River landforms

Label this drainage basin diagram

What is a drainage basin?

An area of land drained by 1 river & all its tributaries

What is the source?

Where the river starts

What is the mouth?

Where the river enters the sea or lake

What is the river channel?

Where the river flows

What is a tributary?

A small stream that flows into a larger stream / river

What is a confluence?

Where 2 tributaries join

What is a watershed?

The boundary of a drainage basin

What are the 3 stages of a river?

Upper course

Middle course

Lower course

What are the defining features of the upper course?

→ River is narrow & shallow

→ Large & angular load

→ Traction is the main transportation type

→ Low velocity & discharge

→ Waterfalls, gorges, v-shaped valleys

What are the defining features of the middle course?

→ River is getting wider & deeper

→ Load is getting smaller & more rounded

→ Suspension is the main transportation type

→ Medium velocity & discharge

→ Meanders, ox-bow lakes, flood plains, levees, eyots

What are the defining features of the lower course?

→ River is wide & deep

→ Fine & rounded load

→ Solution is the main transportation type

→ High velocity & discharge

→ Estuaries, more sinuous meanders

What is the long profile of a river?

A diagram that shows how the river channels gradient changes downstream

How does the long profile change downstream?

The channel gradient decreases

What is the cross profile of a river?

A diagram that shows the cross-section of a river channel

How does the cross profile of a river change downstream?

The cross-section gets wider

How are v-shaped valleys formed?

Vertical erosion occurs when a small river rapidly flows downhill, creating a notch

Hydraulic action & abrasion erode the sides of the notch

The sides become exposed to freeze-thaw weathering which loosens rock & sediment

Some rock & sediment fall into the river & are transported downstream, widening the river channel & creating v-shaped valleys

How are waterfalls formed?

Water flows over a top layer of hard rock & a bottom layer of soft rock

Hydraulic action & abrasion cause the soft rock to erode away first as it is less resistant, leaving an overhang of hard rock

Eventually, the overhang of hard rock collapses into the plunge pool, causing the waterfall to retreat up the river & leave behind a gorge

How are meanders formed?

Erosion occurs on the outer bend because the water flows faster & has more energy, creating river cliffs

Deposition occurs on the inner bend because the water flows slower & has less energy, creating slip-off-slopes

Erosion & deposition work together to make the river channel more sinuous which thus makes meanders

How are ox-bow lakes formed?

Lateral erosion causes the outer bends of a meander to become closer together

This forms a neck which narrows due to erosion

During high flow conditions (flood), the meander neck breaks through

The river now flows through the quicker & more direct route, bypassing the old meander

Sediment is deposited due the decrease in river energy, sealing off the old meander & forming an oxbow lake

How are floodplains formed?

During a flood, water displaces onto the surrounding land

Sediment is deposited onto to the flooded land since the river loses energy

This creates a flood plain which expands overtime due to meander migration & deposition on the inner bend

How are levees formed?

During a flood, the river loses energy & so deposits sediment

The larger sediment is deposited first at the channel edges & the finer sediment is deposited last at the outer parts of the floodplain

After many floods, this builds up a raised ridge on the river bank, known as a levee