CONFIDENTIAL
This report has been prepared by the Institute of Geological and Nuclear Sciences Limited (GNS Science) exclusively for and under contract to Environment Bay of Plenty. Unless otherwise agreed in writing, all liability of GNS Science to any other party other than Environment Bay of Plenty in respect of the report is expressly excluded.
The data presented in this Report are available to GNS Science for other use from March 2009
BIBLIOGRAPHIC REFERENCE
White, P.A.; Della Pasqua, F.; Meilhac, C. 2008. Groundwater resource investigations of the Paengaroa-Matata area stage 1 – conceptual geological and hydrogeological models and preliminary allocation assessment, GNS Science Consultancy Report 2008/134. 110 p.
Project Number: 520W2167 Confidential 2008
CONTENTS
EXECUTIVE SUMMARY ...... IV 1.0 INTRODUCTION ...... 1 2.0 GEOLOGY ...... 1 2.1 Overview...... 1 2.2 Brief description of geological units...... 3 2.2.1 Greywacke (Urewera Greywacke) ...... 3 2.2.2 Otawa Volcanics...... 4 2.2.3 OTP Ignimbrites...... 4 2.2.4 Tauranga Group Sediments - Pleistocene ...... 4 2.2.5 Manawahe volcano ...... 5 2.2.6 Matahina Ignimbrite...... 5 2.2.7 Mamaku Ignimbrite...... 5 2.2.8 Rotoiti Pyroclastics ...... 6 2.2.9 Tauranga Group Sediments - Holocene ...... 7 2.2.10 Other units...... 7 2.3 Drill logs...... 7 2.3.1 Northwest drill logs ...... 7 2.3.2 Northern drill logs ...... 8 2.3.3 Eastern drill logs...... 8 2.3.4 Southern drill logs...... 8 2.3.5 Summary ...... 9 3.0 HYDROGEOLOGY ...... 11 3.1 Hydraulic properties...... 11 3.2 Groundwater levels...... 13 3.2.1 Piezometric map...... 13 3.2.2 Groundwater level trends over time ...... 14 3.3 Groundwater chemistry ...... 17 3.3.1 Groundwater chemistry observations...... 17 3.3.2 Groundwater chemistry trends over time ...... 17 4.0 PAENGAROA-MATATA GEOLOGICAL MODEL...... 23 4.1 Model area...... 23 4.2 Methodology...... 23 4.3 Geological Units ...... 24 4.4 Topographic Surface ...... 25 4.5 Stratigraphic Surface Construction...... 25 4.5.1 Greywacke...... 25 4.5.2 Minden-Otawa volcanics ...... 26 4.5.3 Pleistocene sediments ...... 26 4.5.4 Manawahe volcano ...... 26 4.5.5 Matahina Ignimbrite...... 26 4.5.6 Mamaku Ignimbrite...... 27 4.5.7 Rotoiti Pyroclastics ...... 27 4.5.8 Holocene Sediments ...... 27 4.6 Geological cross sections...... 28 4.7 Volume calculations...... 28 4.7.1 Rock volume...... 28 4.7.2 Saturated rock volume ...... 28 4.7.3 Groundwater volume potentially available for use ...... 29 4.7.3.1 Groundwater volume and groundwater supply prospects ...... 29 5.0 HYDROLOGY ...... 32 5.1 Rainfall in the Matata area ...... 32 5.1.1 NIWA rainfall model...... 32 5.1.2 Rainfall model error ...... 32
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5.2 Surface Water...... 32 5.2.1 Rainfall on catchments ...... 32 5.2.2 Surface water flow measurements...... 33 5.3 Groundwater flow budget and groundwater available for allocation ...... 34 5.3.1 Estimates of rainfall recharge to groundwater (FR) ...... 35 5.3.2 Estimates of baseflow in streams (SS) ...... 37 5.3.3 Rainfall recharge, baseflow and estimated deep groundwater recharge...... 39 5.3.3.1 Errors in estimated deep groundwater recharge and implications for allocation...... 42 5.3.4 Groundwater available for allocation...... 42 5.4 Estimates of deep groundwater recharge in geological units and in sub-catchments 43 5.5 Discharge of deep groundwater ...... 45 6.0 GROUNDWATER ALLOCATION...... 46 6.1 Current groundwater consents ...... 46 6.1.1 Estimates of groundwater use...... 46 6.2 Groundwater available for allocation and existing allocation ...... 47 6.3 Groundwater available for allocation and estimated groundwater use ...... 47 6.4 Existing groundwater allocation by geological unit...... 50 6.5 Environment Bay of Plenty allocation policies...... 50 7.0 RECOMMENDATIONS ...... 51 8.0 ACKNOWLEDGEMENTS ...... 53 9.0 REFERENCES ...... 53
FIGURES
Figure 1.1 Topographic map with boundaries of the study area...... 58 Figure 2.1 Geological map with location of major faults...... 59 Figure 2.2 Geological map with location of the western, central and eastern areas...... 60 Figure 2.3 Location of groundwater bores in EBOP database containing lithological information...... 61 Figure 2.4 Inferred bore lithologies in the north western area wells...... 62 Figure 2.5 Inferred bore lithologies in the northern area wells...... 63 Figure 2.6 Inferred bore lithologies in the north eastern area wells...... 64 Figure 2.7 Inferred bore lithologies in the southern area wells...... 65 Figure 3.1 Groundwater level...... 66 Figure 3.2 Locations of wells in the Paengaroa-Matata area with an analysis of groundwater level measurements by Zemansky (2006)...... 67 Figure 3.3 Locations of wells in the Paengaroa-Matata area with an analysis of groundwater chemistry by Zemansky (2006)...... 68 Figure 4.1 Summary surface geological map of the Paengaroa-Matata area...... 69 Figure 4.2 Tauranga Group Sediments thicknesses (m)...... 70 Figure 4.3 Paengaroa-Matata geological model...... 71 Figure 4.4 Greywacke basement...... 72 Figure 4.5 Minden-Otawa volcanics...... 73 Figure 4.6 Pleistocene sediments...... 74 Figure 4.7 Manawahe volcano...... 75 Figure 4.8 Matahina Ignimbrite...... 76 Figure 4.9 Mamaku Ignimbrite...... 77 Figure 4.10 Rotoiti Pyroclastics...... 78 Figure 4.11 Holocene sediments...... 79 Figure 4.12 Location of geological model cross-sections...... 80 Figure 4.13 Geological model cross-section A-A’...... 81 Figure 4.14 Geological model cross-section B-B’...... 82 Figure 4.15 Geological model cross-section C-C’...... 83 Figure 5.1 Annual rainfall in the Paengaroa-Matata area (mm/year)...... 84 Figure 5.2 Surface water catchments in the Paengaroa-Matata area and topographic map...... 85 Figure 5.3 Surface water catchments in the Paengaroa-Matata area...... 86 Figure 5.4 Mean annual rainfall estimates (mm/year) for surface water catchments...... 87 Figure 5.5 Mean annual rainfall estimates (m3/s) for surface water catchments...... 88 Figure 5.6 Locations of gaugings in the Paengaroa-Matata area...... 89 Figure 5.7 Location of river flow measurement sites – continuous recorder...... 90 Figure 5.8 Rainfall recharge zones...... 91
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Figure 5.9 Gauging site localities and number of measurements...... 92 Figure 5.10 Gauging sites that represent stream flow at the bottom of catchments...... 93 Figure 5.11 Median values of flow at gauging sites that represent stream flow at the bottom of catchments...... 94 Figure 6.1 EBOP cold groundwater consents in the Paengaroa-Matata study area...... 95
TABLES
Table 2.1 Simplified stratigraphy of the central Bay of Plenty area...... 3 Table 2.2 Okatainia Volcanic Centre tephra marker units...... 7 Table 2.3 Stratigraphic summary by geographical area...... 10 Table 3.1 Summary of aquifer hydraulic properties...... 11 Table 3.2 Wells with groundwater level information in the Paengaroa-Matata area, from Zemansky (2006)...... 15 Table 3.3 Summary of groundwater level statistics in the Paengaroa-Matata area, from Zemansky (2006)...... 16 Table 3.4 Wells with groundwater chemistry information in the Paengaroa-Matata area, from Zemansky (2006)...... 18 Table 3.5 Median water quality values in the Paengaroa-Matata area, from Zemansky (2006)...... 19 Table 3.6 Maximum water quality values in the Paengaroa-Matata area, from Zemansky (2006)...... 20 Table 3.7 Groundwater quality sample summary in the Paengaroa-Matata area, from Zemansky (2006)...... 21 Table 3.8 Median water quality values for nutrients and bacteria in the Paengaroa-Matata area, from Zemansky (2006)...... 22 Table 3.9 Maximum nutrient and bacteria values in the Paengaroa-Matata area, from Zemansky (2006)...... 22 Table 3.10 Groundwater quality trends in the Paengaroa-Matata area, from Zemansky (2006)...... 23 Table 4.1 Simplified stratigraphic sequence adopted for the Paengaroa-Matata 3D geological model compared with the summary geological map nomenclature (Figure 4.1). The sequence is consistent with the summary geological sequence used in the Western Bay of Plenty geological model (White et al. 2008)...... 24 Table 4.2 Geological units modelled in the Paengaroa-Matata model and the Western Bay of Plenty geological model...... 25 Table 4.3 Rock volume estimates...... 30 Table 4.4 Estimates of groundwater potentially available for use...... 31 Table 5.1 Surface water catchments, catchment areas and mean annual rainfall (mm/year and m3/s)...... 33 Table 5.2 Continuous flow recording site in the Paengaroa-Matata area. Mean flow and median flow are calculated from Environment Bay of Plenty data...... 33 Table 5.3 Continuous flow measurement sites and gauging sites in each catchment...... 34 Table 5.4 Estimates of rainfall recharge1...... 36 Table 5.5 Base flow discharge estimates for catchments...... 38 Table 5.6 Rainfall recharge, baseflow and estimated deep groundwater recharge...... 40 Table 5.7 Preliminary water budget for Lake Rotoiti and its catchment...... 41 Table 5.8 Preliminary water budget for Lake Rotoehu and its catchment...... 41 Table 5.9 Preliminary water budget for Lake Rotoma and its catchment...... 41 Table 5.10 Groundwater available for allocation...... 43 Table 5.11 Estimated deep groundwater recharge by geological unit from estimates of groundwater flow in each catchment...... 44 Table 6.1 Existing groundwater consents by surface catchment (Appendix 4)...... 46 Table 6.2 Groundwater consents in the Paengaroa-Matata area, existing and consent applications as of 28th May 2008 (Gordon pers. comm.)...... 46 Table 6.3 Estimated use for existing groundwater consents...... 47 Table 6.4 Groundwater available for allocation and existing allocation in the Paengaroa-Matata area...... 48 Table 6.5 Groundwater available for allocation and estimated existing groundwater use...... 49 Table 6.6 Current groundwater allocation by geological unit...... 50
APPENDICES
Appendix 1 Details of the major geological units found in the Paengaroa-Matata area from the youngest to the oldest ...... 97 Appendix 2 Computer files used to generate the Paengaroa-Matata geological model...... 98 Appendix 3 Existing groundwater consents, and consent applications, 28th May 2008 ...... 100 Appendix 4 Existing groundwater consents 29th May 2008, by catchment and by geological unit...... 102
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EXECUTIVE SUMMARY
Environment Bay of Plenty commissioned GNS Science to assess groundwater resources in the Paengaroa-Matata area.
Geology in the area is reviewed and the following geological units are identified that are important at the regional scale:
• Holocene sediments;
• Rotoiti Pyroclastics;
• Mamaku Ignimbrite;
• Manawahe volcano;
• Pleistocene sediments;
• Minden-Otawa volcanics;
• Greywacke basement.
A three dimensional geological model is built to describe the surface and subsurface distribution of these units for the purposes of assessing the groundwater allocation in the area.
Groundwater available for allocation in 15 catchments in the Paengaroa-Matata area is estimated with a water balance model based on estimates of rainfall recharge to groundwater and estimates of stream discharge (baseflow) considering for possible groundwater recharge from lakes and catchments of Rotoehu and Rotoma to the south of Paengaroa-Matata area. Groundwater available for allocation is compared with allocation by Environment Bay of Plenty and compared with estimated use in each catchment. For example the Kaikokopu, Pokopoko and Wharere catchments have the largest concentration of groundwater users in the Paengaroa-Matata area and in these catchments:
• groundwater available for allocation is estimated as 1444 L/s;
• groundwater allocation by Environment Bay of Plenty is estimated as 743.5 L/s as of 28 May 2008 and therefore groundwater allocation is approximately 51% of groundwater available for allocation;
• groundwater use is estimated as 343.1 L/s considering use for frost protection, irrigation and municipalities and therefore groundwater use is approximately 24% of groundwater available for allocation.
Sustainable management of groundwater resources in the area will be aided with Environment Bay of Plenty allocation policies that set groundwater allocation limits on individual users and on the groundwater resource.
It is therefore recommended that Environment Bay of Plenty policies on groundwater allocation aim to:
• maintain baseflow in streams;
• allocate groundwater conservatively;
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• identify annual groundwater allocation limits for users that recognise the type of water use e.g. irrigation, frost, municipal;
• identify annual groundwater resource allocation limits by geographic area or aquifer, for example estimates of groundwater available for allocation in this report;
• develop and maintain datasets of users’ allocation (i.e. allocation by condition of consent) and groundwater allocation limits to monitor consented groundwater allocation against allocation limits set to sustain the aquifer.
Recommendations from this report to improve knowledge on the groundwater resource in the area include:
• groundwater levels, and ground levels, in wells could be checked where the EBOP database has wells with groundwater levels below sea level. Groundwater levels may be static water levels and if so the groundwater levels below sea may indicate a risk for salt water intrusion to groundwater;
• groundwater levels in the La Vigna, JB Family Trust well and RH Hall (Section 3.1) are either close to, or below, sea level during pumping indicating a risk of salt water intrusion to the aquifer. The allocation of groundwater from these bores could consider the risks of salt water intrusion to the aquifer caused by pumpage of these wells;
• in the Pongakawa area, groundwater levels are declining in wells over time. The trend in groundwater levels could be assessed to identify whether the trend is due to climatic changes or is due to groundwater use;
• EBOP could improve knowledge of groundwater in the Kaikokopu, Pokopoko and Wharere catchments, as groundwater is most heavily used in these catchments, by: improving data sets such as well numbers for consents, assessing ground levels and groundwater depths for wells; gauging measurements in streams to better assess river- groundwater allocation; improved assessments of groundwater budgets for the area;
• EBOP could consider purpose-built groundwater level monitoring wells that are not directly influenced by groundwater pumping in the Kaikokopu, Pokopoko and Wharere catchments area to assess risks of salt water intrusion;
• a computer model of groundwater flows is recommended in the future to assess groundwater availability for allocation to improve on the simple water balance used in this report.
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1.0 INTRODUCTION
Water resources in the Paengaroa area of the Bay of Plenty are coming under growing pressure as both population and horticultural activity increase. To avoid inadvertent over- allocation, Environment Bay of Plenty (EBOP) has commissioned GNS Science (GNS) to complete a ‘first-cut’ assessment of groundwater availability in the Paengaroa-Matata area (Figure 1.1). The area under investigation in this report extends between Maketu and Matata along the coast line and the northern surface catchment boundaries of Lake Rotoiti, Lake Rotoehu and Lake Rotoma (Figure 1.1).
This assessment is completed with a synthesis of geological information and hydrological data to estimate groundwater storage volumes and groundwater flows.
Groundwater availability is assessed here following steps used in a groundwater resource investigation of the Western Bay of Plenty area (White et al., 2008):
- identify geological units important to groundwater flow and model these units; - estimate rainfall on sub-catchments; - estimate rainfall recharge on sub-catchments; - estimate baseflow discharge from sub-catchments via streams; - estimate groundwater recharge to streams that is not available for allocation; - estimate ‘deep’ groundwater recharge that is potentially available for allocation; - estimate groundwater storage volumes; - identify wells at risk from salt water intrusion; - assess groundwater chemistry.
Groundwater availability for use is not estimated in this report because decisions on allocation policy are required by EBOP. This report does estimate the maximum available groundwater and these estimates should be a useful guide for groundwater allocation policies in the area. This report analyses groundwater levels and groundwater chemistry to assess salt water intrusion risk as this is a constraint on groundwater allocation. The report also recommends policy considerations for groundwater allocation.
2.0 GEOLOGY
2.1 Overview
The geology of the Paengaroa-Matata area (Table 2.1, a summary derived from a compilation of geological map boundaries held by Environment Bay of Plenty Meilhac 2009 and Appendix 1) consists of late Pliocene to Pleistocene sequence of volcanic rocks and volcanogenic sediments (Figure 2.1) derived from the southern Coromandel Volcanic Zone (CVZ) and from the Taupo Volcanic Zone (TVZ). In general, the study area is underlain by Mesozoic greywacke basement rocks and partially mantled by Rotoiti Pyroclastics. A prominent fault scarp forms the easternmost boundary of the model area.
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The Paengaroa-Matata area is centred on an upthrown block of the Urewera greywacke basement that outcrops in the Ohinepanea Hills. To the east and west of this upthrown block are two coastal fault-bounded basinal areas. Each of these coastal areas comprises distinct structural zones and stratigraphy. For the purpose of this report these areas are referred to as the western, central and eastern areas (Figure 2.2). The western area contains the Te Puke-Maketu basin, where sediments are interlayered with Mamaku Ignimbrite. The eastern area contains the Rangitaiki Plains, where sediments are interlayered with Matahina Ignimbrite. All areas have been covered by the Rotoiti Pyroclastics. The boundaries of these areas (Figure 2.2) are orientated to match regional structural features including:
• major regional faults of the Whakatane graben to the east (Figure 2.1);
• the only fault mapped on the 1:250,000 geological map (Healy et al., 1964);
• outcrop of greywacke (Figure 2.2) and possible basement high in the central area.
Lithological units within the study area are described below and the geology is summarised based on published information. All sources of geological information used in this report are from published literature, EBOP reports, geological maps and EBOP bore log records.
The names for stratigraphic units used in this report are those from published references. GNS Science has a GIS project that is revising the geological maps of New Zealand. The revised geological map which includes the Tauranga area (Leonard and Begg (in prep.)) uses new formation names for some formations. Therefore some formation names used in this report will be revised in geological maps of Leonard and Begg (in prep.).
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Table 2.1 Simplified stratigraphy of the central Bay of Plenty area. Stratigraphic Age (Ma) unit (Reference)
Tauranga Group Modern Beach Recent Sediments
Tauranga Group Holocene Holocene <0.01 Sediments (Environment Bay of Plenty, 1990) Sediments Rotoiti Pleistocene 0.061 Pyroclastics (Wilson et al. 2007)
Tauranga Group Late Pleistocene Pleistocene <0.078 Sediments Sediments (Briggs et al. 2005; Briggs et al. 1996)
Mamaku Pleistocene 0.22–0.24 Ignimbrite (Briggs et al. 2005; Nairn, 2002 ; Gravley et al. 2007)
Matahina Pleistocene 0.28 Ignimbrite (Nairn, 2002)
Manawahe Pleistocene 0.425 volcano (Nairn and Beanland 1989; Environment Bay of Plenty, 1990)
Tauranga Group Mid Pleistocene Pleistocene 0.46-0.95 Sediments Sediments (Nairn and Beanland 1989)
OTP Ignimbrite Papamoa Ignimbrite Pliocene 1.90-2.40 (no outcrop) (Briggs et al. 2005)
Otawa Volcanics Pliocene 2.5-2.9 (no outcrop) (Briggs et al 2005, CH2M Beca Ltd 1999)
Greywacke Mesozoic 100-130 basement
2.2 Brief description of geological units
A brief description of major geological units is provided here, from oldest to youngest.
