The depth to the water table in a well which is not being pumped is known as its static level. It is a very useful measurement to have because it indicates the nature of the underlying aquifer structure. Generally speaking the static levels of wells tapping aquifers beneath the western or southern Wairau Plain are below ground, whereas those in the east or closer to the Cloudy Bay coast tend to be closer to the surface or artesian. This reflects the transition from unconfined to confined aquifers.
The greatest depths to the water table are associated with deep wells tapping the Southern Valleys Aquifers with the maximum being close to 30 metres. The Marlborough District Council has archived the static water level observations recorded by drillers for several thousand Waiaru Plain well records and these are plotted in plan view in the Figure below.
A clear pattern exists whereby red or yellow dots represent wells with aquifer levels below the surface, and blue or green dots marking near surface and artesian pressures. The appearance of green dots coincides with the appearance of the confining layer.
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