TAKAKA VALLEY

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TAKAKA VALLEY

GROUNDWATER MODELLING Technical Investigations

PREPARED FOR MBIE Wheel of Water Research

C15066-03 15/12/2017

PREPARED BY Julian Weir Andrew Fenemor

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Disclaimer

This document has been prepared solely for the benefit of MBIE Wheel of Water Research. No liability is accepted by Aqualinc Research Ltd or any employee or sub-consultant of this Company with respect to its use by any other person.

This disclaimer shall apply notwithstanding that the document may be made available to other persons for an application for p ermission or approval or to fulfil a legal requirement.

Quality Control

Client MBIE Wheel of Water Research

Document Title Takaka Valley Groundwater Modelling: Technical Investigations Document Number 1

Authors Julian Weir (Aqualinc) & Andrew Fenemor (Landcare Research) Reviewed By John Bright (Aqualinc) & Joseph Thomas (TDC)

Approved By John Bright Date Issued 15/12/2017 Project Number C15066-03 Document Status Final

File Name Takaka Valley Groundwater Modelling_FINAL.docx

For more information regarding this document please contact Julian Weir

Senior Engineer

Aqualinc Research Limited (03) 964 6514

[email protected]

The preferred citation for this document is:

Weir J, & Fenemor A, (2017): Takaka Valley Groundwater Modelling: Technical Investigations. MBIE Wheel of Water Research. Aqualinc Research Limited.

© All rights reserved. This publication may not be reproduced or copied in any form, without the permission of the Client. Such permission is to be given only in accordance with the terms of the Client’s contract with Aqualinc Research Ltd. This copyright extends to all forms of copying and any storage of material in any kind of information retrieval system.

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Groundwater Report / Takaka Valley Groundwater Modelling

MBIE Wheel of Water Research / 15/12/2017 © Aqualinc Research Ltd.

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Groundwater Report / Takaka Valley Groundwater Modelling MBIE Wheel of Water Research / 15/12/2017

6 Development Scenarios ... 52

6.1 Scenario Descriptions ... 52

6.1.1 Scenario 1: No Consumptive Use... 52

6.1.2 Scenario 2: Double Irrigation ... 52

6.1.3 Scenario 3: All Existing Irrigation Groundwater Sourced ... 53

6.1.4 Scenario 4: No Cobb Dam... 53

6.1.5 Scenario 5: Waingaro River Recharge ... 55

6.1.6 Scenario 6: No Development ... 55

6.1.7 Scenario 7: Likely Irrigation 1 ... 55

6.2 Scenario Results ... 57

6.2.1 Effects of Irrigation ... 57

6.2.2 Effects of the Cobb Dam ... 62

6.2.3 Effects of Groundwater Recharge from the Waingaro River ... 62

6.2.4 Effects of Human Activity... 62

6.2.5 Effects on Water Quality ... 62

References... 68

Appendix A : Calibration groundwater level hydrographs ... 69

Appendix B : Calibration river flow hydrographs ... 76

Appendix C : Groundwater level hydrographs comparing calibration with Scenarios 1, 2 and 3 ... 80

Appendix D : Flow hydrographs and flow duration curves comparing calibration with Scenarios 1, 2 and 3 ... 84

Appendix E : Groundwater level hydrographs comparing calibration with Scenarios 4-6 ... 91

Appendix F : Flow hydrographs and flow duration curves comparing calibration with Scenarios 4-6 ... 95

Appendix G : Groundwater level hydrographs comparing calibration with Scenarios 7-9 ... 102

Appendix H : Flow hydrographs and flow duration curves comparing calibration with Scenarios 7-9 ... 106

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Table 1: Soil classes ... 13

Table 2: Simplified existing land cover ... 13

Table 3: Overview of surface water flow recorder sites ... 19

Table 4: Summation of river coastal discharge ... 21

Table 5: Summary of total catchment flow ... 25

Table 6: Summary of irrigated areas ... 26

Table 7: Overview of groundwater level monitoring ... 29

Table 8: List of eigenmodels developed ... 45

Table 9: Summary of calibrated model parameters and calibration statistics ... 47

Table 10: Summary of sub-catchment flow ... 48

Table 11: Calculation of surface water nitrate-nitrogen loads ... 49

Table 12: Calculation of land surface nitrate-nitrogen loads ... 50

Table 13: Summary of sub-catchment nitrate-nitrogen loads ... 51

Table 14: River flow statistics ... 58

Table 15: Groundwater level statistics ... 61

Table 16: Modelled nitrate-nitrogen concentrations at Te Waikoropupū Springs for various development scenarios ... 64

Figure 1: Location of the Tasman District and the Takaka catchment ... 6

Figure 2: Takaka water management areas ... 8

Figure 3: Spatial extent of the three aquifer systems ... 9

Figure 4: Simplified geology ... 11

Figure 5: Rainfall and PET station locations and rainfall isohyets ... 12

Figure 6: Soil plant available water classes for 600 mm rooting depth ... 14

Figure 7: Land cover ... 15

Figure 8: Flow and land surface run-off comparisons for Takaka River at Harwood ... 17

Figure 9: Flow and land surface run-off comparisons for Takaka River at Kotinga ... 18

Figure 10: Key river monitoring sites ... 20

Figure 11: Comparison of measured Fish Creek flow and synthesised Te Waikoropupū main spring flow ... 21

Figure 12: Prediction of full-length flow in the Takaka River ... 23

Figure 13: Comparison of land surface recharge and river recharge ... 25

Figure 14: Existing active water take consents ... 27

Figure 15: Existing and proposed irrigated areas and consented peak rates of take ... 28

Figure 16: Groundwater level monitoring wells ... 30

Figure 17: Groundwater level time series ... 31

Figure 18: Comparison of groundwater levels in active AMA wells and Takaka River flows ... 32

Figure 19: Comparison of Main Spring groundwater levels and flows in Te Waikoropupū spring ... 33

Figure 20: Comparison of Motupipi groundwater levels and river flows ... 34

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Figure 21: Groundwater level contours TUGA (2002-06 data) ... 35

