GNS Science Report 2016/13
Lovett, A.P.; White, P.A. 2016. Kā Tū Te Taniwha – Ka Ora Te Tangata: Scientific repository for the Awahou catchment, *GNS Science Report* 2016/13. XX p.
A.P. Lovett GNS Science, Wairakei Research Centre, Private Bag 2000, Taupō 3352, New Zealand
P.A. White GNS Science, Wairakei Research Centre, Private Bag 2000, Taupō 3352, New Zealand
- 1. Lake Rotorua Catchment
- 2. Awahou catchment
- 2.1 Geology
- 2.2 Hydrogeology
- 2.3 Surface water hydrology
- 2.3.1 Surface water quality sites
- 2.3.2 Surface water flow measurements
- 2.4 Consented water takes
- 3 Age dating: surface water and groundwater
- 4 Summary
- 5 Acknowledgements
- 6 References
- Figure 1.1: Surficial geology based on the 1:250,000 map of Leonard etal. (2010) and presented in Daughney et al.(2015).
- Figure 1.2: Selected cold water springs of the Rotorua groundwater production zone, with stars indicating springs utilised for municipal water supply (adapted from Pang et al., 1996).
- Figure 1.3: Groundwater catchments of Hamurana Springs, Awahou Stream and Waitetī Stream as part of the Lake Rotorua best-estimate groundwater catchment boundary (White et al., 2014).
- Figure 1.4: Groundwater catchment polygons developed for Lake Rotorua at a 1:10,000 scale (White et al., 2015).
- Figure 2.1: Geological map of the Awahou groundwater catchment showing QMAP geology (Leonard et al., 2010).
- Figure 2.2: Geological cross-section of the Awahou Catchment including: (yellow) ignimbrite, (grey) sediments, and (blue) lake (White et al., 2007).
- Figure 2.3: Location of bores within the Awahou Catchment and a 200 m buffer zone (Appendix 1).
- Figure 2.4: Geological model profile for location of bore 4007 (NGMP site 58, Pemberton) from the EBOF portal (http://data.gns.cri.nz/ebof/findLocation.jsp).
- Figure 2.5: Water levels for bore 3469 for the period 1996 – 2015 (Appendix 3, Table A 3.1).
- Figure 2.6: Water levels for bore 4007 for the period 1995 – 2015.
- Figure 2.7: Location of monitoring bores drilled at Taniwha Springs (Dewhurst, 1996) (Appendix 1, Table A 1.2). 15
- Figure 2.8: Protection zones for Taniwha Springs and Awahou Springs, as defined by Pang et al. (1996).
- Figure 2.9: Location of BOPRC (seven) and RLC (RDC) (one) surface water quality monitoring sites in the Awahou catchment.
- Figure 2.10: Summary of E.coli concentration at Gloucester Road for the period 1992 – 2013.
- Figure 2.11: Location of surface water gauging sites in the Awahou Catchment, as detailed in Table 2.6.
- Figure 2.12: Model showing streams intersecting with contour lines, and the location of gauging measurements.
- Figure 2.13: Model of baseflow, location of gaugings and location dry stream beds in the Awahou Stream and Awahou Point catchment (White et al., 2007).
- Figure 2.14: Location of the surface water flow measurements completed by BOPRC in March, 2016.
- Figure 2.15: Location and consent number for BOPRC water takes from the Awahou catchment (Hutchby, 2015).
- Figure 3.1: Location of sites in the Awahou catchment that have been sampled for estimation of groundwater age, and estimated MRT.
- Table 2.1: Drillers log for bore 4007 (NGMP site 58, Pemberton; 2015).
- Table 2.2: Summary of statistical analyses for the Pemberton bore completed as part of the national update of groundwater quality indicators (Moreau and Daughney, 2015).
- Table 2.3: Summary of positive coliform occurrences and patterns November 1989 – January 1993 (Donnison, 1993b).
- Table 2.4: Summary of measurements made at the seven BOPRC surface water quality monitoring sites.
- Table 2.5: Summary of key parameters from RLC and BOPRC water quality results from Taniwha Springs.
- Table 2.6: Summary of BOPRC and RLC flow measurements for the Awahou Stream (Hutchby, 2015; Randell, 2015).
- Table 2.7: Summary of flow measurements from Awahou Catchment, excluding those already collated from BOPRC sources (White et al., 2007).
- Table 2.8: Summary of gauging measurements completed in the Awahou Catchment by Bay of Plenty Regional Council on 7/3/2016 (Hutchby, 2016).
- Table 3.1: Summary of bore details and results from groundwater age dating in the Awahou Catchment.
- Appendix 1: Wells
- Appendix 2: Lithological logs
- Appendix 3: Groundwater Levels
- Appendix 4: Groundwater Quality
- Appendix 5: Surface water quality
- Appendix 6: ConsentS 611575
- Appendix 7: Overflow datasets
- Figure A 2.1: Summary of borelogs from the Ngōngōtaha water supply investigation (Dewhurst, 1996).
- Figure A 3.1: Summary of groundwater levels from the Ngōngōtaha water supply investigation (Dewhurst, 1996).
- Figure A 7.1: Distribution plot of spring overflow rate (10 minute data) for the time period when 10 minute data is available (4/8/2009 – 30/6/2010; and 1/7/2011 – 7/9/2011).
- Table A 1.1: Summary of key information for bores located within the Awahou catchment and 200 m buffer zone.
- Table A 1.2: Summary of bore log locations and elevations from the Ngōngōtaha water supply investigation (Dewhurst, 1996).
- Table A 2.1: Lithological logs of bores located within the Awahou Catchment and the 200 m buffer zone.
- Table A 3.1: Summary of water level information for bores located within the Awahou Catchment.
- Table A 4.1: Water quality results for NGMP site 58, Pemberton (BOPRC bore 4007).
- Table A 4.2: Analysis of water samples collected from monitoring bores during the Ngōngōtaha Water Supply Investigation (Dewhurst, 1996).
- Table A 4.3: Summary of ammonium samples collected from the supply spring during the Ngōngōtaha Water Supply Investigation (Dewhurst, 1996).
The Kā Tū Te Taniwha – Ka Ora Te Tangata Programme involves collaboration between Ngāti Rangiwewehi, GNS Science, and Bay of Plenty Regional Council. The two primary objectives of the Ka Tu Te Taniwha Programme are: to combine technical, scientific and Mātauranga-a-iwi information for the Awahou groundwater catchment into an integrated data repository and knowledge resource; and to allow Ngāti Rangiwewehi to incorporate traditional knowledge and understanding of cultural significance to inform and plan for future freshwater development in the Awahou catchment. Information provided in this report addresses the first objective, and is a collation of available scientific information for the Awahou Catchment and Taniwha Springs study area. Information provided in this report will subsequently be uploaded into a web-based portal to be freely accessible by Ngāti Rangiwewehi and project collaborators.
Awahou Stream, Taniwha Springs, Lake Rotorua, groundwater resources, vision mātauranga
The Kā Tū Te Taniwha – Ka Ora Te Tangata Programme is a collaborative project between Ngāti Rangiwewehi, GNS Science and Bay of Plenty Regional Council (BOPRC). The programme is co-funded by the project collaborators and the Ministry of Business, Innovation, and Employment through the Vision Mātauranga Connect Scheme. The programme started in November 2014 and runs until November 2016. The two primary objectives of the Ka Tu Te Taniwha Programme are to combine: technical, scientific and Mātauranga-a-iwi information for the Awahou groundwater catchment into an integrated data repository and knowledge resource; and to allow Ngāti Rangiwewehi to incorporate traditional knowledge and understanding of cultural significance to inform and plan for future freshwater development in the Awahou catchment. In order to achieve the programme objectives, the following four project tasks were developed:
document the ownership, resource consenting and land use history of the Awahou catchment;
compile a scientific repository that includes scientific data and reports relevant to the Awahou groundwater catchment and springs;
compile Mātauranga-a-iwi information including traditional and cultural knowledge about the puna from tangata whenua; and
integrate historical planning, mātauranga, and scientific data to create a tool for informing future decision making.
Various outputs will be produced for each of these tasks, and this report has specifically been developed in response to Task 2, compile a scientific repository. In this report, a range of scientific data and information relating to the Lake Rotorua catchment, Awahou catchment, and Taniwha Springs are compiled. Key information includes geological and hydrogeological descriptions of the region, identification of the catchment boundaries, results of surface water and groundwater monitoring including hydrochemistry, flow rates and age approximation. Scientific datasets compiled in this report were obtained from BOPRC, Rotorua Lakes Council (RLC) (formerly Rotorua District Council (RDC)), GNS Science, and Ngāti Rangiwewehi. In addition, a literature search was completed to identify published information relating to the Awahou catchment. The results of the database and literature searches are presented in the body of this report, and all datasets are presented in the appendices. It is intended that all datasets will subsequently be uploaded into a web-based portal that is being developed as part of the Knowledge Integration component of the programme (Task 4).
