Selwyn-Te Waihora Land and Water Planning; Managing Groundwater Replenishment Using Managed Aquifer Recharge (MAR).

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2 Selwyn-Te Waihora Land and Water Planning; Managing Groundwater Replenishment Using Managed Aquifer Recharge (MAR). Report No. R13/114 ISBN (print) (web) (electronic) Report prepared for Environment Canterbury by Golder Associates

3 Report No. R13/114 ISBN (print) (web) (electronic) PO Box 345 Christchurch 8140 Phone (03) Fax (03) Church Street PO Box 550 Timaru 7940 Phone (03) Fax (03) Website: Customer Services Phone This report represents advice to Environment Canterbury and any views, conclusions or recommendations do not represent Council policy. The information in this report, together with any other information, may be used by the Council to formulate resource management policies, e.g., in the preparation or review of regional plans.

4 REPORT SELWYN-TE WAIHORA LAND AND WATER PLANNING Managing Groundwater Replenishment Using Managed Aquifer Recharge (MAR) Submitted to: Alistair Picken Canterbury Regional Council PO Box 345 Christchurch 8140 Report Number _009_R_Rev0

5 Table of Contents 1.0 INTRODUCTION SCOPE MANAGING GROUNDWATER REPLENISHMENT Sustainable Groundwater Management Managing Groundwater Replenishment with MAR Managing Groundwater Quality with MAR What are the Tools of MAR? MAR Assessment Methodologies Benefits and Challenges of MAR More about MAR Historical background on MAR in Canterbury ASSESSING MAR FOR GROUNDWATER REPLENISHMENT IN SELWYN-TE WAIHORA Overview Land Use Change Scenarios MAR Conceptual Modelling for Solutions Package MAR Modelling Results Quantity, Stream Flows, and Quality Groundwater quantity results Stream flow and water quality results DISCUSSION - GROUNDWATER REPLENISHMENT IN THE SELWYN-TE WAIHORA ZONE WATER AUGMENTATION OPTIONS SELWYN-TE WAIHORA Potential MAR Options Other Potential Augmentation Options SUMMARY LIMITATIONS REFERENCES TABLES Table 1: General Types of Managed Aquifer Recharge applicable to Canterbury Plains... 9 Table 2: History of MAR field trials and groundwater modelling on Canterbury Plains Table 3: Selwyn-Te Waihora Modelling Scenarios (CRC, 2013) Table 4: Selwyn-Te Waihora MAR Results Median Individual Stream Site Flows (L/s) Report No _009_R_Rev0 i

6 Table 5: Selwyn-Te Waihora groundwater allocation zones limits and methods (CRC 2012b) Table 6: Preliminary list of conceptual MAR scheme configurations for Selwyn-Te Waihora Zone FIGURES Figure 1: Managed Aquifer Recharge is a set of physical and regulatory tools aimed at actively managing groundwater systems for quantity and quality Figure 2: Fundamental Catchment Water Balance - Understanding Sustainable Groundwater Storage Figure 3: Catchment scale water balance and use of MAR for sustainable and additional yields Figure 4: Managing Groundwater Replenishment some of the physical tools to deliver water to an aquifer (Dillon 2009) Figure 5: MAR trial upper Hinds River catchment discharging race water into a dry channel bed (Golder 2012b) Figure 6: Selwyn Waihora Zone - Groundwater replenishment scenario using infiltration basins (MAR) adjacent to planned CPW Headrace system Figure 7: MAR Model Results - Distribution of Groundwater Water Budget Changes Figure 8: Selwyn-Te Waihora groundwater level changes related to MAR (Scenario 1 versus Solutions Package 1) Figure 9: Selwyn-Te Waihora groundwater level changes related to MAR (Scenario 2 versus Solutions Package 1) Figure 10: Changes in stream flow related to the conceptual groundwater replenishment (MAR) scheme (Clark 2013) Figure 11: Cross section of Selwyn-Te Waihora Groundwater Replenishment Conceptual Model APPENDICES APPENDIX A Report Limitations APPENDIX B Types of Managed Aquifer Recharge Tools (Dillon 2009) Report No _009_R_Rev0 ii

