Before the recently ended water restrictions it was my belief the Waiwhetu (Hutt) quifer was only used when the Hutt river was unable to provide enough. As it turned out the aquifer is used everyday.
This raised a question in my mind. Water enters aquifers at a specific rate that can be a lot lower than the rate we are able to remove it at. The current iconic example of this is one of the big aquifers under the north central US where we are draining it faster than it is replenished. So how does the Wellington Regional Council stop this from happening?
To try and get an answer I shot off a quick email to the Wellington Regional Council and got a response the next day.
We have a resource consent to take up to 115 MLD provided we do not lower the pressure in the aquifer beyond 2.3 metres, as measured at the Petone foreshore. There is also a practical limit to how much water we can draw from the aquifer due to pumping and system capacity constraints. This is around 100 MLD.
The aquifer pressure is monitored continuously and our supervisory, control and data acquisition (SCADA) system will alert operations staff if the pressure approaches the lower limit.
A quick and useful answer and no one even had to protest. ;) It's as though they're human. :p
Anyways, I was pleased to see that there are rules in place that make sense for the Waiwhetu aquifer. A minimum pressure requirement definitely stops us from removing at a faster rate than replenishment and is much more responsive to changes in the recharge rate. More importantly it also stops aquifer from being infiltrated by salt water from the harbor; that would be very bad.