Lower Waitaki Hydrogeology
Report No. R15/54 ISBN 978-0-478-15216-6 (print) 978-0-478-15217-3 (web)
Lower Waitaki Hydrogeology
Report No. R15/54 ISBN 978-0-478-15216-6 (print) 978-0-478-15217-3 (web)
Hisham Zarour
April 2016
Report No. R15/54 ISBN 978-0-478-15216-6 (print) 978-0-478-15217-3 (web)
200 Tuam Street PO Box 345 Christchurch 8011 Phone (03) 365 3828 Fax (03) 365 3194
75 Church Street PO Box 550 Timaru 7940 Phone (03) 687 7800 Fax (03) 687 7808
Website www.ecan.govt.nz Customer Services Phone 0800 324 636
Lower Waitaki hydrogeology
Summary
Background: The Canterbury Regional Council (Environment Canterbury) and the Waitaki catchment communities have embarked on water quality limit setting process as part of the Canterbury Water Management Strategy (CWMS). This joint venture is aimed at producing a sub-regional chapter in the Land and Water Regional Plan (LWRP).
Objective: This report provides baseline information on the current state of the groundwater resource quantity and flow (hydrogeology) in the lower Waitaki catchment to inform the collaborative sub-regional planning process. This information is important for the development and analysis of future water and land management scenarios.
What we did: I undertook a desktop study with limited field reconnaissance. I synthesised and analysed data from various sources to draw a picture of the current state of groundwater quantity and flow in the lower Waitaki area.
What we found: The lower Waitaki area has a dry climate in New Zealand terms. Irrigation is required during summer to maintain crops. Surface water delivered to farms through lined and unlined races meets most irrigation demand. Border dyke is an important irrigation method in the area. The aquifer system is composed of unconsolidated gravelly alluvial sediments infilling valleys and covering floodplains. The aquifer system is relatively thin and groundwater is shallow. Therefore, about two-thirds of the active wells are less than 10 m deep, and more than three-quarters are no deeper than 20 m. More than a quarter of the area’s wells are used for public and domestic water supply, about one quarter for stock, and the rest of the wells are used for various purposes such as dairy supply and irrigation. There are fewer groundwater abstraction consents in the area and the consented volumes are small compared to the rest of Canterbury. The area’s groundwater system is highly connected with surface water. On average, groundwater loses about 54 million cubic metres per year to the lower Waitaki River surface water system. However, this represents less than 0.5% of the river’s total flow. Wetlands and springs are found on the lower terraces at the toe of higher terraces. Many of these emerge as a result of increased groundwater recharge from irrigation, which has raised the water table. Groundwater flow velocities in the area are high, so changes in land use in areas underlain by aquifers will likely result in measurable and noticeable changes in the quality of groundwater and connected surface waters within 1–5 years.
What it means: In the lower Waitaki catchment, land use changes can affect groundwater and surface water quantity and quality fairly quickly. Local water table mounding and increased spring and seepage flow can occur as a result of increased irrigation. On the other hand, more efficient irrigation and water delivery systems may cause wetlands to shrink and spring flows to drop. Similarly, modernisation of irrigation practices may result in lower dilution (i.e. higher concentrations) of contaminants such as nitrate in groundwater. The contribution of groundwater losses to surface waterways represents a small fraction of the total flow in the lower Waitaki River (less than 0.5%). Nonetheless, groundwater losses to surface water are critical to smaller systems such as Waikākahi Stream and Whitneys Creek, both in terms of quantity and quality. This makes careful consideration of groundwater quantity and quality an integral requirement to environmental management planning in the area.
Environment Canterbury Technical Report i Lower Waitaki hydrogeology
ii Environment Canterbury Technical Report Lower Waitaki hydrogeology
Table of contents
Summary ...... i
1 Introduction ...... 1 1.1 Legal and planning framework ...... 1 1.2 Report scope and coverage ...... 4
2 Methodology and concurrent related work ...... 4
3 Previous work ...... 6 3.1 Geology ...... 6 3.2 Hydrogeology ...... 6 3.3 Groundwater quality and age ...... 6 3.4 Groundwater recharge and allocation limits ...... 7
4 The study area ...... 7 4.1 Extent, definition and main characteristics ...... 7 4.2 Water resources and values ...... 7 4.3 Climate ...... 8 4.4 Physiography and surface water drainage pattern ...... 8 4.5 Geology ...... 10 4.5.1 Basement rock ...... 10 4.5.2 Late Cretaceous strata ...... 14 4.5.3 Paleogene–Neogene strata ...... 14 4.5.4 Late Quaternary deposits ...... 15 4.6 Structural geological setting ...... 16 4.7 Springs and wetlands ...... 16 4.8 Surface water hydrology ...... 17 4.9 Soil ...... 19 4.10 Land use ...... 19 4.11 Irrigation infrastructure ...... 20
5 Hydrogeology ...... 24 5.1 Hydrostratigraphy and groundwater occurrence ...... 24 5.2 Groundwater wells ...... 26 5.3 Hydrogeological parameters ...... 31 5.4 Groundwater levels and flow directions...... 31 5.4.1 Concepts ...... 31 5.4.2 Groundwater flow in the study area ...... 31 5.5 Groundwater recharge and discharge ...... 33 5.6 Effects of topography on groundwater flow ...... 33 5.7 Groundwater flow velocity, travel time and residence time ...... 34 5.8 Groundwater-surface water interaction ...... 34
Environment Canterbury Technical Report iii Lower Waitaki hydrogeology
5.8.1 Waitaki River and main tributaries ...... 34 5.8.2 Coastal streams ...... 38 5.8.3 Wetlands, ponds and springs ...... 39 5.9 Groundwater use and abstraction consents ...... 39 5.10 Hydrological budget and groundwater system summary ...... 42
6 Conclusion ...... 45
7 Acknowledgements ...... 45
8 References ...... 45
Appendix A Rainfall calculations maps ...... 50
Appendix B Subdivision of the Quaternary and QMAP nomenclature 53
Appendix C Previous groundwater level maps ...... 55
List of Figures Figure 1-1: Location map showing the extent, subdivisons and main features in the lower Waitaki catchment ...... 2 Figure 1-2: Waitaki regional plan chapter water management units and subunits in lower Waitaki ...... 3 Figure 2-1: Nutrient load allocation zones in the lower Waitaki catchment ...... 5 Figure 4-1: Averge annual rainfall isohyetal map and climatic zones* ...... 9 Figure 4-2: Structural geology and surface water drainage map ...... 11 Figure 4-3: 3D representation of the physiography of the lower Waitaki catchment...... 12 Figure 4-4: Geological map ...... 13 Figure 4-5: Schematic hydrogeological cross sections through the Taratu Formation in the Maerewhenua Basin ...... 15 Figure 4-6: Major known springs and wetlands in the study area ...... 18 Figure 4-7: Current land use map for the LW excluding Hakataramea ...... 21 Figure 4-8: Land Use Capability (LUC) soil classification map ...... 22 Figure 4-9: Irrigation water delivery infrastructure in the lower Waitaki ...... 23 Figure 5-1: Simplified geological and hydrostratigraphical map ...... 25 Figure 5-2: Hydrogeological map showing bedrock elevation in metres above mean sea level 27 Figure 5-3: Drilled wells in the study area ...... 28 Figure 5-4: Wells with lithological logs in the study area ...... 29 Figure 5-5: Depth of active wells ...... 30 Figure 5-6: Piezometric map for long-term average groundwater conditions ...... 32 Figure 5-7: Effect of terraces on groundwater flow ...... 33 Figure 5-8: Varying groundwater flow paths and travel traveopltimes from points of recharge to points of discharge in the groundwater system ...... 35 Figure 5-9: Possible relationships between groundwater, wetlands and lakes ...... 36 Figure 5-10: Possible relationships between groundwater, rivers and streams ...... 37 Figure 5-11: Method for determing stream-groundwater relationship using groundwater level contour maps ...... 37 Figure 5-12: Active wells productive use ...... 40
iv Environment Canterbury Technical Report Lower Waitaki hydrogeology
Figure 5-13: Types and maximum rates of consented groundwater abstraction ...... 41 Figure 5-14: Schematic diagram of the lower Waitaki Valley groundwater flow system ...... 42 Figure 5-15: Flow of water from precipitation to streams ...... 44 Figure A-1: Isohyetal map for calculating total and average rainfall over the study area ...... 51 Figure A-2: Thiessen polygons map for calculating total and average rainfall over the study area ...... 52 Figure C-1: Piezometric map for the Quaternary aquifer system between the Pareora River and Waitaki River (Waimate County) in 1979 (SCCB, 1979) ...... 56 Figure C-2: Piezometric map for the lower Waitaki Quaternary aquifer prepared by URS (2003a) from groundwater levels measured on 29 June 2001...... 57 Figure C-3: Piezometric map for average groundwater levels in the mid-Waitaki valley by Scott et al. (2012) ...... 58 Figure C-4: Piezometric map for the Quaternary aquifer system in the northern bank of the lower Waitaki in August 2013 by Wilson and Graham (2014) ...... 59
List of Tables Table 4-1: Average monthly rainfall, potential evaporation and soil drainage ...... 8 Table 4-2: Waitaki River and main tributaries flow statistics over the period 1980-2000 ...... 17 Table 4-3: Land Use Capability (LUC) classes in the LW ...... 19 Table 5-1: Geological units in South Canterbury and their groundwater resource potential ..... 24 Table 5-2: Gaining stream and river stretches in the study area ...... 38 Table 5-3: Losing stream and river stretches in the study area ...... 39
Environment Canterbury Technical Report v Lower Waitaki hydrogeology
vi Environment Canterbury Technical Report Lower Waitaki hydrogeology
1 Introduction I prepared this hydrogeological report to support the water quality limit setting process that the Canterbury Regional Council (Environment Canterbury) and the Waitaki catchment communities have embarked on as part of the Canterbury Water Management Strategy (CWMS) (Canterbury Mayoral Forum, 2009). The Waitaki catchment is the southernmost land in the Canterbury region (Figure 1-1). It drains a total area of about 12,120 km², which includes the full length of the Waitaki River and all its tributaries. The catchment straddles the boundary between the Canterbury and Otago regions. Most of the catchment land (c. 11,766 km²) fall within the Canterbury region. The remaining c. 354 km² of the catchment area is in the Otago region. On hydrological basis, the Waitaki catchment is subdivided into upper and lower catchments, which cover 9,657 km² and 2,463 km², respectively. Waitaki’s two catchments connect hydrologically between Kurow and the Waitaki Dam through a bedrock gorge that narrows below Lake Waitaki, marking the division between them. There is no subsurface flow connection between the two catchments because the water-bearing sediments (aquifers) in both catchments are physically disconnected.
1.1 Legal and planning framework The Canterbury Water Management Strategy (CWMS) presents a vision to enable present and future generations to gain the greatest social, economic, recreational and cultural benefits from the water resources in the Canterbury region within an environmentally sustainable framework (Canterbury Mayoral Forum, 2009). The CWMS is the culmination of a process that started in 1999 with the Canterbury Strategic Water Study (CSWS) (Morgan et al., 2002). The Land and Water Regional Plan (LWRP) provides the regulatory framework to implement the community’s aspirations for water management under the Canterbury Water Management Strategy (Environment Canterbury, 2014a). The CWMS divides Canterbury into 10 zones, each of which has its committee. Regional and zone committees are the key delivery mechanism for the CWMS. The Waitaki catchment includes the upper Waitaki (UW) and lower Waitaki (LW) zones. In collaboration between the LW community, the zone committee and the regional council, the LW CWMS zone has been subdivided into water management units and subunits as follows (Figure 1-2): − Hakataramea (899 km²) . u/s1 Cattle Creek confluence (349 km²) . d/s2 Cattle Creek confluence (550 km²) − Waitaki valley and tributaries (1,007 km²) . Waitaki north bank (147 km²) . Waitaki northern fan riverside (29 km²) . Waitaki valley and southern tributaries (831 km²) − Northern fan (203 km²) . Greater Waikākahi (157 km²) • Elephant Hill Stream (56 km²) • Waihuna Stream (30 km²) • Waikākahi Stream (71 km²) . Whitneys Creek (46 km²) − Waitaki catchment in North Otago (354 km²).
