Overland flow: Causes sheet erosion

Water flows over the land surface in much the same way as it flows over a carpet, following paths of least resistance. The difference is that water slowly erodes the land where the flow is concentrated. Overland flow tends to be concentrated along roads, railway banks and contours.

Depending upon irregularities of the land surface, the overland flow may concentrate into narrow to wide paths.

The divides between drainage basins are likewise lowered until they are almost completely flattened leaving finally, a lowland of faint relief with some low resistant remnants called monadnocks standing out here and there.

This type of plain forming as a result of stream erosion is called a peneplain.

Youth

• Streams are few during this stage with poor integration and flow over original slopes showing shallow V-shaped valleys with no floodplains or with very narrow floodplains along trunk streams.
• Streams divides are broad and flat with marshes, swamp and lakes.
• Meanders if present develop over these broad upland surfaces. These meanders may eventually entrench themselves into the uplands.

Mature

• During this stage streams are plenty with good integration.
• The valleys are still V-shaped but deep;
• The flat and broad inter stream areas and swamps and marshes of youth disappear and the stream divides turn sharp. Waterfalls and rapids disappear.

Old

• Smaller tributaries during old age are few with gentle gradients.
• Streams meander freely over vast floodplains showing natural levees, oxbow lakes, etc.
• Divides are broad and flat with lakes, swamps and marshes. Most of the landscape is at or slightly above sea level.