2.2.1 Greywacke (Urewera Greywacke)
In this part of the North Island, greywacke is considered the basal rock unit. It is Mesozoic in age (100-130 My, Environment Bay of Plenty, 1990), well indurated and fractured rock. Greywacke here consists of banded argillite, alternating siltstones and sandstones, conglomerates and some fine-grained volcanic rocks (Environment Bay of Plenty, 1990).
This greywacke unit mostly outcrops outside the study area, to the east, on the eastern rim of the Whakatane graben. Within the study area the greywacke forms three inliers, south of Otamarakau (Figure 2.1), and surrounded by younger Rotoiti Pyroclastics. The origin of these greywacke inliers is still under debate although structurally, they are generally considered to represent allochtonous fault-bounded blocks disconnected from the main
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greywacke basement. For example Nairn and Beanland (1989) describe the inliers as “floating” in a medium of volcanic rock, and Kear (2004) considers the inliers to represent “stranded” blocks on the western limit of the Central Volcanic Region.
2.2.2 Otawa Volcanics
The Otawa Volcanics is a collective term for predominantly hornblende and biotite-phyritic basaltic andesite to andesite (with minor dacite) units. The Otawa Volcanics outcrop in the Western Bay of Plenty area and are exposed inmediately west of the study area, on the Papamoa Ranges (Briggs et al., 1996). Within the study area the Otawa volcanics have been downflaulted beneath the Papamoa Ignimbrite.
Originally, the Otawa Volcanics were mapped as the Beeson’s Island Volcanics by Healy et al. (1964) and incorporated into Miocene age (24 Ma - 5 Ma) rocks of the Coromandel Group (Skinner, 1967 and Skinner 1986). Beeson Volcanics are principally phyritic andesites of mid-Miocene age; this unit is comprised of pyroclastic and epiclastic breccias and comglomerates, flows and plugs (Adams et al. 1994). The type section for Besson Volcanics is on the southern side of the Coromandel harbour where they reach 2750 m thick (Adams et al. 1994). Dating of the Otawa Volcanics revealed much younger ages of 2.54-2.95 Ma (Stipp 1968), and thus this unit is not included in the Coromandel Group. The name Otawa Volcanics was reassigned by Briggs et al. (1996) after the name of the trig station within the Papamoa Ranges. Thus andesite and breccias mapped as Beeson Volcanics in Environment Bay of Plenty (1990), and exposed west of Te Puke are now known as Otawa Volcanics (Briggs et al. 2005). Berryman et al. (1998) also used the term Beeson Volcanics but these are now known as Manahawe volcano.
The total thickness of the Otawa Volcanics is estimated to be no more than 2 km (White et al. 2008) and they have been buried since deposition by younger ignimbrites derived from TVZ such as Mamaku Ignimbrite and Rotoiti Ignimbrite, and by Late Pleistocene sediments. The thickness to Otawa Volcanics within the study, east of Te Puke, is estimated to be less than 150 m.
2.2.3 OTP Ignimbrites
The Papamoa Ignimbrite is of Late Pleistocene age (2.40 to 1.90 My, Briggs et al. 2005) and stratigraphically above the Otawa Volcanics. It outcrops west of Te Puke, on the Papamoa Ranges; and has been downfaulted to the east, beneath the Paengaroa-Matata area. The Papamoa Ignimbrite consists of multiple lava flows and interbedded fall deposits of localised source (Briggs et al. 2005). They are predominantly dacitic in composition, but also contain juvenile scoria and pumice clasts which range widely in composition from basaltic andesite to rhyolite (Briggs et al. 2005).
2.2.4 Tauranga Group Sediments - Pleistocene
In the coastal cliffs of the Matata area, marine siltstones and sandstones of Castlecliffian faunas pass upwards into tuffaceous silts, greywacke gravels and conglomerates. This sedimentary sequence reaches thicknesses of 300 m and is unconformably overlain by Matahina Ignimbrite (Nairn and Beanland 1989). Drill logs approximately 3 km west of Matata indicate thicknesses of at least 125 m of non-marine tuffaceous sediments (Nairn and Beanland 1989). Biotite tuffs of 0.62 My age (Mid-Pleistocene) overlie macrofauna of 0.46-
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0.95 My and Manawahe volcano lavas of 0.425 My age overlie Castlecliffian sediments (Nairn and Beanland 1989).
The coastal plains immediately to the south and southeast of Maketu headland, described as the Pongakawa Plains by CH2M Beca Ltd (1999) and the Te Puke Plains by Environment Bay of Plenty (1990), are infilled by unwelded ignimbrites, fluviate silts, sands and gravels with interbedded pumiceous tuffs. On average these sediments are reported to depths of 50 m to 100 m above welded ignimbrites (CH2M Beca Ltd 1999). These infilling sediments reach 150 m deep at EBOP well 305, south-southwest of Maketu Township (CH2M Beca Ltd 1999).
2.2.5 Manawahe volcano
East of the study area, about 8 km northeast of Manawahe township on the west flank of the Whakatane Graben, is a circular-shaped outcrop representing the eroded remnants of the andesitic to dacitic 0.425 My Manawahe volcano (Duncan 1970; Broughton 1988). Originally correlated with the Beeson’s Island volcanics due to its likely Miocene age (Healy et al. 1964), this volcano was apparently located on the ancient volcanic front, and subsequently partially buried by the Matahina Ignimbrite flow from Okataina (Kear 2004).
2.2.6 Matahina Ignimbrite
Matahina Ignimbrite outcrops are confined to the east of the Paengaroa-Matata area, where it is downfaulted into the Whakatane Graben. Matahina Ignimbrite is a moderately crystal rich, compositionally zoned multiple flow unit erupted from the eastern portion of Okataina caldera complex (Burt et al. 1998). Matahina Ignimbrite overlies an intervening sequence of pyroclastics including the 340 ka Whakamaru Group ignimbrites. Age determinations for the Matahina Ignimbrite yield argon-argon ages of approximately 280 ka (Houghton et al. 1995) and fission track ages of approximately 280 ka (Nairn 1989).
Reported thickness for the Matahina Ignimbrite varies from 5 m to 200 m, and this unit thins out west of the Whakatane Graben (Bailey and Carr 1994). Isopach maps of the Matahina Ignimbrite show a decrease in thickness from approximately 50 m near Matata to less than 15 m, 10 km to the west (Bailey and Carr 1994). West of Matata, the Matahina Ignimbrite rests conformably on 300 m of Pleistocene tuffaceous, shallow-water marine and estuarine Huka Group sediments (Bailey and Carr 1994). These sediments in turn overlie greywacke pebble conglomerates (Bailey and Carr 1994). Matahina Ignimbrite also onlaps lava domes, for example Manawahe and Awakaponga approximately 10 km southwest of Matata. Matahina Ignimbrite has been drilled at shallow depths of 100 m - 200 m (Nairn 2002) in the Kawerau Geothermal Field. Matahina Ignimbrite is mantled by Rotoheu Ash and Rotoiti Pyroclastic deposits.
2.2.7 Mamaku Ignimbrite
The Mamaku Ignimbrite is a massive, soft, pink to grey coloured deposit with conspicuous subhorizontally flattened soft pumice up to 30 mm or more in length (Environment Bay of Plenty 1990).
Mamaku Ignimbrite was erupted during the formation of Rotorua Caldera 220 ka to 240 ka. Its outflow sheet forms a fan north, northwest and southwest of Rotorua, capping the
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Mamaku-Kaimai Plateau (Milner et al. 2003) which dips 1-2˚ beneath the Maketu Basin (CH2M Beca Ltd 1999). Pumice clasts range in composition from dacite to rhyolite and the internal stratigraphy of the Mamaku Ignimbrite is divided into a basal sequence and three main ignimbrite units: lower, middle and upper (Milner et al. 2003; Briggs et al. 2005). The intra-caldera thickness of Mamaku Ignimbrite has been estimated as greater than 1 km beneath Rotorua City (Wood 1992).
Mamaku Ignimbrite outcrops mostly west of Te Puke, outside the study area (Briggs et al. 2005; Briggs et al. 1996; CH2M Beca Ltd 1999). Briggs et al. (2005), Briggs et al. (1996) and CH2M Beca Ltd (1999) also report Mamaku Ignimbrite underlying the Late Pleistocene sediments, thus Mamaku Ignimbrite possibly extends further east, lensing into sediments and underlying Rotoiti Pyroclastics.
Most of the upper part of the Mamaku Ignimbrite is unwelded and eroded (Selby and Lowe 1992) and becomes progressively harder with depth. The outflow sheets of the Mamaku Ignimbrite form a fan that caps the Mamaku-Kaimai Plateau. The Mamaku Ignimbrite has an average thickness of 72.5 m (Milner et al. 2003). It thins westwards towards the Hauraki rift and east of Rotorua, Mamaku Ignimbrite outcrop extends as far as Lake Tarawera (Nairn 1989). Drill logs northeast of Rotorua, in the Guthrie Graben, report Mamaku Ignimbrite of 120 m in thickness (Wood 1992). Approximately 5 km south of Te Puke (west of the study area), the log of well 1564 indicates Mamaku Ignimbrite thickness up to 180 m thick (CH2M Beca Ltd 1999). Beneath the Maketu Basin however, underlying Maketu Ignimbrite is approximately 70 m to 80 m thick (CH2M Beca Ltd 1999 p4). Drill logs from the Pongakawa reinjection well ESZ7 (CH2M Beca Ltd 2005) record alluvium sand and gravels to 126 m, overlaying “Mamaku?” Ignimbrite from 126 m to at least 150 m depth. Lithological interpretations of adjacent well ESZ8 also record Mamaku Ignimbrite below 84 m. These depths are also consistent with nearby Pongakawa groundwater log records of well 3289 where “grey ignimbrite” was recoded below 116 m depth, and also in well 3705 where “hard ignimbrite” was recorded at 121 m depth. To the west, just outside the study area a drill hole records Mamaku Ignimbrite thickness of 120 m (Milner et al. 2003).
2.2.8 Rotoiti Pyroclastics
The Rotoiti Pyroclastics and associated Rotoheu Ash are products of the youngest caldera- forming eruption from the Okataina Volcanic Centre. The Okataina Caldera complex ages range between 35.1 My and 75.1 My (Burt et al. 1998) with the most recent age determinations for the Rotoiti Pyroclastics at 61 ka (Wilson et al. 2007). Rotoiti Pyroclastics includes Rotoiti Ignimbrite, which is a voluminous, compound, non-welded ignimbrite that outcrops north and northeast of the Okataina Volcanic Centre. The deposits consist of unsorted pumice clasts, crystals and lithic fragments in a fine-grained ash matrix (Schmitz and Smith 2004). Outcrops of the Rotoiti Pyroclastics are widespread between Rotorua and the Bay of Plenty (Schmitz and Smith 2004). Rotoiti Pyroclastics are underlain, interbedded and overlain by the multiply-bedded Rotoehu airfall ash (Burt et al. 1998). Burt et al. (1998) subdivide the Rotoiti Pyroclastics into 1) biotite-free plinian ash beds 2) biotite-free ignimbrite, 3) biotite-bearing ignimbrite and 4) biotite-bearing airfall.
The Rotoiti Pyroclastic sequence comprises a basal unit up to 4 m thick, in localities proximal to source, and overlying unwelded pyroclastic flow units that are greater than 50 m thick (Schmitz and Smith 2004). As these represent two out of four units comprising the Rotoiti
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eruption, a minimum thickness of 50 m is assigned to Rotoiti Pyroclastics in the geological model.
2.2.9 Tauranga Group Sediments - Holocene
To the west, stream and coastal alluvium of Holocene age consists predominantly of sands, silts, clays and minor peats less than 20 m thick (CH2M Beca Ltd 1999; Environment Bay of Plenty 1990).
2.2.10 Other units
Stratigraphic tephra marker units (Table 2.2) within the 65 ka to 0.7 ka range, erupted from the Okatainia Volcanic Centre, extend over a large portion of the study area (Nairn 2002). As the individual thickness of these units however is less than 10 m they have been included, for the purpose of the geological model, within Rotoiti Pyroclastics.
Table 2.2 Okatainia Volcanic Centre tephra marker units.
Tephra Unit Age Thickness of unit within study area (ky) Rotoheu 65 3 – 10 m Te Rere 21 0.25 – 1 m Okareka 18? 0.4 – 1 m Rerewhaikaaitu 15 0.2 – 1 m Rotorua 13.5 0.2 – 1 m Waiohau 11 0.2 – 2 m Rotoma 9 0.5 – 3 m Whakatane 5 0.1 – 1 m Kaharoa 0.7 0.1 – 1 m
2.3 Drill logs
EBOP holds a database containing driller’s log records from about 260 groundwater wells within the study area (Figure 2.3). These logs are analysed to obtain additional constraints on formation thicknesses and depths to greywacke basement.
2.3.1 Northwest drill logs
Surface geology in the northwest of the study area is dominated by Late Pleistocene and Holocene sediments. Groundwater wells from this area are up to 180 m in depth and log records indicate mostly volcaniclastic sediments (Figure 2.4). Drillers also record “rhyolite” and “ignimbrite”. Wells 951 (Total Depth, TD=114 m), 1528 (TD=144 m) and 2589 (TD=75 m) for example record the thickest sequences of ignimbrite and rhyolite. In well 951, “soft rhyolite” below 86 m is overlaid by “clay, layered silt, pumice and sands”. In well 1528, “clay and pumice sands” to 54 m overlie rhyolite and in well 2589 ignimbrite is recoded below 3 m depth. Other wells also record ignimbrite: well 645 (TD=180 m) below 162 m, well 3289 (TD=132 m) below 116 m and well 3705 (TD=124 m) below 121 m. A section trending north- south, south of Maketu, along Wilson Road, Paengaroa shows Late Pleistocene sediments underlain by “welded to partially welded ignimbrite” inferred to be Mamaku Ignimbrite (CH2M Beca Ltd 1999). Mamaku Ignimbrite lenses towards the north, into Late Pleistocene sediments, and at approximately 4 km south of Paengaroa, it is interpreted in the range from
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60 m to 150 m depth. Approximately 2 km north of Paengaroa, Mamaku Ignimbrite is at 100 m depth and less than approximately 10 m in thickness.
2.3.2 Northern drill logs
The northern central area is characterised by inliers of outcropping basement rocks. Immediately west of the inliers, groundwater well logs drilled to 160 m depth intersect mostly volcaniclastic sediments that include pumice sands, gravels and silts (Figure 2.5). Wells 10414 (TD=150 m), 10413 (TD=90 m) and 2680 (TD=160 m), intersect at shallow depths (less than 6 m) approximately 80 m to 140 m thickness of ignimbrite. At well 10414 and well 2680 ignimbrite overlies sands and gravels, and well 644 (TD=136 m), to the north, reports 10 m thickness of “rhyolite” in the range 70 m - 80 m depth, interbedded in “sands gravels and pumice”.
Greywacke is only reported in well logs further east. For example well 10052 (TD = 59 m) intersects “silt, pumice, sands and gravels” to 58 m before reaching “greywacke rock”. Well 830 (TD = 117 m) reports “layered soft and firm sands silt pumice and gravels” to 109 m and “bedrock” to 117 m, which could suggest basement at this depth. Well 3302 (TD=114 m) has 54 m of “various silts, sands, pumice, gravels” above “hard dark grey rock”. Thus the available information from well logs would suggest that greywacke basement extends beneath this area, and lies at a depth below 50 m to 100 m beneath the cover of recent Rotoiti Pyroclastics.
2.3.3 Eastern drill logs
Matahina Ignimbrite outcrops over most of this area and most groundwater well logs report volcaniclastic sediments including pumice, sands and gravels (Figure 2.6). For example well 10151 reports “mud, pumice sand” overlying “grey and brown rhyolite” below 128 m. Well 406, situated on a deeply incised valley west of Pokowai Road, reports clay, sands, gravels and pumice to 79 m, rhyolite from 79 m to 116 m, and fine sandstone to 146 m. Further north, well 10009 (TD=150 m) intersects silt, sand and pumice interbedded with a “firm/hard brown ignimbrite” from 32 m to 44 m, and “green/grey ignimbrite” below 114 m.
Log records of three wells drilled further to the northeast describe lithologies that suggest the presence of basement greywacke of the area, namely: “firm rock” 88 m to 148 m in well 3564 (TD=148 m), “hard brown rock” 27 m to 78 m in well 3257 (TD=78 m) and “greywacke gravel” 45 m to 48 m in well 2962 (TD=48 m). Other wells drilled in the coastal areas of the northeast indicate volcanic sediment thicknesses of at least 100 m, for example:
• well 10850 with pumice, sand, silt and charcoal layers to 201 m;
• well 10680 with fossiliferous mudstone, sands and gravels to 48 m; and
• well 3024 with clay sands and gravels to 78 m.
2.3.4 Southern drill logs
Rotoiti Pyroclastics cover most of the southern portion of the study area. Rotoiti Pyroclastics overlie Mamaku Ignimbrite in the southwest and Matahina Ignimbrite to the southeast, however the lateral extent of these underlying units is poorly constrained by log records (Figure 2.7). For example, drill logs from wells south of Pongakawa Valley drilled to depth of
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up to 111 m report mostly volcaniclastic sediments containing mainly pumice sands and gravels. Well 1145 (TD=110 m) reports “grey green rhyolite” from 28 m to 106 m, with pumice and sands above and below. Well 2799 (TD=132 m) and well 3295 (TD=81 m) record volcaniclastic sediments “sands, pumices and silts, gravels” overlying “hard grey ignimbrite” below 84 m and “grey rhyolite” below 76 m, respectively.
2.3.5 Summary
EBOP groundwater well logs in the northwest of the Paengaroa-Matata area consist mostly of volcaniclastic sediments and minor ignimbrite. This area comprises a down-faulted basin, known as the Te Puke basin, and underlying lithologies are exposed west of the faulted boundary, outside the study area. In the Te Puke basin Pleistocene sediments are interlayered with Rotoiti Pyroclastics (50 m - 100 m thick) and Mamaku Ignimbrite (80 m thick). These are in turn underlain by Otawa Volcanics, resting above the 350 m deep greywacke basement. Crude estimates based on known stratigraphic thicknesses suggest a thickness of 200 m for the Otawa Volcanics and 150 m for the Pleistocene sedimentary sequence containing the Mamaku Ignimbrite and Rotoiti Pyroclastics.
Drill logs from the northern area surrounding the greywacke inliers of the Ohinepanea Hills suggest that the basement is approximately 50 m to 100 m below the surface (e.g. wells 830, 3302, 3564 and 10059). This is consistent with the 50-100 metre thickness range of the Rotoiti Pyroclastics, and also with geophysical gravity modelling (Davey et al. 1995).
Northeast of the Paengaroa-Matata area, wells as deep as 200 m intersect mostly volcaniclastic sediments and minor ignimbrite. This is consistent with Nairn and Beanland (1989) who report sediment thickness of up to 300 m near Matata, unconformably overlying Matahina Ignimbrite. Matahina Ignimbrite varies in thickness from 15 m to 50 m, and thins from east to west (Bailey and Carr 1994). Manawahe volcano deposits are onlapped by Matahina Ignimbrite. The combined thickness of volcanic-sedimentary sequences identified from groundwater well logs indicate the basements rocks in the northeast of the Paengaroa- Matata area are at least approximately 400 m deep.
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Table 2.3 Stratigraphic summary by geographical area.
