Water allocation
What to do about water on Waiheke
Waiheke Groundwater Management Plan
Over the last three years the ARC has undertaken research and monitoring to find out about fresh water supplies and use on Waiheke Island. It aims to work with islanders to make a water management plan for the island that will best meet the current and future needs of the community, as well as protect the environment.
Waiheke has no reticulated (centralised) water supply, and while most people on Waiheke use rainwater to supply their needs, there is increasing pressure on the island's aquifer for fresh water.
Follow this link to find out more about the Groundwater Management Plan.
Technical and monitoring
The first phase of the ARC's work was the technical survey and monitoring of the aquifer and wider environment including streams and wetlands.
A major two part survey of the aquifer was completed last year. It created a model that will allow scientists to see the effects that increased water extraction may have on the aquifer, surrounding streams and wetlands and on the quality of the aquifer's water.
Read a synopsis of the report.
In addition there ongoing monitoring of Waiheke's streams. The ARC monitoring team has recently completed its Winter monitoring for 2008. A number of major streams were assessed and you can see the results here.
Questionnaire and public consultation
Phase two of the Groundwater Management Plan was the gathering of information on how people on the island source and use water, the value they place on water and their advice on how it should be best managed now and in the future. When coming up with a management plan for groundwater on Waiheke, we know that the best knowledge is local knowledge.
We sent questionnaires to over 9000 island residents' and home owners. The ARC received a great response - much higher than would be expected from a questionnaire of this nature, and we wish to thank everyone that took the time to send us their views.
The information gathered from the questionnaires was then analyzed. You can view the questionnaire and the results of this questionnaire below.
The results of the questionnaire, and advice we received from residents has now been incorporated into the next stage of the Groundwater management Plan.
Where to from here?
The next phase in the Waiheke Groundwater Management Plan is the preparation of an ‘Issues and Options' paper, which collates and makes recommendations in the light of all the social and technical information received to date. This is currently being prepared by the Groundwater Management Plan team.
It will be presented to councillors at August's meeting of the Regional Strategy and Planning Committee at Auckland Regional Council.
A copy of the Issues and Options paper will be posted on the website shortly.
More on the Waiheke Island Groundwater Management Plan
Waiheke Island's fresh water is generally sourced from rain water or groundwater. Most people (99%) collect and use rain water for domestic use. Groundwater is extracted from the greywacke aquifer to supplement people's rain water supplies and for some domestic and business purposes.
An aquifer is the underground layer of water-bearing rocks from which water can be usefully extracted from deep bores.
As the population of Waiheke grows, demand for groundwater resources continues to increase.
Most groundwater abstraction on Waiheke Island requires consent from ARC. Resource consents are currently issued to take groundwater for water tanker supplies, accommodation, cafes and restaurants, community facilities and irrigation.
However, taking groundwater from the aquifer can have negative impacts on the natural environment. Taking water means that there may be less available to feed wetlands, springs and streams. While many streams are dry in summer, groundwater abstraction may extend the period over which streams are dry which will further reduce the ecological value. Drawing groundwater also increases the risk of saline intrusion. This means that if too much water is taken from the aquifer, salt water may enter, contaminating fresh water supplies.
The Waiheke groundwater Management Plan aims find the balance between the benefits of drawing water for the community and at the same time making sure the resource is available for future generations, and that Waiheke's waterways and environment are protected.
There are many ways we can do this. Setting a limit on how much we draw from the aquifer is one way, but better use of the rainwater and groundwater resources that we already have is equally as important.
In March 2007 the Auckland Regional Council (ARC) commissioned Sinclair Knight Merz (SKM) to develop an extended groundwater flow model of Waiheke Island.
The study was commissioned to investigate the sustainability of increased abstraction from the
greywacke aquifer system on the Island.
A high demand for groundwater resources occurs on Waiheke Island during the summer period due to a lack of perennial surface water resources, particularly in the vicinity of Onetangi and the Ostend Landfill/Industrial Estate.
This work follows a previous study completed by SKM for the western side of Waiheke Island between Oneroa and the west coast (SKM, 2007). Figure 1 shows the locations of the two groundwater models developed by SKM.
The results of these studies will help establish a groundwater allocation policy for the island.
The existing consented and fictitious pumping rates used for model simulation purposes in the
analysis conducted in this study are assumed to follow demand with a peak pumping rate only
required during the summer.
Three scenarios were selected for predictive simulation to assess the effects of abstracting differing proportions of the mean annual recharge. For each scenario the simulation assumed that the fictitious bores assigned to each geological unit (model layer) were all pumped at the same rate.
The predictive simulation provided the following main findings
- Drawdown effects from pumping are highly sensitive to the geology of the target aquifer and the distribution and extent of rock fracturing will be of key importance in determining sustainable pumping rates and bore placement.
- Saline intrusion is determined primarily by groundwater head, so drawdown induced by pumping is the key influence on saline intrusion. Model simulations showed that drawdown and therefore saline intrusion potential relies more heavily on geology of the target aquifer than pump rates.
- Modeling also indicated that the bore location, depth and pumping rate influenced the total abstraction of groundwater.
