SAJC Cluster 2.2 Lecture 15 Notes (Fluvial Landforms(II); Deltas)

St Andrew’s Junior College H2 Cluster 2: Tropical Environments H2_Cluster 2 Lecture 15_2025/pg1 Lecture 15 Fluvial Landforms (II): Deltas KEY QUESTIONS: ✓ What factors influence the formation of deltas in the humid tropics? ✓ What is the importance of deltas in the humid tropics? With the completion of this lecture, attached readings and tutorial, you should be able to: • Identify deltas as a fluvial landform • Discuss the features of deltas: delta plain, delta front, prodelta • Explain the role geomorphic processes, including the role of sediments removal and dispersal by waves and tides, in the formation of deltas in the humid tropics • Discuss the factors influencing the formation of deltas • Discuss the ecosystem services provided by deltas • Discuss the impact of human activities on ecosystem services provided by deltas Lecture Outline 15.1 Deltas 15.1.1 Features of a Delta 15.1.2 Conditions Necessary for the Formation of Deltas 15.1.3 Formation of Deltas (Geomorphic Processes including the Role of Sediments Removal and Dispersal by Waves and Tides in the Formation of Deltas) 15.2 Factors Influencing the Formation of Deltas 15.3 Ecosystem Services Provided by Deltas 15.4 Impact of Human Activities on Ecosystem Services Provided by Deltas 15.5 Conclusion

St Andrew’s Junior College H2 Cluster 2: Tropical Environments H2_Cluster 2 Lecture 15_2025/pg2 15.1 Deltas • Deltas are partly subaerial and partly subaqueous accumulations of riverborne sediment deposited at the mouth of the river, with the sediment reorganised by tides, waves and currents. • Deltas are mainly formed by fluvial depositional process at the mouth of a river, where a river loses velocity and competence as it flows into an ocean. • Deltas are so called because their triangular shape which resembles the Greek Letter Δ. In fact, deltas vary greatly in shape and can be grouped into three basic forms: arcuate, cuspate and bird’s foot (see Fig. 1). Fig.2 shows examples of the different types of deltas. Fig. 1 Basic shapes of deltas Fig. 2 Examples of deltas • In shape, deltas are approximately triangular or lobate. The apex of the triangle starts where the main river first splits into more than one channel. Such channels which branch out from the main river are known as distributaries. The surface of the delta is marked by a number of distributaries and their number generally increases as the delta extends towards the sea or ocean. • In general, gradient or slope of delta is very low as these are nearly at sea level. • Deltas are mainly composed of fine-grained sediments like sand, silt and clay with sand overlying slit and clay. Sediments are reorganised by the tides, wave