1 u/s: upstream. 2 d/s: downstream.
Environment Canterbury Technical Report 1 Lower Waitaki hydrogeology
Figure 1-1: Location map showing the extent, subdivisons and main features in the lower Waitaki catchment
Environment Canterbury Technical Report 2 Lower Waitaki hydrogeology
Figure 1-2: Waitaki regional plan chapter water management units and subunits in lower Waitaki
3 Environment Canterbury Technical Report Lower Waitaki hydrogeology
Allocation of surface water and groundwater in the part of the Waitaki catchment that falls within the Canterbury region, excluding Whitneys Creek sub-catchment, is governed by the Waitaki Catchment Water Allocation Regional Plan (WCWARP) developed by the Waitaki Catchment Water Allocation Board (WCWAB, 2005). The Plan arose from a clear need to manage water allocation and use in the Waitaki Catchment as reflected in the Resource Management (Waitaki Catchment) Amendment Act 2004. Groundwater allocation in the Whitneys Creek part of the catchment is managed under provisions in the Natural Resources Regional Plan (NRRP) and the LWRP. Water quality in the Waitaki catchment is managed under provisions in the NRRP and the LWRP. Rules in the LWRP take into account the water quality within an area (its nutrient allocation zone status) and the amount of nitrogen leaching from farming activities and regulates nitrate leaching accordingly. The LW catchment in Canterbury includes five nutrient allocation zones, namely, Hakataramea, Upper Waitaki at Waitaki Dam, Lower Waitaki, Maerewhenua, and Waikakahi. In Figure 2-1, these zones are colour coded according to their status into green (meets water quality outcomes), orange (at risk) and red (water quality outcomes not met) (Environment Canterbury, 2015). Environment Canterbury chose to prepare a single sub-regional chapter in the LWRP for the part of the Waitaki Catchment that falls within its jurisdiction (11,766 km²). The Waitaki sub-regional chapter is guided by the zone implementation programmes (ZIP) prepared by the UW and LW zone committees (Lower Waitaki South Coastal Canterbury Zone Committee, 2011; Upper Waitaki Zone Committee, 2012, respectively). The Waitaki sub-regional chapter is intended to address only water quality issues because water quantity allocation in the area is covered by the WCWARP as noted above.
1.2 Report scope and coverage Groundwater recharge source, rate, location, flow direction, magnitude and velocity determine the extent of effects that land use practices can have on groundwater quality. In addition, groundwater serves as a medium for transmitting land use quantity and quality effects to surface water systems. Therefore, understanding the hydrogeology of the sub-regional chapter area is a prerequisite to sustainable water quality management planning, the principal focus of the Waitaki sub-regional chapter. This report provides the required background hydrogeological knowledge on the groundwater system in the LW catchment. It does not cover the Hakataramea catchment (899 km²), which constitutes part of the LW catchment as the groundwater in this catchment is hydrogeologically separate from the rest of the Waitaki groundwater system. Environment Canterbury commissioned additional reports that cover LW catchment groundwater quality (Scott, 2014c), upper Waitaki zone (UWZ) hydrogeology and UWZ groundwater quality (Scott, 2014b).
2 Methodology and concurrent related work This report presents the outcome of a desktop study with limited field reconnaissance. To prepare it, I reviewed literature and used data available from Environment Canterbury databases and other sources. Section 8 of this report presents a list of literature cited in this report. In addition to this hydrogeology report, Environment Canterbury commissioned hydrogeological reports for the UW catchments to support the Waitaki sub-regional plan and other technical reports on various aspects relating to the Waitaki sub-regional chapter. This included groundwater quality reports in the UW and LW catchments (Scott, 2014b; Scott, 2014c, respectively), lakes water quality (Clarke, 2014), ecology (Gray, 2014), socio-economics (Taylor Baines and Associates and Harris Consulting, 2014), Ngāi Tahu cultural values (Tipa, 2013) and a summary report of all the above (Environment Canterbury, 2014b).
Environment Canterbury Technical Report 4 Lower Waitaki hydrogeology
Figure 2-1: Nutrient load allocation zones in the lower Waitaki catchment
Environment Canterbury Technical Report 5 Lower Waitaki hydrogeology
3 Previous work
3.1 Geology In 1957, the New Zealand Geological Survey (NZGS) of the Department of Scientific and Industrial Research (DSIR) published the first official geological map and report for the study area (Gage, 1957). The Institute of Geological and Nuclear Sciences Ltd (GNS Science) updated the Waitaki geological map and report as part of the 1:250,000 scale nation-wide geological mapping project known as QMAP (Forsyth, 2001). Geological information and analysis presented in this report are based on QMAP Sheet 19 (Forsyth, 2001) and the work of other researchers who examined lithological well logs to understand the area’s subsurface geology (e.g. Brown and Somerville, 1980; NZGS, 1988; URS, 2003a; URS, 2003b; Forsyth, 2004; Cox and Barrell, 2007; Barrell, 2008; Aitchison-Earl, 2012; Barrell and Strong, 2012).
3.2 Hydrogeology The Ministry of Works and Development commissioned the first groundwater investigation in the LW catchment (Scott, 1977). NZGS (1988) investigated the likely effects of river diversion on the groundwater regime. Otago Regional Council (ORC) investigated the groundwater resource in the part of the LW catchment that falls within their region (ORC, 1993). They also looked at groundwater in the old, deep Taratu Formation which is known as the Papakaio aquifer in the Enfield Basin (ORC, 2000). In 2004, they investigated the same aquifer outside the Enfield Basin (ORC, 2004). In the early 2000s, Meridian Energy Limited commissioned extensive environmental and engineering investigations in the study area as part of Project Aqua. Project Aqua reports relevant to this study include: ₋ Boffa Miskell Ltd (2002) – terrestrial ecology and wetlands report ₋ GPF (2002) – abstractive user’s infrastructure assessment of environmental effects ₋ NIWA (2002) – geomorphology and sediment transport study ₋ R D Keating & Associates and Boffa Miskell (2002) – soil and productive potential values assessment ₋ Tonkin and Taylor (2002) – geotechnical and engineering geology investigation feasibility study ₋ URS (2002a) – geology and seismicity effects assessment ₋ URS (2002b) – water balance assessment. Most importantly from a groundwater point of view, Meridian Energy Limited commissioned a comprehensive hydrogeological study which resulted in the production of a hydrogeological assessment of effects (URS, 2003a, 2003b). The study compiled extensive data from the field and other sources to develop conceptual and numerical models of the area. Opus (2003) studied groundwater level data in the Waitaki floodplain. SKM (2004) completed a review of groundwater information in the Waitaki Catchment for the Ministry for the Environment. Aitchison- Earl (2005) reviewed available data on deep groundwater in the area between Timaru and the Waitaki River. URS (2006) undertook an assessment of hydrogeological effects that may result from the North Bank Tunnel Concept for Meridian Energy Limited. Ezzy (2011) undertook a desktop study to define future investigation priorities for the Kowai Formation, which is locally known as the Cannington Gravel and has limited occurrence in the study area. Wilson and Graham (2014) prepared groundwater level contour maps (piezometric maps) based on a survey they undertook of groundwater levels and river flows across the South Canterbury area, which includes the coastal part of the lower Waitaki Zone (LWZ).
3.3 Groundwater quality and age van der Raaij (2007) undertook a study of groundwater age in the South Canterbury and Orari areas. Burbery and Vincent (2009) studied the hydrochemistry of Tertiary3 aquifers in South Canterbury. Scott et al. (2012) undertook an investigation of groundwater quality in the mid-Waitaki valley. In 2013,
3 The Tertiary is a former term for the geologic period from 66 million to 2.6 million years ago. It is no longer recognised as a formal unit by the International Commission on Stratigraphy (ICS) but the word is still widely used by geologists.
Environment Canterbury Technical Report 6 Lower Waitaki hydrogeology
Environment Canterbury commissioned a project to investigate recharge, discharge mechanisms and flow dynamics for deep groundwater in South Canterbury (Environment Canterbury, 2013). Scott and Hanson (2013) prepared risk maps of nitrate in groundwater in the Canterbury region, including parts of the study area. Scott (2014a) completed a review of groundwater oxygen-18 (¹⁸O) data in the Canterbury region, including parts of the study area.
3.4 Groundwater recharge and allocation limits Groundwater recharge and allocation limits in the study area were subject to a number of studies including White et al. (2003). Aitchison-Earl et al. (2004) prepared guidelines for setting groundwater allocation limits in the Canterbury region. Scott (2004) estimated land surface recharge (LSR) for various catchments in the Canterbury region. WCWAB (2005) prepared the Waitaki Catchment Water Allocation Regional Plan, which was amended by the High Court on 3 July 2006. Thorley and Ettema (2007) reviewed the water allocation limits for the South Canterbury downlands. Thorley et al. (2008) proposed additions to South Canterbury groundwater allocation zones. Poulsen (2013) reported on the hydrogeological significance of loess as a recharge controlling factor in areas such as the loess covered downlands in parts of the LW. Scott (2013) prepared a memorandum on possible ways to study recharge to the Kowai Formation in South Canterbury. Effects of irrigation on groundwater were investigated in several studies, e.g. Hamilton and Elliot (2000).
4 The study area
4.1 Extent, definition and main characteristics The LW catchment (Figure 1-1) stretches between the water divide that separates it from the South Canterbury Coastal Streams (SCCS) and Orari-Temuka-Opihi-Pareora (OTOP) catchments to the north and the boundary between the Canterbury and Otago regions to the south. The western part of the LWZ southern boundary coincides with the water divide until it intersects the McKenzie Road. Thence, the zone’s southern boundary swings northeast to coincide with the Otago- Canterbury regional boundary on the southern bank of the Waitaki River. The LW is bound by the water divide that separates it from the UW to the west and the Pacific Ocean coastline to the east. The Hakataramea River is an important tributary of the Waitaki River. It joins the main river below the Waitaki hydroelectricity dams and man-made lakes. There is no groundwater connection between the Hakataramea catchment and the Waitaki Valley. Therefore, I excluded the Hakataramea catchment from this study. Below Black Point, the Otago-Canterbury regional boundary generally coincides with the southern bank of the Waitaki River. The Waitaki River is suitable as a boundary for hydrogeological studies purposes. However, data from the entire river catchment, including land in Otago region help with hydrogeological analyses. Approximately 354 km² of the LWZ lie within the Otago region and I include them in the study area, bringing the total study area to about 1,563 km² in South Canterbury and North Otago. Administratively, the LW catchment falls within the Waitaki, Waimate and Mackenzie districts. Civil services such as health, education and retail are delivered in the settlements of Kurow, Duntroon and Glenavy (Taylor et al., 2014). Statistics New Zealand data show that the area is sparsely inhabited and predominantly rural. In 2013, it had a total population of about 2,170 people, of which about 1,500 lived in rural lower Waitaki, 310 lived in Kurow, 90 lived in Duntroon and 270 lived in Glenavy.
4.2 Water resources and values The Waitaki River, its tributaries and groundwater associated with these surface waterways represent the freshwater resource in the area. The economy and many of the social and cultural values in the LWZ depend on water (Tipa, 2013; Taylor et al., 2014). Water in the zone is important for various purposes, including life sustenance (human and animals), economic productivity (e.g. irrigation, stock and dairy farming), social organisation, recreation, identities, ways of life and historical linkages to land and waterways.
7 Environment Canterbury Technical Report Lower Waitaki hydrogeology
Groundwater and surface water in the LW are strongly connected. There is a significant groundwater resource in the area but it is not generally used for irrigation. Groundwater has an important ecological role as it emerges in the form of springs and seeps and forms wetlands. In addition, the shallow groundwater may help maintain healthy soil moisture levels during dry summer months. Tangata Whenua identifies many wetlands in the zone as significant sources of mahinga kai.
