the proposed water quality and quantity limits and allocation and the technical analysis that supported their development. This is outlined in Section 8 5.2. SOURCE Model

NIWA had previously developed a model of water quantity and water quality within the Tukituki catchment. The customised model that was developed was known as TRIM. The TRIM model represented generation of nutrients, delivery of nutrients to the stream via surface and groundwater flow pathways and interaction between nutrients and algae within the stream channels. The TRIM model was capable of simulating changes in catchment conditions over periods of several years but contained little detail on simulation at seasonal or daily time scales. This made the TRIM model unsuitable for assessing:

1) The impact on minimum flows at a daily time scale associated with changes in minimum flow levels at which consent holders can divert water from surface or ground water sources;

2) The impact on the availability of water, at a daily time scale, for diverters and the changes in availability of water for changes in minimum flow levels;

3) The impact on both flow and water quality of the potential construction of a new major dam and irrigation supply scheme within the catchment, which would have a substantial impact on the flow regime at a daily time scale downstream of the dam.

Due to these limitation in the existing modelling, it was identified that a model was required that could represent the impact of variability in flow and water quality at a considerably shorter time step (i.e. that could run at a daily time step). eWater’s SOURCE modelling package was adopted and run at a daily time step, in order to simulate some of the aspects that were poorly resolved by previous modelling.

A hydrological model of the Tukituki catchment was constructed to represent catchment scale runoff and nutrient generation from land and transport to ground waters (including representation of nutrient attenuation). The model was constructed in eWater’s SOURCE modelling platform. The

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Australia’s leading State Government water management agencies, water authorities, Universities, research institutes and consulting firms (including SKM). The eWater Source platform has strong core functionality in hydrology, pollutant generation and water management, such as dams (Welsh, et al., 2012), and can be easily customised via plugins, which provides significant flexibility in adapting the model to a variety of water resource issues, such as required by this investigation.

Table 1 outlines the data acquired to develop the Tukituki SOURCE model. Source spatially represents the 39 subcatchments, 6 major landuses and surface water groundwater interactions within the Tukituki catchment(Figure 6) informed by previous modelling conducted by the National Institute of Water and Atmospheric Research (NIWA) (Rutherford, 2013) and information from the Hawkes Bay Regional Council.

Figure 6 major landuses and surface water groundwater interactions

The surface water hydrology was modelled using the Soil Moisture Water Balance Model (SMWBM) developed by SKM. Spatial data grids of daily rainfall and evapotranspiration (NIWA Cliflo, 2013) were used in SMWBM to capture historical trends and spatial variability in climate.

Surface water and groundwater interactions are modelled using a simplified groundwater store model, developed by the Commonwealth Scientific and Industrial Research Organisation (CSIRO).

The simplified groundwater store model represents separately reach of the unconfined aquifers for the Ruataniwha Basin, Otane Basin and The Heretaunga aquifers underlying the Tukituki River, where baseflows and nutrients are routed to represent time lags in a similar manner to TRIM2.

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Surface water and groundwater abstractions were grouped into common allocation requirements, such as direct take, stream depleting, irrigation and potable use.

Nutrient generation from different landuses was represented as flow-weighted Event Mean Concentration (high flows) and Dry Weather Concentration (baseflows) (EMCDWC) generation rates. EMCDWC parameters were determined initially from event based and routine (monthly) monitoring data at the three main flow gauge sites (1. Tukituki@Red Bridge; 2. Waipawa upstream of State Highway 2; 3. Tukituki@Tapairu Road) and adjusted using the OVERSEER mean annual loads for each landuse type (Rutherford, 2013). The Waipawa and Waipukarau Wastewater Treatment Plants (WWTPs) are included as a daily discharge and nutrient concentrations into the Waipawa River and Tukituki River, respectively. The catchment model was run at a daily time step in order to capture changes in the flow regime.

