Guidance: Groundwater Diversion and Dewatering
“Your borehole logs show groundwater, please provide an assessment of whether a groundwater permit is required” are the last words that an applicant wants to see in a further information request from Auckland Council, particularly for a small-scale residential development.
However that is exactly what is often received, as a result of the often onerous groundwater rules and standards in the Auckland Unitary Plan (AUP).
It is also one of the many joys of Auckland Council being a unitary authority, where more complex regional consenting matters get assessed alongside more simple district plan matters.
Auckland Council published a practice and guidance note (PGN) in December 2020 on the topic of groundwater. The guidance was written with the aim of helping applicants and planners alike understand why groundwater consents are required, and what information should be provided with applications.
This post includes a summary of the guidance note, including our own recommendations on how application assessments should approach the matter of groundwater.
1. When might a diversion or dewatering of groundwater occur?
A take or diversion of groundwater can occur:
when undertaking excavation to a depth that will reach groundwater, included perched groundwater
when constructing new buildings or structures that are below the existing surface level of the ground, for example a basement
In most cases, it is the perched groundwater table that is dewatered or diverted.
Dewatering can either occur temporarily during construction, or it can occur long-term because of collector drains and pumps installed as part of a basement construction.
Subsoil drainage for retaining walls, footings etc. can often drain groundwater continuously.
2. AUP Definitions
The AUP defines, in Chapter J1:
Water take as: The activity of removing water from a water body … by pumping and/or gravity, typically for consumptive use, but also including groundwater dewatering …
Groundwater diversion as: Significantly changing the permeability of the aquifer and/or rerouting the ambient groundwater flow regime by draining, piping, or physically impeding the flow of groundwater.
You’re likely to see other terms used in expert assessment reports, such as consolidation settlement, mechanical settlement, total settlement and Burland assessment. See the PGN for more information on what these terms mean.
A take of groundwater associated with a diversion (whether that diversion requires consent or not) is described in the AUP as ‘dewatering’.
Any plan reference to ‘water take’ will also include groundwater de-watering and groundwater removal as part of land drainage.
Any AUP objectives or policies that describe a ‘water take’ also apply to dewatering of groundwater.
3. Under what section(s) of the RMA is resource consent required?
The take or diversion of groundwater are activities that relate to section 14(3) of the Resource Management Act 1991 (RMA).
No person may take or divert any groundwater unless the take or diversion is expressly allowed by a rule in a regional plan, or a resource consent.
The options are clear – the take or diversion must either be expressly allowed by a permitted activity rule, or the applicant must have a resource consent.
Any consent granted under s14 of the RMA can have a maximum duration of 35 years under s123 of the RMA.
4. AUP rules, standards, matters and criteria
The regional plan rules for the take and diversion of groundwater are in AUP Chapter E7 in Table E7.4.1.
See the flow charts appended to the PGN to get a visual understanding of the linkage between activity, rule, and standards.
Dewatering of Groundwater – Permitted
Rule E7.4.1(A17): Dewatering or groundwater level control associated with a permitted activity groundwater diversion is a permitted activity in all zones, and the High-Use Stream Management Areas Overlay.
The dewatering must comply with Standard E7.6.1.6
If a basement/retaining structure is drained (i.e., the basement walls have drainage connected to under-slab drainage which connects to a pumped sump) then the water take will occur beyond the construction period and is therefore unlikely to comply with this standard.
Note: This rule prescribes a restricted discretionary activity status to dewatering within the Wetland Management Areas Overlay where associated with a permitted activity diversion. However, because you cannot undertake a permitted activity diversion within this Overlay, the default rule that will apply instead is Rule E7.4.1(A20).
Dewatering of Groundwater – Restricted Discretionary
Rule E7.4.1(A20): Dewatering or groundwater level control associated with a restricted discretionary activity groundwater diversion, a diversion not meeting Standard E7.6.1.6, or not otherwise specified, is a restricted discretionary activity in all zones and overlays.
Matters of discretion are found at E7.8.1(1) & (4)
Assessment criteria are found at E7.8.2(1), (2), (4), (5), (6), (7) & (9)
Note that this is the default rule for any groundwater dewatering associated with a diversion within the Wetland Management Areas Overlay.
Diversion of Groundwater – Permitted
Rule E7.4.1(A27): Diversion of groundwater caused by any excavation (including trench) or tunnel is a permitted activity in all zones, and the High-Use Stream Management Areas Overlay.
The diversion must comply with Standard E7.6.1.10
Diversion of Groundwater – Restricted Discretionary
Rule E7.4.1(A27): Diversion of groundwater caused by any excavation (including trench) or tunnel is a restricted discretionary activity in the Wetland Management Areas Overlay.
Matters of discretion are found at E7.8.1(1) & (6)
Assessment criteria are found at E7.8.2(1) & (10)
Rule E7.4.1(A28): The diversion of groundwater caused by any excavation, (including trench) or tunnel that does not meet Standard E7.6.1.10, or not otherwise specified, is a restricted discretionary activity in all zones and overlays.
Matters of discretion are found at E7.8.1(1) & (6)
Assessment criteria are found at E7.8.2(1) & (10)
5. Compliance with standards
Only permitted activities in Table E7.4.1 must comply with the standards in AUP Chapter E7.
If the starting presumption is that the activity is permitted, but it is then found to be restricted discretionary for failing to meet a standard, the ‘infringement’ does not require consent under rule C1.9(2).
