Home Back Next Print Exit
Introduction How Rivers Run Stories Value Of A River What We Can Do
Quality of a River - Water Quality
Sediment (pg 2 of 3)


Of the pollutants in our streams, the most expensive to deal with and most damaging to stream life is sediment. It plugs spaces between gravel and rocks (interstices) in the streambed, preventing their use as living spaces for life forms that live on the stream bottom. Sediment can smother eggs of fish, especially trout and salmon, whose eggs rest in the interstices of well-oxygenated gravel beds. An excess of sediment in streams spells the end of natural reproduction in trout.

In most "natural" systems, the input of sediment from the surrounding basin is modest. What enters is shifted and moved throughout the river channel. It is the sudden influx, usually from human activities, that creates problems.

Erosion and sedimentation occur over broad areas and result from many activities. An excess of sediment often results from the following:

  • Construction and use of logging roads and skid trails, especially in steep topography.
  • Road construction, home and commercial construction.
  • Off-road vehicle use.
  • Plowing and other agricultural activities that remove plant cover and loosen topsoil.
  • Overgrazing and continual trampling of streambanks.

Agricultural activities are responsible for three times more sediment pollution than the next greatest source (U.S. EPA, 1990). Damage from sediment is exacerbated by adhesion of nutrients and pollutants washed in with soil. Bare fields, an absence of vegetation, and spring plowing often coincide with spring rains, when cold temperatures increase waters ability to erode and carry sediment (see Temperature).




Next Page

Introduction
Flow
Shape
Connections
Quality
Description
Temperature
Oxygen
Alkalinity
Nutrients
Sediment
Contaminants
Status
Life
Summary
Home | References and Credits | Exit