4.3 Climate The study area has a temperate climate. The temperature range is relatively narrow (c. 0-25 °C). Southerly and south-easterly storms dominate the weather patterns in the area, with occasional north- easterly winds from the coast. Easterly storms can generate large floods in the foothills, contributing to high flows in the LW River (WCWAB, 2005). Table 4-1 presents average monthly rainfall and potential evapotranspiration data for the area during the period 1915 to 2001. The data show that rainfall in the area is generally uniformly distributed throughout the year. Figure 4-1 presents the average annual rainfall distribution over the area. The overall average rainfall in the area is about 565 mm/y, calculated using rain isohyets and Thiessen polygons (Appendix A).
Table 4-1: Average monthly rainfall, potential evaporation and soil drainage (URS, 2003a)
Annual Station Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total
Duntroon rainfall (mm) 59 47 52 41 39 36 41 37 38 45 49 64 548
Tara Hills potential evaporation 140 130 97 75 45 30 29 44 69 98 117 145 1,019 (mm)
Calculated soil drainage with no 2 − 6 − 3 1 12 14 9 2 − 5 54 irrigation4 (mm)
Calculated soil drainage with 110 121 124 77 31 1 12 14 78 107 115 111 902 border dyke irrigation 5 (mm)
4.4 Physiography and surface water drainage pattern Water in the LW catchment generally drains from west to east. The catchment receives surface water flow from the much larger upper catchment (2,462 km² cf. 9,658 km²), which drains an extensive section of the Southern Alps/Kā Tiritiri o te Moana. In addition, the lower Waitaki River receives water from the Hakataramea catchment (c. 899 km²). The UW and Hakataramea catchments drain through single outlets into the main stem of the lower Waitaki River. Both catchments are intermontane (surrounded by mountains), semi-endorheic (semi-closed) basins. The LW catchment is different as it is an exorheic (open) basin that drains to the ocean. The Waitaki River drains the UW catchment into the LW catchment through gorges and valleys it incised in basement rocks that form the Benmore, Hawkdun and St Mary ranges. The mountainous area where the Awakino River West Branch starts in the northwest of the LW catchment rises up to nearly 2,000 metres above sea level (masl). The mountains to the true right of the Waitaki River are higher than those on the river’s true left (Figure 4-3). On their seaward side, the mountains ease into foothills (800-600 masl) and rolling downlands through an alluvial floodplain, which is characterised by flat terraces stepping down to the river (WCWAB, 2005). Along its course through the study area, the Waitaki River base drops from c. 215 masl in the most upstream point in the study area, to about 200 masl at its confluence with the Hakataramea River, eventually to reach sea level at the Pacific Ocean coast.
4 Assuming 90 mm average soil moisture holding capacity and evaporation/evapotranspiration ratio of 1 (URS, 2003a). 5 Based on Lower Waitaki Irrigation Scheme area, assumes average application of 110 mm/14 days. Data normalised for whole area (16,684 hectares) with irrigation varying from 17% to 100% of area during period September through May (URS, 2003a).
Environment Canterbury Technical Report 8 Lower Waitaki hydrogeology
Figure 4-1: Averge annual rainfall isohyetal map and climatic zones* * Data sourced from NIWA’s Virtual Climatic Stations (VCS) network
Environment Canterbury Technical Report 9 Lower Waitaki hydrogeology
The Waitaki River in the study area is braided, running in a Holocene (12 ka6 BP7−present) incision infilled mainly with alluvium gravel of the same age. It receives water from many tributary rivers and streams (Figure 1-1). Most of its main river tributaries in the study area are associated with mainly reverse, conceled, SW-NE striking faults. The Waitaki River itself and its floodplain are associated with the NW-SE striking Waitaki Fault System (Figure 4-2). The Waitaki River runs along the lowest elevations in its catchment. It is bound at both sides by elevated terraces, foothills and mountains. A dendritic (tree-like) drainage pattern dominates the elevated land above the river valley and floodplain (Figure 4-2). In dendritic drainage patterns, tributaries meet at low angles and branch in a random, tree-like pattern. They form on slopping land of erodable impervious or non-porous rocks or sediment, forming V-shaped valleys. They normally form on rock that is of equal resistance to erosion (i.e. rock that contains no relatively weak layers). The Waitaki River floodplain extends between Black Point to the west and the coastline to the east. Near the coast, it is characterised by trellis drainage where short tributaries meet long trunk streams at near right angles (Figure 4-2). The trunks are notably unconnected. In trellis drainage patterns, consequent streams follow the dips and subsequent streams are parallel to strikes. Thus, short juvenile streams flowing to the south and north join secondary streams flowing to the east in this area. This drainage pattern formed because Quaternary age (c. 2.6 Ma8 BP to present) sediments in the floodplain unconformably overlie the bedrock (Paleogene9–Neogene10 and older basement rock), which are faulted and folded.
4.5 Geology The geology of the study area is described in NZGS old Waitaki geological map and report (Gage, 1957), GNS Science QMAP Sheet 19 (Forsyth, 2001), URS (2002a) geology and seismicity report, URS (2003a) hydrogeology report, SKM (2004) Waitaki Catchment groundwater information review, the geological synopsis by Forsyth (2004) and the Waitaki Catchment Water Allocation Regional Plan (WCWAB, 2005). Barrell and Strong (2012) constructed structural contours to identify tops of important layers for groundwater modelling purposes. Unlike all other investigators, Forsyth (2001) and Forsyth (2004) use the new national geological nomenclature system adopted by GNS Science in their QMAP project (see Appendix B for brief explanation of QMAP terminology system). The QMAP nomenclature system is compatible with recent international geology, glaciology and oceanography literature nomenclature systems. This report adopts QMAP nomenclature. Figure 4-4 presents a geological map of the study area, drawn from digital QMAP data provided by GNS Science. The map’s legend lists geological layers in chronological order, from younger to older.
4.5.1 Basement rock The study area, and the whole of New Zealand, is underlain by greywacke and schist basement rocks. These rocks are approximately 300 to 150 million years old (Permian–Jurassic age). Basement rocks underlay all newer strata and crop out in main mountain ranges, e.g. the Southern Alps/Kā Tiritiri o te Moana and the North Island central ranges. Both greywacke and schist are readily recognised in outcrops and well logs. The greywacke consists of hard, light grey quartzofeldspathic sandstone and flaky dark grey argillite (mudstone). The schist is a metamorphic layered rock which splits along the layers. Greywacke is the parent rock for the schist. In the geological map presented in Figure 4-4, basement rock in the study area is coded as units Ytk2b through Ttm. In the study area, the Waitaki River marks the subsurface geological divide between the Torlesse Supergroup greywacke of Canterbury to the north and the Haast Schist of Otago to the south, which is known as the Waitaki Fault (Figure 4-2 and Figure 4-4). Both basement units are part of the Rakaia Terrane, the oldest rock unit in Canterbury. The Waitaki Fault tends to diminish near Black Point, where greywacke and schist basement rocks crop out. The fault resulted in uplifting the schist basement to the south, exposing it in that area.
6 ka: kilo annum (thousand years). 7 BP: Before the present. 8 Ma: Mega annum (million years). 9 66-23 Ma BP. 10 23-2.6 Ma BP.
Environment Canterbury Technical Report 10 Lower Waitaki hydrogeology
Figure 4-2: Structural geology and surface water drainage map
Environment Canterbury Technical Report 11 Lower Waitaki hydrogeology
Figure 4-3: 3D representation of the physiography of the lower Waitaki catchment
12 Environment Canterbury Technical Report Lower Waitaki hydrogeology
Figure 4-4: Geological map (data sourced from GNS QMAP digital records)
Environment Canterbury Technical Report 13 Lower Waitaki hydrogeology
Basement greywacke and schist lack intrinsic porosity and permeability. The lack of useful void space to store water and allow its flow in the bulk of the basement rocks makes them unsuitable as groundwater reservoirs (aquifers). Where basement rocks crop out, the uppermost few metres are commonly weathered and water might be present there. So, some extractable groundwater may be found in places in these rocks, but not in the main part of the basement rocks.
4.5.2 Late Cretaceous strata Late Cretaceous age (c. 90-65 Ma BP) and Paleogene–Neogene age (c. 65-2.5 Ma BP) strata overlie the Permian-Jurassic age basement rocks in the study area. These ‘cover’ rocks form most of the hills and mountains that border the edge of the Waitaki valley and underlie the Pleistocene and Holocene mainly alluvial deposits that form river terraces within the valley (Figure 4-4). The Papakaio Formation (unit KEot(k) in the geological map presented in Figure 4-4) represents Late Cretaceous age strata in the study area. It comprises marine and non-marine deposits. Non-marine sedimentary rocks are extensively preserved along the south side of the Waitaki Valley and are locally present in the lower Hakataramea Valley (Gage, 1957). Their lithologies are dominant by interbedded quartz-rich sands and gravels but carbonaceous silt, clays and low-grade coal seams are present in the upper part of the unit (inland). Late Cretaceous marine sediments have not been found within the study area further inland than Georgetown. The extent of the unit is controlled by one of the faults that constitute the Waitaki Fault System (Figure 4-4). The lower part of the unit has not been reported to be encountered within the valley floor but is common in adjacent hills. Due to their lithological characteristics, structural geological settings and limited outcrop extent, Late Cretaceous rocks have negligible groundwater potential in the study area.
4.5.3 Paleogene–Neogene strata Paleogene–Neogene deposits (referred to as Tertiary strata in older literature) overlie basement and/or Cretaceous strata in the study area. They are subdivided into units that reflect the large-scale geological cycles of sea regression and transgression during this geological time (units KOom(kp) to Plke in the geological map presented in Figure 4-4). The oldest Paleogene–Neogene age unit in the study area is the Onekakara Group, which achieves up to 1,500 m in thickness where totally protected from erosion. Locally known as the Papakaio and Broken River formations, the Taratu Formation represents the bottom unit in this group. It ranges in age from Late Cretaceous in North Otago to Eocene (c. 55-34 Ma BP) in South Canterbury. It consists of quartz conglomerate and sandstone, mudstone and coal. The Taratu Formation is typically less than 50 m. It is absent in the upper Waihao River but can reach up to 120 m thickness in some places. It represents river valleys, plains, swamps and estuaries depositional environments. Silica- and iron- cemented layers are common, especially near the base. Taratu Formation coal seams in the study area are typically no more than 3 m thick. In North Otago, Taratu Formation hosts an important aquifer known as the Papakaio aquifer (Figure 4-5). The stratigraphically higher formations of the Onekakara Group are all marine rocks. These rocks were deposited in a wide range of shallow marine environments, ranging from shoreface to outer shelf and offshore bars. In South Canterbury, the known age range is Early Eocene to Early Oligocene (c. 55- 23 Ma BP). There are no important aquifers in these marine deposits. Miocene in age (c. 23-5.3 Ma BP), White Rock Coal Measures consist of quartz sandstone, carbonaceous mudstone and lignite. The unit thickness varies from 0 to over 60 m. It is found in the study area in the middle Waitaki valley (Aviemore Dam). The unit appears to contain significant amounts of gravel and also significant groundwater (Forsyth, 2004). The Kowai Formation is known locally as Cannington Gravels and Elephant Hill Gravels. It relates mainly to the Early to Middle Pleistocene age (2.6 Ma BP−125 ka BP), but also contains some Pliocene sediments (5.3 Ma BP−2.6 Ma BP). It is widespread along the south side of the Waitaki valley inland from Black Hill, in the Wharekauri Basin and in the lower Hakataramea Valley, and in the south-western part of the Waihao district, flanking the Waitaki Plain. Aitchison-Earl (2012) divided the Kowai Formation is divided into lower and upper units. The lower Kowai Formation unit comprises sands, silt and gravels of marine origin. The upper Kowai Formation unit is of terrestrial origin, consisting of weathered red, orange and brown gravel, sand and mud. The Kowai Formation thickness is not known, estimated by
Environment Canterbury Technical Report 14 Lower Waitaki hydrogeology
original investigators to be more than 150 metres. These rocks do not have good groundwater resource potential in the study area.
Figure 4-5: Schematic hydrogeological cross sections through the Taratu Formation in the Maerewhenua Basin (from ORC, 2004) The locations of these sections are shown on the map in Figure 4-4.
