Shape of a River - Geomorphology
Sediment
Many alluvial streams (those winding through
beds of unconsolidated sediment rather than
bedrock) flow in dynamic equilibrium, in which
sediment load equals its transport capacity. In
other words, healthy streams are able to carry a
certain amount of sediment over time in a
sustainable balance.
With the addition of excessive sediment, such as
soil erosion from farmland, the stream will deposit
excess sediment in the channel as riffles, bars, or
islands. A dramatic reduction in sediment, such as
construction of a dam that traps sediment, will
cause the downstream channel to enlarge by widening
and down cutting.
Long-term changes in the pattern or volume of
discharge (tributaries) will change the amount of
sediment carried by the river, altering channel
width and depth.
Disruptions to this natural relationship occur
through our land use practices and through direct
disruptions to the channel itself.
