Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Report No. R15/139 ISBN 978-1-927299-12-8 (print) 978-1-927299-13-5 (web)
M Dodson
October 2015
Report No. R15/139 ISBN 978-1-927299-12-8 (print) 978-1-927299-13-5 (web)
PO Box 345 Christchurch 8140 Phone (03) 365 3828 Fax (03) 365 3194
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Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Summary
Background: In mid-2016, the limit-setting process for the Waimakariri Canterbury Water Management Strategy (CWMS) zone is scheduled to commence. Before this process begins, Environment Canterbury needs to develop groundwater conceptual models for the Waimakariri CWMS zone. A conceptual model is a picture and/or a narrative that summarises our understanding of a system. My groundwater conceptual model will be used to provide information to communities and decision makers, and as the basis for numerical models. My expectation is that these conceptual models will evolve as further work is undertaken in this CWMS zone.
What I did: I identified and then contacted stakeholders and partners to ask if they had preferred groundwater technical experts to participate in this project. I interviewed ten groundwater technical experts about their understanding of the groundwater system in the Waimakariri CWMS zone. We then held a workshop to work through the points of agreement and disagreement with the intention of identifying potential projects to resolve disagreements. I then used the information gathered from this project and other available information to develop my groundwater conceptual model. Here I describe conceptual models for the Lees Valley, Loburn Fan and Ashley-Waimakariri plains.
What I found: The participating groundwater technical experts agreed on many issues. There were also areas of disagreement, and this disagreement can be used to indicate the degree of uncertainty. This uncertainty will be reduced by undertaking specific work to address areas of disagreement, but it may be that we have to accept a high degree of uncertainty.
The Lees Valley is a closed basin where the outflow occurs via the two main rivers. The Loburn Fan has significant interaction between surface and groundwater, and water infiltrating through soil into groundwater is limited because of the soil properties and topography, particularly around the outer margin of the fan. The Ashley-Waimakariri plains groundwater system is over 400 m thick in places but thins towards the margins. Groundwater generally flows towards the coast where some groundwater discharges offshore and some discharges to the surface, which provides water to the spring-fed steams. In my description of the groundwater conceptual model, I have discussed the major assumptions I made and indicated issues that may be important to the management of water resources in the Waimakariri CWMS zone
Environment Canterbury Technical Report i Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
ii Environment Canterbury Technical Report Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Table of contents
Summary ...... i
1 Introduction ...... 1 1.1 Project aims ...... 1 1.2 Purpose of this report ...... 1
2 Methodology ...... 4
3 Groundwater conceptual model ...... 7 3.1 Lees Valley ...... 7 3.1.1 Physical setting and conceptual model ...... 7 3.1.2 Implications for management ...... 8 3.2 Loburn Fan ...... 12 3.2.1 Physical setting ...... 12 3.2.2 Conceptual model ...... 19 3.2.3 Implications for management ...... 19 3.3 Ashley-Waimakariri plains ...... 21 3.3.1 Physical setting ...... 21 3.3.2 Conceptual model ...... 36 3.3.3 Implications for management ...... 37
4 Uncertainty and recommendations ...... 41 4.1 Lees Valley ...... 41 4.2 Loburn Fan ...... 41 4.3 Hydraulic connection between shallow/deep productive water-bearing zones in the Eyre River GAZ ...... 41 4.4 Offshore discharge...... 42 4.5 Groundwater flow beneath or into the Waimakariri River in the lower reaches ...... 42 4.6 Waimakariri River and groundwater in the upper plains ...... 42 4.7 Conversion of Eyrewell forest and surrounding area ...... 43 4.8 Public water supplies vulnerability to contamination ...... 43 4.9 Lag times and denitrification ...... 43
5 Next steps ...... 43
6 Synopsis ...... 44
7 Acknowledgements ...... 44
8 References ...... 45
Appendix A: Developing a groundwater conceptual model for the Waimakariri CWMS zone ...... 49
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Appendix B: Memo 6 November 2014 ...... 51
Appendix C: Waimakariri groundwater conceptual model project ...... 55
Appendix D: Summary of statements from the interviews ...... 56
Appendix E: Memo 17 February 2015 ...... 60
Appendix F: Workshop PowerPoint presentation ...... 66
Appendix G: Areas of agreement and disagreement ...... 78
List of Figures
Figure 1-1: Waimakariri CWMS zone ...... 2 Figure 1-2: Conceptual model of the Ashley-Waimakariri plains groundwater system ...... 3 Figure 2-1: Process used in the workshop to discuss points of disagreement ...... 6 Figure 3-1: Oblique 3D image of the Waimakariri CWMS zone ...... 7 Figure 3-2: Map of the Lees Valley and irrigated area ...... 9 Figure 3-3: Geological map of the Lees Valley ...... 10 Figure 3-4: Mapped regional wetlands in the Lees Valley ...... 11 Figure 3-5: Waimakariri CWMS zone boundary and GAZ boundaries ...... 13 Figure 3-6: Rivers, streams and mapped springs on the Loburn Fan...... 14 Figure 3-7: Geological map of the Loburn Fan ...... 15 Figure 3-8: Estimated depth of Quaternary deposits ...... 16 Figure 3-9: Average soil profile available water ...... 17 Figure 3-10: Loess soil coverage and irrigated areas on the Loburn Fan ...... 18 Figure 3-11: Piezometric contours based on average groundwater levels ...... 20 Figure 3-12: Geological map of the Waimakariri CWMS zone ...... 23 Figure 3-13: Average soil profile available water ...... 24 Figure 3-14: Estimated depth of Quaternary deposits ...... 25 Figure 3-15: Wells less than 50 m deep by maximum yield near the Eyre River ...... 26 Figure 3-16: Wells greater than 50 m deep by maximum yield near the Eyre River ...... 27 Figure 3-17: Irrigated area in the Waimakariri CWMS zone ...... 28 Figure 3-18: Rivers by type as defined in the Natural Resource Regional Plan ...... 29 Figure 3-19: Springs and wetlands in the Waimakariri CWMS zone ...... 33 Figure 3-20: Nitrate concentration contours from NCCB (1982) ...... 34 Figure 3-21: Piezometric contours, May 2011 ...... 35 Figure 3-22: Conceptual model for the Ashley-Waimakariri plains...... 36 Figure 3-23: Waimakariri Zone Committee proposed management zones ...... 39 Figure 3-24: Boundaries of the Land and Water Regional Plan and the Waimakariri River Regional Plan ...... 40 Figure 5-1: Other groups that need to be consulted about these conceptual models ...... 44
iv Environment Canterbury Technical Report Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
1 Introduction The limit-setting process1 for the Waimakariri Canterbury Water Management Strategy (CWMS) zone is scheduled to begin mid-2016 (Figure 1-1). In preparation for the limit-setting process, Environment Canterbury needs to develop a conceptual model of the Waimakariri groundwater system.
A conceptual model is a picture (Anderson and Woessner, 2002) and/or a narrative in which an understanding of a particular system is presented. An example of a conceptual model for the Ashley- Waimakariri plains groundwater system is in Figure 1-2 (adapted from Sanders, 1997). Sanders (1997) regional scale conceptual model summarises the geology, major elements of the water balance, topography, surface water features and surface-groundwater interactions.
The intention of this project is to develop conceptual groundwater models for the Waimakariri CWMS zone, including the Ashley-Waimakariri plains, Lees Valley and Loburn Fan (Figure 1-1). These conceptual models will be used: • as the basis for numerical models • to produce information to support decision makers and communities • to fill in gaps in areas where there is little data • as the deciding vote if we have contradicting lines of evidence. It is my expectation that these conceptual models will be further refined as more technical assessments are undertaken.
One of the learnings Environment Canterbury has taken on board from previous limit-setting processes is to start discussing issues with partners and stakeholders as early as possible. In the Waimakariri limit-setting process, we are deliberately engaging early with partners, stakeholders and their technical experts. This project is one of the first steps in this process. By listening to the experience and views of the wider hydrological community we will develop more robust conceptual models of the groundwater system. Engaging with partners and stakeholders, and collaborating with external technical experts will help Environment Canterbury’s technical team deliver credible, fit-for- purpose and relevant science to inform decision makers.
1.1 Project aims The aims of this project were to: • begin engaging with partners, stakeholders and their technical experts • identify points where technical experts agree and disagree • develop a regional scale conceptual model for the Waimakariri groundwater system.
1.2 Purpose of this report This technical report serves to: • document the process • consolidate the relevant documents created during this project • describe the conceptual model for the groundwater system of the Waimakariri CWMS zone • record the areas where technical experts agree and disagree • record the recommendations for further work made by the participants during the workshop to address areas of disagreement • record potential strategies for dealing with uncertainly where further work cannot be undertaken or if work is undertaken but the issue is still ambiguous.
1 Often also referred to as a sub-regional planning process
Environment Canterbury Technical Report 1 Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Figure 1-1: Waimakariri CWMS zone
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Figure 1-2: Conceptual model of the Ashley-Waimakariri plains groundwater system (adapted from Sanders, 1997)
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2 Methodology The project plan was to: 1. identify and contact partners and stakeholders 2. identify and contact the partners and stakeholders preferred technical expert 3. prepare a survey questionnaire 4. interview and then summarise the technical experts’ interviews in a memorandum 5. hold a workshop with the technical experts 6. document the process and report via a technical report.
I identified partners and stakeholders by talking with staff at Environment Canterbury and the Waimakariri Zone Committee. The Waimakariri Zone Committee meets occasionally with an ‘industry working group’. Darren Mann2 contacted the stakeholders who attend that meeting on my behalf. Table 2-1 lists the partners and stakeholders identified during this process.
Table 2-1: Partners and stakeholders contacted as a part of this project Partners and stakeholders Te Ngāi Tūāhuriri Rūnanga Dairy NZ Ravensdown Ngāi Tahu Farming FAR Synlait Waimakariri Zone Committee Beef and Lamb Hort NZ Waimakariri Irrigation Limited Forest and Bird Ballance Waimakariri District Council Fish and Game Fonterra Ministry of Primary Industries Irrigation NZ BNZ Department of Conservation Federated Farmers ASB
The partners and stakeholders were contacted by email and asked to nominate a groundwater technical expert (a copy of the letter is shown in Appendix A). I acknowledge that many of the organisations may not have a preferred technical expert, therefore in the letter I had a table listing groundwater technical experts who are prominent in the Waimakariri CWMS zone. I had a number of responses to the letter with stakeholders nominating groundwater technical experts. In total 13 technical experts were nominated and ten agreed to participate in project (Table 2-2). Before interviewing the technical experts, I sent out a brief memorandum to provide them with some background to the project (Appendix B).
Table 2-2: Technical experts who participated in this project Technical expert: Company/institution: Date interviewed: Peter Callander PDP 4 December 2014 Stephen Douglass URS3 10 December 2014 Ian McIndoe Aqualinc Research 2 December 2014 John Talbot Bowden Environmental 18 November 2014 Mike Thorley Beca 4 December 2014 Hugh Thorpe University of Canterbury 11 November 2014 John Weeber GB HydroServices 19 November 2014 Julian Weir Aqualinc Research 2 December 2014 Paul White GNS Science 9 December 2014 Scott Wilson Lincoln Agritech 11 December 2014
In retrospect, one of the learnings I have taken from this phase of the project is to put more effort into identifying and contacting stakeholders. While I believe the technical experts with the most experience with the Waimakariri groundwater system were contacted, more engagement with stakeholders may have led to the nomination of one or two other technical experts.
2 At that point in time Darren was the chair of the industry working group and member of the Waimakariri Zone Committee 3 URS and AECOM have subsequently merged into a single company operating under AECOM
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In preparation for the interviews, I created a questionnaire (Appendix C) that focused specifically on the groundwater system in the Waimakariri CWMS zone and the technical experts’: • experience • conceptual model • understanding of the geology • understanding of the key elements of the water balance • understanding of the surface/groundwater interactions • understanding of groundwater quality and associated processes • any other key hydrology processes that they wanted to discuss.
The interviews were undertaken between 11 November and 9 December 2014, each taking between one hour and two and a half hours. I was present for all interviews. For the most part I was also accompanied by an additional Environment Canterbury staff member. All interviews were undertaken face to face except for Paul White who I interviewed over the phone. Julian Weir and Ian McIndoe were interviewed together, while all other participating technical experts where interviewed individually.
I ran the interviews informally, as technical discussions between peers. I allowed the participating technical expert to talk about whatever they felt was relevant but for the sake of completeness I ran through the questions in Appendix C. While I geared the questions towards a regional scale view of the groundwater system, some participating technical experts discussed issues and processes at smaller scales.
The interviews contained a vast amount of technical information about the Waimakariri CWMS zone groundwater system as summarised in Appendix D. For instance, many people said that rainfall recharge was one of the key inputs into the system. I therefore noted this as one of the statements. I did not list every statement made by each participant, rather I tried to capture the most relevant statements and give some sense of the breadth of the topics covered. I then noted if other participants agreed, disagreed, felt it was plausible, or were unsure with each statement. For instance, seven of the ten participants agreed that rainfall recharge was likely to be a major input into the system, while rainfall recharge as an input was not explicitly mentioned by the other three. Because different people had different amounts of experience in this zone, different background and approaches, not everyone commented on everything. There were also a number of issues raised by a single participant.
For statements that had been commented on by more than one person I classified it as ‘mostly agreed’ if everyone who commented on that statement agreed to it or thought it was plausible. If there were one or more people who were unsure or disagreed then I classified it as ‘some disagreement’. In our example, I classified rainfall recharge as ‘mostly agreed’ because those who did mention it felt it was an important input to the groundwater system. For those statements one person commented on, I classified as ‘N/A’ (see Appendix D). I then sorted these statements into five categories: • geology • water balance • surface/groundwater interaction • water quality • other.
For a number of the statements there was a range of views. For instance, in regards to offshore flow some people were of the view that it was not occurring at all, some were of the view that it was occurring but only from the topmost part of the groundwater system, others were of the view that it occurred over the entire thickness of the system. I noted that the evidence cited to support these hypotheses were sometimes similar. My conclusion was that because of the uncertainty around this issue there is potential for a number of contradictory hypotheses to coexist. The level of agreement and disagreement may be a useful indicator of the level of uncertainty around any particular issue.
Another insight from analysing the interview responses was that even when the technical experts seemed to agree on an issue, there was a call to undertake further work in order to reduce uncertainly around a measurement or to gain a better understanding of a process. For example, the participants
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seemed to agree that the stock and irrigation races are providing recharge to the groundwater system, but there was uncertainty about how much water was being lost and where the losses were occurring.
I summarised my analysis of the interviews in a memorandum (Appendix E) and distributed it to the participants before the workshop. The workshop was held on Thursday 26 February, in the ‘Waimakariri room’ at the BNZ Russley Partners Centre4. At the workshop, we worked through each of the five categories listed above to confirm the points where there was agreement (Appendix F and Table 2-3). For statements where there was disagreement, we used the process shown in Figure 2-1. The intention of this process was to acknowledge, in some cases, the wide range of views held by the participants and then constructively develop a plan to address the disagreement. I have summarised what was discussed at the workshop in a series of tables (Appendix G).
Table 2-3: Agenda for the workshop Time Topic Lead by Starting at 9am Introductions Matt Dodson Setting the scene Claire McKay5 Science and the sub-regional process Ken Taylor6 Outline and plan for the workshop Matt Water balance Matt and Murray Griffin7 Geology Matt and Murray Surface/groundwater interaction Matt and Murray Water quality Matt and Murray 12-1230pm LUNCH Other considerations Matt and Murray Opportunities for collaboration Matt and Murray Ending before 2pm Summary and next steps Matt and Murray
Is the statement significant?
If we agree that the statement is significant, what can be done to resolve the issue (i.e. targeted project)?
What happens if we still can't resolve the issue?
Figure 2-1: Process used in the workshop to discuss points of disagreement
Feedback from participants at and following the workshop was very positive, with people finding the workshop engaging. Many people, myself included, learnt something about the groundwater system in the Waimakariri CWMS zone during the workshop.
