Hydromodification is the alteration of the natural flow of water through a landscape, and often takes the form of channel modification or channelization.
Hydromodification is one of the leading sources of impairment in streams, lakes, estuaries, aquifers, and other water bodies in the United States. Hydromodification activities such as channelization and channel modification, dams, and streambank and shoreline erosion control structures change a water body's physical structure as well as its natural function. These changes can cause problems such as changes in flow, increased sedimentation, higher water temperature, lower dissolved oxygen, degradation of aquatic habitat structure, loss of fish and other aquatic populations, and decreased water quality. It is important to properly manage hydromodification activities to reduce nonpoint source pollution in surface and ground water.
For a some real-world examples of hydromodification and its effects, see this Coastal Blog post.