Environmental impacts of future flood risk

Description/Abstract

Many drivers of flood risk are affected by the environment. For example; agricultural land management affects catchment runoff (Chapter 5); river vegetation affects conveyance (Chapter 6), and relative sea level affects the frequency with which land adjacent to coasts and estuaries is flooded (Chapter 10). In this chapter we consider the other side of the coin – the environmental impacts of floodplain and the environment as a receptor. In particular we:

1. analyse the environment impacts of floodplain and flood risk management in fluvial and coastal zones
2. consider the environment implications of current trends in flood risk management policies
3. examine how the environmental impacts of floodplain might differ under the four Foresight Socio-Economic Futures; and
4. provide an environmental economic assessment of the impacts of flooding.

In so doing our aim is to provide the environmental context for the assessment other impacts of future flood risk. This is because coastal and fluvial flooding affects the physical characteristics of the environment, the coastal riverine and floodplain ecosystems, and the species these ecosystems contain. Moreover, regular flooding is essential for the health and survival of many of these ecosystems. The size of natural alluvial river channels for example generally depends on the magnitude of the flood that occurs every one or two years. Biodiversity in river channels depends on the frequency of flooding and associated movement of sediment. Floodplain wetlands are often maintained by inundation and coastal saltmarshes require regular tidal flooding.

Infrequent ‘large’ floods can disturb landforms and ecosystems which may take significant periods to recover. While these floods can be seen as ‘natural’ parts of the environmental system, a changing frequency of flooding can disturb the equilibrium of a landform or ecosystem,. The result may be seen as adverse environmental consequences: the area of saltmarsh may decline, or a river channel may be destabilised.