Our global water system grows and flows across the land in streams and rivers. The way in which streams form and build into larger rivers can be measured by stream order. Stream order demonstrates the order in which water collects as it flows downstream, defining the hierarchy of stream size as they intersect and unite with other streams to form tributaries and larger rivers. Stream order is an organized, mathematical formula to show the way water collects when it flows downstream. Stream order can be used to model or diagram the structure of a watershed, or other water systems. Site testing for biotic and abiotic features of a river’s water quality can be determined when analyzing the water quality at various points in its stream order.
Figure1. Stream order
The concept of stream order can be compared to the order in which twigs connect to larger stems and then to larger branches which all flow into the truck of a tree to show how the flow of water moves through a tree. Another comparison to demonstrate a flow system is the way our capillaries connect to form veins and then arteries to show how blood flows through the body.