Differential erosion: erosion that occurs at different speeds due to the difference in the resistance of rocks
Parts of a River
Source Course
Confluence Tributary Mouth
Drainage basin Watershed Estuary
Streams flowing down a sloping landscape
The beginning or start of a river The path the river flows along to the sea
The point where two or more rivers join together A smaller river that flows into a bigger river The point where the river enters the sea Area of land drained by the river
A highland area that marks the boundary of the drainage basin Part of a river mouth that is tidal, e.g. the Shannon Estuary
10.2 Drainage Patterns
Sea Dendritic drainage
Streams pick out bands of weaker rock and erode along them
Band of soft rock
Sea
Soft rock
Trellis drainage
Streams drain out from a central dome
Uniform rock type
Drainage patterns refer to the shapes a network of rivers create over an area. The drainage patterns of a river basin are affected by the landscape and rock types over which the river flows. Generally, there are four different types of drainage pattern:
• Dendritic • Trellised
Dendritic Radial drainage
Marsh lakes develop
Rivers do not form a set drainage pattern
The dendritic drainage pattern is the most common type found in river basins. The name ‘dendritic’ comes from the Greek word for ‘tree’, which is used because the drainage pattern resembles a tree trunk and its branches. Tributaries (branches) meet the main river (trunk) at acute angles (less than 90˚). Dendritic drainage normally occurs on gently sloping land with a similar rock type where differential erosion does not occur. The tributaries flow from narrow valleys into the main river, which occupies the largest valley in the area.
Trellised drainage occurs where tributaries meet the main river at a right angle. Trellised drainage normally occurs where the larger river has eroded the softer rock in a valley, leaving the landscape of harder rock elevated above it. Tributaries from these ridges of harder rock then flow downwards, meeting the river at right angles.
