Strahler Order

The Strahler stream order is a system for classifying streams in a river basin based on their hierarchy. It starts with unbranched streams, called first-order streams. When two streams of the same order merge, they create a new stream with an order one higher; for example, two first-order streams combine to form a second-order stream. If two streams of different orders merge, the resulting stream retains the higher of the two orders.