Another dramatic form of land use change Figure 17.3. Waal River Floodplain with Agricultural Use is urbanization, the introduction of housing and industry into the floodplain. The disadvantages of urbanization are the same as for turning floodplains into agricultural land but with the added complication that people who live and work in the floodplain are in immediate danger during high discharges. Urbanization also increases the imperviousness of the subsoil, which increases runoff (Poff, Bledsoe, and Cuhaciyan 2006). This is why some countries, Source: Joop van Houdt, Beeldbank, Rijkswaterstaat like the Netherlands, generally do not allow new houses to be built in floodplains (except for experiments such as floating houses). Living in a floodplain is much more common in other countries, such as the United Kingdom, United States, and France. Changes in land use have temporal as well as physical aspects. They often start with a predevelopment situation in which there is a symbiosis between the “maintainers” of the floodplain and the dynamics of the fluvial system itself. Then, whenever activity is increased, the floodplain becomes more affected by deforestation and the removal of other vegetation and the bare soil is increasingly exposed to erosion. This destabilizes the system because the eroded material is deposited in the main channel. Urbanization (settlements, houses, industrial activity) can be considered a third stage in land use changes. In this stage, the impervious surface area in a floodplain is increased, which, in turn, leads to increased runoff and further disconnection of the floodplain from its river’s main channel. The temporal scale associated with this is typically on the order of centuries. Many hazardous chemicals, including synthetic organic materials, may attach to sediment. Sediment itself is also drained to the river through natural runoff processes. If this sediment is contaminated (e.g., by agricultural fertilizers) and introduced into the river, it has the potential to degrade water quality. It also increases water turbidity, which may affect spawning grounds for fish, decrease the ability of water plants to grow, and affect the food chain by destroying the habitat of the smallest benthic organisms. Suspended sediment is also known to increase water temperature and negatively affect fish populations in multiple ways (canada.ca. 2016). There is evidence for a link between changes in land use and changes in flood risk, although this link seems to depend on a spatial context (related to the watershed) and a temporal aspect (related to the flood event). See, for example, Pattison and Lane (2011) for more information.
17 | Benefits and Challenges in the Application of NNBF in Fluvial Systems
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