SAJC Cluster 2.2 Lecture 10 Notes (Geomorphic Processes Pt.1: Fluvial Processes and their factors)

St Andrew’s Junior College H2 Cluster 2: Tropical Environments H2_Cluster 2 Lecture 10_2024/pg1 Lecture 10 Geomorphic Processes (I): Fluvial Processes and their Factors KEY QUESTIONS: ✓ What influence fluvial processes? With the completion of this lecture, attached readings and tutorial, you should be able to understand the: Fluvial processes: erosion, transportation and deposition of materials by rivers Sources of materials in rivers Influence of river’s energy on fluvial processes Natural and human factors influencing river’s energy Lecture Outline 10.1 Introduction: Rivers as energy systems Box 1: Some useful terms to do with channel morphology What a river does with the energy it has... 10.2 Fluvial Erosion 10.2.1 Corassion 10.2.2 Corrosion 10.2.3 Cavitation 10.3 Fluvial Transportation 10.3.1 Solution 10.3.2 Suspension 10.3.3 Saltation and Traction Box 2: Capacity and Competence 10.4 Fluvial Deposition 10.5 Tying fluvial processes together: The Hjulström Curve Box 3: Where do materials in a river come from? What factors will affect the energy a river has... 10.6 Factors Influencing a River’s Energy 10.6.1 Hydraulic Radius 10.6.2 Channel Slope 10.6.3 Channel Roughness

St Andrew’s Junior College H2 Cluster 2: Tropical Environments H2_Cluster 2 Lecture 10_2024/pg2 10.1 Introduction: Rivers as energy systems Rivers are energy systems. They derive their energy from: • their volume of flow, or discharge (influenced by OVF, TF and BF; recall Lect 5) • flow velocity (which is dependent on a number of factors, see Section 10.6) This energy is expended (or used) through fluvial processes of erosion and transport. Deposition sets in when river energy is low. • At high flow, rivers have surplus energy which is expended on sediment erosion (“picking up” load; see Section 10.2) and transport (“moving” load; see Section 10.3). • At low flow, rivers may deposit (“drop”; see Section 10.4) its load to ensure it has enough energy to overcome the frictional resistance of the channel and keep the water flowing. At any one time, a river will be performing all these processes, but depending on the existent factors, there will be a dominance of one over the other. 10.2 Fluvial Erosion Broadly, erosion refers to the progressive removal of load (i.e. rocks, sediments, and mineral material) from the bed and banks of the channel. Erosion is associated with high energy levels in the river. By the process of erosion a river can deepen (by eroding the river bed), widen (by eroding the river bank) or even lengthen its channel. There are generally three ways through which fluvial erosion can take place (see Fig. 1). These are abrasion, attrition, solution and hydraulic ac