4 I would like to acknowledge Ray Fraser (Corporate Agribusiness Partner, BNZ) for offering the use of BNZ’s conference rooms 5 Chair of the Waimakariri Zone Committee 6 Director of the Science Group, Environment Canterbury 7 Waimakariri CWMS Zone Facilitator, Environment Canterbury
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3 Groundwater conceptual model In this section, I will present my conceptual understanding of the groundwater system in the Waimakariri CWMS zone. It is also my intention in this section to highlight major assumptions and to emphasise matters that may be important to the management of the water resource. I have incorporated the agreed statements from the interviews and workshop into the groundwater conceptual model.
I have separated the Waimakariri CWMS zone into three areas; Lees Valley, Loburn Fan and Ashley- Waimakariri plains based on geographic, hydrologic and geologic considerations (Figure 3-1).
Figure 3-1: Oblique 3D image of the Waimakariri CWMS zone (source: Fouad Alkhaier, senior Hydrogeologist, Environment Canterbury)
3.1 Lees Valley
3.1.1 Physical setting and conceptual model There is very little hydrogeological data and I do not know of any hydrogeological investigations that have been undertaken in the Lees Valley. My conceptual model is based on observations of the geology, hydrology and topography.
The Lees Valley is an inland basin north of Oxford (Figure 1-1 and Figure 3-1). Within the valley, there is approximately 7,500 - 8,000 ha of gently sloping plains surrounded by hills. There are two main rivers in the valley, the Ashley River/Rakahuri and Okuku River. The Ashley River/Rakahuri and its tributaries (Duck Creek, Whistler River and Townshend River) drain a significant portion of the valley and ultimately flow out through a gorge to the southeast of the plains. The Okuku River drains a portion of the northern part of the valley and ultimately flows out through a gorge to the northeast of the plains. All surface water exits the Lees Valley via these two rivers (Figure 3-2).
Geological maps (Forsyth et al., 2008) and bore logs from wells L34/0001 and L34/0039 suggest that the plains are Quaternary aged sediments, predominately composed of gravels with varying quantities of sands, silts and clays. The hills are Torlesse Super Group rocks, predominately composed of alternating sequence of sandstones and mudstones (Figure 3-3).
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I am assuming that the Quaternary sediments are more permeable than the Torlesse Super Group. This assumption is based on geological descriptions of the sediments that can be used to infer their hydraulic properties. Torlesse Super Group rocks are indurated8 but highly fractured sandstones and mudstones, whereas Quaternary deposits are unconsolidated9 gravels, sands, silts and clays. While the rocks of the Torlesse Super Group will transmit some groundwater (mainly though the fractures in the rock), I assume that the volume of this water is small, and the speed with which the water moves through this rock is slow when compared to movement of groundwater within Quaternary sediments. Therefore, groundwater in the Torlesse Super Group will not be a significant part of the water balance calculations for the Quaternary sediments. I conceptualise the Lees Valley as a closed basin where the outflow from the valley occurs via the two main rivers.
I assume that the main groundwater recharge source in Lees Valley is rainfall. There is approximately 100 ha of irrigated area10 on the plains (Figure 3-2), therefore there is also likely to be some irrigation return water. I will use the term Land Surface Recharge (LSR) for recharge from both rainfall and irrigation return water. There are a number of wetlands on the plains, which indicates that there is interaction between surface and groundwater (Figure 3-4). Apart from LSR and perhaps some river recharge, there are no other obvious groundwater recharge sources in the Lees Valley. Groundwater is likely to discharge to the rivers, abstracted as permitted water use from wells, and spring discharge (i.e. wetlands).
3.1.2 Implications for management If the Lees Valley is a closed basin it means that soluble nutrients lost from the base of the root zone will ultimately end up in the rivers. There may be some nutrients that are removed as they move through groundwater but I have not yet attempted to estimate this rate of nutrient loss, nor have I estimated travel times for nutrients to move through the groundwater system to the rivers. However, because there is little to no data available on attenuation processes between base of the soil profile and in-stream water quality, any assessment will need to make assumptions about how much nutrient is removed. Water quality sampling over time of the rivers as they exit the valley will provide an indication of the effectiveness of any nutrient management policies.
In my conceptualisation, groundwater discharges to the rivers. Therefore, to protect water quality outcomes in the river, there will be some requirement to manage land use. Additionally, if the nutrients sourced from Lees Valley reach the Okuku River and Ashley River/Rakahuri, then this load should be added to the Loburn Fan and the Ashley-Waimakariri plains catchment load calculations.
There is currently no groundwater allocation zone (GAZ) or allocation limit defined for the Lees Valley. A limit could be based on average rainfall inputs, or river flows. For the allocation zone area, I would recommend including the entire catchment above the two gorges for convenience of management (see Poulsen and Smith, 2011 for discussion). There are no consented groundwater takes in the Lees Valley and I am not aware of any proposals to use groundwater here, but there is potential for groundwater abstraction (i.e. the presence of a Quaternary gravel basin). I suggest that a groundwater allocation for the Lees Valley be developed solely on the fact that it is better to have a management regime in place before any development of the groundwater resource occurs.
8 The term induration describes how hard or solid a rock is and indurated means it is solid or hard 9 Unconsolidated means the sediments is loose and that groundwater can readily flow through the spaces between the grains 10 This is a surface water take from one of the tributaries of the Ashley River/Rakahuri
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Figure 3-2: Map of the Lees Valley and irrigated area (source Brown, 2015)
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Figure 3-3: Geological map of the Lees Valley (source GNS Science, Q-map series)
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Figure 3-4: Mapped regional wetlands in the Lees Valley
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3.2 Loburn Fan
3.2.1 Physical setting The Loburn Fan is a mix of flat and downlands topography, located to the north of the Ashley River/Rakahuri and to the east of the Lees Valley (Figure 3-1). The Loburn Fan groundwater allocation zone (GAZ) is a management area (Aitchison-Earl et al., 2004; Figure 3-5). The Loburn Fan GAZ and Loburn Fan cover nearly the same area, so in this report I will use the term Loburn Fan unless I am specifically referring to the GAZ.
Many streams, creeks and rivers flow across the Loburn Fan. The larger rivers are the Glentui River, Garry River, Okuku River and Makerikeri River (Figure 3-6). There are four springs mapped in the Loburn Fan area but there are likely to be more in this area than are not recorded on the Environment Canterbury database. These four mapped springs are located in the east of the Loburn Fan.
The geological map of the Loburn Fan shows that the plains have been formed from alluvial Quaternary deposits, composed of gravel, sand, silt and clay. The most recent Quaternary deposits (labelled Q1 in Figure 3-7) are found near the major rivers (Glentui, Garry, Okuku and Makerikeri rivers). Older gravels (deposited more than 125,000 years ago) are found along the hillside margins and are indicated by the symbol Q6 and middle Q in Figure 3-7.
There are approximately 270 wells currently drilled into Quaternary deposits on the Loburn Fan. The average depth is 25 m (minimum depth is 2.1 m and maximum 200 m) and the average maximum yield is 2.2 L/s, which is low when compared to Ashley and Cust GAZs (for the Ashley GAZ the average maximum yield is 7.5 L/s and the average maximum yield for the Cust GAZ is 4.9 L/s). Irrigation is listed as the primary use for 20 wells in the Loburn Fan area, but only four of these have an active consent to take groundwater. The highest maximum yield in the Loburn Fan (61 L/s) is from a gallery near the Okuku River (which has a consent but it is deemed a surface water take). The next highest maximum yield is 15 L/s. Anecdotes from local residents and well drillers indicate that it is difficult to find the volumes of groundwater that some people are seeking. The above information supports this view.
On the northern and western edge of the Loburn Fan are older rocks called the Kowai Formation. The Kowai Formation is composed of conglomerates, sandstones, siltstones and mudstones (Forsyth et al., 2008). Few wells have been drilled into the Kowai Formation in the Loburn Fan. Well drillers do not usually deliberately target the Kowai Formation in North Canterbury because it is not considered particularly productive.
Around the margin of the Loburn Fan are outcrops of what I will refer to as ‘the cover sequence’ (Figure 3-7). The cover sequence is of Cretaceous to Pliocene age and consists of sandstone, greensands, mudstone, claystone, limestone, volcanic rocks, conglomerate and gravel plus minor coal beds at the base of the sequence. Few wells have been drilled into the cover sequence.
The thicknesses of the Quaternary deposits have been estimated by Jongens (2011) (Figure 3-8). The Quaternary deposits are thickest near the Ashley River/Rakahuri, thin and then are absent at the margins of the Loburn Fan. A simplified description of this geometry would be that the Quaternary deposits look like a wedge (with the thicker end towards the river) overlying the cover sequence, which overlies the basement rock.
There are a number of faults in and around the Loburn Fan (Barrell and Begg, 2013; Barrell, and Van Dissen, 2014; see Figure 3-7 and Figure 3-8). Near the Ashley River/Rakahuri there is the Ashley Fault Zone and to the west and north are structures associated with the Porter Pass-Amberley Fault Zone (Cowan, 1992). It is very likely that active deformation has formed and further shaped the Loburn Fan. Given this, and the information presented in earlier paragraphs, it is likely that the geology of the Loburn Fan is complex and locally variable.
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Figure 3-5: Waimakariri CWMS zone boundary and GAZ boundaries
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Figure 3-6: Rivers, streams and mapped springs on the Loburn Fan. Note there actually two springs close to each other to the south of the label for the Makerikeri River
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Figure 3-7: Geological map of the Loburn Fan (Forsyth et al., 2008)
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Figure 3-8: Estimated depth of Quaternary deposits (Jongens, 2011)
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Figure 3-9: Average soil profile available water (source Landcare Research, S-map series)
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Figure 3-10: Loess soil coverage and irrigated areas on the Loburn Fan (source Landcare Research, S-map series; Brown, 2015)
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The average Profile Available Water (PAW) values of soils on the Loburn Fan are shown in Figure 3-9 and the location of loess soils are shown on Figure 3-10. Loess soils cover approximately 8,000 ha of the Loburn Fan GAZ, which is about 40% of its area. Rainfall recharge through loess soils is estimated to be 0.001 to 3 mm/day (Thorley and Ettema, 2007; Poulsen, 2013).
The irrigated area in the Waimakariri CWMS zone has been mapped by Brown (2015). There is approximately 540 ha of irrigated area on the Loburn Fan.
3.2.2 Conceptual model There have been few hydrogeological investigations undertaken in or around the Loburn Fan. I base my conceptual model mostly on observations of the topography, soils, hydrology and geology.
The major recharge source (input) to the groundwater system in the Loburn Fan is likely LSR (Scott, 2004). There is also likely to be stream/river recharge. The major discharge sources (outputs) are spring discharge, groundwater abstraction and groundwater outflow. Groundwater outflow is a term used to describe the volume of water that exits out of the area under consideration. Groundwater outflow from the Loburn Fan either discharges to the Ashley River/Rakahuri or flows into the Ashley- Waimakariri plains groundwater system.
I am assuming that there is little groundwater recharge on areas: • with slopes greater than 15° (Thorley and Ettema, 2007) • covered with loess (Thorley and Ettema, 2007) • composed of Kowai and cover sequence geological units. I propose that most of the groundwater recharge in the Loburn Fan will occur on the soils with very low or moderate to low average PAW capacities (Figure 3-9). In the areas outside of the Quaternary formations there will be a small amount of groundwater recharge but I assume that most rainfall will run-off to the dense network of streams (Figure 3-6).
Many of the streams and rivers that extend the length of the Loburn Fan flow at the top end but tend to be dry in their mid reaches (Burrell, 2001; Chater, 2004). It is likely that many of the streams and rivers lose water through their beds to groundwater (Scott, 2015) with at least some of this water re- emerging before the confluence of the Ashley River/Rakahuri. This observation indicates that there is a high degree of surface/groundwater interaction within Quaternary units, particularly in those sediments located close to rivers and streams (Q1 deposits). Chater (2004) and Smith (2012) found that there was an increase in flow between Bowicks Road to the Okuku - Ashley River/Rakahuri confluence (Figure 3-6). Chater (2004) hypothesised that this gain is due to groundwater discharging into the river. I think this hypothesis is plausible and it would imply that the Loburn Fan groundwater system is directly connected to the Ashley River/Rakahuri.
Environment Canterbury has generated piezometric contours from average groundwater levels and this data for the Loburn Fan is shown in Figure 3-11. Piezometric contours suggest that along the western and eastern sides of the Loburn Fan, groundwater flows east to southeast. However, in the centre of the fan groundwater flows south towards the Ashley River/Rakahuri. This groundwater flow pattern is similar to, but not identical to, the topographic gradient.
3.2.3 Implications for management The information presented in this report suggests that there is scope to review the allocation limit and extent of the Loburn Fan GAZ. I would suggest using a method similar to Thorley and Ettema (2007) to determine the allocation limit. The current allocation limit for the Loburn Fan GAZ is 40.8 m3 x 106/year. At the time of writing11 0.12 m3 x 106 /year has been allocated (or 0.31% of the allocation limit). The low volumes of water allocated in this GAZ are likely caused by the fact it is difficult to find groundwater that will yield the volumes people are seeking.
I recommend extending the boundaries of the Loburn GAZ to align with the surface water catchments, for the convenience of management (see Poulsen and Smith, 2011 for discussion).
11 October 2015
Environment Canterbury Technical Report 19 Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Figure 3-11: Piezometric contours based on average groundwater levels (arrows indicate direction of flow)
20 Environment Canterbury Technical Report Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Most of the wells in the Loburn Fan are used for domestic and/or stockwater purposes. There is a need to manage land use to ensure drinking water meets New Zealand Drinking Water Standards (MoH, 2008). My understanding of the area is that there is a lot of interaction between the surface and groundwater systems, and many of these streams ultimately discharge into the Ashley River/Rakahuri. Therefore, there is a requirement to manage land use to make sure water quality cultural and ecological outcomes are meet. Additionally, it has been hypothesised that the Loburn Fan groundwater system discharges into to the Ashley River/Rakahuri. The implication of this hypothesis for nutrient management is that the load (or part of the load) from the Loburn Fan groundwater system will be transferred to the river. As such, it will require management of the use of land to maintain the values associated with the Ashley River/Rakahuri.
There are no data on attenuation processes between the base of the soil profile and in-stream water quality, which means during the assessments we will have to make assumptions about how much nutrient is removed. Groundwater in places is naturally anoxic (Scott, 2015) which means that denitrification could be a partial mitigation for nitrogen losses in this areas.
3.3 Ashley-Waimakariri plains
3.3.1 Physical setting The Ashley-Waimakariri plains cover approximately 105,000 ha of plains containing a number of isolated hills (e.g. Starvation Hill, Burnt Hill, View Hill). The Ashley-Waimakariri plains is south of Lees Valley and the Loburn Fan. The major towns are Oxford, Rangiora and Kaiapoi (Figure 1-1).
Geology The geology of the Ashley-Waimakariri plains is predominately composed of material deposited in the Quaternary (Figure 3-12; Forsyth et al., 2008). Almost all wells drilled on the plains are screened in Quaternary deposits.
Along the coastal margin of the Ashley-Waimakariri plains, the Quaternary deposits consist of sequences of gravels, sands, silts and clays, which have been formed as a result of changes in sea level and climate. The contrast between the different materials allows mapping of the sequences by interpolating between bore log information (Durney et al., 201112). These deposits form the area often referred to as a coastal confined aquifer system. Within the coastal confined aquifer system there are a number of flowing artesian wells which demonstrate an overall upwards hydraulic gradient near the coast. The coastal confined aquifer system thins towards the north (as viewed in both plan section and in thickness, Durney et al., 2011 and Appendix B of Dodson et al., 2012).
The topmost unit of the coastal confined aquifer system was formed in part in a wetland environment. The remnants of the wetlands are reflected in the soil maps (i.e. moderate to high - very high average PAW in the coastal area in Figure 3-13) and in historical maps (Johnston, 1961). These wetlands have been mostly drained and are used for agricultural and urban purposes. Inland from the coastal confined aquifer system the geology is composed predominately of gravel-dominated strata with occasional (but not laterally extensive) sand, silt and clay layers or lenses. Figure 3-14 shows the estimated depth of the Quaternary sediments. In places, the Quaternary deposits are estimated to be greater than 400 m thick.
