Preliminary Strategic Assessment of Water Infrastructure Option 4: Managed Aquifer Recharge
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Preliminary Strategic Assessment of Water Infrastructure Option 4: Managed Aquifer Recharge π Prepared for Canterbury Water Management Strategy π March 2011 PATTLE DELAMORE PARTNERS LTD Level 2, Radio NZ House, Christchurch Tel +3 363 3100 Fax +3 363 3101 51 Chester Street West, Christchurch Web Site http:/ / www.pdp.co.nz P O Box 389, Christchurch, New Zealand Auckland Wellington Christchurch solutions for your environment
PATTLE DELAMORE PARTNERS LTD i
Preliminary Strategic Assessment of Water Infrastructure Option 4:
Managed Aquifer Recharge
Quality Control Sheet
TITLE Preliminary Strategic Assessment of Water Infrastructure Option 4:
Managed Aquifer Recharge
CLIENT Canterbury Water Management Strategy
VERSION Final
DATE March 2011
JOB REFERENCE C02424500
SOURCE FILE(S) C02424500R001_Final.doc
Prepared by
SIGNATURE
Peter Callander and Lynn Torgerson
Limitations:
The report has been prepared for Canterbury Water Management Strategy, according
to their instructions, for the particular objectives described in the report. The
information contained in the report should not be used by anyone else or for any
other purposes.
C02424500R001_Final_PDF.doc
PATTLE DELAMORE PARTNERS LTD ii
Preliminary Strategic Assessment of Water Infrastructure Option 4:
Managed Aquifer Recharge
Information Sharing Protocol
c General Project Information
Project Canterbury Water Management Strategy Preliminary
Name: Strategic Assessments
Dr Brett Painter
Project
CWMS Assessments Project Leader
Leader:
Environment Canterbury
Date: 17 February 2011 Version: 1.1
e Information Sharing Protocols
This report contains a preliminary Strategic Assessment against the
Canterbury Water Management Strategy (CWMS) Principles and
Targets of one of the short-listed options for water
management/infrastructure identified in the CWMS Strategic
Framework (2009) document.
Each Strategic Assessment contains a unique project brief, set of
assumptions and project team, with unique assessment methods,
gradings and presentation techniques. For this reason, comparison
of assessment gradings across the different reports is not
appropriate.
These reports have already been sent to CWMS Committee
members to assist with their role in recommending improvements
to assessed options with respect to the CWMS Principles and
Targets, and to refine the methods used for future assessments.
The reports are now publicly available for wider discussion on
these matters.
For further information, please contact the project leader noted
above.
C02424500R001_Final_PDF.doc
PATTLE DELAMORE PARTNERS LTD iii Preliminary Strategic Assessment of Water Infrastructure Option 4: Managed Aquifer Recharge Executive Summary Managed Aquifer Recharge (MAR) involves the artificial introduction of additional recharge water into the groundwater system via infiltration mechanisms. In Canterbury, the source of this additional water will most likely be derived from the larger river systems and/or water storage reservoirs. This boost to the groundwater resource can alleviate issues related to over-allocation of groundwater (red zones) and problems caused by low groundwater levels and low flows in spring-fed surface waterways. It will also add good quality water which will reduce nitrate concentrations and add lower temperature water to spring-fed streams. All these changes make a positive contribution to achieving the principles and targets of the CWMS. MAR can also cause potential adverse effects arising from raised groundwater levels affecting land drainage and management of lowland waterways. Therefore, any MAR scheme will need to consider the requirements for additional land drainage works, management of lowland surface waterways and/or financial compensation for affected parties. All these mitigation measures are feasible to achieve, and it is considered that there are no “show-stoppers” that would detract from MAR being a component in the achievement of the CWMS principles and targets. The feasibility of MAR in Canterbury is already demonstrated by the occurrence of artificial recharge that enters the groundwater system via leaky stockwater race networks and large scale surface supplied irrigation schemes such as those operated by RDR and WIL, although these groundwater effects occur in a relatively unmanaged way. Once MAR water is released into the groundwater system, the entity that is managing the MAR scheme ceases to be in control of the water, as the water disperses through the very heterogeneous subsurface strata. For that reason, MAR is a relatively inefficient means of water delivery to a particular abstractive user or surface waterway (perhaps only 50% of MAR water will be available for groundwater abstraction). Therefore, the highest value water with the greatest reliability of supply is more likely to be utilised for direct supply to users via pipelines and water races. The water that is used for MAR is likely to be water that is of lower priority for other users with a correspondingly lower reliability of supply. Direct supply of surface water to irrigators is likely to be more feasible on inland areas of the plains, where groundwater levels tend to be deep and aquifers less permeable, whereas MAR benefits will be greatest in the coastal plains, where groundwater pumping is more efficient (more permeable strata and higher groundwater levels). This area of greatest MAR benefit also coincides with the area of groundwater sourced spring discharges to streams and lakes. Inland ephemeral waterways provide another mechanism for MAR activities which would result in riparian aquifer benefits, as well as in-stream benefits. C02424500R001_Final_PDF.doc
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Preliminary Strategic Assessment of Water Infrastructure Option 4:
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Due to the heterogeneity of groundwater strata, the exact benefits that will arise from a
MAR scheme are difficult to predict in advance and such schemes are best to be
implemented on an iterative basis of recharge-observe-analyse-modify. One of the major
limitations with artificially introducing surface water into the groundwater is the problem
of turbidity in the source water causing clogging to the infiltration systems, which will
require ongoing maintenance. For these reasons, it is recommended that low cost
surface infiltration systems should be used for MAR such as:
π specially constructed surface infiltration basins;
π discharges into naturally ephemeral surface waterways;
π leaky water race distribution networks for surface supply schemes.
