State of Water Resources in Canterbury: November 2016

The latest summary of the state of Canterbury water

 The region has received significant rainfall over the month of November, resulting in many stream and rivers flowing in excess of average monthly values for November. Nevertheless, due to many months of lower than normal rainfall and associated low recharge, groundwater levels and associated spring-fed streams are much slower to respond and remain low in many areas.

North Canterbury has received significant amounts of rainfall in November with the majority of rain gauges in the area receiving over 100% of their November long term average. This has boosted the mean monthly flow in all the larger rivers of North Canterbury but the coastal and foothill rivers are still well below their long term average. Similarly, groundwater levels in the central plains and Lake Ellesmere/Te Waihora area remain below the November average. However, annual totals for most northern rain gauges are still well short of average to the end of November. 

The Kaikoura flow monitoring sites of Lyell and Middle Creeks were severely affected by the 7.8 magnitude earthquake which struck on the 14th of November and no reliable data is currently available past this date. The work to reinstate these is ongoing.

The month of November 2016 has seen the South Canterbury area receive very high rainfall totals pushing the mean monthly flows in the majority of the southern rivers to well in excess of their November long-term averages. The only rivers below their November long term average in the South Canterbury area are the alpine Rangitata, South Ashburton and Ahuriri rivers. Significant rainfall in the foothills and along the coast has substantially increased the rainfall totals and river flows in these areas, with the exception of the spring fed Hinds Drains area where three quarters of the 16 water level recorders have been dry for over 12 months. Groundwater levels in South Canterbury were above the average value for November with the exception of the Ashburton- Hinds area; likely a result of the area’s high rainfall totals in October and November.

Even though November has been wet, after three successive winters with very low recharge of groundwater, we expect:

  • ·         More springs and spring-fed streams to dry up, particularly in the Christchurch and Selwyn areas;
  • ·         Surface water availability, particularly in the lower Canterbury Plains, will be very limited this season due to restrictions on surface abstractions;
  • ·         Groundwater consents tied to adaptive management conditions in the Selwyn-Waimakariri, Rakaia-Selwyn and Valetta-Ashburton River groundwater allocation zones (i.e. the consent holder can’t abstract when groundwater levels are low) will have very poor reliability next summer. The majority of wells in these areas recorded lower than average groundwater levels in November 2016.
  • ·         Some groundwater abstractors will have difficulties with wells either drying up or supplying low volumes.

It is highly unlikely that groundwater levels will recover across Canterbury before the end of summer. Any significant rain from now until the end of summer is likely to moisten the soil and may lead to further localised groundwater recharge.

A number of rivers and streams spent the month on full or partial restriction. The group with the poorest start to the irrigation season continue to be the spring – fed streams, many of which spent the whole month of November below the minimum flow levels.