Alexandra Groundwater Basin Allocation Study . Otago Regional Council Private Bag 1954, 70 Stafford St, Dunedin 9054 Phone 03 474 0827 Fax 03 479 0015 Freephone 0800 474 082 www.orc.govt.nz © Copyright for this publication is held by the Otago Regional Council. This publication may be reproduced in whole or in part, provided the source is fully and clearly acknowledged. ISBN 978-0-478-37646-3 Published September 2012 Foreword Otago’s prosperity is largely based on water. The Clutha River / Mata Au drains much of the Otago region and has the largest annual discharge of any river in New Zealand. However, despite the large total water volumes present in the region’s water bodies, many areas of Otago are short of water. In many cases, irrigation particularly in these drier areas is critical to the continued well being of the people and communities who rely on the primary production it supports. The Regional Policy Statements for Water provide for the Otago people and communities having access to water for their present and reasonably foreseeable needs. Groundwater can be the sole or major source of water to supply basic water needs to communities and stock watering. Currently groundwater only supplies a small proportion of irrigation needs, however there is increasing pressure for people to turn to groundwater because surface water supplies are heavily allocated. Over abstraction can result in loss of supply to other users and therefore careful management is required to keep abstraction rates sustainable. Groundwater resources have varying rates of recharge and often form a complex dependency with adjacent water courses, wetlands and stream networks. The effects of inappropriate land and water use and development on groundwater quantity and quality are often long term, and in some cases permanent. It is therefore important that particular consideration be given to the protection of aquifers for the continuing benefit of present and future generations. Through the Regional Plan: Water and our Annual Plans we ensure linkage with the community to deliver the efficient use and protection of our groundwater aquifers. This report describes future allocation of water from the Alexandra Basin. It is based on local knowledge, scientific evidence and monitoring information. The best way forward is to use to advantage this valuable resource but to maintain control so that over abstraction does not occur. This is a complex topic and further monitoring and review of the aquifer will continue to ensure a sustainable allocation. Alexandra Groundwater Basin Allocation Study 1 Table of Contents Executive summary .................................................................................................................... 5  1  Introduction .................................................................................................................. 7  1.1  Background .................................................................................................... 7  1.2  Study’s objectives .......................................................................................... 7  2  Previous studies ............................................................................................................ 8  2.1  Non-investigation monitoring ........................................................................ 9  2.1.1  Contact Energy Ltd .......................................................................... 9  2.1.2  L & M Mining Ltd ......................................................................... 10  2.1.3  Central Otago District Council ...................................................... 10  2.1.4  Various consent holders ................................................................. 10  2.1.5  Otago Regional Council State of the Environment Monitoring .... 10  3  Existing environment ................................................................................................. 11  3.1  Location ....................................................................................................... 11  3.2  Geology ........................................................................................................ 12  3.2.1  Basement schist ............................................................................. 12  3.2.2  Tertiary terrestrial sediments ......................................................... 12  3.2.3  Quaternary terrestrial sediments .................................................... 13  3.3  Surface-water hydrology .............................................................................. 14  3.4  Groundwater hydrology ............................................................................... 15  3.4.1  Earnscleugh Flat ............................................................................ 15  3.4.2  Dunstan Flats ................................................................................. 16  3.4.3  Manuherikia claybound aquifer ..................................................... 17  3.4.4  Manuherikia alluvium .................................................................... 18  3.5  Groundwater quality .................................................................................... 19  3.5.1  Historical ground water quality ..................................................... 19  3.6  Patterns of groundwater use ......................................................................... 19  3.6.1  Historical patterns .......................................................................... 19  3.6.2  Current water use ........................................................................... 20  4  Aquifer water balance ................................................................................................ 21 2 Alexandra Groundwater Basin Allocation Study 4.1  Recharge modelling ..................................................................................... 22  4.1.1  Approach: Soil-water balance model ............................................. 22  4.1.2  Summary results ............................................................................ 24  4.2  Surface-water recharge ................................................................................ 25  4.2.1  Fraser River ................................................................................... 25  4.2.2  Waikerikeri Creek .......................................................................... 25  4.2.3  Manuherikia Irrigation Scheme – Main Race ................................ 26  4.2.4  Earnscleugh Irrigation Scheme races ............................................. 26  4.2.5  Minor water races .......................................................................... 