In a dendritic drainage network, a 3rd order tributary joins a 4th order tributary. According to the Strahler method of stream ordering, what will be the order of the main river after this confluence?

Step-by-step solution

1. Recall the Strahler rule: When two streams of the same order join, the resulting order increases by one; otherwise, the order remains the maximum of the two.
2. Identify the orders of the joining tributaries: one is 3rd order and the other is 4th order.
3. Since the orders are different, the resultant order is the higher of the two, which is 4.
4. Therefore, the main river after the confluence is a 4th order stream.

Concept tested: Stream ordering (Strahler)

Published 10 October 2026 · How this solution was prepared and checked