Nutrients represented in the Source model will include:

4) Total nitrogen (TN), 5) Total phosphorous (TP), 6) Nitrate-nitrite nitrogen (NNN), 7) Dissolved Inorganic nitrogen (DIN) 8) Ammonical nitrogen (NH3)

9) Dissolved reactive phosphorous (DRP)

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Figure 7. The Tukituki catchment Source model interface showing the subcatchment boundaries, the node-link network representing the river system and landuse areas.

Table 1 Tukituki Catchment SOURCE Model Data Requirements

Dataset Purpose Data source

Subcatchment boundaries

Determination of hydrological flow pathways at 4^th order streams

Provided by Kit Rutherfrd (NIWA) as used in TRIM2 model

Landuse map Current landuse types and areas grouped into 5 major landuses:

Arable Dairy Forest Horticulture Livestock

Non-productive land (eg, urban)

Provided by Kit Rutherfrd (NIWA) as used in TRIM2 model

Climate inputs Daily rainfall and potential

evapotranspiration (PET) as spatially distributed 500 km² grids for 40 year record at 500 km. Data received for

Sourced from NIWA Meteorological database (NIWA Cliflo, 2013)

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Dataset Purpose Data source 1/1/1972 – 31/12/2012

Daily streamflow Daily flow data used for calibration and calculation of nutrient dry weather and wet weather concentrations for EMCDWC models – data spans 1/1/1967 – 1/4/2013

Data provided by HBRC

Nutrient monitoring data

Routine monitoring data (ie, collected monthly) for water quality calibration and calculation of nutrient dry weather and wet weather concentrations for EMCDWC models

Data provided by Kit Rutherford, NIWA

OVEERSEAR model outputs

Used to adjust EMCDWC model

parameters for nutrients generated from different landuses

Data provided by Kit Rutherford, NIWA Wastewater

treatment plants

Point source discharge and nutrient concentrations from the 2 major WWTPs

Data provided by HBRC Groundwater

characterisation (Hydraulic properties, recharge rates, nutrient attenuation)

Information used to configure the

groundwater stores and adjust the surface water – ground water connectivity in a similar manner to TRIM2

Data provided by Kit Rutherford, NIWA and sourced from HBRC previous MODFLOW modelling and reports Water use consents Individual consents were grouped into

categories:

stream depleting

direct surface ware abstraction groundwater abstraction irrigation

non-irrigation (ie, potable)

Data provided by HBRC

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6. Source Model Calibration and Verification

6.1. Calibration to HBRC gauges and naturalised flows

The Tukituki catchment SOURCE model was calibrated firstly against observed flows at the Tukituki at Red Bridge streamflow gauging station and to synthetic naturalised flow dataset provided by HBRC that replicates catchment conditions with no irrigation. Modelled flows were validated against two long-term streamflow gauging stations at Waipawa upstream of state Highway 2 and Tukituki River at Tapairu Road.

The base case model comprised of current landuse, 40 years historical climate record, current abstractions at the maximum weekly take rate. Actual water use data was inadequate to use in calibration as the data was sparse and only annual volumes spanning a five year record was available for some years and/or some consents. Therefore, the “basecase” model represents a fully allocated scenario. The model performance was verification against HBRC naturalised flows, which provided a “best” case scenario in term of calibration to low flows.

Calibration of the rainfall-runoff model was compared to observed flow data and assessed using the Nash-Sutcliffe model efficiency (NSE) coefficient as a statistical measure of fit (correlation) between observed and modelled flows (Table 2). A value close to 1 indicates a strong correlation between observed and modelled, whereas a value close to zero indicates a poor fit between the data.Flow duration curves were used to assess the calibration to low flows. A good agreement was achieved between modelled and observed daily flows

Table 2 Comparison NSE statistic of modelled flows at main flow gauging stations NSE

(scale between 0-1)

Tukituki at Red Bridge

flow gauge Tukituki at Tapairu Road

flow gauge Waipawa upstream of

SH2 Basecase current conditions

model (Scenario 1d) 0.705 0.511 0.554

Naturalised no irrigation model

(Scenario 1a) 0.702 0.665 0.628

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Table 3. Flow exceedance curves comparing observed and modelled flow Naturalised flows

(Scenario 1a)

Basecase current conditions flows (Scenario 1d)

The final rainfall-runoff model parameters generated from the calibration process are given in Table 4.