Figure 22: Groundwater level contours AMA and TLA (2002-06 data) ... 36

Figure 23: Nitrate-nitrogen concentrations in the Takaka River ... 37

Figure 24: Surface water nitrate-nitrogen concentrations ... 38

Figure 25: Groundwater nitrate-nitrogen concentrations ... 39

Figure 26: Annual flows and nitrate-nitrogen loads and concentrations for Te Waikoropupū main spring ... 40

Figure 27: AMA eigenmodel domain ... 42

Figure 28: TLA eigenmodel domain ... 43

Figure 29: TUGA eigenmodel domain ... 44

Figure 30: Existing and plausible irrigable areas ... 54

Figure 31: Likely irrigable areas ... 56

Figure 32: Current and potential irrigation areas in Takaka Valley (supplied by TDC) ... 63

Figure 33: Modelled nitrate-nitrogen concentrations at Te Waikoropupū Springs for scenarios shown in Table 16 ... 65

Figure 34: Existing and predicted groundwater nitrate-nitrogen concentrations under various scenarios ... 67

Figure 35: Existing and predicted surface water nitrate-nitrogen concentration under various scenarios ... 67

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1 EXECUTIVE SUMMARY

As part of Tasman District Council (TDC)’s process for reviewing water allocation in the Takaka catchment, the Takaka Freshwater and Limits Advisory Group (FLAG) has been formed. The purpose of this group is to enable greater community involvement and consultation, and to provide a means through which the community and other stakeholders can assist TDC to develop policy which better manages the water resource of the catchment.

In order to set allocation limits, an understanding of the causes of declines in both water quantity and quality (and subsequent ecosystem health) is needed. The MBIE Wheel of Water research programme (Allen et. al., 2012)¹ has been used to assist the FLAG develop this understanding through the following two levels of modelling:

1. Water Wheel visualisations of trade-offs among key indicators of the values and uses identified as important by the FLAG; and

2. Modelling of the flow and water quality dynamics for selected development scenarios.

This report presents the modelling development and results, contributing to item 2, for groundwater and groundwater dependent systems. Much of the hydrological and hydrogeological basis for the groundwater modelling work has been derived from Thomas & Harvey (2013)² as well as personal communications with Mr Joseph Thomas (TDC). The authors would specifically like to thank Mr Thomas for his contribution to, and review of, this report.

Catchment Overview and Data Sources

The groundwater system of the Takaka catchment is complex and comprises karst systems of international significance overlain by alluvial outwash gravels. There are three main water bearing aquifers within the valley which are directly related to lithology. Thomas & Harvey (2013) describe these as:

 The Arthur Marble Aquifer (AMA);

 The Takaka Limestone Aquifer (TLA); and

 The Takaka Unconfined Gravel Aquifer (TUGA) which interacts with the Takaka River and also discharges at the coast.

Various data sources have been collated to assist this study including geology, climate (both rainfall and evapotranspiration), agricultural soil properties, land coverage, surface water and groundwater measurements (levels, flow and quality) and wells and consents databases. A soil water balance model was used to calculate land surface recharge and estimate irrigation water use and scheduling.

The total average annual flow of water through the catchment (groundwater and surface water combined) is estimated at approximately 73.3 m³/s. Of this, approximately 59.9 m³/s is estimated to discharge off shore via surface waterways and approximately 0.2 m³/s (annual average³) is removed through groundwater abstraction (primarily for irrigation and water supplies). The remaining 13.2 m³/s discharges off shore via groundwater (sub surface). Total recharge to the groundwater system alone equates to approximately 31.9 m³/s (through both the valley floor and the upper catchment).

Approximately 8.5 m³/s of this recharge originates from river recharge, and the remainder from land surface recharge.

1 Allen, W., Fenemor, A., and Wood, D. (2012): Effective Indicators for Freshwater Management: Attributes and frameworks for Development. Report prepared for Aqualinc Research for the MSI Wheel of Water Project. Landcare Research, Nelson.

June 2012.

2 Thomas, J. and Harvey, M. (2013): Water Resources of the Takaka Water Management Area. Tasman District Council.

July 2013.

3 The seasonal peak demand is higher than this.

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Approximately 2,275 ha of land is currently irrigated in the Takaka valley with an additional 533 ha proposed (active consent applications). Of the existing irrigated area, approximately 75% is supplied from surface water and the remainder from groundwater.

By national standards, nitrate-nitrogen concentrations at a catchment scale are low in both surface water and groundwater. There are, however, some areas where local land uses have resulted in elevated concentrations.

Modelling

Interactions between the three main aquifer systems in the Takaka valley and the surface rivers and streams are complex. Furthermore, the location and details of the karst systems are generally unknown. It is therefore difficult to model these specific systems with confidence. What is known, however, is a clear hydraulic response between groundwater inflows (river recharge and land surface recharge), pumping and groundwater outflows (spring flows and off-shore discharge). Because of this, the dynamic response in groundwater levels and spring discharge has been modelled using a series of eigenmodels, as described by Bidwell & Burbery (2011)⁴.

Although eigenmodels are very simplified compared to real aquifers, they are adequate for situations for which dynamic response is the primary interest (Bidwell & Burbery, 2011). They are particularly helpful in situations where the aquifer system is not known in sufficient detail to construct a more detailed numerical model, or where this is prevented by time and budgetary constraints. Consequently, they are suitable for use in the Takaka catchment.

The eigenmodels developed do not simulate contaminant transport. Instead, simple bucket-mixing models have been used to predict changes in water quality from different land use scenarios.

Multiple eigen models have been developed, one for each key observation site in the catchment, as listed in the following table.

Aquifer system Groundwater level site River flow site

AMA

Ball Main Spring

Bennett Fish Creek

Hamama Spring River

Main Spring Savage Sowman

TLA

Cserney Motupipi River Grove Orchard

Motupipi Substation

TUGA

Fire Station (combined) Paynes Ford Jefferson

TDC Offices

Each model was constructed to run from 1 January 1980 through to 31 December 2014 (a total of 34 years). Calibration focussed on the period of measured data, which differed from site to site.

