TP194 North-West Auckland Water Resource Quantity Statement 2003

North-West Auckland Water Resource Quantity Statement 2003 May 2003 Technical Publication 194

Surface water and groundwater resource information, availability and allocation.

Prepared by Gillian Crowcroft, Roger Bannister, Sarah Harvey

Auckland Regional Council Technical Publication No.194, May 2003 ISSN 1175 205X ISBN 0958243700 www.arc.govt.nz

i Executive Summary

This report is an update of one area in the Auckland Water Resource Quantity Statement 2002 (TP171). That report examined the water resources, both ground and surface, throughout the Auckland Region in eight Management areas. It was then proposed to update that report for two of the areas each year and this document fulfils that objective for the Northwest area. As an update, it covers the 2001 – 2002 hydrological year (from June to May). It may therefore be read in conjunction with TP 171 and does not attempt to reiterate data and information from that earlier report where there have been no changes.

The general picture for 2001 – 2002 was of unusually high spring and summer rainfall, in November and December up to 180% of the long term mean for those months. This was reflected in higher surface stream flows and, in particular, a low level of abstraction from both surface and ground water compared to the allocated levels.

One addition to this report from the format in TP 171, is the estimate of water use compared to allocation. For the 2001 – 2002 year approximately 22% of the surface water allocated to consent holders and 61% of the consented groundwater allocation was taken.

Another feature of this type of report is to review outcomes against management objectives and policies. The objectives and policies relating to the taking of water are set out in the Proposed Auckland Regional Plan: Air, Land and Water (PARP:ALW), notified in October 2001. Two particular objectives relevant to Northwest are; to maintain the quality and flow in surface water and maintain the quality, water level and temperature in groundwater. To achieve these objectives there is a policy to take ground water in preference to surface water, where it is available. This is not the case in much of the Northwest where, due to the geology, ground water is less readily available than surface water. This is reflected in the allocation of surface being double that for ground water. However, for the year in review, use of groundwater was higher than surface water by four percent.

The second objective relating to maintaining temperature in the Parakai geothermal aquifer is managed by ensuring the water level in the aquifer is maintained above a prescribed level. Abstraction from the aquifer has been managed to ensure the water level has not fallen below the prescribed limit in the 2001 – 2002 year.

Table of Contents Page

Executive Summary ……………………………………………………………………………….i

Table of Contents ………………………………………………………………………………….ii

1. Introduction...... 1

2. Rainfall...... 2

3. Hydrology...... 3

4. Hydrogeology...... 6

4.1 Parakai Geothermal Aquifer ...... 6

5. Surface Water Management...... 7

6. Groundwater Management ...... 9

6.1 Management of the Parakai Geothermal Resource ...... 11

7. References ...... 12

1. Introduction

The Northwest area drains 1,330 km2 of land to the Kaipara Harbour and Tasman Sea (Figure 1). The area is comparatively hilly with some lower lying alluvial areas along valley floors. Low-lying areas are also found along the coast, particularly around Tapora and the inner Kaipara Harbour.

Most of the Northwest area is rural farmland used for dairying and dry stock. Forestry is also a key land use in the area, with large pine forests in the eastern elevated areas and along the western South Kaipara Peninsula. Horticultural activities are scattered across the area e.g. in Kaukapakapa and Kaipara South Head.

Water demand in the Northwest is principally for pasture irrigation (Hoteo Catchment), horticultural irrigation and geothermal groundwater (at Parakai). Other large water uses include municipal supply, golf course irrigation and poultry farming.

Figure 1. Location map for the Northwest water resource reporting area.

1 2. Rainfall

The ARC operates two automatic rainfall sites in the northwest; Oldfields (643510), in the Hoteo River Catchment, commissioned in 1978 and Kaipara South Head (644211) installed in March 1999. ARC manual rainfall sites include Kaipara Hills (644410) and Kaipara Flats (644511) (Figure 2).

Figure 2. Northwest area rainfall monitoring sites and mean annual rainfall isohyets.