1. Lake Rotorua Catchment
Lake Rotorua is located in a near-circular caldera basin (Figure 1.1) within the Taupō Volcanic Zone (TVZ) in the Central North Island. The TVZ is a NW-SE extension of the subduction of the Pacific plate under the Australian plate, and measures approximately 60 km wide and 300 km long (Wilson et al., 1995; Spinks et al., 2005). Mesozoic greywacke forms the basement rocks in the Lake Rotorua catchment area, and is overlain by younger formations including: rhyolite ignimbrites, rhyolite and dacite lava domes, and lacustrine and alluvial sediments.
Between 2 million and 240,000 thousand years ago (ka) rhyolite lava domes were emplaced in the Lake Rotorua area and volcanic activity from the TVZ created deposition of pyroclastic units (Figure 1.1). These units included the highly welded Waiotapu Ignimbrite (710 ka), a range of variably welded, variably-altered formations of the Whakamaru Group (ca. 350 ka), including the Matahina, Pōkai, and Chimp formations (320 – 270 ka). These ignimbrites are expected to form the primary basal units for groundwater aquifers in the Lake Rotorua catchment (White et al., 2004).
The Mamaku Plateau Formation (220 – 230 ka) was created from an eruption that formed the Rotorua Caldera, and is predominantly composed of a variably-welded, variably-jointed and permeable ignimbrite (Mamaku Ignimbrite). Mamaku Ignimbrite has been reported to extend over an area from 1,200 km^2^ (Leonard et al., 2010) to greater than 3,200 km^2^ (Milner et al., 2003). Soon after the eruption, rhyolitic lavas and domes were extruded through the Mamaku Ignimbrite. A lake began to form in the ring faulted depression, and resulted in the deposition of lacustrine fine ash and pumice sediments, which are commonly referred to as Huka Group sediments (Leonard et al., 2010).
A period of relatively subdued volcanic activity occurred in the area during the period 200 – 61 ka. During this time, thin, widely-dispersed pyroclastic fall deposits were created from a number of eruptions from the Okataina Volcanic Complex (OVC), located to the east of the Rotorua Caldera. Deposition of these sediments caused periodic damming of drainage pathways which led to fluctuations in the water level of Lake Rotorua. In turn, this caused deposition of variably thick Huka Group sediments throughout the Rotorua Caldera. These layers are generally composed of loosely compacted pyroclastic pumice, breccias and tephras with a variable thickness of up to 30 m. The Rotoiti Eruption from the OVC marked an end to the period of quiet volcanic activity. It produced widespread pyroclastic deposits which included non-welded ignimbrites of the Rotoiti Formation. The 61 ka Earthquake Flat Formation is assumed to have erupted immediately following the Rotoiti Formation (Nairn and Kohn, 1973; Wilson et al., 2007) from vents south of the Lake Rotorua catchment. Earthquake Flat Formation has a maximum thickness of 120 m and includes airfall deposits and non-welded ignimbrites (Wood, 1994; Leonard et al., 2010).
The period from 61 ka to the present time has been characterised by numerous OVC eruptions causing deposition of tephra layers throughout the Lake Rotorua catchment, and emplacement of numerous rhyolite lava units. It is likely that periodic deposition of pyroclastic materials caused fluctuations in the lake level, and the current lake level is likely to have been reached within the past 2,000 – 3,000 years (White et al., 2004). During this period, pyroclastic sediments have been subsequently reworked by alluvial processes.
Figure 1.1: Surficial geology based on the 1:250,000 map of Leonard et al. (2010) and presented in Daughney et al. (2015).
1.2 Hydrological and land-use setting
Lake Rotorua has a surface area of 79 km^2^ and has a mean depth of 10.8 m (Burger et al., 2008). Approximately 66% of the total inflow to the lake originates from nine major streams, with direct rainfall, groundwater inflow, and minor surface inflows accounting for the remainder of water inflow (Hoare, 1980; White et al., 2007; Daughney et al., 2015). Surface water outflow from Lake Rotorua flows into Lake Rotoiti through the Ohau Channel, located in the northeast of the lake. Annual rainfall in the Lake Rotorua catchment is strongly affected by topography. Early studies indicated that rainfall ranged from 2,200 mm in the northwest of the lake to 1,400 mm to the southeast of the lake (Hoare, 1980). These values have been extrapolated to the wider catchment based on the relationship between rainfall and topography (Hoare, 1980; White et al., 2007; Rutherford et al., 2008). Based on a variety of climatic and water balance studies, it is estimated that approximately 47 – 58% of rainfall in the catchment infiltrates to the groundwater system (Hoare, 1980; Dell, 1982; White et al., 2004; White et al., 2007; Rutherford et al., 2008). Overland flow in the system is minor, which is supported by water budget measurements of rainfall recharge from lysimeters at the Kaharoa monitoring site (White et al., 2004; White et al., 2007).
Lake Rotorua has a deteriorating water quality which has been recognised since the 1960s. Despite initiation of remediation measures, such as removal of direct sewerage discharge to the lake in 1991, the water quality of Lake Rotorua continues to decline (White et al., 2007; Daughney et al., 2015). Land use intensification in the catchment has continued over the past 50 years. Current land use is predominantly agriculture (48%) and plantation forestry (23%) (Rutherford et al., 2009; Burger et al., 2008). Trends of increasing nitrate concentrations and mass loadings have been observed in the majority of main streams flowing into Lake Rotorua for the period 1968 – 2003 (Rutherford et al., 2009; Hoare, 1987).
Mamaku Ignimbrite is the most productive hydrogeological layer located within the Lake Rotorua catchment (Gordon, 2001). The Mamaku Ingimbrite includes three units: an upper unwelded ignimbrite that is very permeable; a welded ignimbrite which includes joints and fractures that allow groundwater to flow vertically downwards; and a lower unwelded ignimbrite unit which is the main source of groundwater for wells in the Mamaku Plateau. Surface water enters the groundwater system through the upper unwelded unit via large depressions that measure 3 m across and 10 – 30 m in depth (i.e., tomos), mostly during storm events. Horizontal groundwater flow occurs through permeable joints at depth within the unwelded and welded Mamaku Ignimbrite units. Groundwater recharge for the ignimbrite and rhyolite aquifers occurs in the upland plateau and discharges to the springs, rivers and lake (Pang et al., 1996). Water perched on unwelded zones flows down the ignimbrite dip direction and emerges from springs, and maintains baseflow in many streams (Pang et al., 1996; Rosen et al., 1998). Flow rates for cold water springs that emerge around the Lake Rotorua catchment are generally greater than 20 L/s, particularly those that emerge from the ignimbrite (White et al., 2007; Gordon, 2001; Pang et al., 1996). RLC utilise many freshwater springs for municipal supply, including Taniwha (Awahou) Springs (Figure 1.2).
Groundwater contributes to seep, spring, and stream flow, and is estimated to account for approximately 90% of the average baseflow for streams in the Lake Rotorua catchment (Hoare, 1987; White et al., 2007). The mean residence time (MRT) for water in nine streams under baseflow conditions ranged from 10 – 100 years, which indicated this water is likely to be impacted by historic land use (Morgenstern et al., 2004; Morgenstern et al., 2015). Implications of the groundwater age are that nitrate loads to Lake Rotorua are likely to increase in the future as a residue of historic land use, particularly if intensification continues to be consistent with observations of historic water quality in streams (Rutherford, 2003).
Groundwater in the ignimbrite and rhyolite aquifers within the Lake Rotorua catchment is generally of good quality and complies with potable water quality guidelines (Gordon, 2001). Water from ignimbrite aquifers, such as the Mamaku Ignimbrite, can be very soft (e.g., it has low total dissolved solids (TDS) content). The combination of a low TDS content with slightly acidic characteristics results in the water being moderately aggressive, which can cause corrosion of metallic pipes and reticulation systems. Therefore, public water supplies from groundwater are usually treated to reduce the corrosive effects.
Figure 1.2: Selected cold water springs of the Rotorua groundwater production zone, with stars indicating springs utilised for municipal water supply (adapted from Pang et al., 1996).
1.4 Catchment boundary
Surface water and groundwater catchment boundaries for Lake Rotorua have been considered in various assessments of hydrology in the catchment (White et al., 2004; White et al., 2007; Rutherford et al., 2008; White and Rutherford, 2009). The most recent “best-estimate Lake Rotorua groundwater catchment boundary” (Figure 1.3) was developed by White et al. (2014). This work improved previous estimates by using consistent datasets to define the boundary and considered uncertainty in this calculation. The 2014 boundary consisted of a surface catchment boundary that included most of the area between Kaharoa and Mamaku Township; and a groundwater catchment boundary on the Mamaku Plateau. In particular, groundwater catchments of three spring-fed streams that drain the Mamaku Plateau (Hamurana, Awahou and Waitetī) were calculated in the boundary development; these stream catchments provided a control on the location of the best-estimate groundwater boundary across Mamaku Plateau.