Unit Geographical Area Western Central Southern Eastern Modern beach/Holocene sediments <20 m (9) ? - Rotoiti Pyroclastics 50-100 m (4,6) 50-100 m (4,6) 50-100 m (4,6) 50-100 m (4,6) Late Pleistocene sediments 50-150 m (9) ? - - Mamaku Ignimbrite <120 m (Av 70-80 m) (5, 7,9) - ? - Matahina Ignimbrite - - ? 50 To 15 m (3) Manawahe volcano - - - Lavas overlie Mid-Pliocene, Castlecliffian sediments (2) 100-200 m Mid Pleistocene sediments 50-150 m (10) - - 300 m (2,3) Papamoa Ignimbrite <100 m (8) - - - Otawa Volcanics >150 m (6,1) - - - Total Thickness(*) >400 m? 50-100 m? 50-100 m (4,6) >550 m? Basement Depth(#) 350 m 50-100 m (10) 50-100 m (4,6) 350 m (2)
(*)Estimated thickness based on published thicknesses. (#) Depth to basement from published sources. (1) Adams et al., 1994; (2) Nairn and Beanland, 1989; (3) Bailey and Carr, 1994; (4) Schmitz and Smith, 2004; (5) Milner et al., 2003; (6) Environment Bay of Plenty, 1990; (7) Nairn, 2002; (8) White et al., 2008; (9) CH2M Beca Ltd, 1999; (10) Environment Bay of Plenty log records, 2007.
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3.0 HYDROGEOLOGY
3.1 Hydraulic properties
Important geological units in the Paengaroa-Matata area (Section 2.2 and Section 4.5) include, from oldest to youngest:
• Greywacke (Urewera Greywacke);
• Minden-Otawa volcanics;
• Tauranga Group Sediments – Pleistocene;
• Manawahe volcano;
• Matahina Ignimbrite;
• Mamaku Ignimbrite;
• Rotoiti Pyroclastics;
• Tauranga Group Sediments – Holocene.
A summary of hydraulic properties described in the literature is presented in Table 3.1. Transmissivities of the identified aquifers are quite variable, with 10 to 850 m2/d for sediments, up to 800 m2/d for ignimbrite rocks and up to 1400 m2/d for rhyolite.
Table 3.1 Summary of aquifer hydraulic properties.
Unit name Transmissivity Storativity Reference (m2/d) Minden Rhyolite 500 to 1400 2x10-4 to 7x10-4 Gordon (2001) Minden Rhyolite 130 to 150 6 x 10-5 to 1.7 x 10-3 CH2M Beca Ltd (July 2003) OTP Ignimbrites 350 to 800 2.5x10-3 to 7.5x10-4 Gordon (2001) Mamaku Ignimbrite 600 4 x 10-3 Reeves et al. (2005) Tauranga Group Sediments 850 4.5x10-2 KRTA (1982), mean from pump test Tauranga Group Sediments 10 to 100 no data Gordon (2001) Tauranga Group Sediments 86 to 260 1 x 10-3 CH2M Beca Ltd (March 2005) Volcanic/alluvial 350 3.3 x 10-4 Pattle Delamore Partners (2007) Tauranga Group Sediments 1800 7 x 10-4 Bright Spark Group (2004)
Pump tests in the Paengaroa area are summarised by Pattle Delamore Partners (2007), presumably reporting GWS Ltd (2007), including:
• pump tests of Coach bore 1, Coach bore 2, Saga and Omega wells near Paengaroa have geometric averages of parameters from pump test analyses as follows: - transmissivity 350 m2/day; - storage coefficient 3.3 x 10-4; - vertical leakage coefficient 3.3 x 10-4 day-1.
• water-bearing strata include volcanic lava and airfall deposits, some of which may have been reworked by alluvial processes;
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• long term drawdown effects may eventually be transmitted through all the deep water bearing zones;
• some bores are screened over more than one water-bearing zone.
A 24 hour pump test for the La Vigna well (GWS Ltd 2008) near Paengaroa, which is an open hole from 209.5 m to 370 m in ignimbrite, clay layers and pumiceous ignimbrite, has:
2 • transmissivity 97 m /day;
• storage coefficient 0.04 to 0.1.
Groundwater level during pumping of the La Vigna well is estimated at 6 m above sea level to 4 m below sea level.
A 24 hour pump test for JB Family Trust (Waterline Engineering Consultants 2007) in a well near Pongakawa found:
• aquifer in confined sands, gravel and pumice 107 m to 131 m deep;
2 • estimated transmissivity 200 m /day;
• storativity 0.001;
Estimated groundwater level during pumping of the JB Family Trust well is 0.3 m above sea level.
A 24 hour pump test at Domain Park, Paengaroa, in gravels (Bright Spark Group 2004) calculated:
2 • transmissivity 1800 m /day;
• aquifer storativity 0.0007.
Groundwater level during pumping of the Domain Park well is estimated as -16.5 m. i.e. below sea level.
A 24 hour pump test of the RH Hall well (Ken Thorpe Geoconsultancy 2007) estimates;
2 2 • transmissivity 145 m /day to 415 m /day;
• storativity 0.00168 or 0.000168.
Lithology in the well includes pumiceous sands and pumiceous sandy gravels.
Groundwater level during pumping of the RH Hall well is an estimated -44.6 m, i.e. below sea level.
CH2M Beca Ltd (2005) completed a step-drawdown test of well ES28 located on Maniatutu Road. This well has 24 m of screen in the depth interval 60 m to 90 m. The well takes water from sand, gravel and ignimbrite. CH2M Ltd (2005) calculate:
2 • average transmissivity of approximately 260 m /day;
• storativity of 0.001.
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CH2M Beca Ltd (2000) pump tested a well at Pongakawa that takes water from an unscreened section of well between 57 m and 132 m deep. Lithologies in the uncased section of the well include pumiceous sand, silt, gravel and ignimbrite. They found, from analyses of the pump test:
2 • geometric mean transmissivity approximately 650 m /day.
They also found, from analyses of drawdown in the pumped well and monitoring wells:
• geometric mean of transmissivity from observations in the pumped well approximately 350 m2/day;
• geometric mean of transmissivity from observations in monitoring wells approximately 1800 m2/day.
3.2 Groundwater levels 3.2.1 Piezometric map
Groundwater elevation contours are calculated from water level data collected at 111 wells around the Paengaroa-Matata area (Figure 3.1)
Groundwater elevation contours from wells in the Paengaroa-Matata area (Figure 3.1) show that the direction of groundwater flow is generally to the north or northeast (with the exception of the northeast part of the area in the vicinity of Lake Rotorua) and towards the coast. Note however, that groundwater contours in the eastern area are constrained by fewer bore measurements.
Well ID and groundwater level for ten bores with estimated groundwater levels below sea level are listed below. In the Pukehina-Pikowai coastal area for example calculated groundwater elevations are up to 12 m below sea level and at Pongakawa they are 35 m below sea level (Figure 3.1).
• 1218 -11.5 m;
• 1520 -0.2 m;
• 2553 -7.15 m;
• 2956 -12 m;
• 3206 -2 m;
• 3236 -2.7 m;
• 10186 -4.2 m;
• 10669 -24 m;
• 10856 -35 m;
• 10872 -3.5 m.
These reported levels may be due to drawdown during pumping and may not reflect static water level. A risk of salt water intrusion to the aquifers is indicated by groundwater levels below sea level.
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Therefore some wells in the coastal areas may be at risk for salt water intrusion. However, ground and water level estimates used for calculating groundwater elevations should be checked by a more accurate survey before conclusions are drawn about the risk of salt water intrusion.
3.2.2 Groundwater level trends over time
Groundwater level trends over time in the Environment Bay of Plenty region, including wells in the Paengaroa-Matata area, are analysed by Zemansky (2006). Some of the groundwater levels that are part of Zemansky’s (2006) analysis are located in the Paengaroa-Matata area (Figure 3.2, Table 3.2).
According to Zemansky’s (2006) assessment, groundwater level trends over time are generally ‘horizontal’ (i.e. not systematically increasing or systematically decreasing) over time in the Paengaroa-Matata area (Table 3.3).
Well 2822 is the only well with a “falling” (decreasing) trend in groundwater level in the Paengaroa-Matata area (Table 3.2), with an average decrease (1990 to 2006) of 0.061 m/year. Groundwater levels in this well were about 7 m deep in 1990 and were about 8 m deep in 2006 (Zemansky 2006). The well is screened (or open hole) in the depth range 104.85 m to 121.9 m (Table 3.2) and the lithology of the screened (or open hole section) is not recorded in the driller’s log.
Data outliers are not considered an option to explain the decreasing trend observed in well 2822. The primary sources of this variability might be such factor as climate-related annual cycles and/or a result of measurements being made when an installed well pump was in operation in or around the well and would have interfered with the natural static water level.
Although rare, long-term decline in groundwater level due to current groundwater abstraction may be a possibility in the Paengaroa-Matata area.
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Table 3.2 Wells with groundwater level information in the Paengaroa-Matata area, from Zemansky (2006).
Water Level Well Information Well ID Surname Town Area NZMG Coordinates TOC AMD Total Depth Open Interval Geology (m) (m) Easting Northing
0410 Bowyer Paengaroa Te Puke-Maketu 28111000 63670000 - 196.6 118-196.6 Pumice 0951 Paengaroa North K Trust Paengaroa Te Puke-Maketu 28109000 63712000 - 114.3 86.3-114.3 Rhyolite 1520 Tapsell Family Trust Maketu Te Puke-Maketu 28147800 63741100 - 74 50-74 Pumice gravel 2822 Winters Pongakawa Te Puke-Maketu 28162200 63681100 - 121.9 104.85-121.9 Ignimbrite
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Table 3.3 Summary of groundwater level statistics in the Paengaroa-Matata area, from Zemansky (2006).
Summary Water Level Statistics Well ID Deleted Count Data Period Min Median Mean Max Stdev Linear Fit Visual Assessment Trend Outliers Comments LR Slope r2 Deep Shallow
410 0 20 1998-2006 35.40 35.99 35.98 36.69 0.38 -0.0218 0.0161 Horizontal 951 1 55 1990-2006 9.08 9.90 10.10 13.85 0.84 -0.0452 0.0683 Horizontal X 1520 0 56 1990-2006 13.18 26.77 26.56 29.90 1.89 0.0569 0.0226 Horizontal X X 2822 0 57 1990-2006 5.94 7.43 7.55 9.52 0.77 0.0610 0.153 Falling
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3.3 Groundwater chemistry
3.3.1 Groundwater chemistry observations
Groundwater quality in the Environment Bay of Plenty region, including wells in the Paengaroa-Matata area, is analysed by Zemansky (2006). Some of the groundwater chemistry measurements that are part of Zemansky’s (2006) analysis are located in the Paengaroa-Maketu-Pukehina-Pongakawa area (Figure 3.3, Table 3.4, Table 3.5 and Table 3.6).
Sodium is the dominant cation in groundwaters in the area (Table 3.7) probably reflecting the marine-dominated origin of groundwater recharge.
Nitrate-nitrogen concentrations (Table 3.8) are highest in:
• well 4968, with a nitrate-nitrogen concentration of 5.115 mg/L in a 10 m-deep well near Pongakawa;
• well 3566, with a nitrate-nitrogen concentration of 9.25 mg/L in a 122 m-deep well near Pongakawa.
Median nitrate-nitrogen concentrations are elevated in shallow and deep wells as evidenced by concentrations of 5.115 mg/L NO3-N in well 4968 (10 m deep) and 1.782 mg/L NO3-N and 9.25 mg/L NO3-N in wells 1520 (screened at 50 m – 74 m deep) and 3566 respectively.
Similarly, low (less than 0.01 mg/L NO3-N) concentrations are found in other shallow (well 643) and deep (wells 410, 951, 2822) wells. Nitrate concentrations are low in shallow and deep wells where groundwater is naturally devoid of oxygen (in this situation nitrogen is predominantly in the form of ammonium rather than nitrate). As evidenced by shallow well 4968 there is sign of impact of nitrate on water quality of shallow wells in some areas.
Reasons for elevated nitrate-nitrogen concentrations in 2 deep wells (well 1520 and 3566), indicative of human impact, should be further investigated.
McIntosh and Gordon (2002) found, in a survey of shallow wells (i.e. wells less than 10 m deep) in the Environment Bay of Plenty region, that 12% of 112 wells sampled in the Paengaroa-Pongakawa-Maketu area had nitrate-nitrogen concentrations greater than the drinking water standard of 11.3 mg/L. McIntosh and Gordon (2002) class “27 wells in the ‘risk’ category and 13 unacceptable” for nitrate-nitrogen concentrations.
3.3.2 Groundwater chemistry trends over time
Groundwater quality trends over time in the Paengaroa-Matata area (Zemansky, 2006), Table 3.10, include:
• increasing pH in well 1520;
• increasing SO4 in well 1520.
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Table 3.4 Wells with groundwater chemistry information in the Paengaroa-Matata area, from Zemansky (2006).
Water Quality Well Information Well ID Name Town Area NZMG Coordinates Casing-Bore Geology Depth Easting Northing m 410 W & H Bowyer Paengaroa Te Puke-Maketu 2811200 6367000 118-196.6 Pumice 643 A & S Wakefield Pukehina Coastal Plain 2819600 6371600 7-9 Sand 951 Paengaroa North K Trust Paengaroa Te Puke-Maketu 2810900 6371200 86.3-114.3 Rhyolite 1520 W. Tapsell Maketu Te Puke-Maketu 2814700 6373800 50-74 Gravel 2822 RW & S Winters Pongakawa Te Puke-Maketu 2816200 6368100 104.85-121.9 - 3566 G & D Thacker - Te Puke-Maketu 2816600 6366200 70 - 122 - 4968 G & D Thacker Pongakawa Te Puke-Maketu 2817400 6365100 10 -
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Table 3.5 Median water quality values in the Paengaroa-Matata area, from Zemansky (2006).
Median Water Quality Values Well ID Sample Data Field Variables1 Major Cations2 Major Anions2 Silica2 Count Period Cond DO pH Temp Ca Mg K Na HCO3 Cl SO4 410 7 1994-2005 205 ND 6.80 15.3 5.5 3.4 3.4 24.0 102.5 10.0 6.6 76.5 643 10 1991-2004 435 0.5 6.60 16.3 15.9 10.2 5.7 59.3 234.9 28.1 14.4 73.0 951 11 1991-2005 493 4.4 6.90 24.8 28.6 10.4 2.6 63.5 289.1 21.6 0.3 93.1 1520 10 1991-2005 313 4.5 6.55 22.1 8.0 6.1 7.9 48.6 133.0 26.8 2.2 98.0 2822 11 1991-2005 341 3.2 6.60 18.1 7.9 7.7 4.2 49.5 178.1 19.8 0.6 91.2 3566 5 1997-2005 185 ND 6.9 15.1 7.1 3.3 7.1 15.8 34 15.7 4.0 84.6 4968 3 2002-2005 212 ND 6.60 16.4 7.5 3.3 3.5 18.5 25.9 20.1 6.3 88.4
1 Units for "Cond" (conductivity), "DO" (dissolved oxygen), pH, and "Temp" (temperature) are uS/cm, mg/L, units, and oC, respectively. 2 Units for major cations and anions and for silica are mg/L.
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Table 3.6 Maximum water quality values in the Paengaroa-Matata area, from Zemansky (2006).
Max Concentrations Well ID Samples Field Variables1 Major Cations2 Major Anions2 NZDWS - 2 Cond DO pH Temp Ca Mg K Na HCO3 Cl SO4 Silica TDS 1000 - 7.0-8.5 Cool - 200 - 250 250 - 100-300 as CaCO3 410 7 213 0.00 6.60-7.20 15.9 7.5 4.0 7.3 25.4 103.8 11.2 6.8 76.8 643 10 577 0.60 6.40-6.80 16.7 26.7 14.9 9.0 65.7 247.7 37.2 44.9 76.0 951 11 613 8.10 6.70-7.40 54.7 62.0 21.0 5.4 150.0 312.3 47.5 4.5 139.0 1520 10 427 4.90 6.30-7.00 23.3 11.2 8.3 11.0 73.3 207.4 33.0 5.7 108.0 2822 11 358 6.10 6.30-7.00 18.2 10.5 8.2 5.6 52.7 191.5 23.2 4.0 93.4 3566 5 224 0.00 6.20-7.10 16.8 10 4.7 8.9 19.2 46.7 19.5 10.9 97.0 4968 3 215 0.00 6.30-6.70 16.6 8.7 4.1 8.0 25.9 53.8 21.6 7.6 92.6
1 Units for "Cond" (conductivity), "DO" (dissolved oxygen), pH, and "Temp" (temperature) are uS/cm, mg/L, units, and oC, respectively. 2 Units for major cations and anions and for silica are mg/L.
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Table 3.7 Groundwater quality sample summary in the Paengaroa-Matata area, from Zemansky (2006).
Groundwater Quality Sample Summary1 Well ID Water Type CBE Calc TDS Town Area Coordinates Primary2 Geology (%) (mg/L) Easting Northing Cation Anion
410 Na-HCO3 -6.01 314 Paengaroa Te Puke-Maketu 2811200 6367000 Na HCO3 Pumice
643 Na-HCO3 -1.37 536 Pukehina Coastal Plain 2819600 6371600 Na HCO3 Sand
951 Na-Ca-HCO3 -1.74 605 Paengaroa Te Puke-Maketu 2810900 6371200 Na HCO3 Rhyolite
1520 Na-HCO3-Cl 3.20 431 Maketu Te Puke-Maketu 2814700 6373800 Na HCO3 Gravel
2822 Na-HCO3 -2.71 456 Pongakawa Te Puke-Maketu 2816200 6368100 Na HCO3 -
3566 Na-Ca-HCO3-Cl 9.24 266 - Te Puke-Maketu 2816600 6366200 Na HCO3 -
4968 Na-Ca-Cl-HCO3 11.96 267 Pongakawa Te Puke-Maketu 2817400 6365100 Na Cl -
1 Median values from monitoring data provided by EBOP and the NGMP database are entered into Version 4 of AquaChem computer program. "CBE" column indicates charge balance error and "Calc TDS" indicates total dissolved solids calculated by AquaChem from median values. 2 Shading indicates primary cation not sodium (i.e. Ca) and primary anion not bicarbonate (i.e. Cl).
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Table 3.8 Median water quality values for nutrients and bacteria in the Paengaroa-Matata area, from Zemansky (2006).
Median Water Quality Values1 Well ID Nutrients2 Bacteria3
NH3-N NO2-N NO3-N PO4-P TP Entero F_Coli 410 0.070 0.001 0.004 0.008 0.009 ND ND 643 0.105 0.001 0.009 0.409 0.425 18 4 951 0.152 0.001 0.001 0.116 0.325 ND ND 1520 0.004 0.001 1.782 0.071 0.073 ND ND 2822 0.032 0.001 0.005 0.183 0.244 ND ND 3566 0.010 0.001 9.250 0.172 0.172 6 1 4968 0.020 0.001 5.115 0.157 0.156 ND ND
1 Median levels calculated by Excel NGMP calculator program (Daughney, 2005) for 36 variables from 715 samples taken from 62 wells. "ND" indicates fewer than two results and value not determined. 2 Units for nutrients are mg/L as nitrogen ammonia, nitrite, or nitrate or phosphorus (phosphate or total identified as "TP"). 3 Units for bacteria are #/100 mL. "Entero" indicates enterococci and "F_Coli" indicates faecal coliform.
Table 3.9 Maximum nutrient and bacteria values in the Paengaroa-Matata area, from Zemansky (2006).
