RI 2.2 Fluvial Landforms and Ecosystems

CLUSTER 2 | TROPICAL ENVIRONMENTS TOPIC 2.2 LANDFORMS IN THE TROPICS Raffles Institution Year 5-6 Geography. For internal use only. 1 Q = A V 2.2.3 Fluvial Landforms in the Humid Tropics What fluvial landforms can be found in the humid tropics? • Fluvial landforms: meanders, braided channels and deltas • Features of meanders: sinuous channel, river cliff, point bar • Features of braided channels: mid-channel bars • Features of deltas: delta plain, delta front, prodelta Fluvial landforms are landforms produced by the erosion and deposition of streams or rivers, in another words, fluvial processes. Examples of fluvial landforms include bars, levees, braided channels, meanders and deltas. As you have learnt, fluvial processes are affected by both river energy, discharge and sediment characteristics. 1. River Energy Once water reaches the channel, it moves downstream towards the mouth of the river. This moving water possesses energy, which varies along its course. This energy is required for the three main fluvial processes—erosion, transportation and deposition. An increase in river energy usually results in an increase in erosion and transport, whereas a decrease results in deposition. A still body of water at any point above sea level has a certain amount of stored energy as a result of its position. This supply of potential energy, when converted to kinetic energy when the river flows downstream, enables it to erode the river channels and transport the eroded material. The amount of kinetic energy is determined by: 1. The volume of the flowing water. 2. Its mean velocity. The energy possessed by the river is therefore determined by its discharge (defined as a measure of the water flow at a particular point). An increase in any one of these two factors will thus mean an increase in the amount of kinetic energy. 1.1 Measuring River Discharge River discharge varies greatly over time and space. It is calculated as follows:

CLUSTER 2 | TROPICAL ENVIRONMENTS TOPIC 2.2 LANDFORMS IN THE TROPICS Raffles Institution Year 5-6 Geography. For internal use only. 2 V = 1.49 𝑅 2 3 𝑆 1 2 𝑛 𝑆 = ℎ𝑒𝑖𝑔ℎ𝑡 𝑎𝑏𝑜𝑣𝑒 𝑠𝑒𝑎 𝑙𝑒𝑣𝑒𝑙 𝑐ℎ𝑎𝑛𝑛𝑒𝑙 𝑙𝑒𝑛𝑔𝑡ℎ Q = discharge (usually expressed in m3/s) A = cross-sectional area of the river (in m2) V = mean river velocity The volume of water is important since an increase in the amount of water will mean a higher discharge and a more efficient river. This explains why floods can unleash so much energy and cause massive destruction to the environment. 1.2 Measuring river velocity Velocity is one very important determinant of river discharge and energy. Factors affecting the velocity of rivers are spelled out by the Manning’s equation. V = velocity S = channel slope R = hydraulic radius n = coefficient of roughness (1.49 is English units conversion factor, set to 1 for metric. However, you do not need to remember this formula for A Levels) 1.2.1 Channel Slope