Figure 1.3: Groundwater catchments of Hamurana Springs, Awahou Stream and Waitetī Stream as part of the Lake Rotorua best-estimate groundwater catchment boundary (White et al., 2014).
Following delineation of the “best-estimate groundwater catchment” (White et al., 2014), BOPRC commissioned GNS Science to calculate the groundwater catchment boundaries of spring-fed streams within the Lake Rotorua catchment (White et al., 2015). A set of polygons were developed for groundwater catchments including the Awahou Springs catchment, which was reported to cover an area of 38.6 km^2^ (Figure 1.4). The Awahou Stream catchment had an estimated precipitation rate of 2.69 m^3^/s, an estimated Actual Evapotranspiration (AET) rate of 0.95 m^3^/s, and an estimated discharge of 1.74 m^3^/s (Rutherford and Palliser, 2014). In comparison, mean surface water flow from the catchment was reported to be slightly higher than this estimate 1.62 m^3^/s (White et al., 2015). The boundaries defined for the Awahou Stream catchment (i.e., White et al., 2014 and 2015) were used as a basis for the groundwater catchment boundary and associated information presented in this report.
Figure 1.4: Groundwater catchment polygons developed for Lake Rotorua at a 1:10,000 scale (White et al., 2015).
The catchment names reflect the version number of the modified boundary polygon and are represented here for version control.
2. Awahou catchment
The surface geology of the Awahou catchment consists of the following geological units: Mamaku Plateau Formation, Taurangā Group (Pleistocene lake sediments), and Taurangā Group Hinuera Formation (river sediments) (Figure 2.1; Leonard et al., 2010). Mamaku Plateau sediments are predominantly characterised by the Mamaku Ignimbrite can be divided into four different facies (e.g., based on variations in welding, jointing) and is characterised by a strongly welded and highly fractured lower unit; and an un-welded, more friable upper unit (Gordon, 2001). The upper Mamaku Ignimbrite unit is composed of un-compacted, friable pumice that has increased porosity and potentially increased permeability, most likely due to vapour phase alteration caused by hot gas steaming through the sheet soon after emplacement (Rosen et al., 1998).
Pleistocene lake sediments comprise lake terraces that are associated with highstands of the Lake Rotorua caldera during the Pleistocene. The high lake levels were the result of blockages of the paleo-Lake Rotorua outlet by eruptive products from the OVC (e.g., Rotoiti Eruption), Manville et al. (2007). The lake deposits consist primarily of silt, but may include sand, clay or pumice layers that were deposited in the Pleistocene paleo-lake (Leonard et al., 2010). Hinuera Formation river sediments comprise sand and gravel deposits that include clay, pumice and rock fragments. The term “Hinuera Formation’ has generally been applied to river sediments in the central North Island that have been deposited after the Mamaku Ignimbrite eruption and generally consist of reworked and re-deposited eruption products (Manville and Wilson, 2004).
Hinuera Formation can be split into the following three phases (Manville and Wilson, 2004): Hinuera A deposited between the 240 ka Mamaku eruption and the 27 ka Oruanui eruption when the Waikato River flowed across the Hauraki Plains into the Hauraki Gulf; Hinuera B deposited mostly on the Hauraki Plains between 27 ka and about 24 ka before the Waikato River moved to its present course; and Hinuera C deposited in the Hamilton Basin and the Hauraki Plains by the break-out flood from Lake Taupō after the Oruanui eruption.
A cross-section of a simplified geological model provides an indication of the subsurface geology expected for the Awahou catchment (Figure 2.2). Key characteristics include the shallow lake (Lake Rotorua) overlying Taurangā Group sediments which contact with the Mamaku Ignimbrite at a surface elevation of approximately 320 m above mean sea level (MSL).
Figure 2.1: Geological map of the Awahou groundwater catchment showing QMAP geology (Leonard et al., 2010).
Figure 2.2: Geological cross-section of the Awahou Catchment including: (yellow) ignimbrite, (grey) sediments, and (blue) lake (White et al., 2007).
Precipitation that falls on the Mamaku Plateau and in the Awahou catchment infiltrates through the permeable Mamaku Ignimbrite, and recharges the aquifer. Wells drilled in the catchment access this water for municipal and agricultural supply. In addition, groundwater discharges through a series of cold water springs (e.g., Taniwha Springs), to form the baseflow for the Awahou Stream, which flows out of the system and into Lake Rotorua.
2.2.1 Bore locations
A search of the BOPRC groundwater bore database identified a total of 30 bores that are located either within the Awahou Catchment (27 bores), or within a 200 m buffer (3 bores) of the Awahou Catchment (Figure 2.3; Appendix 1:). Information for these bores is varied, and includes lithology (14 bores; Appendix 2:), water levels (3 bores; Appendix 3:), basic hydrochemistry (one bore) and comprehensive chemistry (one bore). Information on hydraulic properties is limited to drawdown tests completed at the time of drilling and from a single pump test completed in 2005 (Reeves et al., 2005). In addition, seven shallow bores (15 – 40 m below ground level (BGL)) that were drilled as part of the Ngōngōtaha water supply investigation were not included in the BOPRC database (Dewhurst, 1996).
Figure 2.3: Location of bores within the Awahou Catchment and a 200 m buffer zone (Appendix 1:).
2.2.2 Bore lithology
Records of bore lithology are variable between sites and some wells do not have well logs. Available well log records indicate that bores within the Awahou catchment range in depth from 20 m – 180 m BGL (Appendix 1:, Table A 1.1). Lithological logs from driller’s records are variable and predominantly indicate the occurrence of pumice, rhyolite, and ignimbrite with finer material including silt and clay (Appendix 2:, Table A 2.1).
Bore 4007 (National Groundwater Monitoring Programme (NGMP) Site 58, Pemberton) is located in the southern catchment near the boundary with the Waitetī Stream catchment (Figure 2.3). A drillers lithological log identifies that the total depth of the bore is 103.6 m BGL and that casing was installed from ground level to 39 m BGL. Lithological layers encountered during drilling were described as pumice clay, rhyolite, and soft fractured rhyolite (Table 2.1). It is important to note that a driller’s log are based on observations of lithology obtained during drilling, and often do not accurately address geological formations. Therefore geological units are generally interpreted as part of the geological modelling process. The geological model profile acquired from the Earth Beneath Our Feet (EBOF) portal estimates that there is approximately 111 m of Mamaku Ignimbrite located beneath the location of bore 4007, below which Pōkai Formation and older formation volcanics are located (Figure 2.4).
It is likely that water sampled from bore 4007 is sourced from the Mamaku Ignimbrite aquifer (39 m – 103.6 m BGL). Groundwater samples have regularly been collected from bore 4007 for the period 1996 – 2015, providing nearly 20 years of groundwater levels (Figure 2.6) and water quality data (Section 22.214.171.124). Samples will continue to be monitored on a quarterly basis as part of the collaboration between the NGMP and BOPRC.
Table 2.1: Drillers log for bore 4007 (NGMP site 58, Pemberton; 2015).
|Driller’s Description||Inferred Geology (Based on Section 2.1)||From (m BGL)||To (m BGL)|
|yellow PUMICE CLAY||Mamaku Plateau Ignimbrite (weathered)||0.0||9.1|
|brown and grey RHYOLITE becoming hard||Mamaku Plateau Ignimbrite||9.1||97.5|
|soft fractured RHYOLITE||Mamaku Plateau Ignimbrite||97.5||103.6|
Figure 2.4: Geological model profile for location of bore 4007 (NGMP site 58, Pemberton) from the EBOF portal (http://data.gns.cri.nz/ebof/findLocation.jsp). Note: co-ordinates shown are in NZMG (1949).
2.2.3 Groundwater levels
Water level information is available for three bores within the Awahou catchment, including long term datasets for bores 3469 (1996 – 2015) and 4007 (1996 – 2015), and a short term dataset for bore 4008 (1995). Water levels will continue to be monitored in bores 3469 and 4007 by BOPRC. Water levels in bore 3469 (Figure 2.5) and bore 4007 (Figure 2.6) appear to have fluctuated at a depth around 50 m BGL. Since about 2010, it appears as though water levels in bore 3469 have been more variable than in the previous period, whereas water levels in bore 4007 did not appear to have changed considerably over time.
In both bore records there are water levels that are outliers and are not likely to represent real values of groundwater levels. Outliers for bore 3469 are water levels of 25.5 m BGL and 16.6 m BGL, and at 26.01 m BGL for bore 4007. These outliers are likely to be caused by human error during the water level sampling, e.g., an incorrect reading of the water level indicator, or an error during entry of the water level into a database. However, it is possible that the values represent measured water levels e.g., due to effects of local pumping on the groundwater level, or if a pump was in operation at the time if sampling.
