The Drainage Basin
- A drainage basin is an open system
- Every drainage basin is unique and is different in shape and size, with different rock types, relief and land use
Drainage basin features
- All drainage basins have some features in common:
- Watershed
- Source
- Confluence
- Tributary
- Mouth
A drainage basin
Channel network
- Every drainage basin is covered by a network of tributaries which connect to the main river channel. The number of tributaries in a drainage basin is referred to as the drainage density:
- Drainage basins with lots of tributaries have a high drainage density
- Drainage basins with few tributaries have a low drainage density
- The drainage density is the result of the soil and rock under the surface
- Where the rock or soil is impermeable this leads to high drainage density because the water cannot infiltrate
- This means it flows over the surface in tributaries
- Where the rock or soil is permeable water can infiltrate leading to low drainage density
Exam Tip
You need to ensure that you are clear about the difference between a closed system such as the hydrological cycle and an open system such as a drainage basin. Remember a closed system has no inputs or outputs whereas an open system has both inputs and outputs.