In terms of the CWMS:
π MAR can make the greatest contribution to:
– Target 1. Ecosystem health/biodiversity Through increased flows of low nutrient
– Target 3. Kaitiakitanga and lower temperature water to
spring-fed surface waterways
– Target 5. Recreational and amenity opportunities
– Target 4. Drinking water Through increased volumes of water within the
groundwater system, with lower nutrient
– Target 7. Irrigated land area
content to aid drinking water and
– Target 10. Environmental limits
environmental limits
π MAR can make a small, poorly quantified, but positive contribution to:
– Target 6. Water use efficiency Due to raised groundwater levels and
– Target 8. Energy security and efficiency the benefits arising from Targets 1, 3,
– Target 9. Indicators of regional and national economy 4, 5, 7 and 10
π MAR could make it more difficult to achieve:
Because the source of supply for many MAR
– Target 2. Natural character, processes and ecological health
schemes is likely to require increased
of braided rivers.
abstractions from braided rivers
Overall, MAR is expected to make a generally positive contribution to achieving the CWMS
targets. It can be implemented relatively quickly and easily, at relatively low cost,
particularly through the use of existing water distribution networks which could be
operated to full capacity, with surplus water recharged via leaky races, bywash soakpits
and discharges to ephemeral waterways. Indicative sizing of recharge structures can be
based on the following size requirements per cumec of recharge:
π infiltration basins – 2 ha;
π ephemeral riverbeds – 4.5 km of river bed;
π stockwater races – 200 km of water races.
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PATTLE DELAMORE PARTNERS LTD v Preliminary Strategic Assessment of Water Infrastructure Option 4: Managed Aquifer Recharge As a standalone scheme, MAR may not be the most efficient way of achieving the CWMS targets. However, it should be incorporated as a component of all other existing and proposed water management schemes in Canterbury. Mitigation measures to deal with surplus water flows in lowland areas need to be considered as part of any MAR development. C02424500R001_Final_PDF.doc
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Table of Contents
SECTION PAGE
Executive Summary iii
1.0 Introduction 1
2.0 Description of Managed Aquifer Recharge
(MAR) in the Canterbury Groundwater Setting 2
2.1 Overview of the Potential Application of MAR in Canterbury 2
2.2 Locations Where MAR is Likely to be Most Effective 4
2.3 Artificial Groundwater Recharge Activities in Canterbury 6
2.4 Guiding Principles for Implementation of MAR in Canterbury 9
3.0 Relevant Information to Assess the MAR Option 11
3.1 Groundwater Information 11
3.2 Other Information Needs 14
3.3 Aspirations for MAR From Key Stakeholder Groups 17
4.0 Analysis of Variance Against the CWMS Principles
and Targets 19
4.1 Information Reliability 22
5.0 Scenario Assessments 23
5.1 Management and Maintenance Systems 26
5.2 Overall Water Resource Management 28
6.0 Conclusions 30
7.0 References 31
Appendices
Appendix A Targets and Goals of the CWMS:
- Goals that can be affected by MAR are shown in bold
- Explanatory comments have been added in italics
Appendix B Figures
Appendix C Kaitiakitanga Target Assessment
(Prepared by Gail Tipa)
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1.0 Introduction
The Canterbury Water Executive of the Canterbury Regional Council has engaged
consultants to provide preliminary Strategic Assessments of five options for water
infrastructure projects in Canterbury. The purpose of each Strategic Assessment is:
π to determine the fit within the principles and targets of the CWMS; and
π to describe the benefits, risks and challenges that arise in implementing each option
in order to meet the requirements of the CWMS.
The preliminary Strategic Assessments will be used for both technical and public
discussion to:
π compare the expected outcome of the five infrastructure options and their ability to
contribute to the principles and targets of the CWMS;
π identify scenarios of how the option can best be implemented;
π provide a base level of information that can be incorporated into subsequent
feasibility studies and cost/benefit assessment.
Pattle Delamore Partners Ltd (PDP) have been engaged to undertake the preliminary
Strategic Assessment of Water Infrastructure Option 4, which is: Managed Aquifer
Recharge (MAR). The assessment has been structured to include the following
information:
π a description of what is involved with MAR and its expected impacts on Canterbury
water resources (Section 2);
π a summary of the relevant data and information that is available to assess the MAR
option (Section 3). This information relates to:
– technical information about the groundwater system;
– the principles and targets of the CWMS;
– aspirations of key stakeholder groups;
π analysis of variance against CWMS targets, consideration of potential benefits and
risks and a consideration of information gaps that currently limit the analysis of the
MAR option (Section 4);
π formulation of scenarios as to how the MAR option could best be implemented, so
as to provide a focus for future assessment work (Section 5).
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2.0 Description of Managed Aquifer Recharge (MAR) in
the Canterbury Groundwater Setting
The principles and targets of the CWMS relate to monitoring and enhancing the values of
water resources for both in-stream and abstractive purposes, as well as broader
environmental and community benefits. The effective management of water resources to
best achieve these principles and targets requires an integrated management approach to
both surface water and groundwater based on a detailed understanding of how these two
water environments interact. Therefore, MAR needs to be assessed within the context of
an overall understanding of Canterbury’s water resources.
2.1 Overview of the Potential Application of MAR in Canterbury
Groundwater is the natural source of supply for spring-fed streams and wetlands,
particularly in the lowland plains, and supports groundwater dependent ecosystems both
in the subsurface and spring-fed stream/wetland environments. It is also a major source
of abstractive water supply across the region. Figure 1 shows an example of a typical
water balance for a section of the Canterbury Plains groundwater system, where
groundwater flow occurs through the gravel aquifer in a general east-south-easterly
direction from the foothills to the coast.
MAR is the artificial introduction of additional recharge into the groundwater system. The
source of this additional recharge water in the Canterbury setting will primarily be derived
from rivers, either directly during times of higher flow or from surface storage reservoirs.