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Table 4 calibrated SMWBM rainfall-runoff parameters

SMWBM calibrated parameters Adopted value

AA - First coefficient in rainfall duration relationship 0.2158

AI - Impervious portion of catchment connect to drainages (%) 0

BB - Second coefficient in rainfall duration relationship 0.2199

DIV - Division of effective rainfall that ponds versus becoming rainfall runoff 0

FT - Groundwater percolation rate maximum (mm/day) 0.1

GL - Groundwater recession parameter (days) 1

PI - Interception storage capacity (mm) 5

POW - Power of the soil moisture-percolation curve 1

QOBS - Observed groundwater discharge on day prior to start of simulation (mm/day) 1 SL - Soil moisture storage where groundwater percolation ceases (mm) 3

ST - Soil moisture storage capacity (mm) 0

TL - Surface routing coefficient (days) 250

ZmaxN - Nominal maximum infiltration rate (mm/hr) 1

ZminN - Nominal minimum infiltration rate (mm/hr) 12

AA - First coefficient in rainfall duration relationship 0

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7. Model Scenarios

Table 5 below summarises the minimum flow and water allocation scenarios that have been modelled using SOURCE. The table links the scenarios to the Plan change 6 provision and to the economic and fish habitat assessments these scenarios inform.

Table 5 Source model minimum flow and allocation

Scenario Question Plan Change

6 provision Model Query Model Results Scenario

ID Aqualink Scenario

ID

Assessment Criteria Model Outputs

Fish Habitat Economics 7 Day MALF Number of days below low flow limit at set flow

locations

Lost irrigation volumes

Flow What are the effects on reliability from increasing minimum flow to PC6?

TT7, 8, 9 Naturalised flow Base case for river 1a 1

TT7, 8, 9 Consented paper allocation.

With and without PC6 minimum flows

Potential maximum effects, in the existing situation

1d /1e 3

TT7, 8, 9 Seasonal allocation proposed in table 5.9.4 Plan Change 6.

PC6 predicted effects.

1f /1g 5

Lower Valley

users Has HBRC accounted for the allocation and effects of the lower river users?

TT7, 8, 9, 11 Seasonal allocation proposed in table 5.9.4 Plan Change 6, adjusted to account for consented groundwater takes that may be surface water depleting.

Revised PC6 predicted effects, with proposed

2a/2b

The results of the scenarios are discussed in Section 8

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8. Water Quantity Results

8.1. Scenario 1a

The Tukituki SOURCE model was configured with current landuse, 40 years of climate data and current abstractions for no irrigation use (ie, potable, industry). Groundwater abstractions were unrestricted.

The 7 day Mean Annual Low Flows under the no irrigation, naturalised scenario is high. There is very good agreement with literature calculations of MALF at the Waipawa and Tukituki at Tapairu Road. At Red Bridge the calibration is good, within 9%.

Table 6 Scenario 1a – naturalised flows with no irrigation abstractions Naturalised MALF (Wilding &

Waldron, 2012)*L/s SOURCE naturalised MALF L/s

Waipawa River at RDS/SH2 3009 3049

Tukituki River at Tapairu Rd 2865 2938

Tukituki River at Red Bridge 6258 6843

8.2. Scenario 1d/e

Allocation

For both 1d and 1e, the Tukituki SOURCE model was configured with current landuse, 40 years of climate data and current consented abstractions (paper allocation) for all water use set at a maximum weekly take.

Minimum flow limit

For 1d, the current minimum flow was adopted. For 1e the groundwater and surface water abstractions were restricted to Plan Change 6 minimum flow limits for both stream depleting and direct irrigation abstractions.

