Indicators: Streambed Fine Sediments

What are streambed fine sediments?

Streambed fine sediments are small (< 2 mm diameter) deposits of sand, silt, clay, and mud located on the streambed. In excess amounts, they can fill in the habitat spaces between stream cobbles and rocks where aquatic organisms live and breed, suffocating the organisms, and their eggs, and negatively affecting habitat quality. 

Why is it important to evaluate streambed sediments?

Human uses of the landscape, such as agriculture, construction, and urbanization, can increase the amount of fine sediments that run off into streams and rivers, especially during storm events. Land uses that increase the amount of impervious (paved) surfaces can also increase the amount, timing and duration of storm water runoff into river and stream channels. These hydrologic alterations can also result in stream bank erosion and incision, and can wash away important aquatic habitat. 

What can streambed sediments tell us about the condition of waterbodies?

The size and quality of streambed sediments found in a river or stream can indicate response to recent changes in flow and sediment inputs. As more fine sediments enter and are deposited in a stream, they can fill the habitat spaces between stream cobbles and rocks and the streambed becomes silty and less stable. Streambed sediments can therefore serve as a valuable physical habitat indicator of biological stress.

How is this indicator used in NARS? 

The National Rivers and Streams Assessment collects data on streambed sediments. This data is available on the NARS data page.  Below the table you access assessment information in current reports. 

National Rivers and Streams Assessment Web Report – Streambed Sediment Results