Max Concentrations1 Well ID Nutrients2 Bacteria3 NZDWS NH3-N NO2-N NO3-N PO4-P TP Entero F_Coli 0.3/1.5 0.2/3 11.3 - - <1 <1 410 0.120 0.002 0.090 0.028 0.028 - - 643 1.300 0.001 0.960 0.502 0.515 27 91 951 0.180 0.011 0.034 0.301 0.345 - - 1520 0.024 0.001 2.670 0.166 0.158 - - 2822 0.050 0.008 0.245 0.272 0.257 - - 3566 0.021 0.001 11.500 0.242 0.247 11 1 4968 0.026 0.001 10.200 0.245 0.247 - -
1 Maximum levels determined by Excel NGMP calculator program (Daughney, 2005) for 36 variables from 715 samples taken from 62 wells. "-" indicates no data. Shaded values indicate level in excess of "DWSNZ2005 (Drinking Water Standards for New Zealand 2005) maximum acceptable value (MAV) or guideline value (GV). 2 Units for nutrients are mg/L as nitrogen ammonia, nitrite, or nitrate or phosphorus (phosphate or total phosphorus identified as "TP"). Two GVs exist for ammonia (one at 0.3 mg/L related to possible effects on chloramine formation and a potential odor threshold at 1.5 mg/L). Shaded value for ammonia indicates in excess of the 0.3 mg/L GV. Bolded box for ammonia indicates also in excess of the 1.5 mg/L GV. 3 Units for bacteria are #/100 mL. "Entero" indicates enterococci and "F_Coli" indicates faecal coliform.
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Table 3.10 Groundwater quality trends in the Paengaroa-Matata area, from Zemansky (2006).
Groundwater Quality Trends1 Well ID Variable Median Trend p Value Slope Area Samples Sen's LR INCREASING TREND 1520 pH 6.55 0.04249 0.03868 0.02891 Te Puke-Maketu 10 1520 SO4 2.2 0.03957 0.24104 0.18321 Te Puke-Maketu 9
1 Variables with increasing or decreasing trends in each well (identified by well ID) as calculated by Excel NGMP calculator (Daughney, 2005). Units for median values are uS/cm for "Cond" (conductivity), units for pH, oC for "Temp" (temperature), and mg/L for all others. "Trend p Value" indicates statistical significance of result (all p values in this table are less than 0.05, indicating statistically significant at the 95 percent confidence level). "Slope" in units/year appropriate to the variable indicates magnitude of annual change over the of record. Values for both Sen's slope estimator and "LR" (linear regression) are listed. "Area" indicates area of region involved. "Samples" indicates number of sample values used in calculations.
4.0 PAENGAROA-MATATA GEOLOGICAL MODEL
A geological model of the Paengaroa-Matata area has been developed with aim of representing geological formations important to groundwater flows as three-dimensional surfaces and volumes.
4.1 Model area
The model area of the Paengaroa-Matata geological model is located between Paengaroa- Maketu to the west, Matata to the east, the northern shores of Rotorua lakes (Lake Rotoiti, Lake Rotoehu and Lake Rotoma) to the south, and the coast to the north (Figure 1.1)
The western boundary of the Paengaroa-Matata model area corresponds to the eastern boundary of the Western Bay of Plenty area model (White et al. 2008).
The Paengaroa-Matata geological model extends five kilometres outside the surface catchment boundaries. The added data points located between the geological model boundary and surface catchment boundary provide much needed edge control of extrapolation in the model. Excessive extrapolation near the edges of the buffer area are then removed from the final displays, leaving only a reasonable model of the main study area.
The model extents are as follows:
Easting Northing Elevation Maximum 2844800 6383800 1000 Minimum 2801000 6339300 -1000
The model cell size is 500 m in easting and northing coordinates and 10 m in the vertical dimension.
4.2 Methodology
A combination of GIS (ESRI ArcMap 9.2) and 2D and 3D modelling software (EarthVision, Dynamic Graphics Inc.) is used to construct the 3D hydrogeologic model.
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The Paengaroa-Matata 3D hydrogeological model is constructed from data extracted from summary geological maps (e.g. Figure 4.1), logs of water wells, published cross-sections and isopach maps. Additional information is sourced from the neighbouring Western Bay of Plenty geological model (White et al. 2008).
The modelling process starts with the generation of a simplified geological map (Figure 4.1), which is consistent with the existing Western Bay of Plenty geological model (White et al. 2008). This simplified geological map along with well logs, isopach contours (Figure 4.2) and other published geological data is assembled in GIS, exported into ASCII files and imported into EarthVision as scattered data.
EarthVision uses a minimum tension (minimum curvature) gridding technique to produce 2D and 3D grids from scattered data. The minimum tension technique is a bicubic spline algorithm which seeks to honour the input data when calculating an evenly spaced grid.
The surfaces of these geological units are modelled to construct the 3D hydrogeological model (Figure 4.3). Each geologic horizon is built sequentially as 2D grids representing the upper surface of each horizon. All the grids are then assembled in stratigraphic sequence to produce a 3D stratigraphic model.
4.3 Geological Units
Selection of hydrogeologically important units is crucial to the construction of the 3D model. A simplified stratigraphic sequence based on rock properties and inferred hydraulic characteristics is used for building a 3D geological model (Table 4.1).
Some units that are thin and/or have limited extent are combined with neighbouring units. For example “Modern Beach”, “Alluvium” and “Terrace deposits younger” units are included in the “Holocene Sediments”. The “OTP Ignimbrites” are combined with the “Otawa Volcanics” into a unit called “Minden-Otawa volcanics”, consistent with geological model layers in the Western Bay of Plenty (White el al. 2008).
Tauranga Group Sediments defined on geological maps are split into “Holocene Sediments” and “Pleistocene sediments” (Figure 4.1) in the Paengaroa-Matata 3D geological model.
Table 4.1 Simplified stratigraphic sequence adopted for the Paengaroa-Matata 3D geological model compared with the summary geological map nomenclature (Figure 4.1). The sequence is consistent with the summary geological sequence used in the Western Bay of Plenty geological model (White et al. 2008).
Unit name – geological map Unit name – Paengaroa-Matata 3D geological model Modern Beach Holocene Sediments Holocene Sediments Rotoiti Pyroclastics Rotoiti Pyroclastics Mamaku Ignimbrite Mamaku Ignimbrite Matahina Ignimbrite Matahina Ignimbrite Manawahe volcano Manawahe volcano Late Pleistocene sediments Pleistocene sediments Mid Pleistocene Sediments OTP Ignimbrite - incl. Papamoa Ignimbrite (no superficial outcrop) Minden-Otawa volcanics (no superficial outcrop) Otawa Volcanics (no superficial outcrop) Greywacke Greywacke
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A total of eight major geological units are identified. Selection of these major units is consistent with the existing Western Bay of Plenty geological model (White et al. 2008).
A comparison between geological units modelled in the Paengaroa-Matata geological model with the Western Bay of Plenty geological model is provided in Table 4.2.
Table 4.2 Geological units modelled in the Paengaroa-Matata model and the Western Bay of Plenty geological model.
Unit name Western Bay of Plenty Paengaroa-Matata model Geological Model Holocene Sediments √ √ Rotoiti Pyroclastics - √ Mamaku Ignimbrite √ √ Matahina Ignimbrite - √ Manawahe volcano - √ Pleistocene sediments √ √ Minden-Otawa volcanics √ √ Greywacke - √
Holocene Sediments, Pleistocene sediments, Mamaku Ignimbrite and Minden-Otawa volcanics are modelled in the Western Bay of Plenty geological model (White et al. 2008) and in the Paengaroa-Matata geological model. Data for these geological units are used for the computation of surfaces in the Paengaroa-Matata model. Rotoiti Pyroclastics, Matahina Ignimbrite, Manawahe Volcano and greywacke are not present in the Western Bay of Plenty geological model.
4.4 Topographic Surface
A Digital Elevation Model (DEM) is gridded with EarthVision to construct the topographic surface. Data for the DEM are derived from a LINZ topographic model and interpolated to a 10 x 10 metre cell grid. The estimated accuracy of this DEM is ±20 metres horizontally and ±10 metres vertically. These are considered the model horizontal and vertical accuracy, respectively.
The gridding process converts northing, easting and elevation scattered data into a regularly- spaced grid, which represents the discretization of the topographic surface. This surface is the top surface of the 3D geological model.
4.5 Stratigraphic Surface Construction
4.5.1 Greywacke
Greywacke outcrops in Ohinepanea, north of Otamarakau (Figure 4.1) and has been encountered in several drillholes within the model area (Section 2.3). In the TVZ area, greywacke is usually considered as bedrock (Section 2.2.1). Hence greywacke is set as the basement of this model. In the 3D geological model, only the top of the greywacke is modelled as the lowest surface of the model (Figure 4.4).
The greywacke surface is modelled as a continuous surface tilted in areas. The surface representing the top of greywacke is at ground level where greywacke outcrops at Ohinepanea (Figure 4.1) are mapped. The greywacke surface is modelled as 100 m below
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ground level in the central area of the Paengaroa-Matata model (Figure 2.2) where greywacke is below the ground surface. The greywacke surface is downfaulted towards the Whakatane graben to a depth of approximately 350 metres below ground level (Nairn and Beanland 1989) in the eastern area of the Paengaroa-Matata model (Figure 2.2). Depth to greywacke is estimated as 350 m (Environment Bay of Plenty 1990) in the western area of the Paengaroa-Matata model.
4.5.2 Minden-Otawa volcanics
For modelling purposes, and similarly to the Western Bay of Plenty geological model (White et al. 2008), the OTP Ignimbrites (incl. Papamoa Ignimbrite) and the Otawa Volcanics are combined into a single unit called the Minden-Otawa volcanics (Figure 4.5).
The Minden-Otawa volcanics do not outcrop in the model area, but are reported at depth in the western area (Section 2.2.2). With reference to literature (Adams et al. 1994; Environment Bay of Plenty 1990) and the existing Western Bay of Plenty geological model (White et al. 2008), the Minden-Otawa volcanics are modelled only in the western area of the Paengaroa-Matata model (Figure 2.2) as a 200 m to 250 m thick unit underlying the Mamaku Ignimbrite.
4.5.3 Pleistocene sediments
The Pleistocene sediments include the Mid and the Late Pleistocene Tauranga Group Sediments and are encountered predominantly on the western and the eastern areas of the Paengaroa-Matata model (Figure 4.6). This sedimentary sequence reaches thicknesses of 300 m and is unconformably overlain by Matahina Ignimbrite (Section 2.2.4).
In the model the Pleistocene sediments reach thicknesses up to 300 m in the eastern area of the Paengaroa-Matata geological model (Figure 2.2). In the western area, Pleistocene sediments thicknesses of 50 m to 150 m are inferred from Environment Bay of Plenty well logs (Section 2.3).
4.5.4 Manawahe volcano
The Manawahe volcano outcrops on the eastern area of the model (Figure 4.7). The Manawahe volcano is modelled in the Paengaroa-Matata geological model as a near- vertically-sided “plug” with a geographic extent the same as the extent of its surface exposure and a thickness ranging from 100 m to 200 m. This unit sits unconformably on Pleistocene Tauranga Group Sediments and is partially buried by the Matahina Ignimbrite flow from Okataina (Section 2.2.5).
4.5.5 Matahina Ignimbrite
Matahina Ignimbrite is exposed at the ground west of Matata, on the eastern area of the Paengaroa-Matata geological model and in the Whakahaupapa valley, west of Manawahe (Figure 4.8).
Reported thicknesses for the Matahina Ignimbrite vary from 5 m to 200 m, and this unit thins out west of the Whakatane Graben (Section 2.2.6).
Sourced from the Okataina caldera complex (Burt et al. 1998), Matahina Ignimbrite is
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modelled as “flooding” much of the area towards the coast and circling the Manawahe volcano already in place. In the Paengaroa-Matata model, thicknesses of the Matahina Ignimbrite vary from less than 50 m to over 200 m. The Matahina Ignimbrite thins out towards the west and southwest.
4.5.6 Mamaku Ignimbrite
Mamaku Ignimbrite has limited surface exposure in the Paengaroa-Matata model. The western side of the Paengaroa-Matata model is similar to the eastern limit of Mamaku Ignimbrite surface exposure.
Only one outcrop of Mamaku Ignimbrite is found on the western area of the model, north of Tokerau (Figure 4.9). Mamaku Ignimbrite is observed in wells ESZ7 and ESZ8 located in Pongakawa at depths of 126 m and 84 m below ground level, respectively (CH2M Beca Ltd 2005).
Considerable vertical variation is recorded in the Mamaku Ignimbrite in the literature (Section 2.2.7). Mamaku-Ignimbrite thicknesses up to 120 m (Milner et al. 2003) and 130 m (Environment Bay of Plenty 1990) are reported, with an average thickness of approximately 80 metres (Milner et al. 2003). In the Paengaroa-Matata geological model, the Mamaku Ignimbrite ranges between 100 m and 150 m in the outcropping area. The unit thins to less than 50 m towards the north where it is buried below Rotoiti Pyroclastics.
4.5.7 Rotoiti Pyroclastics
Rotoiti Pyroclastics cover much of the study area (Figure 4.10). The Rotoiti Pyroclastics are products of the youngest caldera-forming eruption from the Okataina Volcanic Centre (Section 2.2.8).
Thicknesses for the Rotoiti Pyroclastics are reported between 50 m and 100 m in the literature (Schmitz and Smith 2004; Environment Bay of Plenty 1990). Thompson (1970) describes a downwarping of the Mamaku Ignimbrite to form a shallow north-plunging syncline with its axis close to the Pongakawa Stream. This syncline is partially filled with Rotoiti Pyroclastics.
In the Paengaroa-Matata geological model the Rotoiti Pyroclastics vary in thickness between 50 m and 150 m. Thicknesses up to 300 m are modelled in the western area, which might be over estimated.
4.5.8 Holocene Sediments
Deposits of the Tauranga Group Sediments are exposed along the coast between Maketu and Otamarakau and extend inland south of Paengaroa and Pongakawa (Figure 4.11).
Thicknesses up to 20 m are reported for Holocene stream and coastal alluvium of the Tauranga Group Sediments.
EBOP well database includes 187 wells with detailed logs, 90 of which are located in areas where the Tauranga Group Sediments outcrop. For these 90 wells, Tauranga Group Sediments are the shallow unit, which is underlain by volcanic rocks. Detailed geological logs of these 90 wells have been processed to locate the interface between the Tauranga Group
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Sediments and underlying undifferentiated volcanic rocks. Excel functionalities are used to search for key words in the well log.
It is possible to estimate the depth to the bottom (or thickness) of Tauranga Group Sediments in 29 wells out of the 90 wells with detailed geological logs. For each well where the depth to the interface could be estimated, the well elevation above sea level (i.e. the ground level at the well location) is calculated using GIS functionalities to extract digital elevation model data and finally the elevation above sea level of the bottom of Tauranga Group Sediments is calculated by subtracting these two values (i.e. elevation of the bottom of the Tauranga Group Sediments = well elevation - depth to interface). Additional information is provided by 61 wells out of the 90, where minimum thickness for the Tauranga Group Sediments can be estimated. Many wells are too shallow or have not penetrated the bottom of the Tauranga Group Sediments to be able to provide information on locating the interface.
Estimates of Tauranga Group Sediments thicknesses are contoured using ArcMap 9.2 and SURFER Version 8.04 (Figure 4.2). The isopach contours generated in GIS for the Tauranga Group Sediments are exported to EarthVision and gridded to produce a 2D surface. This surface is subtracted from a smoothed version of the DEM to produce an elevation map of the bottom of the Tauranga Group Sediments.
4.6 Geological cross sections
Three cross sections (Figure 4.12) are generated from the geological model:
• Pongakawa (Figure 4.13);
• Otamarakau (Figure 4.14);
• Matata (Figure 4.15).
4.7 Volume calculations
The geological model is used to estimate the volume of rock (Section 4.7.1) in the Paengaroa-Matata area by catchment and by geological unit. Estimates of saturated rock volume are made (Section 4.7.2) from grids (Appendix 2) and groundwater level maps. Groundwater volume is estimated (Section 4.7.3) using saturated rock volume estimates and aquifer storativity estimates.
4.7.1 Rock volume
Volume estimates are made with two-dimensional grids representing each geological unit and polygons representing superficial catchments, as listed in Appendix 2.
Layer volumes are summarised in Table 4.3 as cubic kilometres of rock for units above the basement greywacke. Pleistocene sediments have the largest estimated volume, followed by the Minden-Otawa volcanics, followed by the Rotoiti Pyroclastics.
4.7.2 Saturated rock volume
Geological units are mostly saturated, except the Rotoiti Pyroclastics. Groundwater levels (Figure 3.1) are typically about 50 m below ground level over the area of the Rotoiti
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Pyroclastics and Rotoiti Pyroclastics are typically 50 m to 100 m thick. Therefore Rotoiti Pyroclastics are commonly dry. Saturated volumes for other units are likely to be:
• near 100% for Holocene sediments;
• near 100% for Pleistocene sediments;
• 100% for Minden-Otawa volcanics;
• near 100% for Mamaku Ignimbrite;
• near 100% for basement greywacke.
4.7.3 Groundwater volume potentially available for use
Groundwater volumes are estimated for four likely water-bearing geological units as rock volume (Table 4.3) times estimated storativity (from Table 3.1) with storativity as follows:
-3 • Holocene and Pleistocene sediments storativity 1 x 10 ;
-4 • Minden-Otawa volcanics storativity 1 x 10 ;
-4 • Manawahe volcano storativity 1 x 10 ;
-3 • Mamaku Ignimbrite storativity 4 x 10 ;
-3 • Matahina Ignimbrite storativity 4 x 10 .
Estimated groundwater volume (Table 4.4) is largest for Pleistocene sediments, Matahina Ignimbrite and Mamaku Ignimbrite.
4.7.3.1 Groundwater volume and groundwater supply prospects
Groundwater supply prospects are identified by the geological model and the piezometric map as primarily:
• Pleistocene sediments;
• Minden-Otawa volcanics;
• Mamaku Ignimbrite;
• Matahina Ignimbrite;
• basement greywacke.
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Table 4.3 Rock volume estimates.
Rock volume (km3), rounded No Surface Holocene Rotoiti Mamaku Matahina Manawahe Pleistocene Minden-Otawa TOTAL Catchment Sediments Pyroclastics Ignimbrite Ignimbrite volcano sediments volcanics 1 Hauone 0 1.4 0 0 0 0.8 0 2.2 2 Kaikokopu 0.2 0.1 0.2 0 0 3.2 6.7 10 3 Mimiha 0 1.3 0 4.3 0.7 16 0 23 4 Newdicks 0 0 0 0 0 0.4 0.4 0.8 5 Ohinekoao 0 0 0 0.9 0 2.8 0.0 3.8 6 Ohinepanea 0 0.3 0 0 0 1.4 2.7 4.4 7 Otamarakau 0 0 0 0 0 0 0 0.0 8 Pikowai 0 1.9 0 0.8 0 6.5 0 9.2 9 Pokopoko 0.1 8.3 2.8 0 0 1.6 15 28 10 Pongakawa 0.2 6.2 0 0 0 5.1 5.2 17 11 Pukehina 0.1 0 0 0 0 1.2 2.1 3.4 12 Pukehina Beach 0 0 0 0 0 0.1 0.2 0.3 13 Ruataniwha 0 0.1 0 0.2 0 0.7 0 1.0 14 Waitahanui 0.1 6.1 0 1.0 0 17.5 0 25 15 Wharere 0.1 4.5 0.1 0 0 3.3 9.9 18 TOTAL 0.8 30 3.0 7.3 0.7 61 43 146
Volume estimates greater than 0.1 km3 are included and these estimates are rounded to the nearest 0.1 km3 (volume estimates less than 10 km3) or nearest 1 km3 (volume estimates greater than 10 km3).