Figure 2.5: Water levels for bore 3469 for the period 1996 – 2015 (Appendix 3, Table A 3.1).
Figure 2.6: Water levels for bore 4007 for the period 1995 – 2015. Null values (0 m) have been removed (Appendix 3, Table A 3.1).
2.2.4 Groundwater chemistry
Groundwater chemistry information was obtained from BOPRC and the GNS Science Geothermal and Groundwater Database (NGMP, 2015).
126.96.36.199 BOPRC groundwater quality sampling
In 1990, a single water sample from bore 1446 was been analysed for major ions. Primary constituents of the water sample included sodium (10.4 mg L^-1^), chlorine (7.1 mg L^-1^), calcium (2.9 mg L^-1^), potassium (2.1 mg L^-1^), and magnesium (1.5 mg L^-1^). Minor constituents included manganese (0.34 mg L^-1^), iron (0.23 mg L^-1^) and zinc (0.02 mg L^-1^). No other groundwater chemistry information is available for bores in the catchment, aside from bore 4007 (see below).
188.8.131.52 NGMP sampling results
The NGMP is a long-term research and monitoring programme operated by GNS Science in collaboration with regional authorities throughout New Zealand. Groundwater samples are collected quarterly by regional council staff from over 110 active groundwater monitoring sites (NGMP, 2015). All samples are analysed at the New Zealand Geothermal Analytical Laboratory, GNS Science for 17 water quality indicators including major ions, nutrients, and metals. Interpretation of results from NGMP bores allows for characterisation of the quality of New Zealand’s groundwater resources at the national scale, and permits differentiation of natural chemical signatures from those caused by human activity. In addition, samples are collected two- to three- yearly for analysis of age tracers including tritium (^3^H), chlorofluorocarbons (CFCs) and sulphur hexafluoride (SF~6~). These samples are processed by the GNS Science Water Dating Laboratory (WDL) to determine the groundwater age distribution, which allows for refinement of ages for MRT assessment. All NGMP sample results are stored in the National Groundwater database, which was specifically developed for hosting geochemical and groundwater datasets. The database was developed in the 1990s and has been publically available since 2011.
In general, water quality samples have been collected from the Pemberton bore quarterly for the period 1996 – 2015, and age dating samples were collected in 2005 and 2009 (Appendix 4, Table A 4.1:). Groundwater is characterised by a median temperature of 12.8°C, and a median acidity of pH 6.7. Iron and manganese concentrations are very low, and in most cases are below the respective detection levels. Concentration of nitrate-nitrogen (NO~3~-N) ranges from 0.8 – 2.8 mg/L, with a median concentration of 1.3 mg/L. This concentration is well below the Maximum Acceptable Value of 50 mg/L identified in the Drinking Water Standards for New Zealand (Ministry of Health, 2008). Phosphorus concentration ranges between 0.03 – 0.12 mg/L with a median concentration of 0.08 mg/L.
A state and trends analysis of NGMP bores was completed as part of the national update of groundwater quality indicators and is presented in Table 2.2 (Moreau and Daughney, 2015). Concentrations of metals including iron (Fe) and manganese (Mn) were below their respective detection limits, as was the concentration of ammoniacal-nitrogen (NH~3~-N). Although the median concentration of NO~3~-N was 1.3 mg/L, no trend in concentration was detected over the period. In comparison, the concentration of Dissolved Reactive Phosphorus (DRP) had a median value of 0.08 mg/L and showed an increasing trend of 0.001 mg/L per year. The consistent increasing trend in DRP could indicate that the groundwater system has been impacted by agriculture in the area (Moreau and Daughney, 2015), or that phosphorus is leached from the formation (Morgenstern et al., 2015). Electrical Conductivity (EC) had a median of 84 µs/cm and a decreasing trend of 0.04 µs/cm per year.
Table 2.2: Summary of statistical analyses for the Pemberton bore completed as part of the national update of groundwater quality indicators (Moreau and Daughney, 2015).
|x||Unit||Median Values (2003 – 2013)||MAD (2004 – 2013)||Trend Magnitude (2004 – 2013)||Mann-Kendall p-value||Kruskall-Wallis p-value|
* ND: result was not determined.
2.2.5 Ngōngōtaha water supply spring investigations
Several hydrogeological and investigations have been conducted in the vicinity of Taniwha Springs (e.g., the Ngōngōtaha water supply). These investigations were primarily focussed on understanding potential sources of (low level) faecal coliform contamination (Dewhurst, 1992; Dewhurst, 1993; Donnison, 1993a; Donnison 1993b); Institute of Geological & Nuclear Sciences and Sigma Consultants, 1999), and characterisation of hydrogeology in the area (Pang et al., 1996; Rosen et al., 1998).
Early investigations in the vicinity of Taniwha Springs were conducted in response to intermittent faecal coliform contamination in the water supply during the period 1992 – 1995 (Dewhurst, 1992; Dewhurst, 1993; and Dewhurst, 1996). A short (two day) study of the Taniwha Springs and surrounding was based solely on visual observations of the spring and surrounding catchment, anecdotal information from council staff and local landowners, and the authors hydrogeological understanding (Dewhurst, 1992). This study indicated that the likely source of contamination was either from septic tanks located on the northern side of the spring; or a dairy shed effluent pond located 600 m to the northwest of the spring (Dewhurst, 1992). Intermittent contamination events generally occurred following periods of heavy rainfall.
An investigation was commissioned to determine the geological basis for the spring location and included methods of seismic refraction and field verification (Dewhurst, 1993). Seismic refraction profiles were completed at four sites near Taniwha Spring. Survey results were meaningless at three of the sites due to external noise influencing the measurements, and attenuation of the seismic signal (Dewhurst, 1993). However, one site located on a farm northeast of the Awahou Stream fork (e.g., above the Central Road bridge), was surveyed parallel to the stream. Profile results indicated that an 18 m thick layer of low velocity pumiceous ash and lake deposits overlay an unknown depth of ignimbrite, and that the ignimbrite exhibited a very irregular surface (Dewhurst, 1993). During field verification it was observed that at some locations Awahou Stream flowed between the ignimbrite and ash layers, and that a spring appeared to originate from a fracture in the ignimbrite. In addition, the irregular surface of the ignimbrite was observed in Awahou Stream as several small waterfalls up to 2 m in height. Conclusions of this study were that the springs were likely to be sourced from a set of sub-parallel faults in the ignimbrite associated with the Rotorua Caldera margin. Dewhurst (1993) recommended that if the position and displacement of the fault was required, further investigation should be conducted through a drilling programme rather than geophysical surveys.
A literature review addressing implications of faecal coliform pollution in groundwater was also completed, within the context of contamination observed at Taniwha Springs (Donnison, 1993a). The review identified a number of models that could be applied to determine the source of contamination including survival models and time/distance models. However, it also indicated that application of bacterial models to Taniwha Springs would incorporate considerable limitations and errors. These limitations were associated with the large number of potential contamination sources; the fractured ignimbrite geology or the area; and lack of intensive monitoring data from the springs (Donnison, 1993a). In addition, a high level of error would be induced with applying these models to a specific system. A review of the coliform results from monthly water monitoring at Taniwha Springs during the period November 1989 – May 1993 was also completed by Donnison (1993b). Positive coliform results were observed on three occasions 1990, two occasions in 1991, and on a single occasion in 1992 and 1993 (Table 2.3). Following the positive result in 1992 (5 per 100 mL), an intensive monitoring programme (e.g., daily sampling) was introduced. Results indicated that the coliform levels declined rapidly over the first three to four days, and had returned to normal (e.g., zero) within a month after they were first observed (Table 2.3). E.coli was only encountered in December 1992 (Donnison, 1993b). Overall interpretation of the sampling results suggested that monthly sampling was not intensive enough to identify a contamination pulse, and that more intensive sampling should be conducted following a positive coliform result.
Table 2.3: Summary of positive coliform occurrences and patterns November 1989 – January 1993 (Donnison, 1993b).
|Date||Coliform Count (per 100 mL)||E.coli Count (per 100 mL)|
In 1996, further faecal coliform contamination of the water supply occurred (Dewhurst, 1996). Contamination was thought to either originate from septic tanks located on Central Road properties, or from infiltration of water, that had been contaminated with faecal waste from cattle, into the ignimbrite in the gully near the spring. The Dewhurst (1996) investigation involved drilling seven shallow boreholes (15 – 40 m BGL) below the groundwater table (Figure 2.7). Lithological logs recorded during drilling were fairly consistent for all bores (Figure A 2.1). In general, the logs indicated an upper layer of brown and grey-brown ash with silty clay, which was underlain by a soft ignimbrite (Figure A 2.1). The ignimbrite increased in hardness with depth and was at times fractured. Each bore was cased with 50 mm uPVC, a 1 m long uPVC slotted screen was installed at the base, and a lockable steel toby was installed to secure the top of the monitoring bore (Dewhurst, 1996). Groundwater contours for the area were developed based on water levels encountered during and following drilling (Figure A 3.1). Groundwater was determined to be flowing in a south-eastward direction towards the spring; with bores 1 – 3 being located upstream of the supply spring and bores 4 – 7 being located outside the zone of influence for the supply spring.
