Abstract
Gisborne District Council (GDC) and GNS Science jointly undertook a review and update of information available for the Holocene East Coast alluvial areas (ECAs), excluding Poverty Bay Flats, for the Gisborne region. The aim of this review was to: identify data gaps and provide recommendations regarding further data collection and groundwater monitoring to inform GDC’s sustainable management of these areas, in the context of the National Policy Statement for Freshwater Management and increased interest from the community. This work was funded through an Envirolink medium advice grant, and built on previous collaborative work between GDC and GNS Science, which identified twelve ECAs that potentially host aquifers. To date, no groundwater monitoring activities have been undertaken within any of the ECAs. Geological (GDC bore records, QMAP), hydrological (river gaugings, wetland and spring locations), soil, and land use datasets were collated and reviewed to consider the aquifers’ potential. The geological data review resulted in an update of the 2012 ECA boundaries; and for five of the ECAs (Pakarae, Wharekahika, Muriwai, Uawa and Waiapu), sub-divisions of up to three zones were developed as proposition for management purposes. To improve the conceptual understanding of the ECAs, recharge mechanisms and connections between the ECA and potential adjacent aquifers were also investigated. ECA boundaries, land use and soil data were used to investigate hazards that may have a negative impact on groundwater quantity and quality within the ECAs, e.g., sea water intrusion, or contamination from land use activities. Water budgets were calculated for all ECAs to estimate the amount of groundwater that is potentially available for allocation. Using the estimated groundwater available for allocation (GAA), the possible allocation rate (PAR) for groundwater was calculated for each area. Due to the lack of data (e.g., synoptic gaugings), the water budgets had to be simplified, which also had uncertainty implications for the calculated PAR. Identified data gaps include: systematic recording of well depth and lithological information; borehole information deeper than 5 m; groundwater level information; groundwater quality information; hydraulic properties of individual ECAs; adequate mapping of springs and wetlands within each ECA; and synoptic gaugings and low flow river / stream water chemistry sampling.
Published Version
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