River landforms

Question 1

Straight river channels

Answer 1

Straight channels are rare. Even when they do occur the thalweg (line of maximum velocity) moves from side to side. These channels generally have a central ridge of deposited material, due to the water flow pattern

Question 2

Meandering river channels

Answer 2

Most rivers meander to some extent. Upland streams meander but the most pronounced meanders are found on floodplains where lateral erosion is facilitated by the soft nature of the river banks. Meanders are so common because of spiraling is the normal behaviour of normal flowing fluids on the surface of a rotating planet

Question 3

Braided river channels

Answer 3

Formed by steep channel gradient, large proportion of coarse material, easily erodible bank material and high variable discharge
Common in periglacial and semi arid areas. During periods of high discharge, rivers transport large amounts of sediment. Braiding occurs when sediment exceeds river capacity resulting in deposition. Also occurs when river gradient becomes shallower (lower course). Begins with mid channel bar that grows downstream. Coarse bed load deposited first followed by finer material. Upstream end becomes stabilised with vegetation. Island localises and narrows to form more permanent eyots. Vegetation traps further sediment and increases height of eyot so only briefly covered at periods of very high discharge. E.g. Waitaki river

Question 4

Waterfalls

Answer 4

Band of resistant rock over band of less resistant rock. Differential erosion results in less resistant rock undercutting more resistant rock creating an overhang. Plunge pool created by sediment colliding with bank. As process continues and waterfall retreats, a gorge will be formed