Topography  

Topography, or lay of the land, is an important variable in water erosion. More specifically, the degree of steepness (percent slope), as well as the slope length, is important. Steep slopes have high runoff water velocity. This increases its erosive energy (remember that erosive energy of runoff is a function of runoff velocity and volume). When the slope is longer (length), surface area for water collection also increases and therefore increases the run-off volume.

The ’plan’ is a term used to describe the distribution of water across the slope, that is, whether water flow is evenly distributed across the slope (linear); water flow is concentrated in one area (concave); or water flow is moved away from the slope (convex).

The pattern and speed of water flow will influence the area of most intense soil erosion across the slope.

Click on the animation Hover over a hillside area to see the water flow pattern. Animation by NC State University

Thinking Questions: View the animation and then do the following activity. Below is an example sketch of water flow characteristics of a concave profile with a concave plan. Click here to view the concave profile with a concave plan. Now find the linear profile with a convex plan within the animation. Based on the water flow characteristics, sketch a hillside and show the area of most intense erosion. (This sketch should be similar to the sketch of the concave profile with a concave plan.)