In very broad terms, MAR can contribute to alleviating some adverse water resources
trends that are showing up in Canterbury. These are described in Annex C of the CWMS
Strategic Framework (November 2009) and include:
π a large number of groundwater allocation zones that have been classified as being
over-allocated due to the volume of consented groundwater takes (i.e. red zones), as
shown in Figure 2. MAR can increase the amount of water in an aquifer to improve
the balance between recharge and abstraction;
π concerns about poor quality water, particularly nitrates in groundwater, spring-fed
streams and lowland lakes such as Lake Ellesmere and the effects on drinking water
supplies, ecosystem health and wider cultural values of these waterways. MAR can
add good quality water into the groundwater that is free of the chemicals that are
leached from land use activities, thereby contributing to an overall reduction of
chemical concentrations in groundwater. For example, the concentration of nitrate-
nitrogen in the alpine rivers is significantly lower than in recharge water that
infiltrates through agricultural soils, as shown in Table 1.
C02424500R001_Final_PDF.docPATTLE DELAMORE PARTNERS LTD 3 Preliminary Strategic Assessment of Water Infrastructure Option 4: Managed Aquifer Recharge Table 1: Typical Nitrate-Nitrogen Concentrations in Different Sources of Aquifer Recharge Water Recharge Source Nitrate-Nitrogen Concentration (g/m³) Recharge water derived from alpine rivers
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π the zone of unsaturated strata below wastewater disposal systems and buried waste
dumps provides treatment of the water that drains from those areas before it mixes
with the saturated groundwater flow. Raised groundwater levels can reduce the
effectiveness of that treatment component;
π MAR could represent an inefficient use of the recharge water, relative to other
potential uses, if it is not available at the right time and place to contribute to the
principles and targets of the CWMS.
Therefore, careful consideration of these issues must be given to ensure the successful
implementation of any MAR scheme in Canterbury.
2.2 Locations Where MAR is Likely to be Most Effective
MAR is likely to make the greatest contribution to the principles and targets of the CWMS
in the following areas:
π areas where groundwater is a preferred source of abstractive water supply and the
area has been classified as over-allocated (i.e. red zones). In these areas, MAR
directly adds to the annual volume of water within a groundwater allocation zone;
π areas where there is a substantial source of recharge available, i.e. alpine rivers
and/or existing or proposed storage structures;
π areas where the benefits of recharge are likely to be retained for use during times of
natural low groundwater levels.
Consideration of these three areas is described in the following sections.
2.2.1 Areas Where Groundwater is a Preferred Source of Supply
Groundwater abstraction is a most effective source of water supply where two conditions
are met:
π the strata has a high permeability;
π groundwater pressures are high.
If one or both of these criteria are not present, then groundwater supply for high
abstraction rates (as required for most irrigation supplies) becomes a more costly and
less energy efficient means of water supply relative to a gravity fed surface water supply.
Previous studies have identified areas of central Canterbury plains where conditions are
most favourable for groundwater abstraction. These typically occur at the coastal end of
the plains where the alluvial gravels are better sorted (more permeable) and groundwater
levels are closer to the ground surface. In addition to these permeable areas in the lower
plains, there are a number of ephemeral waterways further inland that could be
considered as a conduit to introduce artificial recharge water to the aquifers. Water
introduced to these inland waterways could also provide another means of water
distribution to abstractive users and in some cases support shallow groundwater supplies
from riparian gravels, such as occur adjacent to the Hororata, Selwyn and Ashburton
Rivers, during the times when their surface flow would otherwise be depleted. These two
C02424500R001_Final_PDF.docPATTLE DELAMORE PARTNERS LTD 5 Preliminary Strategic Assessment of Water Infrastructure Option 4: Managed Aquifer Recharge main areas of groundwater supply are shown in Figure 4 for the main Canterbury Plains aquifers. The coastal areas of preferred groundwater development shown in Figure 4 also include most of the spring-fed surface waterways. So any MAR in these areas where groundwater abstraction is most effective is also likely to contribute to the improved health of these surface waterways. 2.2.2 Sources of Water for MAR The sources of water that will be used to supply MAR activities in Canterbury are expected to be drawn from the alpine-fed rivers, the larger foothills-fed rivers and/or from large water storage structures. However, due to the inefficient link between MAR activities and specific benefits at groundwater abstraction points (both natural abstraction via springs and artificial abstraction via bores), it is expected that the priorities for management of water in alpine rivers will be: π 1st: in-stream values; π 2nd: direct supply to abstractive users; π 3rd: MAR. Similarly, water in storage reservoirs would be expected to primarily be used for direct delivery to abstractive users who are funding the storage activity, with any water for MAR only available once direct supply abstraction demands have been met and where there is certainty that the storage can still be re-filled prior to the next irrigation season. It is important to recognise that once recharge water is released into the groundwater, it is no longer under the control of the organisation that has supplied the recharge water. Therefore, the funding of MAR water will be a key factor to determine its availability. Given the inefficiency of water delivery that occurs through a MAR scheme, it is most likely that the water that is available for MAR is likely to be relatively low reliability river water from rivers during the irrigation months, and surplus storage water towards the end of low demand irrigation seasons. The exception to this could be water introduced to ephemeral waterways (such as the Hororata and Selwyn Rivers), for in-stream benefits that need to be maintained at particular times of year (e.g. during trout migration). If this is done it would primarily be for in-stream benefits, but a secondary groundwater benefit would result from such actions. 2.2.3 Retaining the Benefits of MAR Water Recognising that the availability of water to supply MAR may not always coincide with times of high abstractive demand or naturally low stream flows, it is important to understand whether the benefits of the extra recharge water are available where and when they are required. C02424500R001_Final_PDF.doc
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Overseas examples of MAR are most successful for groundwater systems that occur in
arid basins or in groundwater settings that have lower permeability and/or lower hydraulic
gradients than the Canterbury Plains. This provides for longer term storage of the
recharge water for later re-use. However, it is important to recognise the relatively
unique hydrogeologic characteristics of the Canterbury Plains, as described in Fietje
(1991), who states “… the Plains are composed of a series of coalescing fans consisting
of alluvium deposited by rivers. The sorting and rounding of sediment during transport
has resulted in permeable layers within the fan, allowing water to pass through relatively
quickly. There are not many places in the world where geology and climate have led to
the formation of fans the size of the Canterbury Plains”. In particular, the hydraulic
conductivities and groundwater velocities are much higher than most areas where MAR
has been successfully implemented overseas.
