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Polluted Runoff: Nonpoint Source (NPS) Pollution

Nonpoint Source: Hydromodification and Habitat Alteration

photo of Imperial Dam, Yuma ArizonaImperial Dam, Yuma, Arizona. The siting, construction and operation of dams can adversely impact water quality and contribute to nonpoint source pollution.(Photo courtesy of NRCS)Hydromodification activities include channelization and channel modification, dams, and streambank and shoreline erosion. A frequent result of channelization and channel modification activities is a diminished suitability of instream and streamside habitat for fish and wildlife. They can also alter instream patterns of water temperature and sediment type, as well as the rates and paths of sediment erosion, transport and deposition. Hardening of banks along waterways has increased the movement of nonpoint source pollutants from the upper reaches of watersheds into coastal waters.

Dams can adversely impact the hydraulic regime, surface water quality and habitat in the stream or river where they are located. The siting, construction and operation of these facilities have a variety of impacts on these systems.

The erosion of shorelines and streambanks is a natural process that can have either beneficial or adverse impacts on the creation and maintenance of riparian habitat. Excessively high sediment loads can smother submerged aquatic vegetation, cover shellfish beds and tidal flats, fill in riffle pools, and contribute to increased levels of turbidity and nutrients.

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