7 1.0 INTRODUCTION Canterbury Regional Council (CRC) is undertaking land and water planning for each of 10 sub-catchments within Canterbury including in the Selwyn Waihora management zone. As part of land and water planning, a collaborative process has been undertaken to evaluate the implications of potential future scenarios and recommend limits and policy to achieve desired biophysical, social, cultural, and economic outcomes. Part of the scenario development included targeted mitigations for land and water use impacts. Among the mitigations that have been discussed is the management of groundwater quantity and quality using the artificial recharge mechanisms commonly referred to as managed aquifer recharge (MAR). This report is primarily aimed at providing the public with the background information needed to better understand the general concepts and applications of MAR as a water management tool. The report also reviews groundwater modelling conducted for the Selwyn Waihora Zone where a conceptual MAR recharge scheme was evaluated relative to ground and surface water flows and water quality goals for the catchment. The report will also briefly outline some of the other water augmentation options that have been discussed during the Canterbury Water Management Strategy (CMWS) process. 2.0 SCOPE The objective of this report 1 is to provide a brief synthesis of background on groundwater replenishment using MAR for land and water planning process in the Selwyn-Te Waihora catchment. The report covers: A description of managing groundwater replenishment using Managed Aquifer Recharge (MAR). Functions and benefits expected from MAR. Review of MAR opportunities in the Selwyn-Te Waihora Catchment. A discussion of water augmentation options with potential application in the Selwyn-Te Waihora Catchment. This technical information for various MAR and water augmentation options is solely intended to be provided for the land and water zone committee educational purposes. 3.0 MANAGING GROUNDWATER REPLENISHMENT MAR is a general term used to describe a wide range of physical and regulatory tools aimed at artificially recharging a targeted aquifer for economic, environmental, and cultural benefits (Figure 1). These tools are primarily intended to complement and enhance the natural recharge processes that replenish an aquifer for the purposes of helping to replace and/or restore groundwater supplies (both quantity and quality). The range of applications vary widely based on the particular water management need from rainwater harvesting in urban settings to help restore municipal supplies to engineered wetlands in rural settings that help remove nutrients from source water before recharging to a targeted groundwater system. MAR is not intended to be a stand-alone solution to catchment scale water management issues, and works best when it is incorporated into a complete management package that includes surface storage, water use efficiencies and regulatory frameworks that promote water sharing and banking. Actively managing groundwater replenishment with MAR is, for many, a new concept. We have traditionally viewed aquifers as naturally sustainable catchment features with the assumption that the existing recharge 1 This report is subject to the limitations outlined in appendix A Report No _009_R_Rev0 1

8 processes (e.g. rainfall, river seepage, etc.) will be sufficient to replenish and maintain supplies. The historical development and management of groundwater has solely focused on regulatory controls (e.g. consents, allocation limits, etc.) for the abstraction and protection (e.g. groundwater quality limits, etc) of groundwater. However, once abstractions begin to exceed natural replenishment and/or land use contamination has been introduced to system, this approach offers limited solutions. To best understand MAR as a water management tool, we must first briefly discuss its primary goal; which is the sustainable long-term management of groundwater and the ecosystems that depend on it. Figure 1: Managed Aquifer Recharge is a set of physical and regulatory tools aimed at actively managing groundwater systems for quantity and quality. 3.1 Sustainable Groundwater Management Sustainability is often an elusive concept to define in a precise manner with universal applicability, particularly when it comes to natural resources. The sustainable management of groundwater is commonly defined as the: development and use of groundwater in a manner that can be maintained for an indefinite time without causing unacceptable environmental, economic, or social consequences (USGS 1999). This definition can be further separated into a commonly-identified set of management goals: Long term yields from aquifer(s). Effective use of stored groundwater. Protection of groundwater quality. Preservation of groundwater-dependent ecosystems and flows. Integration of surface water and groundwater into a conjunctively managed system. These goals are consistent with those currently in New Zealand s national and regional regulations and resource management planning processes. At the national level the primary legislation for managing natural Report No _009_R_Rev0 2

9 resources is the Resource Management Act (RMA), which provided the basis for the operative Canterbury Natural Resources Regional Plan (NRRP 2011). The RMA promotes the sustainable management of resources in a way that provides for the needs of current and future generations. In Canterbury the 2012 publication of the Proposed Land and Water Regional Plan (PLWRP) also focuses on this sustainability message. Its objectives include that water is available for sustainable abstraction or use and groundwater continues to provide a sustainable source of high quality water for flows and ecosystem health (CRC 2012a). The PLWRP goes on to discuss storage as being an objective for Canterbury where a regional network of water storage and distribution facilities are developed to help achieve the sustainability of the resource. At the catchment scale, there are essentially two types of water storage; Surface: In the form of lakes, rivers, man-made reservoirs, and also including farm and municipal storage in the ponds, tanks and water towers. Groundwater: In the form of water held in both the soils and underlying aquifers. For most catchments a vast majority of the available storage is found in groundwater. This is consistent with the fact that most human usage also comes from groundwater with surface diversions often being a fraction of the total amount of water consented for use and available throughout the seasons. Most people can picture surface storage as it has historically been applied dating back through human history as a way to trap and store water. However, as water demands have increased, the availability of land become scarce, and the environmental effects of large reservoirs better understood it has become increasingly difficult get public support behind this as a sole solution to increased demand. This progression has driven communities to look to other sources of solving scarcity issues including improving our capacities to better manage groundwater. Additionally, water management science, policy and regulation have shifted away from treating surface and groundwater as separate entities. Our understanding of the relationships between surface and groundwater has led to developing conjunctive management regulatory tools that better manage the interactions of water storage and movement at the catchment scale. The timing and movement of groundwater when viewed at the catchment-scale is difficult to comprehend due to the complexity of the numerous on-going interactions between recharge and discharge activities. A simple method and good starting point for understanding catchment scale groundwater processes uses the fundamental water balance equation which is depicted in Figure 2. This equation represents the concept that the sum of all precipitation falling on a catchment is all the water any catchment has to available. This water is then distributed between four primary water balance components. Discharge includes any surface or subsurface flow of water that leaves the catchment as flows from rivers and streams. Evapotranspiration covers all evaporative or biotic consumption of water that is lost to the atmosphere. These two losses are in equilibrium with changes in both surface and groundwater storage. Surface storage includes reservoirs, ponds while changes in groundwater storage are found in the soils and underlying saturated aquifer systems. Report No _009_R_Rev0 3