Groundwater basin structures are present in Canterbury, in particular the Culverden
Basin, the Cannington Basin and, at a even larger scale, the Upper Waitaki Basin. In
these areas, there is more certainty where MAR water will emerge and which waterways it
will contribute to, although there is still uncertainty as to the timeframe of when those
benefits appear. On the Canterbury Plains aquifers, there is an even greater degree of
uncertainty as to both the location and the timing of the benefits from MAR.
Therefore, successful MAR is more challenging in the Canterbury environment due to the
high permeability strata and the hydraulic gradients which create a level of uncertainty as
to whether the artificially introduced recharge water will be available in the right part of
the aquifer at the right time. Therefore, it is helpful to learn from the experiences of
artificial recharge activities that are already occurring in Canterbury.
2.3 Artificial Groundwater Recharge Activities in Canterbury
Artificial aquifer recharge is already occurring on the Canterbury Plains, from surface
supplied stockwater and irrigation schemes, although these activities are not specifically
managed for aquifer recharge purposes and therefore cannot be considered as examples
of MAR. However, the response of the groundwater system to these recharge activities
provides a useful indication of how the Canterbury aquifers will respond to MAR.
Examples of the existing artificial aquifer recharge effects are:
π stockwater race networks extend across the plains. Information from gauging
surveys show that these races contribute seepage to groundwater on the order of 5
L/s per km of race. Two quantified reviews of stockwater race systems indicate the
following flow distributions:
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Table 2: Examples of Water Race Distribution Networks
Ellesmere Stockwater Race Ashburton Stockwater Race
Network (Selwyn District Network (Ashburton District
Council) (from Opus, 2009) Council) (from Brough, 2009)
Intake (L/s) 1,935 10,016
Water Use
Stockwater drinking (L/s) 60 (3%) 176 (2%)
Evaporation (L/s) 90 (5%) 382 (4%)
Discharges from the end of 60 (3%) 1,220 (12%)
the race network (to surface
waterways or soakpits) (L/s)
Domestic irrigation (L/s) 9.3 (0.5%) -
Seepage to groundwater (L/s) 1,722 (89%) 8,248 (82%)
Similarly, a review of seepage losses from the Paparua stockwater race network on
the south side of the Waimakariri River shows that the water races discharge around
80-90% of their flow to groundwater (Agriculture New Zealand, 1997). These
groundwater discharge flows contribute around 5-15% of the groundwater recharge
to the areas where stockwater race networks occur. This represents a significant
continuous input of a well distributed artificial recharge network for Canterbury
groundwater systems.
Any initiatives to replace water races with piped distribution systems should not be
undertaken solely from a consideration of the efficient delivery of stockwater, but
must also consider the valuable contribution that water race seepage makes to the
groundwater system.
However, given that the Ellesmere and Paparua stockwater systems occur within
groundwater allocation zones that are considered to be over-allocated (i.e. red
zones), it is clear that the stock water races above do not provide sufficient recharge
to overcome current groundwater allocation issues. The potential to overcome that
seems to be more associated with surface supplied irrigation schemes, as noted in
the following two examples;
π the Rangitata Diversion Race (RDR) has been in existence since 1944 and supplies
water to three irrigation schemes: Mayfield-Hinds, Valetta and Ashburton-Lyndhurst
(Figure 5). Monitoring of groundwater levels within the scheme areas show the
effects of the extra surface supplied irrigation water being introduced to the area
with some wells showing seasonally high groundwater levels during the irrigation
season (Figure 6). These groundwater level patterns would suggest that sufficient
artificial recharge into the groundwater system has been occurring as a result of RDR
activities. However, changes to that scheme, such as piped reticulation to replace
water races and border dyke irrigation being replaced with spray irrigation will
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represent a loss of groundwater recharge, which could create a need for MAR in the
future;
π Waimakariri Irrigation Ltd is an example of a modern community supply scheme
utilising spray irrigation systems. The extra recharge induced by water race leakage,
bywash discharges and extra rainfall recharge beneath irrigated paddocks has seen
changes in water level behaviour, with groundwater levels not declining to the
summertime lows that previously occurred (Figures 7 and 8) and spring-fed streams
maintaining higher flows during the summer months (Figure 9).
The response of groundwater levels and spring flows from the WIL scheme, as shown in
Figures 8 and 9 provides an example of the type of response that a MAR scheme should
seek to achieve – i.e. relief from seasonal lows whilst fluctuations still occurring within
their natural range.
However, MAR involves a more targeted introduction of water into the groundwater
system for the specific purpose of improving reliability of supply to groundwater
abstractors and/or relieving wetlands and spring-fed surface waterways of adverse effects
that might otherwise occur at times of low groundwater levels.
Some physical trials of MAR in Canterbury have previously been carried out:
π in June-September 1991 a flow of around 110 L/s from the Paparua stockwater race
was introduced into a soakage pit located on the corner of Old West Coast Road and
State Highway 73 at Yaldhurst(Callander et al; 1991);
π in August-October 1992 a flow of around 112 L/s from the Paparua Stockwater Race
was discharge into a soakage hole at Bells Road, West Melton (Canterbury Regional
Council; 1994);
π in September 2005 a flow of 2.7 m³/s from the head race of the Waimakariri
Irrigation Scheme was discharged into the dry bed of the Eyre River (Pattle Delamore
Partners Ltd; 2007).
