State of Canterbury Region Water Resource 2005 (Report U05/89)

 2005 Water Resource Report  4.5MB [approx 11min on 56k]

Executive Summary

The state of Canterbury’s water resource over the winter through to the start of spring (to October) 2005 is reviewed.

Parts of the Canterbury plains and foothills received very low winter rainfalls, less than 50% of the average for June to September (inclusive). These low rainfalls are expected to occur approximately once in 20 years. Areas in Kaikoura, the Southern Alps and South Canterbury were slightly better off with average rainfall totals between 50 and 95% of average.

These low rainfalls are reflected in the river flows, where nearly all foothills rivers in North Canterbury recorded the lowest ever median flows for this period, with some sites having 30 to 40 years of data. Lowland streams dependent upon upstream contributions to the groundwater system from foothills streams and rainfall over the plains are at their lowest recorded median flows for the June to September period. All other rivers in the region have had flows below the median for this period. Those dependent upon northwest rainfall have better flows and range from 70% to 90% of the long-term median flow. 

Soil moisture levels on the plains and foothills are approximately 20 mm more in deficit than is normal for this time of year. 

Projections for October to December 2005 prepared by NIWA and the New Zealand Meteorological Service, for the Canterbury high country, foothills and plains are for normal rainfall and sunshine, with below average available soil moisture for the foothills and plains.  Alpine rivers are expected to have normal flows while foothills and lowland streams are predicted to be below normal. 

Over most of the Canterbury Plains groundwater levels particularly in deep aquifers are currently 1 to 3 metres lower than the same time last year, and record lows are recorded in many regions.  The exceptions to this, with average groundwater levels, are the Kaikoura and Pareora-Waihao areas, the lower Ashley-Waimakariri area and the coastal Ellesmere area. Many groundwater levels were low at the end of last irrigation season, but the dominant effect responsible for the current lows is the very dry 2005 winter which provided very little recharge.  Recent snowfall and rain has had very little impact on groundwater levels, especially for deeper aquifers. The rain has caused some rivers to flow and shallow wells near these have risen a little.