The foothills west of Oxford, are made up of Torlesse Super Group with deposits along the basin margin. These deposits can also be found at the surface at a number of locations throughout the plains, including Burnt Hill, View Hill, Starvation Hill, Mairaki Downs and several locations along the Waimakariri River (Figure 3-12). Few wells have been drilled into the Torlesse Super Group or the cover sequence and even fewer have screens installed in them. I assume that Torlesse Super Group and the cover sequences act as hydrological barriers because their geological descriptions suggest they are much less productive than the Quaternary deposits. In Dodson (2012), I noted that eight wells near Burnt Hill appear to be drilled into a sand unit which I interpreted to be part of the cover sequence
12 It was pointed out that the term ‘Aquifer 5’ originally was used to describe all the aquifers beneath ‘Wainoni Aquifer’ and as such probably encompasses a number of aquifers and potentially even the top of the Kowai Formation (per comms John Weeber, Hydrogeologist, GB HydroServices, 2015).
Environment Canterbury Technical Report 21 Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
(Eyre Group), though it seems unlikely that this is regionally significant in terms of the groundwater system.
A number of faults and folds have been mapped onshore (summarised in Barrell and Begg, 2013) and beneath Pegasus Bay (Barnes et al., 2011). Figure 3-14 shows the location of the known faults on the Ashley-Waimakariri plains. It is likely that these faults and related folds are having an effect on groundwater flow. For instance, in Dodson (2014) I found that the faults around the Mairaki Downs and west towards Oxford, are acting as a partial hydrological barrier and have effectively created a sub-basin. It may be that this sub-basin is not as hydraulically connected to lower plains as once assumed. I will refer to this area as the Oxford sub-basin (Figure 3-14). Environment Canterbury’s Groundwater Science Section is planning a groundwater chemistry investigation in 2016 to collect more information in the Oxford area. Additionally, a shallow seismic survey has been undertaken on our behalf in this area to provide information towards the seismic risk and the influence of these structures on groundwater flow.
It was noted by a number of the workshop participants that there are zones where well yields are generally higher or lower. For instance, the yields from wells on the Mairaki Downs and in the Oxford sub-basin seem to be overall less than wells that tap into the coastal confined aquifer system or near the Eyre River (PDP, 1993; Sanders, 1997).
A number of workshop participants noted that there appears to be a strip of predominately gravel deposits near the Eyre River that is relatively shallow (30 – 50 m deep), where there are a number of wells with high yields. Figure 3-15 shows wells shallower than 50 m deep by maximum yield, between Oxford and the Eyre River diversion. Wells capable of drawing more than 30 L/s do seem to be located generally near the Eyre River but also below Eyrewell forest and east-southeast of the Mairaki Downs. PDP (1993) and Sanders (1997) also note that the area near the Eyre River has low storage and experiences reduced water supply. This past irrigation season (2014/2015) there were a number of wells that went dry in this particular area. Recently there have been a number of high yielding wells in this same geographic area but they are deeper than 75 m to 80 m (Figure 3-16). There are large differences in heads between the shallow and deep wells, in the order of 10 to 30 m (Dodson, 2013a: Wilson, 2014).
Workshop participants also pointed out that even in the areas where yields are expected to be greater, there is still significant variability at a local scale related to the anisotropic and inhomogeneous nature of fluvially deposited material.
Water balance The major source of recharge to the entire area is LSR (Dodson et al., 2012). Rainfall recharge is spatially and temporally variable due to soil properties and climatic factors. Irrigation return water also recharges the groundwater system through direct losses during irrigation (usually a relatively small proportion of the water applied) and by maintaining a soil moisture content which may allow more rainfall to infiltrate than if it was unirrigated land (pers. comm. MS Srinivasan, Hydrologist NIWA, 2015).
Waimakariri Irrigation Limited (WIL) commenced operating in 1999. WIL has a command area of 40,000 ha with a maximum rate of take of 10.5 m3/s to irrigate 18,000 ha on the Ashley-Waimakariri plains. All irrigation in the WIL scheme is via spray. The irrigation water is delivered to farms via unlined races with estimated losses in the order of 10% (Cooper, 2011). The spatial and temporal losses from the irrigation races are not well defined and could be improved with a specific investigation. Dodson et al. (2012) have shown that WIL has had an impact on groundwater levels, particularly shallow wells within or just down-gradient of the command area. The WIL impact on groundwater is likely caused by a combination of factors including increased race losses, increased LSR and reduction in groundwater abstraction. Brown (2015) estimated that there are currently 38,000 ha of irrigated area in the Waimakariri CWMS zone, with most of this irrigation occurring on the Ashley-Waimakariri plains (Figure 3-17).
22 Environment Canterbury Technical Report Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Figure 3-12: Geological map of the Waimakariri CWMS zone (source GNS science Q map series)
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Figure 3-13: Average soil profile available water (source Landcare Research, S-map series)
24 Environment Canterbury Technical Report Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Figure 3-14: Estimated depth of Quaternary deposits (Jongens, 2011)
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Figure 3-15: Wells less than 50 m deep by maximum yield near the Eyre River
26 Environment Canterbury Technical Report Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Figure 3-16: Wells greater than 50 m deep by maximum yield near the Eyre River
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Figure 3-17: Irrigated area in the Waimakariri CWMS zone (Brown, 2015)
28 Environment Canterbury Technical Report Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Figure 3-18: Rivers by type as defined in the Natural Resource Regional Plan
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There are approximately 1,400 km of unlined stockwater races on the Ashley-Waimakariri plains. The stockwater system is supplied from the Waimakariri River, with a maximum consented rate of take 2.1 m3/s. Opus (2004) and Davey (2005) estimated that between 80 to 90 % of the stockwater infiltrates into the groundwater system. There is some uncertainly around these estimates as the bywash is not regularly monitored and it is not known how much is consumed by stock or how much water is taken for other purposes. There is little information about where the losses may occur. It would be useful to undertake further work on quantifying the losses from the stockwater system.
The Eyre River recharges the groundwater system and is a particularly important source of recharge in the Eyre River GAZ (Earl, 1997; PDP, 2007; Dodson et al., 2012; Wilson, 2014). The Eyre River and Coopers Creek flow all year in the foothills but start losing to groundwater as they flow over the plains (Davey and Smith, 2005; Smith 2012). Often the Eyre River runs dry at or just above Oxford and tends to flow over its entire length only after heavy rainfall events (Figure 3-18). The Eyre River may only flow over its full length once or twice a year. However, during 2013, the river flowed for a number of months following the heavy rainfall events of June and October 2013.
The Cust River has a more complex pattern of losses and gains than the Eyre River (Figure 3-18). The Cust River and the smaller tributaries that drain the foothills behind Oxford tend to flow all year round (Smith, 2012). In the Oxford sub-basin water is lost to groundwater and re-emerges as springs in wetlands on the western side of Mairaki Downs (Figure 3-19; Dodson, 2014). In a typical summer, there is flow in the river until just before Rangiora, where it is often dry. Downstream, the flow in the river picks up significantly (Smith, 2012).
It is well-established that the Ashley River/Rakahuri loses a significant amount of water below the Mairaki Downs (NCCB, 1982; Sanders, 1997; Chater, 2004; Smith, 2012). These losses recharge the groundwater system on the south of the river and provide recharge to the groundwater system to the north near Saltwater Creek (Dodson, 2009). Chater (2004) suggested that there may be a loss of water from the Ashley River/Rakahuri from the gorge to the Mairaki Downs but analysis of recent concurrent gauging data show, that there are negligible losses or gains in this area (Smith, 2012; Dodson, 2014).
The Waimakariri River loses water to groundwater. Much of this recharge is thought to flow south towards Christchurch (Golder, 2013 and references within) but it is likely that a small component of this loss flows north (NCCB, 1986; Dodson 2013b). It appears that the area around Silverstream receives some Waimakariri River water in addition to LSR. However, increasing trends of nitrogen concentrations in the Waimakariri River itself may also indicate discharge from the groundwater system into the river (Ballantine and Davies-Colley, 2010). Environment Canterbury is currently undertaking a water quality study of the lower Waimakariri River, which will potentially provide information about this interaction.
One of the major discharges from the groundwater system is springs that arise near Rangiora and Kaiapoi (Figure 3-19; Sanders, 1997; Dodson et al., 2012). Many of these springs13 have permanent flows. There are also springs along the Eyre River, which flow intermittently and typically only after the river is flowing along the lower reaches. A number of the workshop participants suggested work could be done to improve our estimates of flow from these discharge areas. They felt spring discharge was underestimated by Dodson et al. (2012).
Groundwater abstraction is another major discharge from the system. Historically, it was been difficult to estimate groundwater abstractions as they were often not measured. However, the Waimakariri District Council has recorded their abstractions for more than 20 years. Dodson and Lough (2013) estimated the volume of water used as a permitted take and they found that it is likely to be small relative to consented takes. In the last few years, water meters have become mandatory for takes greater than 20 L/s (since November 2012) and for takes greater than 10 L/s (since November 2014). In the 2012/2013 season 48% of all the consented takes over 5 L/s had a meter (Glubb and Durney, 2014). While there will be significant uncertainly over historic water use, with time we should have a better understanding of how much water is used.
13 Locally often referred to as under-runners or undercurrents
30 Environment Canterbury Technical Report Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Sanders (1997) in his conceptual model of the Ashley-Waimakariri plains indicated that there was a component of flow discharging offshore. At the workshop there were a range of opinions about this issue and I will discuss it more in the next section.
Surface-groundwater interaction The definition for a spring I favour is a point or area where groundwater discharges to the surface. There are a number springs mapped by Environment Canterbury on the Ashley-Waimakariri plains (Figure 3-19) and it is likely that there are other springs that are yet to be mapped.
The Eyre River, as stated in the previous section, tends to flow permanently in the foothills until it reaches the plains and then it is often dry near Oxford. The Eyre River flows along its full length only once or twice a year. When the Eyre River does flow along its full length it loses water to the groundwater system (Sanders, 1997; PDP, 2007; Wilson, 2014) and a number of the intermittent springs also start to flow (Figure 3-19; Earl, 1997). The Eyre River is an important recharge source to its local area.
The flow/loss pattern for the Cust River is described in the previous section. Some workshop participants have suggested that the flows in the lower Cust River have increased since WIL commenced.
Sanders (1997) described the geometry of recharge to the south of the Ashley River/Rakahuri as being shaped as a tapering wedge, thinning away from the river. River recharge is easily identified in shallow wells (30 m deep or less) but the chemistry of the deeper groundwater in this area indicates it is LSR derived. Springs near Rangiora are thought to be recharged from Ashley River/Rakahuri water. Dodson et al. (2012) and Scott (2012) showed that the chemical and isotopic composition of the lowland streams closest to the river is similar to that of the river, but as you move away from the river, the chemistry indicates increased mixing with LSR.
Dodson (2009), also using chemistry and isotopes, showed that the groundwater in the Saltwater Creek area is different from the groundwater beneath the downlands to the north but very similar to the Ashley River/Rakahuri water.
It was accepted by the technical experts that the Waimakariri River loses water to groundwater in its middle to lower reaches. There was some uncertainty around the interaction of the river and groundwater in the upper plains. Some suggested that the Waimakariri above Courtenay Road is perched. Recent work by PDP (2015) indicates that groundwater levels in this area are significantly lower than the river levels, whereas closer to the coast there is little difference between stage height and the water table. More work is needed to characterise this interaction.
A number of technical experts also raised the suggestion of groundwater flowing from the Eyre River beneath the Waimakariri River and onwards towards Christchurch. PDP (2015) analysed available data but found there was little evidence to support this hypothesis.
There is potential for abstractions from wells to impact on surface water flows, particularly abstraction from shallow wells close to a surface water feature. The cumulative impact of these takes on surface water flows will need to be estimated during the limit-setting process.
Water quality Land use can affect water quality. Nitrate is one of the more obvious groundwater contaminants from land use because it is very soluble and easily leached from both arable and pastoral farming. Nitrate is found in low concentrations naturally in Canterbury groundwater, but its concentrations can increase over time as a result of human activities. Along with faecal bacteria, nitrate is the contaminant that most commonly exceeds health-based drinking-water limits (MAVs or Maximum Acceptable Values) in Canterbury Groundwater, but unlike faecal bacteria, nitrate does not decay over time and is more difficult to treat in drinking-water.
It is thought that much of the nitrate leaching into groundwater comes from diffuse agricultural sources such as urine patches from grazing animals, mineralised nitrogen from soil cultivation or the application of nitrogen fertilisers. There is also likely to be a contribution from point sources such as
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septic tanks, wastewater or stormwater discharges. It would be useful to estimate the proportion of nitrate leaching into groundwater from these different sources and Environment Canterbury will do this as part of the technical work undertaken to inform the limit-setting process.
NCCB (1982) indicates that there have been relatively high nitrate concentrations in groundwater in the Ashley-Waimakariri plains for at least 30 years (Figure 3-20). One of the challenges going forward will be estimating the historic nitrate concentrations (or load), lag times and the capacity for nitrate concentrations to be attenuated within groundwater and streams. There are some groundwater age data (Taylor et al., 1989; Stewart et al., 2000; Stewart et al., 2002; van der Raaij, 2011; van der Raaij, 2013) and long-term groundwater quality monitoring data (see methodology of Scott, 2013) that can be used to estimate lag times. Along the coast there are patches of areas where denitrification is likely to be occurring.
There are high concentrations of naturally occurring metals (manganese, iron and arsenic) in some areas particularly around Woodend (PDP, 2001) and Ohoka (Dodson et al., 2012).
Eyrewell forest is being progressively converted from forest to mainly irrigated dairy pasture. There has also been at least one other dairy conversion in the Eyrewell forest area. Estimating the potential impact of these developments is important and is discussed further in section 4.7.
It was suggested during the interviews and workshop that the public water supplies, particularly at Kaiapoi, are vulnerable to contamination as a result of land use. This issue is further discussed in section 4.8.
Other Groundwater flow directions have been estimated from piezometric surveys. There have been a number of piezometric surveys of this area (NCCB, 1982; NCCB, 1986; Dodson et al., 2012). One of the recommendations made repeatedly at the workshop was that it would be very useful to undertake a piezometric survey spanning both sides of the Waimakariri River to get a better understanding of the interaction between the river and the adjacent groundwater system.
In a general sense, groundwater flows towards the coast from the west to the east. All the piezometric surveys show a convergence of flow towards Kaiapoi and losses from the Ashley River/Rakahuri below the Mairaki Downs (Figure 3-21).
Examination of groundwater levels from wells of different depths at similar locations indicates that in the upper plains, there is a downwards hydraulic gradient and near the coast, there is an upwards hydraulic gradient.
Wilson (2014) noted that the Eyrewell forest probably reduced the volume of rainfall recharge occurring in this area. With the forest being progressively cut down and converted into irrigated pasture it is likely that the amount of LSR in this area will increase. This may have implications for the spring-fed streams down gradient.
Also noted at the workshop was the effect of urban areas, which are likely to reduce LSR and increase run-off.
32 Environment Canterbury Technical Report Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Figure 3-19: Springs and wetlands in the Waimakariri CWMS zone
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Figure 3-20: Nitrate concentration contours from NCCB (1982)
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Figure 3-21: Piezometric contours, May 2011
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3.3.2 Conceptual model There have been a number of regional-scale hydrogeological investigations conducted on the Ashley- Waimakariri plains (for example NCCB, 1982; NCCB, 1986; Sanders, 1997; Dodson et al., 2012). My conceptual model of the Ashley-Waimakariri plains attempts to incorporate previous work and the agreed statements of the technical experts who participated in this project. Figure 3-22 shows my conceptual model.
Figure 3-22: Conceptual model for the Ashley-Waimakariri plains
Groundwater generally flows from inland towards the coast. Some water lost from the Waimakariri River flows north towards Kaiapoi below the Eyre River diversion. Waimakariri River losses feed into Silverstream (Dodson, 2013b) and probably into Griggs Drain and Courtenay Stream (Wilks and Meredith, 2011). NCCB (1986) estimated that the contribution from the Waimakariri River in this area was less than 1 m3/s, whereas they estimated 5 to 8 m3/s flowed from the Waimakariri River towards Christchurch. Ballantine and Davies-Colley (2010) and work in progress (pers. comm. Adrian Meredith, Principal Surface Water Quality Scientist, Environment Canterbury, 2015) suggests that groundwater is either discharging directly into the Waimakariri River or to small streams that are flowing into the river from the north. This discharge or stream flow is contributing to the nitrate load in the river.