All these trials have been effective in demonstrating mechanisms by which surface water
recharge can be artificially introduced to the groundwater system. The effects they have
created have been to raise groundwater levels in the local area around the recharge
point, although these effects begin to dissipate as soon as the recharge source is turned
off as the raised groundwater gradients created by the recharge cause groundwater to
spread out and equilibrate with the surrounding groundwater resource. Therefore, with
increasing distance from the MAR location and with increasing time since the MAR trial
ended, the effect of the recharge becomes difficult to identify. That is partly because the
scale of these trials has been small relative to the size of the groundwater resource into
which they occurred. However, the larger scale stockwater and irrigation activities
indicate the wider scale and longer term benefits that MAR can achieve, even within the
gravel aquifers that occur on the Canterbury Plains (Figures 5-9).
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2.4 Guiding Principles for Implementation of MAR in Canterbury
Based on the preceding description of MAR and the Canterbury groundwater environment,
it is considered that the following principles could be applied to help guide the
assessment of MAR options:
(i) Scope of MAR Effects
MAR cannot be assessed solely as a groundwater issue, it must be viewed in terms
of its overall impact on both surface and groundwater resources having regard to
both the source of supply of MAR water and its movement through the subsurface
environment.
(ii) Efficiency of Supply
MAR is a less efficient means of delivering water to an abstractive user or a wetland
or stream relative to the direct delivery of water to the farm gate or into the surface
waterway via a pipeline or water race. This inefficiency arises from the
heterogeneous way in which water moves through the groundwater system.
(iii) Greatest Area of Benefit for Abstractors
The greatest benefit from MAR that will arise for groundwater abstractors occurs in
the areas where permeable gravel strata and high groundwater levels coincide. This
includes the areas on the coastal side of the plains and riparian gravels adjacent to
inland surface waterways during periods when surface flow is occurring, as shown in
Figure 4.
Abstractive users in the areas outside of these main groundwater supply areas will
be more effectively supplied with water delivered directly to the farm gate from rivers
or large storage reservoirs. The provision of surface water supply to these areas will
reduce existing groundwater abstraction in those areas, thereby helping to boost
groundwater levels. Furthermore, the management of this inland surface water
distribution system can provide a useful source of supply for MAR.
(iv) Contribution to Groundwater Allocation
MAR can directly add water into groundwater allocation zones, thereby providing a
direct relief to red zone issues. It also can contribute to improved flows in spring-fed
surface waterways, although those benefits may become more difficult to quantify,
particularly at increasing distance from the recharge area and with increasing time
from the end of the recharge activity.
(v) Contribution to Water Quality
The source water that is utilised for MAR schemes is likely to have low nutrient
concentrations if derived from alpine rivers, the upper reaches of foothills rivers or
storage lakes. Therefore, its addition to the aquifers is likely to contribute to a
reduction in groundwater nitrate concentrations. This benefit is likely to be greatest
if MAR is introduced to shallow groundwater in areas where natural recharge is
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dominated by land surface recharge on agricultural land. This benefit to shallow
groundwater quality will contribute to spring-fed streams, along with increased spring
flows of low temperature water.
(vi) Timing of Benefits
The Canterbury Plains have unique hydrogeologic characteristics which means that in
many of the most permeable aquifers, the raised water pressures cannot be stored
for long periods of time. In these areas, the most direct benefits will occur in the
immediate locality of the MAR activity at the time it is occurring. The benefits from
MAR are more directly defined in groundwater basins, but are less precise on the
Canterbury Plains aquifers.
This could mean the most direct benefits from MAR would require water to be
allocated for the purpose of aquifer recharge during times of high demand in the
waterways providing the source of supply. However, the main sources of supply to
MAR schemes are likely to be from alpine rivers, larger foothills rivers and/or large
water storage structures. MAR activities are likely to be a lower priority supply
compared to in-stream values and direct supplies to irrigators. Therefore, MAR water
may not always be available at the time of lowest groundwater levels and lowest
spring flows.
(vii) Range of Potential Changes
It is desirable to operate MAR activities so that groundwater levels continue to
fluctuate within their natural range, thereby preserving the natural groundwater flow
pattern. In some seasons and at certain times of the year, there is sufficient natural
infiltration to fully recharge the aquifers and no MAR is required. Therefore, the
location and timing of MAR activities should be focused on relieving periods of
seasonally low groundwater levels, which typically occur in the January-May period.
(viii) Management of Drainage Problems
Artificially raised groundwater levels combined with naturally occurring large rainfall
events can cause drainage problems in low lying areas. Therefore, it is prudent for
large scale MAR activities to include a contingency provision for drainage works
and/or land owner compensation. Additional drainage works can be undertaken in a
manner that enhances the surface water environment. Similar contributions to the
management of lowland lakes may also be required.
(ix) Management of Uncertainty
Given the uncertainty in precisely predicting the effects of MAR, it will be best for
MAR to be progressed on a recharge-observe-analyse-modify basis. This approach,
coupled with the inefficient water delivery aspects of MAR, mean that is would be
prudent to utilise infrastructure with a relatively low capital cost.
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(x) Versatility
MAR can be carried out as a standalone option or as a beneficial component that
can be incorporated into a surface water management scheme. It can be
implemented within a short timeframe at relatively low cost, as evidenced by existing
examples of artificial recharge that are already occurring on the plains.
3.0 Relevant Information to Assess the MAR Option
In order to assess the effects of MAR, there is a need for data and information regarding
how the existing groundwater system responds to recharge events and how that can be
expected to change if MAR was implemented. There is also a need for information to
understand how these groundwater changes impact on the principles and targets of the
CWMS and how it will impact on the interests of key stakeholder groups.
3.1 Groundwater Information
For the main Canterbury Plains aquifers, a good body of information and analysis exists.