Generally, there is little monitoring data with which to calibrate prior to approximately 1990. As a result, the reliability of calibration to this earlier period is not known and key outputs have been reported only for the period 1990-2014 (inclusive). Calibration particularly focussed on dry periods (low groundwater levels and flows).

4 Bidwell, V. and Burbery, L. (2011): Groundwater Data Analysis – Quantifying Aquifer Dynamics. Prepared for Envirolink Project 420-NRLC50. Report no. 4110/1. June 2011.

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Development Scenarios and Results

Once models had been calibrated, they were used to predict the response in the groundwater system from various development scenarios, as follows:

Scenario 1: No consumptive use – this represents the state of the groundwater system unaffected by irrigation, other consumptive abstraction (e.g. water supplies) and subsequent use.

Scenario 2: Double irrigation – this scenario represents the approximate state of the groundwater system should the existing irrigated area be doubled.

Scenario 3: All existing irrigation groundwater sourced – this scenario explores the effects on the groundwater system from groundwater abstraction by assuming all existing irrigation is sourced only from groundwater.

Scenario 4: Cobb Dam effects – this scenario represents an estimate of the state of the groundwater system if the Cobb Dam did not exist.

Scenario 5: Waingaro River – to assess the sensitivity of the groundwater system to Waingaro River losses, all groundwater recharge from the river is removed.

Scenario 6: No development – this scenario approximates that state of the environment, without any alteration by human activity, by removing the Cobb Dam (as per Scenario 4) and assuming all existing pasture or native grassland is instead covered in forest.

Scenario 7: Likely irrigation 1 – this scenario is based on the calibrated model with additional irrigation in areas that are most likely to be developed in the near future, as determined by Joseph Thomas (TDC).

Scenario 8: Likely irrigation 2 – based on the ‘Likely Irrigation 1’ scenario, this scenario adds an additional 90 l/s (180 ha) of allocation taken in the upper catchment, as assessed by Joseph Thomas.

Scenario 9: Likely irrigation 3 – Based on the ‘Likely Irrigation 1’ scenario, this scenario adds an additional 150 l/s (300 ha) of allocation taken in the upper catchment, as assessed by Joseph Thomas.

A brief summary of results from these scenarios follows.

Effects of Irrigation

Groundwater abstraction for irrigation typically results in a lowering of groundwater levels. In addition, irrigation results in an increase in land surface recharge into the uppermost aquifer. If the irrigation water source is surface water (rather than groundwater), then this provides additional land surface recharge without a reduction in groundwater levels from pumping. Consequently, surface-water sourced irrigation can result in shallow groundwater levels that are higher compared to a no-irrigation scenario.

Shallow groundwater levels in the TUGA system are predicted to be lower with increased groundwater abstraction. However, when the additional irrigation is sourced from surface water, shallow groundwater levels are predicted to be higher. The shallow TUGA system directly receives the additional land surface recharge from irrigation.

The deeper AMA and TLA systems do not show this recharge effect as they are more disconnected from the surface recharge compared to the TUGA system. Specifically, the coastal TLA system is confined below the TUGA system and therefore does not receive the full benefits of direct additional recharge. As such, groundwater levels are lower with additional irrigation due to the increased abstraction.

The Likely Irrigated scenarios (scenarios 7-9) all present lesser effects than the double irrigation scenario with groundwater levels and river flows not too different from Status Quo.

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Effects of the Cobb Dam

The Cobb Dam has the overall effect of raising groundwater levels, increasing low flows and reducing the number of zero-flow days. This is achieved by augmenting river flows, particular during low-flow periods, by water that has been harvested during higher flow periods (and would otherwise discharge into the sea at that time).

Effects of Groundwater Recharge from the Waingaro River

Groundwater recharge from the Waingaro River has an overall positive benefit on groundwater levels in the lower catchment and subsequent river flows.

Effects of Human Activity

Human activity has the net effect of increasing land surface recharge into the groundwater system (less water is consumed by grass compared to forest). This, combined with no regulating effects of the Cobb Dam, results in lower groundwater levels and lower river and spring flows under the No Development scenario compared to status quo.

Effects on Water Quality

Overall, land use intensification is likely to increase nitrate-nitrogen concentrations in the receiving environment, both groundwater and surface water. Doubling the irrigated area is predicted to result in a relatively small change in groundwater concentrations, but the change is more pronounced in surface waterways. The three likely irrigated area scenarios are predicted to result in very little change in predicted concentrations.

Various additional irrigation scenarios, and the effects at various monitoring sites, were modelled.

Considering the impacts of additional irrigated dairying on Te Waikoropupū springs (for example), modelled nitrate-nitrogen concentrations may increase from a current concentration of approximately 0.42 g/m³ up to approximately 0.54 g/m³ if the full valley floor was irrigated.

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5 1 INTRODUCTION AND BACKGROUND

Tasman District Council (TDC) are in the process of reviewing water allocation for the Takaka catchment (Figure 1). As part of this process, the Takaka Freshwater and Limits Advisory Group (FLAG) has been formed to enable greater community involvement and consultation, and to provide a means through which the community and other stakeholders can assist TDC to develop policy which better manages the water resource of the catchment.

In order to set allocation limits, an understanding of the causes of declines in both water quantity and quality (and subsequent ecosystem health) is needed. Landcare Research (Andrew Fenemor) and Aqualinc Research Ltd (Aqualinc) (Julian Weir and John Bright) are assisting the FLAG to develop this understanding through the MBIE Wheel of Water research programme (Allen et. al., 2012). Additional assistance and local expert knowledge is provided by Joseph Thomas (TDC).

To develop this qualitative understanding of cause and effect, two levels of modelling have been considered:

1. Water Wheel visualisations of trade-offs among key indicators of the values and uses identified as important by the FLAG; and

2. Modelling of flow and water quality dynamics for selected development scenarios.

This report presents the modelling development and results, contributing to item 2, for groundwater and groundwater dependent systems. The report is structured as follows:

 Hydrological and hydrogeological summary;

 Data collection and analyses;

 Modelling concepts;

 Nitrate-nitrogen budgets; and

 Development scenarios.

