The Bradshaw Model: River Characteristics & Downstream Changes
Watch a short video of a local river or a common river scene and note down all the features you can observe (e.g., confluence, tributaries, water shed, meander, oxbow lake, lever, etc).
Possible resource: https://youtu.be/4NspSxMkPS8?si=hV8YD47N2B73FrOK
The Drainage Basin as a System
A drainage basin is the area of land drained by a river and its tributaries. Geographers view this as an open system, defined by inputs (precipitation), throughputs (flows like infiltration and surface runoff), and outputs (river discharge at the mouth).
Possible resources: https://youtu.be/8GOJ3S5jKSI?si=eEAbZxT_f9FxJnES
The boundary of a drainage basin is the watershed, typically a ridge of high land. Within this system, water moves through various storage points, including soil moisture, groundwater, and vegetation interception. Understanding these characteristics is fundamental to managing flood risks and water resources sustainably.
↑ Back to ContentsChannel Characteristics
As a river moves from its source in the uplands to its mouth at the sea, the physical environment changes drastically. These changes are categorized into three sections: the upper, middle, and lower courses.
Upper Course
Characterized by steep gradients, V-shaped valleys, and shallow, turbulent channels. Erosion is predominantly vertical as the river cuts downward into the landscape.
Possible resource: https://youtu.be/zBg5APcAD-Y?si=gqlS_geemTOoWnY4
Middle and Lower Course
The gradient becomes gentler, and the river begins to erode laterally. Valleys widen into floodplains, and the river channel becomes wider and deeper to accommodate the increasing volume of water from tributaries.
Possible resources:
- Middle course: https://youtu.be/nKj1tk_SN-Y?si=JiDIKJxaTBCK8DG4
- Lower course: https://youtu.be/du7HPqaymiI?si=n4Ta_tTx-V9sIse1
The Bradshaw Model Explained
The Bradshaw Model is a geographical theory that describes how specific river characteristics change as a river travels downstream. It is essential for predicting river behavior.
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| Bradshaw Model |
According to the model, several variables increase downstream, including discharge, occupied channel width, channel depth, and average velocity. Conversely, variables such as load particle size, channel roughness, and gradient decrease as the river approaches its base level (where it primarily transports sediment rather than eroding).
↑ Back to ContentsFieldwork: Investigating Change
To validate the Bradshaw Model, geographers conduct fieldwork. This involves selecting multiple sites along a river's long profile and collecting primary data. By measuring cross-sectional area and timing flow velocity, students can calculate discharge and determine if the local river adheres to theoretical expectations.
↑ Back to ContentsCheck for Understanding
1. Which of the following increases as a river moves downstream?
A) Load particle size
B) Channel roughness
C) Discharge
2. What term describes the boundary of a drainage basin?
3. Why does average velocity typically increase downstream?