People have traditionally settled next to rivers and estuaries. Over time this has transformed the natural environment into the towns, cities and ports we see today. Urbanisation comes at a cost to rivers – they have been heavily degraded to enable development, carry waste, supply drinking water and facilitate transport and industry.
Urbanisation affects a river in many ways:
- physical structure: artificial walls replace reed beds and natural river banks, or in many cases the river is hidden underground
- water quality: increased run-off from impervious surfaces such as roads, roofs and gardens, and contamination from industry discharges degrades water quality
- ability to support wildlife: natural corridors, riparian zones and in-channel habitats are lost
- removal of riparian vegetation: reduces organic input, habitat complexity, increases riverine temperature and reduces bank stability
- Geomorphology: urban rivers lack the space to erode their banks and deposit sediment or connect to their floodplain, which leads to altered morphology. Bridges, pipes and other infrastructure alter the width and depth of rivers, and their courses are changed by straightening and bypassing
- water quantity: decreased flow and reduced groundwater levels through abstraction and increased flow from surface run-off, increased frequency of floods and reduced infiltration
- invasive species: urban areas often suffer from introduced non-native species that become dominant and cause damage to the environment.
These stresses make rivers less resilient to the effects of climate change. Current modelling for much of Europe predicts that winter rainfall will be more intense, leading to increased flooding and that summer rainfall will decrease with an increase in very hot summer days, leading to reduced water levels, making communities are less able to deal with an uncertain climate. (European Environment Agency, 2012)