You are here:  ANRA home

On this page

• Introduction
• Character of the groundwater resource
• Are groundwater levels changing?
• Further information

Introduction

The groundwater resource characteristics for the Ascot groundwater managment unit are presented below. This includes technical detail on aquifer properties and water level change for key monitoring bores.

What is the character of Ascot's groundwater resource?

Vital Statistics:

Unconfined fractured Newer Volcanics basalt aquifer. Need explanation of fracture flow and anisotropy?

Method used for determining sustainable yield:

The PAV determined for the Ascot GMA was calculated as 8,166 ML/year, based on the hydrograph fluctuation method. This method involves estimating the fluctuation in groundwater level, and relating this back to the aquifer storativity and porosity to determine the change in volume for that aquifer. This change in volume represents the equivalent recharge over that time period. The volume determined for the Ascot GMU was estimated using limited information and hence has a poor reliability.

The hydrograph fluctuation method proved a reasonable estimate of recharge to the aquifer and subsequently the sustainable yield of the aquifer system. The other method used to assess recharge was rainfall infiltration, which had an equivalent recharge volume to the volume estimated using the hydrograph method.

Discharge at the margins of the lava flows to the underlying Tertiary sediments and basement rock, as well as to streams, springs and lakes was considered. The limiting effect of well interference on aquifer extraction was found to have little influence on the unconfined basalt aquifer.

It should be noted that the PAV applies to a large area and localised intensive extraction is likely to cause local interference effects in the fractured rock aquifers. Under normal climatic conditions it is possible that the allocated licensed volume is not fully extracted in any one year.