1.1 Acknowledgements

The authors would specifically like to thank Joseph Thomas (Tasman District Council) for his contribution to, and review of, this report.

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Figure 1: Location of the Tasman District and the Takaka catchment

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7 2 HYDROLOGICAL AND HYDROGEOLOGICAL SUMMARY

Much of the hydrological and hydrogeological basis for the groundwater modelling work has been derived from Thomas & Harvey (2013) as well as personal communications with Mr Joseph Thomas (TDC). As discussed by Thomas & Harvey, TDC’s water management zones (reproduced in Figure 2) encompass an area of approximately 1,012 km². This consists of the larger Takaka catchment (approximately 940 km²) and the smaller Takaka North catchments (approximately 72 km²). The Takaka North catchments are dominantly surface water systems and therefore have been excluded from this groundwater study. The remaining Takaka catchment is the focus of this study and is shown in Figure 2.

The groundwater system of the Takaka catchment is complex and comprises karst systems of international significance overlain by alluvial outwash gravels. There are three main water bearing aquifers within the valley which are directly related to lithology. Thomas & Harvey (2013) describe these as:

 The Arthur Marble Aquifer (AMA);

 The Takaka Limestone Aquifer (TLA); and

 The Takaka Unconfined Gravel Aquifer (TUGA) which interacts with the Takaka River and also discharges at the coast.

The AMA is a deeper marble-based karst system and is the principal karstic system in the Takaka valley (Thomas & Harvey, 2013). The system is found underneath the valley floor and extends from Upper Takaka through to the coast and beyond. The AMA is unconfined from Upper Takaka to approximately Hamama. Below Hamama, the AMA becomes confined by relatively impervious Motupipi coal measures that overlay the AMA. Recharge to the AMA occurs via direct infiltration on exposed marble outcrops in the upper catchment and also from infiltration of Takaka River water and land surface recharge (excess rainfall and irrigation) through the overlying TUGA. The system discharges primarily to Te Waikoropupū Springs and subsurface off shore.

The TLA occurs between East Takaka and Tarakohe and is formed from karstic Takaka limestone.

The formation is folded into a series of low amplitude synclines and anticlines (Thomas & Harvey, 2013) and has a relatively impermeable lower boundary. Recharge to the TLA occurs primarily via direct infiltration on the exposed limestone outcrops along the eastern boundary and also from the southern end via Takaka River flow seeping into the TUGA and then into the limestone. The system discharges primarily to the Motupipi River and subsurface off shore. Fenemor et al. (2008) present a conceptual water balance for the Motupipi catchment. They calculate that approximately 30% of the nitrogen losses from the Motupipi catchment enter the TLA and that 18 tonnes/year discharge from the TLA annually.

The TUGA comprises recent river gravels and sand deposits which cover most of the Takaka valley from Upper Takaka to the sea. Recharge is primarily derived from the Takaka River and from land surface recharge (excess rainfall and irrigation). The TUGA interacts with the Takaka River and also discharges to the Motupipi River, Spring River and off shore at the coast.

The horizontal spatial extent of the three aquifer systems is shown in Figure 3.

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Figure 2: Takaka water management areas (reproduced from Thomas & Harvey, 2013)

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Figure 3: Spatial extent of the three aquifer systems (reproduced from Thomas & Harvey, 2013)

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10 3 DATA COLLECTION AND ANALYSES

Data for modelling the Takaka valley groundwater system has been collated from various sources, with Tasman District Council being the primary supplier of groundwater and surface water data. Data used for the investigation includes:

 Geological data;

 Climate data;

 Agricultural soil characteristics;

 Land cover;

 Soil water balances, quick flow separation and net land surface recharge;

 Surface water monitoring;

 River recharge;

 Existing consents and irrigated areas; and

 Groundwater level monitoring.

Brief overviews of these data sources, and the transformations applied, are presented in the following sections.

3.1 Geological Data

The study area comprises rocks of varied and complex geology (Thomas & Harvey, 2013). A simplified representation of this geology is presented in Figure 4 which describes where the individual aquifers outcrop to the ground surface. Infiltration into these areas will recharge the respective aquifers. For other areas (the unshaded areas in Figure 4), it has been assumed that any rainfall (less evapotranspiration) will run off to surface water.

A more detailed description of the catchment geology is presented in Thomas & Harvey (2013).

3.2 Climate Data

Daily time series of rainfall and potential evapotranspiration (PET) have been supplied by TDC and NIWA. In addition, a shapefile of rainfall isohyets (mean annual rainfall) has been provided by TDC (Martin Doyle, pers. comm.). This is shown in Figure 5.

The rainfall isohyets have been used to divide the catchment into zones of average annual rainfall against which the nearest rainfall station has been assigned to represent the time-varying (daily) rainfall. Data gaps have been filled with correlations to neighbouring rainfall sites.

PET data is more sparse, but it is not spatially highly variable. Consequently, a single time series of PET (near Kotinga) has been used to represent the entire catchment. Gaps in this data series have been filled via correlations with PET measured at Riwaka.

Time series of rainfall and PET at key stations have been collated for the period 1 January 1980 through 31 December 2014. A start date of 1 January 1980 was chosen as this is approximately the earliest data provided for the Takaka valley.

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Figure 4: Simplified geology

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Figure 5: Rainfall and PET station locations and rainfall isohyets

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13 3.3 Agricultural Soil Characteristics

Soils information for pasture was obtained from Landcare’s S-map and Fundamental Soils Layer (FLS) coverages. These datasets were adjusted for typical rooting depths of 600 mm for pasture, 1 m for inland hill forestry and 2 m for forestry nearer the valley floor. Soils were aggregated into four plant available water (PAW) classes, as shown in Table 1.

Table 1: Soil classes

PAW class for 600 mm rooting depth (mm)

Assigned PAW for 600 mm rooting depth (mm)⁽¹⁾

< 40 40

40-100 80

100-160 120

> 160 140⁽²⁾

(1) Plants with rooting depths greater than 600 mm (e.g. forest) have access to a greater PAW depth than listed here.

