GW completes comprehensive study of Wairarapa Valley's groundwater
An investigation into the Wairarapa Valley’s underground water resources has provided vital information about the interactions between the valley’s aquifers, rivers and streams and what happens to them when water is taken for irrigation or other purposes.
Greater Wellington’s Environmental Monitoring and Investigations (EMI) Department’s initiated the six-year long investigation in 2005, after concerns over the sustainability of annual steady increases in water abstraction and their impact on river and stream flows.
The investigation involved a range of field studies leading to the development of a three-dimensional computer model that can be used to show changes in groundwater (aquifer) levels following water takes. The model also allows the effects of groundwater takes on river and stream flows to be examined.
Among the recommendations arising from the study are that ground and surface waters of the Wairarapa Valley should be managed as a single resource.
This would be a significant change to the way Greater Wellington allocates water – the current Regional Freshwater Plan, now up for review, has separate groundwater and surface water allocation limits.
New groundwater management zones in the Wairarapa Valley are also recommended, with the groundwater takes within these zones categorised by their degree of impact on water flows and levels in neighbouring surface waters.
Typically, shallow groundwater takes that are close to surface water bodies, such as rivers, streams and springs, will have more impact on water flows and levels in these environments than deeper or more distant groundwater takes.
Under the proposed approach there could be less water allocated in the future in some areas identified as already being over-allocated, and more water allocated in other areas.
Te Upoko Taiao – Natural Resource Management Committee Co-Chair Chris Laidlaw says the groundwater investigations provide a strong scientific basis to underpin a review of current water allocation policies being undertaken as part of developing a new regional plan over the next few years.
“These investigations significantly advance our understanding of groundwater resources in the Wairarapa Valley. They will ultimately give us more options to manage water allocation in a sustainable way in the future.”
Greater Wellington last month held a series of meetings attended by more than 100 water take consent holders in the Wairarapa to discuss the study’s findings.
“We intend to consult further on the recommendations of the groundwater investigations with resource users and the wider community,” Cr Laidlaw says.
Click here for the principal report documenting the proposed new groundwater management framework
About the Wairarapa Valley Groundwater Study
The groundwater project had three phases.
- Phase 1 was completed in December 2006 and involved a regional review which highlighted that the groundwater and surface water system are essentially one resource. It also identified three groundwater sub-catchments for modelling purposes – Upper Valley, Middle Valley and Lower Valley.
- Phase 2 of the project involved detailed modelling of each of these catchments and incorporated a range of field studies: the drilling of monitoring bores, a seismic geophysics survey, isotope chemistry sampling to determine groundwater age, a springs survey and the reading of meters on consented water takes. Phase 2 also involved analysis and quantification of rainfall recharge processes, groundwater abstraction and groundwater chemistry. From these studies a 3-D computer model was developed for each of the three sub-catchment areas.
- Phase 3 was undertaken over the past year. It involved modelling different water abstraction scenarios using the groundwater models developed during Phase 2 of the investigation. A key component of Phase 3 of the investigation was to establish the rate of flow depletion that would be expected for rivers, streams, springs and wetlands under varying groundwater abstraction scenarios.