Channelization

Channelization projects are undertaken in order to increase flow depths for navigation or/and reduce flooding, by increasing the overall conveyance capacity, reducing friction and confining the flows into one single channel. This can be accomplished by straightening, widening, deepening, realigning or/and revetting (lining) the channel.

The adverse environmental impacts of channelization are manifold:

Flow regime:

  • Increased channel slope, flow velocity, lower stages, reduced residence time, leading to increased flooding downstream (faster travel times and lower peak attenuation)

Sediment load and channel structure:

  • River bank and bed erosion (scour and degradation)
  • Sedimentation problems downstream
  • Total loss of heterogeneity in channel form

Water quality:

  • Reduction in nutrient and pollution assimilation capacity of river channel
  • In smaller (narrower) streams, increased temperatures
  • Increase in fine sediment load

Habitat, biodiversity and natural resources:

  • Loss of river habitat diversity, backwaters and refuges; loss of native river species
  • Loss of in-stream and riparian vegetation
  • Loss of organic material input
  • Lowering of floodplain water tables, affecting riparian vegetation and floodplain wetlands

Possible mitigation measures

  • Use of natural and permeable materials, i.e. soft revetments, instead of concrete revetments
  • Maintaining or re-introducing coarse woody debris as far as possible

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