river processes

Answer: The long profile is steep in the upper course near the source (1 mark), with high kinetic energy that produces vertical erosion and V-shaped valleys (1 mark). In the middle course, the gradient becomes moderate, and lateral erosion and transportation become the dominant processes (1 mark). In the lower course near the mouth, the gradient is very gentle, energy is low, and deposition dominates, creating wide flood plains and levees (1 mark). The overall shape is concave.

Answer: The long profile is steep in the upper course near the source (1 mark), with high kinetic energy that produces vertical erosion and V-shaped valleys (1 mark). In the middle course, the gradient becomes moderate, and lateral erosion and transportation become the dominant processes (1 mark). In the lower course near the mouth, the gradient is very gentle, energy is low, and deposition dominates, creating wide flood plains and levees (1 mark). The overall shape is concave.

Answer: Abrasion (also called corrasion) is the process by which the river's sediment load is scraped and rubbed against the bed and banks (1 mark). Rocks, pebbles and sand act like sandpaper, wearing away the channel surfaces (1 mark). It is most effective in the upper and middle courses where larger sediment is available as load (1 mark). Abrasion can create distinctive features like potholes where pebbles become trapped in eddies and grind circular depressions into the river bed (1 mark).

Answer: The four transportation processes carry different sizes of sediment. Traction rolls the largest particles (boulders and cobbles) along the river bed (1 mark). Saltation bounces medium particles (sand and small pebbles) along the bed in a hopping motion (1 mark). Suspension carries fine particles (silt and clay) within the water column, making the water appear cloudy - this is the most common process (1 mark). Solution carries dissolved minerals invisibly in the water (1 mark). The process used depends on particle size and river energy - high energy rivers can carry larger loads, while low energy rivers can only transport fine material in suspension and solution (1 mark). As velocity decreases downstream and during floods, the processes shift from traction to saltation to suspension as particles settle out (1 mark).

Answer: I agree that deposition is extremely important in the lower course because the river's gradient and velocity are very low, meaning it cannot carry its sediment load (1 mark). This creates major landforms including levees (raised banks formed by repeated deposition during floods), extensive flood plains (areas of deposited alluvium), and estuaries or deltas at the river mouth (1 mark). However, erosion and transportation still operate in the lower course and are also significant (1 mark). Lateral erosion continues to widen the valley, especially on the outside of meander bends where water velocity is highest (1 mark). Transportation moves vast quantities of fine sediment through the lower course, even if it is ultimately deposited (1 mark). In the middle course, all three processes are roughly balanced, making it difficult to say deposition dominates there (1 mark). The importance of each process varies with conditions - during floods, erosion and transportation increase even in the lower course (1 mark). Ultimately, while deposition is the dominant process in the lower course, it cannot be understood in isolation from erosion and transportation, which supply and move the sediment that is eventually deposited (1 mark). The lower course is best understood as the endpoint of a system where erosion in the upper course produces sediment that is transported and ultimately deposited where energy is lowest (1 mark).