10 Figure 2: Fundamental Catchment Water Balance - Understanding Sustainable Groundwater Storage. As we focus on groundwater storage ( S gw ) we need to consider how it has been both naturally and incidentally recharged or replenished over the years, and how those mechanisms may be changing. Subsequently we need to also to examine what processes have acted to remove or discharge water from groundwater storage and how the two are balanced (Figure 3). The history of groundwater use in rural catchments such as the Selwyn Waihora zone has changed considerably over the past 100 years. Under pre-development conditions (before human influences began) groundwater systems were considered to be in a long-term equilibrium between water that was added to a catchment (recharge) and that coming out of a catchment (discharge). This equilibrium is depicted in Figure 3 as natural yield. As groundwater use has developed, we have changed the water balance by pumping from stored groundwater and changing recharge patterns through irrigation and land use in the catchment. As we begin to explore the sustainable use of groundwater as a storage resource it is important to remember the groundwater conservation principle which is; the one common factor for all groundwater systems is that the total amount of water entering, leaving, and being stored in the system must be conserved. (USGS 1999) This fundamental rule means that if water is used in one location in the catchment it is lost somewhere else in the system; there is only a finite amount of water in any catchment. During the development of groundwater as a resource, this conservation principle has typically been achieved by assuming that natural recharge (rainfall/seepage) would be sufficient to replace and maintain the water being removed from storage. However, in practice, increased groundwater usage typically results in declining groundwater levels, flow reduction in rivers and streams and decreasing flows to spring and wetlands. Changes in total groundwater storage are typically not detectable over short monitoring periods (e.g. days, weeks, months), but become apparent when data is analysed over years to decades. Generally, catchments with aquifers in decline have a wide range of issues beyond just declines in groundwater storage which include declining water quality, declining ecological and culture values, Report No _009_R_Rev0 4

11 limitations for future economic development and increased socio-political conflicts between the various stakeholders. 3.2 Managing Groundwater Replenishment with MAR A simple way of depicting how MAR is used to replenish groundwater is to understand both the history and current status of the mechanisms that balance recharge and discharge. Figure 3 depicts the two different groundwater management scenarios. The first is when groundwater abstractions (discharge) are dependent solely on limited natural recharge processes causing a decline in groundwater levels and storage (Figure 3 Declining Storage). The second scenario depicts the management of both recharge and discharge (using MAR) which would work to sustainably manage the resource and potentially to utilise additional available storage for beneficial use (Figure 3 Managed Storage). There are a number of factors that indicate when an aquifer is in a state of declining storage. These indicators are expressed on the surface as a reduction in baseflows in the rivers, streams and springs. Additionally reductions in storage volume can exacerbate groundwater quality issues with increased contaminant concentrations and may induce increased pumping costs. To understand the current situation in rural catchments, we need to consider the water resource development history of the system. In Canterbury, groundwater pumping likely began in the early 1930s with a significant increase in development occurring since During Canterbury s initial transition 2 from dryland to irrigated agriculture, mainly in the second half of the 20 th century, networks of drains, unlined races, and flood irrigation via border strip or dyke were utilised. These practices helped to incidentally recharge the underlying aquifer and artificially raise water levels in on the Canterbury plains. By incidentally raising groundwater levels they increased the amount of yield available from the aquifer which helped to restore flows in springs. These practices, in effect, where Canterbury s first successful MAR projects as they have been documented to raise groundwater levels and increase spring flows in Canterbury (Davey 2006). Subsequently, over the past years, modern irrigation practices aimed at minimising these replenishing losses have been implemented. While these more efficient irrigation systems help increase the amount of water available at the surface for irrigation, they also act to decrease recharge. Concurrent with these changes has been the dramatic increase in the number and volume of groundwater abstractions resulting in over allocation (Figure 3). Over allocation here is defined as the amount of water being lost from the catchment which exceeds the natural and incidental sources of recharge. 2 Lower Plains were originally an area of coastal wetlands that was drained to make way for arable farm lands. Report No _009_R_Rev0 5

12 Figure 3: Catchment scale water balance and use of MAR for sustainable and additional yields. Balancing the amount of recharge to offset changes to discharge and evapotranspiration while fully utilising the total potential for groundwater storage is depicted (Figure 3 - Managed Storage). In this way MAR can be used to ensure that groundwater pumping is not dependent on losses from streams and rivers to rebalance the system equilibrium. MAR can be used to offset the changes in recharge and discharge which is considered as managed yield. Globally there are examples of MAR being used to generate additional yield using any naturally unsaturated storage or freeboard of an aquifer to store additional water for beneficial uses or longer term drought water management planning purposes. 3.3 Managing Groundwater Quality with MAR Land use development activities can result in groundwater being contaminated by a wide variety of substances. Industrial, agricultural, municipal and other sources of pollution can enter groundwater through a wide range of mechanisms. These contaminants can have a variety of effects on the environment and human health. MAR can be used to help manage groundwater quality by the addition of good quality water into the aquifer. Areas where natural recharge is limited and incidental recharge (often containing contaminants) is high can be targeted for recharge to dilute and disperse the effects of land use. In Canterbury, the dramatic rise in irrigated agriculture has increased the potential for nutrients and soluble organic compounds (SOCs pesticides, herbicides, fungicides, etc.) to enter groundwater. In the Selwyn Waihora zone these contaminants are being recorded in the groundwater, springs and Te Waihora/Lake Ellesmere (Te Waihora). MAR has been shown globally to improve groundwater quality when a source of good quality water is available for recharge. Report No _009_R_Rev0 6

