Channelisation

The straightening and channelisation of rivers involves the removal of obstructions to flow such as bends and rocky areas. This increases the navigational accessibility of the river, improves drainage and aides flood control. Channelisation generally results in steeper stream gradients, reduced average pool depths but a deeper river overall because the stronger current wash away bottom sediments. These sediments often flow the whole course of the river exiting into the ocean. The suspended sediment load increases turbidity of coastal waters and changes seabed composition. Increased turbidity means lower light penetration. Submerged vegetation, such as seagrasses, have reduced rates of photosynthesis and coral reefs are effected because less photosynthesis occurs in the symbiotic zooanthellae inside corals.

A heavily silted river enters the ocean near San Juan, Puerto Rico. Taken by William Folsom, courtesy of NOAA, NMFS.

Effects are not just seen in the oceans but terrestrial wetlands are also effected. The Pantanal, the world's largest wetland / floodplain in the world incorporating extensive areas of Brazil, Bolivia, and Paraguay, acts as a ?sponge? holding much water that feeds the wetland habitats seen throughout the area. However if the infamous Hydrovia river channelisation project is finished it will shrink by an approximated 10%. The lack of water retention and faster currents also decreases the chances for natural pond creation and numbers of river organisms, such as the White Clawed crayfish in the United Kingdom, that reside in the eddies and the slow moving water of rivers.

Each channelisation project has unique pros and cons to consider. In the past many channelisation projects have not investigated the possibility of habitat and wildlife loss and much environmental damage has occurred. Now potential projects do take into consideration the effects of increased flow, coastline sedimentation, less water retention, and the subsequent effects on habitats.