Contents

  • Cover
  • Front matter
  • Introduction
  • Identifying and managing risk
    • Risk overview
    • Working smart and efficiently
    • Starting the job – be prepared
    • The job is not finished until it is signed-off
  • Basics
    • Roading terms
    • Basics about soil
  • Good construction
    • A well-constructed road
    • A well-constructed landing
  • Earthworks
    • The right machine for the task
    • Clearing and stripping
    • Cut and side cast construction
    • Cut and bench fill construction
    • Full bench construction with end-haul
    • Earthworks compaction
    • Landing construction
    • Forming road corners and in-bends
    • Final grading before metalling
    • Stabilising cut/fill slopes
  • Water control
    • Water control overview
    • Ditches
    • Road drainage culverts
    • Berms and cut-outs
    • Flumes
    • Silt traps and soak holes
    • Silt fences
    • Single culvert river crossings
    • Ford crossings
    • Bridges
  • Applying aggregate (metalling)
  • Repairs and maintenance
    • R&M overview
    • R&M common to new construction
    • R&M of road formation
    • R&M during harvesting operations
    • R&M of river crossings
  • Assisting loggers and harvesting rehab
    • Installing deadmen
    • Installing debris traps
    • Harvesting track rehabilitation (rehab)
    • Harvesting track rehabilitation – cut-outs
    • Landing rehab
  • Want to learn more?
  • Glossary

NZ Forest Road Engineering Manual: Operators Guide

  1.  ›
  2. Assisting loggers and harvesting rehab ›
  3. Installing debris traps
 

Installing debris traps

Debris traps are constructed in rivers to catch debris with a high risk of mobilising in a flood. They are often made from rammed railway irons or steel beams threaded with wire rope and anchored solidly at each end. They should be engineered. They can easily fail. Debris traps installed into a riverbed require a resource consent.

  • Debris trap doing its job well but needs to be cleaned out
  • Beams spaced at 1.5 to 2 m
  • Beams were driven in more than 1.5 m
  • 22 mm wire rope was threaded through the beams
  • Wire rope was securely anchored then tensioned
  • Constructed to protect a culvert
  • Put directly across the river
  • Easy to clean out
  • Fish passage is not blocked
  • Water can flow freely
  • Debris traps need to last at least six years
  • Locate in a flat section of the river to reduce the risk of it failing
  • A poor debris trap anchor caused it to fail
  • Consider putting debris traps in the side streams
  • Debris trap failures could lead to lots of wood going downstream at once, causing significant damage
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