36 Environment Canterbury Technical Report Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
I do not see any evidence for losses from the Waimakariri River, inland of the Eyre River diversion, contributing to the groundwater system to the north of the river. NCCB (1982) suggested that inland of the Eyre River diversion the Waimakariri River is perched and the regional groundwater levels are far below the bed of the river. There is significant uncertainly around the interaction between the river and groundwater in this area (discussed further in section 4.6).
The Eyre River is an important recharge source to the groundwater system (Earl, 1997; Sanders, 1997; PDP, 2007; Wilson, 2014). The river often runs dry near Oxford but after heavy rainfall events, it flows along its full length. When it does flow along its length, it feeds intermittently-flowing springs located along its length. There is a strip of recent gravels (Q1 and Q2) either side of the river. These units are also recharged from the river. The thickness of the Q1 and Q2 units is difficult to estimate but they appear to have a combined thickness of up to 50 m in places. The Q1 and Q2 units have low storage because groundwater levels tend to drop quickly when there is no rainfall or river recharge (Sanders, 2000).
At depths of 75 to 80 m and deeper along the Eyre River there appears to be a productive water- bearing zone, particularly south of Oxford (Figure 3-16). The groundwater levels in the deeper wells tend to be in the order of 10 to 30 m deeper than shallower wells, indicating a steep downwards gradient. Deeper groundwater is recharged from the ground surface and shallow and deep productive water-bearing zones are ultimately connected. However, there is an alternate hypothesis discussed in section 4.3.
The Eyrewell forest area was once forest plantation and there were few wells drilled into this area. Few hydrogeological investigations considered this area as there was no real groundwater demand. With the conversion of the forest to irrigated pasture we need to have a better understanding of the hydrogeology of the area. Wilson (2014) found that the shallow water-bearing zone was largely absent from this area and it was suggested that this was because there was less recharge occurring because of the forest (i.e. rainfall intercepted by the canopy and water uptake through the root system of the trees). The 75 to 80 m deeper water-bearing zone was apparent in the area, but less productive than the area south of Oxford (Figure 3-16).
Dodson (2014) found that the Cust River flowed in its uppermost reaches, then lost water as it crossed the plains, and then started flowing again just before the Mairaki Downs. The Cust River gains in an area where there are a number of mapped springs (Figure 3-19) and in an area indicated as a wetland (now mostly drained) by Johnston (1961). The wetland and springs occur to the west of the Mairaki Downs in the Quaternary gravels whereas the Mairaki Downs are composed of Kowai Formation. The hypothesis is that groundwater flows from the foothills towards the Mairaki Downs, but because of the difference in permeabilities between the Kowai and Quaternary formations, some of the groundwater is forced to the surface. The Mairaki Downs was formed by faults and folds (Figure 3-14; Barrell and Begg, 2013). The Cust River again loses its water to groundwater west of Rangiora, but gains significantly thereafter (Smith, 2012).
The Ashley River/Rakahuri loses water in the lower reaches, below the confluence with the Okuku River, but gains in flow near the coast. The gain in flow in the lower end is likely due to streams flowing into the river (i.e. Taranaki Creek and Waikuku Stream). The losses from the Ashley River/Rakahuri flow into the groundwater system either side of the river towards Saltwater Creek and Rangiora. Losses from the Ashley River/Rakahuri on the south side of the river are particularly obvious in piezometric contours (NCCB, 1982; NCCB, 1986; Dodson et al., 2012).
There are a number of springs near the coast, near Rangiora and Kaiapoi (Figure 3-19). The springs close to the Waimakariri and Ashley River/Rakahuri are likely recharged from the rivers. The springs near the coast and in the middle of the plains are likely fed from regional groundwater. This spring discharge indicates that there is a general upwards gradient in the groundwater system approaching the coast. This interpretation would also imply that ultimately groundwater abstraction would have an effect on the flows in the springs and the streams they feed.
3.3.3 Implications for management The Ashley GAZ is located to the south of the Ashley River/Rakahuri. Included in the allocation limit for this zone is a proportion of water lost from the river (Figure 3-5; Scott, 2004). The Saltwater Creek
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catchment is within the Kowai GAZ. The Kowai GAZ allocation limit is based solely on LSR and it does not include losses from the Ashley River/Rakahuri. Previous investigations indicate that both the Ashley GAZ and Saltwater Creek areas are recharged from losses from the Ashley River/Rakahuri. I believe there is justification to review the boundaries and allocation limits of the Kowai and Ashley GAZ.
The Waimakariri Zone Committee, for the purpose of initial engagement with the community, have proposed a number of management zones (Figure 3-23). These zones have been suggested as possible alternatives to the current nutrient allocation boundaries as well as being useful for other management issues. These boundaries are essentially groundwater allocation zones, except the strip along the coast which the Zone Committee believe is different because of the coastal wetland. Historic knowledge of the wetland distributions (Johnston, 1961; NCCB, 1982; Sanders, 1997) and geological interpretation help support the delineation of a coastal wetland management zone.
Stream depletion is managed differently under the Waimakariri River Regional Plan, which covers the southern part of the CWMS zone, and the Land and Water Regional Plan, which covers the rest (Figure 3-24). As the surface-groundwater interaction is similar in both plan areas I would recommend a single set of rules be adopted across the CWMS zone.
The Ashley-Waimakariri plains include both the most intensive agricultural land use and the largest urban areas in the Waimakariri CWMS zone, both of which have significant implications for the management of water quality. In recent times, there has been further intensification of agricultural businesses and peri-urban and urban areas have grown.
One of the challenges is that groundwater quality needs to be managed for multiple uses and outcomes and potentially in different parts of the zone. For instance, groundwater supplies: • spring-fed waterways and coastal lakes/wetlands, including areas of significant cultural value • public supplies for urban, peri-urban areas and Tuahiwi Marae • private drinking-water and stockwater • water to be applied as irrigation.
Waterways on the plains also receive nutrient loads from both the Lees Valley (via Okuku River and Ashley River/Rakahuri) and Loburn Fan (via the Ashley River/Rakahuri). The technical assessments may also need to consider urban sources (e.g. wastewater, stormwater), different susceptibility of groundwater to contamination across the plains including dilution sources (river recharge), areas of potential denitrification/phosphorus mobilisation (anoxic zones) and coastal confined aquifer system.
38 Environment Canterbury Technical Report Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Figure 3-23: Waimakariri Zone Committee proposed management zones
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Figure 3-24: Boundaries of the Land and Water Regional Plan and the Waimakariri River Regional Plan
40 Environment Canterbury Technical Report Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
4 Uncertainty and recommendations There are a number of issues identified during this project where there is significant uncertainly. The purpose of this section is to describe the most important issues that are uncertain and to suggest possible strategies for dealing with this uncertainty.
4.1 Lees Valley There have been few hydrogeological investigations undertaken in Lees Valley. There are only a few wells in the valley and there is little hydrogeological data. Given the difficulty in accessing the Lees Valley and other competing priorities, it is unlikely that Environment Canterbury will initiate a groundwater investigation in the near future.
My conceptual model of the Lees Valley is based primarily on the assumption that the Torlesse Super Group rocks are relatively impermeable and that this area is acting as a closed basin. This assumption could be tested to ensure it is reasonable. There are a number of ways to test the plausibility of this assumption, including • calculating a valley-wide water balance • building a simple groundwater model.
Given the difficulty in accessing the Lees Valley it may be worthwhile exploring remote sensing techniques to see if they may be useful in producing information for this area.
4.2 Loburn Fan There have been few hydrogeological investigations undertaken in the Loburn Fan and there are a number of questions that need answers, including • how does the groundwater system work? • how is the groundwater system recharged? • how much recharge does the groundwater system receive? • what is the hydraulic connection between the Loburn Fan groundwater system and the Ashley River/Rakahuri?
There is some hydrogeological, hydrological, soil and geological information. An investigation into this area focusing on these questions has recently begun (Freeman, in prep).
One of the key areas of uncertainly for the Loburn Fan, and elsewhere in Canterbury, is the amount of groundwater recharge that occurs through loess soils (Poulsen, 2013). I recommend investigating this issue.
4.3 Hydraulic connection between shallow/deep productive water- bearing zones in the Eyre River GAZ In the Eyre River GAZ there appear to be two productive water-bearing zones. The first is approximately 30 m to 50 m deep, located on either side of the Eyre River, inland of approximately Mandeville and probably in the most recent gravels (Q1 and Q2). The second is approximately 75 m to 80 m and deeper and apparently has a similar plan view to the shallow system. There is a significant difference in heads between the shallow and deep productive water-bearing zones, with heads in the deep productive water-bearing zone in the order of 10 m to 30 m below the heads in shallow productive water-bearing zone (Dodson, 2013a; Wilson, 2014). Both these layers and the intervening layer are predominately composed of gravels and it is unknown why this apparent stratification is occurring.
My interpretation is that these zones are ultimately connected and the deeper productive water- bearing zone is recharged via the shallower productive water-bearing zone, and that there is an upwards hydraulic gradient at the coast. An alternative explanation is that the intervening layer is significantly impeding recharge to the deeper productive water-bearing zone and that the deeper productive water-bearing zone has a small recharge area at the foothills end of the plains. This hypothesis would indicate the deeper productive water-bearing zone discharges directly offshore and
Environment Canterbury Technical Report 41 Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
none of the water migrates upwards to the springs near the coast. The possible management implication of this interpretation is that if abstraction from the deeper productive water-bearing zone was exceeding the rate at which it is being replenished it could lead to a decline in aquifer storage and potentially encourage saltwater intrusion near the coast. It would also imply: • that pumping from the deeper productive water-bearing zones would have little effect on spring flows • nitrate from leaching at the top of the plains goes into the deep productive water-bearing zone and offshore i.e. doesn’t contribute nitrate to the spring-fed streams.
As these implications are significant I recommend investigating the hydraulic connection between the shallow and deep productive water-bearing zones in the Eyre River GAZ. If the investigation is unable to provide any conclusive answers to this question then it would be prudent to assume the more conservative scenario in modelling.
4.4 Offshore discharge There are a number of hypotheses about offshore discharge, some suggesting it does occur, others suggest it doesn’t. Similar lines of evidence are cited to support the different hypotheses. The connection between the groundwater system and the ocean is particularly important to the likely effects of abstraction on lowland streams. I recommend undertaking an investigation to look specifically at this question. This investigation could: • allow a hydrological model to determine the volume of water flowing offshore as the difference in the water balance • use analytical methods to estimate offshore flow • determine offshore flow from hydraulic heads near the coast • review groundwater age data.
If the results from this work are ambiguous then it may mean that we have to accept a high level of uncertainty around this question. We could use a hydrological model to undertake a sensitively and uncertainty analysis of different coastal boundaries to test the different hypotheses.
4.5 Groundwater flow beneath or into the Waimakariri River in the lower reaches There were a number of hypotheses about the potential for groundwater to flow under the Waimakariri River from the Eyre River GAZ towards Christchurch, or groundwater to discharge through the riverbed or discharge to springs and streams and then flow into river. PDP (2015) recently concluded that there was little evidence of groundwater flow beneath the lower Waimakariri River. If there was groundwater flowing beneath the river in this location then the implications for Christchurch could be significant. I recommend adding wells of various depths to the groundwater quality network near the southern side of the river to determine if the quality of water is changing. It would also be useful to undertake a piezometric survey with wells on both sides of the Waimakariri River.
Ballantine and Davies-Colley (2010) identified an increasing trend of nitrogen in the Waimakariri River near State Highway 1. Environment Canterbury is currently undertaking a surface water quality study in the lower Waimakariri River, which may provide information about the interaction here. If the results are ambiguous or inconclusive then it would be conservative to assume the nitrogen originated from diffuse sources within the Eyre River GAZ.
4.6 Waimakariri River and groundwater in the upper plains There is uncertainty about the interaction between the Waimakariri River and the groundwater system in the upper plains. Some suggest that the river is perched in this area. Others suggest the Waimakariri River gains flow in this area from groundwater discharge (White et al., 2011). At the workshop others suggested that the river loses water to groundwater in this location.
Some of this uncertainty is caused by a lack of data in and around the river. One way to reduce this uncertainty is to install wells (of varying depths) along the length of the river in areas where there are
42 Environment Canterbury Technical Report Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
few other wells. It may be useful to use geotechnical drilling methods to drill the shallower wells because these methods will allow more cuttings to be captured during drilling which will aid in the construction of a geological bore log and subsequent interpretation. Geotechnical drilling methods will only penetrate down to 10’s of meters below ground level.
I recommend reviewing the concurrent gauging data for the Waimakariri River to determine the pattern of losses and gains. It would be useful to review existing geological and head data from wells near the river to try to determine the interaction between the river and groundwater system. There may not be enough data in this area to draw a definite conclusion, therefore it may be prudent to undertake some sensitively and uncertainty analysis using a hydrological model.
4.7 Conversion of Eyrewell forest and surrounding area Some workshop participants asked what effect the conversion of Eyrewell forest into irrigated pasture, and other diary conversions in this general area, would have on groundwater quality. Similar questions are being asked by the Waimakariri Zone Committee and the general public. Wilson (2014) undertook a desktop assessment and made a number of recommendations including undertaking a piezometric survey on both sides of the Waimakariri River. With more information, it may be useful to re-examine Wilson’s (2014) conceptual model.
It should be noted that Ngai Tahu Farming’s consented activities and development plans will need to be part of scenarios for the model/community process.
4.8 Public water supplies vulnerability to contamination A number of workshop participants raised the idea that some public water supplies (i.e. Kaiapoi and Christchurch) may be vulnerable to contamination. This contamination is thought to be from diffuse land use sources and, because of the direction of groundwater flow, they may be heading towards wells used to provide water for public supplies. Given the implication of these suggestions, it warrants further investigation. One way of determining the risk of contamination to these public supply wells is to run a number of scenarios within a hydrological model. It would be useful to examine the groundwater quality monitoring network to see if it is able to provide forewarning of any contamination.
4.9 Lag times and denitrification The Waimakariri Zone Committee and communities are asking how long it takes nutrients to travel from the land surface through groundwater and to the spring-fed streams. They also want to know what processes occur to remove nutrients from groundwater and how much is removed.
There is some groundwater age data available and long-term groundwater quality monitoring data. It would be useful interrogate this information to gain an understanding of lag times and nutrient removal.
5 Next steps Following on from this project it I intend to ‘ground truth’ my groundwater conceptual model with three groups, being (Figure 5-1); 1. local landowners and farmers 2. Te Ngāi Tūāhuriri Rūnanga 3. surface water and ecology technical experts.
The people in these groups I am sure will add value to my conceptual understanding of the water resources in the Waimakariri CWMS zone.
Environment Canterbury Technical Report 43 Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Surface water/ ecology Local techincal landowners experts Groundwater /farmers conceptual model Iwi/Rūn anga
Figure 5-1: Other groups that need to be consulted about these conceptual models
6 Synopsis This project was initiated to develop conceptual understanding of the regional-scale groundwater system in the Waimakariri CWMS zone. This was achieved by identifying and then engaging with ten groundwater technical experts with a range of backgrounds and experience. This exercise also provided me with an opportunity to identify areas of agreement and disagreement/uncertainty. Identifying areas where there is disagreement and/or uncertainly allows us to address these issues explicitly. This project was also an opportunity to engage with partners, stakeholders and their technical experts before the limit-setting process begins.
In this report, I have presented my conceptual model of the groundwater system in the Waimakariri CWMS zone, which includes the agreed statements of the technical experts. I have also attempted to state my assumptions and identify issues that may be important for the management of the resource.
7 Acknowledgements I would like to thank the following people for agreeing to be involved in this project: Peter Callander, Stephen Douglass, Ian McIndoe, John Talbot, Mike Thorley, Hugh Thorpe, John Weeber, Julian Weir, Paul White and Scott Wilson.
The following people from Environment Canterbury helped me with the interviews and workshops: Lisa Scott, Nicole Calder-Steele, Adrian Meredith, Hamish Graham, Murray Griffin and Ken Taylor.
I would like to thank Darren Mann, Ray Fraser and Claire McKay for their help with this project. I would like to acknowledge all the stakeholders and partners that I contacted in the early stages of this project.
Nicole Calder-Steele, Lisa Scott, Fouad Alkhaier and Carl Hanson reviewed this report.