27  4.2.6  Galloway, Dip Creek and Manorburn Schemes ............................ 27  4.3  Irrigation recharge – land surface ................................................................ 27  4.3.1  Approach ........................................................................................ 28  4.3.2  Summary results ............................................................................ 29  4.4  Combined basin recharge patterns ............................................................... 30  4.4.1  Dunstan aquifer recharge and water balance ................................. 30  4.4.2  Earnscleugh aquifer recharge and water balance ........................... 32  4.4.3  Manuherikia claybound aquifer recharge and water balance ........ 34  4.4.4  Manuherikia alluvial aquifer recharge and water balance ............. 35  4.4.5  Whole basin water balance ............................................................ 37  5  Water resource management ...................................................................................... 39  5.1  Historic water management ......................................................................... 39  5.2  Current water management .......................................................................... 39  5.2.1  Surface-water allocation ................................................................ 39  5.2.2  Groundwater allocation ................................................................. 40  5.3  Future groundwater allocation ..................................................................... 40  6  Groundwater management regime ............................................................................. 42  6.1  Default groundwater management of Alexandra Basin aquifers ................. 43  6.1.1  Dunstan aquifer .............................................................................. 43  6.1.2  Earnscleugh aquifer ....................................................................... 45  6.1.3  Manuherikia claybound aquifer ..................................................... 45  6.1.4  Manuherikia alluvial aquifer .......................................................... 48  7  Conclusions ................................................................................................................ 50  Appendix 1 – Recharge modelling ........................................................................................... 52 Alexandra Groundwater Basin Allocation Study 3 Methodology ............................................................................................................................ 52  Method chosen ........................................................................................................... 52  Required parameters .................................................................................................. 52  SCS curve number ....................................................................................... 52  Profile available water (PAW) ..................................................................... 52  Profile readily available water (PRAW) ...................................................... 53  Fracstor ....................................................................................................... 53  Field capacity (FC) ...................................................................................... 53  Wilting point (WP) ...................................................................................... 53  Methods of defining additional parameters ............................................................... 53  Recharge model inputs ............................................................................................... 54  Rainfall ....................................................................................................... 54  Potential evapotranspiration (PET) .............................................................. 54  Soil properties .............................................................................................. 54  Recharge model outputs ............................................................................................. 55  Appendix 2 – References ......................................................................................................... 58  Table of figures  Figure 1 Location of Alexandra Basin aquifers. Density of bore records is shown by yellow dots .................................................................. 11 Figure 2 Sketch geology of the Alexandra Basin . ..................................................... 14 Figure 3 Graphical representation of estimated Dunstan aquifer water balance ......................................................................................................... 31 Figure 4 Graphical representation of estimated Earnscleugh aquifer water balance ............................................................................................... 33 Figure 5 Graphical representation of estimated Manuherikia claybound aquifer water balance. ................................................................ 34 Figure 6 Graphical representation of estimated Manuherikia alluvial aquifer water balance ................................................................................... 36 4 Alexandra Groundwater Basin Allocation Study Table of tables  Table 1  Major ions in Alexandra basin groundwater ................................................ 19  Table 2  List of soil groups and attributed soil-water parameters .............................. 23  Table 3  Soil groups and extent over the Alexandra Basin aquifers .......................... 23  Table 4  Results of land-surface recharge modelling, with natural rainfall inputs only ....................................................................................... 24  Table 5  Measured and calculated losses and gains in the Fraser River ............................................................................................................. 25  Table 6  Summary of AquaLinc values for pasture used in irrigation – recharge modelling .................................................................................... 28  Table 7  Irrigation scheme and irrigated areas ........................................................... 28  Table 8  Summary: Comparison of rainfall-only and irrigation- induced recharge .......................................................................................... 29  Table 9  Accounting of inflow and outflow to/from the Dunstan aquifer .......................................................................................................... 