This is because the activity table prescribes the activity status of a diversion or dewatering not complying with standards.
However, per rule C1.13(3), when deciding whether an application should be publicly or limited notified, the council must still have regard to the standards for permitted activities as part of the context of the assessment of effects (this is not permitted baseline).
6. Objectives and Policies
The objectives and policies that relate to the take or diversion of groundwater are found in AUP Chapter E2, and are summarised below:
Objectives E2.2(1)-(5)
Policies E2.3(1)-(2)
Priority of water use
Policy E2.3(4)
Efficient allocation and use
Policy E2.3(5)
Water allocation and availability guidelines
Policy E2.3(7)-(11)
Take and use of water
Policies E2.3(13)-(16)
National Policy Statement for Freshwater Management 2014
Policy E2.3(17)
Comprehensive review of consents
Policy E2.3(23)
Diversion of groundwater
7. What is the plan trying to manage for dewatering (take)?
Aquifer water availability and levels
Aquifer consolidation and surface subsidence
Adverse effects on surface water flows, and on terrestrial and freshwater ecosystem habitat
Avoidance of any saltwater intrusion or any other aquifer contamination
Adverse interference effects on neighbouring bores to the extent their owners are prevented from exercising their lawfully established water takes
Ground settlement for buildings and structures, including affecting the ability for these to comply with Building Act or NZBC
Monitoring, and the measurement and recording of ground, buildings and other structures.
That consents are for a set duration include a condition setting the review date(s) of the consent (see s125 of the RMA).
Note: The take of groundwater arising from most excavations is minimal compared to a take of groundwater from a bore for domestic, rural or industrial purposes. The take will generally amount to drainage only. The level and detail of assessment required for the ‘take’ is therefore proportionate to the level of water that is taken, and the permanency (i.e., whether it is a temporary take during excavation, or a long-term take/drainage of water around a constructed building/basement below natural ground level).
8. What is the plan trying to manage for diversion?
That the diversion avoids, remedies or mitigates any adverse effects on:
scheduled historic heritage places and scheduled sites and places of significance to Mana Whenua; and
people and communities.
That the diversion does not cause or exacerbate any flooding
Incorporation of monitoring where appropriate, including to measure water levels and pressures, and of the movement of ground, buildings and other structures.
Incorporation of mitigation where appropriate, including:
minimising the period where the excavation is open/unsealed;
use of low permeability perimeter walls and floors;
use of temporary and permanent systems to retain the excavation; or
re-injection of water to maintain groundwater pressures.
9. What is the council planner’s role in the process?
The Auckland Council planner will first look out for application information that helps determine whether a consent is required or not, before referring to a specialist. Specialist delays are often lengthy.
The planner’s role and the type of information that they might request is scenario dependent. See the different scenarios listed in the Auckland Council PGN for more information (they are summarised in section 10 below).
10. Main scenarios the council encounters
Applicant has applied for a permit
Applicant has said that they need a permit, but have not applied for it
Unclear whether a diversion or dewatering of groundwater is required (permitted or otherwise)
Diversion or dewatering is required, but this has not been assessed
Applicant has assessed that they will divert or dewater groundwater, but it will be permitted
11. Application information
If you’re applying for a groundwater permit, Auckland Council will look for the following:
An assessment of the effects of the proposal against the relevant AUP provisions.
A geotechnical report assessing ground stability.
The identification of the natural groundwater level (that detail might be in the geotechnical report).
Architectural drawings showing cross-sections of the depth of the proposed excavation, groundwater level, the proximity of the excavation to the site boundaries and the proximity of neighbouring assets i.e., building / structures and public services to the site boundary.
A Ground Settlement Monitoring and Contingency Plan (GSCMP) – note that a draft is generally considered acceptable at this stage.
12. Discharge of groundwater
If a take (dewatering) is proposed, details on whether the discharge of the water has been appropriately addressed should be provided with the application, i.e., demonstrated that it will be lawfully discharged - as a permitted activity, by other relevant approval, or resource consent is sought.
The rules for a temporary or permanent discharge of uncontaminated groundwater onto or into land and/or into water can be found in AUP Chapter E4.
A discharge of contaminated groundwater is managed by the rules in AUP Chapter E30.
13. Dewatering of groundwater – don’t forget to address!
Dewatering is usually what isn’t covered as part of the application material. Make sure you comment on it, particularly if groundwater has been identified as present on the site within bore logs, and excavation is proposed.
For example, if there are deep cut retaining walls that will have subsoil drainage, these may ‘take’ groundwater. Same for swimming pools and slabs/footings that have subsoil drainage.
If you’re confident that the risk of encountering groundwater is low (speak to a geotechnical engineer), you could offer an Augier condition in the Assessment of Environmental Effects (AEE) report that no groundwater take will be undertaken.
14. Considering effects on mana whenua values
Iwi have advised Auckland Council via the development of their recently updated “Considering mana whenua values in resource consent processes” PGN that they’re not likely to be interested in groundwater diversion/dewatering proposals, unless the take is significant (rarely will be so), or the diversion is within a sensitive environment, e.g., nearby a watercourse, and/or within a wetland management area. For most domestic or commercial proposals, this won’t be an issue.
If you’re engaging with iwi for other reasons, we still recommend that you put the groundwater proposal forward for comment as to potential cultural effects.
Make sure to cover off in the AEE, don’t be silent on it. While you cannot conclude what the effects on iwi are (that is for them to determine), you can state the likelihood of effects, having regard to the policy hierarchy in the AUP.