44 Environment Canterbury Technical Report Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
8 References Aitchison-Earl, P, Scott, D and R Sanders 2004: Groundwater allocation limits: guidelines for the Canterbury Region; Environment Canterbury Technical Report U04/02, 60 p.
Anderson, M and Woessner, W 2002: Applied Groundwater Modelling. Simulation of Flow and Advective Transport. Academic Press.
Ballantine, D and Davies-Colley, R 2010: Water quality trends at NRWQN sites for the period 1989- 2007. NIWA Client Report: HAM2009-026, 2nd edition, August 2010, NIWA Project: MFE09202
Barnes, P, Castellazzi, C, Gorman, A, and Wilcox, S 2011: Submarine Faulting Beneath Pegasus Bay, Offshore Christchurch. Prepared for the New Zealand Natural Hazards Research Platform. NIWA Project: MFE09202
Barrell, D. J. A. and Begg J. G. 2013. General distribution and characteristics of active faults and folds in the Waimakariri District, North Canterbury, GNS Science Consultancy Report 2012/325. 52 p.
Barrell, D. J. A.; Van Dissen, R. J. 2014. Assessment of active fault ground deformation hazards associated with the Ashley Fault Zone, Loburn, North Canterbury, GNS Science Consultancy Report 2013/173. 59 p.
Bright, J 2011: Projected Effects Of Climate Change On The Proposed Lees Valley Irrigation Scheme As Part Of The Canterbury Water Management Strategy. Community Irrigation Fund (grant 10/02) and Environment Canterbury, 18 p.
Brown, P 2015: Irrigated area mapping: Waimakariri and Orari-Opihi-Paerora. Aqualinc client report, 17 p.
Burrell, G, P 2001: Hyporheic Ecology of Alluvial Rivers in Canterbury, New Zealand. A thesis submitted for the degree of Doctor of Philosophy in Zoology in the University of Canterbury. p 176.
Chater, M 2004: 7-day mean annual low flow mapping for the Ashley catchment area; Environment Canterbury Technical Report U04/16, 28 p.
Cooper, I 2011: Waimakariri Irrigation Limited water use management report; Pattle Delamore Partners Report CJ49506R001 for Waimakariri Irrigation Limited.
Cowan H. A. 1992. Structure, seismicity and tectonics of the Porter's Pass-Amberley fault zone, North Canterbury, New Zealand: a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in the University of Canterbury, 247 p.
Davey, G 2005: Recharge to groundwater from stockwater and irrigation races in the Waimakariri – Ashley plains; Environment Canterbury Technical Report U05/51, 12 p.
Davey, G and E Smith 2005: Losses to groundwater from headwater tributaries of the Eyre River; Environment Canterbury Technical Report U05/50, 6 p + 2 appendices.
Dodson, 2009: Active tectonics, geomorphology and groundwater recharge to the Waipara-Kowai Zone, North Canterbury. Master thesis, University of Canterbury, Christchurch, New Zealand, 160 p.
Dodson, M, P Aitchison-Earl and L Scott 2012: Ashley-Waimakariri groundwater resources investigation; Environment Canterbury Technical Report R12/69, 160 p.
Environment Canterbury Technical Report 45 Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Dodson, M., 2012: Upper Waimakariri Bores – BW22/0001 & BW22/0002. Environment Canterbury Memorandum WATE/INGW/QUAN/ASHL/1-4.
Dodson, M., 2013a: Drilling of groundwater level observation bore BW23/0133, Two Chain Road. Environment Canterbury Memorandum WATE/INGW/QUAN/ASHL/1-1.
Dodson, M., 2013b: Recharge sources to springs along the northern lower Waimakariri River; Environment Canterbury Technical Report R13/50, 35 p.
Dodson, M., Lough H. 2013. Estimating permitted water use in Canterbury. Environment Canterbury Technical Report No. R13/76, 63 p.
Dodson, M 2014: investigating the significance of river recharge from the Ashley River/Rakahuri to the upper Cust groundwater allocation zone. Environment Canterbury Memorandum WATE/INGW/QUAN/ASHL/1-5.
Earl, PL 1997: The hydrogeology of the Eyre River aquifer and its Influence on spring occurrence and distribution; Honours thesis, University of Canterbury, Christchurch, New Zealand, 260 p.
Forsyth, P, Barrell, D, and R Jongens 2008: Geology of the Christchurch Area, 1:250 000 Geological Map 16; Institute of Geological and Nuclear Science, Lower Hutt.
Freeman, in prep: Loburn Groundwater Allocation Zone Investigation. Environment Canterbury Technical Report No. R15/xx.
Glubb, R and Durney, P 2014a: Canterbury Region Water Use Report for the 2012/13 Water Year. Environment Canterbury Technical Report No. R14/4, p 57
Glubb, R and Durney, P 2014b: Canterbury Region Water Use Report for the 2013/14 Water Year. Environment Canterbury Technical Report No. R14/104, p 78.
Golder associates, 2009: Minimum Flows and Aquatic Ecological Values of Lower Waimakariri Tributaries, Golder associates client report prepared for Environment Canterbury, 71 p.
Golder associates, 2013: Recharge of the Christchurch Artesian Aquifer System: State of the Science, Gaps and future work. Golder associates client report, 98 p.
Hayward, S. 2002: Christchurch-West Melton Groundwater Quality: A review of groundwater quality monitoring data from January 1986 to March 2002: Environment Canterbury Technical Report R02/47, 145 p.
Johnston, W.B. 1961: Locating the Vegetation of Early Canterbury: A Map and the Sources. Transactions of the Royal Society of New Zealand, Botany. Vol. 1, No. 2.
Jongens, R 2011: Contours for the base of Quaternary sediments under the Canterbury plains between the Ashley and Rakaia Rivers. GNS Science Consultancy Report 2011/132, 17 p.
MoH, 2008. Drinking-Water Standards for New Zealand 2005 (revised 2008). Published by the New Zealand Ministry of Health, Wellington. 163 pages.
Morgenstern, U., Daughney, C.J. 2012 Groundwater age for identification of baseline groundwater quality and impacts of land-use intensification : The National Groundwater Monitoring Programme of New Zealand. Journal of hydrology, 456/457: 79-93.
NCCB 1982: The water resources of the Ashley catchment; North Canterbury Catchment Board and Regional Water Board, Christchurch, 205 p.
NCCB 1986: Waimakariri River and Catchment Resource Survey; North Canterbury Catchment Board and Regional Water Board, Christchurch, 870 p. in 3 vol.
46 Environment Canterbury Technical Report Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Opus 2004: Waimakariri stockwater scheme efficiency audit. Opus Consulting Report November 2004 for the Waimakariri District Council.
Taylor, CB, Wilson, DD, Brown, LJ, Stewart, MK, Burden, RJ and GW Brailsford 1989: Sources and flow of north Canterbury plains groundwater, New Zealand; Journal of Hydrology, 106, 311- 340.
Thorley, M and Ettema, M 2007: Review of water allocation limits for the South Canterbury downlands. Environment Canterbury Technical Report U07/9, 48 p.
Thorley, M and K Bristow 2008: Preliminary analysis of the occurrence of groundwater using geochemical tracers in the Kaiapoi area. Environment Canterbury Technical Report U08/19, 33 p.
PDP, 1993. Waimakariri-Ashley Irrigation Scheme Groundwater Impact. A summary report. Prepared for Waimakariri-Ashley Irrigation Committee.
PDP 2001: Report on arsenic occurrences in the Woodend-Waikuku-Saltwater Creek area; Environment Canterbury Report U01/32, prepared by Pattle Delamore and Partners for Waimakariri District Council, Environment Canterbury and Crown Public Health, 104 p.
PDP 2007: Report on September 2005 Eyre River aquifer recharge trial. Environment Canterbury Report U07/31, prepared by Pattle Delamore Partners for Waimakariri Irrigation Ltd and Environment Canterbury, 12 p + 5 appendices.
PDP, 2015: Review of Eyre - Christchurch West Melton Groundwater Allocation Zone Interaction. Environment Canterbury Technical Report U07/9, prepared by Pattle Delamore Partners for Environment Canterbury, 73 p.
Sanders, R 1997: Groundwater of the Waimakariri-Ashley plains – a resource summary report; Canterbury Regional Council Technical Report U97/43, 101 p.
Sanders, R 2000: Observations from Ashley - Waimakariri plains groundwater level data during the 1997-99 drought; Environment Canterbury Technical Report U00/26, 123 p.
Scott, D 2004: Groundwater allocation limits: land-based recharge estimates; Environment Canterbury Technical Report U04/97, 39 p.
Scott, L 2012: (Hydrosoc presentation)
Scott, L 2015: Groundwater Quality Investigation In The Loburn Area, Waimakariri Cwms Zone. Environment Canterbury Memorandum WATE/INGW/QUAL/INVE.
Scott, M and Wilson, N 2012: Seawater intrusion network review; Environment Canterbury Technical Report U12/35, 95 p.
Smith, J 2012: Surface water balance components of the Ashley-Waimakariri plains; Environment Canterbury Report R12/58, 78 p.
Stewart, M, Trompetter, V and R van der Raaij 2000: Groundwater recharge investigation using hydrochemistry: CFC dating of groundwater between the Waimakariri and Ashley Rivers and between the Rakaia and Ashburton Rivers (2000); GNS Client Report 2000/132 prepared for Environment Canterbury by Institute of Geological and Nuclear Sciences, 35 p.
Stewart, M, Trompetter, V and R van der Raaij 2002: Age and source of Canterbury groundwaters; Environment Canterbury Report U02/03, prepared by Institute of Geological and Nuclear Sciences, 46 p.
Environment Canterbury Technical Report 47 Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Poulsen, D and Smith, M 2011: Groundwater management and allocation in the Hurunui River catchments. Environment Canterbury Report R11/4, 73 p.
Poulsen, D 2013: The hydrogeological significance of loess in Canterbury. Environment Canterbury Report R13/60, 73 p.
Van der Raaij, R 2011: Age determination and hydrochemistry of groundwater from the Ashley- Waimakariri plains, Canterbury, New Zealand; GNS Science Report 2011/02, 73 p.
Van der Raaij, R 2013: Groundwater age interpretation for Ashley-Waimakariri springs. GNS Science Letter report for Environment Canterbury
White, P 2007: Christchurch Formation and Springston Formation. GNS Science Consultancy report 2007/117, 109 p.
White, P, Weeber, J, Pamer, R Minni, G and Cave S 2007: Identification of Springston gravel lobes in the Christchurch Formation. GNS Science Consultancy report 2007/195, 185 p.
White, P. A. 2008. Riccarton Formation, Burnham Formation and Windwhistle Formation lithologies in the vicinity of Christchurch City. GNS Science report 2008/157 for Environment Canterbury.
White, PA, Kovacova, E, Jebbour, N and C Tshritter 2011. Waimakariri River bed and groundwater surface water interactions; GNS Science Report 2009/41, 77 p.
Wilks, T and A Meredith 2009: Waimakariri tributary report; Environment Canterbury Technical Report R09/11, 27 p.
Wilson, S 2014: Eyrewell Forest groundwater system investigation. Environment Canterbury Technical Report R14/54, 33 p.
48 Environment Canterbury Technical Report Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Appendix A: Developing a groundwater conceptual model for the Waimakariri CWMS zone
Hi all,
The proposed Land and Water Regional Plan is a new planning framework for Canterbury. The plan provides direction on how land and water are to be managed and help deliver community aspirations for water quality – in both urban and rural areas.
There are chapters in the proposed Land and Water Regional Plan14 relating to the ten Canterbury Water Management Strategy (CWMS) zones15. Each of these ten CWMS zones will go through a planning process to put in place policies and rules to help achieve the community goals for freshwater that have been built on the recommendations made by the respective Zone Committees16. I will refer to these as sub-regional plans.
In preparation for the Waimakariri zone’s sub-regional plan, I want to develop a groundwater conceptual model to guide the technical advice that Environment Canterbury will provide to decision makers during the Waimakariri sub-regional planning process. An explanation and example of a conceptual model is provided at the end of this letter.
In developing the groundwater conceptual model for the Waimakariri CWMS zone I want to draw on the knowledge of the wider hydrological community, who represent a range of stakeholders. The key aims of this project are to: • Identify points where technical experts agreed and disagree • Begin engaging with stakeholders and their technical experts.
I am writing to you because you, or the organisation you represent, have been identified as a stakeholder in the Waimakariri CWMS zone. I would like you to nominate a groundwater technical expert, preferably a groundwater technical expert who is familiar with the groundwater resources of the Waimakariri CWMS zone. I understand that some of you will not be in a position to nominate a technical expert, however, I’d like to extend the invitation in any case so that you are aware of this project.
In the table below, I have a list of technical experts that I have already identified. Table A- 1: Table listing the technical experts I have identified TECHNICAL EXPERT ORGANISATION Peter Callander PDP John Talbot Bowden Environmental John Weeber Independent hydrogeologist Russell Sanders Julian Weir Aqualinc Mike Thorley BECA Mark Megaughin URS David Scott ESR Paul White GNS
14 Link to the proposed Land and Water Regional Plan http://ecan.govt.nz/our-responsibilities/regional-plans/regional-plans-under-development/lwrp/Pages/plan- decisions-version.aspx 15 Map showing the locations of the CWMS zones. http://ecan.govt.nz/get-involved/canterburywater/Pages/canterbury-water-zone-map.aspx 16 Link to the Zone Committees page on Canterbury Water http://ecan.govt.nz/get-involved/canterburywater/committees/Pages/Default.aspx
Environment Canterbury Technical Report 49 Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Next Steps Once all the technical experts have been identified the plan is to: • Prepare a survey questionnaire • Interview the technical experts • Summarise the technical experts’ interviews in a memorandum • Hold a workshop with the technical experts to develop the conceptual model • Document process and report via a technical report.
I would really appreciate your participation in this project, and I’m more than happy to share any information and findings gathered with you. Please contact me if you would like any further detail, or you would like to discuss anything. Please note that I will be away from 27 September to the 28 October.
Regards, Matt Dodson, Hydrogeologist
What is a groundwater conceptual model? A conceptual model usually takes the form of a picture representing the groundwater flow system. The image below is an example of conceptual model for the Ashley-Waimakariri plains developed by Russell Sanders in the 1997. Russell’s conceptual model is good but out of date. After Russell developed this conceptual model Waimakariri Irrigation Limited began and there have been a number of groundwater investigations undertaken which have added to our understanding of the system.
Example: Ashley-Waimakariri Plains (source: Sanders, R 1997: Groundwater of the Waimakariri-Ashley plains – a resource summary report; Canterbury Regional Council Technical Report U97/43, 101 pg)
50 Environment Canterbury Technical Report Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Appendix B: Memo 6 November 2014
Date 6 November 2014
MEMORANDUM
File Reference: FROM: MATT DODSON
TO: PARTICIPATING TECHNICAL EXPERTS cc
SUBJECT: WAIMAKARIRI GROUNDWATER CONCEPTUAL MODEL PROJECT
Introduction This memorandum has been written for the technical experts participating in the Waimakariri groundwater conceptual model project. The purpose of this document is to provide the technical experts with the background, rationale, aims and an outline of the methodology for this project.
Background The Canterbury Water Management Strategy17 (CWMS) provides a framework for managing the water resources in Canterbury. Under the CWMS the Canterbury region has been divided into ten CWMS zones18. Each CWMS zone has a zone committee comprised of members of the local community. The zone committee members come from a wide spectrum of backgrounds and represent different interests (e.g. agricultural, environmental, and cultural). Each zone committee has produced a Zone Implementation Programme (ZIP) which gives effect to the CWMS and forms the basis for the regulatory planning document.
The Waimakariri zone committees’ ZIP can be found here19 and the priority outcomes from the ZIP are listed in Table 1.
The sub-regional planning process for the Waimakariri CWMS zone is scheduled to commence in July 2016. Environment Canterbury will support the planning process by providing technical information to decision makers.
