TMJC 2025 JC1H2 C2 Lecture 11 Channel Patterns

Higher 2 (9173) Cluster 2: Tropical Environments TMJC Lecture 11 Channel Patterns and Deltas 2025 Page 1 of 10 LECTURE OBJECTIVES 1. Explain the meandering and braided channel patterns 2. Compare the characteristics and conditions that leads to the formation of meandering and braided channels 3. Explain how the characteristics of the drainage basin affect the drainage efficiency Introduction Channel Patterns: Channel Straight Meander / Sinuous Braided Channel Photo Plan View Cross- section view

Higher 2 (9173) Cluster 2: Tropical Environments TMJC Lecture 11 Channel Patterns and Deltas 2025 Page 2 of 10 (A) WHAT IS A MEANDER CHANNEL PATTERN? 1. A meandering channel is a sinuous channel with a sinuosity index of at least 1.5 with asymmetrical cross-sections, formed by erosion on the outer bank and deposition on the inner bank. 2. In terms of channel features present, meandering channels contain pool and riffle sequences as well as river cliffs and slip-off slopes (Fig. 1). Fig. 1: Meander Channel Pattern Sinuosity is a measure of how irregular a stream’s path is. Sinuosity is measured by the Sinuosity Index, which is obtained by dividing channel length between 2 points by the straight line distance between the two points (also known as the downvalley length). Sinuosity index = Channel length between A and B/Downvalley length Where sinuosity is 1.0, it shows that channel length is equal to the straight line distance, meaning it is a straight channel.

Higher 2 (9173) Cluster 2: Tropical Environments TMJC Lecture 11 Channel Patterns and Deltas 2025 Page 3 of 10 (B) HOW IS A MEANDER CHANNEL PATTERN FORMED? 1. The main condition required for the formation of meander channel patterns is the presence of an alternating pool and riffle sequence. a. Any form of turbulence will create decelerated flow of water resulting in deposition forming a riffle . This deposition result in release of energy allowing for accelerated flow which causes erosion, creating a pool. b. Alternating pool and riffle sequences refer to alternating occurrences of pools (areas of deep water) and riffles (areas of shallow water) along the river channel 1. Typically the distance between the pools are 5–7 times the bed width of the river. c. Pool and riffle sequences may affect channel form by increasing the sinuosity of the channel which will then eventually lead to the formation of meanders once the sinuosity index exceeds 1.5. 2. Thus, meanders form as a result of differences in channel efficiency and competence over space due to the pool and riffle sequence. 3. Along a straight section of a river, a pool and riffle sequence results in a diversion of the thalweg (the path of maximum velocity) from side to side of the river banks due to diffusion over riffles. a. This causes the thalweg to develop a sinuous course. b. As the thalweg swings, it results in erosion on the outer bank