13 3.4 What are the Tools of MAR? MAR encompasses a proven set of recharge tools used throughout the world to manage groundwater quantity and quality. Flood irrigation methods (incidental MAR) date back thousands of years, while modern MAR systems began in Europe in the 1800 s. MAR, in one form or another, is currently used most extensively in countries where water is scarce and droughts are predicted to worsen due to climate change. MAR tools can be generally grouped into a number of broad approaches: Spreading methods where overland flows are dispersed to encourage groundwater recharge. In-channel modification where direct river channel alterations increase recharge. Wells, shafts and borehole recharge where infrastructure is developed to inject water into an aquifer. Induced bank infiltration where groundwater is withdrawn at one location to create or enhance a hydraulic gradient (off a surface water body) that leads to increased recharge. Rainwater harvesting where rain falling on hard surfaces (e.g. roofs, car parks, etc) is captured and allowed to infiltrate to groundwater. There a wide range of tools that can be implemented depending on the conditions of the site and/or catchment where MAR is being considered (Figure 4). Further explanation for each method can be found in APPENDIX B. For the Selwyn-Te Waihora zone there some specific tools that would be more likely to be incorporated into groundwater replenishment programme (Table 1). These tools range from less expensive methods such infiltration through races or purpose-built infiltration basins, through to more expensive direct injection methods via bores. One of the primary lessons learned from other MAR programmes was that the infrastructure and programme management should be integrated into existing water conveyance systems. The people that are already working with water distribution have are the best qualified and staffed to manage MAR sites and operations. The process of determining the feasibility of a site for MAR is based on three primary considerations: Source Water Availability: The availability, timing, and quality of recharge water is an essential evaluation parameter. Typically the non-irrigation or wet season is a time when suitable source water is available. However looking at other sources of high quality water such as stockwater by-wash and rainwater can provide opportunities during the high demand seasons. Hydrogeological Suitability: The target aquifer must have adequate potential storage capacity, sufficient aquifer connectivity (transmissivity) to allow recharge and allow to recovery of the recharged water. Economic, Ecologic and Cultural Viability: Net benefits versus costs for all resource management issues are weighed and incorporated to maximise benefits to all concerned. Other areas of consideration include water regulatory frameworks, groundwater ownership issues, and groundwater crediting and/or banking systems. Report No _009_R_Rev0 7

14 Figure 4: Managing Groundwater Replenishment some of the physical tools to deliver water to an aquifer (Dillon 2009). Report No _009_R_Rev0 8

15 Table 1: General Types of Managed Aquifer Recharge applicable to Canterbury Plains Example Image Type of MAR Recharge Method Applications Type of Aquifer Incidental Recharge - Border Stripe/dyke irrigation Infiltration Historically used to saturate soils for agriculture. Relative Cost Working Examples $ to $$$$ β Unconfined N/A Historically used throughout New Zealand, becoming obsolete due to water efficiency demands and groundwater contamination issues. Controlled river, stream or race channels releases Infiltration Where natural surface water bodies or irrigation distribution systems provide method to infiltrate water. Unconfined $ to $$ Races on Canterbury Plains incidentally recharge water this way. Hinds River RDR MAR Trial (2012), Erye River MAR trial (2007). Basins and natural/engineered wetlands Infiltration Where source water and available land is readily available, least expensive of purpose-built options. Unconfined $ to $$ Used throughout New Zealand for stormwater and industrial by-wash. Engineered wetlands can simultaneously provide recharge while helping to remove nutrients from source water. Photo shows Arizona (USA) CAP race and basins. Infiltration galleries/trenches Infiltration Where surface areas are limited (urban) or subsurface installation is preferred. Unconfined to semi-confined $$ to $$$ Used throughout New Zealand for stormwater and industrial by-wash. Photo shows gallery being incorporated into irrigation scheme (Oregon, USA). Report No _009_R_Rev0 9