17 http://ecan.govt.nz/publications/Plans/cw-canterbury-water-wanagement-strategy-05-11-09.pdf 18 http://ecan.govt.nz/get-involved/canterburywater/Pages/canterbury-water-zone-map.aspx 19 Full link for the ZIP is http://ecan.govt.nz/publications/General/cw-waimakariri-zip.pdf
Environment Canterbury Technical Report 51 Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Table 1: Priority outcomes from the Waimakariri ZIP
Priority Outcome: Lowland streams water quality and water quantity supports mahinga kai gathering and a diversity of aquatic life. The Ashley/Rakahuri River is safe for contact recreation, has improved river habitat, improved fish passage, improved customary use, and flows that support natural coastal processes. The Waimakariri River flows support in-stream ecosystems and coastal processes and the river is protected as an outstanding recreation resource. The zone has safe and reliable Drinking Water, preferably from secure sources, and the Tuahiwi community has a high quality water supply. The Biodiversity of coastal lagoons and foothills wetlands are protected with improved biodiversity on the plains. Highly Reliable Irrigation water, to a target of 95%, is available in the Zone. Optimal Water and Nutrient management is common practice. There is improved contribution to the Regional Economy from the Zone.
Project rationale and aims In preparation for the Waimakariri CWMS zone sub-regional plan, I want to develop a groundwater conceptual model to guide the technical advice that Environment Canterbury will provide to decision makers during the Waimakariri sub-regional planning process. In developing the groundwater conceptual model for the Waimakariri CWMS zone I want to draw on the knowledge of the wider hydrological community who represent a range of stakeholders. The key aims of this project are to: • begin engaging with stakeholders and their technical experts • identify points where technical experts agree and disagree • develop a conceptual model for the Waimakariri groundwater system.
Project methodology Identifying stakeholders and technical experts The first step in this project was to identify the key stakeholders in the Waimakariri zone. The stakeholders where identified by asking the Waimakariri zone committee and Environment Canterbury technical staff. A list of the identified key stakeholders is in Table 2.
Table 2: Key stakeholders in the Waimakariri zone
Stakeholders: Te Ngāi Tūāhuriri Rūnanga Dairy NZ Ravensdown Ngāi Tahu Properties FAR Synlait Waimakariri Zone Committee Federated Farmers (North Hort NZ Canterbury Branch) Waimakariri Irrigation Limited Balance Forest and Bird Waimakariri District Council Fonterra Fish and Game Ministry of Primary Industries Banks Department of Conservation Beef and Lamb Irrigation NZ
52 Environment Canterbury Technical Report Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
We wrote to each of the stakeholders and asked them to nominate a groundwater technical expert to participate in this project. In my letter to the stakeholders I included a list of technical experts that are prominent in the Waimakariri zone, as a guide. We had a number of responses from the stakeholders and where a technical expert was nominated I added that technical expert to my list.
I then contacted the technical experts and asked if they were interested in participating in the project. The technical experts who agreed to participate are listed in Table 3. There were a small number of technical experts who I approached that didn’t want to participate in this project because of other commits or for other reasons.
Table 3: Technical experts who indicated they are willing to participle in this project
Technical expert: Company/institution Peter Callander PDP Stephen Douglass URS Ian McIndoe Aqualinc John Talbot Bowden Environmental Mike Thorley BECA Hugh Thorpe Research Fellow, University of Canterbury John Weeber Independent hydrogeologist Julian Weir Aqualinc Paul White GNS Science Scott Wilson Lincoln Agritech Technical expert interviews I will arrange a time to meet and interview each technical expert. The interviews are likely to take anywhere from an hour upwards. At this stage I am planning to complete the interviews before Christmas but that will depend on the availability of the technical experts. In preparation for the interviews I will create a questionnaire which will focus on: • boundaries to the groundwater system • surface/groundwater interactions • important elements of the water balance • key hydrology processes (i.e. denitrification, recharge, rainfall) • identification of geological/topographic/geomorphic units.
At the end of the interview there will be time for technical experts to discuss other technical issues that they feel is relevant to this project. Please note that this project is concentrating on technical issues, there will be plenty of time in the sub-regional planning process to discuss management options.
The interview will be conducted by one or two members of Environment Canterbury staff or a contractor. I will be present for all the interviews. We will be recording the interviews with a digital dictaphone and then summarising the technical experts’ interviews in a memorandum. A copy of the memorandum will be provided to all of the participating technical experts. Workshop This memorandum will be used as the basis for holding a workshop in the New Year, depending on participant’s availability. The workshop will be held in Christchurch and it will take about half a day. The workshop will be where, as a group, we develop the conceptual model. The intention at the workshop will be to start at a basic and very high level, and then attempt to dive down into more detail. Closer to the time I will provide the participating technical experts more information about the workshop.
Following the workshop I will document the entire process in a technical report. This document will be made available to the technical experts, stakeholders and the general public.
Environment Canterbury Technical Report 53 Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Feedback to stakeholders In addition to the memorandum and technical report, I am intending to offer additional opportunities to stakeholders to inform them of progress/results of this project. The Waimakariri zone committee occasionally meets with industry and environmental groups and I may use this opportunity to present information to them. If you know of any other opportunities to interact with the stakeholders I would be interested in hearing about them.
54 Environment Canterbury Technical Report Towards a collaboratively developed conceptual model of the Waimakariri groundwater system
Appendix C: Waimakariri groundwater conceptual model project
Interview questionnaire Date: Interviewers:
Agenda a) Introductions
b) Project overview and purpose overview of the interview
c) Reimbursement for your time
d) Which parts of the Waimakariri CWMS zone groundwater system are you familiar with?
e) What is your conceptual model of the (from question above e.g. Waimakariri CWMS zone)
groundwater system?
f) Hydrostratigraphy/geology
g) Water balance
h) Groundwater/surface water interactions
i) Groundwater quality
j) Other important hydrological processes
k) Is there anything you would like to talk about?
l) Your preferred date for the workshop?
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Appendix D: Summary of statements from the interviews
Table D- 1: Geology. N/A indicates that only one person raised this issue Sense of Suggested that further Statement agreement work is required Aquifer 5 in Sanders (1997) conceptual model and Durney et N/A Yes al (2011) requires subdividing Confining layers present near the coast/extension of the Mostly agree Christchurch system north Confining system thins to the north/system changes in Mostly agree Yes character to the north Limited deep groundwater resource in the area north of N/A Yes Oxford and west of the Mairaki Downs Deep groundwater resource is vulnerable to ‘groundwater N/A Yes mining’ Deposits from the Eyre River formed much of the gravel Some Yes sequence south of the Cust River disagreement The coastal area between the Waimakariri and Ashley River/Rakahuri west to about SH1 use to be wetland, now Mostly agree mostly drained There are numerous faults/folds in the zone, some of which Mostly agree Yes likely have an impact of the groundwater system The Mairaki Downs is a partial barrier to groundwater flow Mostly agree There is a strip of deep gravels (approximately 80 m +) N/A Yes beneath the Eyre River There is a strip of permeable gravels associated with the Eyre Mostly agree River (from 0 m to approximately 30 m depth) There appears to be, at least, two productive water bearing Some Yes units, being ‘shallow and deeper’ gravels disagreement There is no hydraulic connection between shallow and deep Some Yes productive water bearing disagreement Three aquifers; Waimakariri fan, coastal zone and other Some Yes (older) gravels disagreement At a local scale the gravels are highly variable and Mostly agree Yes heterogeneous There appears to be zones where well yields are generally low Mostly agree Yes and others where higher yields can be obtained
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Table D- 2: Water balance. N/A indicates that only one person raised this issue Sense of Suggested that further Statement agreement work is required Abstraction is one of the key outputs Mostly agree Yes The Ashley River/Rakahuri recharges the groundwater Some Yes system between the gorge down and the Mairaki Downs disagreement The Ashley River/Rakahuri recharges the groundwater Mostly agree system below No.10 Groyne The Cust River recharges the groundwater system in places Mostly agree Yes The Eyre River is a key input into the groundwater system Mostly agree Yes Irrigation return water is recharging the groundwater Mostly agree Yes system Offshore discharge is a key output from the system Some Yes disagreement Losses from irrigation and stockwater races are recharging Mostly agree Yes the groundwater system Rainfall recharge is a key input into the groundwater Mostly agree Yes system Spring discharge (including Saltwater Creek) is a key output Mostly agree Yes from the groundwater system Waimakariri River is recharging the groundwater system in Mostly agree this area In places the groundwater system is discharging into the Some Yes Waimakariri River disagreement Groundwater is flowing from north to south beneath the Some Yes Waimakariri River disagreement
Table D- 3: Surface-groundwater interaction. N/A indicates that only one person raised this issue Suggested that Sense of Statement further work is agreement required The Cust River loses water below Oxford, then gains through the Mairaki Downs area, then loses around Two Chain Road Mostly agree and then gains after that The Eyre River intermittently flows across the plains Mostly agree Yes The Eyre River tends to lose water near the top of the plains Mostly agree Yes There is likely to be a lot of run off on the Loburn Fan Mostly agree Yes There is a hydraulic connection between the Loburn Fan Some Yes groundwater system and the Ashley River/Rakahuri disagreement The Waimakariri River is perched in places Some Yes disagreement The Waimakariri River is ‘isolated’ from the groundwater Some Yes system in the upper-mid plains disagreement The bulk of the Waimakariri River recharges flows towards Mostly agree Christchurch The flows in the Cust River have generally increased since Mostly agree Yes Waimakariri Irrigation Limited started in 1999
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Table D- 4: Quality. N/A indicates that only one person raised this issue Sense of Suggested that further Statement agreement work is required There are areas within the groundwater system where high concentrations of Iron, Manganese and Arsenic have been Mostly agree Yes detected Denitrification is probably occurring within the ‘coastal Mostly agree confined aquifer system’ Relatively high concentrations of Nitrate Nitrogen have been Mostly agree Yes detected on the Ashley-Waimakariri plains since the 1980’s It is important to consider total loads N/A Localised land use effects (septic tanks, management Mostly agree Yes practices, surface run-off) need to be considered There is potential for Nitrate Nitrogen from the Ngai Tahu N/A Yes Farming development to flow towards Christchurch Some of the potable water supplies are vulnerable to N/A Yes contamination caused by landuse affects Landuse affects groundwater quality Mostly agree
Table D- 5: Other. N/A indicates that only one person raised this issue Suggested that Sense of Statement further work is agreement required Ashley River/Rakahuri recharge can be clearly distinguished around Mostly agree Rangiora but mixes with land surface recharge as you move away from the river (i.e. Sanders ‘triangular wedge’ of river recharge) Bywash from stockwater and the irrigation scheme need to be Mostly agree Yes investigated The coastal margin of the plains was wetlands and has been Mostly agree extensively drained Consider undertaking flow net analysis N/A Yes Need to quantify fluxes in/out of the groundwater system N/A Yes The presence of Eyrewell forest is reducing rainfall recharge Some Yes disagreement Need to get a picture of historical irrigation practises Mostly agree Yes Inland there is generally a downwards hydraulic gradient and at Mostly agree the coast there is generally a upwards hydraulic gradient It is important to quantify irrigated area and the source of the Mostly agree Yes water used for irrigating that area Need to include different irrigation types when estimating land N/A Yes surface recharge Consider installing (or re-instating) lysimeters in the area Some Yes disagreement Regional scale modelling will be the most useful tool in this process Mostly agree Need to consider run-off from urban areas in the model N/A Yes Saltwater intrusion not a problem in this area N/A Yes More thought is required in undertaking stream depletion N/A Yes assessments Need to better understand losses from race systems Mostly agree Yes Use current data in the model Mostly agree Apply pressure on NIWA about access to the VCN N/A Yes The Waimakariri River is tidal in the lower reaches N/A
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Suggested that Sense of Statement further work is agreement required There has been an increase in groundwater levels in some shallow Mostly agree Yes wells since Waimakariri Irrigation Limited began in 1999 There is little information, few smaller scale investigations and no Mostly agree Yes catchment wide investigations for the Loburn Fan There is little information, few smaller scale investigations and few Mostly agree Yes catchment wide investigations for the Lees Valley
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Appendix E: Memo 17 February 2015
Date: 17 February 2015
MEMORANDUM
File Reference: WATE/INGW/QUAN/ASHL/2-2
FROM : MATT DODSON
TO : PETER CALLANDER, STEPHEN DOUGLASS, IAN MCINDOE, JOHN TALBOT, MIKE THORLEY, HUGH THORPE, JOHN WEEBER, JULIAN WEIR, PAUL WHITE AND SCOTT WILSON cc Murray Griffin and Carl Hansen
SUBJECT : SUMMARY OF THE INTERVIEWS UNDERTAKEN FOR WAIMAKARIRI GROUNDWATER CONCEPTUAL MODEL PROJECT
INTRODUCTION The Waimakariri Canterbury Water Management Strategy (CWMS) zone (Figure 1) is scheduled to begin its sub-regional planning process in mid-2016. In preparation for the sub-regional planning process I am seeking to develop a conceptual model of the groundwater system. The aims of the Waimakariri groundwater conceptual model project are to: • begin engaging with stakeholders and their technical experts • identify points where technical experts agree and disagree • develop a plan to address disagreement amongst technical experts • develop a conceptual model for the Waimakariri groundwater system.
In the Waimakariri limit-setting processes we are consciously trying to engage and collaborate with stakeholders (including technical experts) early. We are aiming towards the co-production of credible and relevant science to inform decision makers. The development of this conceptual model, with your help, is a first step towards this goal.
A key outcome from this project is identifying where there is agreement and disagreement on technical issues. On issues where there is disagreement, I want to develop a plan to be able address the disagreement.
The groundwater conceptual model will be the basis for the development of model/s20 of the Waimakariri CWMS zone. My expectation is that the conceptual model will be further refined as the model/s are developed. The conceptual model will also be used to fill in gaps in areas where there is little data or if we have contradicting lines of evidence. The model/s will be used to provide information to decision makers during the sub-regional process.
MEMORANDUM AIM The aim of this memorandum is to summarize the findings from the interviews. The memorandum will be distributed to the participating technical experts before the workshop and be used as the basis for the workshop discussions.
20 At this stage I am anticipating the development of a MIKE SHE model for the Ashely-Waimakariri plains and other models for the Loburn and upper Ashley River/Rakahuri catchment.
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Figure 1: Map showing the CWMS zones in North Canterbury and the groundwater allocation zone boundaries
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BACKGROUND TO THE PROJECT The project plan is to: • contact stakeholders and ask who their preferred technical expert is • contact the nominated technical experts • prepare a survey questionnaire • interview the technical experts • summarise the technical experts’ interviews in a memorandum • hold a workshop with the technical experts to develop the conceptual model • document the process and report via a technical report.
The first steps in the project was to identify and then contact by email a range of stakeholders with an interest in the Waimakariri CWMS zone (Table 1). I asked the stakeholders to nominate a groundwater technical expert to participate in this project. In the email to stakeholders I provided a list of prominent technical experts who work in the Waimakariri CWMS zone because some of the stakeholders may not have a preferred technical expert.
Table 1: Stakeholders contacted for this project Stakeholders: Te Ngāi Tūāhuriri Rūnanga Dairy NZ Ravensdown Ngāi Tahu Properties FAR Synlait Waimakariri Zone Committee Federated Farmers (North Hort NZ Canterbury Branch) Waimakariri Irrigation Limited Balance Forest and Bird Waimakariri District Council Fonterra Fish and Game Ministry of Primary Industries Banks Department of Conservation Beef and Lamb Irrigation NZ
I had a number of responses from the stakeholders putting forward technical experts or in some cases consulting companies. I contacted all the nominated groundwater technical experts to ask if they were interested in participating in the project. There were a number of groundwater technical experts who I approached that didn’t want to participate because of other commitments or for other reasons. For the most part, the technical experts where happy to participate (Table 2).
Table 2: Technical experts who are participating in this project Technical expert: Company/institution Date interviewed Peter Callander PDP 4 December 2014 Stephen Douglass URS 10 December 2014 Ian McIndoe Aqualinc 2 December 2014 John Talbot Bowden Environmental 18 November 2014 Mike Thorley Beca 4 December 2014 Hugh Thorpe University of Canterbury 11 November 2014 John Weeber Independent hydrogeologist 19 November 2014 Julian Weir Aqualinc 2 December 2014 Paul White GNS Science 9 December 2014 Scott Wilson Lincoln Agritech 11 December 2014
INTERVIEW FORMAT, STYLE AND RECORD KEEPING In preparation for the interviews I created a questionnaire (Appendix A) which focused on: • the participants experience, their general understanding and their conceptual model of the groundwater system in this zone • their understanding of the hydrostratigraphy/geology
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• what they considered to be the most important elements of the water balance • their understanding of the interactions between surface/groundwater • their understanding of groundwater quality and associated processes • any other key hydrology processes that they wanted to discuss.