Table 7 summarises the outcomes of scenario 1e configuration on minimum flows generated at each of the main flow gauges. . It includes the total number of days where flows are below the MLF and no abstractions are taking place. It also compares the 1d 7 day MALF (with the current MFL) to the observed 7 day MALF, 1d is lower, this is expected because the model scenario is representing the ‘paper allocation’, which is more than is actually used.

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Table 7 Scenario 1e – Current consented allocation abstraction volumes and PC6 minimum flow limits

Flow gauge Minimum

Flow Limit (L/s) - current

Observed(Wilding

& Waldron, 2012) MALF (L/s)

1d MALF

(L/s) SOURCE 1e PC6 MLF Consented Allocation.

MALF L/s

1e Num.

days below MFL in 40 yr record

1e Lost irrigation volume (m³/yr)

Waipawa River at RDS/SH2 2500 2839 2515 2415 426 571,875

Tukituki River at Tapairu Rd 2300 2534 2111

2115

741 279,613

Tukituki River at Red Bridge 4300 5902 5133

4979

110 305,547

Tukituki River at Red Bridge 5200 496 305,859

Table 8 Summarises the number of occasions where consecutive days below MFL, was greater than ten days.

Table 8 1d/e. - Security of supply. Occasions when >10 consecutive days below the MFL during the 40 year model period. (highlighted cells, indicate occasions greater than 1 in 10 years)

Flow gauge Scenario 1d (Current

MFL)

>10 days, in 40 years

(events)

Scenario 1e (PC 6 MFL)

2018

>10 days, in 40 years

(events)

Scenario 1e (PC 6 MFL)

2023

>10 days, in 40 years

(events)

Waipawa River at RDS/SH2 3 28 Unchanged

Tukituki River at Tapairu Rd 19 53 Unchanged

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8.3. Scenario 1f/1g Allocation

For both 1f and 1g, the Tukituki SOURCE model was configured with current landuse, 40 years of climate data and Plan change 6 seasonal allocation abstractions for all consents as the pro rata seasonal allocation volume.

Minimum flow

For 1f, the current minimum flow was adopted. For 1g the groundwater and surface water abstractions were restricted to Plan Change 6 minimum flow limits for both stream depleting and direct irrigation abstractions.

Table 9 summarises the outcomes of scenario 1g configuration on minimum flows generated at each of the main flow gauges and summarises the years where the mean annual low flow is below the minimum flow limit (MFL). It also compares the 1f 7 day MALF (with the current MFL) to the observed 7 day MALF, there is good agreement.

Table 9 Scenario 1g – Plan Change 6 seasonal allocation abstraction volumes and PC6 minimum flow limits

Observed MALF (L/s)

1f MALF

(L/s) SOURCE 1g seasonal Allocation.

PC6 min flow limits L/s

1g Num.

days below MFL in 40 yr record

1g Lost irrigation volume (m³/yr)

Waipawa River at RDS/SH2 2500 2839 2778 2322 127 140,797

Tukituki River at Tapairu Rd 2300 2534

2452 2398

244 160,864

5891 5421

7 99,798

Tukituki River at Red Bridge 5200 5902 5891 181 568,333

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Table 10 1f/1g. - Security of supply. Occasions when >10 consecutive days below the MFL during the 40 year model period. (highlighted cells, indicate greater than 1 in 10 years)

Flow gauge Scenario 1f (Current

MFL)

>10 days, in 40 years (eventss)

Scenario 1g (PC 6 MFL) 2018

>10 days, in 40 years (events)

Scenario 1g (PC 6 MFL) 2023

Waipawa River at RDS/SH2 3 12 Unchanged

Tukituki River at Tapairu Rd 15 15 Unchanged

8.4. Scenario 2a/2b

Allocation

Scenario 2b compares the outcomes of the preliminary Tukituki Streamflow Depletion Assessment, by increasing the abstraction rate by an additional 588 L/s for stream depleting consents in Zone 1.

Minimum flow

For 2a, the current minimum flow was adopted. For 2b the groundwater and surface water abstractions were restricted to Plan Change 6 minimum flow limits for both stream depleting and direct irrigation abstractions.

