Fluvial Processes, Patterns and

Landforms

Exam Questions

Examine the diagrams A, B and C below

Name each of the three river drainage patterns

Explain the formation of any two Irish landforms

caused by surface processes with the aid of

diagrams

Keywords – Introduction to Rivers

Hydrological Cycle

Basin

Watershed

Source

Tributaries

Confluence

Mouth

Discharge

Long Profile

Base Level

CONDENSATIONCONDENSATIONCONDENSATIONCONDENSATION

Drainage Patterns

Dendritic Drainage

• One major river with several small tributaries; the network of streams resembles the branches of a tree converging upon the trunk.

• This pattern will occur on any rock type.

• Rivers Shannon and Boyne are examples of this pattern

Trellis Pattern

• Tributaries flow at right

angles into a main river.

This is because the

surface consists of

alternating hard and soft

rock; the streams erode

the softer rock but find it

difficult to break through

the hard rock

• E.g. the Blackwater River

Radial Pattern

• This pattern will develop

in upland areas where

several streams will flow

outwards and

downwards from a

central point. The various

streams will flow in

different directions

• E.g. Slieve Beagh Co.

Monahan

River Erosion

Keywords

Erosion

Lateral

Vertical

Hydraulic Action

Cavitation

Abrasion

Corrasion

Solution

Attrition

Erosion

• When the river channel is widened it is called

lateral erosion

• Vertical Erosion is the deepening of the river

bed

• http://www.juicygeography.co.uk/downloads/

flash/erosion.swf

Upper Course Features

• Interlocking Spurs

• V Shaped Valleys

• Waterfalls

Mature Stage

• Flood Plain

• Meander

• Ox Bow Lake

Name: MeanderExample

River Boyne in Co. Meath

Description

S shaped bends in a river

Formation

Main processes:

• Lateral erosion

• Hydraulic Action

• Abrasion

• Deposition

Meander

• A meander is a curve in the river. It happens when the river meets a bend.

• As the river flows around it erodes the outside of the bend as the strongest flow is here. This causes a river cliff

• Slacker or shallower water flows on the inside of the bend and have less power deposition happens. This area of deposition is called a point bar

Erosion

River Cliff

Deposition

Point Bar

Name Ox Bow Lakes

Example

River Moy Co. Mayo

Description

Oxbow lakes are the remains of meanders that have been cut off from the rivers course.

Formation

Main Processes

Erosion and Deposition

Ox Bow Lakes

• Ox bow lakes forms when a meander becomes very pronounced.

• A narrow neck develops and in times of flood the main flow cuts across the neck to flow straight.

• It cuts off the loop of the meander and becomes an ox bow lake.

Meander Scar/Mort Lake

Name Flood Plain

Example

River Suir Co. Waterford

Description

A flat area of land either side of a river

Formation

Main Processes Flooding Deposition

Flood Plain

• As a river meanders the land on either side is

gradually worn back into bluffs of higher land.

• It is the flat land in the centre of a valley

Old Stage

Levees

Deltas

Deposition

A river deposits material due to a reduction in

energy. This generally occurs because of

1. Decreasing Velocity

2. Increase in Volume

3. Increase in the size of its load due to

• A fast flowing tributary adding extra material

• Heavy rainfall

Name Levee

Example

River Moy Co. Mayo

Description

A ridge of sediment deposited on river banks

Formation

Deposition

Name Delta

Example Shannon Estuary

Description

Areas of land at the mouth of a river made form deposits of sand and gravel.

Formation

Deposition

A delta forms where a river reaches a sea or lake. It slows down, loses power and deposits the material it has been carrying.

If the sea is sheltered and there is not much wave action this material will build up into a delta.

As it is deposited it falls into different layers

It blocks up the river channel forcing it to break up into smaller river channels called distributaries.

River Channel

Deposition

Distributaries

Types of Deltas