7 - Flood Basins and Deltas

Summary

The final chapter on human impacts to lowland rivers logically ends at the basin terminus, at the coast. Large flood basins and deltas are the most challenging environments to manage because of being impacted by ground subsidence and coastal storm surge events, particularly large populations in delta cities. Artificial floodwater diversion mirrors natural flood pulses, although it also disturbs aquatic ecosystems that requires further management. Challenges with floodwater diversion for environmental management of the lower Sacramento basin links to historic hydraulic gold mining. A major geomorphic phenomenon that influences flood basin environments is channel avulsion, which can be set up by embanked floodplain sedimentation and subsidence. Ground subsidence problems are particularly acute as regards flood control infrastructure, increasing the risk of dike failure during coastal storm surge events. Urban flood basin subsidence and flood control challenges is examined in a review of the epic 2011 Chao Phraya River flooding of Bangkok and the 2005 coastal storm surge flooding of New Orleans by Hurricanes Katrina-Rita.