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Table 4.4 Estimates of groundwater potentially available for use.
Groundwater volume (Million m3) No Surface Holocene Mamaku Matahina Manawahe Pleistocene Minden-Otawa TOTAL Catchment Sediments Ignimbrite Ignimbrite volcano sediments volcanics 1 Hauone 0.0 0.0 0.0 0.0 0.8 0.0 0.8 2 Kaikokopu 0.2 0.8 0.0 0.0 3.2 0.7 4.9 3 Mimiha 0.0 0.0 17.2 0.1 16.0 0.0 33.3 4 Newdicks 0.0 0.0 0.0 0.0 0.4 0.0 0.4 5 Ohinekoao 0.0 0.0 3.6 0.0 2.8 0.0 6.4 6 Ohinepanea 0.0 0.0 0.0 0.0 1.4 0.3 1.7 7 Otamarakau 0.0 0.0 0.0 0.0 0.0 0.0 0.0 8 Pikowai 0.0 0.0 3.2 0.0 6.5 0.0 9.7 9 Pokopoko 0.1 11.2 0.0 0.0 1.6 1.5 14.4 10 Pongakawa 0.2 0.0 0.0 0.0 5.1 0.5 5.8 11 Pukehina 0.1 0.0 0.0 0.0 1.2 0.2 1.5 12 Pukehina Beach 0.0 0.0 0.0 0.0 0.1 0.0 0.1 13 Ruataniwha 0.0 0.0 0.8 0.0 0.7 0.0 1.5 14 Waitahanui 0.1 0.0 4.0 0.0 17.5 0.0 21.6 15 Wharere 0.1 0.4 0.0 0.0 3.3 1.0 4.8 TOTAL 0.8 12.4 28.8 0.1 60.6 4.2 106.9
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5.0 HYDROLOGY
5.1 Rainfall in the Matata area
5.1.1 NIWA rainfall model
NIWA have produced a model of mean annual rainfall in the area (rainfall model: annual_0050p created by Mike Ladd, 20 September 2005). This model has annual mean rainfall on a 500 m by 500 m grid for the Bay of Plenty region.
Features of the rainfall map (Figure 5.1) include:
• rainfall is approximately 1100 - 1300 mm/year at the coast;
• rainfall generally increases with increasing elevation;
• rainfall is greater than 2000 mm/year near Lake Rotoehu and Lake Rotoma;
• rainfall is probably lower on Lake Rotoiti than on Lake Rotoma.
5.1.2 Rainfall model error
The NIWA model provides reasonable estimates of observed annual rainfall. The error of rainfall estimate is assessed by White et al. (2008) for the Western Bay of Plenty area as follows:
• error of the NIWA model estimate is +/- 5%; plus
• error in mean annual rainfall is 18%, considering inter-annual rainfall variability, i.e. 1 standard deviation about the mean. A more scientifically robust analysis of errors in rainfall estimates is beyond the scope of this report.
For example, the error in a NIWA model estimated annual rainfall of 2000 mm/year is:
• +/- 460 mm/year, or +/- 23% of 2000 mm or a range of 1540 mm/year to 2460 mm/year.
The components of this error estimate are:
• +/- 100 mm/year to allow for the quality of the NIWA model i.e. 1900 mm to 2100 mm; plus
• +/- 360 mm/year to allow for inter-annual rainfall variability.
5.2 Surface Water
Surface water catchments in the region (Figure 5.2 and Figure 5.3) are mapped by EBOP in a GIS dataset.
5.2.1 Rainfall on catchments
The surface area of each catchment, and mean annual rainfall on each catchment with the NIWA rainfall model, are assessed using GIS ArcMap (Table 5.1). Mean annual rainfall is lowest in catchments near the coast (Figure 5.4 and Figure 5.5), for example the Newdicks catchment has a mean annual rainfall of 1075 mm/yr (Table 5.1). Mean annual rainfall is
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greatest in the hills; for example mean annual rainfall is 1752 mm/yr in the Pokopoko catchment (Table 5.1).
Table 5.1 Surface water catchments, catchment areas and mean annual rainfall (mm/year and m3/s).
No Catchment area Rainfall Min Rainfall max Mean annual Standard Mean annual Standard name (km2) (mm/y) (mm/y) rainfall deviation rainfall# deviation (mm/y) (mm/y) (m3/s) % 1 Hauone 24.4 1277 1486 1364 58 1.06 4% 2 Kaikokopu 33.5 1150 1570 1306 109 1.39 8% 3 Mimiha 68.1 1300 2000 1622 162 3.50 10% 4 Newdicks 2.2 1050 1100 1075 25 0.07 2% 5 Ohinekoao 9.6 1300 1600 1468 100 0.44 7% 6 Ohinepanea 21.4 1215 1400 1308 44 0.89 3% 7 Otamarakau 1.0 1267 1319 1285 13 0.04 1% 8 Pikowai 30.0 1296 2000 1592 200 1.52 13% 9 Pokopoko 101.2 1277 2000 1752 186 5.62 11% 10 Pongakawa 132.5 1152 2000 1666 230 7.00 14% 11 Pukehina 10.6 1150 1303 1226 75 0.41 6% Pukehina 12 Beach 1.0 1100 1150 1125 25 0.03 2% 13 Ruataniwha 3.2 1298 1400 1343 34 0.14 3% 14 Waitahanui 115.4 1273 2000 1694 221 6.20 13% 15 Wharere 61.0 1154 2000 1507 198 2.91 13% Total 615 31.22
# This value has meaning only with regard to the catchment for which it was calculated.
5.2.2 Surface water flow measurements
The EBOP gauging database holds many records of river flows (Figure 5.6). River flow is currently monitored continuously at one site in the study region (Environment Bay of Plenty 2001) (Figure 5.7, Table 5.2). The number of flow measurement sites (continuous flow measurements and gaugings, Table 5.3) total 93 in the study area.
Table 5.2 Continuous flow recording site in the Paengaroa-Matata area. Mean flow and median flow are calculated from Environment Bay of Plenty data.
Site Name Mean Flow* Median Flow* (L/s) (L/s) 14703 Pongakawa, Old Coach Road 4679 4617
* Statistics from TIDEDA process “PSUMMARY”. These statistics are calculated from the period of record 1998 to 2005.
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Table 5.3 Continuous flow measurement sites and gauging sites in each catchment.
Sub-catchment Sub-catchment Number of continuous flow Number of gauging Number measurement sites sites 1 Hauone 0 2 2 Kaikokopu 0 5 3 Mimiha 0 5 4 Newdicks 0 0 5 Ohinekoao 0 3 6 Ohinepanea 0 1 7 Otamarakau 0 0 8 Pikowai 0 4 9 Pokopoko 0 19 10 Pongakawa 1 17 11 Pukehina Coastal 0 1 12 Pukehina Beach 0 0 13 Ruataniwha 0 0 14 Waitahanui 0 21 15 Wharere 0 15 Total 1 93
5.3 Groundwater flow budget and groundwater available for allocation
A simple groundwater flow budget is used to estimate groundwater available for allocation.
FR = GS + GD where
FR rainfall recharge to groundwater
GS ‘shallow’ groundwater recharge
GD ‘deep’ groundwater recharge
The route that groundwater recharge takes may be ‘shallow’ or ‘deep’:
• ‘shallow’ groundwater recharge is assumed as discharging to streams supporting
baseflow in streams. Observed baseflow in streams (SS) is therefore taken as the ‘shallow’ groundwater recharge;
• ‘deep’ groundwater recharge is assumed as discharging into deeper aquifers and discharging through the coastal boundary.
Baseflow in streams is taken as median surface water discharge as calculated from flow recorder sites and gaugings. An extensive analysis of baseflow is beyond the scope of this report and an analysis of errors in baseflow estimates is also beyond the scope of this report.
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‘Shallow’ groundwater recharge supports baseflow in streams and abstraction of ‘shallow’ groundwater may impact stream flow. Therefore this report assumes ‘shallow’ groundwater recharge is not available for groundwater allocation.
This report assumes that ‘deep’ groundwater recharge is available for allocation. ‘Deep’ groundwater flow is estimated within each surface catchment boundary with:
GD = FR - SS
Published assessments of relevant water balances and groundwater flows in the Paengaroa- Matata area include a water balance for the Te Puke-Maketu groundwater resource estimated by Environment Bay of Plenty (1990).
5.3.1 Estimates of rainfall recharge to groundwater (FR)
Rainfall recharge to groundwater supports baseflow in streams (‘shallow’ groundwater recharge) and supports recharge of deeper aquifers (‘deep’ groundwater recharge). In this study rainfall recharge is assumed as either 30% of rainfall or 50% of rainfall (Figure 5.8). These assumptions are based on the following:
• the 30% rainfall recharge area includes the lithologies of Tauranga Group Sediments;
• the 30% rainfall recharge area has relatively low annual rainfall;
• 30% rainfall recharge through sedimentary deposits is measured by White et al. (2003) in Canterbury;
• rainfall minus PET is 30% of rainfall at Tauranga (Environment Bay of Plenty 1990);
• the 50% rainfall recharge area includes the volcanic lithologies of the Taupo Volcanic Zone;
• approximately 50% rainfall recharge is measured for the Mamaku Plateau discharge through springs and stream around Putaruru (White et al. 2004);
• approximately 50% rainfall recharge is the maximum measured in two lysimeters located at Kaharoa, near Lake Rotorua, in volcanic White et al. (2003);
• rainfall minus PET is 60% of rainfall at Kawerau (Environment Bay of Plenty 1990).
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Table 5.4 Estimates of rainfall recharge1.
50% rainfall recharge area 30% rainfall recharge area No Catchment Area Area with 50% Mean rainfall in area Mean rainfall Mean rainfall Area with 30% Mean rainfall in area Mean rainfall Mean rainfall Total recharge name km2 recharge with 50% recharge recharge 50% recharge 50% recharge with 30% recharge recharge 30% recharge 30% 50% + 30% areas (km2) (mm/y) (mm/y) (L/s) (km2) (mm/y) (mm/y) (L/s) (L/s) 1 Hauone 24.4 17.3 1365 683 375 7.1 1362 409 92 467 2 Kaikokopu 33.5 2.5 1306 653 52 31.0 1306 392 385 437 3 Mimiha 68.1 68.1 1622 811 1750 ** ** ** ** 1750 4 Newdicks 2.2 * * * * 2.2 1075 323 22 22 5 Ohinekoao 9.6 7.2 1502 751 172 2.3 1351 405 30 202 6 Ohinepanea 21.4 10.1 1324 662 212 11.3 1294 388 139 351 7 Otamarakau 0.96 0.9 1285 643 19 0.02 1285 386 0 19 8 Pikowai 30.0 30.0 1529 765 728 ** ** ** ** 728 9 Pokopoko 101.2 83.4 1816 908 2401 17.8 1451 435 246 2647 10 Pongakawa 132.5 107.3 1738 869 2956 25.3 1356 407 326 3282 11 Pukehina 10.6 * * * * 10.6 1226 368 123 123 12 Pukehina Beach 1.0 * * * * 1.0 1125 338 10 10 13 Ruataniwha 3.2 3.2 1343 672 68 ** ** ** ** 68 14 Waitahanui 115.4 103.1 1732 866 2832 12.22 1370 411 159 2991 15 Wharere 61.0 43.5 1589 795 1095 17.50 1300 390 216 1311 Total 614.9 476.6 12660 138.30 1748 14408
1 rounding is used in this table so calculated values presented in this table may not be exact ** Whole catchment is included in the 50% rainfall recharge area * Whole catchment is included in the 30% rainfall recharge area
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These assumptions may over estimate rainfall recharge in mountainous terrain, for example runoff in mountainous terrain (e.g. Kaimai Range and Otawa Hill) may be a much larger proportion of rainfall then in the relatively flat-lying ignimbrite and sedimentary areas.
Rainfall recharge to groundwater totals an estimated 14.4 m3/s in the Paengaroa-Matata area (Table 5.4).
5.3.2 Estimates of baseflow in streams (SS)
The EBOP gauging database and continuous flow records are assessed to estimate the discharge by baseflow from catchments. The process to estimate baseflow discharge from catchments is as follows:
• assign gauging sites and continuous flow sites to catchments;
• identify gauging sites and/or continuous flow sites that may represent stream flow at the bottom of catchments (Figure 5.9, Figure 5.10 and Figure 5.11). Surface water discharges from more than one stream in some catchments; therefore some catchments have discharge measurements from more than one stream;
• calculate mean flow and median flow for the site (Table 5.5).
Some median flow estimates are made from a small number of gaugings. A full analysis of the quality of the gauging data, and the errors in estimated median flows, is beyond the scope of this report.
The approach to estimating baseflows used in this report differs from the Environment Bay of Plenty (1996) approach to estimating low flows. Environment Bay of Plenty (1996) estimate low flows based on a statistical (regression or Gumbel) estimation of the Q5 ‘7-day’ flows but Environment Bay of Plenty (1996) has reservations about the quality of the results: ‘results are tentative at best’ (Environment Bay of Plenty 1996) when applied to gauged flows. Low flow estimates are ‘tentative’ partly because of the small number of gaugings at most sites.
Surface water baseflow discharge from the Paengaroa-Matata area is estimated as a total of approximately 15.8 m3/s (Table 5.5) with median flow estimates preferred over mean flow estimates. Median flow estimates are preferred over mean flow estimates because the baseflow (i.e. groundwater discharge) is probably better represented by median flow than by mean flow.
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Table 5.5 Base flow discharge estimates for catchments.
Sub-catchment Sub-catchment D/s site D/s site D/s site G/F* Number of Mean Median Mean flow Median flow Percentage difference: No. river name name number gaugings flow flow sub-total sub-total mean flow of median flow (L/s) (L/s) (L/s) (L/s) Hauone Above highway 15101 G 3 1 Hauone 199 199 199 199 0 Airstrip creek SH2 Bridge 15102 G 2 Kaikokopu Kaikokopu SH2 Bridge 14724 G 10 548 727 548 727 -25 Hererepuru SH2 Bridge 15106 G 2 995 995 3 Mimiha 1378 1288 7 Miniha SH2 Bridge 15108 G 45 383 293 4 Newdicks ------Ohinekoao Hererepuru Rd 15203 G 27 190 53 190 53 158 5 Ohinekoao C46/1 creek SH2 culvert 15202 G 2 11 11 11 11 0 6 Ohinepanea Ohinepanea Pokare 14901 G 2 44 44 44 44 0 7 Otamarakau G ------8 Pikowai Pokare Above SH2 15103 G 41 1176 1178 1176 1178 0 9 Pokopoko Pokopoko Old Coach Rd 14725 G 17 1769 1764 1769 1764 0 10 Pongakawa Pongakawa Old Coach Rd 14703 F 4679 4617 4679 4617 1 11 Pukehina Pukehina Pukehina Rd Bridge 14742 G 16 72 47 72 47 53 12 Pukehina Beach ------13 Ruataniwha ------14 Waitahanui Waitahanui SH2 Bridge 15001 G 39 5549 5417 5549 5417 2 Wharere Old Coach Rd 14732 G 16 458 389 15 Wharere 525 460 14 Paunene stream Old Coach Rd 14731 G 15 67 71 Total 16140 15805 2
* G: gauging site * F: continuous flow measurement site
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5.3.3 Rainfall recharge, baseflow and estimated deep groundwater recharge
Rainfall recharge to groundwater totals approximately 14.4 m3/s in the Paengaroa-Matata area (Table 5.4) and surface water discharge from the Paengaroa-Matata area is estimated as a total of approximately 15.8 m3/s (Table 5.5). Therefore (Section 5.3) for the Paengaroa- Matata area, deep groundwater recharge is:
3 GD = 14.4 -15.8 m /s = -1.4 m3/s Deep groundwater recharge for each surface catchment is estimated in Table 5.6 from:
• the EBOP rainfall map;
• EBOP surface catchment polygon boundaries;
• groundwater recharge over the ‘50% area’ and the ‘30% area’ (Table 5.4);
• surface water baseflow discharge (Table 5.5).
Estimated surface water baseflow discharge is greater than estimated groundwater recharge from rainfall by about 1397 L/s (Table 5.6) in the Paengaroa-Matata area.
Estimated surface water baseflow is greater than estimated groundwater recharge from rainfall in three catchments: Pikowai, Pongakawa and Waitahanui i.e.:
• Pikowai catchment where surface water baseflow discharge is greater than estimated rainfall recharge by about 450 L/s;
• Pongakawa catchment where surface water baseflow discharge is greater than estimated rainfall recharge by about 1335 L/s;
• Waitahanui surface water baseflow discharge greater than estimated rainfall recharge by about 2426 L/s.
Surface water flow in the Pikowai, Pongakawa and Waitahanui catchments may be augmented by groundwater recharge from three Rotorua lakes (Rotiti, Rotoehu and Rotoma) and their catchments.
Preliminary water budgets for the Rotoiti, Rotoehu and Rotoma (lakes and catchments) estimate nett water balances (i.e. groundwater recharge from the lakes and lake catchments to the Paengaroa-Matata area) as:
• Rotoiti 160 L/s (Table 5.7);
• Rotoehu 2086 L/s (Table 5.8);
• Rotoma 1517 L/s (Table 5.9);
3 • total approximately 3.8 m /s.
The preliminary water budgets for these lakes indicate that groundwater recharge from these lakes may explain the differences between estimated surface water baseflow discharge and estimated groundwater recharge from rainfall in the Pikowai, Pongakawa and Waitahanui catchments. More work is being done to assess these preliminary lake and catchment budgets including an assessment of groundwater inputs to the catchments of these lakes (Gillon 2008).
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Table 5.6 Rainfall recharge, baseflow and estimated deep groundwater recharge.
No Catchment Mean groundwater recharge Median baseflow Estimated baseflow discharge ‘Deep’ groundwater recharge name by rainfall inflow (‘shallow’ groundwater recharge) (i.e. groundwater recharge – baseflow) (L/s) (L/s) (L/s) (L/s) 1 Hauone 467 0 199 268 Kaikokopu- 2, 9, 15 4395 0 2951 1444 Pokopoko-Wharere 3 Mimiha 1750 0 1288 462 4 Newdicks 22 0 0 22 5 Ohinekoao 202 0 64 138 6 Ohinepanea 351 0 44 307 7 Otamarakau 19 0 0 19 8 Pikowai 728 0 1178 -450 10 Pongakawa 3282 0 4617 -1335 11 Pukehina 123 0 47 76 12 Pukehina Beach 10 0 0 10 13 Ruataniwha 68 0 0 68 14 Waitahanui 2991 0 5417 -2426 Total 14408 0 15805 -1397
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Table 5.7 Preliminary water budget for Lake Rotoiti and its catchment.
Water budget component Water flow (L/s) Rotoiti inputs Rainfall, lake and catchment 10287 Ohau Channel 15800
Sub-total inputs 26087
Rotoiti outputs Kaituna River 21090 Evaporation lake 733 Evaporation catchment 4104 Sub-total outputs 25927
Nett 160
Table 5.8 Preliminary water budget for Lake Rotoehu and its catchment.
Water budget component Water flow (L/s) Rotoehu inputs Rainfall, lake and catchment 3988
Sub-total inputs 3988
Rotoehu outputs Evaporation lake 170 Evaporation catchment 1732 Sub-total outputs 1902
Nett 2086
Table 5.9 Preliminary water budget for Lake Rotoma and its catchment.