For example, in the Central Canterbury Plains area from the Waimakariri-Rangitata River
there are:
π groundwater level monitoring records;
π groundwater quality data sampling points;
π spring-fed stream flow monitoring;
π spring-fed stream water quality monitoring;
π monitoring of the level and quality of Lake Ellesmere;
π current assessments of the groundwater balance;
π a further body of information related to existing land drainage issues is known in
general terms, but may need to be defined more precisely regarding the areal extent,
frequency and duration of such situations to provide a benchmark against which
future changes can be judged;
π at a more localised level, understanding the infiltration characteristics in and around
any particular recharge installation will be critical to designing the correct infiltration
system.
All of this information provides an essential benchmark against which the effects of MAR
activities can be judged (just like the extra recharge effects from the WIL scheme can be
judged from the long-term historical levels shown in Figures 8 and 9).
Making predictions in advance of MAR activities taking place is more challenging, and
with a less certain outcome. For some aspects of a potential MAR scheme, some useful
background information already exists. For example:
π annual water balances are available for all the groundwater allocation zones defined
as red zones. Therefore, the volume of water that is to be added via a MAR scheme
can be assessed relative to the overall water budget for the groundwater system to
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indicate the scale and extent of the potential widespread effects that may result.
For example, from an overall water balance point of view, the information presented
in Figure 1 provides an indication of the likely significance of a MAR discharge
relative to other water balance components;
π if rivers, such as the Hororata and Selwyn Rivers, are to be used as recharge
mechanisms then existing patterns of surface flow provide an indication of the
groundwater recharge. For example, Figure 10 indicates that:
– the Hororata River tends to lose seepage until it approaches the Selwyn
confluence;
– the Selwyn River loses seepage into its upper and middle reaches across the
plains and is dry in its middle reaches for around 70-90% of the time. The flow
that is required to maintain a permanent flow along the length of the Selwyn River
channel depends on the surrounding groundwater levels, which vary seasonally.
Naturally occurring recharge to groundwater from this river bed has been
estimated to average around 2.2 m³/s, but at times of very low groundwater
levels, losses of up to 10 m³/s may occur between Whitecliffs and Bealy Road
(CRC, 1996);
– Figure 11 indicates the increasing deviation between surface flow at Whitecliffs
and surface flow at Coes Ford, which is attributed to the combined effects of
increased groundwater abstraction and a decreasing rainfall trend in the middle
and lower plains. It is this type of deviation pattern that a MAR scheme could
seek to address;
π In the lower plains, groundwater levels directly affect flows in spring-fed streams.
Whilst the relationship is not always precise, a particularly good relationship occurs
in the records of flow in Doyleston Drain and groundwater levels in bore M36/0656
located 3 km to the south-west of the drain, as shown in Figures 12 and 13.
MAR will clearly add more water into the lowland areas in terms of raised groundwater
levels and increased spring flow. For the area of the Canterbury Plains between the
Waimakariri and Rakaia Rivers, these potential effects have recently been well canvassed
at the ECan consent hearing for the Central Plains Water Scheme. That hearing panel
concluded that the effects arising from extra aquifer recharge (estimated to be about 90
million m³ per annum of irrigated soil drainage and 70 million m³ per annum of water
race seepage and bywash) would not cause insurmountable problems that could not be
consented, although detailed monitoring, management and mitigation measures were
required. The CPW decision recognises that an integrated catchment management
approach to these issues of water balance and nutrient effects is clearly needed. The
commissioners noted that such an approach is supported by many submissions which
sought a more holistic approach to land and water management. Any consideration of
MAR must take a similarly wide ranging and holistic approach to the consideration of how
it will be implemented and managed, although with the appropriate mitigation measures
the addition of low nutrient recharge water should be beneficial.
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All of these types of relationships provide an indication of what MAR would need to
achieve in terms of releases of water into ephemeral waterways or raising of groundwater
levels in order to achieve corresponding benefits in stream flow.
Predictive models of changes to groundwater levels and spring-fed stream flow are
available in the form of region-wide numerical groundwater flow models and Eigen model
analysis of changes that could be expected at particular monitoring well locations.
However, there is a large degree of uncertainty with such predictive tools, and they
should be viewed as providing a general indication of the type of change that might occur
from a MAR activity, but they do not provide a particularly precise quantification of the
changes that will occur at any particular location or at any particular time. This
uncertainty is simply due to the difficulty in characterising the natural groundwater system
within a framework of numerical equations.
Furthermore, potential groundwater quality changes are even less precisely defined. The
time lag between soil drainage and observed groundwater quality makes it difficult to
explain and predict currently observed trends in groundwater quality. So whilst the type
of change that MAR can create for water quality can be described, it is not expected that
the potential effect will be able to be quantified either in magnitude or timing with any
great precision.
It is worth noting that the other water infrastructure options that are being assessed for
the CWMS involve specific surface water supply schemes in the Hurunui catchment, Lees
Valley and South Canterbury areas, along with improvements to existing irrigation scheme
infrastructure. In all those cases, the area and timing of the benefits can be precisely
defined. Consideration of these surface based options can define water storage volumes
and specific areas where that water can be delivered to a particular area of properties,
resulting in so many hectares of extra irrigation and/or a certain percentage of improved
reliability of supply. In contrast, the exact benefits of MAR need to be considered in more
generic and qualitative terms. In general terms, MAR can raise groundwater levels, boost
spring-fed stream flow, contribute to better water quality, but exactly where, when and by
how much these changes occur cannot be precisely determined in advance.
Therefore, MAR will best be implemented on a recharge-observe-analyse and modify
basis, with adjustments made based on the observational monitoring of initial recharge
activities. The focus of this monitoring will include:
π the quantity and quality of the recharge water being introduced into the ground;
π gauging surveys along any surface waterways to be used as groundwater recharge
pathways;
π monitoring in the receiving environment of:
– groundwater levels;
– groundwater quality;
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– flow in spring-fed streams and levels in downstream lakes;
– water quality in spring-fed streams and levels in downstream lakes;
π surveys of land owners regarding land drainage issues;
π surveys of stakeholder groups regarding groundwater effects.
