Fluvial Processes, Patterns and Landforms

Transcription

1 Fluvial Processes, Patterns and Landforms

2 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

3 Keywords Introduction to Rivers Hydrological Cycle Basin Watershed Source Tributaries Confluence Mouth Discharge Long Profile Base Level

4 CONDENSATION

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6 Drainage Patterns

7 DendriticDrainage 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

8 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

9 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. SlieveBeaghCo. Monahan

10 River Erosion Keywords Erosion Lateral Vertical Hydraulic Action Cavitation Abrasion Corrasion Solution Attrition

11 Erosion When the river channel is widened it is called lateral erosion Vertical Erosion is the deepening of the river bed

12 flash/erosion.swf

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14 Upper Course Features Interlocking Spurs V Shaped Valleys Waterfalls

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16 Mature Stage Flood Plain Meander Ox Bow Lake

17 Example River Boyne in Co. Meath Name: Meander Description S shaped bends in a river Formation Main processes: Lateral erosion Hydraulic Action Abrasion Deposition

18 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

19 Deposition Point Bar Erosion River Cliff

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21 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

22 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.

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24 Meander Scar/Mort Lake

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26 Example River Suir Co. Waterford Name Flood Plain Description A flat area of land either side of a river Formation Main Processes Flooding Deposition

27 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

28 Old Stage Levees Deltas

29 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

30 Example River Moy Co. Mayo Name Levee Description A ridge of sediment deposited on river banks Formation Deposition

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32 Name Delta Example Shannon Estuary Description Areas of land at the mouth of a river made form deposits of sand and gravel. Formation Deposition

33 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.

34 River Channel Deposition Distributaries

35 Types of Deltas