Strahler Stream Order

The Strahler Stream Order is a simple hydrology algorithm used to define stream size based on a hierarchy of its tributaries.The streams range from one at the headwaters (which is a "1") to the most powerful which is the Amazon River which is a "12." The Ohio River is an "8" and the Mississippi River is a "10." 80 percent of the streams and rivers on the planet are first or second order.To qualify as a stream it must be perennial. When two first-order streams come together, they form a second-order stream. When two second-order streams come together, they form a third-order stream. Streams of lower order joining a higher order stream do not change the order of the higher stream. Thus, if a first-order stream joins a second-order stream, it remains a second-order stream. It is not until a second-order stream combines with another second-order stream that it becomes a third-order stream.
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