The annual rainfall for the 2001-2002 year ranges from approximately 1,100mm in the west at Kaipara South Head to between 1,400mm and 1,550mm inland. A comparison between the total for the 2001 – 2002 year and the mean annual for each site is shown in Table 1. Overall

rainfall for the period June 2001– May 2002 was marginally less than normal, 89 – 95% of the long term mean. Table 1. Comparison of 2001-2002 annual rainfall with long term mean at 4 sites. Max Daily Total (mm) % Deviation Highest (mm) Long Term Annual Site Name June 2001 - May from recorded June 2001 Mean (mm) 2002 Normal daily total - May 2002 643510 Oldfields 1397 1292 92.5 180 60.5 644211 Kaipara South Head 1088 1098 100.9 210 54.7 644410 Kaipara Hills 1504 1435 95.4 147 48.3 644511 Kaipara Flats 1554 1384 89.1 135 43.6

A breakdown of variance between monthly rainfall and the long term monthly mean (Figure 3) shows a wetter than average summer but a drier winter in 2001 (June to August) and autumn (March – April) for 2002 at all stations. This was particularly noticeable in the west at Kaipara South Head with monthly rainfall less than 50% of normal in June 2001 but between approximately 170 – 190% of normal in December to February. The effect was less pronounced but still significant at the other stations.

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Percentage Deviation 25

1 2 2 0 -02 un-0 Jul-01 ug-01 ep-01 ct-01 ov-01 ec-01 an-0 eb-02 ar-02 pr- ay J A S O N D J F M A M

Hoteo Oldfields 643510 Kaipara Heads 644211 Hoteo Kaipara Hills 644410 Kaipara Flats 644511 Normal Monthly Mean Deviation

Figure 3. Rainfall: Percentage deviations from long term mean by site for period June 2001 - May 2002.

These figures are generally in line with NIWA’s prediction that neutral atmospheric conditions in respect of El Nińo and the southern oscillation index would result in above average rainfall in the north for the summer of 2001-2002 (Salinger & Griffiths, 2001).

3. Hydrology

Surface water catchments in the Northwest area are variable in size, shape and orientation (Figure 4). Small catchments drain the South Kaipara Peninsula from west to east, whilst larger catchments lie on the eastern side of the Kaipara Harbour. The Hoteo River Catchment is the largest in the Auckland Region with a catchment size of 405 km2.

3 The ARC has three automatic flow recorder sites in the North-west: Hoteo River at Gubbs (45703), Kaukapakapa at Oak Hill (45407) and Waiteitei at Sandersons (45705). The latter site has too many missing readings because of equipment loss and malfunction, to provide meaningful data for 2001-2002. Gubbs is located on the lower reach of the Hoteo River. This site commenced operation in 1977 and has provided data for water allocation, quality and flood flow investigations.

Figure 4. Surface water catchments and flow monitoring sites in the Northwest area.

A low flow frequency curve for Gubbs is shown in figure 5. This shows the one in five year low flow (Q5) as approximately 75% of the mean annual low flow (Q2.33) and approximately twice the one in 10 year low flow (Q10).

At both sites the mean annual flow for 2001-2002 was less than the long term mean (76 – 85%) see Table 2, reflecting the slightly lower rainfall.

The monthly discharges compared to the long term monthly mean (Table 3) reflects the pattern of rainfall with a wet summer. At both sites flow in December was over 190% of the long term mean. Minimum stream flows generally occur during February, and maximum flows occur

during July. For 2001-2002 the low flows in the Kaukapakapa extended from February though April. This is shown graphically at Figure 6.

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45703 1200

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0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 20.0 30.0 40.0 Recurrence Interval (years) Figure 5. Low flow frequency plot at Gubbs (45703) flow monitoring site.

Table 2. Comparison of 2001-2002 flow records with long term mean at Kaukapakapa (Oak Hill) & Hoteo (Gubbs). Min Min 1 Day Long Term Annual Mean % Max Discharge Instantaneous Mean Annual Discharge Deviation (June2001 - Discharge Discharge Site Name Mean (June 2001 - from May 2002) (June 2001 - (June 2001 - Discharge May 2002) Normal (m3/s) May 2002) May 2002) (m3/s) (m3/s) (m3/s) (m3/s) 45407 Kaukapakapa 1.293 0.98 75.8 78.23 - 4 Sept 0.003 - 4 Feb 0.01 - 4 Feb 45703 Hoteo 6.013 5.12 85.1 162.99 - 2 Sept 0.53 - 22 April 0.53 - 23 April