Figure 2.7: Location of monitoring bores drilled at Taniwha Springs (Dewhurst, 1996) (Appendix 1, Table A 1.2).
Water samples were collected during drilling from four sites (bores 1 - 4) on the 20/7/1995, and from all sites on the 17/8/1995 following the completion of drilling (Table A 4.2). Water samples were analysed for parameters including major anions and cations, nutrients, and metals. It is possible that during drilling the groundwater was oxidised, which resulted in lower levels of dissolved iron, manganese and ammonium, which was likely to have affected samples from 20/7/1995 and 24/11/1995. Additional water quality samples were collected from the spring and on two occasions from the bores, during the period 13/11/1995 and 20/2/1996. These samples were only analysed for ammonium, and early samples are likely to have been influenced by the drilling, whereas samples from 20/2/1996 are likely to represent actual groundwater concentrations. Overall, concentrations of ammonium appear to be slightly elevated in bores 4 – 7 (Table A 4.3). Dewhurst (1996) concluded that based on the hydrogeological knowledge at the site, these bores are the most likely to intercept septic tank effluent.
Two tracer studies were completed at the site to confirm the flowpath of groundwater and to determine whether the contamination source was from septic tanks on Central Road. The first tracer test method involved injection of Tiponal CBS-X, a blue fluorescent dye commonly used in environmental applications. Approximately 2 kg of the dye was distributed between the lavatories on Central Road the spring water was sampled to identify florescence. The first trial resulted in a positive result in two bores; however potential contamination of samples occurred. A second trial was completed and no positive results were obtained. Tiponal CBS-X is favoured as an environmental tracer, particularly for groundwater, due to the fact it did not possess toxicological, cariogenic, mutagenic, or eco-toxicological characteristics, and because it is invisible to the naked eye. However, studies have also found that it is non-conservative and often has a poor to very poor recovery in field tracer experiments (Licha et al., 2013).
The second tracer test involved injecting 250 kg of Manganese Sulphate (MnSO~4~) into the groundwater system via a gully located approximately 500 m upstream of the springs on 7/9/1995. MnSO~4~ was selected because it was easily available, cheap, non-toxic, required a low-level of detectability, and because concentrations of manganese and sulphate in the natural groundwater were low (Dewhurst, 1996). Following the injection, the water supply spring was sampled from 9/9/1995 to 6/11/1995 for manganese (Mn) and sulphate (SO~4~). Elevated Mn (> 0.01 ppm) was not detected during this period, however elevated SO~4~ (2.88 ppm) was detected on 9/9/1995. The conclusion of this study was that the effects of the MnSO~4~ injection were not apparent at the spring site, and that the increased sulphate was an unexplained coincidence.
Although results of the water quality analysis and several tracer studies were inconclusive, Dewhurst (1996) concluded that the most likely source of faecal contamination was from the up-gradient septic tanks. Subsequently, a package treatment plant capable of chlorinating the water was installed at the supply spring by RLC in 1996, and BOPRC contracted Environmental Science and Research (ESR) to investigate protection zones for springs in the Rotorua District (Pang et al., 1996). The project involved studying the fate and transport of microorganisms (e.g., bacteria and viruses) in the Rotorua groundwater system; and determining protection zones for major groundwater supply springs, including the Taniwha Springs (Pang et al., 1996). Protection zones for the Taniwha Springs were delineated using the age method, which estimated the time taken for groundwater to travel through the aquifer system. These estimates indicated that it would take groundwater in the Awahou Catchment 176 days to travel 482 m, 263 days to travel 721 m, and 350 days to travel 959 m (Pang et al., 1996), as demonstrated in Figure 2.8.
Further investigations associated with the Ngōngōtaha Water Supply were commissioned by RLC following concerns raised by local residents regarding the dumping of toxic waste (e.g., timber processing and industrial fluids) into unlined pits on Otūroa Road (Gifford, 1989; Dewhurst, 1989). It is understood that the waste disposal sites operating during the 1980s were located within the Awahou groundwater catchment boundary as defined in Figure 1.3. Therefore, these waste products have the potential to contaminate down-gradient systems including the Awahou Stream, Taniwha Springs, and Lake Rotorua systems. An assessment as to the extent of this contamination and any movement of contaminant plumes would be required to determine the potential future impact on the Awahou Stream and water supply.
Figure 2.8: Protection zones for Taniwha Springs and Awahou Springs, as defined by Pang et al. (1996).
2.3 Surface water hydrology
The main surface water features in the Awahou catchment include the Awahou Stream, a series of springs, including the main spring (Taniwha Spring or Te puna o Pekehauā), that flow into the Awahou Stream (Figure 2.9). Additional surface water features include two tributaries of the Awahou Stream, and an unnamed stream that enters Lake Rotorua north of the Awahou Stream. It is estimated that the Awahou Stream contributes approximately 7% of the total surface water inflow to Lake Rotorua (Daughney et al., 2015).
2.3.1 Surface water quality sites
Surface water quality measurements have been collected by BOPRC at seven locations along the Awahou Stream, and include six stream sites and one spring site, Taniwha Spring (Figure 2.9; Hutchby, 2015). Two of the Awahou Stream sites (i.e., Hamurana Road bridge and Gloucester Road) have long-term records of water quality. In comparison, all other sites have been sampled between one and three times in total (Table 2.4). In addition, RLC have seven records of water quality from Taniwha Spring for the period 1964 – 2015 (Table 2.4).
Figure 2.9: Location of BOPRC (seven) and RLC (RDC) (one) surface water quality monitoring sites in the Awahou catchment.
184.108.40.206 Awahou Stream at Hamurana Road bridge
The Awahou at Hamurana Road bridge site has a total of 258 measurements collected for the period 1992 – 2015 (Table 2.4). In the past this site has been named “Awahou at Tauranga Direct Road”, however for the purposes of this report all records have been combined under the Awahou at Hamurana Road bridge site. Although different parameters have been measured over time, the following parameters have been recorded during the majority of sampling occasions: temperature, dissolved oxygen (DO), total suspended sediment, EC, pH, DRP, NH~3~-N, total nitrogen (or NO~3~-N and total Keijdhal nitrogen), total phosphorus (TP) and enterococci. This site is currently operating under the BOPRC Environmental Science Monitoring Programme, and BOPRC have monitored and will continue to monitor the site at monthly intervals.
Table 2.4: Summary of measurements made at BOPRC and RLC surface water quality monitoring sites.
|Site||Description||Easting||Northing||No. Samples||Date Period|
|BOP120002||Awahou at Hamurana Road bridge/Awahou at Tauranga Direct Road||2792200||6345400||258||1992 - 2015|
|RLC||RLC, Taniwha Spring source||NA*||7||1964 - 2015|
|BOP120159||Awahou @ stream mouth (AWA2)||2792900||6345260||3||2006 - 2009|
|BOP120182||Awahou @ Central Road bridge||2791770||6345260||1||2006|
|BOP120211||Awahou @ conf. with Awahou Spring||2791130||6345410||1||2006|
|BOP160118||Awahou @ Gloucester Rd||2792900||6345300||122||1992 - 2014|
* The location for RLC water sampling has not been provided on any sampling sheets, but was identified to be from the spring directly beneath the pump intake at Taniwha Spring (Te puna o Pekehauā).
220.127.116.11 Taniwha Spring
A total of eight water quality results from sampling at Taniwha Spring were provided by RLC and BOPRC (Figure 2.9). The RLC sampling location is taken from the spring directly below the pump intake, and the BOPRC sampling location is within close proximity. These records date from 1964 – 2015 and include various water quality parameters over the period of measurement (Appendix 5:). A summary of key parameters including major anions, major cations, and nutrients are presented in Table 2.5. It is important to note that sampling and analytical procedures have changed over the 50 year period that the samples have been analysed. However, the majority of parameters appear to be relatively constant over time. It is possible that there has been a slight increase in the concentration of NO~3~-N from 1.2 mg L^-1^ in 1981 to 1.58 mg L^-1^ in 2015 (Table 2.5), which would be consistent with long-term trends (Rutherford, 2003). However, none of the other nitrogen parameters from the spring supply appear to have increased.