16 Example Image Type of MAR Recharge Method Rainwater harvesting and infiltration systems Infiltration, passive injection Applications Where rainwater can be safely collected and passively injected into underlying aquifer. Type of Aquifer Unconfined to confined. Relative Cost Working Examples $ to $$$$ β $$ to $$$ Used primarily in semi-arid to arid catchments where water scarcity issues or large impervious urban surfaces limit natural recharge to aquifers. Rainwater capture for household use occurs in New Zealand. Passive injection dry wells Passive Injection Where upper geological profile limits or precludes infiltration but target aquifer is relatively shallow. Semi-confined to confined $$ to $$$$ Used primarily in urban schemes where MAR is incorporated into piped or networked stormwater runoff systems when large surface areas for infiltration basins are limited. Aquifer Recharge (AR), Aquifer Storage and Recover (ASR) bores Direct Injection Where water demands are high and targeted aquifer is difficult to recharge via surface methods. Unconfined to Confined $$$ to $$$$ Used primarily in industrial, municipal or elevated water scarcity situations. Economic costs of infrastructure limit availability to other situations. Examples are found globally but none currently in New Zealand. (Pictured AR system restoring groundwater in Florida Everglades National Park, USA). Note: β $ to $$$$, Relative comparative costs between recharge methods. Some would be less expensive to install but much more expensive to effectively manage. Example using existing race networks would be low infrastructure costs, but be problematic to manage for contamination and potential flooding issues. Report No _009_R_Rev0 10

17 3.5 MAR Assessment Methodologies New Zealand does not currently have an assessment methodology or specific regulations for the development of groundwater replenishment programmes. While rules do exist for protection of groundwater from contamination, a stepwise process to ensure projects are scoped and built in a safe and economically feasible manner has not been developed. When assessing groundwater replenishment opportunities in Australasia, Golder has utilised the assessment framework outlined in Australian guidelines for water recycling: Managing health and environmental risks (Phase 2) Managed Aquifer Recharge (AGWR 2009). This process provides a risk-based, staged, go/no-go decision process for MAR. The guidelines ensure that critical issues such as water quality, ecological and cultural values, economic viability, storage potential and regulatory frameworks are considered while developing groundwater replenishment projects. Golder recommends that we use these guidelines as a starting point for developing New Zealand groundwater replenishment programmes. These guidelines provide a three staged approach that includes: Stage 1: Feasibility Study (FS): Investigations that include data collection, entry-level assessments of aquifer properties, groundwater storage potential, source water availability-timing-consenting, source and target aquifer water quality, review of water distribution networks, preliminary review of economic, cultural, and environmental issues and initial community engagement and education outreach. Stage 2: Pilot Testing (PT): Site specific pilot testing including percolation tests and groundwater mounding modelling, installation of site specific and down-gradient monitoring for tracking recharge effects, project construction and pilot testing analysis and recommendations. Develop more detailed assessments of cultural, economic and environmental needs and issues. Develop funding structures and groundwater regulatory frameworks. Make final recommendations on either additional site testing or commissioning of sites. Stage 3: Program Implementation (PI): Results from pilot testing are utilised to develop further trial-testing or design-build additional MAR sites into the water management infrastructure. Development of water policies and revenue models and other programmatic needs for practical MAR implementation. Develop surface-groundwater monitoring systems to manage groundwater recharge operations, ensure water quality and down-gradient water levels and provide the allocation zone accountability of groundwater replenishment programme. While the Australian guidelines provide a stepwise framework to ensure that projects are developed in a safe and economically feasible manner these guidelines focus more on the safe use of recycled water. Therefore the guidelines focus on human health and groundwater quality risks. In New Zealand the abundance of high quality water for recharge would mean that New Zealand guidelines would focus on other water management needs. Some of these considerations would be: Cultural rights and beliefs: Iwi water-related rights and beliefs are interconnected and complex, and different groups and individuals have overlapping responsibilities. In Canterbury the CRC shares responsibility with the South Island s Ngāi Tahu, along with district territorial authorities, and with many other organisations and local communities. There are three general Iwi issues that require consideration: taking responsibility to protect and maintain the mauri (vitality) of the environment for the benefit and enjoyment of future generations; the mixing of waters; and the continued use of traditional and contemporary natural resources (mahinga kai) including the ability of Maori to maintain foodgathering capacity (CRC 2012a: Section 1.7). Also important specific to the Selwyn-Te Waihora is the health and management of Te Waihora. Groundwater Dependent Ecosystems: Groundwater dependant ecosystems include both aquifers and spring-fed streams and wetlands which they supply. Ecological communities in aquifers play a vital role in assimilating material that washes down from the land above; these processes keep our groundwater clean (Golder 2013). Spring-fed streams and wetlands are habitat to some of New Zealand s most threatened fish and birds, such as the Canterbury mudfish. In addition these areas are Report No _009_R_Rev0 11

