GEOG 210 - Drainage Basins

Drainage Basin

An area of land with a topographic divide that collects rain and snow and discharges most water to a stream, river, or other water body; synonymous with watershed, catchment, or river basin.

Topographic Divide (Watershed Boundary)

The boundary separating one drainage basin from another, often defined by elevation.

What are the spatial scales in geomorphic processes?

1. Local scale (~1 m): Influenced by slope angle.

2. Hillslope scale (~100 m): Influenced by hillslope form and soil properties.

3. Catchment scale (~10 km): Influenced by basin relief, form, and drainage network.

4. Regional scale (~1000 km): Large-scale geomorphic and climatic influences.

Why use drainage basins as hydrological units?

They integrate a range of processes, including:

• Water budget (input, output, and storage of water).

• Sediment budget (movement and storage of sediment).

• Biogeochemical, hydrological, geochemical, biological, and ecological processes.

What is Canada's major 'ocean drainage basin'?

An area that drains all precipitation as runoff into a specific ocean

What are sediment budgets used for?

• Comparing basin conditions.

• Estimating responses to management actions.

• Evaluating impacts of climate, tectonics, or historic land use.

• Understanding river responses to dam construction, gravel mining, etc.

What is drainage pattern, and what influences it?

Arrangement of streams in a drainage basin.
Influences: Geology, climate, and time.
Types: Dendritic, trellis, rectangular, radial.

What is stream order (Strahler system)?

A measure of stream size, from smallest (1st order) to largest (12th order, e.g., Amazon River). The Fraser River is an 8th order stream.

What are the three zones in a drainage basin?

• Erosion zone (upland).

• Transport zone (midland).

• Deposition zone (lowland).

What is a longitudinal stream profile?

A graph of stream elevation against distance downstream.

• Upstream segments: Steeper gradient.

• Downstream segments: Gentler gradient.

What is base level in geomorphology?

• Ultimate base level: Sea level.

• Local base levels: Lakes, dams, or other barriers.

• Theoretical limit for stream erosion.

What are depositional landforms at river mouths?

• Deltas: Formed in standing water.

• Alluvial fans: Cone-shaped deposits on flat land.

• Occur due to reduced water velocity.

Describe alluvial fans.

• Cone-shaped, steep deposits of coarse sediment.

• Form where streams emerge from confined valleys onto flat land.

• Gradient: ~1–4 degrees.

What causes discontinuities in a stream profile ('knick points')?

• Tectonic activity.

• Base level changes.

• Alternating hard and soft rock layers

How do terraces form?

• Stream erodes into a floodplain.

• Creates a new floodplain at a lower elevation.

• Paired terraces indicate periods of erosion.