Water budget component Water flow (L/s) Rotoma inputs Rainfall, lake and catchment 2752 Sub-total inputs 2752
Rotoma outputs Evaporation lake 240 Evaporation catchment 995 Sub-total outputs 1235
Nett 1517
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5.3.3.1 Errors in estimated deep groundwater recharge and implications for allocation
The estimates of deep groundwater recharge are made from an equation and each component of the equation has errors. The components of the equation and estimated errors are summarised as follows:
• rainfall, where error could easily be +/- 23% (Section 5.1.2);
• rainfall recharge, where error could easily be +/- 10%;
• stream baseflow, where error could easily be +/- 5% for larger streams and +/- 100% for smaller streams. For example Table 5.5 lists the percentage difference of mean flow and median flow. For example, errors in the components of the deep groundwater recharge estimate for the Mimiha catchment are:
• +/- 805 L/s i.e. +/- 23% of mean rainfall 3500 L/s (from Table 5.4);
• +/- 350 L/s for the error in rainfall recharge estimation i.e. +/- 10% of mean rainfall 3500 L/s;
• +/- 64 L/s for the error in the estimate of baseflow i.e. +/- 5% of median baseflow 1288 L/s in the Mimiha catchment (Table 5.5).
The error in deep groundwater recharge is the sum of these errors, i.e.
• deep groundwater recharge = 462 +/- 1219 L/s in the Mimiha catchment.
The large error associated with estimates of deep groundwater recharge in this example is probably typical of errors in calculated deep groundwater recharge in other catchments in the study area.
Therefore, errors in estimates of deep groundwater recharge are likely to be large. However, large errors do not prevent use of the method to inform decisions on groundwater allocation limits because:
• a groundwater resource allocation limit is necessary for sustainable management of groundwater allocation;
• groundwater allocation to users could adopt a conservative approach and allocate only a proportion of the groundwater resource allocation limit.
5.3.4 Groundwater available for allocation
Lakes and catchments of Rotoiti, Rotoehu and Rotoma are probably contributing to the water budget of catchments in the Paengaroa-Matata area, i.e. the Pikowai, Pongakawa and Waitahanui catchments where baseflow discharge is greater than estimated rainfall recharge as indicated by negative nett flow in Table 5.6.
The groundwater inflows from the lakes and catchments of Rotoiti, Rotoehu and Rotoma probably contribute a large proportion of the surface flows in Table 5.6. However the actual water inflows from the lake catchments are unknown.
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Estimates of groundwater available for allocation must consider inflows from the lakes and catchments. This is considered here by assuming:
1. groundwater inflows from the lakes balance rainfall recharge inflows and surface water outflows in Pikowai, Pongakawa and Waitahanui catchments; hence 2. a percentage of estimated groundwater recharge is available for groundwater allocation in catchments where inflows and outflows are in balance after applying 1, above.
Groundwater available for allocation is estimated in Table 5.10. These figures are:
• estimated groundwater recharge by rainfall (Table 5.4) minus estimated median surface water baseflow (Table 5.5), where this figure is positive in Table 5.6;
• ten percent of estimated groundwater recharge to the ‘50%’ area (Table 5.4) where baseflow is less than estimated groundwater recharge in the Pikowai, Pongakawa and Waitahanui catchments, i.e. 10% of the estimated deep groundwater recharge is available for groundwater allocation. This is a conservative approach to estimating groundwater available for allocation and largely reflects the unknowns in the water budgets for the Rotoiti, Rotoehu and Rotoma lakes.
Table 5.10 Groundwater available for allocation.
No Catchment Mean groundwater Estimated baseflow discharge Groundwater available name recharge by rainfall (‘shallow’ groundwater recharge) for allocation (L/s) (L/s) (L/s) 1 Hauone 467 199 2681 Kaikokopu- 2, 9, 15 4395 2951 14441 Pokopoko-Wharere 3 Mimiha 1750 1288 4621 4 Newdicks 22 0 221 5 Ohinekoao 202 64 1381 6 Ohinepanea 351 44 3071 7 Otamarakau 19 0 191 8 Pikowai 728 1178 732 10 Pongakawa 3282 4617 2963 11 Pukehina 123 47 761 12 Pukehina Beach 10 0 101 13 Ruataniwha 68 0 681 14 Waitahanui 2991 5417 2834 Total 14408 15805 3466
1 mean groundwater recharge by rainfall minus estimated baseflow groundwater recharge, Table 5.6; 2 10% of the estimated groundwater recharge on the ‘50%’ area of the Pikowai catchment (Table 5.4); 3 10% of the estimated groundwater recharge on the ‘50%’ area of the Pongakawa catchment (Table 5.4); 4 10% of the estimated groundwater recharge on the ‘50%’ area of the Waitahanui catchment (Table 5.4).
5.4 Estimates of deep groundwater recharge in geological units and in sub-catchments
Geological units with significant groundwater storage (Table 4.4) include:
• Pleistocene sediments;
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• Minden-Otawa volcanics;
• Mamaku Ignimbrite;
• Matahina Ignimbrite.
Basement greywacke will have significant groundwater storage. However groundwater storage is not calculated in Table 4.4 because greywacke is generally a low-priority target for groundwater supply. Greywacke is a low-priority target for groundwater supply because permeabilities are typically low and the probability of intersecting fractures in greywacke is generally low.
Deep groundwater recharge available for allocation (Table 5.10) in these units is estimated by the method:
• estimate the distribution of these units by catchment;
• apportion deep groundwater recharge as follows: - Pleistocene sediments/Matahina Ignimbrite take 75% of deep groundwater recharge when the unit is at the surface; - Minden-Otawa volcanics take 20% balance of deep groundwater recharge when the unit is at the surface; - Matahina Ignimbrite takes 75% of deep groundwater recharge when the unit is at the surface; - basement greywacke takes 100% of deep groundwater recharge when the unit is at the surface and the balance where the unit is subsurface.
This apportioning between geological units is arbitrary.
Deep groundwater recharge to each geological unit is estimated according to the likely hydraulic nature of the unit including: type (aquifer, aquitard), hydraulic properties, depth and thickness of the geological units. The hydraulic nature of geological units is represented by factors that represent the relative proportion of a geological unit at the ground surface.
Pleistocene sediments/Mamaku Ignimbrite carry most of the groundwater flow in the area (Table 5.11) as estimated by this simple model. Important units carrying groundwater flow also include Minden-Otawa volcanics, Matahina Ignimbrite and basement greywacke.
Table 5.11 Estimated deep groundwater recharge by geological unit from estimates of groundwater flow in each catchment.
Geological unit Estimated deep groundwater recharge available for allocation (L/s) Pleistocene sediments/ Mamaku Ignimbrite 1721 Minden-Otawa volcanics 434 Matahina Ignimbrite 638 Basement greywacke 673 Sum (L/s) 3466 Sum (m3/day) 299462
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Groundwater flow estimated by the above approach can be checked with application of Darcy’s law:
Q = TwH Q flow in m3/day; T transmissivity in m2/day; w width of formation in m; H groundwater gradient.
For example groundwater flow in the Pleistocene sediments/Mamaku Ignimbrite in the uplands (i.e. ‘50%’ recharge area) in the Kaikokopu, Pokopoko and Wharere catchments is estimated as 448 L/s i.e. 75% of:
• 3548 L/s rainfall recharge to groundwater (Table 5.4); minus
• 2951 L/s surface water discharge from these catchments (Table 5.6).
The upland are of the Kaikokopu, Pokopoko and Wharere catchments has an estimated groundwater flow of 380 L/s from the Darcy equation with:
2 • T about 350 m /day (Section 3.1);
• w 9500 m;
• H about 0.01.
The estimated deep groundwater flow of 448 L/s in the Pleistocene sediments/Mamaku Ignimbrite in the upland area of the Kaikokopu, Pokopoko and Wharere catchments is similar to the estimated groundwater flow of 380 L/s from the Darcy equation. Therefore the estimated deep groundwater flows and estimates of flow by the Darcy equation may be similar. However the actual groundwater flows will be greater than estimated deep groundwater flows, approximately by a factor of eight, because the formation may take the full groundwater recharge.
5.5 Discharge of deep groundwater
Deep groundwater flow will discharge to the sea or to other geological units. Deep groundwater flow to the sea will probably occur with the following aquifers:
• Pleistocene sediments;
• Minden-Otawa volcanics;
• Matahina Ignimbrite;
• Basement greywacke.
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6.0 GROUNDWATER ALLOCATION
6.1 Current groundwater consents
Existing groundwater consents in the Paengaroa-Matata area (Appendix 3), as of 28th May 2008 (Gordon pers. comm.), are all classed by Environment Bay of Plenty as cold groundwater consents (Figure 6.1). Some consents include allocation from multiple wells.
Table 6.1 summarises the distribution of the existing groundwater consents by catchment.
Table 6.1 Existing groundwater consents by surface catchment (Appendix 4).
Surface catchment Surface catchment Number of existing EBOP groundwater number name consents 1 Hauone 1 2 Kaikokopu 21 3 Mimiha no consent 4 Newdicks no consent 5 Ohinekoao no consent 6 Ohinepanea 10 7 Otamarakau no consent 8 Pikowai 2 9 Pokopoko 17 10 Pongakawa 7 11 Pukehina no consent 12 Pukehina Beach no consent 13 Ruataniwha no consent 14 Waitahanui no consent 15 Wharere 18 Total 76
Groundwater allocation, allocation for frost protection and allocation for irrigation is summarised in Table 6.2.
Table 6.2 Groundwater consents in the Paengaroa-Matata area, existing and consent applications as of 28th May 2008 (Gordon pers. comm.).
Groundwater consents Allocation classification Allocation (m3/day) Existing (76 consents) All consents 76,011.8 Existing (76 consents) Frost protection 42,313 Existing (76 consents) Irrigation 63,576 Consent applications (5) All 18,231 Consent applications (5) Frost protection 18,231 Consent applications (5) Irrigation 7,596
Clearly, allocation for frost protection is important in the area: approximately 56% of the existing groundwater allocation is for frost protection.
6.1.1 Estimates of groundwater use
Current groundwater use is estimated in three water use classes:
• frost protection water use for 30 days in the year at the allocated daily rate;
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• irrigation water use for 5 months in the year at the allocated daily rate;
• municipal water use for 365 days in the year at the daily allocated rate.
Annual groundwater use is estimated as an equivalent of 35010 m3/day (Table 6.3).
Estimated water use by irrigation is largest of the three water use classes.
Table 6.3 Estimated use for existing groundwater consents.
Type of use Estimated annual use (m3/day equivalent)
Frost protection 3478 Irrigation 22892 Municipal 8640 Total 35010
6.2 Groundwater available for allocation and existing allocation
Existing allocation, with adjustments for seasonal frost protection, are summed by sub- catchment (Table 6.4), Appendix 4.
Allocation in the Kaikokopu, Pokopoko and Wharere catchments are combined (Table 6.4) because they probably represent a common hydrogeological unit in regards of groundwater allocation.
The Kaikokopu, Pokopoko and Wharere catchments have the largest allocation, as a portion of groundwater available for allocation (Table 6.4). The groundwater resources in these geographic areas are treated as one resource, i.e. groundwater recharge to Tauranga Group Sediments is not differentiated from groundwater recharge to ignimbrite units in the areas.
The groundwater in these areas should be treated as one resource because:
• geological continuity of units, particularly the ignimbrite units, is not obvious from drill logs;
• ignimbrite units are interfingered with sedimentary units leading to potential movement of water between these aquifers during pumping;
• it is common practice to screen across ignimbrite units and sedimentary units in water supply wells;
• in this area “long term drawdown effects may eventually be transmitted” through “all the deep water bearing zones in the bores, from 30 to 18 m below sea level” (Pattle Delamore 2007).
Most allocation is in the Kaikokopu-Pokopoko-Wharere catchments with about 85% of the total groundwater allocation for the Paengaroa-Matata area.
6.3 Groundwater available for allocation and estimated groundwater use
Estimated groundwater use (Section 6.1.1) totals an equivalent of 35010 m3/day (Table 6.3 and Table 6.5). Estimated groundwater use is largest in the Kaikokopu-Pokopoko-Wharere catchments.
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Table 6.4 Groundwater available for allocation and existing allocation in the Paengaroa-Matata area.
Sub-catchment Sub-catchment Groundwater available for EBOP groundwater allocation Allocation/groundwater number name allocation (L/s) recharge (L/s) (%, approximate) 1 Hauone 268 3.8 1 2,9,15 Kaikokopu-Pokopoko-Wharere 1444 743.5 51 3 Mimiha 462 no consent 0 4 Newdicks 22 no consent 0 5 Ohinekoao 138 no consent 0 6 Ohinepanea 307 107.9 35 7 Otamarakau 19 no consent 0 8 Pikowai 73 2.5 3 10 Pongakawa 296 22.1 7 11 Pukehina 76 no consent 0 12 Pukehina Beach 10 no consent 0 13 Ruataniwha 68 no consent 0 14 Waitahanui 283 no consent 0 Sum (L/s) 3466 879.8 25 Sum (m3/d) 299462 76011.8 25
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Table 6.5 Groundwater available for allocation and estimated existing groundwater use.
Sub-catchment Sub-catchment Groundwater available for Estimated existing Estimated existing groundwater number name allocation groundwater use use/groundwater recharge (L/s) (L/s) (%, approximate) 1 Hauone 268 1.6 1 2,9,15 Kaikokopu-Pokopoko-Wharere 1444 343.1 24 3 Mimiha 462 no consent 0 4 Newdicks 22 no consent 0 5 Ohinekoao 138 no consent 0 6 Ohinepanea 307 50.7 17 7 Otamarakau 19 no consent 0 8 Pikowai 73 1 1 10 Pongakawa 296 8.9 3 11 Pukehina 76 no consent 0 12 Pukehina Beach 10 no consent 0 13 Ruataniwha 68 no consent 0 14 Waitahanui 283 no consent 0 Sum (L/s) 3466 405.3 12 Sum (m3/d) 299462 35010 12
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6.4 Existing groundwater allocation by geological unit
Environment Bay of Plenty groundwater allocation of 28th May 2008 (Section 6.1.1) is assigned to geological units where possible (Table 6.6).
Table 6.6 Current groundwater allocation by geological unit.
Geological unit Existing allocation (m3/day) Pleistocene sediments/Mamaku Ignimbrite 32378.2 Matahina Ignimbrite 93.6 Minden-Otawa 16683.3 Basement 4151 Geological unit unknown 22705.6 Sum (m3/day) 76011.7 Sum (L/s) 879.8
The process to assign geological units is as follows:
• identify EBOP well number(s) with the consent (Appendix 3);
• identify screen position, or well depth, for well (Appendix 4);
• assign allocation adjusted for frost protection to well (Appendix 4). Some consents are associated with multiple wells and in these cases the total allocation, adjusted for frost protection, is partitioned equally across all the wells in the consented allocation;
• calculate the ground elevation of the well form NZMG coordinates;
• calculate the reduced level of the screen position, or well depth;
• identify the geological unit from the calculated reduced level of the screen position, or well depth, using the geological model.
Some existing allocation is not assigned to geological unit. This is because either:
• the consent has no record of an EBOP well number (Appendix 3 and Appendix 4); or
• the well has no screen position, or well depth, information.
Pleistocene sediments/Mamaku Ignimbrite are the most commonly used geological units for groundwater in the area with approximately 61% of the allocation that is attributable to geological units.
6.5 Environment Bay of Plenty allocation policies
This report considers maximum ‘groundwater available for allocation’, i.e. the maximum potential groundwater allocation, based on available geological and water balance models. Actual allocation should be less than the maximum groundwater available for allocation.
Groundwater flow and storage may be available for allocation, subject to policies and rules for allocation in the regional plan.
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EBOP’s proposed Regional Water and Land Plan includes policies and objectives for groundwater allocation, e.g.:
• Objective 36, abstraction of groundwater should be sustainable;
• Policy 57, sustainable yield allocation;
• Method 125, ‘instruments’ to manage water takes;
• Method 126, address adverse effects of groundwater takes on surface water.
The authors suggest that EBOP allocation policies could further consider:
• maintenance of baseflow in streams for example zero allocation of shallow groundwater recharge;
• a conservative allocation of deep groundwater recharge;
• identification of groundwater allocation geographic zones or aquifers;
• sub-regional limits for annual groundwater allocation in allocation zones or aquifers;
• annual limits of groundwater allocation for groundwater users;
• development of EBOP datasets on users’ allocation and groundwater allocation limits;
• water-use specific policies for allocation. For example groundwater allocation for frost protection and irrigation should recognise that this water is not required for 365 days of the year (Section 6.1.1) whereas groundwater allocation for municipal use is probably required for 365 days of the year;
• groundwater levels near the coast – ensuring that groundwater levels do not decline below sea level allowing the possibility of salt water intrusion as salt water intrusion may occur when the water table is below sea level;
• groundwater chemistry near the coast – ensuring that wells where indications show the potential for salt water intrusion are assessed;
• groundwater quality in key aquifers is protected from potential effects of agricultural intensification;
• allocation of groundwater from storage in emergency situations only.
Policy decisions on groundwater allocation are beyond the scope of this report.
7.0 RECOMMENDATIONS
The following are recommendations, for consideration by EBOP, of further assessments of groundwater in the Paengaroa-Matata area:
• the drill log records of four wells (no. 4043, 3594 and 4043) in the EBOP database should be checked as the drill log records of these wells are identical in the EBOP data base;
• groundwater levels, and ground levels, in wells should be checked where the EBOP database has wells with groundwater levels below sea level (Section 3.2.1) i.e.: 1218, 1520, 2553, 2956, 3206, 3236, 10186, 10669, 10856 and 10872. The groundwater depth
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measurements in the EBOP database may be measured as the wells were pumped, i.e. the groundwater level is not a static water level. The levels may be static water levels and if so groundwater levels below sea may indicate a risk for salt water intrusion. This risk may be significant as groundwater levels are, in some cases, a substantial distance below sea level;
• groundwater levels in the La Vigna, JB Family Trust well and RH Hall (Section 3.1) are close to, or below, sea level during pumping and this indicates a risk of salt water intrusion to the aquifer. Allocation of groundwater from these bores should consider the risks of salt water intrusion to the aquifer caused by pumpage of these wells;
• groundwater levels are declining over time in well 2822 in the Pongakawa area (Section 3.2.2). The level trend in this well should be assessed to identify whether the trend is due to climatic changes or is due to groundwater use;
• EBOP could improve knowledge of groundwater in the Paengaroa-Pongakawa area because: - groundwater allocation is greatest in the Paengaroa-Pongakawa area with current allocation equal to an estimated 51% of groundwater available for allocation (Table 6.4) - groundwater levels are below sea level (possibly during pumping, possibly static groundwater levels) and well 2822 has a trend of declining groundwater levels with time.
• EBOP could improve knowledge of groundwater in the Paengaroa-Pongakawa area by: improving data sets such as well numbers for consents, assessing ground levels and groundwater depths for wells; gauging measurements in streams to better assess river- groundwater allocation; improved assessments of groundwater budgets for the area;
• EBOP could consider purpose-built groundwater level monitoring wells that are not directly influenced by groundwater pumping. This is to improve the information of groundwater levels trends over time. One well near on the coastal side of the Paengaroa- Pongakawa area would be very useful to assess risks of salt water intrusion;
• groundwater in the Paengaroa-Pongakawa possibly travels from lakes and catchments of Rotoiti, Rotoehu and Rotoma. Improved water budgets for these lakes and catchments are recommended;
• groundwater flows into the lower reaches of the Kaituna catchment, possibly from the Pokopoko and Kaikokopu catchments. White et al. (2008) estimate Kaituna River catchment inflows (surface water and rainfall recharge) as 34.7 m3/s and outflows (surface water and groundwater to the Lake Rotorua catchment) as 42.0 m3/s. Therefore the water budgets of the Pokopoko and Kaikokopu catchments should be assessed, in conjunction with the water budget of Lake Rotoiti and its catchment, to assess groundwater discharge to the lower reaches of the Kaituna catchment;
• the approach taken in this report to assessing the groundwater available for allocation is a simple water balance approach. A computer model of groundwater flows is recommended in the future to assess groundwater availability for allocation.