4.5.4 Late Quaternary deposits The youngest layers in the area’s stratigraphical sequence are less consolidated coastal, river and wind-blown sediments, deposited in the Middle-Late Pleistocene and Holocene ages (c. 780 ka BP to present).
Middle-Late Pleistocene deposits (c. 780 ka BP−12 Ka BP) The deposits are marked in the geological map presented in Figure 4-4 as mQ (Mid-Quaternary) through Q2 (late Last Glacial). This time range covers the period from c. 780 ka BP to 12 Ka BP. However, most of the sediments of this period in the study area are less than c. 360,000 years old, i.e. oxygen isotope stage (OIS)11 10 and younger strata. These deposits can be classified into the following three groups: 1. Alluvial terrace gravels form two well preserved aggradation and one degradation surfaces along the valley floor and across the Waitaki plain, with a further three surfaces preserved as discontinuous remnants of ancient outwash plains that form small plateaus and terraces on the hills that border the valley rising up to 180 m above present river level (units Q2a, Q4a, Q6a, Q10a and mQa in the geological map presented in Figure 4-4). These deposits are typically composed of sandy fine to coarse greywacke gravel, with some schist gravel in places. 2. Fan gravels that form prominent localised features at the mouths of tributary rivers and streams (units Q2f, Q4f, lQf, Q6f, Q8f and mQf in the geological map presented in Figure 4-4). Large, schist-rich fans grade onto the lower terraces along the southern bank of the river; smaller greywacke-rich fans are present on the northern bank. Older fan remnants are present at five levels in some left bank gullies, apparently grading out to higher (older) terrace levels. Pleistocene fan deposits are particularly significant on the south bank of the Waitaki River
11 Sometimes also called marine isotope stage (MIS).
15 Environment Canterbury Technical Report Lower Waitaki hydrogeology
between Kurow and the Otekaieke River valley where they form together with Holocene fan deposits a series of nearly contiguous features (Figure 4-4). 3. Loess12 deposits are preserved on terrace surfaces within the Waitaki Valley, the Waihao Basin and near Morven, but not shown in Figure 4-4. Loess in lithological well logs from the study area is usually described as yellow brown silt or silty clay. Where found at outcrop, several loess sheets can normally be recognised. Loess thickness in the study area normally ranges between 0.5-2 m, and generally decreases seawards. The permeability, effective porosity and general geological setting of Pleistocene alluvium make them suitable as aquifers, unlike the Pleistocene fan and loess deposits.
Holocene deposits (c. 12 Ka BP−the present) Old literature refers to the Holocene period as ‘Post-Glacial’ (e.g. URS, 2003a). The QMAP symbol for this period is Q1 because it coincides with OIS 1. Holocene age deposits in the study area include Q1a and Q1f units, which refer to Holocene alluvium (suffix a) and Holocene fan (suffix f) deposits. Q1a deposits in the study area consist mainly of river gravels underlying the present riverbed, floodplain and tributary streambeds (Figure 4-4). Discontinuous fine material overbank lenses can be found in this unit. Overall, the silt/clay fraction is generally less than 2% by volume. So, fine material has little influence on the overall hydraulic properties of this unit. Holocene fan deposits (Q1f) cover small parts in the study area. They form together with Pleistocene fan deposits a series of nearly contiguous features (Figure 4-4). They have potential as a groundwater resource, but their hydraulic characteristics are lower to much lower than the gravel of the same age because of their immaturity, which makes them poorly sorted (mix of grain sizes), makes their fragments angular rather than rounded and irregularly shaped rather than spherical. In addition, they are normally thin, occurring on steep basement rocks surfaces. Such setting extremely limits their potential as a groundwater resource because they do not have enough volume to store groundwater and their steepness makes them drain water easily.
4.6 Structural geological setting The LW catchment is a structurally complicated area. Folds and faults are shown in Figure 4-2 and Figure 4-4. Faults cut through the Basement rocks, the Paleogene-Neogene rocks and have displaced at least the older Pleistocene gravel deposits. The Waitaki Fault line is part of the Waitaki Fault System. It is the principal boundary between the Haast Schist basement of Otago and the Torlesse greywacke basement of Canterbury. The Waitaki Fault is marked on the land surface by the LW River. Geological structure controls the configuration of aquifers in the area, at least partially.
4.7 Springs and wetlands Springs in the LW have not been comprehensively surveyed. Figure 4-6 depicts the location of major wetlands and springs registered in Environment Canterbury’s Wells Database. Springs, stream-fed springs and wetlands in the study area are generally associated with shallow groundwater. They are used for a variety of purposes (URS, 2003a). The most notable springs in the study area occur on opposite sides of the LW River near Duntroon (SKM, 2004). Significant springs in the study area include Duntroon Spring, Penticotico Spring, the spring feeding Welcome Creek, and the Waikākahi springs. Generally, springs in the study area are located on the Holocene river terrace, at the toe of the older Pleistocene age (c. 2.6 Ma BP−12 ka BP) terraces. Previous invistigators believed that most of the springs discharge water that originate from surface water losses to the shallow groundwater system. So, water reemerges to the land surface as springs where hydraulic conditions suit (URS, 2003a; Scott et al., 2012). Scott et al. (2012) and ORC (2004) suggest that the springs near Duntroon in the Maerewhenua basin and the Awamoko Stream discharge Taratu Formation groundwater through the overlying Quaternary alluvium. Groundwater dependent systems (GDS) such as springs, spring-fed streams and wetlands are influenced by groundwater balance, level and quality. Increasing groundwater recharge through irrigation returns and losses from irrigation infrastructure will result in groundwater level rise and,
12 Loess is wind-blown silt size deposits.
Environment Canterbury Technical Report 16 Lower Waitaki hydrogeology
subsequently, wetter and more extensive GDS. URS (2003a) noted that land use changes that involved irrigation in the 1980s and 1990s resulted in the development of springs and wetlands at the toe of the Pleistocene terraces in areas that were previously dry. Similarly, groundwater abstraction is likely to lower groundwater levels, lessening spring and stream flows and wetlands extents. In addition, chemicals in groundwater end up in GDS, affecting their water quality. The magnitude and extent of groundwater level and quality changes on springs and other GDS depend on their location and sources of their water.
4.8 Surface water hydrology The Waitaki River is the main surface waterway in the LW. It flows in the study area from Lake Waitaki and discharges into the Pacific Ocean near Glenavy. The river valley is relatively narrow from the Waitaki Dam to Kurow. Below Kurow, the river becomes braided and its valley widens slightly. The river valley widens notably below Black Point to form a floodplain. The Waitaki Catchment has some of the longest hydrological records in New Zealand, with data from 1925 (Waugh and Payne, 2003). Duff (2014) notes that there is little seasonal change in flow at Kurow, with flow rate staying between 450-300 m³/s throughout much of the year (c. 9,460-14,190 mcm/y). Waugh and Payne (2003) calculated the mean flow at the Waitaki Dam at 358 m³/s (c. 11,290 mcm/y) over the period 1927 to 2000. Figure 4-2 shows the main course of the Waitaki River and its main tributaries in the study area, which include the Hakataramea, Awakino, Kurow, Otiake, Otekaieke, Maerewhenua, Awamoko rivers and the Penticotico Stream. The Waitaki’s tributary rivers typically have steep headwaters and have low flood plains near the lower reaches, except for the Awakino River which has a prominent gorge near its lower section. Basic flow statistics for the Waitaki River and its main tributaries in the study area over the period 1980-2000 are provided in Table 4-2. The Waitaki Rivers tributaries in the LW collectively provide 2% of the river’s flow (WCWAB, 2005). Additional information on surface water in the study area is provided by (Duff, 2014). Table 4-2: Waitaki River and main tributaries flow statistics over the period 1980-2000 (data sourced from URS, 2002b; Waugh and Payne, 2003)
Daily Flow (m³/s) Mean annual flow River/stream Location Min Max Median Mean (mcm/y)
Waitaki River Waitaki Dam 130.000 2,649.00 373.000 389.00 12,267.50
Waitaki River Kurow13 300.000 450.00 358.00 11,290.00
Waitaki River Priest Road 132.000 2,660.00 379.000 395.00 12,456.72
Waitaki River Black Point 136.000 2,665.00 384.000 401.00 12,645.94
Waitaki River Ferry Road 111.000 2,633.00 364.000 380.00 11,983.68
Waitaki River State Highway 1 112.000 2,635.00 365.000 381.00 12,015.22
Hakataramea SW4 0.470 51.52 3.480 6.01 189.53
Awakino SW3 0.098 59.24 0.480 0.84 26.49
Kurow SW5 0.013 38.27 0.380 0.61 19.24
Otiake SW7 0.130 42.15 0.400 0.66 20.81
Otekaieke SW9 0.130 77.95 0.640 1.10 34.69
Maerewhenua SW16 0.320 186.68 1.620 2.83 89.25
Awamoko SW19 dry 80.57 0.043 0.20 6.31
Penticotico − − − − 5.05
13 Record from 1927 to 2000 (calculations by Waugh & Payne, 2003).
17 Environment Canterbury Technical Report Lower Waitaki hydrogeology
Figure 4-6: Major known springs and wetlands in the study area
Environment Canterbury Technical Report 18 Lower Waitaki hydrogeology
4.9 Soil Soil-covered areas in the LW are flat to gently undulating, except for the elevated terraces. Landcare Research (2014) S-map coverage is incomplete over the study area. Where data exist, the soil is classified as extremely light to light with small areas of heavy soils. Moisture holding capacity of soils in the LW is low because they are generally very pervious. Hence, effects from land use changes can be transduced through the soil relatively quickly, whether they are quality or quantity related. Given the strong connection between groundwater and surface water in the area, effects of land use also have the potential to be transmitted relatively quickly to surface water. R D Keating & Associates and Boffa Miskell (2002) describe the soils in the study area as dry- subhygrous and subhygrous Yellow-Grey Earths, generally sandy and silt loams, and recent soils, generally stony sandy or silt loams. They classified the area’s soil according to the Land Use Capability (LUC) classification system developed by the National Water and Soil Conservation Organisation in the 1970s. The LUC classification system provides a rough approximation of the potential productivity of the land. R D Keating & Associates and Boffa Miskell (2002) found that nearly 50% of the soil in the LWZ is Class III, 25% is Class IV, 3% class II, and 4% of the land consists of Classes VI, VII and VIII, which gives a total of 79% of potentially productive land. The remaining 21% of the land comprise non- productive riverbed land (Table 4-3 and Figure 4-8).
Table 4-3: Land Use Capability (LUC) classes in the LW (adapted from R D Keating & Associates and Boffa Miskell, 2002)
Classification Description Typical use in the LWZ
a. Arable classes: Class II land that has some limitations for production dairying, cropping Class III land with some significant limitations for production dairying, sheep farming, some cropping
Class IV land that has the most limitations for sustained arable dairying, sheep farming use
b. Non-arable classes: Class VI land having some limitations for pastoral production dairying, sheep farming
Class VII land with only a limited capacity for sustained pastoral extensive pastoral use
Groundwater levels in the area can change as a result of changing the river flow and/or stage14, altering groundwater abstraction and/or changing recharge from irrigation returns and irrigation infrastructure losses. Changes in groundwater level may affect moisture levels in overlying soils. The most pronounced effect of changes in river flow and/or stage will occur in the area close to the river course. This area is classified as unproductive riverbed, so the effect on soil from such a change is not significant. The effects of possible changes in groundwater abstraction and/or recharge will be mainly noticed in the area covered by other soil types, mostly close to the area of change.
