Embankments (also referred to as levees or dykes in some countries) are constructed mainly from earth and used to confine stream flow within the specified area along the stream, or to prevent flooding due to sea waves or tides. Since early times, embankments have played a vital role in protecting people on flood plains against frequent flooding and continue to be the most favoured flood management option. However, the construction of embankments is a substantial intervention in the riverine ecosystem which may result in the following impacts:

Flow regime:

  • Higher water stages and velocities at above bank full flows
  • Flood peaks increased downstream

Sediment load and channel structure:

  • Loss of connectivity between river and flood plain
  • Loss of pool and riffle patterns and other heterogeneities in channel form
  • Increased erosion possible (both local scour and overall degradation)
  • Possible sedimentation downstream, of material eroded in embanked reach

Water quality:

  • Loss of exchange of nutrients and carbon with flood plain

Habitat, biodiversity and natural resources:

  • Loss of floodplain refuges and spawning areas for river species
  • Loss of floodplain forests
  • All floodplain structures, processes and species needing frequent inundation are affected
  • No more silt deposition on flood plain
  • No more habitat creation on the flood plain

Possible Mitigation Measures

  • Embankments should be planned in conjunction with other structural measures such as detention basins, as well as non-structural measures
  • Spacing of embankments should allow for the morphological lateral movement of the river
  • Embankment designs should minimize the disruption in lateral connectivity by setting balanced standards of protection based on economic and environmental criteria
  • Setting embankments farther back from river channel depending on land use conditions
  • Removal of embankments as part of river restoration programmes in combination with land use regulation, in full consultation with local stakeholders and where the local development situation allows.

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