(2) PAW was capped at 140 mm (for 600 mm rooting depth) due to the uncertain nature of estimating PAW for these deeper soils. This makes little difference to the calculated drainage through these soils.

The spatial distribution of soil PAW for pasture (600 mm rooting depth) is shown in Figure 6.

3.4 Land Cover

Land cover for the study area has been derived from Terralink’s Land cover Database (Version 4). A simplified summary of this is provided in Table 2 and Figure 7. Land cover is dominated by grass and forest.

Table 2: Simplified existing land cover

Land cover Area (ha) Proportion of study area

Forest 67,400 72%

Grass 24,600 26%

Gravel or rock 1,100 1%

Water 740 0.8%

Town 170 0.2%

Total 94,010 100%

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Figure 6: Soil plant available water classes for 600 mm rooting depth

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Figure 7: Land cover

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16 3.5 Soil Water Balances, Quick Flow Separation and Net Land Surface Recharge

Aqualinc’s in-house crop-soil water balance model (IRRICALC) has been used to generate time series of land surface drainage. The crop-soil water balance model simulates the variable use of water in agriculture accounting for differing crops, agricultural soil types, representative daily climatic conditions and irrigation strategies. The basis of the model is a daily soil moisture balance with an optional irrigation scheduling component.

For the purposes of the Takaka valley groundwater study, the soil water balance model was used to calculate groundwater recharge and irrigation water requirements. Data inputs were:

 Reference evapotranspiration (ET);

 Rainfall;

 Land cover; and

 Soil plant available water (which is a function of soil properties and rooting depth).

Actual ET was derived from the reference ET using the relationship by Allen et al. (1998) described in Equation 1.

Actual ET = ks × kc × reference ET (1)

Where: ks = the water stress reduction factor; and kc = the evapotranspiration crop coefficient.

The water stress reduction factor is a function of soil moisture. As recommended by Allen et al. (1998), it was assumed that ks equalled 1.0 when the soil moisture deficit was less than the plant readily available water, and reduced linearly down to a value of zero at wilting point, when the soil moisture deficit was greater than the plant readily available water. Readily available water was assumed to be equal to 50% of the plant available water at field capacity (PAW). Each day, soil moisture was calculated as:

ASM day i = ASM day i-1 + (rain – actual ET – drainage) day i (2)

Where: ASM = plant available soil moisture.

The model assumes that the maximum water the soil can hold is the PAW. Any infiltration in excess of that required to reach field capacity was assumed to drain beyond the root zone.

Modelling assumes that soils were free draining, and the depth to groundwater was greater than plant rooting depths. Model simulations were run from 1 January 1980 to 31 December 2014, a total of 34 years.

3.5.1 Quick Flow Separation

IRRICALC makes the assumption that all water falling onto the land surface is either evapotranspired by plants, is stored in the soil, or drains into the underlying subsurface. For the Takaka area, some of the drainage would move laterally to nearby streams, either as direct land surface run-off or near- surface lateral flow (via preferential flow paths and other shallow discharge mechanisms). The remainder would drain to deeper recharge of the regional groundwater system. The net land surface recharge to the regional groundwater system is therefore the total land surface recharge less the contribution to river flows (referred to here as the ‘quick-flow’ component). This concept is consistent with the work published by Woodward et. al (2013) for a Taupo catchment and has been applied by Aqualinc to modelling studies in the Waikato, Ruataniwha, Waimea, central Canterbury, south Canterbury and Kakanui areas.

The quick-flow separation for the Takaka valley has been based on measured river flows in the Takaka River at both Harwoods (for the upper catchment) and at Kotinga (for the whole valley) (refer to Section

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3.6). Quick flow run-off was estimated based on daily time series of land surface recharge (LSR) calculated for the catchment over the simulation period (1980-2014). The basis of the quick-flow separation is the assumption that the soils can accept only a finite rate of deep recharge, and the remaining flow is routed directly to rivers as quick-flow. The amount of LSR that is routed as quick- flow was determined by specifying a percentile of the LSR above which flow is assumed to be quick- flow. The percentile value is calibrated based on measured river flows so that average run off matched average measured river flows.

For the Takaka River catchment, the portion of land surface recharge on any day that exceeded the 89 percentile flow was routed to streams. This was based on calibration to measured average flow at Harwood’s from the upper valley catchment only, and subsequently applied to the whole catchment.

For the lower valley, some of this run off water has the opportunity to seep into the TUGA system as the river passes over the valley floor. The remainder stays as quick flow in the river, which equates to approximately 41.4 m³/s.

For comparison to measured flows, an exponentially-weighted average was placed through the quick- flow run off time series to partly account for lag times and storage in the upper soils. This resulted in the flow responses shown in Figure 8 and Figure 9.

Figure 8: Flow and land surface run-off comparisons for Takaka River at Harwood

0 10 20 30 40 50 60 70

01/01/08 01/01/09 01/01/10 01/01/11 01/01/12 01/01/13 01/01/14

River flow (m3/s)

Date

Comparison of Land Surface Run-Off and Takaka River Flows at Harwood

Measured flow Modelled runoff

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Figure 9: Flow and land surface run-off comparisons for Takaka River at Kotinga

While the assessment above sufficiently reproduces the seasonal run-off trends, it cannot reproduce the dynamics of the measured run off to the same level of accuracy as purpose-built rainfall-run-off models. However, the groundwater modelling completed for the Takaka catchment utilises measured river flow time series and therefore does not specifically use this synthesised run off time series.

Instead, the purpose of this comparison is to estimate the slower regional infiltration to deeper groundwater by removing the flow that would eventually run off to rivers.