4.10 Land use Land cover variability in the Waitaki catchment reflects variability in the underlying geology, soil, climatic conditions and history of land use modifications (WCWAB, 2005). Until the early 1960s, land use in the LW was largely extensive pastoral farming with some cropping and little dairying. This is generally a
14 Stage: water surface elevation in metres above sea level (masl).
Environment Canterbury Technical Report 1 9 19 Lower Waitaki hydrogeology
reflection of the soil and rainfall characteristics of the area. Overall, productivity was low, limited by climatic conditions such as regular drought. Stock carrying capacity was low to moderate, and the land was farmed very conservatively (URS, 2003a). In the late 1960s, the LW land use started to drastically change as a result of introducing irrigation schemes, mostly border-dyke irrigation using Waitaki River water. More advanced land management practices helped optimise pastoral farming production and increased stock carrying capacity. Dairying has recently become a major land use but sheep and beef continue to dominate the area’s land use (Figure 4-7). Improvements in dairying economics led to increased irrigation water use and the development of marginal land near the Waitaki River for grazing. This land is very free draining and is particularly valuable for use as dairy ‘runoff’ land in the off-season, as the pasture suffers little pugging damage from hoof pressure while being grazed and recovers quickly (URS, 2003a). Potential land use change can affect groundwater and surface water quantity and quality. For example, irrigation system modernisation will lessen over-watering which has resulted in groundwater level rise since the start of irrigation in the area. Elevated groundwater levels may impact on pastures by increasing ponding and saturation, leading to lower productivity potential. Agricultural intensification can increase nutrients level in surface and groundwater. Dry land farming and cropping can also be affected because of groundwater level changes. Lowering groundwater levels under such land use conditions may necessitate irrigation to maintain production.
4.11 Irrigation infrastructure There are a number of irrigation schemes in the Waitaki catchment. Figure 4-9 shows the layout of irrigation water races in the lower Waitaki area. Losses from these races contribute to groundwater recharge, resulting in water table mounding in the areas they traverse. (Rekker, 2014) estimates that losses from irrigation races in the part of the Waitaki catchment that falls within Otago region amounts to about 26% of the total groundwater recharge in that area. Hence, I assume that reducing leakage from the races may result in lowering water table in places and, possibly, the drying of some groundwater dependent streams, springs and wetlands. Similarly, I anticipate that reducing leakage of high quality water from irrigation races may result in reduced dilution of dissolved chemicals in groundwater, including nitrogen, which may lead to groundwater quality deterioration. I believe that such possible undersirable adverse groundwater quantity and quality effects would be most profound in the Waitaki plain area, downstream of Black Point.
20 Environment Canterbury Technical Report Lower Waitaki hydrogeology
Figure 4-7: Current land use map for the LW excluding Hakataramea The upper legend provides areas in hectares (ha) and percentage (%) of the study area for each land use category.
Environment Canterbury Technical Report 21 Lower Waitaki hydrogeology
Figure 4-8: Land Use Capability (LUC) soil classification map (sourced from R D Keating & Associates and Boffa Miskell, 2002)
22 Environment Canterbury Technical Report Lower Waitaki hydrogeology
Figure 4-9: Irrigation water delivery infrastructure in the lower Waitaki
Environment Canterbury Technical Report 23 Lower Waitaki hydrogeology
5 Hydrogeology
5.1 Hydrostratigraphy and groundwater occurrence Wilson and Graham (2014) summarised the geological sequence in South Canterbury and the groundwater resource potential for various strata (Table 5-1). The LW study area is different than the rest of South Canterbury because of its location on the boundary between the greywacke and schist basement units. Because of the tectonic uplift of the basement in the area affected by the Waitaki fault, greywacke basement rocks occur at rather shallow depths in that area, even near the coastline. This means that the Quaternary sedimentary sequence in the area is rather thin. Table 5-1: Geological units in South Canterbury and their groundwater resource potential (from Wilson and Graham, 2014)
Formation name/ Geological Geological period Group name lithological unit Aquifer name era description
Quaternary River gravels, loess, swamp and beach/estuary deposits (2.6 Ma – Present) Timaru and Geraldine No known aquifer Basalt Upper Kowai aquifer Kowai Formation (known (typically terrestrial) as the Cannington Gravels in south Canterbury) Lower Kowai aquifer Neogene (typically marine) (23-2.6 Ma) White Rock Coal White Rock Coal Measures Measures aquifer Otakou/Motunau Cenozoic Southburn Sand Southburn Sand aquifer Groups
Mount Harris Formation Mount Harris aquifer
Otekaike Limestone No known aquifer Kekenodon Group Kokoamu Greensand No known aquifer Paleogene (66-23 Ma) Marine sandstone, No known aquifer Onekakara/Eyre mudstone and limestone Groups Taratu Formation Taratu Formation aquifer Permian-Triassic Mesozoic Greywacke (sandstone and argillite) basement rock (299-201 Ma)
Examination of well location, depth and lithological log and groundwater abstraction data confirms that the main groundwater resource in the study area is contained within the Quaternary deposits, more specifically in the Middle Pleistocene to Holocene river alluvium. Other layers may be able to yield some water to wells in places. For example, the Paleogene age Taratu Formation is locally used as an aquifer in the Maerewhenua basin (Scott, 2014c). However, such layers do not have the potential to be considered as regionally important resources. The geology of the area can be simplified for hydrogeological purposes into the following four main units (Figure 5-1): 1. Holocene river alluvium (aquifer)
Environment Canterbury Technical Report 24 Lower Waitaki hydrogeology
Figure 5-1: Simplified geological and hydrostratigraphical map
Environment Canterbury Technical Report 25 Lower Waitaki hydrogeology
2. Middle-Late Pleistocene layers (aquifer) 3. Quaternary alluvial fan deposits (marginal deposits, no significance as a groundwater resource) 4. All pre-Late Pleistocene strata (hydrogeological basement). The Quaternary deposits are relatively thin and restricted to narrow alluvial channels and wider floodplains. URS (2003a) mapped the contact between the Quaternary strata and the hydro-geological basement using drillhole data (Figure 5-2). They found that the Quaternary aquifer system is generally thin; mostly less than 20 m thick even in the coastal plains. Equivalent deposits beneath the Canterbury Plains can be more than 300 m thick. URS (2003a) noted that Quaternary gravel is exceptionally thick in a couple of locations in the LW area. They named them the ‘Kurow trench’ and the ‘buried sea cliff’ (Figure 5-2). The Kurow trench is an approximately 100 m deep trench infilled with gravels. It extends from the vicinity of the Kurow Bridge in a southeast direction beneath the river and terminates on the North Bank of the Waitaki River near Wainui Homestead (Figure 5-2). Drillhole data that URS (2003a) obtained as part of Project Aqua indicate that the bedrock surface in the trench is characterised by an abrupt drop in elevation. URS (2003a) noticed that the trench approximately follows the alignment of the Stonewall/Dryburgh fault system and its north and south ends coincide with the cross cutting Kurow Hill and Black Hill Faults, respectively. This suggests that the trench is at least a partially structurally controlled feature rather than just an erosional feature associated with the Waitaki River. They hypothesised that the base of the trench has steadily deepened due to tectonic movement of the faults, and the river has contemporaneously deposited gravels into the trench. URS (2003a) also detected evidence for the presence of an ancient buried sea cliff or scarp approximately 3-5 km west of the State Highway 1 (SH1) bridge (Figure 5-2). The Quaternary gravels thicken significantly east of this location, indicating sudden drop in basement rock. URS (2003a) believe that this subsurface feature may be associated with the north-south striking Waimate Fault. On the Waitaki River southern bank at Black Point, the basement rock is very shallow (about 8 m deep) and there is also a ridge of greywacke which projects into the Waitaki River bed from the north side. These two geological features probably impede most of the groundwater flow and separate the LW catchment into two distinct groundwater basins (Brown, 2000). The Holocene alluvial deposits, mainly gravel, are generally confined to the present river flood channel of the Waitaki River (Figure 5-2). They are generally less than 10 m thick. Along almost the entire length of the river, the flood channel is bordered by Pleistocene terraces. The Pleistocene terraces are notably absent in two locations where the Holocene river flood channel broadens: 1. On the north bank of the Waitaki River between Station Peak and just to the east of the Penticotico Stream, the river appears in the early Holocene to have undergone a major lateral excursion into the valley side, eroding most Pleistocene terrace features and depositing 5-10 m of gravels up to the base of the adjacent greywacke hills. This thin layer of Holocene deposits is underlain in this area by a deep trench feature infilled with older and weathered Pleistocene gravels (Kurow trench). Holocene gravels in this location are overlain in places by up to 1.2 m of silt and clayey overbank deposits, suggesting that the area may have become a wetland backwater. The wetlands have been largely drained over the past 150 years for farming purposes. 2. On the south bank of the Waitaki River between the Maerewhenua River and Black Point a lateral excursion of the river has eroded nearly all of the Pleistocene deposits leaving only a few remnant terraces along the edge of the hills. In this area bedrock is relatively shallow and Holocene gravels (generally less than 7 m thick) directly overlie Paleogene–Neogene age strata.
5.2 Groundwater wells Wells are not only valuable as a source of water, but also as a source of important hydrogeological information. Environment Canterbury’s Wells Database contains records of more than a thousand wells drilled in the study area (Figure 5-3), of which 350 wells have lithological logs (Figure 5-4). Remarkably, about two-thirds of the active wells are no deeper than 10 m, and more than three-quarters are no deeper than 20 m (Figure 5-5).
Environment Canterbury Technical Report 26 Lower Waitaki hydrogeology
Figure 5-2: Hydrogeological map showing bedrock elevation in metres above mean sea level (data sourced from URS, 2003a)
Environment Canterbury Technical Report 27 Lower Waitaki hydrogeology
Figure 5-3: Drilled wells in the study area (data sourced from Environment Canterbury’s Wells Database in September 2014)
28 Environment Canterbury Technical Report Lower Waitaki hydrogeology
Figure 5-4: Wells with lithological logs in the study area (data sourced from Environment Canterbury’s Wells Database in September 2014)
Environment Canterbury Technical Report 29 Lower Waitaki hydrogeology
Figure 5-5: Depth of active wells (data sourced from Environment Canterbury’s Wells Database in September 2014)
30 Environment Canterbury Technical Report Lower Waitaki hydrogeology
5.3 Hydrogeological parameters The aquifer system in the study area is heterogeneous and anisotropic, meaning that its hydraulic properties vary from one place to another and in different directions at the same point. There are very limited pumping tests in the area, but URS (2003a) were able to provide reasonable estimates of the aquifer characteristics. They estimated permeability of the Holocene deposits to be in the range of 600-1,730 m/day and the permeability of the Pleistocene strata to be in the range of 43-86 m/day. However, when calibrating their model, URS (2003b) used permeability values of 430-1,300 m/d and 80-120 m/d for the Holocene and Pleistocene aquifers, respectively. They also estimated the specific yield ( ) of the Holocene and Pleistocene aquifers at 0.23 and 0.27, respectively.
𝑆𝑆𝑦𝑦 5.4 Groundwater levels and flow directions
5.4.1 Concepts Water flows from high potential to low potential positions. The potential of water at a certain point is determined by the relative water level (head). In unconfined aquifers, groundwater level is represented by the water table. In confined aquifers, the groundwater level is represented by piezometric surfaces. Water level contour maps (also known as piezometric maps) present groundwater levels in a similar way as topographic contour maps express land elevations. Groundwater maps use mean sea level as a reference level (datum), just like topographic maps. Normally, piezometric maps are drawn using concurrently collected groundwater level data from wells, springs and other water related features. Groundwater level data collection for piezometric mapping purposes is known as a piezometric survey. Groundwater flow direction can be inferred from piezometric map. Groundwater flows down hydraulic gradient (i.e. from higher value piezometric contours lines to lower value contour lines). The flow direction in isotropic aquifers (i.e. aquifers in which properties are the same in all directions) is perpendicular to the groundwater level contour lines (piezometric lines).
5.4.2 Groundwater flow in the study area No piezometric survey has been undertaken for the entire study area as defined in Section 4.1. However, there are useful groundwater level data in Environment Canterbury’s Wells Database and published piezometric maps that can conjointly provide a good idea about the groundwater flow system and aquifer properties in the study area. This includes the South Canterbury Catchment Board map (SCCB, 1979) (Figure C-1), URS (2003a) map (Figure C-2), Scott et al. (2012) map (Figure C-3), and Wilson and Graham (2014) map (Figure C-4). I used groundwater level data from Environment Canterbury’s Wells Database and combined it with surface water data and the URS (2003a) groundwater level map to produce a piezometric map for long- term average groundwater conditions in the study area (Figure 5-6). This map is generally in agreement with previous maps (Figure C-1 through Figure C-4). This gives me confidence in its representativeness of average conditions in the system. The map in Figure 5-6 suggests that the groundwater flow system has not undergone big changes over the years despite the reported groundwater level changes (mainly rises) in some areas. The map suggests that groundwater flow direction in the main valley and floodplain is similar to the river, from west to east. In valleys of the main tributaries of the Waitaki River, the groundwater similarly follows the direction of the waterway with which it is associated. A higher resolution local-scale piezometric map for Elephant Hill is presented in (Etheridge, 2015).