Given that a trial and monitor approach is required to fully understand the effects of MAR,
it is therefore prudent that MAR should be implemented using relatively low cost
infrastructure, or as a component of a large scale surface supply scheme.
The information needs listed above are equally applicable to areas where aquifer recharge
effects are already occurring, albeit in an unmanaged way (for example, the RDR-supplied
schemes, the Waimakariri Irrigation scheme and the Ashburton, Selwyn and Waimakariri
District stockwater race networks). For these existing systems, it is desirable that the
current level of aquifer recharge should be assessed and consideration given to whether it
can be better managed compared to what is currently the case. This understanding is
particularly important if changes are proposed to the means of water reticulation (water
races vs pipelines), irrigation methods (border dyke vs spray) and/or the management of
bywash (surface discharge vs soakholes). Any such changes will impact on the
groundwater balance of the area and it is important that the implications of such changes
are understood and, where necessary, mitigation soakage discharges are put in place as
part of the scheme changes.
The examples presented in this discussion of groundwater information needs have
focused on the central Canterbury Plains, which has a very high level of existing
information. This provides an example of the type of information that would need to be
gathered if MAR was to be implemented in other areas of Canterbury. In particular a
monitoring database to define the existing groundwater system must be in place to
provide a benchmark against which the changes created by MAR can be observed.
3.2 Other Information Needs
Whilst groundwater information is the key to understanding the changes created by MAR,
there is also a need for information to be available about how those groundwater changes
are impacting on the targets of the CWMS. Many of those information requirements will
be generic to all projects related to CWMS activities, but some specific comments on
information needs for the MAR option are listed below:
π Ecosystem Health/Diversity and Recreational and Amenity Issues – The key
contribution MAR will make to ecosystem health and diversity and recreational and
amenity issues relates to spring-fed surface waterways. Whilst there is also an
ecosystem that exists within the subsurface groundwater environment, it is not
readily observable and may not to be significantly altered by MAR activities, relative
to other factors that are occurring.
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Information on how spring-fed surface waterways and their CWMS targets will
respond to increased groundwater discharge will need to be sourced to ensure that
MAR is focused on achieving the greatest benefit.
Whilst not directly caused by MAR, it is worth noting that if surface waterways such
as the Hororata and Selwyn Rivers are used as the mechanism to introduce extra
recharge into the ground, then the management and effects of that surface release
of water on ecosystem health/diversity and recreational and management issues
would be an important factor to consider;
π Kaitiakitanga – Discussions with Gail Tipa indicate concern about the uncertain
effects of MAR and that it might simply result in increased irrigation. The iwi
consultation has indicated they would like to see MAR trialled and monitored for a
period of time with none of the MAR water assigned to irrigation, so as to
demonstrate the environmental benefit that can be achieved.
There is also concern about the use of natural waterways as a means of introducing
MAR water. If this was to be carried out it might be feasible in dry streambeds with
no connection to natural flowing water, but this would need to be managed in close
consultation with iwi if it was to receive their approval and even then might not be
acceptable.
Close consultation with iwi is recommended for any proposed MAR activities and the
monitoring of effects created by those activities from an iwi perspective will be an
important requirement for any activity.
The report from the Kaitaiakitanga consultation is presented in Appendix C;
π Drinking Water – Effects of MAR on drinking water bores will be incorporated into
the groundwater quality monitoring described in Section 3.1;
π Water Use Efficiency and Energy Security and Efficiency – In terms of MAR,
water use efficiency can be viewed from two aspects.
Firstly, it can relate to the use of water within a MAR scheme compared to other
possible options. This can be assessed in a fairly straightforward manner. For
example, the delivery of water to an abstractive user via a pipe or a water race is far
more efficient than creating additional groundwater recharge. Similarly, the direct
delivery of water to augment a surface waterway or a MAR discharge very close to
spring discharge areas is far more efficient than a more distant MAR discharge.
The second aspect of MAR water use efficiency relates to raised groundwater levels
making groundwater abstraction more efficient. However, in terms of pumping from
existing systems, the type of water level changes shown in Figures 6 and 8 will make
very little difference in practical terms relative to the overall pumping head in an
irrigation system. Consequently, the contribution to energy efficiency from MAR is
likely to be minor;
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π Irrigated Land Area and Regional/National Economics – An increased volume of
groundwater as a result of MAR can contribute to an increase in irrigated land area.
As mentioned in Section 3.1, this is a change that is difficult to quantify. However,
as an initial indication of quantities of water that could be required to alleviate red
zone issues, the following table is helpful.
Table 3: MAR Quantities Required to Alleviate Red Zone Issues
Over-Allocated ECan’s Total Consents Overrun Surplus Recharge Required
Groundwater Zones Recommended Granted and in (million m³) (50% available for allocation)
Allocation Limit Process (million m³) MAR for 365 MAR for 100
(million m³) days per year days per year
(m³/s) (m³/s)
Eyre 81.3 94.49 13.19 0.84 3.06
Selwyn-Waimakariri 121.3 162.44 41.14 2.60 9.52
Rakaia-Selwyn 215 272.76 57.76 3.66 13.38
Chertsey 112.4 135.91 23.51 1.50 5.44
Ashburton-Lyndhurst 126.6 137.26 10.66 0.68 2.46
Ashburton River 69.5 75.72 6.22 0.40 1.44
Rangitata-Orton 42.5 46.84 4.34 0.28 1.0
More specific information is available from the recent hearings for the Selwyn-
Waimakariri and Rakaia-Selwyn zones, which indicated the following numbers.
Table 4: Quantities from Recent Consent Hearings
Groundwater Zone Number of Consent Annual Volume of Area Irrigated (ha)
Applications Groundwater Consented
(m³ per year)
Selwyn-Waimakariri 41 24,301,065 4,822
Rakaia-Selwyn 68 35,373,621 ~7,020
Therefore, based on the guideline criteria used by ECan, it is appropriate to judge
MAR discharges as relieving allocation limits by 50% of the quantity of water
discharged. As a general rule of thumb, the following criteria can be used:
11,000,000 m³ of MAR water per annum (1.3 m³/s over 100 days)
for 1,000 ha of extra irrigation.