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Environment Bay of Plenty could decide policies on groundwater allocation in the Paengaroa-Matata area (Section 6.5) including: - maintenance of baseflow in streams; - a conservative approach to groundwater allocation; - annual allocation limits for groundwater users that recognise the type of use; - annual allocation limits for geographic zones or aquifers; - development and maintenance of EBOP datasets of users’ allocation and groundwater allocation limits to monitor allocation against the limit over time.
8.0 ACKNOWLEDGEMENTS
We would like to particularly thank Dougall Gordon, Environment Bay of Plenty, for assistance with project design and data collection. Thanks also to Glenn Ellery, Environment Bay of Plenty, for surface gauging data and Janine Barber, Environment Bay of Plenty, for reviewing a draft of this report.
9.0 REFERENCES
Adams, C.J.; Graham, I.J.; Seward, D.; Skinner, D.N.B. 1994. Geochronological and geochemical evolution of late Cenozoic volcanism in the Coromandel Peninsula, New Zealand. N.Z. J. Geol. Geophys. 37, pp. 359–379. Bailey, R.; Carr, R. 1994. Physical geology and eruptive history of the Matahina ignimbrite, Taupo Volcanic Zone, North Island, New Zealand. New Zealand Journal of Geology and Geophysics. Vol 37: 319-344. Berryman, K.; Beanland, S.; Wesnousky, S. 1998: Paleoseismicity of the Rotoitipakau Fault Zone, a complex normal fault in the Taupo Volcanic Zone, New Zealand. New Zealand Journal of Geology and Geophysics 41: 449–465. Briggs, R.M.; Hall, G.J.; Harmsworth, G.R.; Hollis, A.G.; Houghton, B.F.; Hughes, G.R.; Morgan, M.D.; Whitbread-Edwards, A.R. 1996. Geology of the Tauranga area: sheet U14. Scale 1:50,000. Hamilton: University of Waikato. Occasional report / Department of Earth Sciences, University of Waikato 22. 57 p. Briggs, R. M.; Houghton, B. F.; McWilliams, M.; Wilson, C. J. N. 2005. 40Ar/39Ar ages of silicic volcanic rocks in the Tauranga-Kaimai area, New Zealand: dating the transition between volcanism in the Coromandel Arc and the Taupo Volcanic Zone. New Zealand Journal of Geology & Geophysics, 2005, Vol. 48: 459–469 Bright Spark Group 2004. Domain Park, Paengaroa 300 mm water well pump test report. Broughton, A. K. 1988. Volcanology and petrology of the Manawahe Volcano, Taupo Volcanic Zone. Geological Society of New Zealand Miscellaneous Publication 41a: 44. Burt, R.M.; Brown, S.J.A.; Cole, J.W.; Shelley, D. and Waight, T.E. 1998. Glass-bearing plutonic fragments from ignimbrites of the Okataina caldera complex, Taupo Volcanic Zone, New Zealand: remnants of a partially molten intrusion associated with preceding eruptions. Journal of Volcanology and Geothermal Research. 84, 209-237 CH2M Beca Ltd. 1999. Groundwater options for water supply Western Bay of Plenty, Part 1: eastern Supply Zone.
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CH2M Beca Ltd 2000. Western Bay of Plenty groundwater investigation Stage 3 Eastern Supply Zone. Report for Western Bay of Plenty District Council. CH2M Beca Ltd. 2003. Completion report. Central supply zone production wells (Contract No. 55/556). Prepared for Western Bay of Plenty District Council. 20p + figures + appendices. CH2M Beca Ltd. 2005. Pongakawa production well completion report. Prepared for Western Bay of Plenty District Council 18p. Daughney, C.J. 2005. Spreadsheet for Automatic Processing of Water Quality Data: Theory, Use and Implementation in Excel. GNS Science Report 2005/35. Davey, F. J.; Henrys S. A.; Lodolo E. 1995. Asymmetric rifting in a continental back-arc environment, North Island, New Zealand. Journal of Volcanology and Geothermal research. Vol. 68, pp. 209-238 Duncan, A. R. 1970. The petrology and petrochemistry of andesite and dacite volcanoes in eastern Bay of Plenty, New Zealand. Victoria University of Wellington. 316 pages and maps. Environment Bay of Plenty. 1990. Te Puke – Maketu groundwater resource evaluation. Unpublished Technical Publication No.1, prepared by W. Russel and C. O’Brian. 60 p. Environment Bay of Plenty 1996. Compliance Monitoring Report 1996. Warm Geothermal Groundwater Users. Tauranga Geothermal Field. Environmental Report 96/4. Environment Bay of Plenty 2001. Environmental data summaries. Air quality meteorology, rainfall, hydrology and water temperature. Report to December 2000. EBOP Environmental Report 2001/01. 555p. Environment Bay of Plenty 2006. Rotorua Lakes Water Quality 2006 Report. Environmental Publication 2007/12. Gillon, N. 2008. Groundwater in the Lake Tarawera catchment. Centre for Biodiversity and Ecology Research. University of Waikato. Gordon D. 2001. Bay of Plenty. In Groundwaters of New Zealand, M.R. Rosen & P.A. White (Eds). Gravley, D.M., Wilson, C.J.N., Leonard, G.S. and Cole, J.W., 2008. Double trouble: paired large ignimbrite eruptions and collateral subsidence in the Taupo Volcanic Zone, New Zealand. GSA Bulletin, 119: 18-30. Healy, J.; Schofield, J.C.; Thompson, B.N. 1964. Geological map of New Zealand 1:250,000 Sheet 5 Rotorua. Wellington: Department of Scientific and Industrial Research. 1 fold. Map. Houghton, B.F.; Wilson, C.J.N.; McWilliams, M.O.; Lanphere, M.A.; Weaver, S.D.; Briggs R.M.; Pringle, M.S.. 1995. Chronology and dynamics of a large silicic magmatic system: central Taupo Volcanic Zone, New Zealand, Geology 23 (1995), pp. 13–16. GWS Ltd 2007. Assessment of effects of groundwater take Paengaroa. Report for Coach Road Orchards. GWS Ltd 2008. Analysis of La Vigna 24 hour pump test. Report to Graeme Neilson. Kear D. 2004. Reassessment of Neogene tectonism and volcanism in North Island, New Zealand. New Zealand Journal of Geology and Geophysics, vol. 47. p.361-374. Ken Thorpe Geoconsultancy 2007. 24 hour pumping test and hydrological report to support water take resource consent application No 64607.
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KRTA. 1982. Report on pump tests carried out on a bore at the Pine Chemicals N.Z. Ltd Distillation Plant, Mt Maunganui Report to NZ Forest Products Limited. 48p. Leonard, G.S. and Begg, J.G., (in prep). Geology of the Rotorua area: scale 1:250,000, Institute of Geological & Nuclear Sciences 1:250,000 geological map 5. 68 p. + 1 folded map, Lower Hutt. Lowe, D.J.; Hogg, A.G. 1995. Age of the Rotoehu Ash. New Zealand Journal of Geology and Geophysics. 38, 399-402. McIntosh, J. and Gordon, G. 2002. Land applications of dairy shed effluent and effects on groundwater quality. Environment Bay of Plenty Environmental Report 2002/09. 74p. Meilhac, C. 2009. Regional geological GIS map. GNS Science consultancy report 2007/316LR. 27 p. +1CD. Milner, D.J.; Cole, J.W.; Wood, C.P. 2003 Mamaku Ignimbrite: a caldera-forming ignimbrite erupted from a compositionally zoned magma chamber in Taupo Volcanic Zone, New Zealand, J. Volcanol. Geotherm. Res. v122, pp. 243–264. Nairn, I.A; Beanland, S. 1989. Geological setting of the 1987 Edgecumbe earthquake, New Zealand; the 1987 Edgecumbe earthquake. New Zealand Journal Geology and Geophysics, 32, p. 1-13. Nairn, I.A., 1989. Sheet V16AC Tarawera; Geological Map of New Zealand 1:50,000, Department of Scientific and Industrial Research, Wellington. Nairn, I.A. 2002. Geology of the Okataina Volcanic Centre: sheets part U15, part U16, part V15 & part V16, scale 1:50,000. Lower Hutt: Institute of Geological & Nuclear Sciences. Institute of Geological & Nuclear Sciences geological map 25. 156 p. + 1 fold. Map. Ota, Y.; Omura, A., Iwata, H. 1989. 230Th-238U age of Rotoehu. Ash and its implications for marine terrace chronology of eastern Bay of Plenty, New Zealand. New Zealand Journal of Geology and Geophysics 32, 327-331. Pattle Delamore Partners. 2007. Interim report reviewing some groundwater level monitoring data and pumping test data in the Paengaroa area. Report for Environment Bay of Plenty. 21p + figures. Reeves, R., White, P.A., Cameron, S.G., Kilgour, G., Morgenstern, U., Daughney, C., Esler, W., Grant, S. 2005. Lake Rotorua groundwater study: results of the 2004-2005 field programme. GNS Client report 2005/66. 67 p. + App. Schmitz, M.; Smith, E. 2004. The petrology of the Rotoiti eruption sequence, Taupo Volcanic Zone: an example of fractionation and mixing in a rhyolitic system. Journal of petrology, vol 45, 2045 Selby, M. J.; Lowe, D. J. 1992: The Middle Waikato Basin and hills. In: Soons, J. M.; Selby, M. J. ed. Landforms of New Zealand. 2nd ed. Auckland, Longman Paul. Pp. 233–255. Skinner, D.N.B. 1967. Geology of the Coromandel region with emphasis on some economic aspects. Unpublished PhD thesis, lodged in the library, University of Auckland, Auckland, New Zealand. Skinner, D.N.B. 1986. Neogene volcanism of the Hauraki Volcanic Region. In: Smith I.E.M. (Ed) late Cenozoic volcanism in New Zealand. Royal Society of New Zealand Bulletin 23:21-47. Stipp, J.J., 1968. The geochronology and petrogenesis of the Cenozoic volcanics of the North Island, New Zealand. Unpublished PhD thesis, lodged in the library, Australian National University, Canberra, Australia.
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Thompson, B.N. 1970. Bay of Plenty Catchment Commission. Kaituna River Major Scheme. Lower Kaituna River Vol. II. Appendices. 53p. Waterline Engineering Consultants 2007. JB Family Trust, Pongakawa. 250 mm water well pump test report. White, P.A., Hong, Y-S., Murray, D., Scott, D.M. Thorpe, H.R. 2003. Evaluation of regional models of rainfall recharge to groundwater by comparison with lysimeter measurements, Canterbury, New Zealand. Journal of Hydrology (NZ) 42(1), 39-64. White, P.A., Reeves, R.R., Cameron, S.G., Daughney, C., Bignall, G., Morgenstern, U. 2004. Proposed field programme to define groundwater and nutrient inflow to Lake Rotorua – discussion document. GNS Client report 2004/130a. 38 p. White P.A.; Meilhac, C.; Zemansky, G.; Kilgour, G. 2008. Groundwater resource investigations of the Western Bay of Plenty area stage 1 – conceptual geological and hydrological models and preliminary allocation assessment. GNS Science Consultancy Report 2006/79. Whitehead, N. E.; Ditchburn, R. G. 1994. Revision of some ages for the Rotoehu Ash. New Zealand Journal of Geology and Geophysics 37, 381-383. Wilson, C. J. N.; Rhoades, D. A.; Lanphere, M. A.; Calvert, A. T.; Houghton, B. F.; Weaver, S. D.; Cole, J. W. 2007. A multiple-approach radiometric age estimate for the Rotoiti and Earthquake Flat eruptions, New Zealand, with implications for the MIS 4/3 boundary. Quaternary Science Reviews, v. 26, iss. 13-14, p. 1861-1870. Wood, C.P. 1992 Geology of the Rotorua geotherma system. Geothermics 21, 729-723. Zemansky, G. 2006. Environment Bay of Plenty State of the Environment: groundwater level and quality. GNS Science report 2006/116 to Environment Bay of Plenty. 84p.
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FIGURES
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Figure 1.1 Topographic map with boundaries of the study area.
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Figure 2.1 Geological map with location of major faults.
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Figure 2.2 Geological map with location of the western, central and eastern areas.
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Figure 2.3 Location of groundwater bores in EBOP database containing lithological information.
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Figure 2.4 Inferred bore lithologies in the north western area wells.
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Figure 2.5 Inferred bore lithologies in the northern area wells.
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Figure 2.6 Inferred bore lithologies in the north eastern area wells.
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Figure 2.7 Inferred bore lithologies in the southern area wells.
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Figure 3.1 Groundwater level.
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Figure 3.2 Locations of wells in the Paengaroa-Matata area with an analysis of groundwater level measurements by Zemansky (2006).
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Figure 3.3 Locations of wells in the Paengaroa-Matata area with an analysis of groundwater chemistry by Zemansky (2006).
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Figure 4.1 Summary surface geological map of the Paengaroa-Matata area.
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Figure 4.2 Tauranga Group Sediments thicknesses (m).
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Figure 4.3 Paengaroa-Matata geological model.
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Figure 4.4 Greywacke basement.
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Figure 4.5 Minden-Otawa volcanics.
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Figure 4.6 Pleistocene sediments.
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Figure 4.7 Manawahe volcano.
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Figure 4.8 Matahina Ignimbrite.
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Figure 4.9 Mamaku Ignimbrite.
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Figure 4.10 Rotoiti Pyroclastics.
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Figure 4.11 Holocene sediments.
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Figure 4.12 Location of geological model cross-sections.
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Figure 4.13 Geological model cross-section A-A’.
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Figure 4.14 Geological model cross-section B-B’.
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Figure 4.15 Geological model cross-section C-C’.
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Figure 5.1 Annual rainfall in the Paengaroa-Matata area (mm/year).
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Figure 5.2 Surface water catchments in the Paengaroa-Matata area and topographic map.
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Figure 5.3 Surface water catchments in the Paengaroa-Matata area.
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Figure 5.4 Mean annual rainfall estimates (mm/year) for surface water catchments.
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Figure 5.5 Mean annual rainfall estimates (m3/s) for surface water catchments.
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Figure 5.6 Locations of gaugings in the Paengaroa-Matata area.
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Figure 5.7 Location of river flow measurement sites – continuous recorder.
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Figure 5.8 Rainfall recharge zones.
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Figure 5.9 Gauging site localities and number of measurements.
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Figure 5.10 Gauging sites that represent stream flow at the bottom of catchments.
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Figure 5.11 Median values of flow at gauging sites that represent stream flow at the bottom of catchments.
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Figure 6.1 EBOP cold groundwater consents in the Paengaroa-Matata study area.
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APPENDICES
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APPENDIX 1 – DETAILS OF THE MAJOR GEOLOGICAL UNITS FOUND IN THE PAENGAROA-MATATA AREA FROM THE YOUNGEST TO THE OLDEST
Unit Name Approx. Age (Ma) Description Deposition Occurrence Reference Modern Beach Recent Unconsolidated beach and Marine transgressions Form a narrow strip along the dune sediments with peat present coast. Holocene <0.05 Unconsolidated alluvial Alternating marine Sediments sediments with alternating transgressions and alluvial 0.01 sequences of clay, peat, deposits from meandering river sand/ pumice and gravel systems interbedded with primary airfall tephra, pyroclastic flows and redeposited tephra Rotoiti 0.065 Nairn, 2002 Pyroclastics 61.0My (Wilson et al. 2007)
35.1±2.8 ka 14C (Whitehead and Ditchburn, 1994)
64±4 ka K–Ar age (Lowe and Hogg 1995)
75.1±6 ka U–Th disequilibrium (Ota et al. 1989) Mamaku 0.22 Ignimbrite 220 to 230 Milner et al. 2003 Matahina 0.28 Pink to grey ignimbrite. Deposited in a subaerial Outcropping to the east of the Ignimbrite ~280 ka (Houghton et al. 1995), Upper part poorly environment close to sea level model area. compacted while lower part Identified by seismic reflection at ~280 ka (Kohn in Nairn, 1989). is fine-grained, welded depths of 21 to 80 mbgl lenticulite. (O’Connor, 1990). Pleistocene 0.29-0.6 Pumice siltstones, Marine, estuarine and fluvial Adjacent to the plain, Nairn and Sediments sandstones and sediments interbedded with outcropping to the south of Beanland, 1989 conglomerates with primary airfall tephra, pyroclastic Whakatane township and to the interbedded tuffs. flows and redeposited tephra east of the Whakatane Fault. Manawahe 0.42 volcano 425 ka (Broughton, 1988) Greywacke Mesozoic Banded argillites, alternating Laid down in deep sea East of the Whakatane Fault and siltstones and sandstones, environments during the south of Whakatane township, conglomerates in places. Jurassic period. between the Whakatane Fault and the Waiohau Fault.
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APPENDIX 2 – COMPUTER FILES USED TO GENERATE THE PAENGAROA- MATATA GEOLOGICAL MODEL
Layer Thickness
Unit name Thickness grid name Rotoiti Pyroclastics rotothick3.2grd Mamaku Ignimbrite mamthick3.2grd Matahina Ignimbrite matathick2.2grd Pleistocene Sediments pleistECW_1newC.2grd Minden Otawa beeson3.2grd Basement basm_ECWnew2.dat
Polygon files
File Name Description AREA.ply Boundary of model area. holo.ply Holocene Sediments outcrop in model area. roto2.ply Rotoiti Pyroclastics outcrop in model area. mama.ply Mamaku Ignimbrite outcrop in model area. mama_extend3.ply Mamaku Ignimbrite subsurface extent in model area. mata.ply Matahina Ignimbrite outcrop in model area. mata_extend.ply Matahina Ignimbrite subsurface extent in model area. edge.ply Manawahe volcano outcrop and subsurface extent in model area. plei.ply Pleistocene Sediments outcrop in model area. pleistW_extend.ply Pleistocene Sediments subsurface extent in the western area. grey.ply Greywacke outcrop in model area. basm_350.ply Extent of greywacke subsurface stepped down to -350 m in the eastern area. basm_100.ply Extent of greywacke subsurface stepped down to -100 m in the central area. basm_450.ply Extent of greywacke subsurface stepped down to -350 m in the western area.
