Rule 31 Small bridges
https://archive.gw.govt.nz/Rule-31-Small-bridges
The erection and maintenance of any bridge over a river bed, is a permitted activity provided the activity complies with the conditions specified below.
Conditions
(1) The bridge is no more than 6 metres in total length.
(2) The bridge does not reduce the ability of the river to convey flood flows.
(3) The bridge does not alter the natural course of the river, including any diversion of water from the natural course during floods.
(4) The bridge is maintained free of any flood debris.
(5) No part of the structure occurs in, on, or under the area of river bed covered by water.
(6) All material used during construction, but which is not part of the bridge, is removed from the river bed and disposed of in an appropriate manner.