Water allocation

Groundwater

Groundwater Management

Most groundwater use in the Auckland Region is abstracted from high use aquifer management areas. These aquifers are considered to be at risk from over-pumping or water abstraction. Management objectives are aimed to ensure that groundwater allocation and use is within the availability.

• there are 32 Groundwater management areas in the Auckland Region
• there are 13 High Use Aquifer Management Areas
• long Term groundwater levels are useful indicators of the aquifer health. Groundwater levels should not continue to fall over the long term
• in general, falling groundwater levels suggest that discharge is greater than recharge and rising levels suggest the reverse .

Groundwater availability

The maximum amount of water that can sustainably be allocated from an aquifer (the water availability) is determined by taking into account

• Aquifer recharge
• The spatial distribution of bores; and
• Outflow requirements of the aquifer, including
  i. Flow at the coast, to prevent saltwater intrusion;
  ii. Requirements of streams and springs;
  iii. Recharge of adjacent or underlying aquifers; and
  iv. In the case of geothermal aquifers, water levels or outflow to prevent cold groundwater or seawater intrusion and reduction in aquifer temperatures.

Groundwater availability and allocations

Section 1.4 of the latest Auckland Water Quantity Statement report outlines the groundwater availability, allocation and use in the high use aquifer management areas

Effects of Taking Groundwater

Changed water level and flow regimes in aquifers caused by the taking of groundwater may lead to:

• reductions in spring and stream base flow
• the degradation of freshwater ecosystems and wetlands
• the degradation of water quality through saltwater intrusion and contaminant transport
• loss of recharge to adjacent aquifers
• aquifer consolidation and
• reduction in the temperature of geothermal waters.

Such changes can result in reduced water availability, both for present and future generations.

The potential of aquifers in the Auckland Region, particularly in high use areas, will be sustained for current and future generations through the careful management of groundwater allocation.

High Use Aquifers

Aquifers are important as direct sources of water supply for domestic, industrial and rural use. They are also the major contributors to the base flow of many streams, particularly in the southern parts of the region. As such, aquifers contribute to the overall quality and diversity of surface water bodies.

The main aquifers in the region are:

• Greywacke, which comprises much of the SE part of the region, including the Hunua Ranges and some Hauraki Gulf Islands. It is a comparatively poor aquifer, and most groundwater movement is through fracture zones
• Waitemata Group sandstone and mudstone. Apart from a few locations it forms the local basement. Again most groundwater movement is through fracture zones. Bores are generally drilled to 200-400m depth, and yields range from a few cubic metres to over 1000 cubic metres per day. Water levels naturally fluctuate seasonally by only a few metres, with lowest levels around May. In many part of the region the Waitemata aquifer is overlain by shallower viable aquifer
• Basaltic volcanic fields occur in the Auckland-western Manukau area, and in Papakura/Franklin. Both fields are important sources of groundwater. Bores are typically drilled to depths of 20-150m. The aquifers are recharged by direct rainflall and groundwater levels respond quickly to rainfall events. Urban aquifers are also recharged through stormwater soakage.
• Kaawa Formation which is an important aquifer in the Franklin lowlands from Waiuku to Paerata, and in the Auckland airport and Middlemore areas in Manukau. The shell lenses within the green cemented sands comprise a good aquifer. The depth to the aquifer increases south towards the Waikato river. From Waiuku to Paerata the aquifer is fairly shallow (less than 100m below sea level), while at Puni it is quite deep (300m below sea level). Bores are generally screened across the coarse shell beds. Bore yields are typically 800-1200 m3/day for a 100-150mm diameter bore.
• Gravels and sands, that are younger than the Kaawa formation, form an important aquifer in the Drury area and in Clevedon valley. The Drury sand aquifer is relatively low yielding with 100mm diameter bores producing 150 m3/day or less. In contrast the Clevedon gravel aquifer is moderately high yielding, with up to 1000 m3/day from a 150mm diameter bore.

Some aquifers in the Auckland Region are under threat, being highly allocated (more than fifty per cent allocated and/or are major sources of spring and stream flow) and/or being adversely affected by over pumping, or are in areas of high potential growth where they are very likely to become highly allocated over the life the Regional Plan. These aquifers have been identified in the Plan as High Use Aquifer Management Areas. In order to continue to meeting existing and future water abstraction demands and to provide base flow for surface streams, careful management of water availability within these aquifers is required. The management areas are (from north to south):

• Tomorata Waitemata
• Omaha Waitemata
• Kumeu-Hobsonville Waitemata
• Onehunga-Mt Wellington Volcanic
• Waiheke (all aquifers)
• Manukau City Waitemata (west of motorway)
• Manukau City Kaawa
• Clevedon Waitemata
• Franklin Volcanic (Bombay, Pukekohe & Glenbrook aquifers)
• Franklin Kaawa ( excludes Awhitu Peninsula)
• Drury Sand-Volcanic (north of Maketu Road)
• Waiwera Geothermal
• Parakai Geothermal

The area in which these High Use Aquifer Management Areas are located are identified on the PARP: ALW October 2004 Map Series two (sheets 1-19). They are described in section 3.8 of the PARP: ALW June 2005.