Report: TR 2008/22

Author: Hannah Jones

Abstract

There are 56 species of fish in New Zealand, of which 35 are indigenous. In the Waikato Region, there are 22 species of indigenous and 14 species of introduced fish. Of the 35 native fish species, 18 are diadromous (Kelly and Collier, 2007).

Diadromy is the movement of fish between marine and freshwater environments and is a critical part of life history. The diadromous species that make these migrations between freshwater and marine environments have varying abilities to negotiate instream barriers, such as culverts, fords, weirs and dams (Barnes, 2004).

Some species, such as shortfinned and longfinned eels have the ability to move both in and out of water. Other species, such as lamprey, juvenile kokupu and juvenile koaro, can climb wetted margins of waterfalls or spillways, and some species, such as inanga and smelt, primarily swim to move past obstacles and rely on low velocity flow to rest while moving upstream (Kelly and Collier, 2007).

Poorly designed or installed structures can pose a barrier to fish migration if:

• the water flow is too high and/or there are no resting places provided within the
  structure
• there is no low velocity zone or wetted margin provided at the water edge
• water turbulence is too great (usually because the culvert is too narrow or too steep)
• the crossing is too dark (because the culvert is too long or too small)
• water depth within the culvert is too shallow
• the river bed within the culvert is too smooth for bottom swimmers (often because the culvert has a concrete or steel bottom and normal bed material has not been able to develop)
• the gradient is too steep
• the bed level of the crossing has been raised (e.g. culvert floor is perched above the streambed)
• debris has built up and formed a weir
• scouring has occurred and caused the culvert to become perched.

(Speirs and Ryan, 2006)

In catchments not exceeding 100 hectares permitted activity rule 4.2.9.2 of the Waikato Regional Plan allows the use, erection,  reconstruction, placement, alteration or extension of a culvert as a permitted activity, subject to a number of conditions. These
conditions include that “the structure shall provide for safe passage of fish both upstream and downstream” (Waikato Regional Plan, Environment Waikato, 2007).

In order to assess the effectiveness of the permissive approach, 60 catchments less than 100 hectares have been selected randomly from across the Waikato Region and culverts within those catchments identified and assessed for fish passage restriction.

Compliance with Permitted Activity Rule 4.2.9.2: Ensuring Culverts Provide Safe passage for Fish [PDF, 72 KB]