Table 11 summarises the outcomes of scenario 2b configuration on minimum flows generated at each of the main flow gauges summarises the years where the mean annual low flow is below the minimum flow limit (MFL). It also compares the 2a 7 day MALF (with the current MFL) to the observed 7 day MALF, there is good agreement.

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Table 11 Scenario 2b– alternative seasonal allocation abstraction volumes and PC6 minimum flow limits

Observed

MALF (L/s) 2a

MALF (L/s) 2b Num.

days below

MFL

2b Lost irrigation

volume (m³/s)

5308

94 258,502

Tukituki River at Red Bridge 5200 5902 5308 300 568,333

Table 12 2a/2b. - Security of supply. Occasions when >10 consecutive days below the MFL during the 40 year model period. (highlighted cells, indicate greater than 1 in 10 years)

Flow gauge Scenario 2a (Current

MFL)

Scenario 2b (PC6 MFL) 2018

Scenario 2b (PC6 MFL) 2023

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9. Results Discussion

9.1. Impacts on water availability

The proposed PC6 makes two changes that would impact upon access to water for existing consented takes: modifying the minimum flow rates at which consented takes can be made from the river, implementing seasonal allocation limits on extractions (in addition to the current maximum instantaneous and maximum weekly takes). The scenarios that were modelled in this analysis allow each of these three modifications that are proposed under PC6 to be assessed separately or in combination with one another.

The scenarios presented in 1d and 1e are based on the current consented “paper” allocation. In this scenario, with the current minimum flow limits, there is poor security of supply at Taipairu Road with 3 out of 10 years expected to experience flow restrictions of ten consecutive days or longer.

When the current consented allocation and the proposed minimum flow limits are tested, there is poor security of supply at Waipawa RDS/SH2 and Taipairu Road, with flow restrictions for a period of ten consecutive days or more, predicted to occur 7 in 10 years at Tapairu Road and 4 in 10 years at Waipawa RDS/SH2. At Red Bridge, with the 2018 limit 1.25 days in 10 are expected to have flow restrictions for a period of ten consecutive days or more. With the 2023 proposed limit, the security of supply at Red Bridge drops to 5 in 10 years predicted to experience flow restrictions for a period ten consecutive days or longer.

The scenarios presented in 1f/1g are based on the proposed seasonal allocation in Plan Change 6.

When the 2018 minimum flow limits are tested, flow restrictions for ten or more consecutive days are predicted to occur at Waipawa RDS/SH2 on average 2 in 10 years, with 10 or more

consecutive days below the minimum flow limit at Taipairu Road expected 3 in 10 years. At Red Bridge, the security of supply is met with the 2018 limit. When the 2023 proposed limit is applied at Red Bridge the security of supply at this site drops to a predicted 2 in 10 years experiencing restrictions for a period of ten consecutive days or more.

The final scenario we have tested only relates to the Tukituki at Red Bridge. This scenario uses the seasonal allocation proposed in Plan Change 6, but adjusts the allocation to account for streamflow depleting takes, as discussed in Tukituki Streamflow Depletion Assessment (SKM 2013a). When this scenario is tested, the security of supply threshold is met in the existing situation. At 2018, the predicted security of supply drops to on average 1.25 in 10 years predicted to experience flow restrictions for period of ten consecutive days or longer. When the 2023 limits is applied, the model predicts water restriction of ten consecutive days or longer, on average 4 out every 10 years.

9.2. Future modelling and model enhancements

Further enhancements are possible of the SOURCE model that was developed for this

assessment. The existing model currently includes an estimated demand pattern for surface water

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This is a simplified representation of the actual takes, which would vary across each irrigation season in response to changes in weather conditions – primarily rainfall, temperature, wind speed and evaporation. The SOURCE model of the Tukituki catchment could be enhanced to represent the takes in a more realistic pattern by incorporation of a crop model to calculate irrigation requirements. The Morgan method could be “built” into the model as a plugin model to more directly assess seasonal variability in climate and water supply and how that may relate to other water resource management activities in the catchment.