Environment Canterbury Technical Report 31 Lower Waitaki hydrogeology
Figure 5-6: Piezometric map for long-term average groundwater conditions
Environment Canterbury Technical Report 32 Lower Waitaki hydrogeology
5.5 Groundwater recharge and discharge The piezometric map presented in Figure 5-6 enables the identification of recharge sources and discharge zones. The Quaternary aquifer system in the study area receives recharge from rain and excess irrigation water. Recharge from rain and recharge from irrigation are jointly referred to as land surface recharge (LSR). URS (2003a) calculated LSR over non-irrigated land to be about 54 mm/y and around 902 mm/y in border dyke irrigation areas (Table 4-1). Given that most irrigated land is on elevated terraces, it is understandable that part of the irrigation recharge water will end up as terrace flow (Figure 5-7). As a result, wetlands and springs emerge in the study area on the Holocene terrace at the toe of the Pleistocene terraces (Figure 5-6).
(a) (b)
Figure 5-7: Effect of terraces on groundwater flow (sourced from Winter et al., 1998) (a) In broad river valleys, small local groundwater flow (b) In coastal terrain, small local groundwater systems associated with terraces overlie more flow cells associated with terraces overlie regional groundwater flow systems. Recharge more regional groundwater flow systems. In from flood waters superimposed on these the tidal zone, saline and brackish surface groundwater flow systems further complicates the water mixes with fresh groundwater from hydrology of river. local and regional flow systems.
In addition to LSR, there is a large potential for surface waterways and irrigation races to recharge the Quaternary aquifer. However, this is not evident in the piezometric map (Figure 5-6). The rivers on the southern bank of the Waitaki River lose water to the aquifer and that water may re-emerge down further stream as springs or seeps. It may also flow below the ground and discharge into the Waitaki River. For example, at low flow the Maerewhenua River is dry near the Earthquake Bridge, but it re-emerges downstream, several kilometres before the confluence with the Waitaki River, where limestone deposits are found (Chater, 1998). Duntroon springs, which flow directly to the Waitaki River, are most likely sourced from the Maerewhenua River. The Kurow, Otiake and Otekaieke river valleys have different geology to the valley of the Maerewhenua River, so groundwater there may not necessarily re-emerge before it reaches the Waitaki River. Any groundwater present in the Awakino River catchment is likely to re-emerge before the gorge, although previous measurements have suggested some losses to groundwater between the confluence of the east and west branches and a measuring point at SH83.
5.6 Effects of topography on groundwater flow The existence of terraces in the study area influences the groundwater flow system. According to Winter et al. (1998), if terraces are present in an alluvial valley, local groundwater flow systems may be associated with each of them, and lakes and wetlands may be formed because of this source of water. At some locations, such as at the valley wall and at the river, local and regional groundwater flow systems may discharge in close proximity. Furthermore, in large alluvial valleys, significant down-valley components of flow in the streambed and in the shallow alluvium also may be present (Figure 5-7a). In coastal areas, local-, intermediate- and regional-scale flow systems can also coexist (Figure 5-7b). As a result, groundwater will feed into streams which act like drains. The groundwater level map presented in Figure 5-6 shows that the Waikākahi Stream and Whitneys Creek act as drains to the aquifer in the coastal plain area.
Environment Canterbury Technical Report 33 Lower Waitaki hydrogeology
5.7 Groundwater flow velocity, travel time and residence time Actual groundwater flow velocity can be calculated from the following equation:
= η Equation 5-1 𝐾𝐾 𝑖𝑖 where is the𝑣𝑣 groundwater velocity in m/d, is the aquifer permeability in m/d, is the hydraulic gradient and η is the effective porosity. Both and η are dimensionless (i.e. they do not have units). 𝑣𝑣 𝐾𝐾 𝑖𝑖 I estimated the average hydraulic 𝑖𝑖gradient ( ) from the map presented in Figure 5-6 at around 3.75 x 10 ³ (i.e. 0.00375). Solving the above equation using typical values for the Holocene aquifer ( = 1,150 m/d and η = 0.25) gives groundwater flow𝑖𝑖 velocity of 17.25 m/d, which is extremely high flow velocity for⁻ groundwater. Solving the equation using typical values for the Middle-Late Pleistocene𝐾𝐾 aquifer ( = 65 m/d and η = 0.25) gives groundwater velocity of 0.975 m/d, which is very high flow velocity for groundwater. 𝐾𝐾 The travel time between any two points along a groundwater flow line can be calculated using Equation 5-2:
= Equation 5-2 𝑙𝑙 where is 𝑡𝑡groundwater travel time in days and is the distance between the two points in metres. 𝑣𝑣 The above𝑡𝑡 -estimated groundwater flow velocities𝑙𝑙 indicate that in most circumstances changes in land use over the recognised aquifers will likely result in measurable change to groundwater quality in vicinity of receiving surface waters within a relatively short time period of 1–5 years. The slower the movement of groundwater the longer is its travel time and residence time in the aquifer (i.e. the older it is) (Figure 5-8). van der Raaij (2007) reported that a sample collected from Well J40/0620 to the northeast of Ikawai was found to be tritium-free, indicating mean groundwater age in excess of 110 years. Well J40/0620 is 89 m deep and has artesian head. The relatively old age of such groundwater may be due to any combination of the following conditions: 1. the aquifer is recharged slowly, which would make it prone to over-abstraction 2. the well’s screen is situated near an impervious boundary, where groundwater flow velocity approaches zero, so water is stagnant in this part of the aquifer 3. the sample is collected from a relatively deep, regional flow system where groundwater flow paths are longer and groundwater flow velocities are relatively slow (see Figure 5-8 for illustration).
5.8 Groundwater-surface water interaction Most often, groundwater and surface water constitute a single, integrated resource. Groundwater can provide flow to surface waterways or gain water from them. Figure 5-9 schematically shows possible relationships between groundwater, wetlands and lakes and Figure 5-10 shows possible relationships between groundwater, rivers and streams. The relationship between surface water and groundwater can be determined from piezometric maps as briefly explained in Figure 5-11. In the study area, groundwater and surface water systems exchange flow nearly continuously. For example, Heller and Williamson (2004) estimated that half of the groundwater within the Glenavy basin ends up in the Waitaki River and the other half flows directly out to sea. The rivers may lose water to groundwater, but that water either re-emerges lower downstream or flows directly towards the Waitaki River.
5.8.1 Waitaki River and main tributaries The shape of the contour lines in groundwater level map presented in Figure 5-6 suggest that the groundwater in the Quaternary aquifer loses water to the Waitaki River almost along the entire course of the river in the study area, i.e. the Waitaki River is a regional groundwater sink in the area. This process is controlled by gravity that drains the groundwater from the elevated terraces into the river that occupies the lowest topographic position in the catchment (Figure 5-7).
34 Environment Canterbury Technical Report Lower Waitaki hydrogeology
Figure 5-8: Varying groundwater flow paths and travel traveopltimes from points of recharge to points of discharge in the groundwater system (from Winter et al., 1998)
Environment Canterbury Technical Report 35 Lower Waitaki hydrogeology
Wetlands Lakes
(a) Fens (d) Gaining lake Fens are wetlands that commonly receive Groundwater level is higher than the lake water groundwater discharge; therefore, they receive level. Hence, water moves from the shallow a continuous supply of chemical constituents aquifer into the lake. dissolved in the groundwater.
(b) Riverine wetlands (e) Losing lake Many wetlands are present along streams, Groundwater level is lower than the lake water especially slow-moving streams. Although level. Hence, water moves from the lake into these riverine wetlands commonly receive the shallow aquifer. groundwater discharge, they are dependent primarily on the stream for their water supply.
(c) Bogs (f) Groundwater flow through lake Bogs are wetlands that occupy uplands or Groundwater level is higher than the lake water extensive flat areas, and they receive much of level in one side and lower in the other side. their water and chemical constituents from Hence, part of the groundwater moves in the precipitation. They have the potential to affect shallow aquifer from one side to the other groundwater quality. through the lake.
Figure 5-9: Possible relationships between groundwater, wetlands and lakes (sourced from Winter et al., 1998)
36 Environment Canterbury Technical Report Lower Waitaki hydrogeology
(a) Gaining stream (b) Losing stream Gaining streams receive water from the Losing streams lose water to the groundwater groundwater system. system.
(c) Disconnected stream (d) Stream bank storage Disconnected streams are separated from If stream levels rise higher than adjacent the groundwater system by an unsaturated groundwater levels, stream water moves into zone. the stream banks as bank storage.
Figure 5-10: Possible relationships between groundwater, rivers and streams (sourced from Winter et al., 1998)
(a) Gaining stream (b) Losing stream Gaining streams (e.g. Figure 5-10a) can be Losing streams (e.g. Figure 5-10b) can be identified from water table contour maps identified from water table contour maps because the contour lines point in the because the contour lines point in the upstream direction where they cross the downstream direction where they cross the stream. stream.
Figure 5-11: Method for determing stream-groundwater relationship using groundwater level contour maps (also known as piezometric maps) (sourced from Winter et al., 1998)
Environment Canterbury Technical Report 37 Lower Waitaki hydrogeology
URS (2003a) used groundwater level and surface water flow data to determine gaining and losing surface water features in the study area (Tables 5-2 and 5-3, respectively). Table 5-2 suggests that overall groundwater loses an average of about 229 mcm/y to surface water, whereas Table 5-3 suggests that overall groundwater gains an average of about 175 mcm/y from surface water in the area. Hence, LW groundwater systems average net loss to surface water can be estimated at 54 mcm/y, the equivelant to 1,712 L/s, which represent only about 0.48% of the river’s flow sourced from the upper Waitaki catchyment. Groundwater loss to the Waitaki River is in line with the conceptualisation of the Waitaki River being the main hydrological sink feature for both grounwater and surface water in the study area. The shape of the groundwater level contours around the river shown in Figure 5-6 clearly imply that groundwater feeds the river along its course in the LW area, especially below Black Point. Additional information on surface water flows, losses and gains is provided in (Gabites and Horrell, 2005).
