Classifying Your Stream Slope

Determine your stream slope by following the steps and equation below.

The slope of a stream measures the vertical distance that a stream drops over a given horizontal length. The slope is usually shown as a percentage. A stream’s slope influences a number of items such as how quickly the water is moving through the stream, how much sediment the stream will carry and how the streambed may erode. Understanding your stream’s slope will help you to understand how and why the stream is behaving the way it does and determine specific details for stewardship and recovery strategies.

Classifying stream slope example

How to determine your stream slope:

Step 1

Determine a length of area you want to work with (at least 100 ft. long), mark the upstream & downstream points. Measure the distance while keeping a string level. This is the Run.

Step 2

Place a stake with string. Pull string to downstream mark. Level & measure the distance from ground. This is your Rise.

Step 3

Calculate your slope using the equation:

Step 4

Use your Slope% to classify your stream as Steep, Moderate, or Gentle.

What is your stream slope?___________________________

The slope of a stream directly influences the velocity and characteristics of the stream’s flow. This impacts the shape and behavior of this reach of the stream. Streams naturally shift to reach a balanced slope where the alignment and shape of the stream settles into a stable state. This balance, or equilibrium, is often achieved by meandering in unconfined valleys. Steeper slopes can also achieve a stable equilibrium in confined, mountainous valleys where the streambed material is large enough to withstand the erosive forces caused by the increased velocities. Ultimately, the slope of a stream can provide some indication of its stability. The slope of a stream can change quickly, and your property may have multiple ranges of slopes.

What does your stream’s slope tell you?

Steep slopes are usually found in mountainous areas, and often result in increased velocities in the channel. Erosion from this can be a concern in areas with finer streambed materials like sand. Steep slopes are frequently associated with more entrenched streams where the flow is confined to the channel on either side.

Moderate slopes are common along the foothill areas where the mountainous terrain begins to flatten onto the plains. Flow velocities in reaches with a moderate slope can still cause erosion under certain conditions, especially when the stream is entrenched. Erosion of the stream may be less of a concern in non-entrenched reaches with a moderate slope.

A stream with a gentle slope will generally have lower velocities and reduced energy compared with steeper slopes. Streams with gentle slopes are usually found along the plains where they are able to find their equilibrium slope by meandering through their unconfined valley. Due to reduced velocities and overall energy, these streams can deposit any sediment picked up in higher energy (faster) areas upstream. Sediment deposition at these locations may cause shifts in the general stream alignment and shape.