3.5.2 Resulting Land Surface Recharge

The direct land surface recharge to the groundwater system averages approximately 23.4 m³/s over the entire study area of 940 km². This equates to an average annual recharge of approximately 790 mm/year. Of the 23.4 m³/s, approximately 12.5 m³/s is estimated to infiltrate directly to the AMA, approximately 0.7 m³/s to the TLA and the remaining approximately 10.2 m³/s to the TUGA. Once underground, the infiltrated water passes between aquifer systems along common boundaries. Hence, these values do not represent the total flows in each system. For example, some of the TUGA water eventually flows into the AMA and TLA systems. River recharge also contributes to groundwater flow (discussed in Section 3.7).

0 20 40 60 80 100 120

01/01/08 01/01/09 01/01/10 01/01/11 01/01/12 01/01/13 01/01/14

River flow (m3/s)

Date

Comparison of Land Surface Run-Off and Takaka River Flows at Kotinga

Measured flow Modelled runoff

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19 3.6 Surface Water Monitoring

TDC operate a series of river flow recorder sites and conduct additional spot flow gaugings throughout the catchment. In addition, Trust Power report flow at the Cobb dam (both actual and naturalised).

Figure 10 shows the locations of key flow recorder sites (labelled) and the various gauging sites considered (not labelled). Table 3 summarises the stored data for the key recorder sites. Data from individual gaugings are too numerous to include herein.

Table 3: Overview of surface water flow recorder sites

River name Monitoring site Start date End date Completeness

Cobb River Cobb Dam 6/6/85 Current 93%

Takaka River Harwood 26/3/75 Current ~100%

Takaka River Kotinga 9/10/70 Current 88%

Waingaro River Hanging Rock 6/9/79 Current 99%

Anatoki River Happy Sams 6/9/79 Current 97%

Powell Creek U/S Motupipi River 14/12/06 Current ~100%

Motupipi River Reillys Bridge 23/11/06 Current 99%

Fish Creek Main Springs 5/4/85 Current 98%

Te Waikoropupū River Spring River 13/12/74 Current 80%

3.6.1 Te Waikoropupū Main Spring Flows

A key surface water feature of the catchment is Te Waikoropupū springs. Flow from the main springs are not automatically measured by TDC. However, TDC have synthesised flows from this main spring based on adjacent groundwater levels (Main Spring groundwater) and gaugings. This flow synthesis is reliable from approximately 1999 onwards, when the Main Spring groundwater well was installed.

Prior to this, the synthesis is less accurate.

Figure 11 plots a comparison between measured Fish Creek flow and synthesised flow (from Main Spring groundwater) from 1999 onwards (both daily average flow). Although there is some scatter in this correlation, the following observations are made:

 There is a relatively linear relationship between flows in Fish Creek and flows from the main spring. This suggests that the two systems are hydraulically similar.

 Fish Creek is likely to go dry at approximately the same time as flows in Te Waikoropupū main spring drop to approximately 7.8 m³/s (and below).

 For every 1 m³/s increase in flow from Te Waikoropupū main spring, Fish Creek increases by approximately 0.65 m³/s.

 Fish Creek is influenced by overland flows at times of high flows, and main spring flow is not. Hence, the relationship between the two flows sites is unreliable at high flows.

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20

Figure 10: Key river monitoring sites

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Figure 11: Comparison of measured Fish Creek flow and synthesised Te Waikoropupū main spring flow

3.6.2 Coastal Surface Water Discharge

The rate of surface water discharging into the sea from rivers has been estimated by summing the average flows in the coastal monitoring sites.

Table 4: Summation of river coastal discharge

River name Monitoring site Average flow

(m³/s)

Takaka River Kotinga 33.4

Anatoki River One Spec Bridge ~ 11.9 ⁽¹⁾

One Spec Creek Takaka River confluence ~ 0.3

Motupipi River Reillys Bridge 0.5

Te Waikoropupū main spring Main spring 10.0

Fish Creek Te Waikoropupū Springs 3.3

Misc. eastern streams

(Motupipi through Pohara) Various ~ 0.5

Total ~ 59.9

(1) This flow is estimated as there is an insufficient range of gauged flows to accurately calculate an average (Thomas & Harvey, 2013).

y = 0.6554x + 7.8194 R² = 0.5911

4 6 8 10 12 14 16 18 20

0 2 4 6 8 10 12 14 16 18

Calculated Te Waikoropupū main spring flow (m3/s)

Measured Fish Creek flow (m³/s)

Flow Correlation

Fish Creek Versus Te Waikoropupū Main Spring (1999-2014)

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22 3.7 River Recharge

River recharge to the groundwater system occurs primarily from the Takaka River, but also from the smaller streams and rivers. These sources are each discussed below.

3.7.1 Takaka River Recharge

The estimation of river recharge from the Takaka River to the groundwater system has been separated into two zones: above and below the Harwood recorder. The Harwood recorder is located near where the Takaka River exits the hill catchment and begins to flow along the valley floor. It is therefore a suitable location for a natural distinction between the upper (hill) catchment and the lower (valley floor) river.

Due to the distance from the monitoring locations on the valley floor, the hydraulic response of groundwater recharge from the river channels in the upper (hill) catchment is difficult to separate from the effects of land surface recharge. Consequently, it has been assumed that there is no direct recharge from river channels in this upper catchment and instead land surface recharge alone has been used, which acts as a surrogate for the combined effect of both river and land surface recharge to the groundwater system.

Below the Harwood recorder and out onto the valley floor, river recharge to groundwater is dependent (among several factors) on whether or not the river flows continuously along its entire length. If the Takaka River does not flow continuously along its entire length (even if there is only a short dry reach mid-river), then all of the river flow measured at Harwood drains into the groundwater system. When the river flows full length, some of the flow will drain to groundwater and some will remain in the river channel and discharge into the sea. Therefore, to calculate the rate of river recharge to groundwater, it is necessary to know when the river is partially dry and when it is fully flowing. There are very few recorded observations of this, so a simple relationship has been developed to predict when the river may have historically been partially dry. This relationship has been based on work presented by White et al. (2001) and Young et al. (2001). Specifically:

 An average loss of 600 l/s has been applied between Harwood recorder and Lindsay’s bridge, based on gaugings. The magnitude of loss is reported by White et al. (2001) to be relatively independent of river flows. A constant average loss has been assumed.