5.8.2 Coastal streams Whitneys Creek and Waikākahi Stream are small waterways which receive little runoff from the rolling hills in their respective catchments. Except for periods following significant rainfall events, they are primarily sourced from shallow groundwater. The Waikākahi Stream joins the Waitaki River about 4 km before its end but Whitneys Creek discharges directly to the Pacific Ocean about 2 km north of the Waitaki River Mouth (Figure 1-1). Although these two waterways are primarily groundwater-fed, they may lose water into the aquifer in some places and at sometimes. The data available are coarse and do not allow site specific assessment of the situation at these two coastal streams. However, I believe that both streams are connected to groundwater that occurs to the south of the surface water divide (i.e. within the LW area), and they will not be influenced by activities happening in the SCCS area. Table 5-2: Gaining stream and river stretches in the study area (data sourced from URS, 2002b)
Gain to surface water from groundwater
River stretch Min Max Median Mean Mean (m³/s) (m³/s) (m³/s) (m³/s) (mcm/y)
Kurow River valley gravels 0.13 1.70 0.38 0.51 16.083
Otiake River valley gravels 0.13 1.70 0.40 0.54 17.029
General seepage from terrace gravels bordering river between Kurow and Otekaieke 1.00 1.00 1.00 1.00 31.536
Otekaieke River valley gravels 0.13 1.90 0.67 0.85 26.806
From gravels (North Bank) to spring fed streams at Wainui Station 0.96 1.50 1.21 1.16 36.582
From gravels (North Bank) to spring fed streams between Penticotico Stream and Stone Wall 0.96 1.80 1.21 1.22 38.474
Maerewhenua River valley gravels 0.26 0.26 0.26 0.26 8.199
General seepage from terrace gravels bordering river between Otekaieke and Black Point 1.00 1.00 1.00 1.00 31.536
From gravels due to narrowing of valley above Stone Wall 0.22 0.22 0.22 0.22 6.938
General seepage from terrace gravels bordering river between Ferry Road and SH1 0.50 0.50 0.50 0.50 15.768
38 Environment Canterbury Technical Report Lower Waitaki hydrogeology
Table 5-3: Losing stream and river stretches in the study area (data sourced from URS, 2002b)
Loss from surface water to groundwater
River stretch Min Max Median Mean Mean (m³/s) (m³/s) (m³/s) (m³/s) (mcm/y)
Waitaki River at Kurow to Holocene gravels 0.66 0.66 0.660 0.660 20.814
Kurow River to Kurow River valley gravels 0.13 1.70 0.400 0.510 16.083
Otiake River to Otiake River valley gravels 0.13 1.70 0.420 0.540 17.029
Waitaki River to Holocene gravels below Station Peak 1.90 2.90 2.400 2.300 72.533
Otekaieke River to Otekaieke River valley gravels 0.14 1.90 0.710 0.850 26.806
Penticotico River to Holocene gravels 0.00 3.00 0.030 0.060 1.892
Maerewhenua River to Maerewhenua River valley gravels 0.26 0.26 0.260 0.260 8.199
Waitaki River to Holocene gravels below Black Point 0.22 0.22 0.220 0.220 6.938
Awamoko River to Holocene gravels 0.00 0.20 0.040 0.070 2.208
Elephant Hill River to Holocene gravels 0.00 0.20 0.030 0.050 1.577
Waikākahi Stream to Holocene gravels 0.00 0.15 0.007 0.018 0.568
Relatively deep (50-60 m) wells in the Whitneys Creek area are claimed to be tapping Early Pleistocene strata (upper part of the Kowai Formation/Cannington Gravel) (e.g. McCabe, 2013; ESC, 2014). There is no solid evidence to support this assumption. The wells are very likely screened in the Quaternary aquifer. It is impossible to upper Kowai Formation material from Middle-Late Pleistocene sediments using lithological well log data alone. Differentiation between these two geological units requires micro- paleontological (microfossils) or isotope analysis (e.g. tritium and carbon-14). However, and most importantly, the two aquifer units are hydrogeologically connected, even if they belong to two different geological units. Even at such depth (50-60 m), there is potential for interaction between groundwater and surface water, e.g. in the Whitneys Creek area, depending on local hydrological conditions.
5.8.3 Wetlands, ponds and springs Many wetlands, ponds and springs in the study area are dependent on groundwater (Figure 5-9 a,b,c) There are no site-specific data to enable the determination of the relationship between each of such features and groundwater. However, I expect that some groundwater dependent systems will be impacted by any reduction in groundwater recharge that originates as leakage from irrigation races or from excess irrigation water, especially border dyke systems. The impact will have both quantity and quality dimensions. So, environmental, socio-economic and cultural effects of such happenings must be adequately investigated before encouraging any changes to the current water situation in the study area.
5.9 Groundwater use and abstraction consents Water producing wells in the study area are used for various purposes. About half these wells are used for life sustenance purposes (human and stock) and the other half is used for other economical purposes such as dairy supply and irrigation (Figure 5-12). From the numbers in Figure 5-12, groundwater is an important source of drinking water in the study area (more than one quarter of the wells are used for public and domestic water supply). Compared to the rest of the Canterbury region, there are a small number of groundwater abstraction consents in the study area and the consented volumes are relatively small (Figure 5-13). This is due to the easier availability of surface water either to take directly or through water schemes.
Environment Canterbury Technical Report 39 Lower Waitaki hydrogeology
Figure 5-12: Active wells productive use (i.e. excluding investigations and monitoring)
Environment Canterbury Technical Report 40 Lower Waitaki hydrogeology
Figure 5-13: Types and maximum rates of consented groundwater abstraction
41 Environment Canterbury Technical Report Lower Waitaki hydrogeology
5.10 Hydrological budget and groundwater system summary The Waitaki River is the principal water resource in the LW area. On average, it receives an estimated 11,290 million cubic metres of water per year (mcm/y) from the upper Waitaki catchment through the Waitaki Dam. Average annual rainfall over the LW area is calculated at about 565 mm/y. WCWAB (2005) estimates that lower Waitaki River tributaries provide only 2% of the river’s total flow (c. 230 mcm/y), the equivalent to about 25% of the total rainfall over the LW area (230 mcm/y ÷ 913 mcm/y). URS (2003a) estimated groundwater recharge from rain at about 54 mm/y (c. 9.55%). Hence, effective15 rainfall over the area can be estimated at 34.55% (25% + 9.55%). Subsequently, average actual evapotranspiration from non-irrigated land can be calculated at 65.45%, making the area’s climate dry as described in Section 4.3.
Figure 5-14: Schematic diagram of the lower Waitaki Valley groundwater flow system (not to scale) (from URS, 2003a)
Groundwater in the study area mainly occurs in Holocene and Middle-Late Pleistocene alluvial deposits. Figure 5-14 schematically shows part of the groundwater system in the area. The Holocene deposits are more permeable than the Pleistocene deposits. Both stratigraphical units of the lower Waitaki aquifer system are hydraulically connected and they receive recharge from rain. The Pleistocene aquifer receives additional recharge from irrigation returns. Springs and wetlands occur on the Holocene terrace at the toe of the Pleistocene terraces. There is a very high degree of interconnectivity between surface water, the Holocene aquifer, and the Pleistocene aquifer. As a matter of fact, the three systems are one, but water flows fastest in rivers and streams (metres per second), relatively very fast in the Holocene aquifer (metres per hour), and relatively fast in the Pleistocene layers (metres per day). Typically, groundwater flows in the order of centimetres to millimetres per day, or even slower. Aquifers in the study area occur in limited places, principally in the Quaternary river valley and terraces. Groundwater flow in the Quaternary aquifer is relatively fast. Hence, groundwater will be relatively quickly affected by land use changes, especially in terms of its quality. Even in areas where groundwater
15 Effective rainfall is the amount of rainfall that replenishes surface water and groundwater resources.
Environment Canterbury Technical Report 42 Lower Waitaki hydrogeology
does not exist as a resource, water flow in soil has the potential to affect surface water and groundwater quality down-gradient. According to Winter et al. (1998), there are three possible pathways along which water from precipitation can move into mountain streams (Figure 5-15). Between periods of rain, most inflow to streams is from groundwater (Figure 5-15 A). During periods of rain, the water table will rise to the land surface and flow to the stream is from groundwater, soil water, and overland runoff (Figure 5-15 B). In arid areas where soils are very dry and plants are sparse, infiltration is impeded and runoff from precipitation can occur as overland flow (Figure 5-15 C). This concept is particularly important in places like Elephant Hill, where soil is almost absent and no aquifer underlies the area.
43 Environment Canterbury Technical Report Lower Waitaki hydrogeology
Figure 5-15: Flow of water from precipitation to streams (from Winter et al., 1998)
Environment Canterbury Technical Report 44 Lower Waitaki hydrogeology
6 Conclusion Groundwater in the LW area occurs in Holocene river gravel and Middle-Late Pleistocene alluvial deposits. Irrigation system losses and application returns augment the limited rainfall infiltration and the aquifer system. Groundwater contribution to the lower Waitaki River flow is estimated at 54 mcm/y, which represents merely 0.48% of the river’s total flow. The aquifer system is strongly connected to the surface water system, especially in the Holocene river gravel area. Wetlands and springs are found on the Holocene surface at the toe of the Pleistocene terraces; many of these wetlands and springs have emerged as a result of increased recharge from irrigation. Groundwater also helps maintain soil moisture levels during the dry summer months. Land use changes can affect groundwater and surface water quantity and quality relatively quickly. Local water table mounding and increased spring and seepage flow can occur as a result of increased irrigation. On the other hand, more efficient irrigation systems may cause wetlands to shrink and spring flows to drop. Groundwater quantity and quality aspects must be considered carefully in all environmental management plans.
7 Acknowledgements I would like to thank Nicole Calder-Steele for her help with data compilation for the research report, Carl Hanson, Philippa Aitchison-Earl, Nicola Kaelin, Marta Scott, Helen Shaw and Kelly Palmer for undertaking internal review of the report and providing valuable review comments. I also acknowledge the useful review of Tom Heller of Environmental Associates Ltd.
8 References AITCHISON-EARL, P. 2005. Deep aquifer review: Timaru-Waitaki River. Environment Canterbury Report No. U05/02. Environment Canterbury. AITCHISON-EARL, P. 2012. Geological re-coding of the Kowai Formation (Cannington Gravels) in South Canterbury wells. File note C14C/1729. Environment Canterbury. AITCHISON-EARL, P., SCOTT, D. & SANDERS, R. 2004. Groundwater allocation limits: guidelines for the Canterbury Region. Environment Canterbury Report No. U04/02. BARRELL, D. J. A. 2008. Geologic assessment of water bore records: Timaru-Pleasant Point- Geraldine areas, South Canterbury. GNS Sciences Consultancy Report 2008/089. BARRELL, D. J. A. & STRONG, D. T. 2012. Geological contours for groundwater modelling, South Canterbury. GNS Science Consultancy Report 2012/245. BOFFA MISKELL LTD. 2002. Project Aqua-terrestrial ecology and wetlands report, prepared for Meridian Energy Limited. BROWN. 2000. Groundwaters of the Canterbury region. (Revised by JH Weeber, May 2002). Environment Canterbury Report No. R00/10. BROWN, L. J. & SOMERVILLE, M. J. 1980. Water well data, South Canterbury-North Otago. New Zealand Geological Survey Report. New Zealand Geological Survey. BURBERY, L. & VINCENT, C. 2009. Hydrochemistry of south Canterbury Tertiary aquifers. Environment Canterbury Report No. R09/34. Environment Canterbury. CANTERBURY MAYORAL FORUM. 2009. Canterbury Water Management Strategy, strategic framework - November 2009, with updated targets, provisional July 2010. Canterbury Water. CHATER, M. 1998. Maerewhenua River, low flow data investigation, Canterbury Regional Council report U99/12.: Canterbury Regional Council.
45 Environment Canterbury Technical Report Lower Waitaki hydrogeology
CLARKE, G. 2014. The current water quality state of lakes in the Waitaki Catchment. Environment Canterbury report (in press). Environment Canterbury. COX, S. C. & BARRELL, D. J. A. 2007. Geology of the Aoraki area. Institute of Geological and Nuclear Sciences 1:250 000 geological map 15. Lower Hutt: Institute of Geological and Nuclear Sciences. DUFF, K. 2014. Lower Waitaki surface water report (unpublished). Environment Canterbury. ENVIRONMENT CANTERBURY. 2015. Canterbury Land and Water Regional Plan-Volume 1, December 2015. ENVIRONMENT CANTERBURY. 2013. Project brief for consultants-recharge, discharge mechanisms and flow dynamics for deep groundwater in South Canterbury. Environment Canterbury. ENVIRONMENT CANTERBURY. 2014a. Canterbury Land and Water Regional Plan. Environment Canterbury. ENVIRONMENT CANTERBURY. 2014b. Technical overview of the current status of the lower Waitaki River catchment in 2014. Environment Canterbury. ESC. 2014. Assessment of effects of variation of resource consent CRC141963 (Increase rate of groundwater take from bores CB19/5017 and CB19/5020, and change depth of take for Bore CB19/5017). Assessment of effects on other groundwater users and on surface water resources. Prepared for Babbage Consultants Limited. Timaru: ENVIRONMENTAL CONSULTANCY SERVICES LIMITED. ETHERIDGE, Z. 2015. Elephant Hill nitrogen load fate and transport assessment. Unpublished internal technical memorandum to Kelly Palmer and Helen Shaw dated 26/5/2015. Christchurch: Environment Canterbury. EZZY, T. 2011. Cannington gravel aquifer: literature review for the purpose of defining future investigation priorities. Environment Canterbury memorandum WATE/INGW/QUAN/PARE/1. FORSYTH, P. J. 2001. Geology of the Waitaki area. Lower Hutt, New Zealand. FORSYTH, P. J. 2004. South Canterbury groundwater geology. Environment Canterbury Report No. U04/62. GNS Client Services Report No. 2004/61. Prepared for Environment Canterbury by Institute of Geological & Nuclear Sciences Limited. Lower Hutt. GABITES, S. & HORRELL, G. 2005. Seven day mean annual low flow mapping of the tributaries of the Waitaki River. Report No. R05/16. Christchurch. GAGE, M. 1957. The geology of Waitaki Subdivison. New Zealand Geological Survey. New Zealand Department of Scientific and Industrial Research. GPF. 2002. Private irrigators mitigation study-Project Aqua, prepared for Meridian Energy Limited. Glasson Potts Fowler. GRAY, D. 2014. Upper Waitaki catchment flows, water quality and ecology: state and trend (in press). Environment Canterbury. HAMILTON, D. J. & ELLIOT, G. L. 2000. Lower Waitaki Irrigation Scheme: 25 years on. Conference on Engineering in Agriculture. Lincoln University. HELLER & WILLIAMSON. 2004. Hydrogeological assessment of groundwater quantity in the Waitaki Catchment. Ministry for the Environment. LANDCARE RESEARCH. 2014. S-Map. LOWER WAITAKI SOUTH COASTAL CANTERBURY ZONE COMMITTEE. 2011. Lower Waitaki South Coastal Canterbury Zone Implementation Programme. Environment Canterbury Report No. U03/38. Environment Canterbury. MCCABE, B. 2013. Oceania Dairy Ltd-Application for consents to install and use groundwater bores & to take and use. Groundwater assessment of environmental effects. Volume 3 for Oceania Dairy Ltd. Auckland: Babbage. MORGAN, M., BIDWELL, V., BRIGHT, J., MCINDOE, I. & ROBB, C. 2002. Canterbury strategic water study. Prepared for MAF, ECan, MfE (Lincoln Environmental Report No 4557/1, August 2002). Lincoln Environmental. Lincoln University.