Table 3. Comparison of monthly flow record with long term mean at Hoteo (Gubbs) and Kaukapapa (Oak Hill). Hoteo Kaukapakapa

Long Term Monthly Mean Long Term Monthly Mean Monthly Mean Discharge (m3/s) % Deviation Monthly Mean Discharge (m3/s) % Deviation 3 3 Discharge (m /s) (June 2001 - May from Normal Discharge (m /s) (June 2001 - May from Normal (mm) 2002) (mm) 2002)

Jun 2.210 1.264 57.2 9.810 6.327 64.5 July 3.250 1.531 47.1 13.200 5.244 39.7 Aug 2.180 1.153 52.9 10.000 5.913 59.1 Sep 2.010 3.426 170.4 7.670 18.880 246.2 Oct 1.010 0.413 40.9 4.840 3.569 73.7 Nov 0.704 0.539 76.6 4.040 5.244 129.8 Dec 0.604 1.159 191.9 3.580 6.825 190.6 Jan 0.616 0.411 66.7 3.770 4.510 119.6 Feb 0.150 0.114 76.0 1.970 1.500 76.1 Mar 0.420 0.343 81.7 3.480 1.136 32.6 Apr 0.534 0.440 82.4 3.330 1.035 31.1 May 0.965 0.938 97.2 4.730 2.142 45.3

The lowest flow at Kaukapakapa at Oak Hill in 2001 – 2002 was 0.01m3/s on 4 February (see 3 3 Table 2). The Q2.33 is 0.0197m /s and the Q5 is 0.0032m /s, so the lowest flow in the 2001 – 2002 season was only half the mean annual low flow. This reflects the general lower than average rainfall from February to April.

3 3 For the Hoteo, the lowest flow, on 23 April 2003 of 0.53m /s (see Table 2), the Q2.33 is 0.35 m /s 3 and the Q5 is 0.272m /s so the lowest flow in the period was higher than the mean annual low flow.

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75 Percentage Deviation Percentage 50

1 2 2 0 -02 un-0 Jul-01 ug-01 ep-01 ct-01 ov-01 ec-01 an-0 eb-02 ar-02 pr- ay J A S O N D J F M A M 45407 Kaukapakapa 45703 Hoteo Gubbs Normal Mean Monthly Deviation Figure 6. Monthly percentage flow deviations from normal June 2001 to May 2002.

4. Hydrogeology

There are two main aquifer types in the Northwest, Waitemata Group and Pliocene/Pleistocene sands. No new data has been obtained on the Kaipara Sands aquifer during the year. Similarly there has been no development in terms of research or testing on the cold water aquifer in the Waitemata sandstone.

4.1 Parakai Geothermal Aquifer The Waitemata Group Aquifer is also a reservoir for geothermal water at Parakai. Temperature, resistivity, water level and water chemistry delineate a geothermal field centred on the Paraki Springs Trust (Aquatic Park) and elongated to the north east. The Parakai geothermal water has naturally high chloride, 1000ppm but the sulphate level is only 6ppm indicating there is no salt water intrusion (ARC, 1993). The geothermal field cover approximately 30ha and bore production temperatures range from 40 – 650C.

The ARC monitors the water level in two groundwater monitoring bores at Parakai (6464007 & 6464009), the former is 250m deep with a higher temperature and responds to aquifer pumping, the latter is 58m deep and somewhat cooler.

Groundwater levels in both ARC monitoring bores are continuing to rise (Figure 7), which can be attributed to more efficient geothermal use and better maintained bores. The maintenance of bores is critical to maintaining geothermal pressures and temperatures as leaky bores allow water to run to waste. 4.0

6464007 6464009 3.5

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Water level (m amsl) 2.0

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1.0 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002

Year Figure 7. Groundwater levels (metres above mean sea level (amsl)) in two monitoring bores at the Parakai Geothermal field. 6464007 is the deep bore and 6464009 is shallower, towards the periphery of the field and cooler.

5. Surface Water Management

The Northwest area comprises five surface water management areas (Figure 9). The numbers of consents and total daily allocation in each management area are shown in table 4.