18 highly significant spiritually, culturally and socially being places of historic importance, locations for gathering food, recreation and communing with nature. Water allocation, water trading and other water governance issues: The development of regulatory frameworks that would support the implementation of groundwater replenishment programmes. Consenting processes that ensure water availability, groundwater quality and an integrated water management structure including incorporation into groundwater allocation planning. Community based planning and goal setting processes: It is important to integrate all stakeholders into the development of a groundwater replenishment programme. An understanding of groundwater replenishment using artificial recharge requires education and outreach to ensure acceptance and success. It is also important to ensure that groundwater replenishment is incorporated into a wider integrated water management strategy. In Canterbury the development of the Canterbury Water Management Strategy (CWMS) through zone committee planning processes is an excellent mechanism to engage the community. Catchment-scale water management: The development of a catchment-scale approach to managing groundwater is the best approach for New Zealand. Canterbury s current efforts to manage groundwater through allocation zone frameworks will help focus on groundwater storage balance processes. Elsewhere in the world individual water rights/consents make it difficult to manage groundwater replenishment as the rules focus on case-by-case individual allocations. A systems approach could also help develop a revenue structure to build and maintain a replenishment system. 3.6 Benefits and Challenges of MAR Weighing up the benefits and challenges of implementing a groundwater replenishment programme needs to be done through a carefully constructed stepwise process. Throughout the development of groundwater replenishment programmes internationally there have been some recurring benefits and challenges that have been identified. There are catchment and/or site specific items that would also need to be considered, but a general list would include: Benefits Groundwater Stabilisation and Restoration: Actively recharging an aquifer provides an alternative management option to clawing back existing consents and/or limiting the available groundwater in a system. A sustainably managed aquifer can provide more certainty for economic and environmental interests while helping to better plan for the uncertainties of a changing climate. Increased Yields: The use of additional groundwater storage capacity can provide for extra water for out-of-stream uses. Hydrogeological modelling coupled with a carefully planned MAR pilot project can help maximise aquifer yield while helping to manage for groundwater quality. Cost effective: When groundwater replenishment programmes are compared with other more traditional storage methods they are often considerably less expensive. Cost savings include allayed environmental and recreational concerns and where land and space are at a premium MAR requires less investment than surface storage. Water distribution and benefits: Sustainably managed groundwater is a preferable means to distributed water across a wide area. In aquifer systems like the Canterbury plains, water users can access groundwater via on-site bores. Recharged water is distributed to both environmental and consumptive beneficial uses as controlled by the natural subsurface features. Water Quality: The purposeful recharge of high quality water into an aquifer with declining current or predicted water quality may off-set the impacts of land use. Targeted recharge sites can be used to focus on particular sub-catchment or water quality impacted areas if required. Report No _009_R_Rev0 12

19 System Understanding: The purposeful recharge of water provides excellent scientific information on the aquifer being tested. This information helps refine both modelling and management understanding of a system which results in robust, long term solutions. Low Tech and Stepwise Development: Most recharge technologies are relatively 'low tech' and available for implementation in most locations. Proven tools often are simple to design, install and operate based on common civil engineering and hydrogeologic principles. Two generally accepted rules of thumb for MAR have been if we can take water out, we are very likely to be able to put it in again. Secondly it is advisable to start with small pilots, learn how the groundwater system acts/reacts and build upon that information. A step-wise approach helps to incorporate MAR sites into an overall, longer term water management strategy. Carbon Footprint: The use of natural aquifer and catchment features to manage and storage water provides a low-carbon footprint alternative to methods that rely upon the use of fossil fuels for construction and operations. Challenges Public Education and Understanding: The sustainable management of groundwater systems remains an unfamiliar area for most of the general public. An important challenge to sustainable groundwater management is to make particular efforts to engage with the community to ensure that issues and solutions are clearly presented and understood as you develop the MAR tools. Stepwise programme development helps to support this process by sharing the information being collected, discussing concerns and issues as they arise, and providing the community as a whole a better understanding of their resources. Water Availability: In catchments where groundwater resources are under pressure, water available for recharge is often limited. High demand summer and/or irrigation season surface water sources are often fully allocated which may have initiated the development of groundwater. Low demand winter and/or non-irrigation season water is also important in waterways for natural river processes, ecological needs and channel forming flows. MAR is often developed using water which does not cause a conflict with these other needs. Clogging: The biological and physical clogging of the recharge structure is a primary concern to MAR operators. Seasonal increases in water temperature and nutrients lead to increased biofilms and algae growth which can act to reduce effective recharge rates. Physical clogging from source sediments can also lead to the surface clogging. Understanding the potential and measured clogging at a site (through pilot testing) is critical for the development of the appropriate design and/or maintenance solutions. Water Quality: The quality of source water quality needs to be understood sufficiently to avoid a risk of pollution to groundwater supplies. Any hydrochemical interactions of recharged source and groundwater needs to be assessed and understood. Topographical Considerations: The management of catchment scale groundwater systems relies on a robust understanding of how groundwater interacts with surface water bodies and other groundwater connected features. Flow routing, drainage and flooding, water balances for lowland lakes, and elevated groundwater levels can lead to downgradient issues. Well-developed surface and groundwater monitoring systems coupled with a step-wise replenishment programme development is often the most prudent and cost effective approach to avoid adverse effects. For aquifer systems like the Selwyn-Te Waihora, measuring groundwater fed springs would be an excellent system indicator as they represent the spillway responses for the groundwater reservoir. Report No _009_R_Rev0 13

