River Landforms And Processes

Erosion

The wearing away and removal of rocks from cliffs, river beds and banks

Weathering

The wearing away of rock in its original place

Chemical Weathering

The decomposition of rock caused by a chemical change within that rock as a result of weak acids in rain or sea water

Freeze Thaw Weathering

Water gets into the cracks of rocks, freezes and melts repeatedly as temperatures change, resulting in the weakening and breaking away of the rock. This is an example of mechanical weathering

Abrasion

The wearing away of rock by sediment scraping against it like sandpaper

Attrition

Erosion caused by rocks and boulders transported by water hit eachother and breaker into smaller, rounder pieces

Deposition

Occurs when material being transported by the water is dropped due to the water losing energy

Transportation

The movement of eroded material by water

Hard Engineering

The use of concrete and large artificial structures to defend land against natural erosional processes

Soft Engineering

Managing erosion by working with natural processes to help restore natural landscapes

Mass Movement

The downhill movement of weathered material under the force of gravity

Long Profile

The gradient of a river from its sourse to its mouth

Cross Profile

The side to side cross section of a river channel and/or valley

Lateral Erosion

Sideways erosion by a river on the outside of a meander channel

Vertical Erosion

Downward erosion of a river bed

Solution

Soluble particles are dissolved into the river and carried by the water

Saltation

Particles bouncing down a river bed

Traction

The rolling of boulders and pebbles along a river bed

Suspension

Fine solid material held in the water while the water is moving

Discharge

The quantity of water that passes a given point eithin a given period of time

Estuary

The tidal mouth of a river where it meets the sea, wide banks of deposited mud are exposed at low tide

Flood Plain

The relatively flat area forming the valley floor on either side of a river channel, which is sometimes flooded

Describe interlocking spurs

They are projections of highland that alternate from either side of a valley and are formed by fluvial erosion

1?

Waterfalls occur when a band of hard rock overlies a softer rock. Falling rock and water particles erode the soft rock below creating a plunge pool

2?

The soft rock is undercut by erosional processes such as hydraulic action and abrasion creating a plunge pool where water and debris swirl around eroding the rock through corrosion further deepening it and creating an overhang

3?

Hard rock overhang above the plunge pool collapses as its weight is no longer supported

4?

Erosion continues and the waterfall retreats upstream leaving behind a gorge

Rapids

Fast flowing, turbulent sections of a river

Name two landforms found in the middle course

• Meanders

• Oxbow lakes

A?

Fast flowing water on the outside bank causes lateral erosion through abrasion and hydraulic actio, which undercuts the bank to form a river cliff

B?

The current is slower on the inside bend because the river channel is shallower (more friction). Eroded materials are deposited on the inside bend forming slip off slopes

C?

Over time curves increase due to erosion on the outside banks and deposition on the inside, slowly moving the position of the river

D?

Oxbow lakes are formed by old meanders that have curved so far that when there is very high discharge the water cuts across the neck and eventually cuts of the meader

Name 3 landforms from the lower course

• Levees

• Floodplains

• Estuary

Describe the formation of a levee in four stages

Sediment that has been eroded further upstream is transported downstream. When the river floods, friction with the land reduces velocity and causes deposition

2?

Heavy sediment is deposited closest to the river. the size of sediment gets progressively smaller with increased distance from the river

3?

After many floods, the sediment builds up to increase the height of the river banks meaning that the channel can carry more water and flooding is less likely

Describe the formation of a floodplain in three stages

During a flood water containing large quantities of silt pours out over the valley

Stage 2 of a floodplain formation?

The water slowly soaks away leaving behind the deposited sediment. The height of the floodplain increases as material is deposited on either side

Stage 3 of a floodplain formation?

Repeated flooding forms a thick silt deposit which is fertile and often used for farming

Give 5 characteristics of estuarys

• Tidal part of a river where freshwater meets with salt water

• Hight tidal range

• Very wide

• Mudflats - visible at low tide, some mud covered by salt marshes

• Tidal bores - huge waves that funnel up the river

What is the path of a river as it flows downhill called?

Its course

What does the long profile of a river look like?

A steep upper course, a gently sloping middle course and an almost flat lower course

What does the long profile of a river show you?

How the gradient changes

What do rivers form as they flow downhill?

Channels and valleys

What do rivers do to the landscape?

Erode the landscape and transport eroded material to somewhere further along the course, where it is deposited

Why does the shape of the valley change along the river?

Depends on whether erosion or deposition is the dominant process

1?

Steep

2?

V-shaped valley, steep sides. Narrow, shallow channel

3?

Medium

4?

Gently sloping valley sides. Wider, deeper channel

5?

Gentle

6?

Very wide, almost flat valley. Very wide, deep channel

Why might a river deposit material?

Volume of water falls, the amount of eroded material increases, the water is shallower, the river reaches its mouth

Step 1 of interlocking spurs formation

In the upper course of a river, most erosion is vertically downwards. This creates steep, v-shaped valleys

Step 2 of interlocking spurs formation

The rivers lack power to erode laterally, so they have to wind around the high hillsides that stick out into theirs paths on either side

Step 3 of interlocking spurs formation

The hillsides that interlock with each other as the river winds around them are called interlocking spurs

Step 1 of the formation of an estuary?

Estauries are founf at river mouths. The land is close to sea level and the river valley is at its widest

Step 2 of the formation of an estuary?

The water here is tidal - the river level rises and falls each day

Step 3 of the formation of an estuary?

When the water floods over the banks of the river, it carries silt and sand onto the valley floor

Step 4 of the formation of an estuary

As the tide reaches its highest point, the water moves slowly and has little energy, so it deposits sediment

Step 5 of the formation of an estuary?

At low tide, the wide, muddy banks are exposed

How can contour lines be used to tell the direction the river flows?

A river flows from higher contour lines to lower ones

How can you identify the upper course of a river on a map?

Identify waterfalls which will be marked on the map, high land, river crosses a lot of contour lines over a short distance, the river line is narrow

How can you identify the middle course of a river on a map?

Low nearby land, doesn’t cross many contour lines (gently sloping), meanders, the river line is wide