Stream Order: All You Need to Know

Stream order is defined as the strategy of giving a numeric order to the streams, depending on their tributaries. Also known as the waterbody order, stream order calculation has become one of the common techniques in hydrology. The method is most commonly used for identifying as well as categorizing the structure and types of streams. The most common reason why researchers have been investing their time and resources in stream order is that it is possible to identify the characteristics of the stream just by identifying their order. In addition to that, the type of stream is mainly used for identifying the place of the river in the large water network.

With the help of the Geographic Information System (GIS), scientists can identify not only the type of streams but the numeric order. This information gives them a better idea of the structure of the stream and the river’s place. Take the first-order streams, for example. They do not comprise the concentrated upstream flow. It is identified as the main reason why this network is highly likely to get polluted easily. Basically, there are two popular techniques a researcher has to assign orders for different streams. These are called Strahler and Shreve methods. In this post, we are going to discuss each method in brief. Keep reading.

Strahler Method

According to the Strahler method, each link that isn’t associated with the tributaries is given order 1 and is called first order. Note that the order increases automatically as soon as the same types and order of the streams intersect. In this method, the two same order link intersections will result in the two-order link. Similarly, when the two two-order links are joined, they lead to a third-order link.

There is no denying that the Strahler method is the most popular and widely used stream ordering technique we have discovered so far. It is also the only method to deliver the most accurate results when identifying the type and order of a stream. The reason is pretty simple. The method takes only the ordered links into account. The order increases as soon as more links of the same order intersect with each other, instead of including the random links in the calculation. It is also important to note that the Strahler method could be a little sensitive when it comes to adding new links or removing the existing ones from the network.

Shreve Method

Unlike the above-mentioned technique, the Shreve method identifies the order and type of streams in a different way. The method is different from the Strahler method in that it takes all the links present in the network into account. Similar to the above technique, each link in this method is given the order of 1 (so long as these are exterior links). The method, however, uses an additive technique. For instance, the first and second-order intersection results in the third-order link, which is totally opposite from the Strahler method where order links are generated based on the intersection of the same orders.