 When the river does not flow full length, the loss to groundwater below Lindsay’s bridge equals the remaining river flow. Young et al. (2001) concluded that when groundwater levels are high, river drying will occur when river flows (at Harwood) drop below approximately 7,000 l/s. However, if groundwater levels are low, then flows as high as 15,000-20,000 l/s are required to maintain full surface flow. Given this, a relationship between river drying and river flow with groundwater levels at the Sowman monitoring well (Section 3.10) has been developed to predict the days when the river dried somewhere along its each. This relationship has been further adjusted to match anecdotal evidence from local residents. Figure 12 presents the prediction of full-length flow from 1 June 2010 to 31 December 2014.

 For days when the river flows full length, it has been assumed that the losses are the same as the maximum losses for the same groundwater level.

 Provision of surface water takes for irrigation in the upper valley below the Harwood recorder have been included in the assessment. Takes have been calculated using IRRICALC (Section 3.5) for the irrigated area sourced from surface water in losing reaches of the Takaka River and adjacent tributaries.

To calculate river recharge to groundwater, the location of where the river dries does not need to be known; only if it goes dry.

Given the above methodology, the resulting recharge to groundwater from the Takaka River below Lindsay’s bridge ranges between nearly zero and 14.4 m³/s.

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Figure 12: Prediction of full-length flow in the Takaka River

(white space (y-axis = 0) are days when the river is predicted to be partially flowing; blue space (y-axis = 1) are days when the river is predicted to be full flowing)

3.7.2 River Recharge from Smaller Streams and Rivers

In addition to groundwater recharge from the Takaka River, some of the smaller streams and rivers also contribute recharge to the groundwater system. Their contributions to groundwater recharge have been estimated based on limited spot gaugings, as follows:

 Waitui and Aaron creeks feed into the Takaka River near the Harwood recorder. Gauged flows from these two creeks sum to 334 l/s, but they go dry at times. Therefore it has been assumed that, on average, 50% of their flow (167 l/s) recharges the groundwater system.

 Waingaro River loses 646 l/s on average, with some reaches losing and some gaining at different times, largely uncorrelated to flow. A steady groundwater recharge rate of 646 l/s has been assumed, which is approximately 15% of the flow at the uppermost gauging site.

This has been further adjusted for irrigation takes from the river. Half of the Waingaro River recharge has been assigned to the AMA system and half to the TUGA, as suggested by Joseph Thomas (TDC, pers. comm.).

 Craigieburn Creek gaugings report an average flow of 92 l/s. It is assumed that 15% of this flow recharges groundwater (assumed same as Waingaro River percentage losses), which equates to 14 l/s.

 The Anatoki River gains ~120 l/s over its length. Therefore, no groundwater recharge is assumed from this river. It will, however, receive discharge from the groundwater system.

 Smaller eastern streams accounted for as follows:

• Ellis Creek: based on gaugings, this creek gains ~11 l/s; therefore it has been assumed that it does not contribute to groundwater recharge.

0 1

Jun-10 Jun-11 Jun-12 Jun-13 Jun-14

Date (1 Jan yyyy)

Prediction of Full-Length Flow in the Takaka River

~ 170 days

~ 180 days

~ 190 days

Partial-length flow

days per year ~ 90 days

(to 31 Dec '14)

~ 160 days

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• Richmond Creek: there is insufficient gauging data for this creek; hence it has been assumed to be similar to Ellis Creek, gaining flow with no contribution to groundwater recharge.

• Gibson Creek: gauging suggests a gaining stream; hence no groundwater contribution has been assumed.

• Rameka Creek: again, insufficient gauging data; hence no groundwater contribution has been assumed.

• Dry Creek: insufficient data (measured zero flow); hence no groundwater contribution has been assumed.

• Kite Te Kahu Creek: insufficient data (measured zero flow); hence no groundwater contribution has been assumed.

Based on local knowledge, the eastern streams tend to lose flow in their upper reaches to the underlying TLA system and then gain flow again in the lower reaches as they pass over the TUGA system. However, there is insufficient data to quantity this. If this is the case, then the contribution to the TLA system is likely to be relatively small (compared to other sources) and therefore it has been conservatively assumed that the groundwater contribution is zero.

3.7.3 Combined River Recharge to Groundwater

From the above sources, the combined long-term average groundwater recharge from rivers equates to approximately 8.5 m³/s.

3.8 Comparison of Land Surface Recharge, River Recharge and Catchment Flows

From Section 3.7.3, the long-term average groundwater recharge from rivers equates to approximately 8.5 m³/s. As discussed in Section 3.5.2, the long-term average land surface recharge to groundwater equates to approximately 23.4 m³/s. These combine to total 31.9 m³/s.

Figure 13 shows time series of land surface recharge compared to river recharge. This plot has been prepared with an exponentially-weighted moving average run through the individual data sets to provide a comparison of trends and patterns. The key observations are:

 On average, land surface recharge is approximately three times larger than river recharge;

 Land surface recharge is significantly more dynamic (has larger annual variations) than river recharge; and

 The catchment experienced a period of below-average land surface recharge from 1992 through to 1995, and again from 2005 through to 2011 (approximately).

Some of the groundwater recharge re-emerges in surface waters in the lower catchment (e.g. in the Takaka River and Te Waikoropupū Spring).

The total water flowing through the catchment (groundwater and surface water combined) is estimated at approximately 73.3 m³/s. Of this, approximately 59.9 m³/s is estimated to discharge at the coast via surface waterways (Table 4). Approximately 0.2 m³/s (annual average⁵) is removed through groundwater abstraction (primarily for irrigation and water supplies). The remaining 13.2 m³/s therefore discharges off shore via groundwater (sub surface). Table 5 summarises the estimated total catchment flow balance.

