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Impacts

Both flood protection infrastructures and drainage affect floodplains and the connectivity of rivers and streams to floodplains, as they cause changes to the land area surrounding water bodies. This can have major implications for the integrity of both riparian and aquatic ecosystems (Amoros and Roux, 1988; Junk et al., 1989, Junk and Wantzen, 2004). In a natural system, lateral connectivity between rivers and their floodplains allows the exchange of water, sediment, biota as well as nutrients. The loss of lateral connectivity leads to the loss of key habitats and as a result to the decline of species and biodiversity both on the floodplain itself and in the aquatic environment. Further, physical processes are disturbed related to the natural water retention capacity of floodplains as well as sediment dynamics.

Artificial bank protections that serve flood protection (embankments, levees or dikes) affect the morphology and dynamics of the river channel by restricting the channel width and the sediment supply from the river banks. Bank reinforcement and levee construction can also lead to bed incision because of the resulting high flow velocities; in its turn, bed incision reduces the connectivity between the river and its floodplain (lateral connectivity). The reduction of this lateral connectivity damages the functioning of the riparian zone and reduces productivity, nutrient exchange and dispersal of biota more widely across the floodplain.[2]

As far as land drainage is concerned, natural channels have been straightened and deepened for surface drainage ditches with significant effects on channel morphology, instream habitats for aquatic organisms, floodplain and riparian connectivity, sediment dynamics, and nutrient cycling (Blann et al, 2009).[3] Further, the regular maintenance of drainage ditches and rivers (via dredging and weed cutting) leads to physical disturbances and morphological changes in water bodies (Vartia et al., 2018).

[2] REFORM wiki “Embankments, levees or dikes“, available online at http://wiki.reformrivers.eu/index.php/Embankments,_levees_or_dikes#Useful_references

[3] https://www.researchgate.net/publication/241682569_Effects_of_Agricultural_Drainage_on_Aquatic_Ecosystems_A_Review