Table 2.5: Summary of key parameters from RLC and BOPRC water quality results from Taniwha Springs. Results for additional parameters are presented in Appendix 5:.
|Major Anions and Cations|
18.104.22.168 Awahou Stream at Gloucester Road
A total of 122 samples have been collected from the Gloucester Road site from 1992 – 2014, which appears to be the same location as sampling site as Awahou at Stream mouth (Figure 2.9; Hutchby, 2015). A limited set of parameters has been analysed including: DO, temperature, and Enteroccoci for the period 1992 – 2000; with the addition of E.coli for the period 1992 – 2013 (Figure 2.10). Concentration of E.coli ranges from 0.5 – 330 cfu/100 mL, with an average concentration of 39 cfu/100 mL. The most recent sample taken from the Awahou at Gloucester Road was in March 2014, and this site is no longer routinely sampled by BOPRC.
Figure 2.10: Summary of E.coli concentration at Gloucester Road for the period 1992 – 2013. This site is no longer routinely sampled by BOPRC for E.coli.
2.3.2 Surface water flow measurements
22.214.171.124 Spring gauging
Total flow for the Taniwha Springs complex was estimated to be 1.36 m^3^/s (GNS Science and Sigma Consultants, 1999). Specific flow measurements for individual springs were not obtained from any sources; however RLC are required to measure overflow at the pumping station to satisfy their resource consent (Appendix 6:). An indication of flow from the main spring (e.g., Taniwha Spring/Te puna o Pekehauā) was obtained from the high resolution (e.g., 10 min) overflow datasets during periods when there was no pumping. The main spring flow rate is estimated to be between 180 – 210 L/s (Appendix 7:, Figure A 7.1).
126.96.36.199 Stream gauging
Records from BOPRC indicated that the Awahou Stream has been gauged in four locations (Figure 2.11; Table 2.6). Flow records from the Hamurana Road bridge (formerly known as Tauranga Direct Road bridge) are available for 166 occasions from BOPRC and for 25 occasions from RLC (Table 2.6). Overall, flow rate of the Awahou Stream at the Hamurana Road bridge has ranged from 1.3 to 6.9 m^3^/s, with an average flow rate of 1.65 m^3^/s (Hutchby, 2015; Randell, 2015). In comparison, the flow rate at the other three sites has been measured on one occasion only. Although Awahou Stream was gauged on different dates, flow measurements increase from 0.04 m^3^ s^-1^ at the u/s spring flow site, to 0.37 m^3^ s^-1^ at the Central Road culvert site, and 1.82 m^3^ s^-1^ at the stream mouth.
Figure 2.11: Location of surface water gauging sites in the Awahou Catchment, as detailed in Table 2.6.
Table 2.6: Summary of BOPRC and RLC flow measurements for the Awahou Stream (Hutchby, 2015; Randell, 2015).
|Source||Site Name||No.||Average Flow (m^3^/s)||Flow Range||Dates|
|BOPRC||Awahou at Hamurana Road bridge||166||1.7||1.3 - 6.9||1992 - 2015|
|RLC||Awahou at Hamurana Road bridge||25||1.7||1.5 - 1.9||2013 - 2015|
|BOPRC||Awahou at US Spring Flow||1||-||0.04||2006|
|BOPRC||Awahou at Central Road culvert||1||-||0.37||2006|
|BOPRC||Awahou at Mouth Flow||1||-||1.82||2006|
188.8.131.52 Modelled flow measurements
As part of a project to better understand the groundwater systems of the greater Lake Rotorua catchment, White et al. (2007) completed a review of stream flow measurements in the Awahou catchment (Table 2.6; Table 2.7). Results of this survey indicated that flowing water occurred in: Awahou Stream for the majority of its course; two tributaries of Awahou Stream; and an unnamed stream north of the Awahou Stream, near the lake (White et al., 2007). In addition, stream bed elevation was estimated using a GIS model, and was confirmed to be flowing at 12 of the 33 locations that the stream bed intersected topographic contours (Figure 2.12). Groundwater levels in the catchment appeared to be below the stream bed elevation at elevations > 300 m above MSL. The Awahou Stream baseflow model showed that most streams in the catchment are either dry or maintain low flows (Figure 2.13; White et al., 2007). Measured flows in the Awahou Stream indicate that the stream gains the majority of flow from springs and seeps below the 320 m contour (Table 2.6). For example, flow of 0.34 m^3^/s at Central Road bridge increases to an average of 1.7 m^3^/s at Hamurana Road bridge. It is important to note that this project was completed using catchment boundaries that have since been updated (Section 1.4).
Table 2.7: Summary of flow measurements from Awahou Catchment, excluding those already collated from BOPRC sources (White et al., 2007).
|Source||Site Name||No.||Average Flow (L/s)||Dates|
|White et al. (2007)||Awahou at Robinsons Farm||6||0.4||1973 - 1974|
|White et al. (2007)||Awahou at Central Road bridge||6||339||1973 -1974|
|White et al. (2007)||Taniwha Gully (above spring)||6||0||1973 - 1974|
|White et al. (2007)||Awahou at Mouth||1||1176||2004|
|White et al. (2007)||Unnamed stream, site 168||1||0.25||2004|
|White et al. (2007)||Unnamed stream, site 172||1||0.06||2004|
|White et al. (2007)||Unnamed stream, site 170||1||1||2004|
|White et al. (2007)||Awahou Stream||1||42||2006|
Figure 2.12: Model showing streams intersecting with contour lines, and the location of gauging measurements.
Figure 2.13: Model of baseflow, location of gaugings and location dry stream beds in the Awahou Stream and Awahou Point catchment (White et al., 2007).
184.108.40.206 Summer low-flow gauging survey
A summer low-flow gauging survey was developed to enhance the understanding of: baseflow in the Awahou Stream catchment < 320 m; inflows into Awahou Stream above 320 m; areas of dry stream bed in Awahou Stream; and groundwater flows in the Mamaku Plateau (White et al., 2007; White et al., 2014). A total of 14 sites in the lower Awahou Catchment were selected for stream gauging and were located between the 320 m contour and Lake Rotorua; and a total of 10 sites in the upper Awahou catchment were selected to determine flows into Awahou Stream above the 320 m contour (Figure 2.14; Table 2.8).
Figure 2.14: Location of the surface water flow measurements completed by BOPRC in March, 2016.
The gauging survey was initially planned for the week 22 – 26 February 2016, however due to reasonably heavy rainfall the preceding week, the survey was delayed. The preceding rainfall was likely to have increased flow in all streams in the catchment, and therefore provided conditions that were not representative of baseflow. A minimum period of five days without rainfall was required to provide representative baseflow in spring-fed streams. It is believed that low-flow conditions were reached prior to sampling which was conducted on the 7 March, 2016 (Hutchby, 2016). A total of 24 sites were accessed for gauging (Table 2.8). Two sites were unable to be sampled, and including Site 3 as tributary flow was < 0.2 L/sec (Putt, 2016); and Site 6 since the spring in the vicinity of these coordinates could not be located. There were various springs further up the left branch (towards the RLC water take) but BOPRC staff could not recall going into this area in 2006 (Putt, 2016).
Flow in Awahou Stream at Hamurana Road bridge (1.43 m^3^/s) was slightly lower than average flow of 1.7 m^3^/s from previous measurements (Table 2.6). Similarly, flow in Awahou Stream at Central Road culvert (0.26 m^3^/s) was lower than previous measurements of 0.37 m^3^/s (Table 2.6) and 0.34 m^3^/s (Table 2.7). It is likely that these flow rates were lower than previously recorded due to a combination of: pumping that was occurring from the main spring at the time of sampling; and it being a dry summer, respectively.
Table 2.8: Summary of gauging measurements completed in the Awahou Catchment by Bay of Plenty Regional Council on 7/3/2016 (Hutchby, 2016).
