December 20, 2006

Canterbury groundwater on healthy levels

Shallow and intermediate aquifers throughout the Canterbury region continue to display average to above average levels. However Environment Canterbury groundwater scientists say there is a slight seasonal declining trend visible in most records. This decline is the expected seasonal pattern associated with increased irrigation demand and a corresponding decrease in effective rainfall.

"Deeper aquifers are showing a significant increase to average levels and groundwater levels in the very deep aquifers have also started to rise. Some of these very deep wells in the Central and Ashburton plains have achieved average to slightly below average levels, though the response is still patchy", says ECan Hydrogeologist, Dr Howard Williams.

He says the slow increase in groundwater levels in the deeper aquifers is due to the slow rate at which infiltrating rainfall recharge travels down to the aquifers. In the shallower aquifers, rainfall and associated snowfall combined to create a rapid increase in groundwater level in June and July. In some of these wells, groundwater levels reached new highs. "The equivalent recharge effect in the very deep aquifers is only just now beginning to be observable; let's hope it continues through the summer," says Dr Williams.

In the Central Plains between the Rakaia and Waimakariri rivers, almost all monitoring wells indicate groundwater is at average to above average levels. Similarly, in the Ashburton Plains, all but very deep wells north of State Highway 1, show average levels.

In South Canterbury, in the Levels Plains area and around Temuka, groundwater in most shallow and moderate depth wells has recovered to average levels and these are now exhibiting a slow seasonal decline.

In North Canterbury, wells in the Rangiora, Kaiapoi and Oxford areas are indicating that groundwater levels are higher than this time last year.

Groundwater in aquifers serving the Christchurch water supply and industry indicate average to above average levels.

"Apart from the dry month of September, rainfall has continued during the spring period, with the result that irrigation demand is probably less than anticipated", says Dr Williams. ”Lower irrigation demand would be expected to result in a smaller decline in groundwater levels in comparison to previous years.” He says soil moisture results from Lincoln and Winchmore indicate that moisture levels are slightly higher than average for this time of year and significantly greater than this time last year. At Hororata, the moisture levels are recovering from the dry spring, with soil moisture levels just below average for the time of year.

“All in all it’s good news when compared to last year’s levels that set new record lows throughout the Canterbury plains.

ENDS

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