20 3.7 More about MAR There is a wide range of MAR tools, operating replenishment programmes and examples of regulatory frameworks that encourage sustainable groundwater management. A full list of these is beyond the brief of this report but we have provided a quick reference list below. Operating Groundwater Replenishment Programmes: Orange County California found itself groundwater limited nearly 100 years ago making theirs one of the longest run programmes in the world. Their response was the step-wise development of a groundwater recharge system that is now managed as part of their Groundwater Replenishment System (GWRS). They have doubled the yield of their groundwater system and are considered one of the world leaders on MAR and water reuse. Other working examples can be found at the ISMAR conference site(s), below. Orange County GWRS Scientific Advances in MAR: While artificial recharge has been around for centuries the modern application of it to replenish groundwater supplies has become more directed in the past 30 years. The International Symposium on Managed Aquifer Recharge (ISMAR) brings together scientists, engineers, water managers, and industry to present and discuss the various new develops in the field ISMAR Conference Proceedings (Dubai) Sustainable Groundwater Development: The United States Geological survey wrote a seminal paper on sustainable groundwater management. UNESCO, World Bank, and other globally positioned aide organisations concerned with the sustainable management of water resources have commissioned a number of reports discussing the applications of MAR. The low-cost and low-tech attributes of MAR have made it a favourable water supply tool for many water-scarce parts of the world. Sustainability of groundwater resources (USGS 1999) Strategies for Managed Aquifer Recharge in Semi-arid Regions (UNESCO 2005) MAR Guidelines and Methods - Standard Guidelines for Artificial Recharge of Ground Water Standard Guidelines for Artificial Recharge of Ground Water (34-01). (American Society of Civil Engineers 1998) Water Reclamation Technologies for Safe Managed Aquifer Recharge (Karzer, Wintgens, Dillon 2012) Groundwater Recharge and Wells: A guide to Aquifer Storage Recovery (Pyne 1995) Historical background on MAR in Canterbury Canterbury has had a number of feasibility studies and pilot projects to evaluate the use of MAR as a water management tool. The first known field trial was done in the Levels Plains area near Washdyke, in South Canterbury dating back to The aquifer recharge of unused irrigation water was undertaken using a combination of methods including infiltration (quarry and trench) and bore injection on the Levels Plains Golf Course. An early modelling and monitoring study by Bird (1986) indicated that artificial recharge of the aquifer was successful during the short time-scale of the experiment, but the recommendation that the experiment be continued on a larger scale does not appear to have been taken up (Williams 2013). A list of known Canterbury MAR field trials is shown in Table 2. The two primary MAR methods that have been piloted in Canterbury have used infiltration basins and ephemeral river channels. Generally the reports have found that the benefits MAR were measureable and could contribute to helping replenish groundwater supplies. However, these reports focused on localised responses so the results are difficult to extrapolate out to catchment-scale groundwater applications. To understand the system response it is necessary to utilise groundwater modelling tools. Report No _009_R_Rev0 14

21 Recent catchment-scale modelling projects have been undertaken to assess some of the uncertainties (Table 2). Two independent modelling efforts both focused on Selwyn-Te Waihora groundwater systems indicated MAR would be effective at restoring flows in low-land streams and improving irrigation reliability (Table 2). One modelling project in particular was conducted for the Selwyn-Te Waihora zone and will be discussed in more detail in Section 4.0. However, it should be noted that catchment-scale models have inherent uncertainties with regards to the accuracy of prediction for specific spring flows or groundwater levels. Table 2: History of MAR field trials and groundwater modelling on Canterbury Plains. Project Year Type Evaluation Period Method Average Recharge Rate Volume Recharged m 3 /s million m 3 Level Plains Trial 120 days Basin(s) Yaldhurst Trial 21 days Basin West Melton Trial 30 days Basin West Melton Trial 91 days Basin Eyre River Trial 23 days River Channel Selwyn Te Waihora 2011 Model 153 days 8 Eigen Modelling 5 Modelling Selwyn Te Waihora: 2012 Model 153 days 8 Modelling CWMS Modelling 6 RDR-Hinds River MAR 2012 Trial 4 days River Channel N/A 2.3 trial 7 Notes: 0 Bird, 1986, 1 - PDP, 1996, 2 ECan, 1993, 3 ECan, 1994, 4 -PDP, 2007, 5 Williams, 2011, 6 Golder, 2012, 7 Golder, 2012a. N/A Average Not Available, days = Canterbury irrigation season. MAR has been evaluated as a tool for water management planning in Canterbury in several recent reports. An SKM (2010) draft report reviewed the use of deep bore injection in the Central Canterbury Plains. While the report found MAR was a potentially favourable tool, SKM focused its conceptualisation on a deep injection bore scheme along the proposed Central Plains Water race scheme. The final scheme was generally considered to be relatively expensive when compared to lower-tech surface infiltration methods which would also be potentially viable in the catchment. Subsequent to the SKM report, CRC commissioned a preliminary strategic assessment of MAR relative to water management options for the CWMS (PDP 2011). The study found that MAR was 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. It went on to summarise that MAR could be implemented relatively quickly and easily, with little economic costs relative to other water management infrastructure options. Further, it recommended for the Canterbury Plains that surface infiltration (rather than deep injection) be the preferred method due to hydrogeologic conditions, and focused on the use of infiltration basins or discharge into ephemeral waterways and/or utilising leaky water race distribution networks. We should note here a few significant differences in Golder s conceptual understanding of sustainable groundwater management using the tools of MAR to that of past Canterbury trials and MAR technical reviews. Former work in region focused on trials and schemes where the conceptual scope of the project was localised to a sub-catchment or specific site. Golder looks at the successful implementation of a groundwater replenishment programme to a catchment scale solution where various MAR tools are used where appropriate to stabilise and restore groundwater supplies. Further, localised trials have also looked specifically at the groundwater mounding created by the recharge during operation of the site. Golder finds that the intention of MAR tools is not to temporarily raise the water table from such mounding. Mounding is a short term response based on localised changes in groundwater pressures and saturated groundwater flows. Report No _009_R_Rev0 15

