Freshwater monthly snapshot
Groundwater levels in November were average across Canterbury. Following a relatively dry October, November rainfall across the region was well above average, with monthly records at some sites (e.g. Blandswood, Geraldine Forest, and Hadlow). Rivers had higher than average flows for the month, which caused damage to many water level recorders. On 9 November the Rakaia River at Fighting Hill peaked at 4,194 m3/s, the highest flow since January 2013.
The maps above summarise rainfall, surface water flow, and groundwater levels. They are based on amalgamated data and give a good approximation of conditions across the region in the month past, measured on a five-point scale based on standard deviations.
The rainfall and surface water flow maps are based on geographic and topographic conditions and the groundwater map by Canterbury Water Management Strategy zones.
Climate outlook: December 2018 – February 2019
An El Niño weather pattern is predicted this summer. For Canterbury this often leads to frequent nor’westerlies, meaning hot and dry on the plains (more irrigation demand) and wet in the mountains (higher flows in the big alpine-fed rivers).
Niwa forecast for November 2018 – January 2019
- Temperatures likely above average
- Rainfall likely average
- Soil moisture likely average
- Riverflows likely average
Surface take restrictions for irrigation
The number of sites on restriction are low compared to the same time last year (to the right) due to a wet November, with only a very small handful of sites on full restriction. The monitoring sites on restriction include those on smaller spring-fed streams and some of the lower-reliability bands on the alpine rivers.
In late November/early December last year there were around 70 sites on partial or full restriction.
Groundwater levels and forecast
They are currently at average levels for the time of year. The graph to the right shows the cycle since 2010 in an indicator well west of Christchurch.
Selwyn River/Waikirikiri flows
The good news for the Selwyn River / Waikirikiri, particularly the lower part below Chamberlains Ford, is that groundwater levels are high and there are likely to be sustained good flows over summer. Groundwater has been recharged from a wet 2017 winter and a wet 2018 autumn and spring.
The Selwyn River / Waikirikiri was high in late November (38-40 cumecs), following high rainfall, and was flowing all the way across the plains (see below).
It is likely that the drying across the plains will happen during summer and the lower parts of the river will continue to flow well because they are groundwater fed.
Outlook for summer
It is likely the Selwyn River / Waikirikiri will probably dry across the plains and below in the lower reaches; this is normal summer conditions for the river.
Chamberlains Ford may go dry, but it is unlikely that Coes Ford will do so.