The red zones are the most critical areas where MAR is required, and/or an alternate
surface supply scheme provided. Without that occurring, future irrigation options are
severely limited, and even irrigation activities for those with recently granted
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consents may be severely limited due to the restrictive consent conditions which
result in uncertainty regarding the supply availability from year to year.
The benefits of MAR to regional and national economics will primarily be related to
the flow on benefits from increased irrigation areas supplied by groundwater and can
be judged from economic assessments of that water use;
π Environmental Limits – The contribution of MAR to achieving environmental limits
will be established by the information sets described in Section 3.1.
It is desirable to compile all these information requirements prior to planning and
implementing a MAR scheme to ensure that it is targeted at achieving specific benefits
and that there is a monitoring framework in place to measure the changes created by
MAR.
3.3 Aspirations for MAR From Key Stakeholder Groups
It is anticipated that the following key stakeholder groups will have a particular interest in
MAR, and will have the following expectations and concerns.
Table 5: Stakeholder Views of MAR
Stakeholder Group Supportive Expectations for MAR Concerned Reservations About MAR
Groundwater abstractors Likely to support MAR and expect it
to deliver raised groundwater levels
and improved groundwater quality,
thereby making groundwater
abstraction more reliable. A subset
of this group will be holders of
consents from recent area-wide
consent hearings on the Canterbury
Plains that have resulted in onerous
consent conditions creating
considerable uncertainty over their
future ability to fully exercise their
consents. These consent holders
should be strong supporters of MAR
as a mechanism to overcome a less
than satisfactory outcome from their
consent applications.
Land owners in lowland Groundwater users within this group Likely to be concerned about land
areas see benefits to MAR creating drainage problems arising from raised
improved flows in spring-fed streams groundwater levels. Their agreement to
which currently trigger restrictive mitigation options related to new
conditions on their groundwater take drainage works and/or compensation
consents. measures will be an important
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component to the implementation of
MAR activities.
People interested in Likely to support MAR and expect it Possible concern about increased spring
lowland waterways to deliver increased spring flows of flows allowing trout migration (and
improved quality (through lower predation) further up into lowland
nutrient concentrations and cooler streams.
temperature water). Any drainage
works required to address land
drainage problems also provide an
opportunity to carry out these works
in a way that creates an enlarged
area of quality surface water habitat.
People interested in Will be interested in the prospect of Will be concerned about extra recharge
lowland lakes e.g. Lake lower nutrient inflows into these impacting on lake levels. For lakes that
Ellesmere lakes and an ability to maintain are managed by artificial openings, such
higher lake levels during dry summer as Lake Ellesmere, this would require
periods. more frequent openings. In particular,
concern has been expressed from the
ECan Regional Engineer about the
considerable amount of effort that has
gone into understanding the hydraulic
balance and the management of
openings at Lake Ellesmere. If MAR
activities were to significantly alter this,
then there would be a need for the
participants in the MAR activities to
contribute financially to revising the
research and management strategies
regarding Lake Ellesmere and its
openings.
People interested in inland Will be interested in the possibility of Will want to carefully consider the
ephemeral waterways these waterways being used as a magnitude, quality and timing of any
means of achieving MAR. Good artificially introduced water.
management of these water releases
is essential if this mechanism for
MAR is to be achieved and these in-
stream interests are likely to be the
determining criteria of what can be
achieved in terms of MAR via this
mechanism.
People interested in alpine Will be concerned about the prospect of
rivers additional abstraction to supply MAR
schemes and will want to ensure that it
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does not adversely impact on the alpine
river environment. Meeting these
concerns is likely to lead to a lower
reliability of water able to supply MAR
schemes.
People interested in storage May support MAR as a secondary Will be concerned about the use of their
reservoirs lower priority use of their supply high value stored water for MAR. Are
likely to want their water delivered
directly to users who contribute to their
scheme.
Iwi MAR can enhance groundwater that The major concern is that MAR will
is a source of water for lowland simply be used to allow more irrigation
streams. For iwi to support MAR, it to occur.
should first be conducted on a trial Iwi are also concerned about the use of
basis, with no increase in irrigation, existing river channels to introduce MAR
and monitoring in place so that the water due to mixing of waters.
environmental benefits of MAR can
The uncertainty as to the ultimate
be measured and understood.
destination and use of MAR water is a
concern.
It is essential that the provision of information described in Sections 3.1 and 3.2 is
gathered to quantify how the expectations and concerns of the various stakeholder
interest groups are met.
4.0 Analysis of Variance Against the CWMS Principles
and Targets
Based on the description in Section 2 of this report, it can be difficult to quantify the
precise impact of MAR in achieving the principles and targets of the CWMS. In particular,
it is a relatively inefficient means of delivering water to abstractive users or for surface
flow enhancement and its benefits within the wider scale aquifers of the Canterbury
Plains can be difficult to precisely quantify with increasing time and distance from the
point of recharge. Despite this lack of quantifiable precision, MAR can make a very
useful contribution to the overall volume and quality of the groundwater resource and the
surface water springs that are fed from groundwater. Furthermore, MAR is an option that
can be implemented within a wide range of time periods and scales. At its simplest, it
can be implemented quickly using low cost structures, as evidenced by the uncontrolled
recharge effects that are already occurring in connection with existing water distribution
networks, as described in Section 2.3 of this report.
Appendix A has been prepared to summarise the CWMS targets and goals (as set out on
the CWMS website) and to highlight those that can be addressed via MAR. In particular,
those goals that can be affected by MAR are shown in bold, whereas those in fainter text
would not be achieved by MAR. Brief explanatory comments are added in italics.
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