Groundwater science due
Scientific modelling has shown for the first time a potential correlation between deep groundwater around the Waimakariri River and water quality in Christchurch and Kaiapoi.
Over the past 20 years, scientists working on the Waimakariri groundwater system have developed an understanding of how water from the river enters the shallow groundwater system south of the river and flows towards Christchurch, where it replenishes the aquifers under the city.
There is, however, some uncertainty over what happens at deeper levels in what is a complex system, and over longer periods of 50 to 100 years. While the possibility of the deeper groundwater moving under the river towards Christchurch had previously been discussed, an Environment Canterbury (ECan) spokesperson said there had been no evidence until this recent modelling.
For this reason, the Waimakariri sub-regional planning process has been lengthened to allow more time to reach an agreed understanding on the nature of groundwater movements. A series of nine wells in three separate locations, five of which have already been drilled, will measure groundwater at depths of 50m, 100m and 150m.
A survey being held in two weeks’ time will see 150 wells in the region measured to give an idea of groundwater levels, flows and water quality, the spokesperson said. The new data from the wells and survey will be analysed by the technical group overseeing the investigations, which includes scientists from ECan, Lincoln AgriTech, GNS, and consultant experts.
With the scientific work now due to be completed by the end of the year, the Waimakariri Water Zone Committee plans to establish a programme of recommendations, the Zone Implementation Programme Addendum, by September 2018.
The extra time will allow the committee and the community more time to consider how best to deal with the freshwater and ecological issues facing the zone, the spokesperson said. This included river flows, surface water quality, and groundwater recharge and movement.
The recommendations will be used by ECan to set water quality and allocation limits for the Waimakariri zone, through a plan change to the Canterbury Land and Water Regional Plan.
The Waimakariri work is one of a series of plan changes to the Canterbury Land and Water Regional Plan, introduced by ECan in 2012, to provide more specific rules to manage water quality and quantity for each major catchment.