Ashburton water consents review
Environment Canterbury reviewed 87 resource consents that take surface water or stream-depleting groundwater in the Hakatere/Ashburton River catchment.
This review was designed to implement the minimum flows which were developed with the community to protect the waterways' values and to ensure there is a reliable source of water for the environment, community and consent holders.
All reviews have now been decided:
- Three consents were surrendered
- 10 consent reviews were declined, and these consents continue to operate under preexisting conditions
- 74 consent reviews were granted, and new minimum flow conditions have been applied to those consents.
Deciding on consent reviews
The Resource Management Act (RMA) guides what we can consider when deciding consent reviews (see Section 131 of the RMA).
Considerations include the actual and potential effects on the environment of allowing the activity, relevant plan provisions, and whether the activity allowed by the consent will continue to be viable after the change. We may also consider the way the consent has been used.
Under the RMA, a council can only consider the impact of the review on the activity authorised by the consent that is being reviewed, not the impact on the consent holder's farming business as a whole, or on any other resource consents they may hold.
Proposing alternative conditions
People whose consents are under review had the right to propose alternative conditions to those outlined in the review notice.
An allocation was made in our plans to make changing consents easier if consent holders wish to swap your shallow groundwater or direct surface water takes to deep groundwater takes.
However, if alternative proposals would include a higher minimum flow or a delayed date for the minimum flow to apply, the consent review may be publicly notified.
Rangitata Diversion Race consent
The Rangitata Diversion Race (RDR) consent to take water from the south branch of the Ashburton River was reviewed. Some 2,000 litres per second of allocated water has been moved from the "A block" to the "B block", which makes it subject to a higher minimum flow. This has reduced the overall amount of water allocated to the A block, which will create more water availability for all other consent holders, as well as provide further benefits to the health and wellbeing of the waterways.
Find out more about the consent review process
Our team engaged with the community to explain how the catchments' waterways interact, how minimum flows are set and achieved, and what this means for river users.
If you have any questions about our Ashburton consent review process, email them to consentsreviews@ecan.govt.nz.
River modelling and stream depletion
How do we calculate the stream depletion effects of groundwater takes?
For assessing stream depletion effects of groundwater takes, we must calculate the distance of the groundwater take to the nearest river.
To do this, Environment Canterbury used its river classification GIS layer and made some adjustments to take account of river zones and alpine river extents. When considering river zones, the riparian area was included to ensure stream depletion effects were accurately assessed. No maximum distance from the nearest river was applied.
We are happy to consider alternative information to address any assumptions in our model that are not met - this will need detailed site-specific investigations of the stream depletion model inputs to provide a separate assessment of the potential for depletion, i.e. verified distance to the river zone along with hydraulic parameters established through aquifer testing on the subject bore(s).
Hakatere/Ashburton River Modelling for Consent Review
This document outlines how we used hydrological modelling to estimate the impact that the consent review will have on consent holders' ability to abstract water.
Desktop estimate of stream depletion in Canterbury
A desktop exercise has been undertaken to estimate potential stream depletion in the Canterbury Region.
Because of the lack of real, site specific testing, the Theis (1941) stream depletion solution model has been used as the calculation method of stream depletion rates.
This solution requires the least number of input parameters and is a good first estimate because of the conservative assumptions used in the model.
These assumptions will tend to overestimate depletion. However, a storativity value of 0.1 which is considered to be high (when compared to aquifer testing) has been used.
This value reduces the amount of water that the model will predict is coming from surface water (i.e. stream depletion).
The potential for the Theis model to overestimate stream depletion means that this model is a good initial method for determining which consents should be subject to minimum flows, and included in allocation blocks, however, a consequence of the conservative estimation of stream depletion is that the surface water allocation blocks may appear more utilised than will be the case in reality.
Field-testing (aquifer tests and stream conductance surveys) would refine the estimates of stream depletion, and this could result in lower estimates of stream depletion.
Method
The Theis (1941) stream depletion solution has been used to estimate stream depletion rates over 7 and 150 day pumping periods.
The resulting depletion rate is then used to classify the hydraulic connection of the takes using Schedule 9 of the Canterbury Land and Water Regional Plan (LWRP).
Inputs for the stream depletion model were obtained from the Environment Canterbury wells database, Environment Canterbury consents database and Environment Canterbury GIS layers.
Key points:
- The wells which have been modelled are linked to active abstraction consents to take and use groundwater.
- The Q7 (short term (7 day) pumping rate) and Q150 (long term (150 day) pumping rate) were obtained from Environment Canterbury databases, and represent maximum pumping regimes for the granted consents.
- All wells screened less than 35 metres were considered. Where no screen information was available a maximum well depth of 40 metres was used.
- Distance to the nearest river as shown by Environment Canterbury GIS layers; primarily the River Classification layer with adjustments made for River Zones and alpine river extents. No maximum distance from the river was applied.
- Aquifer parameters derived from aquifer tests or estimates of T derived from Winsorized mean specific capacity data within 2.5 km of the subject bore using Bal (1996) this has been constrained to a lower limit of 500 and an upper limit of 10,000m² day. T estimates where no specific capacity data or aquifer test data is present a T of 1500m²/day has been adopted.
- Assumed storativity of 0.1
References
Bal, AA., 1996. Valley fills and coastal cliffs buried beneath an alluvial plain: evidence from variation of permeabilities in gravel aquifers, Canterbury Plains, New Zealand. Journal of Hydrology (NZ) 35 No. 1.Environment Canterbury, 2015. Canterbury Land And Water Regional Plan volume 1 December 2016.Theis, C.V., 1941. The effect of a Well on the Flow of a Nearby Stream. Transactions of the American Geophysics Union, Vol. 22, pp 734-738.
Stream depletion chart for consent holders
Supporting information for stream depletion chart including a key to help you understand the chart.
This information is designed to be read together to give you a better idea of how we have calculated stream depletion.
If you would like more information or want to contact staff about the Ashburton consent reviews, please email us at consentsreviews@ecan.govt.nz.
Key
WAP - Water abstraction point (your bore number)
T m²/d - Transmissivity (metres²/day)
S - Storativity
Q7 - The maximum rate which can be pumped over 7 days, or the average rate of daily or weekly volume (if applicable)
Q150 - The average rate of take required to pump the full annual volume over 150 days, or volume entered in the consents database where no consented annual volume.
SD - Stream depletion rate – this is the rate considered to be coming from the water body over 7 or 150 days.
% SD - The stream depletion effect over 7 or 150 days, recorded as a % of the pumping rate for the same timeframe.
Degree of connection - As per Schedule 9 LWRP
Points to note/matters for you to explore
- You can use Version 3 of the stream depletion tools found here. Use the Theis Jenkins sheet within this document.
- Assumptions – irrigation efficiency (100%) and separation distance/L2 (0m).
- Estimation has been done at the recorded location of the WAP, not the consented location. You may wish to confirm that your bore is located at this location.
- Where the actual location differs to the location specified on your resource consent, you may wish to investigate updating your consent to the correct location.
- Schedule 9 of the Canterbury Land and Water Regional Plan sets the methodology to determine the degree of connection a hydraulically connected groundwater abstraction may have.
- If you have carried out an aquifer test, you may be able to use these results to determine your degree of classification.