Identifying and classifying pipeline water crossings are key elements in creating an effective crossing management program. However, it can be challenging to properly do this using traditional approaches.
The most common approach traditionally has been to classify crossing based on the scale of the water body impacted by the pipeline crossing. So, the larger the water body, the greater the potential risk for a crossing. This scale is based on a subjective interpretation of whether a body of water would appear on a map at a designated scale. The most common scales are 1:1,000,000, 1: 250,000 and 1:50,000.
Historically, regulatory requirements have dictated that operators must register an Environmental Crossing for any pipeline that crosses a water body which would appear at a 1:1,000,000 scale. However, this definition does not have an objective standard, and is left to the interpretation of the viewer of the map. Further, this subjective interpretation may also be based on old or incorrect source data. When using this as a guideline, crossings may be missed altogether, or the significance of the crossing may be understated.
Therefore, it is important to analyze your entire pipeline inventory to identify and validate crossings. This includes working with a more objective approach to classifying the size of a water body.
One approach to doing this is to apply the Strahler Stream Order classification. Strahler Stream Order is an objective approach to defining stream size based on a hierarchy of tributaries.
Here’s how it works…
First, each water body is assigned a number. This begins by giving the outermost tributaries an order of 1.
If two bodies of the same order merge, the resulting stream is given a number that is one higher. If two bodies with different stream orders merge, the resulting stream is given the higher of the two numbers. So, if two 1s come together, they will form a 2. If a 2 joins into a 3, the resulting stream will retain the ranking of 3.
Applying this objective scoring system gives us a more accurate depiction of the relative size of a water body to help assess the priority of any associated pipeline water crossings.
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