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Elevation data to build geological model on 500 m grid
File Name Description DEMcontours.dat Elevation on a 500 m grid holo_2.dat Area within holo.ply set to ground elevation +100 m. Area outside holo.ply stepped down to -1000 m. rotoelev4.dat Area within roto2.ply set to ground elevation +100 m. Area outside roto2.ply set to -1000 m. mamelev3new.dat • area within mama.ply set to ground elevation +100 m; • area outside mama_extend3.ply set to -1000 m; • area within mama_extend3.ply set to dtm-Rotoiti. mataelev4.dat • area within mata.ply set to ground elevation +100 m; • set to dtm-Rotoiti where Rotoiti is over Matahina; • area outside mata_extend.ply set to -1000 m. manawahe.dat • set to elevation +1000 m inside edge.ply; • set to -1500 outside edge.ply; • outside of dome to be stepped. pleistECW_2newi.dat • area within plei.ply set to ground elevation +100 m; • set to -1000 m in central area (within basm_100.ply); • set to -1000 m outside pleistW_extend.ply in western area (within basm_450.ply); • set to dtm-Holocene where Holocene is over Pleistocene; • set to dtm-Rotoiti where Rotoiti is over Pleistocene; • set to dtm-Matahina where Matahina is over Pleistocene; • set to dtm-(Rotoiti+Matahina) where Rotoiti and Matahina are over Pleistocene; • set to dtm-Mamaku where Mamaku is over Pleistocene; • set to dtm-(Rotoiti+Mamaku) where Rotoiti and Mamaku are over Pleistocene. beeson4.dat • modelled only in the western area (basm_450.ply); • set to basement +200 m; • area outside basm_450 set to -500 m. basm_ECWoutcropsnew2.dat • base of the model; • this is the top of the greywacke basement; • set to ground elevation -350 m in the western (basm_450.ply) and Eastern area (basm_350.ply); • set to ground elevation -100 m in the central area (basm_100.ply); • Area within grey.ply set to ground elevation +100 m.
Model generation
File Name Description matata_0403.seq • sequence file for the model; all layers are depositional except DEMcontours.dat unconformity. matata_0403.unsliced.faces • model generated by this sequence and cut by DEMcontours.dat and cut by AREA.ply
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APPENDIX 3 – EXISTING GROUNDWATER CONSENTS, AND CONSENT APPLICATIONS, 28TH MAY 2008
EBOP consent Name Status1 Easting Northing Maximum daily allocation Maximum daily allocation, frost protection EBOP bore log number (m3/day) (m3/day) number 20298-0 MacDougall & Sons C 2824565.06 6368199.69 123 0 4377 20468-0 Hickson Family Trust PA C 2815317.69 6368227.14 1087 1087 4600, 4275 20479-0 Fannin FJ & JM C 2817883.02 6367174.68 162 0 171 20814-0 Bonny Dale Farm Ltd C 2811277.32 6366513.81 200 0 1074 20839-0 Lotz G & C C 2813997.25 6366715.47 182 0 4367 20892-0 Growell Nurseries C 2817448 6369517 54.6 0 4251 20935-0 Leppard Orchards Ltd C 2809136.52 6367186.78 400 0 2419, 418, 1698 20936-0 Rosnagalla Farms Limited C 2811558.96 6367658.97 260 0 4823 20952-0 Hayward R & S C 2828805.11 6359056.44 93.6 0 406 20986-0 Paengaroa North B9 Trust C 2811858.88 6372039.72 270 0 953 21018-0 Blennerhasset DJ C 2817864.3 6366949.56 170 0 4665 21190-0 Spedding PG C 2814460.16 6368190.39 218 0 4599, 4627 21288-0 Farnum P & E C 2816651.2 6367646.87 125 0 4200 21289-0 Matai Pacific Limited C 2816749.07 6367761.13 598 0 4205 21322-0 Lyford PB & PM C 2809600 6368252.45 70 0 4845 21343-0 Roberts SA & JM C 2817792.64 6367076.73 160 0 249 21474-0 Coach Road Coolstores Ltd C 2811155.41 6366922.71 432 0 410 21518-0 Ashby Trust HE C 2813875.05 6368504.68 176 0 1051 21536-0 McCosh R C 2814041.11 6367445.5 540 0 1144 21555-0 McNaughton GD & IC C 2812389.02 6369354.81 159 0 4416 21587-0 Wilson S & K C 2808931.13 6363923.56 223 0 4454 21595-0 McNaughton GD & IC C 2811484.87 6368081.56 109 0 4417 21611-0 Peake KF & AR C 2813979.45 6367859.09 41 0 2013 21629-0 McDowell DF & EST EW McDowell C 2812782.97 6367411.67 350 0 106 21667-0 Birley A C 2812958.13 6371646.86 240 0 4069 21713-0 Balsom Family Trust C 2817722.09 6367082.28 178 0 1073 21801-1 Chetwin RL & L C 2810603.29 6368917.48 129.6 0 4123 21806-0 Boyle WJ & JR C 2814110.28 6365368.06 170 0 4088 21819-0 Birleys Family Trust C 2816423.63 6369641.36 270 0 4071 21823-1 Stewart MC & JM C 2812578.77 6369001.97 324 0 4644 21830-0 Cumming AJ&GJ C 2810882.71 6366561.05 100 0 4152 21835-0 Fowler JR & LM C 2809815.75 6361594.09 270 0 2005 21858-0 Tebbutt RA & RF C 2822547.88 6369858.72 108 0 4673 21866-0 Taylor SM & K C 2822623.69 6369971.92 136 0 1069 21878-0 Henderson H & L & A Kosoof C 2822275.8 6369097.12 480 0 4736 21895-0 Neilson, Graeme T/A Coach Road Orchards C 2812146.87 6367187.65 197 0 2358 21908-0 Blennerhasset DJ C 2827604.23 6367678.17 327 0 21915-1 Garwood J C 2823202.69 6367444.49 105 0 4222 21930-0 Leppard Orchards Ltd C 2809152.63 6367392.89 220 0 4452 21947-0 Avery Family Trust NM & LM C 2816917.73 6367172.78 200 0 4112 21951-0 Equine Estate Ltd C 2816913.47 6353450.53 37 0 4260, 4188 22023-0 McLaren R & S C 2811750.1 6369982.86 208 0 4101 22081-0 Roberts KT&JP C 2811659.22 6366834.37 108 0 4882 22102-3 Steel SG C 2809582.19 6368725.72 187 0 4636 22142-0 Davies K & R C 2816840.81 6367741.33 52 0 4156 22150-0 Crusader Farms Ltd C 2816512.53 6366691.25 189 0 4607
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EBOP consent Name Status1 Easting Northing Maximum daily allocation Maximum daily allocation, frost protection EBOP bore log number (m3/day) (m3/day) number 25097-0 Wright Geoffery A & Sonia N C 2813858.19 6373981.48 450 0 25162-0 Black G & J C 2817797.36 6368801.32 9000 0 4043, 3594, 4010 60422-0 Paengaroa North K Trust C 2810930 6371220 780 0 1699, 952 60976-0 Natusch A & J C 2821660 6362420 500 0 2680, 10042 61265-0 Awanuiarangi Road Residents C 2831070 6362910 120 0 10009 61978-0 Omega Kiwifruit Ltd C 2813977.46 6368571.19 2020 0 3722 62109-0 Trott Family Trust-I & C Trott C 2820231.74 6364745.34 700 700 10415, 10413 62369-0 BJ & JM Bragg Family Trust C 2812910.28 6373383.31 648 518 10542 62445-0 Milsom Ta Jace Group Farms S C 2817014.07 6366572.93 5120 2640 10991 62763-0 Voyager Trust C 2822529.44 6369002.09 3850 3850 62766-0 Bassett DN & MJ C 2823738.18 6367628.72 308 308 10852 62778-0 Fowler RA & AC C 2809823.52 6363049.13 288 288 10818 62789-0 Elmsly CJ C 2810858.62 6369897.94 396 198 2586 62812-0 Mackenzie & S Ceiriog-Jones R C 2823579.35 6367585.23 2000 2000 10868 62846-0 Jobo Family Trust/The Trustees C 2817470.07 6368252.26 1332 1332 62864-0 MY Wilkins, NM Wilkins & Dean Wearne Trustee C 2814052.16 6369696.38 1350 1350 2656 62957-0 Western BOP District Council C 2814166.91 6369454.84 8640 0 10919 63124-0 McKenzie IR C 2823259.73 6367536.21 1201 1201 10892 63135-0 Boyle K & C C 2814655.72 6365696.12 432 432 10662 63202-0 Cassey GE C 2815109.85 6367948.68 432 432 10905 63233-0 Hickson Family Trust PA C 2815261.2 6368213.25 2880 2851 10669 63256-0 Lyons Family Trust VJ C 2812932 6373716.08 880 880 10934 63257-0 Warwick Farms Ltd C 2814570 6369320 5000 5000 11395 63286-0 Toru Enterprises Ltd C 2809509.2 6368222.04 720 720 10952 63389-0 ? C 2809913 6367390 2592 2592 2659 63393-0 Paengaroa North K Trust C 2811171.17 6371290.97 900 900 2681 64582-0 Aronia Corporation Ltd C 2811873 6372119 4680 4680 3883 64607-0 RH Hall Group Limited C 2821770 6370150 1010 1010 10631 64839-0 Lindisfarne Ltd C 2809360 6367590 2160 2160 1493 64839-1 Lindisfarne Ltd C 2809950 6367370 5184 5184 2659 Total 76011.8 42313 64929-0 Seaview Orchards A 2812550 6367042 5270 5270 2674 64929-1 Seaview Orchards A 2812137 6367178 5961 5961 2691 65205-0 Saga A 2811910 6367351 2500 2500 2693 65329-0 La Vigna A 2811878 6366358 3000 3000 10800 65346-0 JB Family Trust A 2816089 6369098 1500 1500 2692 Total 18231 18231
1 Status C = existing groundwater allocation A = groundwater allocation application
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APPENDIX 4 – EXISTING GROUNDWATER CONSENTS 29TH MAY 2008, BY CATCHMENT AND BY GEOLOGICAL UNIT
EBOP EBOP Bore NZMG NZMG Maximum daily Surface Geological unit Remark Consent number log Number Easting Northing allocation partitioned by well and aquifer catchment (m3/d) 20298-0 4377 2824565 6368200 123 Ohinepanea geological unit unknown well depth unknown 20468-0 4275 2815318 6368227 543.5 Wharere geological unit unknown well depth unknown 20468-0 4600 2815318 6368227 543.5 Wharere geological unit unknown well depth unknown 20479-0 171 2817883 6367175 162 Pongakawa Pleistocene Sediments no screen depth 1 (well assumed to be open at the bottom of casing) 20814-0 1074 2811277 6366514 200 Pokopoko Minden-Otawa no screen depth (well assumed to be open at the bottom of casing) 20839-0 4367 2813997 6366715 182 Wharere Pleistocene Sediments no screen or casing depth (well assumed to be open at the bottom) 20892-0 4251 2817448 6369517 54.6 Wharere Geological unit unknown well depth unknown 20935-0 418 2809137 6367187 133.3 Kaikokopu Pleistocene Sediments no screen depth (well assumed to be open at the bottom of casing) 20935-0 1698 2809137 6367187 133.3 Kaikokopu Minden-Otawa no screen depth (well assumed to be open at the bottom of casing) 20935-0 2419 2809137 6367187 133.3 Kaikokopu Pleistocene Sediments no screen depth (well assumed to be open at the bottom of casing) 20936-0 4823 2811559 6367659 260 Pokopoko Pleistocene Sediments no screen depth (well assumed to be open at the bottom of casing) 20952-0 406 2828805 6359056 93.6 Pikowai Matahina Ignimbrite no screen depth (well assumed to be open at the bottom of casing) 20986-0 953 2811859 6372040 270 Kaikokopu Pleistocene Sediments 21018-0 4665 2817864 6366950 170 Pongakawa Pleistocene Sediments no screen or casing depth (well assumed to be open at the bottom ) 21190-0 4599 2814460 6368190 109 Kaikokopu geological unit unknown well depth unknown 21190-0 4627 2814460 6368190 109 Kaikokopu Pleistocene Sediments no screen or casing depth (well assumed to be open at the bottom ) 21288-0 4200 2816651 6367647 125 Wharere geological unit unknown well depth unknown 21289-0 4205 2816749 6367761 598 Wharere geological unit unknown well depth unknown 21322-0 4845 2809600 6368252 70 Kaikokopu geological unit unknown well depth unknown 21343-0 249 2817793 6367077 160 Pongakawa Pleistocene Sediments 21474-0 410 2811155 6366923 432 Pokopoko Pleistocene Sediments no screen depth (well assumed to be open at the bottom of casing) 21518-0 1051 2813875 6368505 176 Kaikokopu Pleistocene Sediments no screen depth (well assumed to be open at the bottom of casing) 21536-0 1144 2814041 6367446 540 Wharere Pleistocene Sediments no screen depth (well assumed to be open at the bottom of casing) 21555-0 4416 2812389 6369355 159 Pokopoko Minden-Otawa no screen depth (well assumed to be open at the bottom of casing) 21587-0 4454 2808931 6363924 223 Pokopoko Pleistocene Sediments no screen depth (well assumed to be open at the bottom of casing) 21595-0 4417 2811485 6368082 109 Pokopoko Pleistocene Sediments no screen depth (well assumed to be open at the bottom of casing) 21611-0 2013 2813979 6367859 41 Kaikokopu Minden-Otawa 21629-0 106 2812783 6367412 350 Pokopoko Minden-Otawa no screen depth (well assumed to be open at the bottom of casing) 21667-0 4069 2812958 6371647 240 Kaikokopu Minden-Otawa no screen or casing depth (well assumed to be open at the bottom) 21713-0 1073 2817722 6367082 178 Pongakawa Minden-Otawa no screen/casing depth (well assumed to be open at the bottom ) 21801-1 4123 2810603 6368917 129.6 Kaikokopu Pleistocene Sediments no screen depth (well assumed to be open at the bottom of casing) 21806-0 4088 2814110 6365368 170 Wharere Minden-Otawa no screen or casing depth (well assumed to be open at the bottom) 21819-0 4071 2816424 6369641 270 Wharere Pleistocene Sediments no screen or casing depth (well assumed to be open at the bottom) 21823-1 4644 2812579 6369002 324 Pokopoko geological unit unknown well depth unknown 21830-0 4152 2810883 6366561 100 Pokopoko geological unit unknown well depth unknown 21835-0 2005 2809816 6361594 270 Pokopoko Minden-Otawa 21858-0 4673 2822548 6369859 108 Ohinepanea Pleistocene Sediments no screen or casing depth (well assumed to be open at the bottom ) 21866-0 1069 2822624 6369972 136 Ohinepanea Pleistocene Sediments 21878-0 4736 2822276 6369097 480 Ohinepanea Pleistocene Sediments no screen or casing depth (well assumed to be open at the bottom ) 21895-0 2358 2812147 6367188 197 Pokopoko Pleistocene Sediments no screen depth (well assumed to be open at the bottom of casing) 21908-0 no bore number 2827604 6367678 327 Hauone geological unit unknown well depth unknown 21915-1 4222 2823203 6367444 105 Ohinepanea Basement no screen depth (well assumed to be open at the bottom of casing) 21930-0 4452 2809153 6367393 220 Kaikokopu geological unit unknown well depth unknown 21947-0 4112 2816918 6367173 200 Wharere geological unit unknown well depth unknown 21951-0 4188 2816913 6353451 18.5 Pongakawa Basement no screen depth (well assumed to be open at the bottom of casing) 21951-0 4260 2816913 6353451 18.5 Pongakawa Basement no screen depth (well assumed to be open at the bottom of casing)
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EBOP EBOP Bore NZMG NZMG Maximum daily Surface Geological unit Remark Consent number log Number Easting Northing allocation partitioned by well and aquifer catchment (m3/d) 22023-0 4101 2811750 6369983 208 Pokopoko geological unit unknown well depth unknown 22081-0 4882 2811659 6366834 108 Pokopoko geological unit unknown well depth unknown 22102-3 4636 2809582 6368726 187 Pokopoko geological unit unknown well depth unknown 22142-0 4156 2816841 6367741 52 Wharere geological unit unknown well depth unknown 22150-0 4607 2816513 6366691 189 Wharere geological unit unknown well depth unknown 25097-0 no bore number 2813858 6373981 450 Kaikokopu geological unit unknown well depth unknown 25162-0 3594 2817797 6368801 Wharere Pleistocene Sediments no screen depth (well assumed to be open at the bottom of casing) 25162-0 4043 2817797 6368801 4500 Wharere Pleistocene Sediments no screen depth (well assumed to be open at the bottom of casing) 25162-0 4010 2817797 6368801 4500 Wharere Minden-Otawa no screen or casing depth (well assumed to be open at the bottom) 60422-0 1699 2810930 6371220 390 Kaikokopu Minden-Otawa no screen depth (well assumed to be open at the bottom of casing) 60422-0 952 2810930 6371220 390 Kaikokopu Pleistocene Sediments 60976-0 2680 2821660 6362420 250 Pongakawa Basement 60976-0 10042 2821660 6362420 250 Pongakawa Basement 61265-0 10009 2831070 6362910 120 Pikowai Pleistocene Sediments 61978-0 3722 2813977 6368571 2020 Kaikokopu Pleistocene Sediments 62109-0 10415 2820232 6364745 350 Pongakawa Pleistocene Sediments 62109-0 10413 2820232 6364745 350 Pongakawa Pleistocene Sediments 62369-0 10542 2812910 6373383 648 Kaikokopu Pleistocene Sediments 62445-0 10991 2817014 6366573 5120 Wharere Minden-Otawa no screen depth (well assumed to be open at the bottom of casing) 62763-0 no bore number 2822529 6369002 3850 Ohinepanea geological unit unknown well depth unknown 62766-0 10852 2823738 6367629 308 Ohinepanea Basement no screen depth (well assumed to be open at the bottom of casing) 62778-0 10818 2809824 6363049 288 Pokopoko Minden-Otawa no screen depth (well assumed to be open at the bottom of casing) 62789-0 2586 2810859 6369898 396 Kaikokopu Pleistocene Sediments 62812-0 10868 2823579 6367585 2000 Ohinepanea Basement no screen depth (well assumed to be open at the bottom of casing) 62846-0 no bore number 2817470 6368252 1332 Wharere geological unit unknown well depth unknown 62864-0 2656 2814052 6369696 1350 Kaikokopu Pleistocene Sediments 62957-0 10919 2814167 6369455 8640 Kaikokopu Pleistocene Sediments 63124-0 10892 2823260 6367536 1201 Ohinepanea Basement no screen depth (well assumed to be open at the bottom of casing) 63135-0 10662 2814656 6365696 432 Wharere Minden-Otawa 63202-0 10905 2815110 6367949 432 Wharere Minden-Otawa 63233-0 10669 2815261 6368213 2880 Wharere Minden-Otawa 63256-0 10934 2812932 6373716 880 Kaikokopu Pleistocene Sediments 63257-0 11395 2814570 6369320 5000 Kaikokopu geological unit unknown well depth unknown 63286-0 10952 2809509 6368222 720 Kaikokopu Minden-Otawa 63389-0 2659 2809913 6367390 2592 Kaikokopu geological unit unknown well depth uknown 63393-0 2681 2811171 6371291 900 Kaikokopu Minden-Otawa 64582-0 3883 2811873 6372119 4680 Kaikokopu geological unit unknown well depth unknown 64607-0 10631 2821770 6370150 1010 Ohinepanea Pleistocene Sediments 64839-0 1493 2809360 6367590 2160 Pokopoko Pleistocene Sediments no screen depth (well assumed to be open at the bottom of casing) 64839-1 2659 2809950 6367370 5184 Pokopoko Pleistocene Sediments no screen depth (well assumed to be open at the bottom of casing)
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Principal Location Other Locations
1 Fairway Drive Dunedin Research Centre Wairakei Research Centre National Isotope Centre Avalon 764 Cumberland Street 114 Karetoto Road 30 Gracefield Road PO Box 30368 Private Bag 1930 Wairakei PO Box 31312 Lower Hutt Dunedin Private Bag 2000, Taupo Lower Hutt New Zealand New Zealand New Zealand New Zealand T +64-4-570 1444 T +64-3-477 4050 T +64-7-374 8211 T +64-4-570 1444 www.gns.cri.nz F +64-4-570 4600 F +64-3-477 5232 F +64-7-374 8199 F +64-4-570 4657