|Date||Time (24 hr)||Site Name||Flow (m^3^/sec)||BOPRC ID||Easting (NZTM)||Northing (NZTM)|
|7/3/2016||0901||Awahou at Awahou bridge||0.2320||DL571660||1875713||5786608|
|7/3/2016||0944||Awahou at D/S of Confluence||0.1934||DL895597||1878953||5785970|
|7/3/2016||1015||Awahou at U/S Spring (#77 Central Rd)||0.0010||EL134387||1881344||5783875|
|7/3/2016||1036||Awahou at confluence with Awahou Spring (#77 Central Rd)||0.0851||DL912578||1879127||5785780|
|7/3/2016||1128||Awahou L/B Tributary at Central Road, #77||0.0529||EL161373||1881611||5783734|
|7/3/2016||1230||Awahou L/Branch Tributary at Central Rd, #85||Dry||EL147378||1881470||5783785|
|7/3/2016||1230||Awahou R/Branch Tributary at Central Rd, #85||Dry||EL097388||1880974||5783884|
|7/3/2016||1300||Awahou Spring at Scott Douglas Drive, #115||Dry||EL123393||1881228||5783926|
|7/3/2016||1418||Mangorewa at Old Tauranga Road||0.0258||EL204387||1882047||5783876|
|7/3/2016||0845||Awahou at Central Road, #31||0.2400||EL120403||1882744||5783736|
|7/3/2016||0920||Awahou at Central Road bridge||0.2640||EL274373||1877910||5786680|
|7/3/2016||1148||Awahou L/B Tributary at Below RLC Water Take (#20 Central Rd)||1.2440||DL791668||1879970||5785045|
|7/3/2016||1246||Awahou L/B Tributary at Hamurana Road||0.0002||DL997504||1880974||5783890|
|7/3/2016||1315||Awahou at Hamurana Road bridge||1.4260||EL097389||1880562||5785340|
|7/3/2016||1441||Awahou at Mouth (AWA2)||1.4800||DL056534||1881790||5783870|
|7/3/2016||0755||Ephemeral Flow at Jackson Road Culvert||Dry||EL179387||1881199||5784028|
|7/3/2016||0800||Awahou Drain at Sharp Road||Dry||EL219391||1882190||5783910|
|7/3/2016||0910||Awahou at Sharp Road||0.0001111||EL117427||1881169||5784270|
|7/3/2016||1035||Awahou R/B Tributary at above Power Lines Confluence||0.0000068||DL892588||1878920||5785880|
|7/3/2016||1100||Awahou at above Power Lines Confluence||0.0000169||EL114426||1881140||5784256|
|7/3/2016||1130||Awahou at below Power Lines Confluence||0.0000172||DL966640||1879657||5786398|
|7/3/2016||1240||Awahou at Oturoa Road||stagnant water, no flow||EL105592||1881051||5785920|
|7/3/2016||1325||Anderson Road Stream at Tui Ridge Park||0.0000400||DM860350||1878605||5793508|
|7/3/2016||1450||Ohaupara at Old Tauranga Road||0.0000154||DM852377||1878527||5793778|
2.4 Consented water takes
There are two consented water takes in the Awahou catchment (Figure 2.15). Tui Ridge Park, Otūroa Road has consent (number 63366) for abstraction of water for the purposes of private supply. The consent allows a maximum take of 230 m^3^/day at a maximum rate of 3 L/s. In addition, RLC have consent (number 61175) for abstraction of water from Taniwha Springs for municipal supply to Ngōngōtaha community and the surrounding rural area (Appendix 6:). The consent allows RLC to place and use a structure (e.g., pumping station) over the bed of Taniwha Spring and to take water from Taniwha Spring. The consent allows for a maximum take of 7,340 m^3^/day (Appendix 6:). An increased take of 9,936 m^3^/day, at a maximum rate of 115 L/s is permissible in the case of an emergency (e.g., natural disaster, power failure). There are several conditions of the consent, for example RLC are required to provide monthly stream gauging measurements for the Awahou Stream (Table 2.6; Figure 2.11). To satisfy this condition, RLC have engaged the National Institute of Water and Atmospheric Research (NIWA) to complete the gauging on monthly basis at the Hamurana Road bridge gauging site. Datasets for these gauging results are currently held by Ngāti Rangiwewehi.
Figure 2.15: Location and consent number for BOPRC water takes from the Awahou catchment (Hutchby, 2015).
3. Age dating: surface water and groundwater
Water samples have been collected from seven sites in the Awahou catchment for age dating analysis, including four surface water sites and three groundwater sites (Figure 3.1). A summary of the bore information for groundwater sampling is provided in Table 3.1. All water samples were collected following the standard procedures for age dating, and were analysed for tritium (~3~H) at the GNS Science WDL. The estimated MRT for groundwater in the Awahou catchment ranges from 31 years at the Awahou Stream confluence with Awahou Spring No.1 and groundwater bore 10964, to 150 years at groundwater bore 1561 (Figure 3.1; Table 3.1).
Figure 3.1: Location of sites in the Awahou catchment that have been sampled for estimation of groundwater age, and estimated MRT.
Table 3.1: Summary of bore details and results from groundwater age dating in the Awahou Catchment.
|Bore ID||Water Level (m BGL)||Well Depth (m BGL)||Screened Interval (m BGL)||Estimated Age (years)|
|1561||15||73.1||63 - 73.1||150|
|10964||16||45||39 - 45||31|
|3691||60||118.5||78 - 118.5||57|
Overall, a range of scientific data and information relating to the Lake Rotorua catchment, and more specifically the Awahou catchment, and Taniwha Springs has been compiled. Key information includes geological and hydrogeological descriptions of the region, identification of catchment boundaries, results of surface water and groundwater monitoring including hydrochemistry, flow rates, and age approximation. Scientific datasets compiled in this report were obtained from BOPRC, RLC, GNS Science, and Ngāti Rangiwewehi. In addition, a literature search was completed to identify published information relating to the Awahou catchment. The results of the database and literature searches are presented in this report, and datasets are presented in the appendices. It is intended that all datasets will subsequently be uploaded into a web-based portal that is being developed as part of the knowledge integration component of the programme.
Staff members from Bay of Plenty Regional Council staff are acknowledged for providing datasets from the Awahou Catchment (Brent Hutchby); and for conducting and processing the stream gauging measurements (Brent Hutchby, Craig Putt, and Lisa Bevan). Rotorua Lakes Council (formerly Rotorua District Council), in particular Justine Randall, are thanked for providing resource consent, flow measurement, pumping rates, and water quality information. In addition, this report has benefitted from information provided by GNS Science staff including Connie Tschritter, Uwe Morgenstern, Magali Moreau, and Gina Pelham. Reviewers from the project team including Kahuariki Hancock (Ngāti Rangiwewehi) and Brent Hutchby (BOPRC) are thanked for providing helpful review comments on a draft of this report.
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Daughney, C.J.; Toews, M.W.; Ancelet, T.; White, P.A.; Cornaton, F.J.; Stokes, K.; Maxwell, D.; Jackson, B.M.; Tshritter, C. 2015 Implementing and evaluating models of steady-state groundwater flow under baseflow conditions, Lake Rotorua catchment, New Zealand, GNS Science report 2015/52. 128 p.
Dell, P.M. 1982 The effect of afforestation on the water resources of the Mamaku Plateau region. M.s.c Thesis, University of Waikato, New Zealand.
Dewhurst, R. 1989 Report on liquid waste disposal pits near Oturoa Road prepared for the Rotorua District Council, March 1989. 8 p.
Dewhurst, R.H. 1992 Faecal Coliform bacterial contamination of the Ngongotaha Water Supply Spring. Report prepared for Rotorua District Council by Roger Dewhurst, Consulting Geologist.
Dewhurst, R.H. 1993 Seismic refraction and geological investigation near the Ngongotaha Water Supply Spring. Report prepared for Rotorua District Council by Roger Dewhurst, Consulting Geologist and Hydrogeologist.
