The regeneration of watercourses within urbanized areas. Some considerations about relevance, strategies, and design tools
From Firenze University Press Journal: Ri-vista
Paola Sabbion, Università di Genova
Anthropogenic alterations to river systems The effects of urbanisation on river ecosystems are well-known and have been identified as ‘the urban stream syndrome’ (Walsh et al., 2005). Both direct and indirect anthropogenic activities alter river environments, resulting in critical changes in watershed processes and habitat conditions, which cause the degradation of biological and even cultural diversity (Wantzen et al., 2016).Alterations to river systems arise from various causes, including demands for water, energy production, urban growth, flood control, and agricultural, industrial, and navigation needs. Exploitation and pollu-tion, dredging, changes in the flow regime, exces-sive fishing, vegetation removal, and the introduc-tion of invasive species decrease the natural com-plexity of riverine landscapes and cause the loss of many ecological functions. Intensive exploitation of rivers began over 500 years ago in the Western world, increasing significantly in the late 19th and 20th centuries. Rivers have suffered considerable harm to their natural environment, particularly since the dawn of the industrial era. As a result, nearly 80% of the world’s population faces high levels of threats caused by water insecurity and degraded riverine habitats, which are also considered the main cause of extinction in aquatic ecosystems (Vörösmarty et al., 2010). Currently, only a small portion of the flood-prone areas that existed in the 19th century remain. More than half of the world’s rivers are polluted or at risk of drying up and there is an increased risk of water pollution and pathogenic contamination due to flooding or higher pollutant concentrations during droughts. Moreover, the quality of water is ex-pected to continue to deteriorate in the future, as a result of elevated water temperatures, reduced dissolved oxygen, and water’s self-purifying ability (UN Water, 2020).Direct anthropogenic alterations in riverine eco-systems involve watershed-scale processes such as erosion and nutrient delivery, which lead to imbalances in stream flow, water quality, and biological interactions. Construction of channel diversions or size reductions, dams, and flood control devices significantly reduce the transport and storage of organic matter, resulting in simplified habitats and biodiversity. Levee construction and bank armouring also reduce habitats and biological diversity by eliminating natural flood flows, bank erosion, channel migration, connectivity, and river-floodplain inter-actions that affect riparian ecosystem conditions (Roni and Beechie, 2012). Furthermore, human ac-tivities can indirectly cause variations due to chang-es in land use within the catchment area. Filling wetlands or removing riparian vegetation for agriculture, urban development, or construction of impervious surfaces impacts habitat diversity and bio-logical capacity. Within the catchment area, subsurface flow intercepted by impervious surfaces rapidly runs into watercourses, increasing flood risk. Increased impervious surface cover and road construction also increase sediment supply, deliver-ing pollutants such as pesticides, urban and in-dustrial waste, and agricultural land nutrients to streamflow, affecting riverine habitats and biota (Gravrilescu, 2021).Regarding the aforementioned dynamics, it is essential to emphasize that, contrary to common planning practices of the last two centuries, rivers are not mere water collectors. They naturally fulfil a range of geomorphological, hydrological, and bi-ological processes, including erosion and sediment transport, nutrients and organic matter distribu-tion, providing vital conditions and habitats that are essential for ecosystem functions, including feeding and reproduction (Guimarães et al., 2021). In natural conditions, riverine landscapes continuously change due to normal habitat variation dynamics, such as discharge, bank erosion, bar deposition, and lateral channel migration (Harrison et al., 2015). All of these determine the biological diversi-ty of floodplain habitats. Habitat and biological diversity are supported by specific riverbed forms and channel features such as depth, velocity, and roughness (McCabe, 2011). Environmental changes, channel structure, and floodplain interactions influence erosion, transport, and storage of inorganic and organic matter produced within streams and riparian areas (Harms et al., 2021); however, the pattern and distribution of habitat types remain substantially stable over time. Imbalances are due to anthropogenic activities (Gilvear et al., 2013), threatening river integrity and affecting the structure, flow, and quality of watercourses.
DOI: https://doi.org/10.36253/rv-14139
Read Full Text: https://oaj.fupress.net/index.php/ri-vista/article/view/14139