22 The goal of MAR is to increase the net total recharge to a targeted aquifer when it is viewed as a complete and sustainable storage system. Finally, Golder also finds that groundwater (over surface diversions) is natural means of effectively and efficiently distributing water when the replenishment and uses are adequately managed. The most recent field trial in Canterbury was in 2012, when Golder worked with CRC and area irrigators in the Hinds River catchment to trial the use of an ephemeral river channel to recharge water to two groundwater allocation zones (Golder 2012b). The project goals were not only aimed at pilot testing MAR using an dry (ephemeral) river channel bed but also at working with the Ashburton Zone committee (CWMS) process in the development and reporting of the project outcomes (Figure 5). The pilot was successful in recharging source water to the targeted groundwater system as well as helping to develop a model for collaborative partnerships between irrigators, regional council, and the community. Figure 5: MAR trial upper Hinds River catchment discharging race water into a dry channel bed (Golder 2012b). 4.0 ASSESSING MAR FOR GROUNDWATER REPLENISHMENT IN SELWYN-TE WAIHORA 4.1 Overview The assessment of groundwater replenishment using MAR in the Selwyn-Te Waihora zone was undertaken in support of the Canterbury Water Management Strategy (CMWS) planning process. Canterbury Regional Council (CRC) is currently reviewing water management within the Canterbury region under the objectives of the CWMS. The CWMS process is underway in each of the 10 sub-catchments in Canterbury and represents a shift in focus away from historical water management processes that independently considered nutrients, stream flow and water allocation limits in Canterbury catchments. The process focuses on community-based representation (zone committees) of various stakeholder groups (e.g. Iwi, irrigation, environment, recreation, etc.) to help develop restoration goals and actions. When the goals for water management have been developed they are outlined in Zone Implementation Programmes (ZIP). The Report No _009_R_Rev0 16

23 Selwyn-Te Waihora zone ZIP was completed and approved in early The plan focuses on a whole of waterways approach, which is consistent with the Maori concept of mountains to the sea (Ki Uta Ki Tai) (CRC 2012c). 4.2 Land Use Change Scenarios The CWMS collaborative process has been undertaken to evaluate the implications of potential future scenarios and recommend limits and policy to achieve desired outcomes. This evaluation process has been undertaken as a multidisciplinary modelling exercise including the use of numerical models coupled with expert opinions. This has involved assessing the impacts of different land-use, water abstraction and mitigation scenarios which includes the use of MAR on water quality and water quantity in groundwater, streams and Te Waihora (Table 3). This modelling has been undertaken in a hydrologically complex catchment and is described in detail in a number of technical reports (Scott and Weir 2013, Hanson 2013, and Clark 2013). Solutions Package 1 includes a modelling assessment of a conceptual MAR scenario was to compare not only the implications of potential future land-use with that observed currently, but also with the naturalised state if all abstraction were to be stopped (Scenario 0) (Scott and Weir 2013). Table 3: Selwyn-Te Waihora Modelling Scenarios (CRC, 2013) Scenario Name Description Scenario 0 - No Usage Scenario 1 - Baseline Scenario 2 Increased Irrigation (30,000 ha development) Scenario 3 Trophic Level Target (TLI 6) Solutions Package 1 Managed Aquifer Recharge No groundwater abstraction or irrigation in the catchment. Assumes current (2011) land use and that all flow and nutrient load effects of 2011 land use have arrived at the lake (i.e. after lag times in the order of 20 years). For the groundwater flow simulations current land use has been assumed to be pasture with irrigation extent as determined from remote sensing. This scenario is based on a surface water supply providing for 60,000 ha of irrigation. This will comprise approximately 30,000 ha of new irrigation on the plains and also replacement of some existing groundwater takes with surface water. The scenario recognises that other enterprises and land uses in the catchment will also intensify. All flow and nutrient load effects are assumed to have arrived at the lake (i.e. after all lag times). This scenario is based on aiming to achieve the specified environmental outcome of a Trophic Level Index (TLI) of 6.0 in Te Waihora (Lake Ellesmere). A TLI of 6.0 is also the Natural Resources Regional Plan (NRRP 2011) target for the lake. The Solutions Package 1 is based on 30,000 ha new irrigation plus on-farm nutrient reduction measures at a level mid-way between good management practice and advanced (maximum) mitigation. It includes managed aquifer recharge (MAR), catchment mitigations (riparian buffers and wetlands), further lake interventions (i.e. a lake level and opening control structure, P-inactivation measures, macrophtye bed and marginal wetland restoration, and construction of floating wetlands), as well as economic/social mechanisms, point source pollution control, and planning policies. A comprehensive description of the scenarios listed in Table 3 including assumptions are described in detail in the groundwater modelling report (Scott and Weir 2013). Report No _009_R_Rev0 17