Environment Canterbury Technical Report 46 Lower Waitaki hydrogeology
NIWA. 2002. Project Aqua: Lower Waitaki River geomorphology and sediment transport, prepared for Meridian Energy Limited. NZGS. 1988. Lower Waitaki power investigations-summary and assessment of engineering geological investigations up to December 1987. Lower Hutt: New Zealand Geological Survey. OPUS. 2003. Waitaki flood plain groundwater level data. ORC. 1993. North Otago groundwater investigations-Volume 1: Main Report. Otago Regional Council. ORC. 2000. Papakaio aquifer Enfield Basin status report. Otago Regional Council. ORC. 2004. Papakaio aquifer report: outside of the Enfield Basin North Otago. Otago Regional Council. POULSEN, D. 2013. The hydrogeological significance of loess in Canterbury. Environment Canterbury technical report No. R13/60. Environment Canterbury. R D KEATING & ASSOCIATES & BOFFA MISKELL. 2002. Project Aqua: assessment of soil and productive potential values, prepared for Meridian Energy Limited. REKKER, J. 2014. Technical note on nitrate dilution with MAR and parallels with other irrigation schemes. Memo to Bob Bower and Brett Sinclair, Environment Canterbury. Project No. 1478110257. Dunedin: Golder Associates. SCCB. 1979. Waimate County groundwater survey. Plan No. W52/4.: South Canterbury Catchment Board. SCOTT, D. 2004. Groundwater allocation limits: land-based recharge estimates. Environment Canterbury Technical Report U04/97. Environment Canterbury. SCOTT, D. 2013. Understanding Kowai Formation recharge. Memorandum to Philippa Aitchison-Earl, 12 December 2013. Environment Canterbury reference C14C/025394. Environment Canterbury. SCOTT, G. L. 1977. Lower Waitaki groundwater investigations. Unpublished report prepared for Ministry of Works and Development. SCOTT, L. 2014a. Review of Environment Canterbury’s groundwater oxygen-18 data. Environment Canterbury technical report (in press). Environment Canterbury. SCOTT, L., HANSON, C. & CRESSY, R. 2012. Groundwater quality investigation of the mid-Waitaki valley. Environment Canterbury Report No. R12/71. Environment Canterbury. SCOTT, M. 2014b. Waitaki project area - groundwater quality Part 1 - Upper Waitaki (in press). Environment Canterbury. SCOTT, M. 2014c. Waitaki project area - groundwater quality Part 2 - Lower Waitaki (in press). Environment Canterbury. SCOTT, M. & HANSON, C. 2013. Risk maps of nitrate in Canterbury groundwater. Environment Canterbury report. Environment Canterbury. SKM. 2004. Waitaki Catchment groundwater information. Report prepared by Sinclair Knight Merz for the Ministry for the Environment. ME Report No 569. TAYLOR, MCCLINTOCK & HARRIS. 2014. Upper Waitaki Social Economic Assessment of scenarios vs Current State (in press). TAYLOR BAINES AND ASSOCIATES & HARRIS CONSULTING 2014. Upper Waitaki Social Economic Assessment of scenarios vs Current State. THORLEY, M., AITCHISON-EARL, P., RITSON, J. & HAYWARD, S. 2008. Proposed additions to South Canterbury groundwater allocation zones. Environment Canterbury technical report No. R08/42. Environment Canterbury. THORLEY, M. & ETTEMA, M. 2007. Review of water allocation limits for the South Canterbury downlands. Environment Canterbury technical report No. U07/09. TIPA. 2013. Cultural values and water management issues for a selection of South Canterbury catchments (in presss). TONKIN AND TAYLOR. 2002. Project Aqua-geotechnical and engineering geology investigation feasibility study, Volume 3 of 3, prepared for Meridian Energy Limited. UPPER WAITAKI ZONE COMMITTEE. 2012. Upper Waitaki Zone Implementation Programme. Environment Canterbury.
47 Environment Canterbury Technical Report Lower Waitaki hydrogeology
URS. 2002a. Project Aqua - assessment of effects on geology and seismicity. Prepared for Meridian Energy Ltd. URS. 2002b. Project Aqua-water balance, prepared for Meridian Energy Ltd. URS. 2003a. Project Aqua-hydrogeological assessment of effects. Prepared for Meridian Energy Ltd. Volume 1 of 2 - main report. URS. 2003b. Project Aqua-hydrogeological assessment of effects. Prepared for Meridian Energy Ltd. Volume 2 of 2 - appendices. URS. 2006. North Bank Tunnel Concept hydrogeological assessment of effects. Prepared for Meridian Energy Limited (Appendix 17 of AEE for NBTC consent application). VAN DER RAAIJ, R. 2007. Groundwater age-dating in South Canterbury and Orari areas. GNS Science Consultancy Report 2007/294. WAUGH & PAYNE. 2003. Project Aqua Waitaki River Hydrology Study. WCWAB. 2005. Waitaki Catchment Water Allocation Regional Plan, prepared by the Waitaki Catchment Water Allocation Board, September 2005, incorporating amendments as directed by the High Court on 3 July 2006. Waitaki Catchment Water Allocation Board (WCWAB). WHITE, P. A., HONG, Y. S., MURRAY, D. L., SCOTT, D. M. & THORPE, H. R. 2003. Evaluation of regional models of rainfall recharge to groundwater by comparison with lysimeter measurements, Canterbury, New Zealand. Journal of Hydrology (NZ), 42, 39-64. WILSON, N. & GRAHAM, H. 2014. Survey of groundwater levels and river flows across South Coastal Canterbury (in press). Environment Canterbury. WINTER, T. C., HARVEY, J. W., FRANKEM, O. L. & ALLEY, W. M. 1998. Ground water and surface water a single resource. Denver, Colorado: United States Geological Survey. ZAROUR, H. 2008. Groundwater resources in the Manawatu-Wanganui Region: technical report to support policy development. Palmerston North, New Zealand: Horizons Regional Council. Report number: 2008/EXT/948.
Environment Canterbury Technical Report 48 Lower Waitaki hydrogeology
49 Environment Canterbury Technical Report Lower Waitaki hydrogeology
Appendix A Rainfall calculations maps
Environment Canterbury Technical Report 50 Lower Waitaki hydrogeology
Figure A-1: Isohyetal map for calculating total and average rainfall over the study area (Data sourced from NIWA’s Virtual Climatic Stations (VCS) network. Values in zones denote average annual rainfall in mm)
Environment Canterbury Technical Report 51 Lower Waitaki hydrogeology
Figure A-2: Thiessen polygons map for calculating total and average rainfall over the study area (Data sourced from NIWA’s Virtual Climatic Stations (VCS) network. Values in polygons denote average annual rainfall in mm)
52 Environment Canterbury Technical Report Lower Waitaki hydrogeology
Appendix B Subdivision of the Quaternary and QMAP nomenclature
Environment Canterbury Technical Report 53 Lower Waitaki hydrogeology
Subdivision of the Quaternary and QMAP nomenclature system (Adapted from Zarour, 2008)
Most of the LW groundwater potential occurs in Late Quaternary deposits. Hence, it is particularly important to understand the nomenclature used for this period, especially with respect to GNS’s Quarter million Map Project (QMAP). The QMAP programme is intended to improve knowledge of the geology of New Zealand by mapping and exploring relationships between rock types and their geological origins. Additional information on this initiative is available from GNS’s website16. Throughout the Pliocene17-Pleistocene18 time, the climate of the Earth has been changing with increasing amplitude. Alternating warm and cool periods in the Earth's paleoclimate, deduced from oxygen isotope data reflecting temperature curves derived from data from deep sea core samples, represent distinct marine isotopic stages (MIS), which is also referred to as oxygen isotope stages (OIS). Each stage represents a period of higher or lower temperature, and stages follow in a cyclic pattern. The cycles were found to correspond to terrestrial evidence of glacials and interglacials. Each stage represents a glacial, interglacial, stadial19 or interstadial20. Interglacials are assigned odd numbers and glacials are given even numbers, one for each stage, starting from the present and working backwards in time. For example, the Holocene is OIS 1. The previous interglacial is OIS 5, and so forth. Exceptionally, OIS 2 - OIS 4 refer to the last glacial, because when initially interpreted OIS 3 looked like an interglacial. Stadials and interstadials are identified by a letter following the corresponding glacial or interglacial, e.g. OIS 5a, OIS 5b, etc. Quaternary units in the QMAP project are labelled in a way that alludes to its age and sometimes, its genesis. For a certain unit, the prefix ‘Q’ and the subsequent numeral indicate that it is a Quaternary unit belonging to the oxygen isotope stage indicated by the number. An appended letter (following the oxygen isotope stage number) indicates the depositional environment of the unit. The suffix ‘a’ indicates alluvial deposits, ‘m’ indicates marine or marginal marine deposits, ‘dm’ indicates active sand dunes, and so on.
16 http://www.gns.cri.nz 17 The period about 5.3 million to 2.6 million years before present. 18 The period about 2.6 million years to 12,000 years before present. 19 Period of colder temperatures during an interglacial that is not of sufficient duration or intensity to be considered a distinct glacial period. 20 A warmer period during a glacial event which is not of sufficient duration or intensity to be considered a distinct interglacial period
54 Environment Canterbury Technical Report Lower Waitaki hydrogeology
Appendix C Previous groundwater level maps
Environment Canterbury Technical Report 55 Lower Waitaki hydrogeology
Figure C-1: Piezometric map for the Quaternary aquifer system between the Pareora River and Waitaki River (Waimate County) in 1979 (SCCB, 1979)
Environment Canterbury Technical Report 56 Lower Waitaki hydrogeology
Figure C-2: Piezometric map for the lower Waitaki Quaternary aquifer prepared by URS (2003a) from groundwater levels measured on 29 June 2001
57 Environment Canterbury Technical Report Lower Waitaki hydrogeology
Figure C-3: Piezometric map for average groundwater levels in the mid-Waitaki valley by Scott et al. (2012)
Environment Canterbury Technical Report 58 Lower Waitaki hydrogeology
Figure C-4: Piezometric map for the Quaternary aquifer system in the northern bank of the lower Waitaki in August 2013 by Wilson and Graham (2014)
59 Environment Canterbury Technical Report