TP194 North-West Auckland Water Resource Quantity Statement 2003
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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. ii 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 ii 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 2 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. 200 175 150 125 100 75 50 Percentage Deviation 25 0 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 4 during July. For 2001-2002 the low flows in the Kaukapakapa extended from February though April. This is shown graphically at Figure 6. 1400 45703 1200 1000 800 600 400 Daily stream discharge (l/s) 200 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