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|Alluvial sediment:||Material that is eroded or is reworked and deposited by fluvial (water) action (e.g., by rivers, floods, lakes).|
|Ammoniacal-nitrogen (NH~3~-N):||A measure for the amount of ammonia, a pollutant often found in waste products, such as sewage, liquid manure and other liquid organic waste products.|
|Baseflow:||The portion of stream flow that is not runoff and results from seepage of water from the ground into a channel slowly over time. This is the primary source of running water in the Lake Rotorua catchment and commonly the only source of stream flow during dry weather.|
|Best-estimate:||The most probable outcome based on a set of factors. In this report it refers to the Lake Rotorua catchment boundary.|
|Breccia:||A rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix.|
|Caldera Basin:||A large crater at the top of a volcano formed by the collapse or explosion of the cone.|
|Catchment:||An area of land where surface water from rain, snow, or ice converges to a single point at a lower elevation, usually the exit of the basin, where the waters join another water body, such as a river, lake, wetland, or sea.|
|Chlorofluorocarbons (CFCs):||Organic compounds that contains carbon, chlorine, and fluorine, produced as a volatile derivative of methane and ethane. When released into the atmosphere CFCs contribute to the destruction of the ozone gas in upper atmosphere. CFCs can be used to determine the age of water.|
|Detection limit:||The lowest quantity of a substance that can be distinguished from the absence of that substance (a blank value) within a stated confidence limit (generally 1%). Used in reporting of water quality results.|
|Dissolved Oxygen (DO):||Oxygen that is dissolved in water. It is an important parameter in assessing water quality because of its influence on the organisms living within water.|
|Dissolved Reactive Phosphorus (DRP):||A measure of the dissolved (soluble) phosphorus compound that is readily available for use by plants and algae. DRP concentrations are an indication of a waterbody’s ability to support nuisance algal or plant growths (algal blooms).|
|Electrical conductivity (EC):||A measure of a material’s ability to conduct electric current.|
|Evapotranspiration:||The sum of evaporation and plant transpiration from the earth’s land and ocean surface to the atmosphere.|
|Facies:||A part of a rock body that can be differentiated from another part of the body by textural or compositional variations.|
|Gauging:||A method used to estimate the discharge (volume) of water flowing in a surface water body (e.g., stream, spring or river).|
|Groundwater:||Water located below the ground surface, e.g., within soil, volcanic rock and alluvial deposits.|
|Groundwater recharge:||A hydrologic process where water moves downward from the atmosphere, or surface water, to groundwater.|
|Ignimbrite:||A pumice-dominated pyroclastic flow deposit formed from the cooling of pyroclastic material ejected from an explosive volcanic eruption.|
|Lacustrine sediments:||Sediments deposited in lakes.|
|MAD:||Median Absolute Deviation, used in statistical analysis of water quality parameters for determining the amount of variation between samples.|
|MAV:||Maximum Acceptable Value for particular water quality parameters that specify the upper limit of that value for human consumption, as described in the drinking-water standards (Ministry of Health, 2008).|
|Mean Residence Time (MRT):||The average amount of time that a water molecule spends in a particular groundwater system. A representation of how long it takes for the concentration to significantly change in the sediment.|
|Mesozoic:||Name of the geological period that occurred 252 to 66 million years ago.|
|NGMP:||National Groundwater Monitoring Programme, involves routine sampling of around 110 bores throughout New Zealand, including one site in the Awahou catchment.|
|Nitrate-nitrogen (NO~3~-N):||A nutrient in water that is associated with land use. The term describes nitrogen concentrations in the nitrate form.|
|NTU:||Nephelometric Turbidity Units, a unit used to describe the turbidity of a water sample (see turbidity).|
|Okataina Volcanic Complex (OVC):||An area in the North Island, within the TVZ, that incorporates several volcanic calders (e.g., Haroharo caldera, Tarawera rhyolite dome complexes).|
|Perched:||An accumulation of groundwater that is above the water table in the unsaturated zone.|
|Pleistocene:||Geological time period that occurred 2.6 Million years ago to 11,700 years ago.|
|Pyroclastic flow:||A fast-moving current of hot gas and rock emitted from a volcano.|
|Sulphur Hexafluoride (SF~6~):||An inorganic, colourless, odourless, non-flammable, greenhouse gas. Concentrations of SF~6~ in water can be used to assist with age determination.|
|Surface water:||Water that flows across the land surface, in channels (e.g., rivers, streams), or is contained in depressions on the land surface (e.g., ponds, lakes).|
|Taupo Volcanic Zone (TVZ):||A highly active volcanic area in the North Island of New Zealand that extends from Ruapehu in the south to White Island in the north.|
|Tephra:||Fragmental material produced by a volcanic eruption.|
|Total dissolved solids (TDS):||Measurement of any minerals, salts, metals, cations or anions dissolved in water.|
|Total Keijdhal Nitrogen (TKN):||The sum of organic nitrogen (N), ammoniacal-nitrogen (NH~3~-N), and ammonium (NH~4~-N).|
|Total Phosphorus (TP):||The sum of all phosphorus compounds (reactive, condensed and organic phosphorus) that occur in various forms.|
|Tritium (^3^H):||A radioactive isotope of hydrogen that is used to assist with age interpretation of water.|
|Turbidity:||The degree to which light is scattered by particles suspended in a liquid which provides an indication of the suspended sediment concentration in a water sample, measured in NTU (see above).|
|Welded:||Rock formed from materials that weld together upon cooling, impact or upon compaction, e.g., welded ignimbrite.|
|Vapour phase alteration:||Where vapour is the pressure-controlling phase that alters a minerals composition.|
Appendix 1. Wells
Table A 1.1: Summary of key information for bores located within the Awahou catchment and 200 m buffer zone.
|Well Number||Easting (NZTM)||Northing (NZTM)||Bore Depth||Casing Depth||SWL*|
* SWL: Static Water Level, often taken at the time of drilling the bore.
Table A 1.2: Summary of bore log locations and elevations from the Ngōngōtaha water supply investigation (Dewhurst, 1996).
|Bore Number||East Co-ordinate||North Co-ordinate||R.L.^*^||Casing to R.L.^*^|
* During monitoring bore construction, bolts were set into the concrete pads, and the relative level (R.L.) was measured from the bolt. The uPVC casing extends to a point above the bolt.
Appendix 2. Lithological logs
Table A 2.1: Lithological logs of bores located within the Awahou Catchment and the 200 m buffer zone. Locations for bores can be found in Appendix 1: – Table A 1.1 (Hutchby, 2015).
|Well Number||Unit Top||Unit Bottom||Description|
|237||6.0||15.0||PUMICE SANDS and SILT|
|1056||0.0||4.6||CLAY and yellow PUMICE|
|1056||76.2||94.5||soft SANDS and PUMICE|
|1056||94.5||134.1||pumiceous IGNIMBRITE with layered GRAVELS and SANDS|
|1057||103.6||134.1||firm IGNIMBRITE with fine layered white grey brown Undiff. S|
|1446||0.0||10.0||Clay and pumice|
|1446||10.0||87.0||Mamaku ignimbrite soft but becoming firm with depth. Fractured.|
|3691||6.0||118.5||Rhyolite pink - some fractured|
|4007||0.0||9.1||yellow PUMICE CLAY|
|4007||9.1||97.5||brown and grey RHYOLITE becoming hard|
|4007||97.5||103.6||soft fractured RHYOLITE|
|10965||0.2||2.5||Fine pumice and brown silt (damp)|
|10965||2.5||3.8||Pumice (coarse and damp)|
|10965||3.8||4.0||Fine pumice ash (silty)|
|10965||33.0||41.5||Very hard ignimbrite|
|10965||41.5||42.8||Slightly softer ignimbrite|
|10965||42.8||44.5||Very hard ignimbrite|
|10965||44.5||67.0||Softer browny red ignimbrite|
|10965||67.0||92.0||Fractured browny red ignimbrite (water bearing)|
|10965||92.0||100.0||Pumice up to 30mm pieces (lost in circulation)|
|10965||100.0||104.0||Lost circulation, no return|
|10965||104.0||105.0||Pumice ignimbrite 10mm to 30mm pieces|
|10965||105.0||120.0||Pumice ignimbrite (lost circulation)|
|10965||120.5||122.0||Clay bound pumice|
|10965||122.0||151.5||Clay bound pumice and gravel mix|
|11063||3.0||9.0||Silt and Fine Pumice Sand|
|11063||9.0||49.0||Medium Brown Sand|
|11063||49.0||122.0||Firm Rhyolite with Fracturing|
|11807||4.0||19.0||Firm grey rhyolite|
|11807||19.0||50.0||Fractured red, brown and grey rhyolite|
|11807||50.0||68.0||Hard fractured red brown rhyolite|
|11807||68.0||120.0||White ignimbrite with brown and black layers|
Figure A 2.1: Summary of borelogs from the Ngōngōtaha water supply investigation (Dewhurst, 1996).
Appendix 3. Groundwater Levels
Table A 3.1: Summary of water level information for bores 3469 (a), 4007 (b) and 4008 (c), located within the Awahou Catchment.
Table A 3.1 continued: a) Bore 3469 * Erroneous values from the BOPRC dataset have been modified or removed.
|1881059 E||5785178 N|
Table A 3.1 continued: b) Bore 4007 * Erroneous values from the BOPRC dataset have been modified or removed.
|1879166 E||5783154 N|
Table A 3.1 continued: c) Bore 4008 * Erroneous values from the BOPRC dataset have been modified or removed.
|1878438 E||5785072 N|
Figure A 3.1: Summary of groundwater levels from the Ngōngōtaha water supply investigation (Dewhurst, 1996).
Appendix 4. Groundwater Quality
Table A 4.1: Water quality results for NGMP site 58, Pemberton (BOPRC bore 4007).
- Download Excel Spreadsheet here:
Table A 4.2: Analysis of water samples collected from monitoring bores during the Ngōngōtaha Water Supply Investigation (Dewhurst, 1996).
Table A 4.3: Summary of ammonium samples collected from the supply spring during the Ngōngōtaha Water Supply Investigation (Dewhurst, 1996).
Appendix 5. Surface water quality
A5.1. Taniwha Springs 1964
A5.2. Taniwha Springs 1981
A5.3. Taniwha Springs 1986
A5.4. Taniwha Springs June 1991
A5.5. Taniwha Springs July 1991
A5.6. Taniwha Springs 1995
A5.7. Taniwha Springs 2014
A5.8. Taniwha Springs 2015
Appendix 6. Consents 611575
Appendix 7. Overflow datasets
Figure A 7.1: Distribution plot of spring overflow rate (10 minute data) for the time period when 10 minute data is available (4/8/2009 – 30/6/2010; and 1/7/2011 – 7/9/2011). Original datasets were provided by RLC (Randall, 2015).