Deltas
When
a stream enters a standing body of water such as a lake
or ocean, again there is a sudden decrease in velocity
and the stream deposits its sediment in a deposit called
a delta. Deltas build outward from the coastline, but
will only survive if the ocean currents are not strong
enough to remove the sediment. As the velocity of a stream
decreases on entering the delta, the stream becomes choked
with sediment and conditions become favorable to those
of a braided stream channel, but instead of braiding,
the stream breaks into many smaller streams called distributary
streams.
Drainage systems
Drainage Basins and Divides - Drainage systems develop in such a way as to efficiently move water off the land. Each stream in a drainage system drains a certain area, called a drainage basin. In a single drainage basin, all water falling in the basin drains into the same stream. Drainage basins can range in size from a few km2, for small streams, to extremely large areas, such as the Mississippi River drainage basin which covers about 40% of the contiguous United States . A divide separates each drainage basin from other drainage basins.
Stream order
The
smallest streams in a drainage network have no tributary
streams. These are called first order streams. Two first
order streams unite to form a second order stream. Second
order streams only have first-order streams as tributaries.
Third order streams only have second and first order
streams as tributaries, etc. As the order of the stream
increases, the discharge increases, the gradient decreases,
the velocity increases, and the channel dimensions (width
and depth) increase to accommodate the increased discharge.