One or two Environment Canterbury staff members were present at the interviews and I was present for all of them. Except for the interview with Paul White, the interviews were face to face and recorded with a digital dictaphone. Pauls interview was conducted over the phone while I took notes. Paul was given an opportunity afterwards to review my notes to ensure they were accurate. Ian McIndoe and Julian Weir (both work for Aqualinc) were interviewed at the same time, all the other participants were interviewed by themselves.
The digital records of the interviews were transcribed by Adept STS Ltd. Adept STS Ltd had difficulty interpreting and translating some of the technical jargon and names. I have not corrected the transcripts as yet, because they are sufficient for this stage of the process and I won’t have time before the workshop to correct them. The transcripts will be corrected and summarised before the release of the final report. Each participant will receive a copy of the transcript and digital recording of their interview.
I tried to keep the interviews as informal and relaxed as possible. While I had questions prepared, I deliberately allowed the participants to talk about whatever they felt was relevant. For completeness sake, I did run through all the questions listed in Appendix A. The questions were targeted at a regional scale. Some participants, when they felt it was appropriate, discussed processes or issues at smaller scales.
Individual interviews spanned from one hour to two and half hours in length. In total there is 12 hours and 41 minutes of digital recordings.
INITIAL ANALYSIS OF THE INTERVIEWS After completing the interviews I listened to the recordings and read through the transcripts. Contained in these documents and recordings is a vast amount of information, covering a range of topics. Some people focused specifically on the zone and the hydrological processes, while others gave advice on how to approach modelling in general and others discussed data limitations.
In order to sort and make sense of this information I created a spreadsheet in which I recorded relevant statements made by the participants. For instance many people said that rainfall recharge was one of the key inputs into the system therefore I noted this as one of the statements (Appendix D). I have not listed every statement made by every participant, rather I tried to capture the major points and I have tried to give some sense of the width of the topics covered. I then noted if other participants agreed, disagreed, felt it was plausible or were unsure with each statement. For instance seven of the ten participants agreed that rainfall recharge was likely to be a major input into the system, while rainfall recharge as an input was not explicitly mentioned by the other three. Because different people had different amounts of experience in this zone, different background and approaches, not everyone commented on everything. There were also a number of issues only raised by a single participant.
For each statement, if they had been commented on by more than one person, I classified it as ‘mostly agreed’ if everyone who commented on that statement agreed to it or thought it was plausible. If there were one or more people who were unsure or disagreed then I classified it as ‘some disagreement’. In our example I classified rainfall recharge as ‘mostly agreed’ because those who did mention it felt it was an important input to the groundwater system.
I then sorted these statements into five categories, being; • geology • water balance • surface/groundwater interaction • water quality • other
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INITIAL RESULTS OF THE INTERVIEW On a personal level I learnt something from each and every participant. I believe it was a worthwhile exercise as it tested many of my ideas and will prompt me to look in more detail at certain datasets or issues.
In a general and from a regional view, most people agreed on many things but there were a number of issues where there are significant differences in opinions. For some of the statements where there is disagreement it was noted that there are often three or more competing hypotheses. Sometimes these competing hypotheses draw on similar evidence or datasets. The fact that there are a range of competing hypotheses gives me a sense of the uncertainty around these issues.
I also noted that even when people agreed with a statement, there were still calls for further investigation to reduce uncertainty or to gain a better understanding of the process. This in itself is valuable, but I will need to be realistic about how much work can be done before and during this sub- regional process. At some point after the workshop these recommendations for further work will need to be prioritised.
In Tables D3 to D7 I have presented a number of the statements and the sense of agreement for each of those statements. Each of the five categories discussed previously has its own table.
WORKSHOP FORMAT AND AGENDA Before the workshop I encourage you to read through the Tables D3 to D7 to ensure that it reflects your understanding of the groundwater system.
At the workshop together we will work through the five categories. Initially I want to confirm the points where we agree. For statements on which we disagree, we will use the following process:
Is the statement significant?
If we agree that the statement is significant, what can be done to resolve the issue (i.e. targeted project)?
What happens if we still can't resolve the issue?
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The proposed agenda for the workshop is:
Time Topic Lead by Starting at 9am Introductions Matt Dodson Setting the scene Claire McKay21 Science and the sub-regional process Ken Taylor22 Outline and plan for the workshop Matt Geology Matt and Murray Griffin23 Water balance Matt and Murray Surface/groundwater interaction Matt and Murray Water quality Matt and Murray 12-1230pm LUNCH Other considerations Matt and Murray Opportunities for collaboration Matt and Murray Ending before 2pm Summary and next steps Matt and Murray
CONCLUDING REMARKS I would like to thank you all for participating in this project and I look forward to seeing you at the workshop to be held on the Thursday 26 February.
21 Chair of the Waimakariri Zone Committee 22 Director Investigations & Monitoring 23 Zone Facilitator, Waimakariri CWMS zone
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Appendix F: Workshop PowerPoint presentation
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Appendix G: Areas of agreement and disagreement
The format I used to present at the workshop was to summarise what I understood to be the areas of agreement between the technical experts, with an a
opportunity for people to provide feedback. We then collectively discussed the areas of disagreement with an emphasis on developing a plan to address the collaborati disagreement. In the following section, I record the areas where technical experts agree and disagree.
Agreement
Geology developedvely conceptual model Table G- 1: Areas where technical experts agreed about the geology Statement Explanation Suggestion for further Related references work Aquifer 5 in Sanders (1997) conceptual Aquifer 5, when the term was first proposed, was used to Re-examine bore log data Sanders (1997) model and Durney et al. (2011) could be describe a group of sediments (including the Kowai to better define Durney et al. (2011) subdivided. Formation) which could not be separated at the time due stratigraphy. Dodson et al. (2012) to a lack of deep bore logs. Confining layers present near the coast. Along the coastal margin of the Ashley-Waimakariri plains Dodson (2009) These layers are likely an extension of and Waipara-Ashley area there is an alternating sequence Durney et al. (2011)
the Christchurch system north of terrestrial and marginal marine/marine deposits. These Dodson et al. (2012)
Environment CanterburyTechnical Report deposits predominately represent changes in climate and
sea level. Confining system thins to the north past A number of the technical experts pointed out that there Re-examine well, Sanders (1997) of the Waimakariri groundwater system Kaiapoi. Groundwater heads in and seems to be a difference between the coastal confined groundwater level and Durney et al. (2011) around Kaiapoi tend to be flowing aquifer system north of Kaiapoi and to the south. To the well yield data. Dodson et al. (2012) artesian, whereas north of Kaiapoi heads south of Kaiapoi the yield are generally higher, and there are often below the ground surface. are a large number of wells with flowing artesian heads. To the north, wells with flowing artesian heads are rarer. The coastal confined aquifer system tends to thin north in both plan and in total thickness.
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Environment CanterburyTechnical Report Statement Explanation Suggestion for further Related references work There are numerous tectonic structures, The northern boundary of the Waimakariri CWMS zone is Review geological and Cowan (1992) a
which have shaped the basin and marked by the Porters Pass-Amberley Fault Zone. There tectonic information. Finnemore (2004) collaborati influence the groundwater system. are also numerous other mapped faults within the zone Indo-Pacific Energy Ltd (see Barrell and Begg, 2013). It is my interpretation that (2000) this tectonic activity has shaped the basin and in places it Forsyth et al. (2008) has juxtaposed material of significantly different hydraulic Jongens (2011) properties. Dodson (2012) developedvely conceptual model Barrell and Begg (2013) Dodson (2014) Tectonic deformation has formed a sub- The Ashley-Loburn and associated faults have formed Review technical Johnston (1961) basin north of Oxford town and south of Salvation Hill and the Mairaki Downs. The effect of these information and make Dodson (2014) the Ashley River/Rakahuri (I will refer to structures is that there may be limited groundwater recommendations to this area as the Oxford sub-basin). connection between the Oxford sub-basin and the Cust decisions makers. Groundwater Allocation Zone (GAZ). This may have implications for the allocation boundaries and calculations.
Oxford sub-basin has a limited deep It was put forward that there is a limited ‘deep’ Review existing well and NCCB (1982) groundwater resource groundwater resource in the area south of the Ashley geological data. Sanders (1997) River/Rakahuri, north of Oxford and to the west of the Dodson (2014) Mairaki Downs.
The coastal area below Rangiora and Before European settlement there were wetlands located Digitise historical survey Johnston (1961) south to Kaiapoi was an area of wetlands along the length of the coastal margin of the Ashley- maps (black maps). NCCB (1986) of the Waimakariri groundwater system that now has been mostly drained. Waimakariri plains, extending inland to where Rangiora is now. Much of these wetlands have since been drained. 79
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Statement Explanation Suggestion for further Related references work There is a strip of Q1 or Q2 deposits The Q1 or Q2 deposits associated with the Eyre River Determine the boundaries NCCB (1982)
(Forsyth et al, 2008) either side of the spread a few kilometres either side of the river. These of this unit and estimate NCCB (1986) a Eyre River. These deposits are more deposits are more permeable than older Q gravels (Figure their bulk properties. Sanders (1997) collaborati permeable than the older Q gravels. 3-12). They are also episodically recharged from water Earl (1997) lost from the Eyre River24. PDP (2007) Forsyth et al. (2008)
Dodson et al. (2012) developedvely conceptual model Wilson (2014) Plus various groundwater Assessments of Environmental Effects (AEEs) There appears to be a deeper A number of technical expert pointed out that there are Review well and Wilson (2014) (approximately 80 m) productive water- deep and productive (i.e. high yielding) wells located geological data. Plus various bearing layer below the Eyre River. The within a similar geographic extent as the younger Q groundwater AEEs deeper layer has similar plan dimensions deposits discussed above. The yield of deep wells
as the younger Q deposits. generally reduces towards Eyrewell Forest (Figure 3-16). One participating technical expert describes the extent as
Environment CanterburyTechnical Report tram tracks along the either side of the river.
Inland of about Mandeville North and The groundwater levels in wells approximately 30 m to 50 Review well and Dodson et al. (2012) of the Waimakariri groundwater system west along the Eyre River there is a m deep are meters to tens of meters higher than the groundwater level Dodson (2013a) significant difference in heads between groundwater levels in wells approximately 75 m to 80 m. information. Wilson (2014) the shallow productive water-bearing The difference in heads indicates that there is a PDP (2015) zones and the deeper productive water- downwards hydraulic gradient inland. bearing zones. Aquifers related to fan surfaces One participating technical expert conceptualises that Review well and there are three major fans in the Waimakariri CWMS groundwater level zone: Waimakariri fan, older surfaces fan and the coastal information. confined aquifer system.
24 The Eyre River flows intermittently across the plains and usually only after significant rainfall. The Eyre River tends to lose water as it flows across the plains and is typically dry near Oxford.
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Environment CanterburyTechnical Report Statement Explanation Suggestion for further Related references work At fine-local scales, the quaternary At a regional scale, it is appropriate and reasonable to use a
deposits are heterogeneous and averages to represent the bulk properties of the aquifer collaborati anisotropic. materials. We have to acknowledge that these averages may not hold at fine-local scales.
Water balance Statement Explanation Suggestion for Related references developedvely conceptual model further work One of the major outputs from the Pumping from wells is one of the major outputs from the Review water use NCCB (1982) groundwater system is abstraction of groundwater system. data. NCCB (1986) water from wells. Sanders (1997) Dodson et al. (2012) Dodson and Lough (2013) Glubb and Durney (2014a) Glubb and Durney (2014b)
The Ashley River/Rakahuri, Water is lost through the bed of the Ashley River/Rakahuri and NCCB (1982) coastward of confluence with the enters groundwater in the area downstream of the confluence NCCB (1986)
Okuku River, recharges groundwater. of the Okuku River. Chater (2004) Smith (2012)
Dodson et al. (2012) of the Waimakariri groundwater system The Cust River loses water to The Cust River loses flow in it top reaches after it starts Smith (2012) groundwater in places and gains flow flowing over the plains and in summer can dry at Carleton Dodson et al. (2012) in other places. Road bridge. The Cust River will then gain flow before Dodson (2014) Bennetts Road. Farther downstream the Cust River in summer dries up before Swannanoa Road. Flow in the Cust River increases downstream from Swannanoa Road. The Eyre River provides recharge to The Eyre River is likely to be permanently flowing in its Review gauging NCCB (1986) the groundwater system. headwaters but as starts flowing across the plains, it loses data. Consider Sanders (1997) water to groundwater. Typically the Eyre River is dry installing temporary Earl (1997) downstream of the Oxford Bridge. It usually only flows after flow recorders on Sanders (2000) significant rainfall events. Coopers Creek and PDP (2007) Eyre River above Smith (2012) Oxford. Dodson et al. (2012) Wilson (2014) 81
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Statement Explanation Suggestion for Related references further work A percentage of rain that falls onto Rainfall recharge occurs over the entire Waimakariri CWMS Scott (2004)
the ground surface infiltrates through zone. More rainfall recharge will occur on the plains (in the Thorley and Ettema (2007) a the vadose zone and then down into order of 10-30% of average annual rainfall) and substantially collaborati groundwater. less in areas where the surface slopes more than 15°. A percentage of the irrigation water A percentage of irrigation water applied to the ground surface Review information Scott (2004) applied recharges groundwater or will seep through the soil and recharge the groundwater from NIWA’s Bright (2011)
potentially aids in more rainfall system. The actual amount of irrigation water that reaches irrigation lysimeter developedvely conceptual model recharge groundwater depends on the soil, climate, irrigation system study. and the management of that irrigation system. Rainfall and irrigation return recharge is often calculated simultaneously and referred to as Land Surface Recharge (LSR). Irrigation and stock water races Some water that flows along irrigation and stock water races is Better estimates of Opus (2004) provide recharge to groundwater. lost though the base of the race and down into groundwater. the volume and Davey (2005) spatial distribution of Cooper (2011) race losses by Dodson et al. (2012) working with WIL and Wilson (2014) the Waimakariri
District Council. One of the major outputs from the There are numerous springs located in the Waimakariri Refine our estimates Earl (1997) Environment CanterburyTechnical Report groundwater system is spring flow. District. The lowland streams are fed from springs, many of of mean and 7 day Chater (2009)
Many of these springs are located which flow all year round. There are also a number mean annual low Golder (2009) of the Waimakariri groundwater system near the coast at the head of the intermittently flowing springs near the Eyre River which tend to flow. Smith (2012) lowland streams. flow only when the river is flowing. Losses from the Waimakariri River Water is lost through the bed of the Waimakariri River and NCCB (1982) flow northwards into the Ashley- some of this water flows northwards into the Ashley- NCCB (1986) Waimakariri plains. Waimakariri plains. Sanders (1997) White et al. (2011) Dodson et al. (2012) Dodson (2013) Small intermittent streams along the There are a large number of small intermittent streams that Gauge or collate and Davey and Smith (2005) foothills provide recharge to the drain the foothills and flow onto the plains and lose water. analyse data from Smith (2012) groundwater system. These streams drain the hills around the Loburn Fan, Eyre these small River and Cust GAZ. These streams are potentially providing intermittent streams. recharge to the groundwater system but there contribution is largely unknown.