The model can be used to assess the impact of river regulation on water supply, water security and impact on downstream users. Assessment of priority takes, such as from the perspective of water users/consents priority or for environmental watering, can be explicitly included and optimised to a set of resource targets.

No scenarios were run to represent the inclusion of the proposed Ruataniwha Dam and the

associated downstream irrigation infrastructure. Operation of the dam would modify the flow regime downstream of the dam. The SOURCE model could be modified to include additional scenarios that represent the dam, to estimate changes in in-stream flow and water quality in the catchment and changes in water availability for all water users in the catchment.

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10. Review of Limits and Allocation

This section provides a review of the proposed Plan Change 6 water quality and water quantity limits and allocation, with reference to the technical work that supported their development.

10.1. Nitrate limits and targets.

The Plan Change 6 approach:

Plan Change 6 has relied on nitrate toxicity data to derive nitrate limits. The limits provide 99%

ecological protection trigger for Zone 4, 95% ecological protection trigger for Zone 1 and 5 and 90% ecological protection trigger for Zones 2 and 3.

The Macroinvertebrate Community Index (MCI) is a bio-monitoring tool. Uytendaal et al (2013) recommend that the MCI is used as an overall indicator of stream health in relation to life

supporting capacity, native fish habitat, trout habitat and trout spawning values for Plan Change 6.

Error! Reference source not found. below describes the ecosystem condition associated with MCI scores.

The rivers in Zone 3 have “good” quality using the MCI standard, there is less data for Zone 2, with a “fair” rating. .Zone 1 rivers also have a “fair” rating. (Table 25, Uytendaal 2013).

Table 13 Macroinvertebrate Community Index

MCI Score Stream Health

>120 Excellent Quality, clean water

100 - 119 Good Quality, possible mild

pollution

80 - 99 Fair Quality, probably moderate

pollution

<80 Poor quality, probably severe

pollution

Our comments on the approach:

The ANZEEC guidelines describe ecosystem conditions, these are used as the basis for selecting appropriate ecological protection triggers. Plan Change 6 has selected the “highly disturbed”

condition for managing Zones 2 and 3 and “slightly to moderately disturbed” condition for Zone 1

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The ANZECC descriptions are provided below:

“Slightly to moderately disturbed systems 95%— ecosystems in which aquatic biological diversity may have been adversely affected to a relatively small but measurable degree by human activity.

The biological communities remain in a healthy condition and ecosystem integrity is largely retained. Typically, freshwater systems would have slightly to moderately cleared catchments and/or reasonably intact riparian vegetation; marine systems would have largely intact habitats and associated biological communities. Slightly– moderately disturbed systems could include rural streams receiving runoff from land disturbed to varying degrees by grazing or pastoralism, or marine ecosystems lying immediately adjacent to metropolitan areas.”

“Highly disturbed system 80% -90%: “These are measurably degraded ecosystems of lower ecological value. Examples of highly disturbed systems would be some shipping ports and sections of harbours serving coastal cities, urban streams receiving road and stormwater runoff, or rural streams receiving runoff from intensive horticulture” (ANZECC 2000)

When considering “highly disturbed” ecosystems, the ANZECC Guidelines advises that:

“For ecosystems that can be classified as highly disturbed, the 95% protection trigger values can still apply. However, depending on the state of the ecosystem, the management goals and the approval of the appropriate state or regional authority in consultation with the community, it can be appropriate to apply a less stringent guideline trigger value, say protection of 90% of species, or perhaps even 80%. These values are provided as intermediate targets for water quality

improvement.”

As proposed Plan Change 6 does not intend to use the 90% nitrate limit as an “intermediate targets for water quality improvement” therefore it is questioned whether using a 90% limit is appropriate.

Data presented by the HBRC identifies that the existing nitrate levels, based on data collected between 2004 – 2011, are all well below the proposed 90% limits, (Table 29 and 30 Uytendaal, 2013). In the existing situation, nitrate levels in Zones 2 and 3, are also below the 95% limit, with the exception of the Porangahau Stream, which meets the median standard, but not the 95^th percentile.

