(a) With the aid of diagrams, describe the characteristics of any two of the following features: (i) meanders; (ii) flood plain; (iii) braided stream.

Answer Details

Characteristics of any two river features (with diagrams)

(i) Meanders

• They are the wide, looping bends or curves of a river, well developed in the middle and lower courses where the valley is gentle and the river swings freely.
• Each bend has an outer (concave) bank that is steep and cut back by erosion (river cliff), where the current is fast and the water deep, and an inner (convex) bank that is a gentle, shelving slip-off slope where deposition takes place and the water is shallow.
• The river erodes sideways (lateral erosion), so meanders slowly grow and shift down-valley; when a loop is cut through at the neck it may be abandoned to form an ox-bow lake.
• Diagram: a plan view of a winding channel showing erosion on the outer bank and deposition (slip-off slope) on the inner bank.

(ii) Flood plain

• A flood plain is the wide, flat, low-lying area of land on either side of a river in its lower course, built up of alluvium (fine silt and mud) deposited when the river overflows its banks in flood.
• It is very fertile and level, and may carry features such as meanders, ox-bow lakes, and natural levees (raised banks of coarser material along the channel).
• It grows wider as the river shifts across it by lateral erosion and deposition, and is often used for farming and settlement.
• Diagram: a cross-section showing the river channel with levees, the flat alluvium-covered plain on both sides, and the valley bluffs at the edges.

(iii) Braided stream

• A braided stream is a river that splits into several separate channels which divide and rejoin around numerous islands or bars of sand and gravel, giving a plaited or interwoven appearance.
• It forms where the river carries a heavy load but has a variable or reduced discharge, so it drops the coarse material to build the mid-channel bars that force the water to divide.
• It is common on gentle gradients with easily eroded banks, for example near glacier snouts and on dry-region river beds.
• Diagram: a plan view showing one river dividing into interlacing channels around sand/gravel bars.