Rule 39 Maintenance of drains
https://archive.gw.govt.nz/Rule-39-Maintenance-of-drains
The removal of vegetation and any associated sediment from any drain [, including any associated disturbance of the drain bed,] for the purpose of maintaining the original grade or cross section of the channel is a permitted activity provided it complies with the conditions specified below.
Conditions
(1) No contaminants (including but not limited to oil, petrol, diesel, paint, or solvent) shall be released to water from equipment being used for the operation.
(2) All reasonable steps shall be taken to minimise the release of sediment to water during the activity.
Note: For the purpose of this rule, "drain" means a highly modified watercourse or river that is channelled to such an extent that it has the characteristics of a farm drainage canal (see section 3 of the Plan).
Note: The spray application of agrichemicals over water bodies or over river and lake beds is addressed in the Regional Air Quality Management Plan.
In Rule 39, the words in square brackets were inserted by Decisions on Plan change 1 to the Regional Freshwater Plan December 2002