Figure 8. Surface water management areas in the Northwest

Table 4. Surface water consent allocations and numbers in the Northwest area at 30 June 2002. Surface Water Number of take consents Combined Maximum Total surface Management area allocation m3/day water allocation Stream Dam Stream Dam m3/d Hoteo River 7 5 6,028 9,355 15,383 Upper Kaipara Streams 0 6 0 3,998 3,998 Kaukapakapa 6 4 760 525 1,285 South Kaipara Head 3 1 914 120 1,034 Araparera, Makarau 1 1 2 95 97 TOTAL 17 17 7,702 14,093 21,797

Consented surface water use in the Northwest area is dominated by water taken for pasture irrigation for dairying in the Hoteo River Catchment and the Upper Kaipara Streams management area. There are 7 consents for this activity, 4 of which have allocation in excess of 200,000m3/year. Four of the pasture irrigation Consents are met from dam abstractions rather than run of stream flow.

The largest consent in the Hoteo River Management Area is a combined surface and ground water consent for Hoteo Farms for 500,000m3/year. The Consent includes a condition that surface water is taken in preference to ground water. For the purposes of this report, the annual allocation (and usage figure) has been divided between surface (85%) and ground water (15%) based on actual data, although this split is not fixed.

Rodney District Council have consent to take 1300 m3/day from the Hoteo River for municipal supply for Wellsford. This consent has expired and is currently being renewed.

In the Kaukapakapa River Catchment water demand is greatest on the Waikahikatea, Waipapakura and Waitoki Streams and the main river. Water is abstracted primarily for horticulture, although a golf course and quarry operations also hold water permits.

Allocations from run of stream are generally given as a volume per day as the resource is ecologically sensitive to daily fluctuation. The allocations therefore are determined in relation to a given flow rate. However, for the purpose of comparisons of use an annual figure is used. Where an annual figure is not specifically stated in a consent, a figure has been derived using the maximum daily and a generic figure for the number of days' abstraction at the maximum rate for a given activity. The annual allocation figures are shown in Table 5.

In order to manage the resource effectively it is important to have an understanding of the actual use as opposed to the theoretical demand (allocation) taking into account climatic factors such as rainfall. Historical data on levels of abstraction have not been reliable or accurate but a programme to improve the standards in this area is underway. For this report an estimated use figure for both ground and surface water is included. The estimate of actual use is based on metered flow, recorded by individual Consent Holders and submitted quarterly to the ARC. The level of data received for surface water in the Northwest covers 63% of the consents. Non-returns are generally from smaller users so a simple extrapolation of the total data is not appropriate. Recent endeavours to raise the level of return should see this figure become firmer in future years. It should be noted that use refers only to Consent Holders who are required to have a meter and does not include those with low-level takes (Permitted Activities) or those taking water for domestic and stock drinking purposes only. The estimated use is shown in Table 5, it is noted that on average only 22% of the allocated volume of water was abstracted. This may be a reflection of the spring and summer rainfall being significantly above the historic mean levels over those months (Figure 3).

Table 5. Comparison of surface water allocation and use. Figure may not total because of rounding. Surface water Water Water Estimated Water Percentage of Management Area allocation Allocation Use Consent Holders m3/day 000m3/year 000m3/year providing returns Hoteo River 15,383 1,362 338 58 Upper Kaipara Streams 3,998 407 64 100 Kaukapakapa 1,285 118 20 78 Araparera, Makarau 1,034 16 0 0 South Kaipara Head 97 152 31 80 TOTAL 21,797 2,058 454 -

6. Groundwater Management

There are five groundwater management areas in the Northwest, including the Parakai Geothermal area, refer to Figure 9.

Figure 9. Groundwater management areas in the Northwest. There are 59 consents to take groundwater in the Northwest at May 2002 (Table 6). The largest single user of groundwater in the area is Hoteo Farms, refer to paragraph 1.5.1. Tapora Farming Community Water Supply has consent to take water from up to 6 bores to supply a number of farms in the Okahukura Peninsula. This is primarily emergency or supplementary source in addition to their two large dams.

Water for horticultural purposes is generally for small-scale developments although some large (5 ha.) glass and plastic house developments have been established in the last 5 years. The combined annual allocation of all consents, including the 15% of Hoteo Farms Ltd combined groundwater/surface water allocation was 1,091,640m3. After pastoral irrigation the largest groundwater use is from the Parakai Geothermal Aquifer used for recreational bathing.