The 90% ecological protection trigger is an unusual standard to be applied to a New Zealand river.

For example, The Horizons One Plan and the Proposed Canterbury Land and Water Regional Plan both use the 99% or 95% ecological trigger for limiting toxicants in all rivers.

In Plan Change 6, the 99% or 95% ecological protection trigger is proposed for all toxicants, with the exception of nitrate. The reasoning presented by HBRC for assigning the lower ecological level of protection for nitrate only, is discussed and commented on in the following sections.

In order to determine nitrate limits for the Zones, Hawkes Bay Regional Council developed a framework for managing nitrate risk. This included developing management classifications, to

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replace the ecosystem condition descriptors commonly used in the ANZECC guidelines. Table 14 below provides a comparison of these descriptors.

Table 14 Hawkes Bay Regional Council ecosystem condition descriptors and the ANZECC equivalent.

ANZECC Ecological Protection Trigger

ANZECC Ecosystem Condition Descriptor

Hawkes Bay Regional Council Management Classification

99% High Conservation Excellent

95% Slightly to Moderately Disturbed Very good

90% Highly Disturbed Good

80% Highly Disturbed Fair

This framework replaces the ANZECC descriptor of “Highly disturbed” with a management classification of “good”, for the same level of ecosystem protection. In other words, HBRC are applying an ecological protection limit intended for “Highly disturbed systems” to Zones 2 and 3, but have changed the name of the ecosystem condition descriptor to ‘Good’.

The second aspect of the framework is the regional descriptions of management classes for each management classification. These are also quite different to the descriptions in the ANZECC guidelines for the equivalent level of ecosystem protection. Described in Table 15 below.

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Table 15 Hawkes Bay Regional Council framework for managing nitrate risk for freshwater species ANZECC Ecosystem

Condition Descriptor

Hawkes Bay Regional Council Management Classification

Hawkes Bay Regional Council Management Class

High conservation Excellent Pristine environment with high biodiversity and conservation values.

Slightly to moderately disturbed

Very good Environments which are subject to a range of disturbances from human activities, but with minor effects.

Highly Disturbed Good Environments which have multiple

disturbances from human activities and seasonally elevated concentrations for significant periods of the year (1-3 months).

Highly Disturbed Fair Environment which are measurably

degraded and which have seasonally elevated concentrations for significant periods of the year (1-3 months).

Using the Hawkes Bay Regional Council framework for managing nitrate risk, Zone 1, 2 and 3 should be in the same category. Zones 1, 2 and 3 are all subject to “seasonally elevated

concentrations significant periods of the year (1-3 months)”, (Dr Uytendaal paragraph 6.8 (c)), and all Zones are subject to a “range” and or “multiple” human disturbances, with “minor effects”. The effects of existing human disturbances, can be estimated using the MCI method, using this method Zone 1 has slightly poorer quality than Zone 3, (Table 25, Uytendaal 2013).

The third aspect of the management framework, is the management objectives. Zone 1 is managed for migrating whitebait and rainbow trout. Zones 2 and 3 are managed for raninbow trout and native fish.

Dr Hickey, when discussing the limitations of the nitrate database in his evidence(paragraph 7.11), states: “The database is relatively limited in native species, with only seven species resident in New Zealand and two native species (mayfly and inanga).” Ingana, while relevant to the lower Tukituki, are not likely to be present in Zones 2 and 3, (Cameron 2012).

In response to concerns raised about nitrate limits by EDS, Dr Hickey states, in his evidence (paragraph 12.4 (ii)), “I have described in my evidence the conservation basis on which the nitrate

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toxicity guidelines have been derived. The combined factors include…(ii) incorporating a sensitive long-term species in the database – so providing a surrogate for fish species not tested”

No native fish likely to be present in Zones 2 and 3 were tested. The most sensitive species that was tested was lake trout fry. Dr Hickey, in his evidence, describes the effects on lake trout fry, at the 90% ecological trigger, as “Moderate” (CWH9).

