Regulatory barriers to uptake of farm-scale diffuse pollution mitigation measures

The issue

Constructed wetlands, detention bunds, woodchip denitrification filters and planted riparian buffers are examples of a growing suite of edge-of-field and farm-scale mitigation systems that are being trialled across rural New Zealand to reduce the impact of diffuse pollution on freshwater quality.

While the evidence base for the efficacy of these mitigation systems continues to grow, a wide range of social, cultural, economic and regulatory barriers may limit their adoption by landowners. In terms of regulatory barriers, many activities related to the construction, operation and maintenance of diffuse-pollution mitigation systems, including earthworks, stream diversions, and discharges to land or water, can trigger the need for resource consents in accordance with regional plans prepared under the Resource Management Act (RMA) 1991. The time and cost involved with obtaining consent may deter landowners from investing in mitigation systems.


We reviewed regional plan requirements that are relevant to the construction, operation and maintenance of mitigation systems, particularly when sited close to or within waterways and drains. Our evaluation focused on the following edge-of-field systems: constructed wetlands, seepage wetlands, riparian buffers, N-bioreactors, P-filters, detainment bunds, two-stage ditches, bank re-battering, silt traps and in-channel remediation works (e.g., wood or woodchip addition).

We also reviewed resource consent applications and consent officers’ reports for five mitigation projects and carried out face-to-face meetings with regulatory and  land management staff from four regional councils to establish how plan rules were interpreted.

This work was funded by The Ministry of Business, Innovation and Employment and DairyNZ.

Key findings

Permitted activity rules exist for many of the steps used to  construct, operate and maintain edge-of-field mitigation systems. These include earthworks, damming and diverting water, streambed disturbances, and the installing weirs, and discharging  stormwater. However, the rules vary from region to region and are typically accompanied by lengthy lists of conditions. Failure to meet one or more of these conditions triggers the need for resource consent.

Significant regional variation exists in the conditions of permitted activities, such as the maximum upstream catchment areas and design criteria for construction of culverts, dams and other structures). This variation, and variation in the use and definition of specific terms in plans (e.g. drain/drainage canal/farm drainage canal/ land drainage canal), means that regional plans must be checked closely when designing mitigation systems.

Examination of five recent edge-of-field mitigation projects across four regions indicated that it is difficult to meet many of the conditions associated with permitted activity rules. In some cases, conditions were not met on technical grounds or there was no relevant permitted activity rule that applied to an activity. In three of the projects, the overall regional plan rule classification for the suite of activities associated with the resource consent application defaulted to discretionary and, in one project, non-complying. This occurred even though the mitigation projects had the primary or sole purpose of environmental enhancement.

It is unlikely that many edge-of-field mitigations systems can be implemented through permitted (or controlled) activity rules, particularly those located in or near the beds of rivers and other natural waterbodies. In these cases, resource consents will generally be required. This is because design and construction of the mitigation system must be customised to address specific site and environmental requirements, making it more difficult to establish a single set of standard conditions that could be applied to a permitted or controlled activity rule.

Although consents may be unavoidable, it should be possible to simplify the process to obtain them. More information is needed on how various mitigation systems work, including guidance on how to manage potential adverse environmental effects associated with their construction, operation and maintenance. This guidance could inform the development of new rules as part of plan changes or review processes that specifically address diffuse pollution mitigation systems.

For more details on this project please refer to the report below.

Next steps

We are exploring opportunities to work with central government, regional councils, industry and practitioners to co-develop guidance that will assist with the more efficient implementation of edge-of-field and farm-scale diffuse pollution mitigation measures.

NIWA Contacts

Resource Management Scientist
Page last updated: 
21 September 2020
Farm run-off treatment wetland. [Photo: Chris Tanner, NIWA]