State of Canterbury's Water
State of Canterbury's Water
Environment Canterbury (ECan) says that regional groundwater levels and surface flows are likely to become critical for some users later in the irrigation season, which could lead to restrictions based on minimum flows and water depth.
An analysis of Canterbury’s water resources for December 2008 shows that although recent rainfall has alleviated dry soil conditions, it is unlikely to arrest the declining state of the groundwater and surface water resources.
Rainfall for October was at 70 percent of the long-term average across the region. November rainfall had record low totals at some recording sites with only one quarter of the long-term monthly average having fallen that month. However, many areas have received more than their average rainfall for December.
Selected foothill rivers and streams reflect these patterns, with flows below average for October, and less than half of the long-term monthly average for November. The significant rainfall in mid-December has raised flows in most rivers although the large alpine rivers were flowing at slightly above average levels for October and November.
When measured prior to the December rainfall, groundwater levels were rapidly declining, especially in shallow and moderate depth wells. Many deep wells exhibit groundwater at very low levels, similar to those experienced in the 2005-6 summer.
Soil moisture levels have now recovered to mean or above mean levels except in the northern part of Canterbury.
General state of groundwater
An analysis of the groundwater levels across the region indicates that 60 percent of the moderate to deep monitoring wells (more than 30 metres deep) exhibit below average groundwater levels. Similarly, 60 percent of the region’s shallow monitoring wells (less than 30 metres deep) exhibit below average groundwater levels.
Kaikoura and Waipara areas are generally recording average groundwater levels but showing rapid seasonal decline.
Most wells in the Ashley–Waimakariri zone also display average to above average levels of groundwater but exhibit similar seasonal trends to those in Waipara.
Christchurch-West Melton monitoring wells show groundwater levels above those at which restrictions are triggered to be much higher than at this time last year.
In the Christchurch area, most wells are exhibiting groundwater levels to be at or above average.
In the Central Plains, most shallow and some moderate to deep wells are still exhibiting above average levels. Some deep wells are exhibiting groundwater levels below average and in some cases, below those at this time last year. In almost all wells, the decline of groundwater levels is rapid.
In the Ashburton-Rakaia zone, almost all wells indicate groundwater measurements at or below average levels; two deep wells display very low levels.
In the Mayfield-Hinds-Valetta zone, almost all groundwater levels are at or below average levels and declining rapidly.
In the Orari zone, most of the monitoring wells are at average levels or below with some deeper wells showing low levels.
In the Timaru – Pareora – Waitaki zone, many monitoring wells are showing average or below groundwater levels with the remainder showing levels well below average.
The outlook for groundwater within deep strata in the Central Plains and Chertsey areas is for continued declines to record low levels. Groundwater in areas receiving benefit of localised alpine river recharge is likely to remain at average to below average levels.
For information contact Adam Martin, ECan Surface Water Scientist, 03 372 7350;
Howard Williams, ECan Groundwater Scientist, 03 372 7175.
Groundwater levels can be checked on the Environment Canterbury website: http://www.ecan.govt.nz/Our+Environment/Water/Groundwater/Groundwater+Levels/Latest-groundwater-levels.htm