The use of groundwater has been estimated in the same manner as for surface water (refer to section 1.5.1). The level of consents covered by the estimate is 77%, which gives a more reliable indication of actual use than that for surface water. For the year under review the take by Consent Holders amounted to over 490,000m3 or 61% of the volume allocated.

Table 6. Groundwater consent allocations and estimated use in the Northwest as at May 2002. Figures may not total because of rounding.

Groundwater Management Number of Water Estimated Percentage of Area consents allocation Water Use Consent Holders 3 3 providing returns 000m /year 000m /year Hoteo Groundwater 8 152 62 67

North west Groundwater 22 213 29 77

Okahukura 8 266 275 88

Parakai Thermal 24 252 158 75

South Kaipara Head 21 210 125 79

TOTAL 59 1093 491 -

6.1 Management of the Parakai Geothermal Resource The management objective for the Parakai geothermal field is to maintain aquifer water levels sufficient to avoid cold groundwater or seawater intrusion, which could result in a reduction in aquifer temperatures (ARC, 1993). The management regime to achieve this is to maintain greater pressure in the centre of the field (by way of a higher water level) as a means to limiting intrusion of cold water. Figure 7 provides a twelve-year history, showing water level in the deeper bore (6464007) generally is higher than the shallower, cooler bore 6464009.

An envelope plot is used to trace the mean monthly water level over the twelve months from June 2001 to May 2002, compared with the historic monthly means. In Figure 10, the pale shaded area represents plus and minus one standard deviation from the long term record mean for that month. In theory 68% of the monthly mean readings will fall within this bracket.

The darker shading represents up to two standard deviations from the mean. Therefore 95% of all monthly means should lie within the total shaded area. Figure 10 plots the monthly mean for the two bores over the 12 months (June 2001 – May 2002) within the boundary of plus and minus one and two standard deviations of the long term (from 1989) monthly mean.

6464007 3.5

2.5 PARP:ALW Plan level depth (m) 2 6464009

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1 JJASONDJFMAM months 2 Standard Deviations 1 standard deviation Monthly Mean

Figure 10. Groundwater level monthly mean (2001 – 2002) for the deep Parakai bore (6464007) within an envelope of standard deviations of the long term monthly mean. The level of the shallower bore (6464009) and the PARP:ALW Plan minimum depth are included for reference.

The Proposed Auckland Regional Plan: Air, Land and Water (PARP:ALW) sets a minimum ground water level for the deeper bore (6464007) at 2.5m above mean sea level. The level of this bore is consistently above that mark, as shown in Figure 10. For the months December though March the level in the main bore was higher than 2 standard deviations above the mean that is, this level would occur less than 5% of the time. There is no information to detail the reason for this but may be related to ambient air temperature and lack of use of geothermal pools.

Water levels in any one month respond strongly to pumping in that month with rainfall having little effect on water level. Universal metering was implemented in 1984 and this resulted in reduced water use and the increase in water levels from 1984 to 1990. Since 1997 seven

11 geothermal bores in the vicinity of Springs Rd have had their casings modified to prevent previous flowing artesian conditions. This reduction in uncontrolled flow is believed to be responsible for the consistent increase in water levels in bore 6464007 since 1998.

There are 24 geothermal groundwater consent holders who are collectively allocated 251,850m3 annually. The largest daily allocations of geothermal water at Parakai are the three public pool complexes: Parakai Springs Trust (Aquatic Park), Rex Swensson (Palm Springs) and Parkhurst Corporation totalling over 570 m3/day. Smaller allocations are granted for motels, a proposed resort and a home for the elderly (total 131 m3/day). The balance of geothermal groundwater allocation at Parakai is mostly for domestic users. Use is 63% of the allocation and this figure represents 75% of the consent holders who returned water meter readings from June 2001 to May 2002.

All Consents to take geothermal groundwater at Parakai expired in December 2002 and replacement consent applications are being processed.

7. References

Auckland Regional Council, 1993: Draft Parakai geothermal groundwater resource statement and management plan

Crowcroft, G.M. & Scoble, R.G. 1999: Drilling Report Rimmer Road, Helensville monitoring bore. Auckland Regional Council TP 120. P6-7.

NZ Geological Survey, 1961: Whangarei map 1:250,000 DSIR, Wellington, New Zealand.

Salinger, J. & Griffiths, G., 2001. The ARC Climate report, NIWA, Auckland p22.