A declining trend in Wairau Aquifer levels has been observed at western Wairau Plain MDC monitor wells since 1973, which pre-dates the Marlborough wine industry. While the declining trend of around 1 metre over 50 years may not appear large at an average of 20 mm/year, the risk is if it continues over the very long-term, groundwater springs may dry up and ultimately there could be seawater intrusion of our coastal aquifers. Given the depleted storage volume of the Wairau Aquifer after a series of dry summers since 2014 and minor Wairau River activity through the past winter recharge period, current levels of consented abstraction are also compounding the issue. Identifying the drivers via the Gravel Bed Rivers Project (GBR) is a priority project for MDC, given the longer term regional scale implications for flood control, reliability of consented water consents, wetland health and security of coastal groundwater supply.
The causes of the decline are known to be incremental and long-acting. These drivers have been actively investigated over the past decade, but research is challenging because most of what goes on is hidden beneath the surface with measurements often indirect in nature.
You can learn more about this project by downloading these two files from the MDC website. The original report from June 2020 is available here (Agenda item 5) and the update from April 2021 is available here (Agenda item 4).
An excellent report was prepared by NIWA scientists for the MDC Councillors and staff. It was presented to the Environment Committee by Gregor Macara on April 22nd, 2021 and updated them on the latest information on climate change projections and impacts for the Marlborough region. It's well worth looking at just to see the the Executive Summary. Drought potential is projected to increase across Marlborough, with annual accumulated Potential Evapotranspiration Deficit (PED) totals increasing with time and Climate change projections and impacts for Marlborough 9increasing greenhouse gas concentrations. By 2040, PED totals are projected to increase by 50-150 mm. By 2090, PED totals are projected to increase by 50-200 mm (medium concentration pathway) or 75-250 mm (high concentration pathway). Another significant projection is that mean annual low flow (MALF) magnitudes are expected to decrease across both
greenhouse gas concentration pathways and future time periods for most catchments. A decrease in MALF is expected to exceed 50% for most of the river systems in the region with increased greenhouse gas concentration and time.
The full pdf file can be downloaded here -