Information used in this indicator has been compiled from groundwater resource consents and estimates of permitted groundwater takes in the Waikato region. Check out our map showing the density and distribution of consented groundwater takes in our region.
Waikato Regional Council estimated the number of permitted users based on a database of wells drilled since 1988 (and some before this date) and a model of likely use based on both the number of people and animals in each aquifer zone. Check out the methodology of the model for calculating the ‘permitted’ water use as described for surface water catchments in Technical Report 2007/47.
Data for this indicator were collected from groundwater resource consents and estimates of permitted groundwater takes up to 2015.
The natural flow patterns of groundwater systems are complex. It is difficult to accurately estimate the volume of water moving into and out of an aquifer. Waikato Regional Council estimates the amount of groundwater in an aquifer by:
1. Estimating the amount of available groundwater
We estimate the annual daily average of available groundwater using the following equation:
A = (RR x Pr x Ga x Ra) / 365 days
A = annual daily average of groundwater availability – cubic metres per day (m3/day).
RR = average annual rainfall over the aquifer – metres per year (m/year).
Pr = estimate of rainfall recharge to groundwater as a fraction of the average annual rainfall over the aquifer. This will usually range from 0.22 (22 percent) to 0.4 (40 percent) in the Waikato region.
Ga = groundwater recharge available for allocation. This is estimated to be 50 percent (0.5 in the equation), allowing the remaining 50 percent of recharge to be lost via springs and submarine discharges.
RA = the size (area) of the aquifer – square metres (m2). The size of the aquifers are in line with the aquifers listed in Table 3-6 of Variation 6 (Water Allocation chapter) to the Waikato Regional Plan.
The location of aquifers can be seen here on the water allocation maps.
The above equation assumes:
2. The percentage of ‘available’ groundwater that is allocated for use
We compare an aquifer’s volume of ‘available’ groundwater with the amount allocated (the maximum that can be used by consented and permitted takes). From this we can estimate the level of stress groundwater resources are under. This approach does not take into account the allocation status of any connected streams and rivers which may restrict any further allocation of groundwater even if the aquifer is in the low stress category.
We divide monitored groundwater resources in our region into three categories of ‘stress’:
This provides us with a guideline to identify potential problem areas which may need more intensive monitoring to manage impacts within the aquifer. Most of the monitored groundwater areas in our region are under low to medium stress.
Proposed National Environmental Standard on Ecological Flows and Water Levels – Discussion Document. Ministry for the Environment March 2008.
Waikato Regional Plan Policy 3.3.5: Determining Sustainable yields.