32  Table 10  Accounting of inflow and outflow to/from the Earnscleugh aquifer .......................................................................................................... 33  Table 11  Accounting of inflow and outflow to/from the Manuherikia claybound aquifer......................................................................................... 35  Table 12  Accounting of inflow and outflow to/from the Manuherikia alluvial aquifer ............................................................................................. 37  Table 13  Whole basin flow routing ............................................................................. 37  Table 14  Alexandra Basin groundwater allocation, by aquifer .................................. 40  Table 15  Comparison of mean annual recharge and groundwater allocated in consents within the Dunstan aquifer ........................................ 44  Table 16  Comparison of mean annual recharge and groundwater allocated in consents within the Earnscleugh aquifer .................................. 45  Table 17  Comparison of mean annual recharge and groundwater allocated in consents within the Manuherikia claybound aquifer .......................................................................................................... 47  Table 18  Comparison of mean annual recharge and groundwater allocated in consents within the Manuherikia alluvial aquifer .......................................................................................................... 49  Table 19  List of aquifers, numbers of takes, recharge and groundwater allocation issued in current consents ...................................... 51 Alexandra Groundwater Basin Allocation Study 5 Executive summary The four aquifers in the Alexandra groundwater basin are located within glacial outwash, alluvial fans or flood plains. The Earnscleugh Terrace aquifer and the Dunstan Flats aquifer have a common origin, in that they result from a glacial outwash following the Albert Town glacial advance; however, they differ in that the Dunstan Flats aquifer is in closer hydraulic communication with the Clutha River that divides them. The Manuherikia claybound aquifer, overlooking the Dunstan Flats, is composed of high permeability, deep water-table Lindis outwash, and also low permeability alluvial fans that have formed on the slopes below Leaning Rock. The Manuherikia alluvium is more closely associated with the Manuherikia River, in both its formation as flood plain alluvium and its linkage between the river and groundwater system. The aquifers are largely unconfined, although they vary greatly in terms of depth to water table, aquifer properties and hydraulic communication to the adjoining surface water system. The Lindis outwash terraces of the Manuherikia claybound aquifers tend to have high permeability and large depths to the water table. The Manuherikia alluvial aquifer has shallow saturated thickness and a shallow water table. All aquifers are replenished or recharged at the land surface by a combination of water infiltrating from excess rainfall, pasture irrigation losses, leakage from water races and by-wash soak holes. The Fraser River, as it crosses the permeable surface of Earnscleugh Flat, loses a substantial portion of its base flow to the underlying aquifer, with an average of 25 million cubic metres (Mm3/y) of water entering the Earnscleugh aquifer by this vector every year. The net excess of the groundwater that recharges the Alexandra Basin aquifers percolates through the gravel deposits between the water table and base of the gravels until it discharges at one or more of the following surface water bodies: • miscellaneous springs and seepage drains along the other edges of outwash terraces • Clutha River • lower Manuherikia River • lower Fraser River. Groundwater recharge modelling has been used to develop a more comprehensive understanding of the aquifer water balances and to assess the groundwater allocation status of each aquifer. The recharge and groundwater allocation settings are summarised below. Summary of aquifers, numbers of takes, recharge and groundwater allocation issued in current consents 50% of mean Mean annual annual Consented No. of takes recharge recharge allocation (Mm3/y) (Mm3/y) (Mm3/y) Dunstan aquifer 34 3.68 1.84 1.45 Earnscleugh aquifer 4 25.5 12.75 0.514 Manuherikia claybound aquifer 11 1.36 0.68 0.610 Manuherikia alluvium aquifer 4 1.41 0.7 0.014 Alexandra Basin: Total 53 15.97 2.59 6 Alexandra Groundwater Basin Allocation Study None of the aquifers in the Alexandra Basin are allocated at more than 50% of the mean annual recharge, although the Dunstan and Manuherikia claybound aquifers approach this point. In accordance with policy 6.4.10A(ii)(1) of the Regional Plan: Water (RPW), which stipulates that the default allocation limit must be 50% of the calculated mean annual recharge, all of the basin’s aquifers can be considered “under allocated”. It is considered that this allocation status and volume setting is appropriate for the groundwater management of the Alexandra Basin aquifers. Alexandra Groundwater Basin Allocation Study 7 1 Introduction 1.1 Background While the infrastructure and population contained within the Alexandra sedimentary basin is mainly centred on Alexandra, it also includes the township of Clyde and the communities of Earnscleugh, Springvale and Galloway. Geologically, the sedimentary basin has produced the conditions for enhanced groundwater resources from such sediments as sandy gravel. In 1995, the combination of water demand to support the basin’s population and industries, and the available underground water resources, motivated Otago Regional Council (ORC) to investigate and monitor the area’s aquifers. ORC commissioned field investigations then, and in 2001, used the field data to extend existing geo-hydrological analyses. In 2005, the council presented its initial strategy on the allocation of groundwater in the Alexandra basin. As part of ORC’s renewed approach to allocating groundwater and surface-water, ORC has resolved to prepare a groundwater allocation plan for the Alexandra Basin, which includes Dunstan Flats, Earnscleugh Flat, Manuherikia claybound and the lower Manuherikia alluvial aquifers. This investigation intends to examine the aquifer-recharge processes and dynamics in order to develop a physical basis for allocating groundwater in the Alexandra basin. 1.2 Study’s objectives The study’s objectives are to provide: • a basis for recommending groundwater allocation limits for the Alexandra basin • an updated reference to the basin’s groundwater hydrology.