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Table 5: Summary of total catchment flow

Flow component Report reference Flow (m³/s) Inflows

Land surface recharge Section 3.5.2 23.4

River recharge Section 3.7.3 8.5

River run off down catchment Section 3.5.1 41.4 Total in 73.3 Outflows

Surface water Table 4 59.9

Pumping - 0.2⁽⁶⁾

Groundwater (off shore) Remaining balance 13.2 Total out 73.3

Figure 13: Comparison of land surface recharge and river recharge

4 6 8 10 12 14 16 18 20 22 24 26 28 30 32

1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

Recharge (m3/s)

Date (1/1/yyyy)

Average Groundwater Recharge

(Exponentially Weighted Moving Average)

Land surface recharge Average land surface recharge River recharge Average river recharge

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26 3.9 Existing Consents and Irrigated Areas

The locations of existing active water take consents (for both surface water and groundwater) have been supplied by TDC. These are shown in Figure 14. Many of the consents are for irrigation, but consented uses also include water supply and water storage.

Subsequently, Aqualinc has digitised the existing and proposed irrigated areas for the Takaka valley (as at April 2015). This was achieved by using a method similar to Aqualinc (2015) and utilising the following data sources:

 Farm boundary extents (as provided by LINZ);

 Aerial photographs (from different sources and different time periods including TDC, Google Maps and Bing);

 Consent locations and consented areas (as supplied by TDC); and

 Multispectural satellite imagery (mapping of the normalised difference vegetation index, NDVI) from LandSat imagery on 7 March 2015 to distinguish between actively growing areas (likely to be irrigated) and dry areas.

The digitised areas were also reviewed by the FLAG and further adjusted. Both existing and proposed consented areas were included in this analysis. Figure 15 shows the resulting mapped areas, which are summarised in Table 6. For comparison, Figure 15 also includes the peak consented rates of take for each consent.

Table 6: Summary of irrigated areas Irrigation type Area (ha) K-line or long lateral 1,465

Pivot 340

Solid set 433

Gun 15

Drip/micro 22

Total existing 2,275

Proposed 533

Total incl. proposed 2,808

For comparison, TDC’s calculation of current and proposed irrigated areas are 2,284 ha and 553 ha respectively, which is similar to the total listed in Table 6. Approximately 75% of the consented irrigated area is sourced from surface water, and the remainder from groundwater.

The irrigation crop water requirements and associated irrigated land surface recharge have been calculated for each consent using the IRRICALC crop-soil water balance model discussed in Section 3.5. Maximum on-farm application rates of 5 mm/day have been assumed, which is consistent with TDC’s allocation methods. Restrictions to surface water takes have been applied based on river flows and typical consent conditions.

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Figure 14: Existing active water take consents

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Figure 15: Existing and proposed irrigated areas and consented peak rates of take

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29 3.10 Groundwater Level Monitoring

TDC operate a small network of groundwater level monitoring wells in the Takaka valley. The locations of these wells are shown in Figure 16. Some of these wells are currently active (i.e. TDC still record groundwater levels regularly) and some are now closed (they are no longer monitored). Table 7 summarises the stored data for each monitoring well.

Table 7: Overview of groundwater level monitoring

Well name Well number Aquifer Start date End date Completeness

Jefferson WWD 6829 TUGA 6/2/98 16/7/02 99%

TDC Offices WWD 6339 TUGA 2/6/99 Current 95%

Takaka Firestation WWD 6535 TUGA 29/7/04 4/2/11 98%

Takaka Fire 2 WWD 23648 TUGA 5/2/11 Current 98%

Cserney WWD 6418 TLA 29/10/87 17/10/06 99%

Grove Orchard WWD 6224 TLA 12/8/95 27/4/98 78%

Motupipi Substation WWD 6413 TLA 3/10/81 28/1/88 52%

Ball WWD 6011 AMA 2/6/94 22/3/04 95%

Bennett WWD 6815 AMA 26/6/96 3/12/98 97%

Hamama WWD 6710 AMA 25/2/88 7/4/05 82%

Te Waikoropupū Main Spring WWD 6013 AMA 20/8/99 Current 99%

Savage WWD 6713 AMA 18/7/02 Current 99%

Sowman WWD 6912 AMA 26/8/99 Current 95%

Figure 17 plots the groundwater level records for the wells. Although this is a complex graph to visualise, it has been provided for the following key features:

 Groundwater levels in wells located inland have higher groundwater level elevations than those located closer to the coast;

 Wells located in the deeper AMA aquifer have larger seasonal variation in groundwater levels (25+ m range; the saw-tooth effect) compared to wells in the TLA system (5-10 m range), and wells in the TLA system have larger variation than wells located in the TUGA system (2-3 m range). The exception is groundwater levels in the Main Spring well, which is moderated by discharge to the spring.

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Figure 16: Groundwater level monitoring wells

TAKAKA VALLEY

TAKAKA VALLEY

GROUNDWATER MODELLING Technical Investigations

PREPARED FOR MBIE Wheel of Water Research

C15066-03 15/12/2017

i

TABLE OF CONTENTS

ii

iii

iv

1

EXECUTIVE SUMMARY

2

3

4

5

1 INTRODUCTION AND BACKGROUND

1.1 Acknowledgements

6

7

2 HYDROLOGICAL AND HYDROGEOLOGICAL SUMMARY

8

9

10

3 DATA COLLECTION AND ANALYSES

3.1 Geological Data

3.2 Climate Data

11

12

13

3.3 Agricultural Soil Characteristics

3.4 Land Cover

14

15

16

3.5 Soil Water Balances, Quick Flow Separation and Net Land Surface Recharge

3.5.1 Quick Flow Separation

17

18

3.5.2 Resulting Land Surface Recharge

19

3.6 Surface Water Monitoring

3.6.1 Te Waikoropupū Main Spring Flows

20

21

3.6.2 Coastal Surface Water Discharge

22

3.7 River Recharge

3.7.1 Takaka River Recharge

23

3.7.2 River Recharge from Smaller Streams and Rivers

24

3.7.3 Combined River Recharge to Groundwater

3.8 Comparison of Land Surface Recharge, River Recharge and Catchment Flows

25

26

3.9 Existing Consents and Irrigated Areas

27

28

29

3.10 Groundwater Level Monitoring

30