2. Background information
Existing data on groundwater resources in the Waitaki River Catchment is available from the following sources:
- Environment Canterbury and Otago Regional Council 'Wells' databases
- Waitaki Catchment Commission, Environment Canterbury, Otago Regional Council-commissioned water resource reports
- records from drillers operating in the area (Washingtons Drilling & Exploration, Timaru, McMillan Water Wells/Drilling Ltd, Christchurch, McNeill Drilling, Alexandra)
- individual bore owner information, which also may have current groundwater (take) consents or consent applications
- Electricity Corporation of New Zealand (ECNZ) reports for drilling and groundwater investigations commissioned over a number of years as part of the pre-feasibility studies for the Upper Waitaki Hydroelectric Scheme
- Project Aqua Assessment of Environmental Effects (predominantly the URS groundwater bore data for the Lower Waitaki)
- anecdotal information from long-term Waitaki Catchment landowners.
2.1 Previous reports
There have been various studies and reports compiled for regional councils and for Project Aqua. The information contained in existing reports mainly relates to groundwater resources in the lower Waitaki Catchment downstream of Kurow. The existing groundwater information presented in this report is attributed to the following sources:
- Sinclair Knight Merz (2000), Lower Waitaki Groundwater Investigation
- Opus (2003), Project Aqua Waitaki River Hydrology Study
- URS (2003), Project Aqua Water Balance
- URS (2003), Project Aqua Hydrogeological Assessment of Effects
- Montgomery Watson Harza (2004), Papakaio Aquifer Report: Outside of the Enfield Basin North Otago
- Sinclair Knight Merz (2004), Draft National Cost Benefit Analysis of Proposals to Take Water from the Waitaki River.
2.1.1 Upper Waitaki groundwater
ECNZ commissioned the Ministry of Works and Development to perform a number of drilling and groundwater investigations over the years (1960s to 1970s) as part of the pre-feasibility studies for the Upper Waitaki Hydroelectric Scheme. However, overall information on groundwater in the upper Waitaki is limited and this signifies that there has been little groundwater development in the area to date.
Recent drilling for groundwater has been undertaken in the general vicinity of Twizel township for domestic and irrigation use in the shallow unconfined gravel aquifer adjacent to Lake Ruataniwha (Environment Canterbury, 2004).
In recent times, a number of bores have been drilled by individual stations prospecting for irrigation water supply. Results from those bores indicate that groundwater can be encountered at significant depth in basins in the upper Waitaki Catchment (greater than 80 metres).
The Waitaki Catchment Commission (1982) states that groundwater immediately downstream of the lakes in the Mackenzie Basin tend to lie at great depths. It is unclear whether this refers to groundwater levels pre- or post-canal development. The report indicates that groundwater within the river valleys may be perched above glacial silt layers deposited in the riverbed.
2.1.2 Lower Waitaki groundwater
Groundwater investigations within the lower Waitaki have been undertaken since the late 1970s associated with the hydroelectricity generation investigations for the Lower Waitaki Scheme. Since then a number of small investigations have been undertaken by the Waitaki Catchment Commission in 1986 and the Otago Regional Council in 1993-1994. In 1999, the Otago Regional Council commissioned a major investigation of the lower Waitaki alluvium on the south side of the river. The study comprised a comprehensive bore survey, nine months of groundwater quality and level monitoring, and an assessment of groundwater quantity and sustainability (SKM, 2000).
Environment Canterbury (2002) has undertaken an extensive (mainly water quality) investigation of the Glenavy (north bank) zone of the Lower Waitaki. Since this time, additional information has been compiled and a broader study encompassing Otago Regional Council and Environment Canterbury data, including further hydraulic analyses from test pumping and test pit data, has been completed as part of the Project Aqua Assessment of Environmental Effects (URS, 2003b). Bore surveys along the left and right banks of the Waitaki River from Kurow to Black Point were also completed as part of the study.
The Otago Regional Council commissioned Montgomery Watson Harza (MWH) to report on the groundwater resources of the Papakaio Formation in 2003. MWH (2004) discusses the occurrence and allocation of groundwater in the Maerewhenua Basin.
From the above reports the indications are that by far the highest yielding and important aquifers in the lower Waitaki are the Pleistocene and Post-Glacial gravel alluvium deposits, representing the upper and lower terraces of the lower Waitaki Valley, respectively (Glenavy and Waitaki areas - Figure 1). These aquifers are used for potable household domestic and stock drinking water, dairy shed washdown and irrigation. The biggest consumptive use of groundwater on an annual basis is related to dairying (excluding dairy farm irrigation); however while only a handful of bores use groundwater for irrigation, the maximum irrigation take during summer is nearly double that of non-irrigation use.
While most bores appear capable of yields between 2-5 l/s, groundwater is secondary to surface water sourced from the various irrigation schemes for irrigation and stock water (SKM, 2000).
Other sources of groundwater in the lower Waitaki include the cemented sedimentary and limestone aquifers associated with the Papakaio Formation (URS, 2003; MWH, 2004).
2.2 Bore and spring inventory
Bore information in the upper Waitaki Catchment has been gained from the existing Environment Canterbury Wells database and has also been compiled for the historic ECNZ investigations during the 1960s and 1970s, although to our knowledge, none of these wells is currently used for the monitoring of groundwater. The ECNZ bores generally consisted of a drilled and driven 50mm galvanised pipe (Plate 1 - Figure 1). The piezometers were normally left one metre above local ground surface, with a screw cap to enable access to probe groundwater level.
There are more than 300 bores utilised in the lower Waitaki catchment, mainly centred on the lower Waitaki alluvium areas. Appendix A contains a summary of the bores contained in the URS well inventory for Project Aqua investigations, which has been obtained predominantly from existing Environment Canterbury and Otago Regional Council Wells databases.
Plate 1. Typical ECNZ piezometer in the Twizel Basin
2.3 This study
The information contained in the listings above have been utilised where applicable to derive groundwater maps and hydrogeological interpretation for the Waitaki River Catchment. In addition, a field exercise focusing mainly on the upper Waitaki Catchment was completed to gain piezometric information in areas where existing information was limited. The field data consisted of water table levels measured from various (historic) ECNZ boreholes, installed as part of the pre-feasibility studies for the Upper Waitaki Hydroelectric Scheme.
Field investigations also centred on the visual assessment of shallow water table, springs and smaller tributary river systems of the Waitaki Catchment.
