Surface Runoff and Erosion: Processes and Landforms

Surface Runoff: Definition and Impact

Surface runoff forms when terrain becomes saturated and water begins to flow along the surface. This type of surface water is called runoff because it does not flow in a valley or riverbed; it simply moves as a layer of water over the terrain. It possesses great erosive power. As this water moves to lower regions, it can pull significant material with it and erode rock.

Factors Influencing Surface Runoff

• Climate: Influences how much rain falls, the intensity of precipitation, and evaporation rates.
• Type of Erosion: Erosion occurs more easily in sandy soil compared to solid rock like granite.
• Terrain Gradient: Steeper gradients increase water velocity, leading to more severe erosion.
• Vegetation: Plants decrease water velocity and their roots hold soil in place, increasing resistance to erosion.

Areas with dense vegetation are significantly more resistant to erosion than barren landscapes.

Landforms Created by Runoff

• Hoodoos: Formed when terrain consists of two materials that respond differently to the same erosive force.
• Rills: Small paths created as overland flow erodes the surface of the terrain.

Torrents: Characteristics and Courses

A torrent is a short, fast-flowing stream with a fixed course but a variable flow rate. Flow rate is the volume of water moved by the river in a specific amount of time. Torrents are divided into three courses:

• Catch Basin: The upper, funnel-shaped course where the majority of erosion occurs.
• Main Channel: The middle section where water transports eroded material. Erosion continues here, which widens the valley.
• Alluvial Fan: A fan-shaped formation resulting from the deposition of eroded material.

Rivers