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The Cust River loses The Cust River loses flow in it top reaches after it starts flowing over the Smith (2012) collaborati water to groundwater in plains and in summer can dry at Carleton Road bridge. The Cust River Dodson et al. (2012) places and gains flow in will then gain flow before Bennetts Road. Further downstream the Cust Dodson (2014) other places. River in summer dries up before Swannanoa Road. Flow in the Cust River increase downstream from Swannanoa Road. The Eyre River flows The Eyre River likely has permanent flow near its headwaters but loses Review gauging data. NCCB (1986) developedvely conceptual model intermittently along its full and is typically dry near Oxford. The Eyre River only flows along its Consider installing Sanders (1997) length. length after significant rainfall has fallen in its catchment. There is temporary flow recorders Earl (1997) anecdotal evidence that suggests that the Eyre River used to flow all on Coopers Creek and Sanders (2000) year round. Eyre River above Oxford. Davey and Smith (2005) PDP (2007) Smith (2012) Dodson et al. (2012) Wilson (2014) There is likely to be a lot of The Loburn Fan in places is relatively steep and it is likely that in places Review geology, soil and run off following rainfall there are relatively low-permeable soils (i.e. loess). It is hypothesised that topographic information over the Loburn Fan. in places that rain is more likely to run-off than to infiltrate into the (similar to the assessment groundwater system. of Thorley and Ettema,
2007). of the Waimakariri groundwater system Most of the losses from The Waimakariri River loses water through the base of its bed and into Golders (2013) and the Waimakariri River flow groundwater. The Waimakariri River tends to lose most of it water reference therein southwards towards downstream of Courtney Road. Many workers have estimated the total Christchurch. loss from the river and concluded that most of the recharge flows northwards towards Christchurch. Flows in the Cust River A number of workers have suggested that flows in the Cust River have Undertaken trend analysis seem to have increased increased since WIL began. of data from the river record since the WIL scheme on the Cust River. began. The Lees Valley is a The Lees Valley is surrounded by the Torlesse Super Group rocks that Water balance to confirm closed basin. are often assumed to be impermeable (compared to Quaternary gravels). that inputs are similar to The basin is filled with gravel, sands and silts. Therefore it is assumed outputs. that all the discharge from the basin occurs via the rivers.
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Water quality Statement Explanation Suggestion for further Related references work
There are areas within the A number of wells in the Waimakariri District, particularly near Review of the data in the PDP (2001) a groundwater system where there or within the coastal confined aquifer system, when sampled coastal area in view of Dodson et al. (2012) collaborati are measured concentrations of have concentrations of Iron, Manganese and Arsenic. It may be denitrification processes Iron, Manganese and Arsenic. that these metals are related to material and reducing and metals. conditions within the groundwater system.
Denitrification is likely to be Denitrification is likely to be occurring within the groundwater Review of the data in the Dodson et al. (2012) developedvely conceptual model occurring in places. system, particularly along close to the coast. coastal area in view of denitrification processes and metals. Nitrate-Nitrogen concentrations in Some wells within the Ashley-Waimakariri plains have been Review all Nitrate-Nitrogen NCCB (1982) groundwater have been near or sampled for Nitrate-Nitrogen since the 1980’s. Some of these data for wells in the above half the Maximum wells have measured concentrations near or above MAV. Waimakariri District. Acceptable Value (MAV)25 since the Trend analysis on time- 1980’s. series data. Localised landuse activities affects In some areas water quality will be affected by some landuse Review and undertake risk (septic tanks, surface run-off etc) activities. analysis of landuse
are likely to be having an effect on activities that are likely to water quality. have an effect on water Environment CanterburyTechnical Report quality.
Water quality is affected by landuse. Landuse can affect water quality, for instance through leaching Review leaching potential Dodson et al. (2012) of the Waimakariri groundwater system of Nitrate through the soil profile and into groundwater. of current landuse. Morgenstern et al. (2012) Wilson (2014) PDP (2015)
25 As defined by the New Zealand Drinking Water Standards (2005, revised 2008).
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Environment CanterburyTechnical Report Other Statement Explanation Suggestion for further Related references work a
Ashley River/Rakahuri recharge Ashley River/Rakahuri below the Mairaki Downs recharges a Sanders (1997) collaborati has a definable area. triangle shaped area in plan view. The recharge appears to be wedged shaped in 3D (i.e. thickness nearest the river tapering away in thickness away from the river). Hydrogeology of the Eyrewell Still significant uncertainties related to limited datasets. Appears Look at hydraulic gradients. Wilson (2014) Forest area. to be a steep hydraulic gradient away from the river. The Review geology. PDP (2015) developedvely conceptual model hydrogeology of the Eyrewell Forest area is different from the Review recharges patterns. Various AEE’s Burnt Hill area to the west. The irrigation and stock water The irrigation and stock water schemes are gravity driven Better estimates of the Opus (2004) schemes have bywash. therefore in order to delivery water to the end of the scheme volume and spatial Davey (2005) there needs to be some bywash. Up to this point water balance distribution of races loses Cooper (2011) estimates have assumed that there is no bywash. by working with WIL and Dodson et al. (2012) the Waimakariri District Council.
There is extensive drainage of Historical survey and soils maps show that coastward of Johnston (1961) wetlands in the Waimakariri Rangiora and Eyreton (Figure 3-13), before European NCCB (1982) District. settlement, there was a network of wetlands. Much of these NCCB (1986) wetlands have now been drained.
It would be useful to record historical irrigation practises. of the Waimakariri groundwater system On the Ashley-Waimakariri plains The Ashley-Waimakariri plains groundwater system is gravity NCCB (1982) generally the hydraulic gradients driven. Therefore, inland at elevations well above sea level the NCCB (1986) are downwards inland and upwards hydraulic gradient is downwards. At the coast there is a general Dodson et al. (2012) at the coast. upwards gradient. This pattern is determined from analysing groundwater levels. Some key datasets are irrigated Two key datasets have been identified. First, current irrigated Verify irrigated area map Dodson et al. (2012) area and also identifying the area. This work has been started by Brown (2015). Brown and irrigator type. Review Brown (2015) source water used to irrigate. (2015) have also identified the irrigator type and the locations of consent information. storage ponds. Second, identifying the source of water being Discuss with WIL. used by irrigators. LSR calculations could be LSR estimates could be improved by identifying the type of Verify irrigator type map. Brown (2015) improved by taking into account the irrigator that is being used. Then incorporate existing knowledge Review irrigation literature. type of irrigator used. of how the irrigators operate and how irrigation is scheduled into the LSR calculations. 85
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Statement Explanation Suggestion for further Related references work The model should be concentrated Integrated hydrological models are best suited at informing
at a regional scale. Use other tools questions at regional scales. Where local scale questions arise it a to inform local questions. is better to inform these debates with other tools. collaborati The integrated hydrological models Pavement and structures within urban areas will reduce the should consider run-off from urban amount of rainfall infiltration that will occur and promote more areas. rainfall run-off. This may be important and should be considered
in the model. developedvely conceptual model Study on losses from races It is well known that irrigation and stock water races lose water, Review information related Opus (2004) but it is less known how much is occurring and where the losses to race losses. Davey (2005) are occurring. Cooper (2011) Dodson et al. (2012) Wilson (2014) Use current data in the model. Many workers suggested using the most recently collected data. Use current data in the By using the most recently collected data and presenting that to model. people, it allows people to put the information into context. Virtual Climate Data (VCN) At the time of writing, some organisations no longer have access to VCN data. Many of the workers commented that no longer
having access to the VCN data is quite frustrating. Waimakariri River at the Old The Waimakariri River is tidally affected to at least the Old Environment CanterburyTechnical Report Highway Bridge recorder is tidal. Highway Bridge recorder.
WIL has had an effect on Environment Canterbury monitors the groundwater levels in a Dodson et al. (2012) of the Waimakariri groundwater system groundwater levels. number of wells throughout the Waimakariri District. Some of the groundwater levels in these wells seem to be affected by WIL. It is likely that this effect is caused by, 1) increased LSR, 2) increased irrigation and stock water losses, 3) reduction in groundwater abstraction, 4) combination of factors 1-3. Little is known about the The Loburn Fan GAZ is approximately 0% allocated. As such Undertake an investigation Scott (2004) hydrogeology of the Loburn Fan. historical there has been little effort been spent in attempting to into the groundwater Scott (2015) understand the groundwater system and its interaction with system and develop a Freeman (in prep) surface water. As a result there is little hydrogeological data and conceptual model. few GAZ or catchment wide investigations undertaken. Undertake an investigation into the interactions between the groundwater system and surface water.
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Environment CanterburyTechnical Report Statement Explanation Suggestion for further Related references work Little is known about the Historical there has been little effort been spent in attempting to a
hydrogeology of the Lees Valley. understand the groundwater system and its interaction with collaborati surface water. As a result there is little hydrogeological data and few catchment wide investigations undertaken. Analyse flow record from Dalleys Russel Sanders always considered this spring to be an indicator Analyse flow record. weir of the Ashley-Waimakariri groundwater system. vely developedvely conceptual model
Disagreement Geology Statement Alternative view/s Suggestion for further work Related references The Eyre River has deposited that much of The Waimakariri and Ashley River/Rakahuri have Interesting and worthy of discussion, Forsyth et al. the gravel material north of the Waimakariri deposited most of the gravels on the Ashley- but not immediately relevant to the (2008) River and south of the Ashley Waimakariri plains. The Eyre River deposits are sub-regional process. Dodson et al. River/Rakahuri. relatively thin, narrow but extend from the foothills to (2012) near the coast. That there is no direct hydraulic connection That there is direct hydraulic connection between Review geological, groundwater between wells screened in the shallow and wells screened in the shallow and deep productive level, groundwater chemistry data. deep productive water-bearing zones of the zones. This interpretation is based on the difference in Review groundwater age.
Eyre GAZ. This interpretation is based on heads between the zones and the presence of Mutli-level piezometers. of the Waimakariri groundwater system the difference in heads between the zones. elevated Nitrate concentrations (as per the classification of Morgenstern and Daughney, 2012). If there is no direct hydraulic connection That there is direct hydraulic connection between Review geological, groundwater Dodson et al. between the shallow and deep productive wells screened in the shallow and deep productive level, groundwater chemistry data. (2012) water-bearing zones, then there is potential zones. The shallow productive zone provides Review groundwater age. Wilson (2014) that abstraction from the deep productive recharge to the deeper productive zone. Mutli-level piezometers. water-bearing zone is mining the resource. Water balance calculations. This is because the deep productive zone Groundwater quality and isotope would have limited recharge area and information. therefore limited recharge volumes. 87
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Statement Alternative view/s Suggestion for further work Related references Inland of the coastal confined aquifer That the aquifers structures are related to fan surface. Review geological, groundwater White (2007)
system there generally two productive The major aquifers could be defined as Waimakariri level, groundwater chemistry data. White et al. a zones. One is shallow and the other is fan, coastal zone and other (older) gravels Review LIDAR. (2007) collaborati deeper. Targeted geotechnical drilling. White (2008) Pollen analysis. Dodson et al. Collaborate with well drillers. (2012)
Review aquifer test data. Dodson developedvely conceptual model Paleogeographic studies. (2013a) Wilson (2014) Various AEE’s
Water balance Statement Alternative view/s Suggestion for further work Related references That between the gorge and Bowicks Road That between the gorge and Bowicks Road the Review concurrent gauging and NCCB (1982) the Ashley River/Rakahuri loses water and Ashley River/Rakahuri loses on average a small geological data. NCCB (1986) this water recharges the groundwater amount of water but it is unlikely that this water Chater (2004)
system along the southern bank. recharges the groundwater system along the southern Smith (2012) bank. Dodson et al. Environment CanterburyTechnical Report (2012)
Dodson (2014) of the Waimakariri groundwater system
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Environment CanterburyTechnical Report Statement Alternative view/s Suggestion for further work Related references That groundwater originating from the Eyre That groundwater originating from the Eyre River GAZ Review surface water quality data. Ballantine and a
River GAZ discharges into the Waimakariri does not discharge into the Waimakariri River. Walk along the lower northern side Davies-Colley collaborati River or discharges as spring flow on the of the Waimakariri River to look for (2010) northern side of the river and subsequently springs and small streams Dodson (2013) flows into the Waimakariri River. This has (preferable in winter). been suggested to occur in two areas, in Relate groundwater levels to river the Courtney area and further east below stage. developedvely conceptual model the Eyre River diversion. Review information on border dyke irrigation and its influence. Review geology, particularly around the river. Piezometric survey of both sides of the river, and to include shallow and wells close to the river. Review hydraulic gradients. Review groundwater chemistry Groundwater originating in the Eyre River 1. Groundwater originating in the Eyre River PDP (2015) have reviewed Sanders (1997) GAZ does not flow beneath the GAZ flows beneath the Waimakariri River in groundwater level data, topographic, Stewart et al. Waimakariri River towards Christchurch. the area around Eyreton-Belfast. chemistry, isotope and groundwater (2002) 2. Groundwater originating in the Eyre River age information on our behalf. The Hayward
GAZ flows beneath the Waimakariri River in major finding of this study was that (2002) of the Waimakariri groundwater system the area around Kaiapoi- most of the evidence suggests flow Thorley and Brooklands/Spencerville. is not occurring. Bristow (2008) 3. Shallow groundwater originating in the Eyre Review stream and river gauging Dodson et al. River GAZ flows beneath the Waimakariri data. (2012) River towards Christchurch. Review stream and river quality Dodson (2013) 4. Deep groundwater originating in the Eyre data. Wilson (2014) River GAZ flows beneath the Waimakariri Review geology, geomorphology, River towards Christchurch. and topographic information (i.e. 5. Groundwater originating near Eyrewell Forest LiDAR). flows beneath the Waimakariri River towards Review seismic data and tectonic Christchurch. studies. Piezometric survey of both sides of the river. 89
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Statement Alternative view/s Suggestion for further work Related references That groundwater is not discharging 1. That groundwater is discharging offshore but Review LiDAR and geology. NCCB (1982)
offshore. only through the topmost gravel aquifer. Review stream gaugings. Sanders (1997) a 2. That groundwater is discharging offshore. Review gaugings for the Waimakariri Dodson et al. collaborati River. (2012) Review groundwater quality data and de-nitrification potential
(dissolved oxygen and metals etc). developedvely conceptual model Review hydraulic head information. Review water balance and concentrate on inputs. Review groundwater age data. Investigate gradients and hydraulic fluxes. Undertake or review piezometric surveys.
Surface/groundwater interaction
Statement Alternative view/s Suggestion for further work Related references Environment CanterburyTechnical Report There is a hydraulic connection between The Loburn Fan GAZ and the Ashley River/Rakahuri Review concurrent gauging, NCCB (1982)
the Loburn Fan GAZ and the Ashley are not hydraulically connected. groundwater levels, chemistry and Chater (2004) of the Waimakariri groundwater system River/Rakahuri geological data. Smith (2012) Piezometric survey. Calculate water budgets.
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Environment CanterburyTechnical Report Statement Alternative view/s Suggestion for further work Related references Waimakariri River is directly connected to 1. The Waimakariri River is perched in the upper Review concurrent gauging (loss Golders (2013) a
groundwater system along its full length. to mid plains. and gain), groundwater levels, and reference collaborati 2. The Waimakariri River is ‘isolated’ from chemistry and geological data. therein groundwater in the upper-mid plains. Piezometric survey. Mapping wetted area of the river (drones or ask river engineers). Gauging programme for the developedvely conceptual model Waimakariri River. Cross sections across the river to show regional groundwater level. Targeted investigation to see connection between river and groundwater level beneath the river. ADCP concurrent gaugings at higher flows along the river.
Water quality Statement Alternative view/s Suggestion for further work Related references
Potable water supplies at Kaiapoi are Potable water supplies at Kaiapoi are secure. Review groundwater level, vulnerable to contamination. chemistry, isotope and groundwater of the Waimakariri groundwater system age data. Discussion with Waimakariri District Council, age determination. Risk assessment. There is potential for contaminants leached There is potential for contaminants leached from the Collaborate with Ngāi Tahu Farming. Wilson (2014) from the Ngāi Tahu Farming development Ngāi Tahu Farming development to flow towards to flow towards Christchurch. Kaiapoi.
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Other Statement Alternative view/s Suggestion for further work Related references
Eyrewell Forest has reduced the amount of The forest has had little to no impact on rainfall Continue to monitor groundwater Wilson (2014) a rainfall recharge that has occurred on the recharge on the plains. levels. collaborati plains Lysimeters under irrigation will be helpful. It may be challenging to get meaningful information Discuss with NIWA and WIL from lysimeters on light soils.
Saltwater intrusion is unlikely to be a Saltwater intrusion is unlikely to be a problem on the Continue to monitoring programme. Scott and developedvely conceptual model problem on the Ashley-Waimakariri plains. Ashley-Waimakariri plains. Wilson (2012) The way stream depletion is calculated The method and tools to estimate stream depletion in Review stream depletion methods could be re-assessed. the Waimakariri CWMS zone are sufficient. and tools.
Environment CanterburyTechnical Report
of the Waimakariri groundwater system