Dr Uytendaal in his evidence (paragraph 6.13) states that “Taking into account the timing of the spawning of native fish species and the moderate water hardness of the streams and rivers in this zone, as discussed above, I believe the 90% threshold provides an adequate level of protection”.

The method within the ANZECC guidelines for accounting for water hardness, is to alter the toxicity limit, rather than to select the ecological condition on the basis of water hardness. Furthermore, the water hardness in Zone 1 is higher, on average, than in Zones 2 and 3. (Uytendaal 2013,Table c- 1).

Hawkes Bay Regional Council engaged Dr Hickey to, among other things, comment on “whether or not the proposed framework is consistent with how the nitrate toxicity guidelines are intended to be used” (Hickey, 2013).

In response, Dr Hickey states: “The ultimate decision on the level of environmental protection involves both technical and community input, which must consider and balance resource use and value judgements on development and potential degradation, together with abstractive uses.”

(Hickey 2013)

Dr Hickey’s response does not reflect the philosophy described in the ANZECC guidelines: When describing ecosystem condition and levels of protection, the guidelines advise: “Key stakeholders in a region would normally be expected to decide upon an appropriate level of protection through determination of the management goals and based on the community’s long-term desires for the ecosystem. The philosophy behind selecting a level of protection should be (1) maintain the existing ecosystem condition, or (2) enhance a modified ecosystem by targeting the most appropriate condition level.” (ANZECC 2000)

Summary

The Hawkes Bay Regional Council’s nitrate risk management framework makes changes to the ANZECC guidelines framework, the outcome of which is to assign a lower level of ecological protection to Zones 2 and 3, than would more usually be applied.

An adoption of limits based on the 95% ecological protection trigger, would appear to be more appropriate for all toxicants and all zones of the catchment to protect the current monitored ecological values.

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10.2. Nitrate allocation

When the limits are considered in conjunction with the proposed allocation framework in Plan change 6, the implications of the adopted “highly disturbed” ecosystem management standard for Zones 2 and 3 is apparent.

Because the proposed nitrate toxicity standards in Zone 2 and 3, are high, and the existing nitrate concentrations in these Zones are relatively low, under the proposed Plan Change 6 nitrate limits, there will be a surplus of unallocated nitrate. Provided there is sufficient water to support intensive farming, the surplus nitrate would continue to be allocated until the concentration of nitrate

increases to meet the proposed limits.

Zones 2 and 3 make up 45% of the Tukituki catchment. Elevated nitrate concentrations will inevitably, be discharged out of Zones 2 and 3 into Zone 1 and to groundwater. How the allocation process accounts for allocation in the downstream Zone 1 is uncertain.

Further analysis is required to better understand the existing allocation and limits, and to test methods of allocating nutrient loads in an equitable manner which recognises existing users and also meets water quality limits set to achieve objective TT1.

10.3. Surface water and groundwater allocation

The Tukituki Streamflow Depletion Assessment (SKM 2013a), describes modelling undertaken to estimate the volume of streamflow depletion as a result of Policy TT11, Table 5.9.4 of Plan Change 6.

The Tukituki Streamflow Depletion Assessment (SKM 2013) provides a high level estimation of the streamflow depletion component of groundwater takes in the Lower Tukituki. This additional allocation component has been used in a SOURCE scenario 2a to test the effect of the increased allocation of days of lost irrigation, to inform the economic assessment of effects, discussed in Stuart Ford’s evidence.

Existing users are uncertain whether the streamflow depletion component of their existing water abstraction will be allocated under the Tukituki surface water allocation, and if the groundwater component will be allocated under a future groundwater allocation.

The uncertainty around the relationship between surface water and groundwater in the lower Tukituki also presents a risk for the long term sustainable management of the lower Tukituki groundwater resource. In Plan Change 6, groundwater allocation zones have been determined for the Ruataniwha basin south and north and the Otane basin, but no groundwater allocation has been determined for the lower Tukituki.