6 - Dikes and Floodplains

Summary

This chapter singularly focuses on the impacts of dikes (levees), including their design, management, and influence on hydrologic and fluvial sedimentary processes. Floodplain embankment commonly removes ~75% of the natural floodplain from annual flood pulse dynamics. Flood control by embankment fundamentally alters fluvial processes between, along, and beyond dikes. Over longer timescales dikes result in a unique floodplain environment characterized by distinctive morphologic, hydrologic, and sedimentary features that do not exist on natural floodplains. Dike breach ponds are distinctive hydrologic features along dikes that provide valuable ecosystem services. Embanked floodplains trap flood deposits that results in thicker and somewhat coarser flood deposits, which buries natural wetlands and infills floodplain lakes. This results in a channel belt ‘perched’ above low-lying flood basins, which increases the risk of avulsion. The chapter closes by integrating concepts related to channel engineering (Chapter 5) and floodplain embankment to arrive at an evolutionary model for engineered rivers, which provides a segue to flood basin management (Chapter 7).