There is a drainage basin surrounding every stream. That is simply defined as the area that is drained by the stream and all of its tributaries.

When water flows to a different basin it is separated by a divide. A divide is the separator of drainage basins.

Streams can be ordered by assigning them numbers.

1.) First Order - a stream with NO (0) tributaries

2.) Second Order - has only first order tributaries

3.) Third Order - has first or second order tributaries.

etc. etc.

This diagram shows a drainage basin with the streams numbered. There are always more first order than second order, and second order than 3rd order, etc. Because it takes at least two of a lower order to produce a higher order.

Stream capture is the action of one stream taking over another. It happens when the stream system is still under development. Capture can easily occur when one stream creates a deeper channel and becomes the favored (by gravity) path for water to flow.

The study of stream direction and flow of an entire drainage basin can aid in mapping the geology below the stream.

As we have already seen in contour mapping, stream flow forms "Y" when two stream join pointing in the down hill direction. The combined directional response of the "Y" patterns can tell us much about the elevations around the pattern.

The stream directions will often map the underlying rock hardness or geology in a drainage basin. Stream will always cut through the softer rock and will follow natural lines of rock down hill.

Streams that have run a good distance, will have cut more into the underlying rock, and will follow the path of least resistance.